SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES ? NUMBER 16
Late Quaternary Sedimentation
and Stratigraphy in
the Strait of Sicily
Andres Maldonado
and Daniel Jean Stanley
ISSUED
AUG3 1378
SMITHSONIAN INSTITUTION PRESS
City of Washington
1976
ABSTRACT
Maldonado, Andres, and Daniel Jean Stanley. Late Quaternary Sedimentation
and Stratigraphy in the Strait of Sicily. Smithsonian Contributions to the Earth
Sciences, number 16, 73 pages, 39 figures, 5 tables, 1976.?The Strait of Sicily,
a broad, elongate, topographically complex platform in the central Mediter-
ranean, separates the deep Ionian Basin from the Algero-Balearic and Tyrrhenian
basins to the west. A detailed core analysis shows that the late Quaternary sec-
tions in the different sectors of the Strait are distinct from those in the deep
Mediterranean basins. Strait lithofacies are characteristically uniform, highly
bioturbated, and contain significant amounts of coarse calcareous sediment. Five
major sediment types (coarse calcareous sand, sand- to silt-size sediment, ash,
mud, and sapropel) are grouped into natural vertical successions termed
sequences. The three major sequences defined in the Strait are upward-coarsening
and upward-fining, uniform, and turbiditic (including both mud and sand-silt
turbidites); sapropel sequences are recovered in cores on the Ionian slope east
of the Strait.
The direct relation between sediment type, lateral lithofacies distribution,
water depth, and structural displacement is demonstrated. For example, the
proportion of turbiditic mud increases while that of hemipelagic mud and bio-
turbated strata decreases with depth. The effects of regional Quaternary events,
particularly climatic changes and eustatic sea level oscillations, are well recorded
in cores collected in shallow platform and neritic-bathyal environments; here
the upper sediment sequences are truncated and fining- and coarsening-upward
sequences, which include coarse calcareous sand layers interbedded with mud and
sandy lutite, prevail. In contrast, well stratified units comprising sand (including
gravity flow units and volcanic ash) alternating with hemipelagic and turbiditic
mud form the surficial deposits in the deep (>1000 m) elongate Linosa, Pantel-
leria, and Malta basins. Homogeneous bioturbated light olive gray to dusty
yellow muddy sequences predominate in the intermediate depth neritic-bathyal
environments.
Stratigraphic correlation of cores based on carbon-14 analyses shows that indi-
vidual units or sequences are not correlatable across the Strait or even within
small basins, although it is possible to recognize a general vertical succession of
depositional patterns. Sedimentation rates generally decrease with increasing
depth. Rates in the deep basins have been relatively uniform from the late
Quaternary to the present, while upper (Holocene) sequences in the shallow
platform and neritic-bathyal environments have been truncated. Correlation of
reflectors on high-resolution subbottom profiles indicates that faulting in many
sectors of the Strait is of recent or subrecent origin and that the vertical displace-
ment rate is locally in excess of the average sedimentation rate (i.e., greater than
20 cm per 1000 years).
The absence of sapropel layers in the Strait basins indicates that these depres-
sions remained ventilated during periods when anaerobic conditions prevailed
in the deep basins in the eastern and central Mediterranean. An early Holocene
paleooceanographic model depicting a possible reversal of currents in the Strait
of Sicily region is postulated.
OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded
in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 6166. SERIES COVER DESIGN:Aerial view of Ulawun Volcano, New Britain.
Library of Congress Cataloging in Publication DataMaldonado, Andres.
Late Quaternary sedimentation and stratigraphy in the Strait of Sicily.(Smithsonian contributions to the earth sciences ; no. 16)
Bibliography: p.Supt. of Docs, no.: SI 1.26:16
1. Geology, Stratigraphic?Quaternary. 2. Sediments (Geology)?Sicily, Strait of. 3. Geology?
Sicily, Strait of. I. Stanley, Daniel J., joint author. II. Title. III. Series: SmithsonianInstitution. Smithsonian contributions to the earth sciences ; no. 16.
QE1.S227 no. 16 [QE696] 55O'.8s [551.4'62'1] 75-619369
Contents
Page
Introduction 1
General 1
Acknowledgments 1
Structural-Stratigraphic Framework 3
Hydrography 4
Methodology 7
Defining the Major Strait Environments 8
General 8
Environments 11
Slope (Environment 1) 11
Neritic-Bathyal Borderland (Environments 2, 3, 4, 5) 11
Basin (Environments 6, 7) 18
Shallow Platform (Environment 8) 18
Marked Topographic High (Environment 9) 19
Canyon (Environment 10) 20
The Strait Narrows (Environment 11) 20
Sediment Types in the Strait of Sicily 21
General Distribution of Sediment Types 21
Definition of Major Sediment Types in Cores 22
Coarse Calcareous Sand 23
Sand-Silt Size Sediments 23
Volcanic Ash 24
Muds 24
Sapropel and Organic Ooze 24
Sand Fraction Composition 25
General 25
Coarse Calcareous Sand Type 25
Sand-Silt Sediment Type 29
Volcanic Ash Type 29
Shallow Water Mud Type 29
Hemipelagic Mud Type 30
Turbiditic Mud Type 30
Sapropel Type 30
Organic Ooze Type 31
Bryozoan Content 31
SEM Analysis of the Lutite Fraction 31
Sea-Floor Photography 36
Structures Observed in X-Radiographs and Split Cores 37
Definition of Sequences 44
General 44
Upward-Fining and Upward-Coarsening Sequences 46
Uniform Sequence 47
Turbiditic Sequence 48
Sapropel Sequence 51
Sedimentation and Stratigraphy in the Strait Environments 51
Regional Distribution of Sequences 51
Environmental Factors Controlling the Strait Sedimentation 55
Bioturbation as an Environmental Indicator 59
Rates of Sedimentation 61
Implications of Strait Sedimentation to Current Reversals 65
Summary 66
Literature Cited 69
iii
Late Quaternary Sedimentation
and Stratigraphy in
the Strait of Sicily
Andres Maldonado
and Daniel Jean Stanley
Introduction
GENERAL
The Strait of Sicily is the submerged surface of
the large topographic high which separates the
Ionian Sea in the eastern Mediterranean from the
Tyrrhenian and Alge'ro-Balearic seas in the west-
ern Mediterranean. This morphologically complex
platform lying between Sicily and Tunisia is long,
broad, and trapezoid-shaped (Figure 1). The Strait
comprises shallow banks, ridges, volcanoes (includ-
ing submerged mounts and islands), gentle depres-
sions, and deep basins, and its relief (which locally
exceeds 1000 m) and morphologic configuration
are considerably more irregular than those of
most shelves and continental borderlands.
A sedimentological investigation of this region
is warranted for several reasons: the Strait includes
a series of highly varied environments; it is geo-
logically and hydrographically distinct from the
large, deep basins bordering the Strait; and, to
date, comprehensive regional studies have not
been made relating processes and deposits in time
and space. Earlier studies of the Strait of Sicily
have emphasized sediments in the shallower en-
Andres Maldonado, Seccidn de Estratigrafia y Sedimentologia,
C.S.I.C., Universidad de Barcelona, Avenida de Jose Antonio,
585, Barcelona, Spain. Daniel Jean Stanley, Division of Sedi-
mentology, National Museum of Natural History, Smith-
sonian Institution, Washington, D.C. 20560.
vironments (Blanc, 1958, 1972; Poizat, 1970; Akal,
1972; Emelyanov, 1972; Colantoni and Borsetti,
1973). The sedimentation patterns in the deeper
environments have received less attention (Blanc,
1958; U.S. Naval Oceanographic Office, 1965, 1967;
Emelyanov, 1972; Chassefiere and Monaco, 1973;
and an ongoing investigation of the "Campagne
Gesite 1973" materials collected by the Station de
Geodynamique de Villefranche of the University
of Paris, Blanc-Vernet et al., 1975 and C. Bobier,
personal communication).
The present study defines the major Quaternary
lithologic facies in the various Strait environments
and compares the sedimentation patterns in this
region with those of the adjacent, but much deeper,
Balearic and Ionian basins. More specifically, this
investigation establishes the relationship between
sedimentary processes, associated facies, and sedi-
mentary environments of the Strait. Sedimentary
sequences, defined on the basis of recently collected
core data, are interpreted in light of the Quaternary
dynamics which affected the Mediterranean region.
ACKNOWLEDGMENTS
This study, like most modern oceanographic in-
vestigations, is the result of the effort of many
people and institutions. We are indebted to a num-
ber of organizations for their generous backing,
including financial aid, ship-time, equipment, ma-
terials (including X-radiographs) and facilities.
1
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
CORES
oLYNCHH
36? D VEMA 14
? SAN PABLO 8-7
A CHAIN 61
0 PILLSBURY 6510
A ATLANTIC SEAL
? GESITE -1973
CAMERA
0VEMA 14
ATLANTIS 151
SOUNDINGS IN FATHOMS
0 , 100 200 Km.
34?
10
FIGURE 1.?Strait of Sicily showing major physiographic features discussed in text and position of
cores and bottom camera data used in study. (Chart base is Mediterranean Sea chart N.O. 310,
Defense Mapping Agency Hydrographic Center; depth in fathoms: 1 fm = 1.829 m.)
This study was made possible primarily with the
aid of the following: Smithsonian Research Foun-
dation; Consejo Superior de Investigaciones Cien-
tificas (CSIC); Laboratoire de Ge*odynamique
Marine, Villefranche-sur-Mer (CNRS); Lamont-
Doherty Geological Observatory of Columbia
University; Marine Geology and Geophysics Lab-
oratory, National Oceanic and Atmospheric Ad-
ministration, Miami; Program of Cultural Cooper-
ation between the United States of America and
Spain; Rosenstiel School of Marine and Atmos-
pheric Science of the University of Miami; U.S.
Naval Oceanographic Office (NAVOCEANO); and
Woods Hole Oceanographic Institution.
Bottom and subbottom profiles, core samples
and bottom photographs were collected on the
R/V Atlantic (AS 6), 1965-1967; R/V Chain 61;
USNS Lynch II, 1972; R/V Vema 14; R/V Pills-
bury, 6510; R/V San Pablo and N/O Charcot, 1973.
The captains, officers, and crew of these ships are
thanked for support so efficiently given in the work
at sea. We thank Dr. R. Stuckenrath of the Smith-
NUMBER 16
sonian Radiocarbon Laboratory for providing the
carbon-14 data. One radiocarbon date was pro-
vided by the Laboratoire de Geodynamique Ma-
rine de Villefranche-sur-Mer.
We acknowledge with gratitude the many per-
sons with whom we have had an opportunity to
discuss the various problems raised in this study.
We thank, in particular, Drs. R. Stuckenrath,
J. W. Pierce and I. Macintyre, Smithsonian In-
stitution; Dr. Salvador Reguant, University of
Barcelona; Dr. F. W. McCoy, Lamont-Doherty
Geological Observatory; Dr. Charles Smith, U.S.
Geological Survey, Washington; Mr. T. Durdan,
University of Miami; Mr. D. Lambert, NOAA-
AOML, Miami; Drs. C. Bobier, J. Poutiers and F.
Fernex, all of the Station de Geodynamique de
Villefranche; and Mr. D. Le Boulicaut, Centre de
Sedimentologie Marine of the University of Perpig-
nan.
We thank Messrs. L. Isham and H. Sheng,
Smithsonian Institution, for their assistance with
drafting and processing of data and samples, and
Ms. M. J. Mann and Mr. W. R. Brown for their
help with the scanning electron microscopic analy-
sis. Drs. J. W. Pierce, Smithsonian Institution,
R. S. J. Sparks, University of Lancaster, and T. -C.
Huang, University of Rhode Island, read the
manuscript and provided helpful suggestions im-
proving the text.
Financial support for this investigation, part of
the Mediterranean Basin (MEDIBA) Project, has
been provided by the Smithsonian Research Foun-
dation grants 450137 and 430035 to D. J. Stanley.
Support for ship-time and collection of cores and
photographs by the Lamont-Doherty Geological
Observatory was provided by grants number ONR
(N00014-67-A-0108-0004) and NSF-GA-35454.
This project was undertaken at the Smithsonian
Institution while Dr. Maldonado held a postdoc-
toral fellowship of the Program of Cultural Co-
operation between the United States and Spain.
Travel funds for the final preparation of the paper
have been provided to Maldonado by the Subdirec-
cion General de Promocion Estudiantil (Ministerio
de Educacion y Ciencia).
STRUCTURAL-STRATIGRAPHIC FRAMEWORK
The Strait of Sicily platform occupies a geologi-
cally strategic position between the deep, fault-
bounded basins of the Balearic, Tyrrhenian, and
Ionian seas and the emerged North African and
southern European regions bounding it. Most
workers envision this shallow area as a prolonga-
tion of the Tunisian-Southern Sicilian land mass
and as a link between the North African Atlas
chain and the Sicilian-Italian Apennine chain.
The different tectonic provinces of the Strait re-
gion have been defined and mapped by Burollet
(1967) and Zarudzki (1972). Seismic reflection
exploration has provided both deep penetration
(excellent Flexotir records of Finetti and Morelli,
1972a, b) and shallower subbottom coverage
(Woods Hole Oceanographic Institution sparker
and air gun profiles, Zarudzki, 1972).
Flexotir records show that this zone, separating
the distinct eastern and western Mediterranean
geodynamic sections, consists of thick continental
crust comprising a generally thin Pliocene-
Quaternary unconsolidated section above a thick
sequence of Triassic to Miocene rock units (Finetti
and Morelli, 1972a). The reduced thickness of un-
consolidated Pliocene and Quaternary sediments
(except in some depressions such as the Malta
Graben where these exceed 1 second, penetration
two-way travel time) can be contrasted with the
thick sections in the Balearic Basin west of the
Strait. The underlying Upper Miocene units, cor-
related with limestone and dolomite sequences in
cores and land sections, thicken toward Tunisia
(Burollet, 1967).
There is ample evidence of geologically recent
(post-Miocene) structural displacement, and the
different morphological-tectonic sectors of the
Strait can be related to major fault patterns. Mag-
netic and gravity studies reveal that the main
structural trends are oriented west northwest-east
southeast, i.e., parallel to the major orientation of
the Sicily Channel (Allan and Morelli, 1971;
Morelli, 1972; Colantoni and Zarudzki, 1973; and
others). A northeast-southwest trend predominates
at the westernmost sector of the Strait (Auzende,
1971; Auzende et al., 1974). The largely vertical
structural displacement gives rise to a complex
configuration of horsts (shallow tabular-shaped
banks) and grabens (narrow, deep linear basins).
Seismic profiles clearly display the vertical and
subvertical offset of reflectors. The intensity of
structural ' offset and seismicity (shallow earth-
quake epicenters), and the concentration of vol-
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
canoes (most are submarine cones) increase in the
northern sector of the Strait.
The islands of Linosa and Pantelleria reflect the
importance of Pliocene and Quaternary eruptions
in this part of the Mediterranean. Pantelleria,
interpreted as a composite stratovolcano, rises from
the 1300-m-deep Pantelleria Basin. The position
of other volcanic deposits, including some which
accumulated in historic time, are plotted by Zarud-
zki (1972, fig. 3) and Finetti and Morelli (1972a,
fig. 5); these are concentrated mostly in the north-
ern sector of the Strait. The presence of dike
swarms or narrow lava streams are also suggested
on the basis of magnetic anomalies and appear
aligned parallel to the principal tectonic prov-
inces. Some Mesozoic and early Tertiary intru-
sions also have been penetrated by petroleum
exploratory wells.
In terms of regional Mediterranean-Alpine tec-
tonics, the thick crustal sections of the platform
are considered part of the African Plate, which
underthrusts the Euro-Asiatic plate in the Ustica-
Lipari region of Sicily (Caputo et al., 1970).
Finetti and Morelli (1972b, fig. 19) also empha-
size the role of compression but prefer to relate
plate motion to subduction of the African Plate
below what they define as the Mediterranean Plate.
Like most geophysicists, these latter authors tend
to agree that much of the Mediterranean?in par-
ticular the deep basins bounding the Strait?has
undergone considerable subsidence since the end of
the Miocene. Benson (1972) has proposed that the
Strait platform was deeper during the Pliocene
than at present. The development of vertical faults
with offsets to 1000 m in the upper crust is believed
to reflect isostatic adjustment following the main
Alpine orogeny. Additional structural offset may
also be due to alternating phases of compression
and distension. Zarudzki (1972) relates the gentle
folding of the more than 300 m of section in the
northwest end of the Pantelleria Trough, as ob-
served in continuous seismic profiles, to the above-
cited recent, postorogenic tectonic activity. The
fault development, volcanism, and seismicity of
this region are not unlike those postulated in some
subduction models (tension and rifting behind the
leading edge of a subducted plate margin, cf. Isacks
et al., 1968, fig. 7; Ninkovich and Hays, 1972, fig.
12, and others). An interpretative diagram show-
ing the origin of this modern rift-tension relief in
the Strait and associated volcanism in relation to
subduction is presented by Akal (1972, fig. 16).
That volcanic activity, fault displacement, and
sedimentation have been concurrent is clearly of
importance in this study. These Quaternary neo-
tectonic factors will be emphasized in the context
of sedimentary processes and sedimentation rates
in the Strait region. Physiographic and structural
considerations are considered in greater detail in
later sections.
HYDROGRAPHY
The general hydrographic and current trends in
the central Mediterranean and Strait of Sicily re-
gion are reasonably well known (cf. Lacombe and
Tchernia, 1960, 1972; Wiist, 1961.) The dominant
pattern is one of exchange of two well-defined
water masses, one flowing above the other in op-
posite directions. This exchange across the broad,
shallow platform is similar to, but not as intense
as, the one measured in the narrower Strait of
Gibraltar some 1280 km to the west. The water
flowing across the Strait of Sicily must pass over a
series of sills (eastern and western sills at opposite
ends of the Strait) and across a much longer and
broader area than that at Gibraltar.
Surface waters, primarily of Atlantic origin,
move toward the east-southeast at velocities of 10 to
90 cm/sec (Frassettp, 1972). The lower part of
this water mass extends to depths of 200 to 300 m
(depths increase in winter) and has a salinity of
approximately 37.4 %o; temperatures are seasonably
variable (13? to over 23?C). Below this lies the
Intermediate or Levantine water, which originates
by convective sinking of cooled surface water in
the Levantine Basin east of the Strait. The Inter-
mediate water, with an average salinity of 38.7 %o
and temperature of about 14?C, flows from the
Ionian Basin across the sill toward the western
Mediterranean. This water mass fills the deep
Strait basins and is renewed rapidly as a result of
the undercurrent (Morel, 1972). The exchange
between Surface and Intermediate water is related
to the higher evaporation rates in the eastern
Mediterranean which entrain the less saline waters
as a replacement (outgoing versus ingoing flux
calculations are provided by Morel, 1972). Deep
waters in the Ionian and Balearic basins are
NUMBER 16
SALINITY %eSection C215 - 16 MAY
C. BON Pta. STAGNONE
\ 1 2 3 4 5 6 7 8 9 9A 10 11 12 12 A 13 14
I I I I I I I I I
40 50 60 70
B
FIGURE 2.?Profiles across the Strait of Sicily Narrows between Punta Stagnone near Marsala,
Sicily, and Cape Bon, Tunisia: A, salinity profile in May 1970; B, opposite current flow patterns
of the Levantine and less saline surface water masses. (From Molcard, 1972.)
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
38
=?= (q) Uplift
^iP^ (r) Faulted Margin
TUNISIA
SOUNDINGS IN FATHOMS
0 100 200 Km
\T
FIGURE 3.?Track (dark solid line) of the USNS Lynch (cruise II, 1972) in the Strait of Sicily
region. The dominant structural features observed on 3.5 kHz and 30,000 J sparker are depicted
(explanation in text). The specific topographic environments (code 1 to 10) are displayed on
the thin line (offset from the track line); these are denned in the text. The scale on this line is
shown in kilometers (a total of about 1100 km between the Ionian slope east of the Strait and
the Algero-Balearic Basin). The major structural trends of the Strait are also depicted (modified
after Burollet, 1967; Finetti and Morelli, 1972a, b; Zarudzki, 1972).
blocked by the sill and do not cross from the east-
ern to western Mediterranean.
The surface waters are a source of suspended
sediment in the form of pelagic tests (planktonic
foraminifera, etc.) and terrigenous fraction (over
1.0 mg/1, according to Emelyanov and Shimkus,
1972). The influence of this Atlantic water should
be more intense on the Tunisian margin inasmuch
as the flow is thicker and less saline in this sector
than on the Sicilian side. On the other hand,
Levantine water flows along the sea floor and is
thus an agent of transport and erosion as we shall
demonstrate in later sections (Pierce and Stanley,
1975). Further transport is perhaps also related to
NUMBER 16
TABLE 1.?Position, water depth, and length of Strait of Sicily cores analyzed in this study
(specific environment, defined in text, and geographical location of each core also listed)
CRUISE CORE NO.
Lynch II 3
4
5
5A
6
6A
7
Pillsbury 6510 34
33
Atlantic Seal 6 8
7
San Pablo 8 7
Vema 14 138
139
140
Chain 61 19
Gesite 73 KS 12
KS 23
KS 33
KS 53
KS 63
KS 69
KS 76
KS 78
KS 100
KS 104
KS 105
KS 109
KS 110
KS 118
KS 120
KS 125
LATITUDE
35?02'N
35?05'N
36O25.3'N
35?34'N
38?16.8'N
38?13.2'N
38?02.7'N
36?22'N
36-27.5'N
36?22'N
37?19.6'N
37-56'N
36?19'N
36-28'N
37?10.5'N
35?46.6'N
37?33.2'N
37-26.5'N
36?37.0'N
36?08.4'N
35?42.8'N
35?50.4'N
35?50.6'N
35?29.2'N
35-58.7'N
36?31.6'N
35?47.7'N
36?27.3'N
36?27.9'N
35?46.9'N
35?51.l'N
35?59.6'N
LONGITUDE
16-42'E
14?30'E
12-46'E
12?30'E
11-19.8'E
10-57.2'E
8?09.2'E
12-33'E
13-28.5'E
11-13'E
12?39.5'E
11-09.9'E
14-48'E
13"31'E
11-47.5'E
13-05.8'E
11-29.0'E
11?24.51E
12-05.0'E
12-51.7'E
13-14.9'E
13-02.3'E
13?03.2'E
13-42.9'E
13-52.8'E
13-26.6'E
13-18.5'E
13-12.2'E
13-08.0'E
13?09.7'E
13-02.8'E
12-36.0'E
WATER
DEPTH
(in m)
2432
604
1089
1257
1217
755
2588
1294
1549
93
183
350
124
1703
166
1475
956
1200
1164
805
1428
1484
1463
769
1088
1087
580
1688
1492
1493
1454
785
CORE
LENGTH
(in cm)
575
380
332
600
500
610
342
109
119
555
770
540
245
576
420
1030
700
725
715
678
850
608
740
659
669
208
626
732
110
825
701
785
ENVIRONMENT
(1)
(4)
(6)
(7)
(7)
(5-4)
(1)
(7)
(7)
(8)
(8)
(8-4)
(8)
(7)
(8)
(7)
(6)
(7)
(7)
(4-5)
(7)
(7)
(7)
(5-4)
(6)
(6)
(4)
(7)
(7)
(7)
(7)
(5-4)
GEOGRAPHIC LOCATION
Ionian Slope
Pelagian Shelf
Pantelleria Intermedian
Basin
Pantelleria Trough
North Marittimo
Galite
Tyrrhenian-Balearic Slope
Pantelleria Trough
Malta Trough
Tunisian Shelf
Adventure Bank
Strait Narrows
South Sicily Uplift
Malta Trough
Strait Narrows
Linosa Trough
Strait Narrows
Pantelleria Trough
Pantelleria Trough
Linosa Platform
Linosa Trough
Linosa Trough
Linosa Trough
Pelagian Shelf
Malta (Intermediate)
Basin
Malta (Intermediate)
Basin
South Sicily Basin
Malta Trough
Malta Trough
Linosa Trough
Linosa Trough
Linosa Platform
turbulence, vertical mixing, and internal waves
formed along the shear zone between the two
water masses.
Short-term current-measurements above the bot-
tom at the western end of the Strait (Figure 2)
between Cape Bon (Tunisia) and Punta Stagnone
(Sicily) revealed currents in excess of 30 cm per
second (Molcard, 1972). Velocities to 50 cm per
second have been recorded by other workers (La-
combe and Tchernia, 1972). Bottom photographs
in the same region, which show crinoids heeling
over (cf., Akal, 1972, fig. 8, upper right), provide
further evidence of the strong current flow above
the sea floor.
METHODOLOGY
The b#sic material for this study was collected
during the March-April 1972 cruise of the USNS
Lynch (LY 11-72). Positioning of the ship was
8 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
made with satellite and radar navigation. Seven
Ewing piston cores were retrieved along a transect
between the Ionian and Balearic basins crossing
different environments of the Strait. Continuous
(3.5 kHz) echo-sounding and sparker (30,000
Joules) records were obtained along the ship track
(Figure 3). These subbottom profiles have been
reduced photographically to the same horizontal
scale (Figures 5-15).
Additional core data have been obtained from
the following organizations (Figure 1, Table 1):
United States Naval Marine Geophysical Survey
Program 1965-1967, Area 6, cores AS 6-7 and AS
6-8 (U.S. Naval Oceanographic Office, 1967); Uni-
versity of Miami cores P 6510-G33 and P 6510-
G34; Groupe des Geologues Marins Mediterra-
neans, Campagne "Gesite"-1973, cores KS 12, KS
23, KS 33, KS 53, KS 63, KS 69, KS 76, KS 78, KS
100, KS 104, KS 105, KS 109, KS 110, KS 118, KS
120 and KS 125; Lamont-Doherty Geological Ob-
servatory, cores Vema 14, 138, 139, and 140, and
San Pablo 8, 7; Woods Hole Oceanographic Insti-
tution, core Chain 61, 19. A total of 32 cores have
been analyzed by us for this study (Figure 1). A
set of deep-sea camera station photographs (Fig-
ure 1) was provided by the Lamont-Doherty Geo-
logical Observatory (station Vema 14, K 53) and
six camera stations from Woods Hole Oceano-
graphic Institution (stations Atlantis 151, 56, 58,
59, 60, 61, and 62). The camera station positions
are listed in Table 2.
The Gesite cores were X-radiographed before
splitting, while Lynch and Pillsbury cores were
radiographed (half cores) after splitting and be-
fore sampling. Detailed core logs record texture,
sedimentary and biogenic structures, color, and
other characteristics observed visually and on X-
radiographs. Gross texture and composition of the
sand and lutite fraction of over 200 selected sam-
ples have been processed for mineralogical analy-
sis. The relative percentages of 14 compositional
components of the sand fraction in 48 of these
samples have been calculated. The lutite fraction
(silt plus clay) was examined by means of the
Scanning Electron Microscope; samples prepared
for SEM analysis were soaked in 30% hydrogen
peroxide for at least 24 hours to destroy organic
matter. The core thickness sampled ranged from 4
to 12 mm.
Large samples of mud (comprising between 15
TABLE 2.?Position and water depth of camera stations in the
Strait of Sicily
CRUISE
Vema 14
Atlantis 151
CAMERA STATION
K-53
56
58
59
60
61
62
LATITUDE
36?29'N
36?25'N
37?12'N
37?18'N
37?181N
38?22'N
38?14'N
LONGITUDE
13?23'E
11?43'E
11?34'E
11?33'E
ll?07'E
11?23'E
11-31'E
WATER DEPTH
(in m)
1588
119
567
88
106
381
134
to 45 cm of core section) were sieved and the frac-
tion coarser than 63 microns extracted for radio-
carbon dating. Carbon-14 age determinations also
have been made on bulk samples of about 15
cm-long sections of cores. Our tests have shown
that dates obtained with the total (or bulk) core
samples provide comparable dates to those ob-
tained with the coarse fraction. We favor dating
with bulk samples inasmuch as it allows us to use
much less core for dating. A total of 40 samples
were age-dated (R. Stuckenrath, Smithsonian Ra-
diocarbon Laboratory, pers. comm.).
In calculating sediment thicknesses on subbut-
tom profiles we have assumed an average velocity
of 1800 m per second (Finetti and Morelli, 1972a,
b); the scales in the figures are given in two-way
travel time.
Defining the Major Strait Environments
GENERAL
In this study "Strait of Sicily" is the general geo-
graphic term applicable to the entire region be-
tween Tunisia and Sicily. The term "Strait Nar-
rows" is applied to the narrowest passage (about
160 km in width) between Cape Bon (Tunisia)
and Punta Stagnone or Marsala (southwest coast
of Sicily). The Strait trends in a northeast-
southwest direction and is approximately 450 to
700 km in length. It is broadest (over 500 km)
along a north-south transect between southeast
Sicily and Libya. Recent charts (Carter et al.,
1972; Finetti and Morelli, 1972a) of the central
Mediterranean show that the total area exceeds
175,000 km2, and that over one-third of this sur-
face (approximately 80,000 km2) is shallower than
NUMBER 16
|:::::::|CONTINENTAL SHELVES
CONTINENTAL SLOPES
CONTINENTAL RISES
PLATEAUS
CONTINENTAL BORDERLANDS
BANKS
KNOLLS
DEPRESSIONS
TERRACES
STRAIT OF SICILY
PHYSIOGRAPHIC REGIONS
FIGURE 4.?Physiographic chart of the Strait of Sicily showing highly irregular topography of
this region. (From Akal, 1972.)
200 m (shown as shelf on Figure 4). The deeper,
elongate regions, including deep basins, known by
some authors as the Sicily Channel, parallel the
main trend of the Strait platform, i.e., northwest-
southeast. Three narrow, steep-walled, elongate
basins (Malta, Pantelleria, and Linosa) are 1700,
1300, and 1600 m in depth, respectively. These
three distinct depressions are separated from each
other by a neritic bathyal platform. The Gela or
South Sicily Basin is a shallower but much larger
basin lying south of Sicily and northwest of Malta.
The larger islands include Malta and Gozo, Pantel-
leria, Linosa, Lampedusa, Kerkennah, Galite, Ma-
rettimo, and Djerba south of the Gulf of Gabes.
The region is characterized by some extensive,
shallow, generally flat-topped or tabular, platforms
of which the one east of Tunisia and the South
Sicily-Medina and Adventure Banks south of Sicily
are the largest (Figure 1).
Of particular interest are the two shallow banks
at both ends of the Strait Platform: Skerki Bank
(Blanc, 1958), north-northwest of Cape Bon, and
Medina Bank, southeast of Malta. These elongate
topographic highs serve as important barriers to
water masses flowing across the platform. These
shallow platforms at opposite ends of the Strait
platform are also called Eastern Sill and Western
Sill.
Names assigned to the various other morpho-
logical features depicted in Figures 1 and 3 are
shown on charts in Blanc (1958), Burollet (1967),
Allan and Morelli (1971), and Carter et al. (1972).
In the Strait six major physiographic units or
morphological-sedimentary environments are rec-
10 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
NORTHWEST
km 622
400 fm SOUTHEAST
km 590
km
FIGURE 5.?Sparker (30,000 Joules) and 3.5 kHz profiles (spacing between horizontal lines is 20
fms, or 37 m, in all 3.5 kHz records) reproduced at the same horizontal scale showing slope
transect from Pantelleria Trough to Adventure Bank. Near-horizontal Pliocene and Quaternary
(P-Q) sediment of the basin distinct in both records is shown abutting against the base of the
slope, which appears relatively free of sediment cover. (Some of the normal faults are indicated
by the dashed lines. Depth in seconds, two-way travel time.)
ognized: (a) slope; (b) neritic-bathyal borderland;
(c) basin; (d) shallow platform (shelf and bank);
(e) marked topographic high (submarine mounts,
volcanoes, diapirs, etc.); and (f) canyon. Two of
these units (b, c) can be subdivided. In addition,
the Strait Narrows (g) between Cape Bon and
Marsala is considered as a separate entity. A total
of 11 environments (Figure 3) are identified, and
these are denned in following sections.
These sections also describe the structural con-
figuration of the unconsolidated sediment se-
quences (largely Pliocene and Quaternary, P-Q)
that lie above Miocene and older units as observed
in seismic records. The top of the consolidated
NUMBER 16 11
Miocene is identified and correlated with sequence
A of Finetti and Morelli (1972a, b).
ENVIRONMENTS
SLOPE (Environment 1).?The slopes considered
here are those that flank the Strait of Sicily on the
east (Ionian) margin and the west (Algero-
Balearic) margin, and steep slopes which bound the
major deep basins of the Strait. A transect from
Pantelleria Trough to the Adventure Bank (km
590 to 615, on Figure 3) crossing a slope of the
type discussed here is shown in Figure 5. This
highly irregular slope appears on 3.5 kHz records
as a series of single or multiple hyperbolic pat-
terns. Poor definition of stratification or sediment
ponding is in part an acoustic artifact (roughness
and steepness of the slope); poor penetration also
may be due to a reduction of the unconsolidated
sediment cover.
Outcrops of older Tertiary deposits have been
reported from slopes bounding the major basins of
the Strait (Colantoni and Borsetti, 1973). Such
slopes average about 2.5?, but attain much higher
values locally; they commonly display a steplike
configuration as a result of fault offsets (Figure 5).
Two cores retrieved from this environment show
rather distinct lithofacies: core LY II?7 on the
Alge*ro-Balearic margin includes an alternating se-
quence of turbidites and hemipelagic mud, while
core LY II?3 on the Ionian Basin margin com-
prises distinctive gray to black organic-rich sapro-
pel layers as well as turbidites and hemipelagic
mud.
NERITIC-BATHYAL BORDERLAND (Environments 2,
3, 4, 5).?Somewhat more than half of the Strait
area lies within a depth range of 200 to 700 m.
This zone is morphologically complex and the
sparker profiles reveal the importance of vertical
structural displacement that has broken the sea
floor into a complex net of horsts and grabens.
Four subzones are recognized.
Outer Margin, Faulted (Environment 2): An
outer margin, faulted zone, distinguished at the
eastern end of the Strait (km 68-115, Figures 3,
6A), comprises the transitional area between the
Strait proper and the margin slopes. The sea floor
on the 3.5 kHz records presents an irregular,
rugged topography with a reduced sediment cover.
This area corresponds to the faulted and flexured
zone defined by Burollet (1967) and Finetti and
Morelli (1972a).
Broad Uplift (Environment 3): This zone in-
cludes those areas occupying positive structural
axes (Burollet, 1967); e.g., the South-Sicily Medina
Uplift, Jeffara-Malta axis (km 110-160, Figure
6c), and the northeastern extension of the Galite
Archipelago (km 908-983, Figure 6BJ, B2). The
latter is deeply cut by a canyon. These areas are
characterized by a broad, convex-up topography
(probably gentle anticlinal-like folds) and small
distinct valleys. Faulting is not as prominent a
feature in this zone as in the other outer margin
environments of the Strait. The reduced sediment
cover on the convex-up topography suggests a slow,
uniform rate of sediment accumulation, or erosion
by bottom currents (Pierce and Stanley, 1975), or
both.
Neritic-Bathyal Platform (Environment 4): The
neritic-bathyal platform includes essentially flat,
depressed areas although the sea floor in this zone
is not completely confined as are the basins. De-
positional processes dominate here. Two platform
sectors are traversed: the Pelagian Shelf, km 160-
365 (Figures 7, 8), and the Galite Platform, km
850-908 (Figure 9).
The platform environment is characterized by
thick sequences of deposits which pinch out locally
on topographic highs (cf. symbol on Figure 3, km
160, km 908) and less frequently on the platform
proper (Figure 7, a, km 305; km 780). Thinning
of strata is the result of simultaneous deposition
and vertical fault offset, which may also result in
the development of an offlap sequence (Figure 8,
a, km 325) or truncation. Growth-faults (Figure 7)
with thickening of sediment layers on the down-
thrown block are observed; similar phenomena are
described by Hardin and Hardin (1961) in the
Gulf of Mexico.
The fault offsets observed in seismic records are
associated with tilted blocks, small grabens and
horsts (Figure 7), and small mounts (Figure 9, km
880). The ratio of height to width of these tectoni-
cally displaced blocks is approximately 1 to 100;
the maximum throw of these faults observed in our
records is about 200 m (Figure 7); and the maxi-
mum topographic relief is about 170 m. Displaced
(slumped) Quaternary deposits (Figure 8, b, km
365; Figure 9, a, km 870), and gentle anticlinal
(km 220) and synclinal (km 180, km 200) struc-
12 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
WEST
km 160
EAST
km 110
Northeast Extension of Galite Archipelagol
FIGURE 6.?Selected 3.5 kHz and sparker records of neritic-bathyal environments: A, Outer margin,
faulted at eastern end of the Strait; note reduced sediment cover on the 3.5 kHz record. Bx
(sparker) and B2 (3.5 kHz), Across the northeast extension of Galite archipelago (arrows denote
marked topographic high (? volcano, B); note reduced sediment cover), c, South Sicily Medina
Uplift, Jeffara-Malta axis, showing some sediment in contrast to A; steps and other topographic
breaks are almost certainly fault-controlled.
tures are also observed in this environment (cf.
Figure 3).
The thickness of the Pliocene-Quaternary sedi-
ment section recorded on sparker profiles is highly
variable. An average of 0.4 seconds (or 360 m, two-
way travel time) is generally present throughout
the area; it thickens to 0.7 seconds (630 m) in the
axis of the depressions (Figure 7, arrow b) and is
reduced or absent on mounts. If a velocity of about
1800 m per second is assigned to these unconsoli-
dated Pliocene-Quaternary sequences (Finetti and
Morelli, 1972a, b), we estimate a sediment thick-
ness which ranges from 0 to about 650 m.
Cores collected in this neritic-bathyal platform
environment (LY II-4, KS 105) and those from
the zone of transition to the next environment
("Neritic-Bathyal Depression" environment dis-
cussed in the following section) (LY 11-64, KS 78,
NORTHWEST
km 325 ?
SOUTHEAST
I km 280
km
FIGURE 7.?Example of neritic-bathyal platform environment, showing marked topographic
irregularities and displacement of the Pliocene and Quaternary (P-Q) and pre-Pliocene (A)
sediment sequences by fault offset (a = pinchout of surficial sediment cover, b = thickening of
sediment on a downthrown block, c = recent fault scarp exposing uppermost sedimentary
sequences).
NORTHWEST ;
km 365 -,,4 -,- -'i~4f
,~1 'II SOUTHEAST
?JL, km 320
' if
FIGURE 8.?Neritic-bathyal platform (Pelagian Shelf) showing the offlapping of the Pliocene-
Quaternary (P-Q) cover off an actively uplifted block (arrows a). Note also slumping of recent
sediment in a small fault-produced depression (arrow b).
14 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
WEST
km 902
f If EAST
km 860
FIGURE 9.?Neritic-bathyal platform (near Skerki Bank) showing topographic high (horst)
underlain by basement (B) and reduced, deformed Pliocene-Quaternary (P-Q) cover. Accumu-
lation of recent sediment is noted in small depression (arrow a).
KS 125) display a characteristic lithological uni-
formity. No prominent sand layers are recovered
and only subtle structures are revealed in the core
X-radiographs. Bioturbation structures are present
throughout the cored sedimentary sequences.
Although the cores are generally structureless it
should be noted that some laterally continuous re-
flectors can be traced on the 3.5 kHz records; these
reflectors are locally displaced vertically by faults.
The limited length of the cores has not allowed re-
covery of sediment sections forming some of these
major subbottom reflectors. However, their lateral
continuity suggests some process which has re-
sulted in their regional distribution; this mech-
anism is discussed later.
The importance of neotectonics affecting these
reflectors is readily apparent. The high-resolution
3.5 kHz profiles show that faulting has occurred
after deposition (Figure 7, arrow c). In some lo-
calities tectonic displacement and sedimentation
rates have occurred simultaneously, resulting in
the development of pinch-out (Figure 7, arrow a)
and offlap sequences (Figure 8, arrow a). The
youngest faults reveal a vertical throw of as much
as 50 meters (Figure 7, arrow c).
Neritic-Bathyal Depression (Environment 5):
There are numerous depressions on the border-
land, and four of these have been traversed: the
gentle Malta-Linosa depression, a low between the
Malta Trough and the Linosa Trough (km 365-
470, Figures 10, 11), and three smaller, more
marked depressions, north of Adventure Bank (km
NUMBER 16 15
*C, ,,,. I tiSOUTHEAST
FIGURE 10.?Neritic-bathyal depression, between Malta and Linosa troughs, showing vertically
displaced (locally thickened) section of Pliocene and Quaternary (P-Q) sequences. Fault dis-
placement at a is over 100 m. (See Figure 11 for continuation of profiles.)
NORTHWEST
km 482
SOUTHfAST
km 423
FIGURE 11.?Neritic-bathyal depression between Malta and Linosa troughs (continuation of
profiles on Figure 10) showing truncation by fault offset of the Pliocene and Quaternary (P-Q)
cover at the edge of the depression.
16 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
725-735, km 750-762 in Figure 12, and km 770-
780 in Figure 13BX, B2). The transition between
some of these depressions and the Neritic-Bathyal
platform is subtle. These depressions are differ-
entiated from the adjacent platform surfaces on
the basis of a thicker sedimentary cover (range
from 0.5-0.8 seconds, 450-720 m), broad basinal
morphology, and a marked tectonic pinching out
of the sedimentary sequences against the depres-
sion margins.
The Malta-Linosa depression is wide (105 km)
and displays vertical tectonic structures analogous
to those described on the platform (Figures 3, 10,
11). Structurally, this depression is a gentle syn-
cline without major sea mounts or knolls; seismic
profiles show the faulted margin of the depression.
The fault which has affected the most surficial re-
flectors displays a downthrow of over 100 m (Fig-
ure 10). This depression extends north of Linosa
Island and forms the northwest end of the Pantel-
leria Trough (Zarudzki, 1972:20). The Pliocene-
Quaternary strata are truncated by faults at the
edge of the depression.
The small northwestern basin (km 770-780, Fig-
ure 13B!, B2) is characterized by intense folding
and distortion of the sediment within the depres-
sion, suggesting compression (cf. Zarudzki, 1972).
This zone provides evidence of recent tectonic
movement as indicated by the tilting and folding
of the surficial reflectors visible in the 3.5 kHz
records (Figure 13B2).
The Gela Basin (Zarudzki, 1972), also called the
South Sicily Basin (Finetti and Morelli, 1972), is
located between the Malta Trough and Sicily and
may be assigned to this environment.
Sediments in cores are characterized by their ap-
NORTHWEST SOUTHEAST
FIGURE 12.?Profiles north of Adventure Bank showing two distinct, small depressions on the
neritic-bathyal borderland. Note topographic high devoid of Pliocene-Quaternary sediment cover
between the depressions.
NUMBER 16 17
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18 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
parent uniformity and lack of stratification (i.e.,
core KS 53). However, it is possible to individu-
alize some vertically graded mud turbidite se-
quences on the basis of X-radiography. The reflec-
tors on the 3.5 kHz records are more apparent in
this environment than on the flatter platform. As
in the case of environment 4 these reflectors do not
appear to correlate with prominent layers in the
cores.
BASIN (Environments 6, 7).?This zone includes
the major elongate, troughlike basins of Malta,
Pantelleria, and Linosa, as well as small basins oc-
curring either as deep depressions on the conti-
nental borderland and on the slopes of the three
major deep troughs. Two subdivisions are made,
based on the depth and aerial importance of these
basins.
Intermediate Depth Basin (Environment 6):
The intermediate depth basins are small depres-
sions, partially enclosed and characterized by a
considerable thickness of sediment. Figure 13 (A,
km 480-495) shows one of these basins located on
the slope of the Pantelleria Trough.
Visual examination of split cores collected in
this environment (i.e., cores LY II-5, KS 100, KS
104) reveals sedimentary sequences almost as
uniform as .those in environments 4 and 5.
X-radiographs, however, show enhanced stratifica-
tion attributed to turbidite sequences and a de-
crease in the degree of bioturbation, particularly
in the deeper basins.
Core KS 12, located in one intermediate depth
basin in the Strait Narrows, is exceptional because
it shows well-marked stratification and includes
several coarse layers of bioclastic sand. These char-
acteristics, attributed to the particular geographic
position of this core, are discussed later.
Deep Basin (Environment 7): Three narrow,
deep, elongate basins, accounting for somewhat less
than three percent of the Strait area, occur in the
center of the Strait and all three parallel its
northwest-southeast trending axis: (1) Malta, 150
km long and 30 km wide; (2) Pantelleria, 90 km
long and 30 km wide (Figure 13c); (3) Linosa,
75 km long and 17 km wide. Respective depths are
about 1700, 1300, and 1600 m. Other basins, such
as the one west of Marettimo Island (Figure 13B./)
also have been sampled (cf. core LY II-6).
The three deep, troughlike basins stand out by
their straight, fault-bounded steep walls apparent
in seismic profiles (Figure 5); they have been in-
terpreted as grabens related to postorogenic fault-
ing (Zarudzki, 1972; Finetti and Morelli, 1972a).
These deep basins have trapped a thick sequence
of unconsolidated sediments; approximately 1000
m of sediments (to about 1.2 seconds penetration)
are measured in the Malta Trough (Finetti and
Morelli, 1972a). The bottom is a smooth, flat sur-
face resulting from sediment accretion. The strata
pinch out sharply against the walls of the depres-
sion, and no prominent rise is developed at the
foot of the slope (Figure 5, a; Figure 13B2', c).
Cores collected in the deep basins show distinct
stratification and the most diverse assemblage of
sediment types observed in the Strait. The most
characteristic types are turbidite sequences, but
terphra (ash) layers are also important locally.
Bioclastic sand layers are present, usually at the
base of the turbidite sequences. Evidence of slump-
ing is also noted in some basin cores (i.e., core
139, Vema 14). Orderly layering and lateral con-
tinuity of strata are apparent on the 3.5 kHz rec-
ords (Figure 13).
SHALLOW PLATFORM (Environment 8).?About
45% of the surface of the Strait is shallower than
200 m. The seismic profiles show that the shallow
platform, for the most part, is covered by a con-
siderably reduced unconsolidated sediment cover.
The unconsolidated strata are gently tilted, tectoni-
cally offset, and truncated (Figure 14, arrow a).
Adventure Bank (km 630-718, Figure 14) is es-
sentially a horst structure consisting of Tertiary
and Mesozoic deposits. Well-defined terraces are
cut at about 107 (? 3) m (arrow b) and at 140
(? 10) m (arrow c) on some bank margins. The
terrace at 140 m forms a gently dipping seaward
slope, which may represent a foreshore surface.
Most of the bank surfaces are characterized by a
gentle slope, interrupted by small mounts and
gentle depressions. This topography is largely the
result of alternating erosion and deposition related
to the Quaternary oscillations of sea level; recent
structural activity, including diapirism and vol-
canism, also has affected this zone. In this respect,
submarine mounts on the northern Adventure
Bank have been interpreted as diapiric structures
(Zarudzki, 1972), and the southeast extension of
this bank is interpreted as the most active volcanic
area in the Strait (Finetti and Morelli, 1972a;
Zarudzki, 1972).
NUMBER 16 19
NORTHWEST
km
SOUTHEAST
:m 618
FIGURE 14.?Profiles across part of Adventure Bank off southwest Sicily showing reduced uncon-
solidated cover above Neogene (A) older units (a = truncated strata, b = terrace at 107 ?3 m,
c = terrace at 140 ?10 m).
Maps of the surficial sediment based on bot-
tom photographs, grab samples, and cores (i.e.,
AS 6-8, AS 6-7, V 14-138, V 14-140) show a mo-
saic distribution which is not strictly depth con-
trolled. Sediment types include mud to coarse-
grained, largely bioclastic and biogenic (calcareous
algae, bryozoans, molluscs, foraminifera, etc.) sedi-
ment types (cf., Blanc, 1958; Poizat, 1970; Akal,
1972). However, gross texture appears to be
broadly related with morphology and depth:
coarser sediment types are concentrated on shallow
banks and mud in the somewhat deeper and de-
pressed areas.
Layers of cemented crusts and oxidized clasts,
mostly biogenic and Pleistocene rock surfaces bare
of sediment, are important locally. These horizons
can be likened to "hard grounds" recorded in the
ancient sedimentary rock record (Blanc, 1958).
MARKED TOPOGRAPHIC HIGH (Environment 9).?
The topographic highs are of two major types: (a)
those showing a sedimentary cover in the 3.5 kHz
records and (b) those without any kind of reflectors
or stratification in the records. The first type is in
some instances strongly deformed (Figure 13A_, km
510), or appears as an anticline (Figure 11, km
470). Some highs without reflectors (an acoustic
reflector appears to pierce younger units) can be
interpreted as volcanoes (cf., Figure 6Blt B2, km
1010; Figure 9, km 880; Figure 12, km 740), ig-
neous intrusive masses (granite of the Galite Archi-
pelago, Auzende et al., 1974), strongly metamor-
phosed rock, or diapiric structures (Burollet, 1967;
Zarudzki, 1972). The sequence of highs shown in
seismic records collected between km 775 and km
790 (Figure 13B!, B2) may represent an extension
of the Skerki Bank; this feature displays Quater-
20 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
EAST
FIGURE 15.?Profiles
sparker record) and
valley floor (arrow,
across the head of Bizerte Canyon showing fault displacement (arrow on
unconsolidated sediment in the axis. The irregular configuration of the
3.5 kHz profile) suggests slumping.
nary reef and diapiric structures on its northwest
slope (Zarudzki, 1972:18).
CANYON (Environment 10).?One major subma-
rine valley, the Bizerte Canyon, has been recorded
in our records on the northern part of the Strait
(Figure 15, km 930-970). This canyon extends
north-northeast to the Tyrrhenian Basin plain
(Carter et ah, 1972), and cuts deeply into the
northeast extension of the Galite Archipelago
(broad uplift environment 3). The eastern wall of
this canyon appears somewhat steeper. The sparker
profile (see arrow) shows possible fault offset under
the canyon axis; this feature may be related with
the predominant northeast-southwest structural
trend mapped at the western end of the Strait
(Auzende et ah, 1974, fig. 3). Unconsolidated
Pliocene-Quaternary sequences are recorded in the
canyon head; the irregular surface of the axis (ar-
row on 3.5 kHz record) may be due to displacement
of the recent sediment fill.
THE STRAIT NARROWS (Environment 11).?The
narrowest portion of the Strait between Sicily and
Tunisia presents a diverse topography including
shallow banks, intermediate depth basins, and
bathyal-neritic environments. Cores in this region
are distinctive in that they include a high propor-
tion of coarse bioclastic sand. Core KS 12 (956
meters) in the deeper, small, enclosed basin (en-
vironment 6) in the center of the Strait is inter-
esting in this respect. The prominent coarse sand
NUMBER 16 21
layers in this core probably were introduced peri-
odically into the depression by turbidity currents
and mass flow mechanisms. The organic origin
(shells, calcareous algae, and others) of the sedi-
ment and the removal of the finest fraction by bot-
tom currents is discussed later.
Sediment Types in the Strait of Sicily
GENERAL DISTRIBUTION OF SEDIMENT TYPES
High-resolution seismic surveys indicate that the
unconsolidated section of Pliocene and Quaternary
sediments is generally much thinner in the Strait
than in the deeper Alge'ro-Balearic and Ionian
basins bounding it. A concentration of distinct re-
flectors defines the Miocene-Pliocene boundary
(contact at top of A in Figures 5-15). Subbottom
profiles show that the unconsolidated units are ir-
regularly distributed, i.e., generally thin to absent
on topographic highs and thicker accumulations in
depressions (Finetti and Morelli, 1972a, b; Za-
rudzki, 1972). Over 300 m of gently folded, un-
consolidated sediment are noted in the northwest
sector of the Pantelleria Basin; these may have
been transported from the Adventure Bank and
Sicily (Zarudzki, 1972). The Malta Basin has
trapped a sediment section of about 1000 m (Fi-
netti and Morelli, 1972a), and the Linosa Basin to
the south comprises over 1000 m; the latter may be
derived from the African craton and adjacent plat-
form (Zarudzki, 1972). A fourth important but
shallower (about 700 m) depression, the Gela (or
South Sicily) Basin northwest of Malta has ponded
over 500 m of unconsolidated sediment according
to the above-cited authors. A Flexotir profile trend-
ing north northeast-south southwest across this
basin (Finetti and Morelli, 1972b, fig. 8a) also
shows a thickening of the sediment section toward
Sicily and a general southward progradation of the
deposits into the Basin.
The grain size distribution of the Strait surficial
sediment has been measured by Blanc (1958) and
textural maps of this area compiled by the U.S.
Naval Oceanograph'ic Office (1965), Fraser et al.
(1970), Poizat (1970), Emelyanov (1972), and
Akal (1972). Texture appears to be broadly re-
lated with morphology: coarser sediment types (silt
to sand and coarser) are concentrated on shallow
banks, and mud (silt and clay mixtures) in envi-
ronments deeper than about 200 m (Figure 16).
However, detailed mapping of texture, particularly
in the shallow environments, indicates that the
grain-size pattern is mosaic-like and not strictly
depth controlled (Poizat, 1970).
The coarse bioclastic sands are interpreted as
current-modified coarse lag deposits resulting from
the winnowing of the fine fractions. The bioclastic
fragments are reworked as indicated by the local
concentrations of oxidized "pralines" ( = algal balls,
some with volcanic nuclei and cemented crusts;
Blanc, 1959, 1972). Oxidized organic fragments in-
clude relict Pleistocene faunas, particularly on the
shallow banks. These are sometimes entrained into
deeper environments by currents or slumping on
the margins of shallow banks. Pleistocene rock sur-
faces bare of sediment are also present. Terrige-
nous input at river mouths and material provided
by erosion along the coast, by wind, and by vol-
canic eruptions account for only a small fraction
of the total sediment cover of the Strait.
Cores collected at shallow to intermediate depths
contain alternating mud and coarse bioclastic lay-
ers (Akal, 1972; Chassefiere and Monaco, 1973).
The upper mud and sandy mud layers are oxidized
(light yellow coloration) to a depth of 1 m (Blanc,
1958; Chassefiere and Monaco, 1973). Neritic-
bathyal cores are constituted entirely by mud,
while deep basin cores contain alternating se-
quences of sand, volcanic ash, and mud layers.
Fines, presumably winnowed from bank areas, are
transported by suspended sediment mechanisms to
depths generally in excess of 50 m. Other mech-
anisms also play an important role in the erosion,
transport, and deposition of mud in the deeper en-
vironments. Bottom currents flowing across the sills
at the margins of the Strait resuspend fine sedi-
ments as demonstrated by the increase of suspen-
sate concentrations in near-bottom waters (Pierce
and Stanley, 1975). Moreover, mud turbidites are
also important constituents of deep cores, as dis-
cussed later.
In addition to the characteristically high values
of MgCO3, and locally, volcanic ash and lava frag-
ments, the Strait sediment contains high values of
montmorillonite (Emelyanov, 1972). The mont-
morillonite content which appears to increase in
the sector near Sicily (Chassefiere and Monaco,
1973; Pierce and Stanley, 1975) and the island of
Pantelleria (Blanc-Vernet et al., 1975) may be
22 SMITHSONIAN CONTRIBUTIONS TO THE. EARTH SCIENCES
/%b////////////////////,
yyvV" /7x/v \
J"7 '? '/'/' S^/' /'//'/ ~J , , A /
FIGURE 16.?Map showing surficial sediment distribution in the Strait of Sicily.
(From Akal, 1972.)
related to a volcanic source. A survey of the clay
minerals in various Strait of Sicily environments
is detailed by Blanc-Vernet and others (1975).
DEFINITION OF MAJOR SEDIMENT TYPES IN CORES
Our study emphasizes the vertical and regional
distribution of sediment types recovered in cores.
Three main assemblages are recognized in Strait of
Sicily cores: (1) coarse, calcareous sand layers in-
terbedded with mud and sandy lutite deposits; this
association prevails on shallow banks; (2) pre-
dominantly homogeneous (nonstratified, biotur-
bated) light olive gray (5 Y 5/2) to dusty yellow
(5 Y 6/4) mud in which the most important struc-
tures are biogenic ones; this type occurs most com-
monly in the neritic-bathyal environments and also
is found in some basins; (3) moderate to well-
stratified sand and mud units that include gravity
flow deposits (sand and mud turbidites, grain flow
units) and/or ash layers interbedded with hemi-
pelagic mud; this assemblage is typical of deep
basins and the Strait Narrows. Gradual transition
from one lithological assemblage to another is also
recorded in the cores.
Cores containing assemblages 2 and 3 generally
display an upper 5- to 40-cm thick layer of oxidized
light brown (5 YR 6/3) or yellowish brown (10
YR 6/4) mud; olive gray mud lies below this and
the vertical color change is usually transitional.
The five major sediment types distinguished in
Strait of Sicily cores include: (1) coarse calcareous
sand; (2) sand- to silt-size sediment; (3) ash; (4)
mud; and (5) sapropel and organic ooze.
NUMBER 16 23
COARSE CALCAREOUS SAND.?The sediments in-
cluded in this group are characterized by a high
percentage of calcareous organic fragments,1 form-
ing generally more than 30% and not less than 15%
of the samples. Grain count values as high as 90%
are displayed by some samples. The grain size is
variable, with a median comprised between 0.5 and
2.5 mm. The content of fines (silt and clay) also is
highly variable and ranges from 0.5 to 30%. The
calcareous components are largely molluscs
(mainly gastropods and pelecypods), coralline al-
gae, echinoderms, bryozoans, and forams.
This sediment type has been observed on various
other shelves and banks of the Mediterranean Sea
(Dangeard, 1929; Blanc, 1958, 1972; Caulet, 1972a,
b; Milliman et al., 1972; and others). On these
shelves two main facies are distinguished on the
basis of composition: (1) shelly and bryozoan de-
posits and (2) coralline sands. The first type can
be differentiated into several subtypes which appear
depth related: (a) "muddy shelly sands" tend to be
more important as depth increases (Milliman et
al., 1972); (b) "very coarse shelly sands" (cf.,
Posidonia facies as described by Blanc, 1972) also
may be represented at shallower depths (about
40 m); and (c) "clean fine-grained shelly sands" are
generally found in the nearshore-inner neritic
environment.
The second facies, the coralline sands, are domi-
nated by particles of calcareous algae, which con-
stitute as much as 70% of the sediment. Three main
subtypes are distinguished on the basis of the cal-
careous algal type: (a) algal ball facies ("fonds a
pralines," cf., Blanc, 1958); (b) encrusting cal-
careous red algae, commonly developed on rocky
substrates; (c) coralline gravel consisting of the ac-
cumulations of debris of the red calcareous algae
Lithotamnium calcareum and Lithotamnium cor-
allioides, with a subordinate association of mol-
luscs, bryozoans, and foraminifera (this forms the
sediment type termed "maerl" by French authors;
cf. Caulet, 1972).
All of the calcareous deposits described above
also may be classified into modern, relict, and resid-
*In this study we call "bioclastic" grains those clasts of
organic origin which display evidence of transport and
reworking (rounding and shape or other indirect evidence);
grains of organic origin which do not show clear evidence
of reworking by transport processes are referred to by the
more general term, "biogenic."
ual sediment types where age is taken into con-
sideration (Emery, 1952, 1968). In many parts of
the Mediterranean maerl appears to accumulate at
present between the intracoastal complex and the
inner-outer shelf transition zone. Relict maerl,
originating in outcrops on the middle to outer
shelf, developed during the last glacial and the
subsequent rise of sea level (Caulet, 1972a, b).
Since this rise in sea level, a fine fraction has been
added, thus modifying the aspect of the original
carbonate sediment (cf. discussion in Swift, 1974;
Kulm et al., 1975). As an example, Milliman et al.
(1972:254) have shown that calcareous sediments
on banks in the Alboran Sea are relict and orig-
inally formed at depths of 70 to 100 m during
lower stands of early Holocene sea level. Residual
deposits are well differentiated in these calcareous
sediments: they display mixed thanatocoenoses
from different environments, and the various
components show different states of preservation.
The coarse calcareous sands are present in all
shallow platform cores of the Strait, and also are
well represented in Strait Narrows cores. Typical
shelly coarse sand, abundant in the shallower plat-
form cores, is also found in cores collected in
deeper environments (e.g., core SP 8-7, 350 m).
Moreover, some cores in deep basins (e.g., KS-12)
also display this facies; here the sands have been
transported from shallower environments and de-
posited downslope by gravity flow mechanisms.
Coralline sands were not recovered in our cores,
but have been reported from the Strait (Blanc,
1958); they also appear in some bottom photo-
graphs (Figure 21; Akal, 1972).
SAND-SILT SIZE SEDIMENTS.?The sand-silt sedi-
ment type is distinguished on the basis of structure,
texture and, to a lesser extent, composition. This
type includes sediments which range in size from
sand to fine silt, and includes a host of intermediate
sizes.
Sand-silt varieties are encountered in the shal-
low platform environment and in the deep basins,
but are uncommon to rare in the neritic-bathyal
cores. This sediment type is generally structureless
in the shallow platform environment. It is geneti-
cally related to the coarse calcareous sand type,
and usually shows a gradational transition with
these coarser deposits both laterally and vertically.
The coarser sediment (median to coarse sand) ob-
served in deep basin cores displays distinct and
24 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
well-defined sedimentary structures including cross-
lamination and oblique lamination, graded bed-
ding, and diverse types of parallel or ripple lamina-
tion. The base of this type of layer usually is sharp
and erosional, and locally displays scour and fill
structures.
The fine silt deposits of this sediment type show
structural and lithologic continuity with some
coarser deposits, i.e., they usually fine upward tex-
turally (graded bedding) from silt to mud. The
most common structures of the silts are parallel
and low-angle oblique lamination. Their sand con-
tent is low, usually less than 5% and frequently
only about 1%.
The composition of this type is variable. There
are bioclastic and foraminiferal sands, where the
coarse fraction is dominated by biogenic carbon-
ates and/or planktonic foraminifera; in other in-
stances the sand consists almost entirely of volcanic
ash. Volcanic ash layers also could be included in
this group, but their characteristic composition
and origin warrant their assignment in another
facies category. Sand composed in part of detrital
feldspathic grains is less common.
VOLCANIC ASH.?Volcanic tephra layers are ob-
served in the deep basin cores, especially those
from Linosa Trough. Although texturally analo-
gous to the former type, they stand out by their
characteristic composition. These deposits do not
represent a major sediment type in Strait cores in
terms of total thickness.
Two different types of layers containing vol-
canic ash and dust are distinguished: (1) air-borne
tephra layers, derived directly from ash flows, mud
flows, or base surges consisting predominantly of
volcanic vitric ash and variable amounts of mud;
and (2) layers of volcanic ash particles or turbidite
layers, which include a significant benthonic
and planktonic calcareous bioclastic sand-size frac-
tion. These two types can be differentiated on the
basis of petrographic characteristics and primary
sedimentary structures (compare the ash layers in
cores KS 69, KS 118, KS 120; cf. Figures 27, 31).
The carbonate-free tephra layers display a vertical
grain-size gradation (fining or coarsening upward),
parallel lamination, or in some instances they are
structureless. The mixed volcanic-bioclastic layers
show well-developed structures and may be similar
to the sand-silt type sediments described in the pre-
vious section.
MUDS.?The mud type is by far the most abun-
dant deposit in the cores studied. Neritic-bathyal
environment cores consist almost exclusively of
mud. Genetically there are three main types of
mud which can be recognized on the basis of sedi-
mentary structures and composition. These are:
shallow water mud, hemipelagic mud, and turbi-
ditic mud. In many cases these are transitional,
and not clearly distinguishable.
Shallow water muds collected at neritic depths
are structurally homogeneous and the only types of
sedimentary structures commonly recognized are
biogenic ones. This mud type may contain a rela-
tively high (to 10%?15%) percentage of sand
fraction, including either biogenic (mostly well-
preserved neritic molluscs and benthic and plank-
tonic foraminifera) or clastic grains. The hemi-
pelagic muds are homogeneous calcareous oozes
which also lack well-defined primary sedimentary
structures, including lamination, and generally are
characterized by vertical bioturbation. The sand
fraction content, lower than in the shallow water
mud, consists largely of calcareous planktonic com-
ponents. The turbiditic muds are characterized by
a delicate basal lamination or small-scale biotur-
bation visible in X-radiographs, and a smooth
uniform aspect in split cores. They occasionally
show continuity and gradation with the sand-silt
sediment type in terms of structure and gross lith-
ology (Rupke and Stanley, 1974).
SAPROPEL AND ORGANIC OOZE.?Sapropels are dis-
tinctive dark gray to black deposits which have
been extensively studied in the eastern Mediter-
ranean (Olausson, 1961; Ryan, 1972; van Straaten,
1972; Nesteroff, 1973; Maldonado and Stanley,
1975; and others). Recently described sequences
from the Black Sea appear similar to Mediterra-
nean sapropels (Ross and Degens, 1974, unit 2).
This sediment type is commonly encountered in
the eastern Mediterranean basin from cores col-
lected at depths exceeding 700 to 1000 m. Sapropels
are retrieved on the slope east of the Strait (LY
II-3, 2432 m). However, cores in the Strait of
Sicily proper (including the deep Pantelleria,
Malta, or Linosa troughs) and in the western Med-
iterranean have not recovered this type of deposit.
The typical sapropel is formed by an alternating
sequence of delicate horizontal laminae of white
(coccolith rich) and black (largely mud) layers.
The sand-size fraction content is about 10%, most of
NUMBER 16 25
which includes planktonic foraminifera.
Organic ooze layers are usually associated with
sapropel. These two sediment types are composi-
tionally transitional. However, in the split cores
the contact between the two is very well marked by
a sharp color change: organic oozes are pale olive
(10 Y 6/2-5 Y 5/2), while sapropels are dark gray-
olive (5 Y 3/2-5 Y 2/1). This contact is also noted
on X-radiographs. A type of sediment that resem-
bles organic ooze is present in the Linosa Trough
and perhaps also in the Malta and Pantelleria
troughs; this type also displays some petrological
affinities with the hemipelagic mud type.
A third type of sediment, protosapropel, is as-
sociated with this group. While genetically and
lithologically related, the protosapropel is not con-
sidered a true sapropel because it does not display
the typical lamination of the sapropel and may be
bioturbated to some extent (Maldonado and Stan-
ley, 1975).
Sand Fraction Composition
GENERAL
The fraction larger than 63 microns was col-
lected from all samples by wet sieving after re-
moval of the organic matter with hydrogen per-
oxide. The identification of grains was made using
a binocular microscope, and relative frequencies
were determined by counting 300 to 400 grains per
sample. The grain counts were made by unit area
measurements as opposed to point counting. The
following parameters were determined: pteropods
(1); molluscs (2) consisting largely of gastropods
and pelecypods; shell fragments (3); planktonic
foraminiferida (4); benthonic foraminifera (5);
ostracoda (6); bryozoa (7); other invertebrates
(8); plant debris (9); heavy minerals (10), in-
cluding opaque and some characteristic nonopaque
minerals; mica (11); pyrite 2 and strongly pyritized
tests and burrows (12); light minerals (13), in-
cluding carbonates and gypsum; and ash (14). The
components 1 to 9 represent the biogenic fraction
while 10 to 14 are grouped as inorganic fraction.
The results of these counts are listed in Table 3,
and the different components have been grouped
2 "Pyrite" as used here is applied to various possible fer-
rous sulfide types.
in triangular plots shown in Figure 17. In one tri-
angle (Figure 17A2), the end points represent the
inorganic fraction (components 10 to 14), plank-
tonic foraminifera (component 4) and the remain-
der of the biogenic fraction (components 1 to 9,
except component 4).
The end members of the other triangle (Figure
17AJ) represent the percent of total sand fraction
in the bulk sample, the total biogenic fraction in
the sand fraction, and the total planktonic fora-
minifera fraction in the sand fraction; all of these
are recalculated to 100%. In this representation any
component could actually be as high as 100%; how-
ever, the total planktonic foraminifera is equal to,
or lower than, the total biogenic fraction. In this
type of representation all of the samples plotted
are concentrated on the left half of the triangle.
The different lines on the triangle mark the bound-
aries of different components.
Core samples have been assigned a letter symbol
on Table 3 and in Figure 17; the numbers associ-
ated with the letter key (Table 3) identify their
depth (in centimeters) from the top of the core.
COARSE CALCAREOUS SAND TYPE
The samples selected for this study are of the
shelly bioclastic sand type as defined in the pre-
vious section. The modern, relict, or residual frac-
tions generally can be distinguished on the basis of
abrasion and preservation of the skeletal material.
Modern biogenic components do not show signifi-
cant evidence of transport, although tests may be
broken. Relict and residual calcareous components
are composed of organic remains deposited during
the Pleistocene and early Holocene (see core AS
6-8, Figure 34), or reworked from older deposits;
these bioclastic particles are characterized by an
iron oxide stain and the rounded, worn shape of
the grain edges. In the Strait of Sicily the sand
fraction of relict sediments also is characterized by
a relatively high feldspathic content (Blanc, 1958);
the modern biogenic sediment is generally associ-
ated with a low feldspar content.
Other organic components of the calcareous
sand type are bryozoa, echinoderma, calcareous
algae, crustacean fragments, and plant debris. Py-
rite is not very common, and where present is usu-
ally oxidized, particularly in relict and residual
sands. Glauconite is more abundant. Gypsum frag-
26 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENGES
TABLE 3.?Percentage of sand fraction (>63 (im) and major components in selected
CORE
LY II-3
LY II-3
LY II-3
LY II-3
LY II-3
LY II-3
LY II-3
LY II-3
LY II-3
LY II-3
LY II-3
LY II-4
LY II-4
LY II-5
LY II-5
LY II-5A
LY II-5A
LY II-5A
LY II-5A
LY II-5A
LY II-5A
LY II-5A
LY II-5A
LY II-5A
LY II-5A
LY II-6
LY II-6
LY II-6
LY II-6
LY II-6
LY II-6
LY II-6
LY II-6A
LY II-6A
LY II-6A
LY II-7
LY II-7
LY II-7
AS 6-8
AS 6-8
AS 6-8
AS 6-8
AS 6-7
AS 6-7
AS 6-7
KS 63
KS 63
KS 63
SAMPLE DEPTH
IN CORE (cm)
5(a)
210-255(b)
338(c)
408(d)
412(e)
415(f)
418 (g)
428 (h)
465(i)
467-512(j)
557(k)
70-115(a)
298-351(b)
60-100(a)
270-310 (b)
15(a)
20-60(b)
61 (c)
105 to)
125(e)
133(f)
270(g)
270-310 (h)
318(i>
550-590(j)
5 (a)
45-85 (b)
90(c)
263(d)
273(e)
285(f)
450-490 (g)
10-50 (a)
230-270 (b)
530-570(c)
260(a)
270(b)
275(c)
33-65
(>200tim)
33-65
(200-63um)
33-65(a)
510-550 (b)
O-45(a)
185-200(b)
685-728(c)
200-250 (a)
500-550(b)
800-850(c)
PTEROPODS
9.3
0.6
-
-
10.5
7.2
"
0.3
-
2.6
-
0.3
-
0.9
1.9
1.1
1.8
5.5
0.6
-
2.1
1.2
5.4
0.3
3.8
1.2
0.5
0.8
1.3
2.5
1.2
-
0.5
1.9
10.5
1.2
2.1
-
-
-
0.8
-
0.3
-
3.3
-
MOLLUSKS
-
0.6
-
-
0.8
-
-
-
-
-
0.6
0.6
0.9
-
0.8
0.6
-
0.9
-
1.2
0.3
-
-
-
0.6
-
-
0.3
-
0.3
-
0.6
-
0.6
-
-
0.8
3.6
"
1.8
1.3
1.0
26.5
-
1.6
3.9
2.6
TEST
FRAGMENTS
14.9
8.5
13.7
5.7
10.0
16.1
0.9
0.8
14.4
1.2
16.9
5.8
28.1
24.3
12.9
18.2
7.3
6.4
2.5
5.9
15.5
11.1
19.6
13.9
31.3
6.9
1.0
5.0
7.7
19.4
9.7
11.8
9.0
9.9
1.0
0.8
11.3
8.6
3.2
5.9
9.4
12.1
13.4
5.5
10.0
11.5
8.8
BIOGENIC FRACTION
PLANKTOKIC
FORAMS
68.0
66.4
73.5
84.5
65.3
57.3
0.3
85.3
54.7
92.8
29.4
55.3
60.8
39.6
30.7
65.3
38.4
35.7
2.7
9.6
24.2
57.5
24.7
49.9
38.4
82.5
96.5
62.7
69.9
49.5
66.1
77.0
72.1
66.8
72.3
62.1
43.4
2.8
2.9
2.8
2.2
14.4
0.6
4.0
5.6
27.9
5.2
BENTHONIC
FORAMS
-
0.6
8.4
-
0.5
1.8
2.3
"
4.6
2.6
0.6
8.6
8.4
1.2
0.9
4.3
3.8
4.2
19.1
9.2
8.1
7.3
7.5
0.3
0.5
2.2
3.5
11.5
5.3
5.0
6.2
4.5
1.2
3.5
4.2
30.1
7.8
18.9
11.8
36.8
19.7
15.3
4.7
15.4
5.9
OSTRACODS
2.7
-
-
0.6
1.5
0.3
0.9
1.3
0.8
2.2
"
0.6
"
0.7
4.2
2.2
1.8
1.9
1.4
1.8
-
0.6
1.3
1.6
0.9
2.2
1.9
1.0
0.8
0.5
1.2
13.1
1.5
7.3
5.3
3.8
1.0
3.2
0.9
7.1
1.6
BRYOZOANS OTHERS
1.5
2.4
0.9
3.4
6.7
1.5
3.1
5.2
1.6
6.9
3.8
0.5
2.2
0.6
4.6
4.2
13.9
0.6 2.2
2.7
2.2
10.4
3.9
23.1
2.6
3.2
2.9
1.9
6.0
3.2
1.2
4.3
0.9 17-9
0.4 9-?
5.0
0.4 10-8
4.7
4.3
10.0
11.2
4.9
PLANT
DEBRIS
6.3
0.3
"
2.0
0.8
0.9
3.2
1.2
-
-
0.6
0.5
1.5
-
0.3
1.2
3.5
0.3
-
0.3
0.6
-
-
-
9.7
4.1
6.9
0.9
0.5
0.3
1.7
1.9
3.3
0.3
'Fine Silt Q
Volcanic Ash Coarse Calc
NUMBER 16 27
samples from different Strait of Sicily sedimentary environments
INORGANIC FRACTION
HEAVY LIGHT VOLCANIC
MINERALS MICA PYRITE MINERALS ASH
iL GRAINS
XJNTED
335
329
321
349
389
335
322
334
375
339
326
326
311
332
312
371
319
344
328
480
426
330
315
332
317
345
332
120
360
309
313
340
321
370
314
289
3 05
316
420
338
-
320
450
305
347
319
3 53
306
%BIOGENIC/
%INORGANIC
100/0
82.1/17.9
96.5/3.5
95.6/4.4
87.9/12.1
83.8/16.2
0/100
1.5/98.5
96.0/4.0
75.5/24.5
98.3/1.7
58.5/41.5
66.2/33.8
99.1/0.9
79.5/20.5
55.2/44.8
92.1/7.9
52.1/47.9
49.1/50.9
13.6/86.4
26.3/73.7
80.8/19.2
84.1/15.9
62.6/37.4
76.7/23.3
96.9/3.1
96.9/3.1
98.5/1.5
94.7/5.3
86.6/13.4
88/12
86.7/13.3
98.5/1.5
95.7/4.3
87.9/12.1
87.0/13.0
68.1/31.9
67.3/32.7
86.7/13.3
19.5/80.5
53.1/46.9
35.9/64.1
80.6/19.4
66.2/33.8
34.3/65.7
34.7/65.3
83.6/16.4
29.3/70.7
%SAND FRACTION
(>63p)
7.4
4.6
6.4
4.8
8.0
1.4
34.5
64.2
6.9
5.2
10.9
9.5
3.1
4.2
3.5
29.3
4.2
5.8
41.4
10.7
8.6
4.6
2.8
1.3
2.8
4.9
0.1
0.1
5.7
24.8
32.5
5.3
5.9
6.2
5.4
5.8
1.3
3.2
-
-
90.2
21.9
3.2
25.0
8.0
2.5
6.0
3.5
SEDIMENT SYMBOI
ON FIGURES
?0
0
??
?
A
A
?0/D
??/o
0/O
0
0
?/A
0
A
/A
A
A
Q
0/?
Q
0
<8>/0
?
?
?
0/?
0
0
0/?
0
?
?
?
?
O
?
O
0/?
0
0/?
3.9
0.7
-
1.0
4. 8
5.9
1.5
-
8.1
-
23.3
12.8
0.6
7.7
9.7
0.6
3.5
9.1
5.2
1.2
6.4
7.5
10.5
2.8
1.7
0.3
-
1.7
2.3
4.1
3.5
0.6
1.9
2.2
1.1
6.8
5.7
1.2
18.4
9.8
20.0
3.0
14.8
7.8
8.8
2.2
12.4
11.9
1.9
0.7
3.6
5.7
0.3
-
-
2.3
-
4.0
4.8
-
2.9
1.3
3.1
-
-
3.1
0.7
0.9
0.6
0.6
2.2
0.8
-
0.3
2.2
1.3
0.9
3.2
0.3
0.3
1.2
3.1
8.9
6.3
"
0.6
0.3
0.6
0.7
0.6
1.2
3.7
1.7
1.9
-
3.7
5.9
-
-
-
4.0
4.4
1.5
1.2
-
-
5.5
0.5
0.3
-
0.6
-
-
1.5
4.4
7.8
8.2
-
2.8
1.2
0.6
1.3
1.9
4.4
0.6
1.1
2.5
3.8
1.0
0.5
-
-
-
0.9
5.1
2.0
1.1
10.1
2.6
3.1
1.2
0.9
-
1.0
1.8
5.9
0.9
-
4.7
0.2
8.1
14.6
0.3
2. 2
18.3
3.9
1.7
11.3
2.1
4.0
8.2
2.5
18.5
10.1
0.6
-
-
0.8
8.5
5.1
2.2
-
1.0
6.2
5.0
15.2
20.2
12.1
61.5
36.8
42.6
10.6
16.4
55.6
42.7
9.9
53.3
0.9
-
-
0.6
3.9
87.9
96.1
-
5.0
-
4.9
1.6
-
2.2
15.1
-
42.7
29,9
76.0
67.8
2.2
0.9
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Shallow-Water Mud Q
Hemipelaglc Mud Q)
Turbiditic Mud
28 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
Total Sand Fraction (>63/jm)
g
h
A
Total Biogenic Fraction ( >63 urn) sand = 0 b
Biogenic Fraction Total Planktonic _
without Planktonic F.) Foraminiferal Fraction
(>63>,m)
Planktonic Foraminifera
Total Sand Fraction Inorganic Fraction
B
Plankton i c Foram in ifc
FIGURE 17.?Mineralogical analysis of selected samples from 10 cores collected in different en-
vironments: A, plots of the actual sand fraction from samples analyzed (letter code given in
Table 3); B, interpretation of data plotted in (A) showing the distribution of some major sedi-
ment types based on several components of the sand fraction. (Explanation in text.)
NUMBER 16 29
ments are also present in some samples, probably
resulting from the erosion of outcrops on the shelf
during the eustatic low stands of sea level.
SAND-SILT SEDIMENT TYPE
In the sand-silt type we consider all textural
types ranging from sand to silty sand to sandy silt
to silt. In the coarse sand-silt type, the sand con-
tent is above 20% of the entire fraction, and the
sand fraction generally comprises more than 50%
calcareous biogenic components. However, in shal-
low platform samples (i.e., AS 6-8b) the calcareous
content is lower due to a masking effect produced
by the addition of detrital material.
The sand-silt sediments collected in the shallow
environments have a biogenic content usually well
represented by shells, shell fragments, benthonic
foraminifera, and other calcareous biogenic com-
ponents similar to those of the coarse and bio-
clastic sands. Planktonic components are also
present.
The composition of the organic fraction in the
majority of the sand-silt samples collected in the
deep environments is more varied: planktonic and
benthonic foraminifera, echinoderm spicules and
fragments, bryozoa, calcareous algae, sponge spic-
ules, mollusc shell and shell fragments, plants, etc.
Radiolarian fragments, pteropods, and diatoms
also occur. In general, this type of "mixed" bio-
clastic assemblage is interpreted as a thanatocoeno-
sis containing biogenic remains derived from
various environments (Parker, 1958). Thus, it is
interpreted as a resedimented deposit.
Quartz and feldspar account for much of the
inorganic fraction except in volcanic ash layers.
Heavy minerals, glauconite, and mica also occur.
The composition of the sand fraction of this
sediment type provides some information as to (1)
sediment provenance and depositional environ-
ment, and (2) hydrodynamic processes. The first
factor is interpreted mainly on the basis of the
biogenic components and, to a lesser extent, the
inorganic (mostly authigenic minerals) fraction;
insight as to the processes is provided by the physi-
cal character of the grains, particularly density and
particle shape. As an example, the mica and flaky
particles, including shell fragments, tend to be con-
centrated in parallel laminae, i.e., either as part of
the d-division of the Bouma turbidite sequence or
as horizontal laminations produced by bottom cur-
rents. These concentrations can be interpreted in
terms of hydraulic equivalents inasmuch as the
large flaky grains are more easily maintained in
suspension than the smaller round ones. The rela-
tively denser and more spherical particles, such as
heavy minerals, tend to be concentrated in the
lower turbidite divisions although they are smaller
in size than the majority of grains with which they
are associated (Rupke and Stanley, 1974).
VOLCANIC ASH TYPE
The volcanic ash layers, as in the above-described
sediment type, also comprise a textural mix of
sand- and silt-size grades. However, composition-
ally this type is quite characteristic and is thus dis-
cussed as a separate entity. Ash layers usually
contain a high sand fraction (above 30%), much of
which is constituted by fragments of volcanic ori-
gin; there are many textural varieties ranging from
sand to mud. Two distinct types are recognized.
The first is characterized by its calcareous biogenic
content in the sand fraction, which is composed
mostly of foraminifera, pteropods, and minor sub-
ordinate amounts of other biogenic components.
The composition of this calcareous fraction is simi-
lar to the one displayed in the hemipelagic mud
type, defined later. The second type of volcanic
ash layer presents a more variable calcareous frac-
tion, represented by mixed biogenic assemblage
from different environments (i.e., similar to that
of the sand-silt sediment type). The first type re-
sults from pelagic settling of volcanic air-borne
ash, which may eventually be winnowed and modi-
fied by bottom currents (cf. tephra layers described
by Ninkovich and Heezen, 1965; Keller et al.,
1974). The second type of volcanic ash layer is re-
lated with turbiditic sedimentation (Sarnthein and
Bartolini, 1973).
SHALLOW WATER MUD TYPE
The shallow water mud type is highly variable
in both sand-size content (4%-20%) and biogenic
content (30%-90%). There is a gradual transition
between this type and the sand-silt type from shal-
low water environments described earlier. The
sand fraction in the mud includes benthonic fora-
minifera and a relatively low (< 30%) planktonic
30 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
foraminiferal content. In these samples the rela-
tion of planktonic to benthonic tests can be used
as an indication of depth (Boltouskoy, 1965). How-
ever, use of this ratio is valid only if the sediment
accumulates in situ; interpretation of these ratios
is difficult when sediments are transported to
deeper environments (for example in the case of
turbiditic muds). Some samples (cf., LY II-4a),
located in intermediate to deep water, are inter-
preted as a sediment type transitional between
shallow water mud and turbiditic mud. Such sam-
ples have a relatively high benthonic foraminifera
and shell fragment content and the degree of abra-
sion observed indicates that they have been re-
worked to some extent prior to final deposition.
Compositional plots of samples from this type of
mud are shown in Figure 17A. Here the samples
tend to be distributed on the left side of the tri-
angular diagrams. Figure 17B reveals a relatively
high biogenic fraction but a low planktonic fora-
minifera content in the sand fraction.
HEMIPELAGIC MUD TYPE
The hemipelagic muds have a sand content of
2.5% to 6.5%. This sand fraction is 80% to 99%,
biogenic and usually comprises more than 40% of
planktonic foraminifera3 (Figure 17, Table 3).
Other components of the biogenic fraction include
pteropods, mollusks, radiolaria, diatoms, sponge
spicules, ostracoda, fecal pellets, and benthonic
foraminifera. The inorganic clastic fraction con-
sists of quartz, mica, pyrite, heavy minerals, glau-
conite, and volcanic ash. Fragments of pyritized
burrow tubes also are common in some samples.
The compositional plots of this type of mud
tend to be distributed in the lower right sector of
the triangular representation (Figure 17B). The
position occupied by this type of mud is distinct
from that of the shallow water mud type in tri-
angular diagrams AX and B1 in Figure 17.
TURBIDITIC MUD TYPE
The two end members of the turbiditic mud type
3 A list of planktonic foraminifera identified in cores KS 33,
78, and 105 and an evaluation of their vertical distribution are
presented by Blanc-Vernet et al. (1975).
are contrasted as follows: one has a very low sand
fraction (= 1%) which is mostly bioclastic (^ 70%),
and the other is a more sandy terrigenous turbi-
ditic mud (~ 5% sand fraction of which 50 to 80%
is bioclastic). In the first type the calcareous frac-
tion includes mostly planktonic foraminifera, while
the second type has a higher content of benthonic
foraminifera and shell fragments. The terrigenous
components are analogous to those of hemipelagic
muds, although the burrows and tubes are rare.
The composition of the sand fraction in the
turbiditic and hemipelagic muds differs from that
in the Algero-Balearic Basin described by Rupke
and Stanley (1972). This difference reflects (1) a
higher terrigenous influx in the Strait of Sicily, as
a result of proximity to land (i.e., important
clastic influence) and (2) more extensive vertical
bioturbation of the sediments. In some cases, it is
difficult to distinguish between hemipelagic and
turbiditic mud on the basis of composition because
of reworking by currents (see Table 3).
The turbiditic mud samples occupy a random
distribution and are not distinctly concentrated on
the triangular representation in Figure 17A2. How-
ever, this sediment type is better delineated in the
triangular diagrams AX and Bj in Figure 17; here
turbiditic mud occupies an intermediate position
between hemipelagic and the shallow water mud.
The three types of mud appear transitional on the
basis of composition.
SAPROPEL TYPE
The sand content in the sapropel type ranges
from 5% to 10%, and is mostly biogenic (95%-
100%). The inorganic fraction consists of authigenic
minerals (pyrite and gypsum) and, to a lesser extent,
mica. The calcareous sand fraction is dominated by
planktonic foraminifera (generally ^ 70%) and also
includes plant fragments, pteropods, radiolaria,
and diatoms. A high proportion of foraminiferal
tests are pyritized. All these components indicate
a low detrital input during deposition, although
normal turbidites can be intercalated in the sapro-
pel deposits (van Straaten, 1972; Nesteroff, 1973).
The characteristic composition of sapropel sam-
ples is shown in triangular representations BX and
B2 in Figure 17. Sapropel deposits are concentrated
in the lower right corner of both types of triangle.
NUMBER 16
ORGANIC OOZE TYPE
The organic ooze and protosapropel types are
transitional between the hemipelagic mud and the
sapropel types in terms of sand-fraction composi-
tion, texture, and structure. Thus, a small amount
of clastic sand fraction is present as well as a less
uniform biogenic fraction in contrast to the sapro-
pel type. Organic ooze is characterized by the fre-
quent occurrence of pyritized worm tubes; these
are concentrated at the top of the organic ooze
layer and are well displayed in the core X-
radiographs (Figure 28).
BRYOZOAN CONTENT
The sand fraction of 44 samples from different
environments (cores LY II and AS) were exam-
ined for bryozoan content (Salvador Reguant, Uni-
versity of Barcelona, Spain, pers. coram.). The
bryozoan content is low except in shallow platform
cores. Bryozoan fragments may be transported in
the various environments in the same fashion as
are the planktonic foraminiferal tests associated
with them; fragments of cellariiform zooarial tubes
and, locally, of catenicelliform species (in LY
II?6, g) disintegrate when animals die and can be
transported in suspension prior to deposition.
Rapid burial in fine sediment is necessary for the
preservation of these delicate fragments.
Sample AS 6-8, a, is of interest because it con-
tains an assemblage of species indicative of a some-
what low energy environment although the core
was collected at a depth of 93 m. An examination
of 97 fragments reveals the following zoaria: mem-
braniporiform (3); celleporiform (2); adeoniform
(12); vinculariiform (30); reteporiform (8); cel-
lariiform (42). This zoarial assemblage is closely
related to that reported from slope environment
(cf., Caulet, 1972:239, 243). It is difficult to ex-
plain in terms of the sea-floor depth where this
core was collected and the age of this sample
(17,000 to 20,000 years BP, Table 5). One possible
interpretation is that this sample consists of re-
sidual material (i.e., a thanatocoenosis) from a
different environment. The possibility of reworking
of older material appears corroborated by the
abundance of gypsum grains in the same sample,
also believed to have been eroded from outcrops of
the shelf.
SEM Analysis of the Lutite Fraction
A scanning electron microscopic analysis serves
to determine the composition of the lutite fraction
and provides a rough quantitative approximation
of the different components. In order to prepare
the samples for electron microscopy, the organic
matter is first destroyed with 30% hydrogen per-
oxide. Then the sample is wet sieved to separate
the fraction coarser than 63 microns. The residue
is then placed in suspension. A drop of this sus-
pension is pippeted immediately after mixing and
placed on a standard metal specimen plug. The
sample is then dried at room temperature and
coated with gold. No sticking tape was used. In the
case of some coarser grained samples, grains were
glued (Elmer's glue) to the plug to avoid discharge.
The plug was examined with a Cambridge In-
strument Stereoscan. Photographs were made of
each sample using SEM low magnification (100-
500 magnification), which reveals details of sedi-
ment texture and a rapid inventory of the fossil,
authigenic, and detrital assemblages in the silt
fraction. Individual grains and the fine silt and
clay fraction have been examined systematically
using high (X 2000) magnification.
The identification of the different particles is
based on a comparison with previous works and, in
particular, those of Stieglitz (1972) and Milliman
(1974) for the calcareous fraction. The distinc-
tion between the calcareous biogenic and the in-
organic clastic particles is often subtle, especially
in the finest fractions.
The common components of the lutite fraction
are clay-size particles and aggregates, calcareous
fragments of tests, siliceous grains, aggregate
grains, calcareous inorganic grains, calcareous nan-
noplankton, spicules, foraminifera, and volcanic
ash fragments. Pollen, dinoflagellate cysts, pyrite
framboids, diatoms, plant fragments, and silico-
flagellates are abundant in some samples.
The composition of the lutite fraction of the
sand-silt sediment type (Figures 18, 19A-C) is the
most variable of all the sediment types studied.
Calcareous biogenic and bioclastic particles and
terrigenous feldspathic grains are predominant in
the coarse silt fraction (c and / in Figure 18A,B).
The biogenic calcareous grains, mostly calcareous
algae and foraminiferal test fragments (c), are the
dominant components (Figure 18B). Well-
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
FIGURE 18.?SEM photographs showing silt and clay fraction of the sand-silt sediment type:
A-D, sample LY-II-6, d; E-F, LY II-5A, g (c = calcareous biogenic grain, / = feldspathic clastic
grain, t = tunicate ascidian spicule). (Poorly defined clay and silt-sized crystals, needles, aggre-
gates, and coccoliths shown in E and F; explanation in text.)
NUMBER 16
' !. **'
?> r -
: . pS"
FIGURE 19.?SEM photographs showing silt and clay fraction of the sand-silt sediment type
(A-C), turbidite mud (D), hemipelagic mud (E), and shallow water mud (F): A, B, sample LY
II-5A, i; c, LY II-6, f; D, LY II-6, c; E, LY II-6, a; F, AS^ 6-7, a (a = aggregate grain, c =
calcareous bioclastic grain, d = discoaster). (High concentration of irregular plates, needles;
aggregate grains and poorly defined crystals are shown in E and F; explanation in text.)
34 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
preserved and broken tests of foraminifera and
calcareous tunicate spicules are also commonly
associated with this sediment type (Figure 18B).
The presence of calcareous ascidian (tunicates, t)
spicules (Figure 18B-D) are of primary interest
because they characterize the turbidite sand-silt
sediment type. Factors controlling the distribution
of living ascidians are the bathymetric range and
the nature of the substrate. The didemnids, a com-
mon type of ascidian, extend from the intertidal
zone (very abundant) to about 500 m; they prefer
a hard substrate on which to build their colonies
(P. Mather, pers. coram.; Hekel, 1973:10). Thus,
the presence of a high concentration of ascidian
spicules in samples collected in deep water may
indicate an original shallow water origin and sub-
sequent transport downslope.
In the fine silt and clay fraction of the sand-silt
sediment type (Figures 18E,F, 19A-C) the more
common components are calcareous nannoplank-
ton, especially coccoliths, aggregate grains (Figure
19B, a), terrigenous clay-size particles, and non-
identified calcareous grains of biogenic origin.
Coccoliths may represent up to 50% of this fraction.
Their characteristic is a poor preservation and a
mixed thanatocoenosis, which may include re-
worked Tertiary species (e.g., discoaster, Figure
19B, d). However, all the samples studied belong to
the Emiliania huxleyi zone of Upper Quaternary
age.
The terrigenous grains usually show an angular
to round outline and well-developed facets (Figure
18A, /). In general, the surface texture characteris-
tics of the siliceous grains (regardless of their min-
eralogy) in this very fine fraction cannot be cor-
related with similar structures observed on coarser
grains (Krinsley and Doormkamp, 1973; Krinsley
et al., 1973; Margolis and Krinsley, 1974; Whalley
and Krinsley, 1974). For instance most of the fine
silt-size grains investigated show very high relief
conchoidal breakage pattern, imbricated breakage
blocks, and other grain surface features which have
been related to glacial action by these authors.
This interpretation is probably not applicable to
these Mediterranean sediments.
Turbiditic mud (Figure 19D) displays many of
the same characteristics as the sand-silt sediment
type. However, fine turbidites are better sorted to-
ward the fine fraction and there is a noticeable
scarcity of intact fossil remains. Emiliania huxleyi
and Cyclococcolithus leptoporus account for most
of the nannoplankton remains, but a detailed
analysis of the coccoliths has not been made.
The coarse silt fraction of the hemipelagic mud
type is dominated by biogenic calcareous and ag-
gregate grains (Figure 19E). In the fine fraction
two subtypes are distinguished: (1) sediments rich
in coccoliths, and (2) sediments rich in poorly
defined fine silt- to clay-size crystals, needles, plates,
and irregularly shaped grains, with a relatively low
coccolith content (Figure 19E). The general aspect
of this second type resembles the magnesian calcite
sediments of the eastern Mediterranean (Milliman
and Miiller, 1973).
The silt fraction of the shallow water mud shows
a high percent of needles, plates, and irregularly
shaped grains, and, in general, a lower nanno-
plankton content (Figure 19F) than in the other
mud types sampled. However, coccolith-rich mud
has been reported elsewhere from shallow water
environments (Scholle and Kling, 1972).
The coarse fraction of the shallow water mud is
dominated by calcareous biogenic grains. The bet-
ter state of preservation of these grains facilitates
their identification on the basis of grain surface
texture (cf., Stieglitz, 1972). Calcareous algae, fora-
miniferal, and molluscan fragments are among the
most characteristic calcareous components.
Volcanic ash is well distinguished with the aid of
the SEM (Heiken, 1974). Two main types of ash
particles have been identified: (a) broken droplets
with abundant vesicles, and (b) angular glass
shard, where inclusions are rare (Figure 20A).
Furthermore, the carbonate-poor tephra air-borne
layers are characterized by a decrease in calcareous
(usually nannoplankton) components, while ash
layers reworked by turbidity currents, slumps and
other subaqueous gravity mechanisms contain a
significant calcareous fraction derived from several
shallow to deepwater environments. The first type
represents an essentially primary ash layer deposit,
while the second type is identified as a downslope
reworked unit.
The organic oozes are characterized by a great
abundance and variety of nannoplankton species
(Figure 20C.D). Coccolithus pelagicus (Wallich)
Schiller, and Scyphosphaera apsteini Lohmann
are among the abundant species in these oozes;
they are reported from cold water (Mclntyre and
Be, 1956; Miiller, 1973). The other major com-
FIGURE 20.?SEM photographs showing silt and clay fraction of the volcanic ash type (A),
organic ooze (B-D), and sapropel (E and F): A, sample LY II-3, h; B-D, LY II-3, e; E-F, LY II?3,
i (/ = feldspathic grain, p = pyrite framboid). (Volcanic glass shards in A; explanation in text.)
36 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
ponents of these oozes are aggregate grains, nee-
dles, and irregularly shaped grains, many of which
are attributed to terrigenous clay particles.
The fine fraction of sapropel (Figure 20E,F) is
characterized by an impoverishment in the number
of species and the amount of nannoplancton in
the black clayey laminae and a high coccolith con-
tent, represented by only a few species, in the white
lamine. Helicopostosphaera kamptneri Hay and
Mohler and/or Emiliani huxleyi may be the only
species present in these white lamine and consti-
tute as much as 100% of the bulk sediment.
An association of nannoplankton interpreted as
a warm water assemblage is reported from sapropel
layers in the eastern Mediterranean (Miiller,
1973). Thin laminae of diatoms, radiolarians, and
silicoflagellates may also be associated with sapro-
pel or organic oozes. Pyrite framboids (p) are also
characteristic of sapropel (Figure 20E). The sphe-
roidal form of the framboids is an inherited char-
acteristic provided by a preexisting template (Rick-
ard, 1970; Sweeney and Kaplan, 1973). They are
attributed to the pseudomorphism processes of py-
rite formation (Rickard, 1970) during early dia-
genesis of the sediment or in the water column
(Ross and Degens, 1974:187). Twin-gypsum crys-
tals also are common in the sapropel; they are
attributed to neogenesis processes (Nesteroff, 1973:
719).
Sea-Floor Photography
Sea-floor photographs collected in the different
Strait of Sicily environments illustrate some sur-
ficial sediment types described in the previous sec-
tions. These photos are of some assistance in the
interpretation of biogenic structures recorded in
the cores.
The shallow platform and banks are character-
ized by a generally flat bottom with many small
irregularities resulting from biological activity.
The most typical surface type is one covered by
coarse sediment with little or total absence of re-
lief (Figure 21). Calcareous algae is a common
biogenic component. Three of the photographs
illustrated in Figure 21 (A,B.,D) show sand and
calcareous algae (algal balls) of the type described
in the shallow platform environment by Blanc
(1958); this sediment type has been termed "maerl"
(Caulet, 1972). A coarse calcareous shelly sand is
shown in Figure 21c.
The importance of bioturbation which predomi-
nates on such well-oxygenated shallow platforms is
well documented (Sarnthein, 1972; Reineck, 1973),
but burrowing of the sediment is not clearly ap-
parent on the Strait of Sicily photographs. The
absence of biogenic and current-produced struc-
tures such as ripples, scour shadows, and grooves is
not necessarily an indication of lack of vigorous
bottom current activity. Strong bottom currents
have been measured in this part of the Strait
(Molcard, 1972). Some photographs, for instance,
show crinoids heeling over (Akal, 1972, fig. 8);
this and the absence of fines together reflect the
effect of strong flow capable of modifying the sea
floor. An analogous set of observations has been
made on the banks of the Alboran Sea by Milliman
and others (1972), who record the heeling over of
organisms but find little evidence of current-
produced structures in the coarse-textured sea floor.
It appears that coarse, poorly sorted sediment of
the type observed on the shallow banks does not
preserve such features well.
The sea floor of neritic-bathyal environments
(Figure 22) is characterized by strongly pitted and
trailed muddy sediments. Most of the sediment sur-
face has been intensely disturbed and burrowed, re-
flecting significantly high activity by benthic or-
ganisms. Broad depressions, small holes, and plow
marks or grooves are also common. The biogenic
bottom structures in these environments are well
preserved, while evidence of bottom current ac-
tivity is not well displayed by the sediment.
Photographs of the deep basin environment (cf.
Malta Trough, Figure 23) show a mud floor al-
most entirely reworked by benthic organisms, al-
though burrowing appears to be less extensive and
less varied than in the former environment. The
most characteristic feature is the high density of
granular mud rods identified as large fecal pellets.
Holothurians, the most common of the mud-eating
benthic organisms (Ewing and Davis, 1967; Hee-
zen and Hollister, 1971), are probably the pro-
ducers of these pellets. Biogenic structures include
small to medium-size mounds with apical holes
(holothurian) and depressions, and sinuous trails
left by wandering gastropods or echinoderms. One
large rim crater (Figure 23D) resembles fish-
produced structures described elsewhere (Stanley,
1970; Heezen and Hollister, 1971).
NUMBER 16 37
FIGURE 21.?Bottom photographs collected in shallow environments in the Strait of Sicily: A,
Patches of sand and gravel showing coarse, calcareous sediment, including calcareous algae, algal
balls and shells; station 151-59, 88 m, a shallow bank in the Strait Narrows, B, Calcareous sand
and gravel, including shell and algae, on a bank south of Pantelleria Island; station 151-56,
119 m. c, Shelly sand on a shallow bank north of Cape Bon in the Strait Narrows; station
151-60, 106 m. D, Crinoids on a coarse calcareous sand and gravel, including calcareous algae and
shell (example of maerl) on a bank northwest of Marettimo Island, north of the Strait Nar-
rows; station 151-62, 133 m. (Photos courtesy of the Woods Hole Oceanographic Institution.)
One photograph (Figure 23A) shows the close
relation between sedimentation and bioturbation:
the fecal pellet-covered sea floor in the Malta
Trough is partially veneered by a thin, smooth
layer of fine-grained sediment. The lack of tracks
on this smooth coating suggests that the mud layer
has been recently deposited, although the transport
process involved (gravity assisted bottom or tur-
bidity current?) is unknown.
Structures Observed in X-Radiographs
and Split Cores
Core radiography is a valuable technique for the
definition of the different Strait of Sicily sediment
types which in earlier sections were identified on
the basis, of texture and composition. X-radiographs
are of particular importance for the recognition of
the different mud types, and this technique also
38 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
FIGURE 22.?Bottom photographs collected at intermediate depths in the neritic-bathyal platform
showing bioturbated, oxidized hemipelagic mud surface: A, northwest of Marettimo Island;
station 151-61, 380 m; B, Strait Narrows; station 151-58, 567 m. (Worm tubes?see shadows?
are noted in lower photograph; photos courtesy of the Woods Hole Oceanographic Institution.)
NUMBER 16 39
FIGURE 23.?Bottom photographs collected in Malta Trough (station V 14-K53, 1587 m) showing
typical deep basin surficial sediment cover consisting of bioturbated structures and fecal pellets:
A, partially buried biogenic structures and pellets by fine-grained sediment; B, meandering plow
marks (holothurian or echinoid trails) and small volcano-like mound with apical vents; c,
conical mounds and locally partially buried fecal pellets; D, large depression, possibly fish
produced structure. (Photos courtesy of the Lamont-Doherty Geological Observatory of Columbia
University.)
40 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
FIGURE 24.?Selected X-radiographs (negative prints) of cores collected in the shallow platform
environment: A, B, coarse calcareous sand type; c, D, sand-silt shallow water sediment type;
E-G, shallow water mud type (b = burrow, g = gastropod, p = pelecypod, m = mycellia).
(Vertical scale given in centimeters from top of core; see also Figure 34 for core logs.
NUMBER 16 41
FIGURE 25.?Selected X-radiographs (negatives, except D) of cores showing turbibite sequences
collected on the Ionian slope (LY II-3) east of the Strait and in deep basins (LY II-5A,
Pantelleria; KS-120, Linosa). Sand and silt laminae appear light in negative prints (Tb-Td =
Bouma turbidite sequence; Te(t) = turbidite mud; Te(p) = hemipelagic mud; b = burrow;
pt = pteropod). (See also Figures 34 and 35 for core logs.)
42 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
serves to define sediment sequences. The X-
radiographs illustrated in this study (Figures 24-
32) in most cases are negatives (identical to the
original radiograph, where silt and sand layers ap-
pear as light-toned bands); in a few cases we have
used positives (Gesite cores in Figures 27, 31, 32).
The coarse calcareous sand type can easily be
recognized in both split cores and X-radiographs.
It does not show any primary stratification or grad-
ing (Figure 24A,B), and well-preserved shell, small
shell fragments, and detrital grains are well mixed
texturally. Different degrees of abrasion are dis-
played by the coarse calcareous debris of relict and
residual origin. These characteristics are the result
of intense vertical bioturbation (cf., Sarnthein,
1972; Reineck, 1973; Kulm et al., 1975). Burrow-
ing activity revealed in cores includes thick bur-
rows and pods filled with coarse calcareous
materials.
The sand-silt sediment type generally presents
an excellent set of structures: parallel, ripple, and
cross lamination are the most common. Sets of 1
mm or less in thickness prevail, while the cosets
range from a few millimeters to several centi-
meters (Figures 25B,E,F, 32B). The basal contact
of the sand and ? silt layers records erosion, as indi-
cated by scour-and-fill structures (Figure 25E).
However, some of the finest grained silt deposits do
not display an erosional basal contact (cf., Balearic
Basin plain deposits discussed by Rupke and Stan-
ley, 1974). Vertical graded bedding is usually visi-
ble in the lower member of the layers; a general
upward decrease in grain size within the sand to
silt grades is also present. Parallel lamination of
fine silt and mud (darker zones in the X-
radiograph negative prints) are in continuity with
the basal silt or sandy layer (Figure 25F). Biogenic
structures are rare in these deposits, except for
some so-called "escape" traces.
The two basic types of ash layers differentiated
earlier are also well marked in the X-radiographs.
The pelagic settling type of volcanic air-borne ash
is in most cases nonlaminated (Figure 27A,B); how-
ever, an upward coarsening or fining (i.e., an in-
crease or a decrease in the amount and size of ash
particles in the mud) is often apparent (Figure
27A,B). This gradual vertical change in the
amount of ash particles in the mud is reflected in
X-radiographs by a gradual change in tonality,
from gray to black. Individual coarse grains of ash
in the mud are represented by black spots dis-
seminated in a light matrix (Figure 27B).
Tephra layers also may display horizontal lami-
nation (Figure 27c). However, the other types of
structures recorded in the sand-silt sediments, par-
ticularly cross and ripple lamination, are uncom-
mon in these deposits. The type of tephra layer
structures are related to some degree with the dis-
tance from the volcano and the type of explosive
activity.
Turbiditic ash layers, on the contrary, show the
same type of structures as reported from the sand-
silt type sediment (Figure 32B) and are difficult to
differentiate from typical terrigenous turbidites on
the basis of structures alone.
The shallow water, hemipelagic, and turbiditic
mud types are differentiated in X-radiographs on
the basis of the degree of bioturbation and the cal-
careous biogenic fraction disseminated in the mud
matrix. Shallow water mud is highly bioturbated
and contains abundant mollusc shells (gastropods,
pelecypods) floating in the mud matrix (Figure
24E-F, arrows g, p). This mud types does not show
any kind of lamination or other type of primary
sedimentary structure. Biogenic structures are
abundant and include various types of burrows
(mycellia in Figure 24G, arrow m; coils and spiral-
shaped burrows; single cylindrical burrows; etc.).
Shallow water mud is usually gradually transi-
tional with the sand-silt type of shallow water
deposits (Figure 24C,D); both types display similar
features in the X-radiographs.
The hemipelagic mud type is characterized by
diverse types of biogenic structures (see Uniform
Sequences, next section), light specks dispersed in
the mud matrix and pteropod shells "floating" in
the fine matrix (Figures 25, 26.) The speckled as-
pect is produced by large numbers of foraminiferal
tests and small fragments of pteropods (cf., Rupke
and Stanley, 1974).
The turbiditic mud type displays a generally
smooth, uniform aspect in the X-radiographs; its
basal part, however, may be finely laminated (Fig-
ure 258,0). This mud type is generally not bio-
turbated, but may show threadlike vertical tubes
(Figure 25c). Mycellia, although uncommon in
this type of mud, is sometimes observed (Figure
25B).
Sapropel layers are characterized by fine, hori-
zontal laminae and no biogenic structures (Figure
NUMBER 16 43
!-V I: 6
170-
IY I. 5
175-
i 180-
FIGURE 26.?Selected X-radiographs (negatives) showing hemipelagic mud and biogenic struc-
tures: A, Neritic-bathyal environment; speckling produced by foraminifera (/). B, Intermediate
depth basin environment; core section shows intense bioturbation and coiled burrow (&).
c, D, Mycellia small fucoid-like tubes (m) and pelecypod (p) (dark laminae may be a reworked
turbidite mud layer), E, Intensely mottled mud in Pantelleria Basin, F, Uniform hemipelagic
mud with mycellia in the North Marettimo Basin. (See also Figure 34 for core logs.)
44 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
180-
185-
FIGURE 27.?Selected X-radiographs (positives) showing exam-
ples of volcanic ash interbedded in mud from cores in
Linosa Trough: A, vertically graded ash layer (194-185 cm);
B, coarsening-upward ash layer; c, laminated type (open
triangle = ash; open circle and Te<p) = hemipelagic mud).
(See also Figure 35 for core logs; explanation in text.)
28, black square symbol). In contrast, the organic
ooze displays evidence of burrowing activity (Fig-
ure 28, open square). A layer of concentrated py-
ritized tubes (b) is commonly associated with this
type of deposit. The organic ooze extends verti-
cally to the base of protosapropel deposits (par-
tially blackened square symbol). The burrowing
activity decreases sharply in the protosapropel
sediment proper and phases out in the overlying
sapropel.
Definition of Sequences
GENERAL
The late Quaternary Strait of Sicily lithofacies
can be distinguished from those in the adjacent
deep basins (Balearic, Ionian) by a high degree of
bioturbation and mixing of sediment by organisms,
which results in textural uniformity, and by the
presence of relatively large amounts of coarse bio-
clastic sediment. Cores east of the Strait on the
Ionian Basin slope (cf. core LY II?3) are more
highly variable both in terms of facies and se-
quences; cores on the western slope into the Algero-
Balearic Basin comprise a large proportion of
turbiditic sequences (sand and mud turbidites).
Cores collected in the Strait proper are distinct
and generally not transitional with those of the
contiguous slopes and adjacent deep basins. We
can demonstrate that regional sedimentation pat-
terns and petrology in the Strait are closely related
with geographic setting and specific depositional
environment, including proximity to the Strait
Narrows.
The different types of sediment present in each
Strait of Sicily core can be grouped into major as-
semblages. The sediment types grouped within
each of these assemblages are termed sequences,
and these are defined on petrologic characteristics
which present distinct natural lateral and vertical
trending lithological transitions. Each sequence is
defined on the basis of a succession of sediment
types that reflect deposition resulting from either a
specific sedimentary process (turbidity current,
mass flow, etc.) or a regionally important, large-
scale environmental event (cf., climatic changes
significant enough to alter water mass stratifica-
tion and flow, eustatic oscillatory sea level patterns,
and/or biogenic production).
NUMBER 16 45
.:Te<
FIGURE 28.?Selected X-radiographs (negatives) from core LY II-3 collected on the Ionian slope
east of the Strait of Sicily (see Figure 34): A, B, illustrate the sapropel sequence which includes,
from the base up, organic ooze, protosapropel, and sapropel. (Symbols explained in Figure 29;
note high concentration of pyritized burrows (b) in the organic ooze layer; see Figure 34 for
core log.)
46 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
The sediment types within most sequences are
gradational and transitional with each other; in
some cases, however, there is a sharp distinction
between the sediment types. An example of the
latter case are the sapropel deposits that record
marked changes in environmental factors. A se-
quence can be related to a plexus of specific sedi-
mentary processes and thus it represents a natural
grouping of sediments (cf., Visher, 1965). Each
sequence comprises several lithosomes ("a body of
sediment deposited under uniform physicochemi-
cal conditions," American Geological Institute,
1972:413).
Four major sequences are distinguished (Figure
29): (1) upward-coarsening or upward-fining se-
quence; (2) uniform sequence; (3) turbiditic se-
quence; (4) sapropel sequence. Probably the most
characteristic of these in the Strait of Sicily is the
uniform sequence. The upward-fining and upward-
coarsening sequences are also well represented,
particularly on the shallow platform and banks.
UPWARD-FINING AND UPWARD-COARSENING
SEQUENCES
The upward-fining and upward-coarsening se-
quences (Figure 29A) are best developed in the
shallow platform environment (8); they comprise
bioclastic sands (Figure 24A,B) and shallow water
muds (Figure 24E,F,G). The transition between the
different terms of these sequences is often gradual
and the limits are not well defined (Figure 24C,D).
The upward-coarsening sequence shows an up-
ward increase in sand and coarser fractions (largely
bioclastic), including shells (largely molluscan).
The basal mud of this sequence (Figure 24E,F,G)
contains a neritic faunal assemblage, including
benthic foraminifera. The transitional facies show
a gradual change between the extreme textural
types. The total thickness of the sequence can ex-
ceed 5m (Figure 34, cores AS 6-7, 6-8). The
upward-fining sequence shows an inverse develop
ment of texture and sedimentary structures (cf.,
Figure 34, upper part of core AS 6-7).
Of the four major sequences, these show the
most gradational transition between the different
sediment types. In some cases, however, the bio-
clastic sand layer displays an irregular basal con-
tact as a result of erosion or nondeposition. Where
the base is sharply defined, evidence of biogenic
activity is preserved in the form of sand burrows
in the underlying mud just below the coarse cal-
careous sand layer.
Cores in the Strait Narrows are interesting in
that, although recovered from greater depths, they
display sequences similar to those described as typi-
cal of shallow platform sedimentation. Core 140,
Vema 14, at 166 m (Figure 33), shows a marked
upward-fining sequence, like those in other shal-
low depth bank environments, while core KS 12 at
956 m (Figure 35) shows distinct alternations of
thick (to 90 m) coarse sands and bioturbated muds.
The sands have been introduced periodically by
turbidity currents (graded sand to mud units) and
mass flow mechanisms (texturally clean grain flow
to muddy debris flow units). One core, 7, San Pablo
?s-
UPWARD-COARSENING AND
UPWARD-FINING SEQUENCES
B
mud
sand-silt
sand
UNIFORM SEQUENCE COMPLETE TURBIDITE SEQUENCE
^^1 I Hemipelagic mud
mudanic oozes
^ Sapropel
2 Proto-Sapropel
D Organic oozes
Hemipelagic mud
SAPROPEL SEQUENCE
FIGURE 29.?Schematic representation of the major sediment sequences discussed in text.
(Symbols here are used in core logs (Figures 33-35) and on X-radiographs (Figure 24-32);
explanation in text.)
NUMBER 16 47
8, at 166 m (Figure 33), collected near the center of
the Strait at intermediate depths (350 m), shows
a lithology transitional with the types described
above: i.e., a vague upward-fining sequence with
intercalations of coarse bioclastic sand layers and
muds toward the upper portion of the sequence.
The coarsening- and fining-upward sequences
are similar to those cored in deltaic environments
(Oomkens, 1970; Maldonado, 1975). The upward-
fining type may be analogous to transgressive del-
taic sequences while the upward-coarsening se-
quences correspond to deltaic offlap sequences.
However, the assemblage of sedimentary structures
present in the Strait cores are not closely similar
to those of deltaic origin, and the source and com-
position of detrital material is also different. The
upward-fining sequences in the Strait and deltas in
general essentially are produced by the same type
of sedimentary event, i.e., the postglacial eustatic
rise of sea level. On the other hand, the upward-
coarsening sequences in deltas are the result of
progradation as reflected by a high detrital influx;
in the Strait this vertical progression is related to
eustatic changes of the sea level across the Strait
surface. These oscillations altered productivity
and current activity and thus controlled the sub-
sequent deposition of coarse biogenic deposits.
On some banks, fine grained sediments have ac-
cumulated since the last rise of sea level, thus de-
veloping an upward-fining sequence. On others,
truncation and continued nondeposition have pre-
vailed since the last eustatic low stand.
Radiocarbon dating (Milliman et al., 1972, dis-
cussion in later section) substantiates the theory
that the coarse calcareous sand is best developed
during the rising stages of sea level rather than
during the lowering or lowest sea level stage. In
any case, there can be little doubt that these se-
quences are closely associated with dynamic sea
level changes. During periods of stabilized sea level
(such as at present) the rate of sedimentation has
been notably reduced, at least in the deeper sectors
of the shelf.
UNIFORM SEQUENCE
The most diagnostic features of cores from the
neritic-bathyal environments are (1) their ex-
tremely uniform, homogeneous aspect, even in
X-radiographs, and (2) the abundance of biotur-
bation structures. Poorly stratified mud layers are
noted in a few cases. Typical examples of such
uniform cores include, among others, LY II-4 and
6A (Figure 34), and KS 78 and 105 (Figure 35).
Another distinction is the low sand content (2%-
7%) in the mud; this fraction consists mostly of
planktonic foraminifera, pteropods, and a minor
but diverse assemblage of faunal remains.
The uniform sequence includes hemipelagic
and, less frequently, turbiditic muds which have
been intensively homogenized by biogenic sedi-
mentary structures (Figure 26). These sequences
are most prominent in neritic-bathyal platform
and depression environments (4, 5). The most
common structure is subtle mottling visible in
X-radiographs (Figure 26E). Bioturbation is ver-
tically developed and not of the "layer-by-layer"
type characteristic in some areas of the Mediter-
ranean such as the Strait of Otranto (cf. Hesse and
von Rad, 1972). There are various types of dis-
tinct burrows in addition to mottled structures.
The finest deposits display tiny light-colored
threadlike shafts (Frey, 1973); these are straight or
slightly curved, sometimes sharply bent, and are
usually less than 0.5 mm thick and several deci-
meters in length (Figure 26F). This structure is
similar to the fine stringlike feature called mycel-
lia (Bouma, 1964; Reineck and Singh, 1973:406),
also noted elsewhere in the Mediterranean
(Huang and Stanley, 1972). Burrow systems of
small fucoid-like or chondrite-like tubes are similar
to the above; these are a few millimeters long and
branch dendritically (Figure 26c). The burrow
casts of both types include either carbonate or
pyritized material. According to Hesse and von
Rad (1972), the chondrite-like burrows and bur-
row casts are possibly the hyphae of marine fungi.
Nevertheless, Howard and Frey (1973) describe
the burrows of capitellid polychaetes in estuarine
muds, which are similar to both mycellia and
chondrite-like types. The laterally stopping struc-
tures (Hesse and von Rad, 1972), or press struc-
tures of Reineck and Singh (1973:141), are also
abundant, and these are interpreted as sea-urchin
tracks (Howard et al., 1974). Other burrows in-
clude tunnels, shafts, and spiral-shaped coils that
are between 2 to 20 mm wide and a few centimeters
or decimeters long (Figure 26B). These burrows
are attributed to acorn worms. The simple, bifur-
cated burrow perpendicular, or inclined, to bed-
48 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
ding can be ascribed to dwelling structures; the
single cylindrical type may be feeding and/or
dwelling structures, while the spiral pattern bur-
row may represent travel traces (Seilacher, 1953;
Frey, 1973).
The processes that result in homogeneous se-
quences are either of primary or secondary origin.
Homogeneous sediments result from regular, uni-
form deposition or very high sedimentation rates
(= primary type, cf. Moore and Scruton, 1957).
Homogeneity of deposits can also result by a total
destruction of minor internal structures by bur-
rowing organisms (= secondary origin); this process
has been described in the Gulf of Mexico (Moore
and Scruton, 1957). The presence of poorly pre-
served turbiditic layers intercalated with uniform
sequences and a rate of sedimentation which is not
particularly high suggest that the latter origin is of
greater importance in the Strait of Sicily.
TURBIDITIC SEQUENCE
The most distinctive sediment types in basin
cores (environments 6 and 7) are the turbiditic
units alternating^ with hemipelagic mud. The tur-
bidites include classic sand and silt turbidites (Fig-
ures 30, 31) displaying various terms denned by
Bouma (1962) and others, as well as mud turbi-
dites, Te(t), as described in detail by Rupke and
Stanley (1974). Only rarely is the complete Bouma
sequence (Figure 29c) observed; one example of a
sequence of Ta-b-c-d units is shown in Figure 30.
Most of the turbidites in Strait basins are base-cut
units of the Bouma division, i.e., Tb-c-d, Td
(Figure 25).
The mud turbidite sequences are important in
this area. These display all of the characteristics of
sand turbidites including fine lamination (analo-
gous to the d-division of sand-silt turbidites),
vertical sorting of the components, and graded bed-
ding. Evidence for this type of fine-grained tur-
bidite has been provided during the past few years
by several authors (van Straaten, 1970; Piper,
1973; Rupke and Stanley, 1974; etc.). Neverthe-
less, it should be noted that other depositional
mechanisms have been proposed for vertically
graded pelitic sediments, in addition to pelagic
settling and turbidity currents. For instance, nor-
mal bottom currents, and in particular geostrophic
currents (Heezen et al., 1966; Flood and Hollister,
1974), have been suggested as a major factor in
deepsea sediment deposition although it is ques-
tionable that they would result in graded deposits.
Other proposed mechanisms are low-density and
gravity-assisted flows carrying fine-grained sedi-
ments to deep marine environments (Moore, 1969;
Stanley et al., 1970, 1971; Huang and Stanley,
1972; van Straaten, 1972).
The base of turbidites in Strait basins sometimes
includes calcareous sand, but more often the turbi-
dites consist almost completely of silt and clay.
Compositionally, the bioclastic sand fraction in
turbidites is comparable to sands on the shallow
and neritic-bathyal platform above the basins but
contains a higher percentage of planktonic
foraminifera.
In some cores, particularly those in the Linosa
Trough, tephra (ash) layers are important (Fig-
ure 27, 31); a number of these sand-size deposits
also present typical turbidite structures including
graded bedding (Figure 31A). Although some vol-
canic sands have been transported into the basins
by turbidity currents, we suggest that graded vol-
canic layers also can form by lateral wind and
water transport of ash and subsequent settling of
these particles through the water column.
Some layers composed largely of ash particles
show the typical sequence of turbidite structures
(Figure 31A, 108-30 cm; 31B, 530-508 cm; Fig-
ure 35). Sarnthein and Bartolini (1973) discussed
this type of sedimentation in the Tyrrhenian Sea.
In contrast, air-borne tephra layers lack the verti-
cal sequence of primary sedimentary structures
associated with the typical turbidites although
they may display reversed or normal grading
(either coarsening upward, Figure 27B, 345-328
cm or fining upward, Figure 27A, 194-187 cm and
Figure 31A, 115-111 cm) or horizontal lamination
(Figure 27c, 150-143 cm). These two structures
reflect different types of explosive activity.
The adjacent islands of Linosa (di Paola, 1973)
and Pantelleria (Villari, 1969) shed some informa-
tion on this matter. Pantelleria, for example, is
composed of a large number of interbedded ignim-
brites, and both welded and unwelded pumice fall
deposits and some well-stratified fine ash (R.S.J.
Sparks, pers. comm.). Gas-blast eruptions of the
Plinian or sub-Plinian type are known to generally
produce poorly stratified and often reversely graded
deposits (Sparks et al., 1973; Walker, 1973). Well-
NUMBER 16 49
LY II 6 LY II 6
ltd]
-250
-285
Mel |Te
lTd
-255
-290
ITal
-260i
-295,
|Te(
FIGURE 30.?Selected X-radiographs (negatives) from core LY II-6 collected in the North
Marettimo depression showing one complete vertically graded sand to mud turbidite sequence.
(See Figure 34 for core log.)
50 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
KS-69 I
FIGURE 31.?Selected X-radiographs (positives) o? core KS 69 from Linosa Trough showing
turbidite sequence and ash layer between mud units. (Open triangle = volcanic ash; open circle
and te<p> = hemipelagic mud; circle with dot = calcareous bioclastic sand; other symbols on
Figure 29; see Figure 35 for core log.)
NUMBER 16 51
stratified deposits on land are associated with
phreatomagmatic eruptions or vulcanian pulse
eruptions. The structures observed in the Strait
may be analogous. Each graded ash layer probably
records a single eruption. Base surge density flows
(Moore, 1967) as well as ash flows may be of some
importance in the formation of the volcanic de-
posits cored in the Strait.
Another type of gravity flow deposit is illustrated
in Figure 32. Core KS 12 collected in a small basin
in the Strait Narrows displays thick layers of sand
and sandy mud interbedded with mud (Figure 35).
These layers consist of calcareous sand, in some in-
stances clean and in some instances muddy, without
grading or sharp contact in some cases. Mech-
anisms other than turbidity currents are postu-
lated: in the case of clean sand, grain flow trans-
port is envisioned; debris flow or slumping may
explain the sandy mud and muddy sand mixtures
(Hampton, 1972; Middleton and Hampton, 1973).
Further evidence of slumping is recorded in basins,
such as a 70-cm thick contorted unit in core 139,
Vema 14, at 1703 m in the Malta Trough (Figure
33).
SAPROPEL SEQUENCE
The sapropel sequence is found only in cores on
the eastern margin of the Strait (i.e., on the slope
extending into the Ionian Basin) but not in the
Strait proper. The idealized complete sapropel se-
quence (Figure 29) based on an analysis of core
LY II?3 (Figure 34) comprises a basal organic
ooze layer (Figure 28) usually in continuity over
gray hemipelagic mud. The organic ooze is inten-
sively bioturbated (presence of burrows, etc.) and
frequently includes a zone of pyritized worm tubes
(Figure 28, b) toward the top. Organic ooze grades
upward into a protosapropel sediment type distin-
guished by a low degree of bioturbation. The
black, organic rich sapropel layer proper is usually
well defined, particularly in X-radiographs, where
it appears as a bundle of thin parallel laminae
(Figure 28A) consisting of alternating calcareous
coccolith-rich muds and somewhat thicker layers of
calcareous-poor terrigenous mud. The sapropel is
capped by a thin protosapropel layer, which grades
upward into an organic ooze (Figure 28B). The
sequence is covered by a layer of light brown to
dark yellowish orange (5 YR 5/6-10 YR 6/6) oxi-
dized mud. In core LY II?3 the sequence is about
20 m thick and is usually complete.
Sapropels in the eastern and central Mediter-
ranean are believed to have accumulated during
stagnant phases associated with stratification of
water masses and formation of H2S-rich anaerobic
bottom waters (Olausson, 1961; Ryan, 1972; van
Straaten, 1972). The vertical sequence appears to
closely reflect large-scale oceanographic fluctua-
tions. The organic ooze indicates that, initially,
conditions (including vertical mixing and oxygena-
tion of water masses) fostered a high degree of
benthic activity as attested by the importance of
bioturbation. Evidence that the water mass above
the sea floor became progressively anaerobic and
rich in H2S is provided by an increase of pyritized
burrows and eventual absence of any bottom or-
ganic activity in the protosapropel and sapropel.
The sapropel proper records a major anaerobic
phase (van Straaten, 1972). The varvelike sapro-
pel laminations, unlike those of the protosapropel,
are attributed to periodic high coccolith produc-
tivity possibly resulting from seasonal upwelling
and subsequent sinking of the coccoliths (cf., Gulf
of California, van Andel, 1964; Black Sea, Degens
and Ross, 1974). A progression to more normal
open ocean conditions and vertical mixing is in-
dicated by the subsequent deposition of protosa-
propel and organic ooze. The upper orange oxi-
dized layer represents a return to oxygen-rich
bottom water conditions. It is concluded that sapro-
pel sequences observed east of the Strait are com-
parable to those in the Herodotus Abyssal Plain
and Nile Cone areas detailed by Maldonado and
Stanley (1975).
Sedimentation and Stratigraphy in the Strait
Environments
REGIONAL DISTRIBUTION OF SEQUENCES
Our regional survey of sediment types and se-
quences reveals the close correlation between the
Strait of Sicily depositional environments and the
resulting Quaternary sedimentary facies. This re-
lation is illustrated in Figures 33, 34, and 35. The
shallow platform environment is characterized by
coarsening- and fining-upward sequences, which
result from the association of two major sediment
types: coarse calcareous sand and shallow water
52 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
KS-12
0/O
315-
325-
330-
335-
320-
340-
345-
FIGURE 32.?Selected X-radiographs: positives of core KS 12 from small basin in the Strait Nar-
rows showing sandy mud and muddy sand layers interpreted as gravity flow deposits. (Open
circle = hemipelagic mud; circle with dot = calcareous bioclastic sand; other symbols on Figure
29; see also Figure 35 for core log.)
NUMBER 16 53
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54 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
saaiaw NI 3aoo JO HION3I
NUMBER 16 55
mud. The uniform sequence prevails in the neritic-
bathyal environments; here sedimentation of hemi-
pelagic muds is dominant. The muds are sub-
sequently bioturbated; intercalations of mud
turbidite sequences are also present in these en-
vironments. Sedimentation in the basin environ-
ments is similar in some respects to that in the
neritic-bathyal environments. However, deep basin
deposits are recognized on the basis of well-
stratified units including alternating layers of tur-
biditic sequences, hemipelagic mud, and volcanic
ash layers. Gravity flow deposits such as slump and
grain flow units also occur in the basin environ-
ment. Environments in or close to the Strait Nar-
rows are generally typified by a relatively higher
proportion of coarse calcareous sand deposits.
Certain coarse calcareous sand layers encoun-
tered in all of the shallow platform environments
may be lithostratigraphically correlatable. How-
ever, the age of this lithosome need not be strictly
isochronous since such deposits are closely related
to depth, and thus in turn to the rise or lowering
of sea level and productivity as explained earlier.
It is conceivable that the calcareous sand recovered
in different cores collected at the same depth may
be of the same age. However, it has not been as-
certained that the beds are continuous laterally
and they may in fact be related to several different
Pleistocene eustatic oscillations.
We were unable to correlate individual layers or
sequences between the cores collected in other en-
vironments, even within the small deep basins.
One of the difficulties in the case of the neritic-
bathyal cores is their uniformity and lack of dis-
tinct correlatable horizons. Furthermore, sapropel
sequences which are useful for correlation pur-
poses, particularly in the eastern Mediterranean
(Ryan, 1972; Maldonado and Stanley, 1975), do
not occur in the Strait proper. Even well-stratified
basin cores in specific basins could not be corre-
lated on the basis of individual turbiditic sequences
*and tephra ash layers. Cores KS 120, KS 69, and
KS 118 (Figure 35), and CH 61-19 (Figure 33)
from the Linosa Trough are particularly inter-
esting in this respect, for all were collected at
about the same depth (within less than 40-m depth
difference) along a transect about 20 km in length
across the basin plain. Although these cores are
similar in general appearance, the radiocarbon
dates (Figure 35) indicate that correlation either
by individual layers or by sequences is not reliable.
This does not rule out the possibility that some
techniques, such as detailed chemistry and petro-
logic analysis of tephra layers (Keller et al., 1974;
F. W. McCoy, pers. comm.), may be used in this
respect. It should be recalled, however, that turbi-
ditic ash layers tend to have a more limited aerial
distribution than that of air-borne volcanic ash
layers.
A discussion of correlation of Strait of Sicily
cores by carbon-14 techniques will be treated in a
later section.
ENVIRONMENTAL FACTORS CONTROLLING THE STRAIT
SEDIMENTATION
In the following discussion we shall consider
several aspects of the Strait of Sicily sedimentation
in terms of environmental factors. In particular
the following will be considered: (1) the role of
Quaternary dynamics, including the factors related
to the changes of climate and eustatic sea level
oscillations; (2) the importance of depth; and (3)
the biological factors. Although lateral correlation
of specific units has not been accomplished, it is
nevertheless possible to distinguish dominant pat-
terns of sedimentation in each of the major en-
vironments. As will be recalled, three main param-
eters control sedimentation in any given
environment: physical, chemical, and biological.
Within the first group are included such factors as
climate, depth, temperature, salinity, current sys-
tems, and boundary conditions of the environment
(geometry, bathymetry, and geology, among
others).
The Quaternary sea level oscillations related to
major climatic changes are the most important
factors that have determined the sedimentary proc-
esses in the shallow water platform environment.
As demonstrated, the different sediment types and
sequences developed here are to a large extent re-
lated directly to depth. As a consequence of depth
changes, there have been alterations in current
patterns and intensity, salinity and temperatures
which inevitably affected the vertical evolution of
the sediment sequences in this environment. It is
apparent that the shallow platform lithofacies
would be considerably more uniform had there
been no Quaternary oscillations.
Moreover, the sediment types in the neritic-
56 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
H.
DC ?_
Z CO
J t
aft *pJi
IX 1
fIS ^ ?
ii
s
| ;*? ?? (v. T
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13 T3
S3 C
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I i i i i i i i i i I i
S8313W Nl 3!IO3 dO H13N31
NUMBER 16 57
Strait of Sicily
? coarse calcareous sand
O shallow water mud
0 hemipelagic mud
? furbiditic mud
O sand-silt
0 turbiditic sand
Q organic ooze
? sapropel
1000 1500 2000
DEPTH IN METERS
100
coarse calcareous sand
plus shallow water mud
b|| | | || hemipelagic mud
sand - silt and turbiditic sand
upper limit of probability
lower limit of probability
1000 1500 2000
DEPTH IN METERS
FIGURE 36.?Plots showing relation between sediment types in the different Strait of Sicily
environments and depth: A, Percent of sediment type in core versus depth (solid line = regres-
sion line for hemipelagic mud type in Strait environments; dotted line = regression line for
turbiditic mud in Strait environments; dashed line (for hemipelagic mud) and triple dotted line
(turbiditic mud) = regression lines for Balearic Basin plain (includes data from Rupke and
Stanley, 1974); this figure shows the inverse relation between depth and the percent of hemi-
pelagic mud and the direct relation between depth and turbiditic mud), B, Cumulative percent
of sediment types versus depth (cumulative percent of each group of sediment is calculated as
follows: a, a + b,a + b + c,a + b + c + d; thin line = upper cumulative limit of proba-
bility for a given sediment group; heavy line = lower cumulative limit of probability for same
sediment group; this diagram serves to predict the relative amounts of sediment types at given
depths: at 1000 m, for example, 0% of type a, 65-100% of b, 0-18% of c, and 0-5% of d; at
2500 m, 0% of type a, 40-70% of type b, 10-35% of type c, 5-25% of d).
58 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
TABLE 4.?Percent and cumulative percent (in parentheses) of different sediment types in Strait
of Sicily cores (percent of bioturbated section of total core thickness also shown; only two main
types of sediments differentiated in shallow platform cores; coarse and bioclastic sand, and
shallow water mud; sand-silt fraction of these cores attributed to either one type or another)
CORE
LY II-3
LY II-4
LY II-5
LY 11-5 A
LY II-6
LY II-6A
LY II-7
P6510-34
P651O-33
AS 6-8
AS 6-7
SP 8-7
V14 138
V14 139(1)
V14 140
CH61 19(2)
KS 12
KS 23<3)
KS 33
KS 53
KS 69'4)
KS 78
KS 100
KS 104
KS 105
KS 110
KS 118(5)
KS 120(6>
KS 125
COARSE
CALCAREOUS SAND
32/(32)
6/(6)
71/(71)
50/(50)
100/(100)
4/(4)
SHALLOW
WATER MUD
68/(100)
97/(100)
29/(100)
50/(100)
HEMIPELAGIC
MUD
68/(68)
97/(97)
98/(98)
87/(87)
79/(79)
97/(97)
62/(62)
66/(66)
90/(90)
60/(60)
79/(79)
67/(71)
86/(86)
72/(72)
96/(96)
72/(72)
97/(97)
96/(96)
96/(96)
95/(95)
91/(91)
86/(86)
82/(82)
97/(97)
TURBIDITIC
MUD
16/(84)
3/(100)
2/(100)
10/(97)
14/(93)
3/(100)
37/(99)
28/(94)
7/(97)
35/(95)
12/(91)
7/(78)
14/(100)
22/(94)
4/(100)
19/(91)
3/(100)
4/(100)
4/(100)
5/(100)
9/(100)
11/(97)
14/(96)
3/(100)
SAND-SILT
2/(99)
6/(99)
1/(100)
4/(98)
3/(100)
3/(98)
1/(92)
21/(99)
4/(98)
9/(100)
2/(99)
3/(99)
TURBIDITIC
SAND
1/(85)
1/(100)
1/(100)
2/(100)
2/(100)
1/(93)
1/(100)
2/(100)
1/(100)
1/(100)
ORGANIC
OOZE SAPROPEL BIOTURBATION
10/(95) 5/(100) 14
100
97
36
60
98
6
18
10
7
7/(100) 7
67
26
26
75
5
91
92
94
100
(74)
43
14
91
(1) Slump sediment: 76 cm (not computed); (2) Ash: 22 cm (not computed); (3) Ash: 1 cm (not computed);
(4) Ash: 39 cm (not computed); (5) Ash: 4 cm (not computed); (6) Ash: 28 cm (not computed).
bathyal environments and basin environment show
a clear correlation with present depth, particularly
the hemipelagic mud and turbiditic mud types
which form the major components of cores in
these environments. The close correlation between
sediment type and depth is illustrated in Figure
36A, where the percent of the different types of de-
posits in each core are plotted against depth (cf.
Table 4).
Shallow water mud and coarse calcareous sand
tend to be restricted to depths less than 500 m.
Core KS 12 in the Strait Narrows does not follow
NUMBER 16 59
this trend because other specific depositional mech-
anisms particular to this environment are involved
(discussed in a later section).
The distribution of turbiditic sand and sand-silt
sediments appears independent of depth. Other
environmental factors related to the boundary con-
ditions of the environment (such as distribution of
channels, natural levees, small basins, etc.) may be
of primary importance in their distribution.
Hemipelagic mud is more closely related to
depth, showing a decrease with an increase in
depth. The turbiditic mud type also shows a cor-
relation with depth, but in contrast to the hemi-
pelagic mud, its importance increases with depth.
The correlation coefficients between depth and the
percent of sediment type in the cores and the re-
gression lines have been calculated for both types
of mud (Figure 35A). The value for hemipelagic
mud is r = -0.69, y = 106.7 - 0.018x; for turbiditic
mud it is r = 0.70, y = -5.8 + 0.014x. Both cor-
relations are statistically significant at the a = 0.01
level.
The correlation is not very strong in either case,
inasmuch as only about half of the variance (47%
for the hemipelagic and 49% for the turbiditic mud)
in the percent of sediment type in cores can be ex-
plained by a change in depth. However, it is
interesting that depth, which is only one of several
possible environmental factors, apparently con-
trols about half of the variance in the distribution
of these sediment types.
Another significant aspect of the relationship
between depth and sediment distribution can be
inferred from the graphic representation. Core data
from the Balearic Basin plain (Rupke and Stan-
ley, 1974) have also been plotted. A sharp change
in trend of the regression line is clearly evident
when the data from the Balearic plain are com-
pared to the data from the Strait of Sicily cores.
The intersection of the regression lines from both
sets of data occurs just beyond 2500 m, which cor-
responds well with the depth of the basin plain-
base of slope break.
This type of correlation between sediment se-
quences and depth may be applicable in other
parts of the Mediterranean, but further testing is
needed. This model, taking into account the sta-
tistical limitations of the technique, also may be of
considerable importance for the interpretation of
depth of paleoslope and recognition of base-of-
slope environments in ancient sediments.
The cumulative percent of the different sediment
types in each core also has been calculated (Table
4). This was accomplished as follows. First, the
total percent in each core of four major sediment
groups (legend a, b, c, d in Figure 36B) were cal-
culated. Then the cumulative percent of each
group of sediment was calculated in the following
sequence: a, a + b, a + b + c, and a + b + c +
d. The results are shown schematically in the inter-
pretative diagram in Figure 36B,, which displays
the variance of sediment types in cores as a func-
tion of depth. For each sediment type two graphic
limits are depicted: one corresponds to the upper
cumulative limit of probability of a given sediment
group (thin line); the other represents the lower
cumulative limit of probability for this sediment
group (heavy line). It is apparent from this graph
that hemipelagic mud is the most important sedi-
ment type in the neritic-bathyal environment. The
importance of the turbiditic mud type increases
with depth; below 2500 m the percent of turbiditic
mud increases sharply and becomes as important as
hemipelagic mud. The sand-silt sediment type also
increases in cores paralleling an increase in depth.
Coarse calcareous sand and shallow water mud are
ubiquitous in the shallow water environment and
their importance decreases sharply below the 200
to 500 m zone. The distribution of sapropel, or-
ganic ooze, and related deposits which do not occur
on the Strait proper is not depicted on the graph.
BlOTURBATION AS AN ENVIRONMENTAL INDICATOR
Bioturbation, an indicator of biomass and ben-
thic activity, is considered in this discussion of
Strait sedimentation. The preservation of primary
structures in marine sediments is the result of a
delicate balance between rate of sedimentation and
rate of benthic activity on, and just below, the
water-sediment interface (Moore and Scruton,
1957). The degree of bioturbation in cores against
depth is depicted graphically in Figure 37. The
correlation coefficient is r = ?0.87 (significant at
the a = 0.01 level) and the regression line is y =
169.6-0.101x. Data from core KS 110, a deep basin
core, was not used in the calculation; it is too short
to provide reliable data. The correlation between
depth and degree of bioturbation (about 75% of the
variance) is higher than the correlation between
60 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
???
Strait of Sicily
Shallow
CPlatfor? Neritic-Bathyal <?
100 . <,,,!,,,>,
Basin Ionian and Balearic Margins(Slope)
I
o
u
110
Q
LJJI?
1 50
i?
o
o
I?z
LLJ
1 1 1 i r
1000 1500 1 ! '2000 2500
DEPTH IN METERS
FIGURE 37.?Percent of bioturbated strata in cores versus depth in different Strait of Sicily
environments. Regression line and correlation coefficient shows close relation between depth and
degree of benthic activity. Data from core KS 110 was not used in the calculation. (Explanation
in text.)
sediment type and depth described in the previous
section. Benthic organisms are closely depth con-
trolled and the resulting degree of bioturbation
should closely correlate with depth. Bioturbation is
a function of the number of organisms, type of ac-
tivity, and rate of sedimentation. Inasmuch as the
first two appear so closely related to depth, we sup-
pose that the other factor, less important than
the rate of biological activity, is the rate of
sedimentation.
The regression line shown on Figure 37 inter-
sects the 100% abscissa at about 700 m. The neritic-
bathyal cores shallower than this depth are com-
pletely bioturbated (examples: cores LY II-4 in
Figure 34 and KS 105 in Figure 35). Even in
coarse-grade sediments of the shallow platform,
bioturbation is an important factor (Figure 24A,
B); in some cases, however, the coarse texture of
sediments in shallow water cores masks biogenic
structures.
There is a general decrease in the relative
amount of bioturbated core section between about
NUMBER 16 61
700 and 1600 m, and below a depth of 1600 m the
degree of bioturbation is quite low (i.e., about 10%
of the core). This low value of reworking by or-
ganisms probably reflects a decrease in the amount
of biogenic activity concurrent with an increase in
the rate of sedimentation.
RATES OF SEDIMENTATION
During the course of this study, 41 radiocarbon
dates were obtained (Table 5), and these data have
been plotted on the core log diagrams (Figures
34, 35). These diagrams show that the top of the
cores are of highly variable age, and some of them
are very old. When all age data are plotted against
core sample depth no coherent pattern emerges,
indicating an absence of uniform trend in the rate
of sedimentation from core to core. However, when
the core data are grouped in terms of environment
more distinct trends appear as to the rate of sedi-
mentation and the age of the sediment at the top
of the core (Figure 38).
The shallow platform environment (cores AS
6-7, AS 6-8) is characterized by (1) a high rate of
sedimentation (52 cm/100 years for core AS 6-8
in the Gulf of Hammamat) and (2) a truncation
(or lack of sedimentation) in some of the cores be-
fore the end of the Pleistocene (Figure 34). The
sedimentation rate calculated for core AS 6-8 is
the highest measured except for sections of two
cores in the deep basin environment (Figure 38).
In the neritic-bathyal environments, rates of
sedimentation range from 16 to 40 cm/1000 years
(average of about 25 cm/1000 years), and the tops
of a number of cores in this environment terminate
in the early Holocene (Figure 38A). One core (KS
105), unlike the above, shows a lower sedimenta-
tion rate (similar to that of the deep basins) and
continued deposition through much of the
Holocene.
The rates of sedimentation in the basins ap-
proximate 20 to 25 cm per 1000 years (Figure
38B). The much higher rates in two core sections
(lower half of KS 109 in Malta Basin, and in the
upper half of KS 63 in Linosa Basin) are the result
of a greater abundance of turbidite and ash incur-
sions at these two localities. It should be noted that
in contrast to cores at shallower depths, deep basin
deposits accumulated on a more continuous basis
until the present (Figure 38 B). Sedimentation
rates in core LY II-6 in the small depression west
of Marettimo Island are similar to those in other
deep basin cores.
Carbon-14 data of core Ges-12 in the small Strait
Narrows basin indicate relatively low (15 cm/1000
years) sedimentation rates, but continuous deposi-
tion from the late Pleistocene until recent time
(Figure 38B).
The cores examined from the Ionian margin
(LY II-3) and Balearic margin (LY II-7) slopes
provide an average sedimentation rate of 30 cm
and 15 cm per 1000 years, respectively (Figure
38A). On the Balearic Basin plain an average rate
of sedimentation of 23 cm/1000 years is reported
(Rupke and Stanley, 1974).
Three aspects of the sedimentation pattern in
the environments discussed earlier are considered:
(1) rate of deposition; (2) uniformity of these
rates in time; and (3) the age of the sediments at
the top of the cores, or the degree of continuity in
sedimentation from the Pleistocene to the present.
Sedimentation rates (with some exceptions) gen-
erally decrease with increasing bathymetric depth,
i.e., from the shallow banks to the neritic-bathyal
platform to the deep basins. With the available
carbon-14 data, it appears that deposition in all
environments, except in the two deep basin cores
(KS 63 and KS 109, which have higher ash and
turbidite layers), has been relatively uniform in
the late Quaternary.
However, there is a significant difference in the
age of sediments at the tops of cores in the differ-
ent environments. On shallow banks, the tops of
some cores are truncated in the late Pleistocene to
early Holocene; in the neritic-bathyal environ-
ments in early Holocene; and in the deep basins,
sediments have accumulated on a fairly continuous
basis from the Pleistocene until the recent (Figures
34, 35). As discussed in earlier sections, sedimenta-
tion in the shallow platform environment is closely
related to Quaternary events. It has been empha-
sized, for example, that the upward-coarsening and
upward-fining sequences in shallow environments
are a direct response to eustatic oscillations.
We have demonstrated that in the neritic-bathyal
environments bioturbation is an important factor
and that the rate of reworking by benthic orga-
nisms has1 continued during deposition of the en-
tire core sections. Equally significant are the
carbon-14 dates, which indicate that oceanographic
62 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
TABLE 5.?Radiocarbon dates
selected
based on carbonate sand fraction and bulk sample from cores
in different Strait of Sicily environments
CORE
LY II-3
LY II-3
LY II-4
LY II-4
LY II-5
LY II-5
LY II-5A
LY II-5A
LY II-5A
LY II-6
LY II-6
LY II-6A
LY II-6A
LY II-6A
AS 6-7
AS 6-7
AS 6-7
AS 6-8
AS 6-8
AS 6-8
KS 63
KS 63
KS 63
KS 12
KS 12
KS 53
KS 53
KS 53
KS 100
KS 100
KS 105
KS 105
KS 109
KS 109
KS 109
KS 118
KS 118
KS 118
KS 120
KS 120
KS 120
AVERAGE
DEPTH
235
490
93
325
80
290
40
290
570
65
470
30
250
550
225
192
701
49
49
530
225
525
825
92
687
131
579
639
85
607
65
530
122
362
695
87
423
786
73
359
688
SAMPLE DEPTH
210-255
467-512
70-115
298-351
60-100
270-310
20- 60
270-310
550-590
45- 85
450-490
10- 50
230-270
530-570
0- 45
185-200
685-728
33- 65
33- 65
510-550
200-250
500-550
800-850
85-100
680-695
124-138
574-585
632-646
77- 94
599-616
58- 71
524-537
113-131
354-370
687-703
79- 95
415-432
778-795
66- 81
351-367
681-695
SAMPLE
WEIGHT
(gin)
16.7
18.8
34.1
13.0
13.5
11.1
13.3
9.0
11.0
1.0
16.8
19.0
19.8
17.3
5.7
16.0
14.0
40.0
40.0
35.0
15.8
9. 5
23.4
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
CARBONATE
MATERIAL
Forams (>63ym)
Forams (>63um)
Forams (>63lJm)
Forams (>63(jm)
Forams (>63pm)
Forams (>63)im)
Forams (>63ym)
Forams (>63pm)
Forams (>63Pm)
Forams (>63um)
Forams (>63pm)
Forams (>63um)
Forams (>63ym)
Forams (>63ym)
Forams + Shells
(>63ym)
Shells (Forams)
(>63iim)
Forams (Shells)
(>63um)
Shells (>210ym)
Forams (>63ym)
Forams + Shells
(>63um)
Forams + Shells
(>63um)
(>63pm)
Forams (Shells)
(>63um)
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
Bulk Sample
RADIOCARBON
(in years
19,830 ?
28,390 ? 1
15,495 ?
25,925 ?
4,100 ?
12,580 ?
3,680 ?
13,685 ?
DATE
3.P.)
450
200
200
525
80
345
90
450
No Date
No Date
15,265 ?
11,550 ?
17,290 ?
24,790 ?
No Dat
16,005 ?
12,680 ?
17,565 ?
19,555 ?
26,865 ?
18,465 ?
19,980 ?
9,530 ?
48,950 ? 7
15,340 ?
35,160 ? 1
34,550 ? 1,
6,310 ?
26,000 ?
7,245 ?
36,620 ? 1,
5,145 ?
16,895 ?
19,950 ?
7,050 ?
19,500 ?
41,700 ? 4,
8,640 ?
23,940 ?
42,850 ? 6,
240
175
365
680
2
220
360
230
230
715
240
380
140
370
145
970
870
95
375
115
800
55
175
300
95
425
500
105
610
680
Small
Small
Small
Small
Small
Small
Small
Sample
Sample
Small
Small
Sample
Small
Small
Appare
NOTATIONS
sample
sample
sample
sample
sample
sample
sample
too s
, diluted
, diluted
, diluted
, diluted
, diluted
, diluted
, diluted
mall
too small
sample
sample
, diluted
, diluted
too small
sample
sample
nt age
Age reversed
below
Age reversed
above
Apparent age
, diluted
, diluted
with sample
with sample
Core LY II-7 radiocarbon dates from Rupke and Stanley (1974, their Table 8, p. 32).
NUMBER 16 63
conditions directly affecting the seafloor changed
markedly between the late Pleistocene and the
early Holocene, and that nondeposition and/or
erosion have prevailed since about 10,000 years
BP in the neritic-bathyal and shallow platform
environments.
In contrast, none of the above patterns are noted
in the deep Strait basins. Rates of sedimentation
approximate those on the neritic-bathyal environ-
ments but lower benthic populations on the basin
floors have resulted in less bioturbation and better
preservation of stratification. Furthermore, no ob-
vious changes either in lithofacies sequence pat-
terns or sedimentation rates are recorded in this
deep environment between the late Pleistocene
and the recent, i.e., a period of at least 30,000
years.
However, other studies indicate that rates of
sedimentation in deep basins of the Mediterranean
(Huang and Stanley, 1972; Rupke and Stanley,
1974; and others) and the Black Sea (Ross and
Degens, 1974) have not been constant during the
upper Quaternary. A decrease in the rate of sedi-
mentation is reported in most Mediterranean areas
during the late Pleistocene to Holocene.
An anomolous reversal in the age of some core
samples (cf. cores KS 53 in Figure 35 and AS 6-7'
in Figure 34) may be the result of mixing by
organisms. Vertical mixing of 3 to 4 m, for ex-
ample, has been noted in some Holocene shelf
cores in the Persian Gulf (Sarnthein, 1972).
Another aspect that should be considered in ana-
lyzing radiocarbon dates is that different types of
carbonate material within the same sample may
give different radiocarbon dates (Milliman et al.,
1972). An example of this is shown by two samples
from the upper coarse calcareous layer (^ 30 cm)
in core AS 6-8 (Figure 34). Here, the age of a
largely shelly coarse sample (> 203 microns) is
slightly younger than that of the finer grade frac-
tion (63-203 microns) consisting primarily of
foraminiferal tests. A petrographic analysis of these
samples suggests that the fine fraction may have
been more intensively reworked than the coarse
shelly fraction.
The correlation between cores based on the
carbon-14 analyses is shown in Figures 34 and 35.
Cores without available radiocarbon dates were
correlated by extrapolation with radiocarbon dated
cores in the same environment. Lithostratigraphic
distribution of sedimentary sequences was also con-
sidered in the correlation of cores (Figure 33). The
isochrons in Figures 33 to 35 reveal the thicker
sediment accumulations in the deep basins and
also show the truncation of Holocene sections at
the top of the neritic-bathyal and shallow platform
cores.
The importance of volcanic activity between
5000 and 25,000 years BP in Linosa Trough is
demonstrated by the radiocarbon data on cores KS
120 and KS 118 in Figure 35. Volcanism at about
this time is also reported elsewhere in the Mediter-
ranean (Keller et al., 1974).
The relation between rate of sedimentation and
fault displacement can also be considered in light
of the available carbon-14 dates. That deposition
and faulting are contemporaneous in the neritic-
bathyal environments is well displayed in 3.5 kHz
records (Figures 7, 10). The development of some
faults apparently stopped in the upper Pleistocene
(Figure 7, arrow B). In this area, the core tops are
dated at about 10,000 years BP (core LY II-4); on
3.5 kHz profiles the uppermost sediment sections
are offset slightly by faults. The underlying Plio-
cene and Quaternary sequences also accumulated
contemporaneously with fault movement as re-
vealed by the thickening of sediments in down-
thrown fault blocks (see sparker profile in Figure
7, b). In some sectors faulting appears to be active
at present (Figures 7, c, 8, 10), and locally the off-
set of identical reflectors on opposite fault scarps
indicates a displacement rate in excess of the sedi-
mentation rate. Thus, vertical displacement of cer-
tain parts of the neritic-bathyal sea floor exceeds
20 cm per 1000 years.
The nature of well-defined reflectors on 3.5 kHz
records is difficult to ascertain. Core analysis (LY
II-4, Figure 7; Figure 34) shows that sand layers
and other distinct lithologic layers are not present
in cores retrieved from this environment. As has
been emphasized, the cores are characterized by
their uniformity. Although many of the distinct
reflectors that appear on the 3.5 kHz records could
not be sampled because of core length limitations,
we believe that late Quaternary deposits in this
neritic-bathyal environment present a general ho-
mogeneous pattern. Thus, the lateral continuity
and regional uniformity of subbottom reflectors in
3.5 kHz records suggest a lithofacies change related
to some type of regional event. We exclude a tur-
YEARS BEFORE PRESENT (X1O3)
LU
LJ
L?J200
u
LUm
Ou
i
Q_
Q
AS-8(c) AS-8(b)
? o SHALLOW PLATFORM .
NERITIC-BATHYAL -
DEEP SLOPE
(Ionian, Balearic)
CORES
LYNCH II - 3,4,5,5A,6,6A,7
ATLANTIC SEAL- A-7,A-8
GESITE - KS-I2,53,63,69,100,105,109,118,120
33 = RATE OF SEDIMENTATION
IN CM/YEARS I03
FIGURE 38.?Rates of sedimentation based on carbon-14 data from cores in the different Strait of
Sicily environments: A, shallow platform, neritic-bathyal, and deep slope environments; B, deep
basins and small Strait Narrows basin. (Data from core KS 69 provided by the Station de
Geologie Sous-Marine de Villefranche of the University of Paris, and from LY II-7 from Rupke
and Stanley, 1974.)
NUMBER 16 65
biditic origin for the origin inasmuch as these re-
flectors are continuous over a highly irregular to-
pography. One possible origin of continuous layers
are surfaces of nondeposition, perhaps related to
critical sea level stands. A marked acoustic reflector
also may indicate a marked change in the physical
properties of the mud such as water content and
porosity rather than a change in texture. Still
another possible explanation for regionally exten-
sive subbottom horizons might be concentrations
of foraminiferal tests or other microfossils. An
example of this, recorded in the Alboran Sea
(Huang and Stanley, 1972), is attributed to a re-
gional "bloom" related to a basin-wide event.
IMPLICATIONS OF STRAIT SEDIMENTATION TO
CURRENT REVERSALS
It is noteworthy that sapropels and associated
sediment types which are distributed throughout
the eastern Mediterranean do not occur in the
Strait of Sicily proper. Sapropel is cored only to
the east on the slope trending into the Ionian Ba-
sin. Most workers are of the opinion that these
dark organic-rich units are associated with water
mass stratification-anaerobic conditions; they ac-
cumulated during the warming phase of the Qua-
ternary climatic cycles, and not during the glacial
maximum (Ryan, 1972; and others). We assume
that the upper sapropel layer on the slope east of
the Strait (core LY II?3 on Figure 34) is equiva-
lent to the upper sapropel layer in the eastern
Mediterranean, which has been dated at between
7500 and 9000 years BP (Ryan, 1972; van Straaten,
1972).
We accept the hypothesis which relates the depo-
sition of these organic layers with phases of anaero-
bic conditions and water mass stratification.
Whether this stratification is the result of increased
outflow of low salinity waters from the Black Sea
into the eastern Mediterranean coupled with de-
creased evaporation rates (Olausson, 1961; Ryan,
1972; Cita and Ryan, 1973; and others), or surface
water warming (van Straaten, 1972), or an excess
inflow of fresh water from rivers and melting ice
and associated current reversals at the Strait of
Gibraltar (Mars, 1963; Huang et al., 1972; Nester-
off, 1973) is not determined. Miiller (1973) pro-
poses an alternative hypothesis on the basis of
nannoplankton analysis, i.e., that layering of water
masses in the eastern Mediterranean is the result of
increased evaporation and less fresh water dis-
charge or rainfall during cold periods; thus, in
this case, water stratification would be produced by
the influx of less saline and less dense water from
the Atlantic Ocean. In any case it is apparent that
repetitive phases of stratification and stagnation
during the Quaternary were basin-wide phenom-
ena. Other examples of recent sapropel and
sapropel-like deposits are reported from the Cari-
aco Trench (Heezen et al., 1961), the Gulf of
California (Byrne and Emery, 1960; van Andel
and Shor, 1964), and the Black Sea (Ross and
Degens, 1974).
In general the sapropel depositional models are
characterized by: (a) layering of water masses;
(b) stagnation of the bottom water, with forma-
tion of an H2S rich zone; (c) seasonal (winter-
summer) or periodical (eustatic changes) upwell-
ing and vertical mixing of water. These factors
favor the development and preservation of varve-
like bedding (Figure 28A).
Although the depth of the three deep Strait of
Sicily basin plains (1300-1700 m) is well below
that at which sapropel layers are found elsewhere
in the central (Adriatic) and eastern (Ionian,
Levantine basins) Mediterranean, no sapropels or
other distinct evidence of stagnation are noted in
the basin cores. On the contrary, structures pro-
duced by benthic organisms are commonly ob-
served, indicating that these deep narrow basins
remained sufficiently oxygenated to support ben-
thic populations throughout the late Quaternary.
Thus, it appears that vertical mixing prevailed on
an almost continuing basis as a result of water mass
movement across the Strait of Sicily at a time when
sapropels were accumulating under stagnant con-
ditions in the adjacent eastern Mediterranean.
In this respect, core LY II-6A west of the Strait
Narrows (Figure 34) is of interest. The rate of
sedimentation here is higher than in many other
sectors of the Strait. The mud at the top of core
LY II-6A is dated as early Holocene (about 11,000
to 10,000 years BP), or well after sea level had be-
gun to rise. Inasmuch as this core lies at a depth
of 755 m, the eustatic oscillation alone is not be-
lieved to be the primary factor for erosion or non-
deposition in this sector. The region just west of
the Strait Narrows may be critical for interpreting
Quaternary oceanographic fluctuations since it oc-
66 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
cupies a zone of particularly strong current regime
(Molcard, 1972). Currents accelerate in the con-
stricted narrows and decelerate as the Strait widens,
with a probable increase in deposition away from
the Narrows. Thus we would expect that cores
collected in the vicinity of the Narrows would pro-
vide the best record of water mass-bottom current
fluctuations during the recent geological past.
It is probably not accidental that there is an ap-
parent correlation between the time of truncation
of core tops in the Strait neritic-bathyal environ-
ments and that of the most recent protosapropel
and sapropel formation (dated at about 9000 to
7500 years BP) in the eastern and central Mediter-
ranean. Independently, other workers (Colantoni
and Borsetti, 1973) record microfaunal changes in
the Linosa and Malta basins at about this period.
One possible explanation for these early Holocene
depositional and faunal changes is a temporary
short-term reversal of surface and deeper water
flow (Olausson, 1961; Mars, 1963; Huang et al.,
1972; Nesteroff, 1973; Huang and Stanley, 1974;
and others). At present, less dense water flows
(> 30 cm/sec) southeastward above northwestward
flowing (32 cm/sec) Levantine water (Molcard,
1972). We propose a contrasting early Holocene
short-term current reversal model in which less
dense surface water flowed to the northwest in
response to the early Holocene climatic evolution
(Figure 39). Surface water salinity and tempera-
ture conditions (Farrand, 1971; Fairbridge, 1972)
undoubtedly were modified in the Mediterranean
during the warming phase of the climatic curve,
but the degree of stratification resulting from this
remains a point of conjecture (Letolle and
Vergnaud-Grazzini, 1973).
Our core analysis shows (1) that the sea floor of
the Strait of Sicily remained ventilated and swept
by currents at a time when anaerobic conditions
prevailed in the Ionian-Levantine basins east of
the Strait, and (2) that the Strait although a broad
sill apparently did not completely block circula-
tion between the eastern and western Mediterra-
nean basins. We conclude that the regional litho-
facies distribution observed is best explained in
terms of early Holocene paleooceanographic
changes including possible reversal of currents.
The latter concept requires further testing and we
suggest that the Strait of Sicily, the major sill
separating sapropel-rich eastern Mediterranean ba-
sins from nonsapropel basins in the west, is clearly
one of the key sites in which to investigate this
problem.
Summary
1. This marine sedimentological study defines
the major Quaternary lithofacies observed in cores
collected in the different sectors of the Strait of
Sicily and establishes the relationship between
sedimentary facies, depositional environment,
structural displacement, transport processes, and
late Quaternary events which affected the central
Mediterranean region.
2. The major depositional environments in, and
immediately adjacent to, the Strait of Sicily are as
follows: slope; neritic-bathyal borderland; basin
(intermediate and deep); shallow platform;
marked topographic high (submarine mounts, vol-
canoes, diapirs); canyon; and the Strait Narrows
between Cape Bon, Tunisia, and Marsala, Sicily.
These environments are broadly defined on the
basis of morphology, structural configuration, and
thickness and attitude of the sedimentary cover as
measured in seismic records. The shallow platform,
neritic-bathyal borderland, and basins are the most
characteristic environments in the Strait.
3. The lithologic uniformity of core sections,
the high degree of bioturbation, and the impor-
tance of coarse calcareous sediments serve to dis-
tinguish the late Quaternary Strait of Sicily litho-
facies from those of the adjacent deep Ionian and
Balearic basins.
4. Three major Strait lithofacies assemblages are
recognized: (1) coarse calcareous sand layers inter-
bedded with mud and sandy lutite deposits prevail
on shallow banks; (2) homogeneous, bioturbated
light olive gray to dusty yellow muddy sequences
predominate in the neritic-bathyal environments
and are also found in some basins; (3) moderate-
to well-stratified sand (including gravity sediment
flow units and ash) alternating with hemipelagic
and turbiditic mud are generally present in deep
basin and Strait Narrows cores.
5. Five major sediment types are distinguished:
(1) coarse calcareous sand; (2) sand- to silt-size
sediments; (3) ash; (4) mud; and (5) sapropel
and organic ooze (the latter type is retrieved only
in cores on the Ionian margin east of the Strait).
The sediment types are defined on the basis of the
(a) sand fraction (> 63 microns) content and com-
NUMBER 16 67
IO?W
currents
less dense
surface water
stagnant (H^S-rich)
deep water
ventilated partly
water unventilated
water
FIGURE 39.?Schematic showing possible early Holocene water mass changes in the Mediterranean.
The model depicts stratification and reversal of currents during the warming phase of the
climatic curve. The present study indicates that deep Strait basins remained ventilated at the
time that sapropel layers accumulated in the eastern Mediterranean. (Topographic base after
Wiist, 1961.)
position, (b) SEM investigation of the lutite frac-
tion, (c) sedimentary structures observed in X-
radiographs and split cores, and (d) examination
of the sea floor by underwater photography.
6. The sediment types are grouped into se-
quences, each of which is defined on the basis of a
succession of sediment types. A sequence represents
deposition resulting from a specific sedimentary
accident (turbidity current, mass flow, etc.) or from
a regionally important, large-scale environmental
event. An example of the latter: the Quaternary
climatic changes which were significant enough to
alter water mass stratification and movement, eu-
static oscillatory patterns, and biogenic production.
The four major sequences distinguished are (1)
upward-coarsening and upward-fining; (2) uni-
form; (3) turbiditic (includes mud and sand-silt
turbidites); and (4) sapropel sequences.
7. The close relation between sediment type, se-
quences, lateral distribution, and depth is demon-
strated. The coarse calcareous deposits on banks,
comparable to those on shallow shelves and plat-
forms elsewhere in the Mediterranean, are typified
by upward-fining and upward-coarsening se-
quences. Sediment facies in the shallow platform
environments are directly related to Quaternary
sea level oscillations. The sediments in the some-
what deeper neritic-bathyal environments are typi-
cally uniform muds devoid of marked stratification,
while the more variable and well-stratified deep
basin sediment sections include turbidites, volcanic
ash layers, and hemipelagic mud sequences.
8. Two types of layers containing volcanic sedi-
ment are distinguished: (1) air-borne tephra
layers, and (2) turbiditic ash-rich layers. The
former display a vertical gradation in grain size
(fining or coarsening upward), parallel lamina-
tion, or in some cases are structureless. The latter
68 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
type, composed of bioclastic as well as volcanic
material, shows the vertical sequence of sedimen-
tary structures characteristic of typical terrigenous
turbidites.
9. Stratigraphic correlation of the cores is based
on 41 carbon-14 analyses. The study shows that
specific sediment units or sequences generally are
not correlatable across the Strait or even within a
single environment such as a small deep basin. It
is possible, however, to recognize a general succes-
sion of sedimentation patterns in each major
environment.
10. Depositional patterns in the Strait have been
controlled mainly by three major factors: regional
Quaternary events related to changes of climate and
eustatic sea level oscillations, depth, and organisms.
The Quaternary climatic and associated sea level
oscillations are reflected primarily by the trunca-
tion of the upper sediment sequences on the shal-
low platform and in neritic-bathyal environments,
and development of fining- and coarsening-upward
sequences on the shallow platform. The distribu-
tion of hemipelagic and turbiditic mud lithofacies
in the neritic-bathyal environments is related to
the present sea level stand. In contrast, the well-
stratified sections?in the deep enclosed basins show
a uniform rate of sedimentation from the late Qua-
ternary to the present, and core to core differences
have resulted from variations in the number of
turbiditic and volcanic ash incursions into the
deep basins.
11. The close relation between sediment type
and depth is well demonstrated by the inverse re-
lation of turbiditic mud, which increases, and
hemipelagic mud, which decreases with increasing
depth. About three-quarters of the variance in the
degree of bioturbation in the Strait cores also can
be explained as a function of depth. These rela-
tions between sedimentation and depth may be ap-
plicable in the interpretation of ancient deposits.
12. Sedimentation rates in the Strait (with
some exceptions) generally decrease with increas-
ing depth and have been relatively uniform during
the late Quaternary. However, there is a significant
difference in the age of sediment sequences at the
top of cores in the different environments: on shal-
low banks, the top of some cores are truncated in
the late Pleistocene to early Holocene; in the
neritic-bathyal environments in the early Holo-
cene; and in the deep basins, sediments have ac-
cumulated on a fairly continuous basis from the
late Pleistocene until the recent.
13. Faulting in many sectors of the Strait is of
recent or subrecent origin, and correlation of re-
flectors on high-resolution subbottom profiles indi-
cates that this vertical displacement is commonly
in excess of the sedimentation rate, i.e., in excess of
20 cm per 1000 years.
14. No sapropel layers are noted in basin cores,
although the three deep Strait of Sicily basin
plains lie at a depth (1300 to 1700 m) well below
that at which sapropel deposits are found else-
where in the central and western Mediterranean.
It appears that these deep basins remained venti-
lated during the periods when anaerobic condi-
tions prevailed in the Ionian-Levantine basins east
of the Strait. Apparently the Strait did not com-
pletely block the circulation of water masses be-
tween the eastern and western Mediterranean ba-
sins in the late Quaternary.
15. An early Holocene paleooceanographic
model in which a possible reversal of currents is
postulated would help explain the particular dis-
tribution of sedimentary sequences and different
rates of sedimentation observed in the various
Strait of Sicily environments.
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