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 \ V--I I "I ? ' i UJ ?if: > NOUViS NO NOIJ.V1S NO U?** 5 IH >i ?a .a 2 "S. ,6 s C OH .. . N O-i eo S ? a ? .5 II ?s-g O, S .2 3 S-s ?3 "8.2 a "& s= s 1| I.! 0-.42a ? T3 "= O | ?I S "1 -8 eo rt ^?2S w e s C ?5 rt ? 3 W ?M O OJ H S O LJ 5 S ^ . fi ^ -s ^ 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
= 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 (O-< ffi < < ? - - -Is -_ __. t 1 < 'i a ?$ ? Ill1 III a \ \ H 0 \ i? 5 H i ILJ A < K- -W. 1B.~ . _ (350 m) : ?'. ? : - ??? [ ' 1 ? ? I S!I313W Nl 3)IO3 dO H1ON31 1111 <<_ I i o 0 2 z zo < ? I ait ID ssing j b nsectS [ona logs chron55 >?i icily. 'o 2 the ironmem nd basin e ?d g /3 car ?? inoo a eo urebp core; it ?> parisona ased on cc oi CM 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. 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