Late Quaternary Sedimentation and Stratigraphy in the Strait of Sicily

Abstract

The Strait of Sicily, a broad, elongate, topographically complex platform in the central Mediterranean, separates the deep Ionian Basin from the Alg?ro-Balearic and Tyrrhenian basins to the west. A detailed core analysis shows that the late Quaternary sections 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 bioturbated 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, Pantelleria, 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 individual 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 displacement 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 depressions 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.