Chronostratigraphic framework at sites GeoB14403 and GeoB14414 from the Gela Basin, Sicily Channel

A multi-proxy chronological framework along with sequence-stratigraphic interpretations unveils composite Milankovitch cyclicity in the sedimentary records of the Last GlacialeInterglacial cycle at NE Gela Basin on the Sicilian continental margin. Chronostratigraphic data (including foraminifera-based eco-biostratigraphy and d18O records, tephrochronological markers and 14C AMS radiometric datings) was derived from the shallow-shelf drill sites GeoB14403 (54.6 m recovery) and GeoB14414 (27.5 m), collected with both gravity and drilled MeBo cores in 193 m and 146 m water depth, respectively. The recovered intervals record Marine Isotope Stages and Substages (MIS) from MIS 5 to MIS 1, thus comprising major stratigraphic parts of the progradational deposits that form the last 100-ka depositional sequence. Calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher-frequency (20-ka) sea level cycles punctuating this 100-ka cycle. This becomes most evident in the alternation of thick interstadial highstand (HST) wedges and thinner glacial forced-regression (FSST) units mirroring seaward shifts in coastal progradation. Albeit their relatively short-lived depositional phase, these subordinate HST units form the bulk of the 100-ka depositional sequence. Two mechanisms are proposed that likely account for enhanced sediment accumulation ratios (SAR) of up to 200 cm/ka during these intervals: (1) intensified activity of deep and intermediate Levantine Intermediate Water (LIW) associated to the drowning of Mediterranean shelves, and (2) amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions. Equally, the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of MIS 5 Interstadials, which bear a striking resemblance to modern equivalents forming on late-Holocene prodeltas of other Mediterranean shallow-shelf settings.

Geochemistry at DSDP Legs 36 and 71 Holes

For Middle Jurassic to Pleistocene times, clay mineralogical and geochemical data provide information on the evolution of continental and marine paleoenvironments. They are a source of information on marginal instability, on the continental and shallow marine environments related to the development of the Southern Ocean during the Middle and Late Jurassic, and on tectonic relaxation of the continental margins at the end of the Late Jurassic. They also provide evidence for the influences of the South Atlantic opening and the movement of the Falkland Plateau in a reduced marine environment until Aptian-Albian times, and the transition to an open marine environment during Albian time; the influences of the Albian-Turonian and Coniacian-Santonian Andean deformations in an open marine environment; the limited tectonic effects and strong influence of marine currents at the Cretaceous/Tertiary boundary; the influences of the global climatic cooling and inferred bottom water circulation during the late Eocene and Oligocene; the widening of the South Atlantic Ocean during Oligocene time, which was accompanied by an increased influence of the biogenic components on sedimentation; increased carbonate dissolution from late Oligocene to early Miocene, related to the deepening of the ocean; limited mineralogical and important geochemical modifications when the Drake Passage opened in the early Miocene; the influence of the late Miocene development of the Antarctic ice-sheet; the major Antarctic cooling and Patagonian glaciation during Pliocene time; and the change in the Antarctic Bottom Water circulation at the Pliocene/Pleistocene boundary.