The combined effect of sea level and supply during Milankovitch cyclicity: Evidence from shallow-marine delta O-18 records and sequence architecture (Adriatic margin)

The combination of sequence stratigraphy and multiproxy chronostratigraphic data, including delta O-18 records, unravels the record of Milankovitch cyclicity through the past similar to 400 ka on the Adriatic margin. Chronostratigraphic data and stable isotope records from planktic and benthic foraminifera are derived from borehole PRAD1-2, a 71 m continuous core drilled on the Western Adriatic slope. The cored interval encompasses the distal parts of stacked progradational wedges that are the main building blocks of 100 ka depositional sequences. These sequences and their internal progradational units reflect a cyclic interplay between sea level and oceanographic circulation, with relevant feedbacks on sediment supply fluctuations and regional long-shore sediment dispersal. Calibration of slope units with isotope stratigraphy and direct slope-shelf correlation indicates that two types of progradational clinoforms alternate in phase with the pattern of composite climate and sea-level changes figured by delta O-18 records. Changes in clinoform geometry of the kind observed in the Adriatic are consistent with a mechanism of switching supply from dominant advection on a flooded shelf, during highstands, to overall sediment starvation on a narrowed shelf, during lowstands. Seismic and core data document that this mechanism is related to similar to 100 and 20 ka cyclicity reflecting rearrangement of the oceanographic setting and sediment pathways during the last four glacial-interglacial cycles.