Sedimentary response to climate and sea level changes during the past ∼400 ka from borehole PRAD1–2 (Adriatic margin)

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Abstract

[1] Borehole PRAD1–2 was drilled in ∼186 m water depth on the upper slope of the central Adriatic, in the frame of Profiles across Mediterranean Sedimentary Systems (PROMESS1) European Union-funded project. The borehole penetrated 71.2 m through a stratigraphic interval characterized by subparallel seismic reflections and uniform seismic units. According to an age-depth model based on several independent proxies (including foraminifera and nannoplankton stratigraphy, ∂18O curves, and magnetostratigraphy) the cored interval records Marine Isotope Stages and Substages (MIS) from MIS1 to the top of MIS11, thus encompassing the past ∼370 ka. PRAD1–2 therefore represents an unprecedented continuous record through the last four glacial-interglacial cycles from a proximal continental margin setting where depositional sequences are typically composed of progradational units. These progradational units record dominantly interglacial intervals (MIS5, MIS7, and MIS9) and appear composed of thicker highstand deposits (HST) formed during interstadials and thinner forced-regression units (FSST) deposited during stadials above distinctive downward shift surfaces. The development of thicker highstand deposits with a distinctively thicker bottomset reflects enhanced shore-parallel advection any time sea level rise leads to the drowning of the Adriatic shelf, triggering the formation of dense water and vigorous cyclonic circulation. This advection mechanism persisted in each cycle throughout the early phases of the sea level fall but progressively decreased as sea level fall proceeded approaching the maximum lowstand position, when most of the shelf became exposed. Relative sea level falls punctuating interglacials within each 100-ka cycle were thus accompanied by a dearth in sediment flux on the outer shelf. The alternation of HST and FSST progradational wedges with markedly different thickness and downlap geometry of their bottomsets is the most evident stratigraphic signature, within each 100-ka depositional cycle, of the impact on the shelf of higher-frequency (∼20 ka) sea level cycles and concomitant supply fluctuations.

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