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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.

Recent seismicity in and around the Gargano Promontory, an uplifted portion of the Southern Adriatic Foreland domain, indicates active E-W strike-slip faulting in a region that has also been struck by large historical earthquakes, particularly along the Mattinata Fault. Seismic profiles published in the past two decades show that the pattern of tectonic deformation along the E-W-trending segment of the Gondola Fault Zone, the offshore counterpart of the Mattinata Fault, is strikingly similar to that observed onshore during the Eocene-Pliocene interval. Based on the lack of instrumental seismicity in the south Adriatic offshore, however, and on standard seismic reflection data showing an undisturbed Quaternary succession above the Gondola Fault Zone, this fault zone has been interpreted as essentially inactive since the Pliocene. Nevertheless, many investigators emphasised the genetic relationships and physical continuity between the Mattinata Fault, a positively active tectonic feature, and the Gondola Fault Zone. The seismotectonic potential of the system formed by these two faults has never been investigated in detail. Recent investigations of Quaternary sedimentary successions on the Adriatic shelf, by means of very high-resolution seismic-stratigraphic data, have led to the identification of fold growth and fault propagation in Middle-Upper Pleistocene and Holocene units. The inferred pattern of gentle folding and shallow faulting indicates that sediments deposited during the past ca. 450 ka were recurrently deformed along the E-W branch of the Gondola Fault Zone. We performed a detailed reconstruction and kinematic interpretation of the most recent deformation observed along the Gondola Fault Zone and interpret it in the broader context of the seismotectonic setting of the Southern Apennines-foreland region.We hypothesise that the entire 180 km-long Molise-Gondola Shear Zone is presently active and speculate that also its offshore portion, the Gondola Fault Zone, has a seismogenic behaviour.

[1] Borehole PRAD1-2 was drilled in similar to 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, delta(18)O curves, and magnetostratigraphy) the cored interval records Marine Isotope Stages and Substages (MIS) from MIS1 to the top of MIS11, thus encompassing the past similar to 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 (similar to 20 ka) sea level cycles and concomitant supply fluctuations.