Eustatic and tectonic control on deposition and lateral variability of Quaternary regressive sequences in the Adriatic basin (Italy)

During the late Pleistocene, sea level variations related to glacio-eustatic cycles induced the deposition of four regressive sequences on the western continental shelf of the Adriatic basin. The four sequences are bounded by erosion surfaces that formed during sea level fall, sub-aerial exposure of the shelf and subsequent sea level rise and erosional reworking. The sequences and the erosion surfaces at their top (numbered 1-4 top-down) are correlated on distances in the order of 300 km, in the central and south Adriatic. Core control on deposits of the most recent depositional sequence (sequence 1) suggests that each sequence records a fourth-order (ca. 100-120 kyr) cyclicity of sea level change. Within each depositional sequence, progradational units representing highstand to forced regression are dominant, whereas transgressive deposits are absent or reduced in both thickness and lateral extent. Sequences are thus referred to as regressive sequences. Deposition during sea level fall occurred on an overall subsiding shelf, through the dispersal of fine-grained sediment supplied from the adjacent Alpine and Apennine chains. This resulted in stacked forced-regression deposits thick enough to survive complete removal during subsequent phases of sub-aerial and marine erosion. Erosion and/or non-deposition were enhanced only where tectonic uplift and morphological highs further reduced the remaining accommodation space, resulting in local thickness reduction or in the non-preservation of the regressive sequences. At larger scale, thickness variability and depocenter distribution north and south of the Gargano Promontory (an uplifted block bisecting the Adriatic foreland) reflect differential deposition and preservation of regressive deposits, as a function of contrasting tectonic setting and resulting physiography of the shelf and upper slope. (C) 2002 Elsevier Science B.V. All rights reserved.