Modeling of sequence geometry north of Gargano Peninsula by changing sediment pathways in the Adriatic Sea

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Continental Shelf Research
Journal Date: 
Feb 1
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Sea level changes can reorganize sediment pathways on continental shelves in ways that can alter sediment supply and the resulting sedimentary deposits. The Adriatic Sea is one place where changing sediment pathways and along-strike currents have a major impact on sequence architecture. The Adriatic Sea, the marine portion of the Apenninic and Dinaric-Hellenic foreland basins, is being filled longitudinally, similar to other active forelands, and sediment transport patterns dramatically reorganized during Quaternary sea level cycles. We investigate the dynamics of sequence formation in the central Adriatic near the Gargano Promontory and the Mid-Adriatic Deep (MAD), where four depositional sequences each recording 100-kyr glacio-eustatic cycles have been mapped. These sequences are composed primarily of progradational units separated by regional unconformities. The geometry of the units is such that the constitutive clinoforms flatten out at their seaward termination into relatively planar strata, particularly in the upper parts of each sequence. Attempts to numerically simulate the sequences using the modeling software SFQUENCE4 were frustrated by the difficulty of flattening the clinoforms seaward of the rollover (or depositional shelf break). The clinoform flattening observed in the Adriatic sequences contrasts with clinoform and depositional shelf break development that is characteristic of both conceptual and numerical models of sequences, including the one used here. We, therefore, modified the numerical model to account for the changes in sediment pathways that occur in the Adriatic Sea. During times with high sea level, such as the present, sediment from the Po and smaller Apennine Rivers is transported southwards along the coast by marine coastal currents and storms. At times of low sea level, fluvial transport of an enlarged Po River, in which the Apennine Rivers are likely captured as tributaries, discharges directly into the MAD basin. This produces a reciprocal sediment supply pattern where the coastal dispersal at high sea level produces prograding clinoforms, but cuts off as the exposure of the northern shelf at low sea level switches supply to the fluvial system, which discharges into the 260-m deep MAD. When the model is adapted for the shift in supply, the clinoforms flatten as nearshore sediment supply decreases and is replaced by deposition in the MAD during sea level lowstands. Including these sediment supply changes as a function of sea level enabled us to obtain a good fit to the overall stratigraphic architecture, supporting conceptual depositional models based on seismic stratigraphy. Similar dramatic shifts in sediment supply and sequence architecture may also occur at other settings, such as where canyons capture fluvial systems and bypass the terrigenous sediment supply to the deep basin. The paucity of observations of the unusual geometry seen at the Adriatic margin suggests that only rarely does the shore and fluvial sediment discharge overreach the shelf edge and cut off along-strike sediment transport to continental margins. (c) 2006 Elsevier Ltd. All rights reserved.


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DOI 10.1016/j.csr.2006.11.007