Anatomy of a compound delta from the post-glacial transgressive record in the Adriatic Sea

Abstract

On the Mediterranean continental shelves the post-glacial transgressive succession is a complex picture composed of seaward progradations, related to sea level stillstands and/or increased sediment supply to the coasts, and minor flooding surfaces, associated with phases of enhanced rates of sea level rise. Among Late Pleistocene examples, major mid-shelf progradations have been related to the short-term climatic reversal of the Younger Dryas event, a period during which the combination of increased sediment supply from rivers and reduced rates of sea level rise promoted the formation of progradations up to tens-meter thick. While the documentation of coastal and subaqueous progradations recording the Younger Dryas interval is widely reported in literature, the model of compound progradation within transgressive deposits has not yet been proposed. Here we present the documentation of a deltaic system where both delta front sands and related fine-grained subaqueous progradations (prodeltaic to shallow marine) have been preserved. The Paleo Gargano Compound Delta (PGCD) formed offshore the modern Gargano Promontory (southern Adriatic Sea), and is composed of a coastal coarse-grained delta of reduced thickness and a muddy subaqueous clinoform, up to 30 m thick. The PGCD, probably the first worldwide documentation of a compound delta within the transgressive record, provides the opportunity to investigate the processes controlling the formation of a compound delta system during an overall sea level rise and the factors that allowed its preservation. The finding of the PGCD provides the opportunity for a comparison with modern worldwide compound systems.

Clinoforms and clinoform systems: Review and dynamic classification scheme for shorelines, subaqueous deltas, shelf edges and continental margins

“…5). This contrasts with the accumulation rate and thickness profiles of constructional clinoforms, characterized by sedimentation rates greatest along the foreset portion and significantly lower towards both the topset and the bottomset (e.g., Alexander et al, 1991;Leithold, 1993;Michels et al, 1998;Pirmez et al, 1998;Walsh et al, 2004;Palinkas and Nittrouer, 2006;Cattaneo et al, 2007;Pellegrini et al, 2015) (Figs. 10-18).…”

“…Most clinoforms are formed during either highstands or lowstands, when sediment supply is expected to outpace the rate of relative sea-level rise (Neal and Abreu, 2009). Other clinoforms may be formed by regressive transits under overall transgressive conditions (e.g., Postma, 1995;Helland-Hansen and Martinsen, 1996;Plink-Björklund and Steel, 2002;Pellegrini et al, 2015), or when relative sea-level is falling (e.g. Plint and Nummedal, 2000).…”

“…Although delta-scale compound clinoform progradation during overall transgressive conditions have been recently reported (Pellegrini et al, 2015), compound clinoforms are typically developed during early highstands, after a prior transgression lead to the physical separation of shorelines and shelf-edge. During many subsequent episodes of crossshelf shoreline transits, however, due to the exponential differences in progradation rates between clinoforms at the shoreline (c. 1,000-100,000 m/kyr), subaqueous delta (c. 100-20,000 m/kyr), shelfedge (c. 1-100 m/kyr) and continental margin (c. 0.1-10 m/kyr) (Fig.…”

Tordera River Delta system build up (NE Iberian Peninsula): sedimentary sequences and offshore correlation

“…This is the case on the Losna and Antnsjo sandy braid deltas (Bogen 1983). Along the Mediterranean coast, the coarse sand deltas described consist of gravel pleistocene-Holocene fan deltas influenced by recent tectonic and wave activity (Massari and Parea 1990, Dabrio et al 1991, Pellegrini et al 2015. Only two examples of sandy braid deltas have been cited: Goynuk Delta in the gulf of Antalya (Ayranci et al 2010) and the Tordera delta, analysed here.…”

“…The geometry and evolution of a delta are the consequence of the fluvial regime, the sediment grain size, the tectonics of the area and the oceanic system of the receiving basin (Liu et al 2000, Pellegrini 2015. In addition to the classification of deltas as a function of the dominant processes in the delta front area (Wright andColeman 1972, Galloway 1975), two important factors should be considered to account for delta dynamics: sediment supply and grain size.…”