Anatomy of a Compound Delta From the Post-Glacial Transgressive Record in the Adriatic Sea
On the Mediterranean continental shelves the post-glacial transgressive succession is a complex picture composed by backstepping units, associated to phases of enhanced rates of sea level rise, and seaward progradations, related to sea level stillstands and/or increased sediment transport toward the coast. Among Late Pleistocene examples, mid-shelf progradational deposits has been related to the short-term climatic variability 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 tens-meters thick muddy subaqueous progradations. We present the documentation of a deltaic system where both delta front sands and related fine-grained subaqueous progradations (prodeltaic to shallow marine) has been completely preserved. This compound delta systems formed offshore the modern Gargano Promontory (southern Adriatic Sea) during the Younger Dryas cold event and probably may be considered the first documentation of a compound delta preserved within transgressive deposits; this provides the opportunity to investigate the processes controlling the formation and preservation of a complex deltaic system during an overall sea level rise and to compare ancient and modern compound systems. The finding of the PGCD, in agreement with further documentation worldwide (especially for the Amazon delta), suggests that subaqueous deltas are always genetically linked delta front deposits, characterized by a shallower rollover point. The formation of this compound system within the short time window of the Younger Dryas event implies that the time required for the development of this kind of deltaic deposits may take place in few centuries; this notion may be useful in interpreting ancient stratigraphic record where a much lower geochronological resolution may lead to assume or imply much slower rates of sediment accumulation.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015