Facies architecture and latest Pleistocene-Holocene depositional history of the Po Delta (Comacchio area), Italy

Integrated sedimentological and micropaleontological study of 16 cores and 137 piezocone penetration tests, approximately 40 m deep, in the Comacchio area enables the documentation of the depositional history of southeastern Po Plain in the last 30 ka, in response to fluctuating sea level. Sedimentation within an alluvial plain was the dominant feature across the entire study area during the pronounced sea level fall that culminated in the Last Glacial Maximum. Thin lowstand fluvial sediments form the lower part of a shallow incised valley above the Last Glacial Maximum unconformity, whereas a characteristic paleosol separates the last glacial alluvial plain deposits from the overlying postglacial deposits in the interfluves. Transgressive and highstand deposits show a well-developed stacking pattern of retrogradational (coastal plain and estuarine) and progradational (deltaic) facies. Detailed reconstruction of transgressive paleogeography shows evolutionary features that can be useful for refined interpretation of coeval and ancient analogs. At relatively early stages of transgression (10.5-9 ka B. P.), sedimentation in a coastal plain was restricted to the incised valley, whereas nondeposition and pedogenesis took place on the interfluves. With rising sea level (9-6 ka B. P.), a wave-dominated, barred estuary developed in the former topographic low. At peak transgression, after filling up of the estuarine systems with coastal, back-barrier sediments, wide areas outside the valleys were flooded, aggradation extended onto the interfluve unconformity, and a shallow marine depositional environment developed across most of the study area. The depositional history during the subsequent highstand phase was dominated by progradation of the early Po Delta and reflects the complex interplay between high-frequency sea level fluctuations, climate, subsidence, and autocyclic processes.