Physical stratigraphy and sedimentology of the Late Pleistocene-Holocene Tiber Delta depositional sequence

The Tiber delta lies on the passive continental margin of central western Italy. The delta is a Late Pleistocene-Holocene sedimentary succession and constitutes an " incomplete " high-frequency depositional sequence (5th or 6th order), which developed from the last post-glacial rise in sea level to the present still-stand. It is bound by a type 1 basal unconformity which cuts Pleistocene deposits. Five depositional systems have been identified: 1) coastal barrier-lagoon; 2) shelf-transition; 3) fluvial braided; 4) Tiber lagoonal deltas (T1,T2,T3) and, 5) Tiber wave-dominated delta. The first four systems constitute the Transgressive System Tract (TST) which is characterized by a retrogradational parasequences set, while the fifth system represents the Highstand System Tract (HST) characterized by only one parasequence (progradational). The evolution of these depositional systems has been mostly controlled by sea level rise, which was not continuous, but punctuated by eight minor stillstands and rapid rises. This mechanism of sea level change led to the formation of parasequences that developed within the depositional systems. From a palaeogeographic point of view the present Tiber delta area was mainly characterized by a coastal barrier, lagoon, and Tiber lagoonal deltas (T1, T2, T3), which migrated landwards during the sea level rise. Throughout the time of the present stillstand, the T3 lagoonal delta prograded rapidly into the lagoon, reaching the coastal barrier, and the lagoon was replaced first by marshes and then by the alluvial plain. Finally, the Tiber River overcame the littoral barrier supplying the coast, giving rise to the present wave-dominated delta.