Sand composition and sedimentary evolution of a late quaternary depositional sequence, northwestern Adriatic Coast, Italy

In order to detect temporal and spatial variations in detrital supply in th e upper part of the last depositional sequence of late Pleistorene-Holocene age, we conducted a combined petrographic and stratigraphic study in the R omagna coastal plain, south of the Po delta, Northern Italy. We analyzed heavy minerals and the bulk composition of sands from cores and surface samples. By using petrographic and stratigraphic data on compositi on of modern beach and major river deposits, new aspects of detrital disper sal mechanisms and the depositional history of the study area are documente d. The heavy mineral distribution, coupled with the dolostone and volcanic roc k fragment contents of bulk sands, allow identification of three different petrofacies: Petrofacies A, Petrofacies B, and Petrofacies C, which have be en interpreted as of apenninic, mixed Eastern ALps/Po River basin, and Po R iver catchment basin provenance, respectively. Distribution of the three pe trofacies changed through time in response to landward and seaward shifting of the coastline. During the late Pleistocene lowstand, a pure Apenninic p rovenance character-ized the Romagna coastal plain (Petrofacies A), During the Holocene transgression, when the shoreline migrated tens of kilometers west of its present position, eastern Alpine sediment sources fed littoral facies (Petrofacies B), probably as a result of southward transport by litt oral drift, This sediment supply continued during the early regressive phas es and was cut off by a change in coastal morphology related to the develop ment of the early Po delta. This led to the establishment of a sediment sup ply entirely related to the Po River catchment basin (Petrofacies C), Chang es in the compositional signature of sand in the youngest beach ridges mark the abandonment of the early Po delta due to an avulsion event and testify to the establishment of a coastal system fed by rivers draining the Apenni nes (Petrofacies A). We emphasize sand petrograpfy as an important tool in studying the internal architecture of sandy elastic: depositional units on detailed spatial scal es, and its use in deciphering the depositional history of complex sediment ary successions.