LATEST PLEISTOCENE TO HOLOCENE ENVIRONMENTAL CHANGES IN THE NORTHERN TYRRHENIAN AREA (CENTRAL MEDITERRANEAN). A CASE STUDY FROM SOUTHERN ELBA ISLAND.

Abstract

Geological and geomorphological studies, within the framework of the Geomorphological Sheet “Isola d’Elba” (1:50,000, ISPRA-Servizio Geologico d’Italia) have been implemented by sedimentological, geochronological and biostratigraphical (foraminifers, malacofauna, and palynology) analyses on sedimentary cores retrieved during four continuous mechanical drillings near the Marina di Campo village. Drill cores (S1-S4), up to 23-25 m deep, in sedimentary deposits referable to the last glacio-eustatic cycle allowed the reconstruction of the paleoenvironmental history of the southern sector of the Elba Island, since the Last Glacial Maximum (LGM). A significant fall in sea level (Lowstand Systems Tract - LST) determines the complete emergence and incision of the Tuscan continental shelf, including the sector in front of Marina di Campo, during the LGM. Thick fluvial sediments, mainly consisting of gravel, sand and silt alternations filled the river incisions. During the subsequent transgressive phase (Transgressive Systems Tract - TST), there was a progressive reduction of fluvial sedimentation and coastline retreat. Starting from about 7,000 cal. yr BP a shallow marine environment extended in the eastern sector of the Marina di Campo plain (S2 at about -10.60 m a.s.l.). Meanwhile, in the innermost portion of the plain dark gray organic clays and silts accumulated in brackish lagoons (S3). In both sector, continental deposits that interrupt marine and lagoon sedimentation, attest a brief regressive episode between ~6,600 and 5,800 cal. yr BP. Immediately after the regressive episode, the sedimentation of sand, sandy silt and biocalcarenites occurs in a relatively deeper sea (S2, between -8.41 and -3.91 m a.s.l.). In the innermost areas, however, organic clays and silts continue to accumulate in lagoons, whereas in upper areas fluvial sedimentation dominates. With the start of the sea level highstand phase (Highstand Systems Tract - HST), around 6,000 cal. yr BP, the ongoing progradation of the barrier-lagoon system determines a regression of the coastline and the eastward extension of brackish lagoons. With the definitive closure of the communication with the open sea, between ca1,500 and 1,300-1,200 cal. yr BP, the Marina di Campo lagoons were progressively transformed into freshwater coastal ponds. In the areas surrounding the ancient coastal ponds, river sedimentation persisted until today as attested by the current floodplain.