Paleocene palustrine and ephemeral alluvial facies in southern Sardinia (Italy)

Abstract

Paleocene ephemeral alluvial and palustrine deposits have been recognized in several small outcrops in southern Sardinia. Three sedimentary units have been distinguished: the basal one, mainly terrigenous, made up of alluvial pedogenized deposits, the intermediate one, entirely carbonate, made up of pedogenized fresh water deposits, and the third one, terrigenous-carbonate, recording the beginning of the Thanetian marine ingression in Sardinia. The carbonate deposits are the most developed and are mainly characterized by the presence of Microcodium, both with corn-cob aggregates, in some cases forming palisades or reef-like buildups, and with disarticulated grains forming resedimented deposits; charophyte stems and gyrogonites and stromatolites are also present, in some cases frequent. Deposits rich in charophyte stems indicate the presence of perennial water ponds. Alternances of humid and dry periods favoured erosive fluctuations, as indicated by the frequence of resedimented intraclasts of fresh water sediments, biotic remains as charophytes and stromatolites and, over all, detrital disaggregated Microcodium grains. The studied small outcrops are the only remnants of a probably wide Paleocene continental sedimentary cover, and provide informations on a variety of depositional facies, which are useful proxies for depicting a landscape with wetlands and detrital Microcodium deposits, similar to the coheval continental landscape widespread in southern France and in northeastern Spain.