Palaeoenvironmental analysis of Early Pleistocene brackish marshes in the Rieti and Tiberino intrapenninic basins (Latium and Umbria, Italy) using ostracods (Crustacea)

Abstract

Recent palaeontological and sedimentological studies on the Upper Pliocene–Lower Pleistocene continental deposits of the Rieti and Tiberino basins (Latium and Umbria, Italy) showed the existence of brackish marshes influenced by the Early Pleistocene Tyrrhenian sea. The micropaleontological analyses carried out on five sections cropping out in the northern sector of the Rieti Basin and on one section cropping out in the southwestern branch of the Tiberino Basin showed the repeated alternance of two ostracod assemblages. The first is characterized by a very abundant ostracod association dominated by Cyprideis torosa, typical of brackish waters; the second one is less rich in specimens and dominated by several species of freshwater Candoninae. This alternance allowed the recognition of several changes in the water salinity that could be related to many Early Pleistocene sea-level changes. Palaeosalinities were estimated for both the Tiberino and the Rieti Basin using the morphological analysis of the shell of Cyprideis torosa (ornamentation, nodosities and percentages of sieve-type pore canals). The obtained palaeosalinity values, ranging from freshwater to oligohaline, show slightly higher salinities for the Tiberino Basin, located nearer the ancient coastline, than for the Rieti Basin.