Environmental evolution of the Miocene palaeolake of Venta del Moro (Valencia, Spain): a study of foraminifers, thecamoebians (Arcellinida) and ostracods

Abstract

ABSTRACT The Venta del Moro site (Valencia, Spain) is especially known for its rich content in Late Miocene fossil mammals but it also holds other fossil vertebrates, invertebrates and plants. A micropalaeontological study of a 70-cm long sedimentary section carried out in the lacustrine beds of the site has yielded 2 foraminifer, 7 thecamoebian and 19 ostracod taxa (two of these last probably new species). A constrained cluster analysis allowed the recognition of three consecutive zones based on their micropalaeontological content. The variation of the microfossil assemblages closely matches lithology and reflects environmental changes in a palaeolake that was subject to a gradual drying process. Anoxic bottom conditions at the base of the sequence (Zone 1) prevented the occurrence of aerobic benthic microorganisms. Later, the appearance of ostracods and thecamoebians (Zone 2) documents the increasing oxygenation of the lake and suggests a permanent freshwater to slightly brackish lake with low temperature and stream influence. The dominance of foraminifers and the changes in the thecamoebian and ostracod assemblages in the upper part of the sequence (Zone 3) reflect more stable and oxygenised conditions and probably increasing temperature and evaporation in oligohaline temporary waters, during the final drying phase of the lake.