The aim of this study is an attempt to record the Aptian and Albian ostracod species of the Jura Mountains (eastern France, northwestern Switzerland) and to use these species as biostratigraphical, paleoecological and paleogeographical tools.
Aptian and Albian sediments in the Jura Mountains are known since the last century. At that time they had been studied mainly near Bellegarde (Perte du Rhône) and Ste-Croix, where the sedimentary sequence was nearly complete. Numerous macrofossils were found and studied. Unfortunately, the historical outcrop of the Perte du Rhône has been immersed and the other outcrops are reduced and scattered.
The Aptian and Albian ostracod species in the Jura Mountains were mentionned for the first time in 1965 near Ste-Croix. Since that time only few works include ostracod studies. In 1977, some Albian ostracod species of the Joux Valley were illustrated. ln the present work 113 species (52 Aptian and 61 Albian species) are described and illustrated. 12 new species are named and 27 are left under open nomenclature. These species were obtained from 20 bore-holes and 27 outcrops. The main ostracod sites are located along the Haute Chaîne in the South and South-East. Several additional sites are found in the central and northern parts of the Jura Mountains.
The stratigraphic distribution of the species results from using different pieces of information: facies changes, presence of rare identifiable ammonites, of planktonic foraminifera and orbitolinids, and stratigraphic distribution of the ostracode faunas of the neighboring regions (Paris Basin and Vocontian Basin). This distribution covers parts of the Middle and Upper Bedoulian in the Aptian sediments and the upper part of the Lower Albian up to the Albian/Cenomanian boundary. Range charts for each borehole are presented.
In the Bedoulian one ostracod zone is recognized: the Asciocythere ? bellegardensis / A. ? posteroaculeata Zone subdivided into two ostracod subzones, the Centrocythere cf. bordeti and the Cythereis (R.) geometrica Subzones. In the Albian, four ostracod zones are recognized: the Platycythereis degenerata / Cornicythereis cornueli Zone, the Cornicythereis oweni / Cythereis (C.) trispinata Zone, the Cornicythereis larivourensis / Cythereis (R.) confossa Zone and the Cytherelloidea stricta / Platycythereis gaultina Zone. An attempt to apply these ostracod zones to the outcrops is made.
Statistical analyses of the ostracode populations of each sample are made (males / females, adults / juveniles, and carapaces / isolated valves ratios, SIMPSON diversity index) with the aim of reconstructing paleoenvironements. The results of these analyses are supported by lithological and paleontological (apart from ostracodes) features of the sediments. They indicate a marginal shallow marine environment with some currents during the Bedoulian and an open and quiet deeper marine environment during the Albian. [...]
