Ostracod Assemblages and Paleosalinity Reconstruction in Early Jurassic Basins

Ostracods are highly sensitive to salinity fluctuations and represent reliable indicators for reconstructing paleoenvironmental conditions in marginal marine and continental basins. During the Early Jurassic, significant climatic transitions and regional tectonic reorganization influenced hydrological regimes across epicontinental seas and rift-related basins. This study examines ostracod assemblages from selected Early Jurassic successions to evaluate their taxonomic composition, ecological structure, and application in paleosalinity reconstruction. Quantitative analysis of species abundance, diversity indices, and morphogroup distribution reveals distinct assemblage shifts corresponding to salinity gradients ranging from freshwater to fully marine conditions. Euryhaline taxa dominate transitional intervals, while stenohaline marine forms characterize open-marine phases. Variations in valve ornamentation, size distribution, and carapace morphology further reflect ecological stress linked to salinity instability. Multivariate statistical methods identify salinity as the principal environmental gradient controlling assemblage differentiation, supported by associated sedimentological indicators such as evaporite horizons, lagoonal mudstones, and marine carbonates.