Bajocian Ostracods from the Krachoua Formation (Beni Kheddache, Southern Tunisia): Implications for Biostratigraphy and Paleoecology

Abstract

Ostracods and charophytes are considered as biological indicators of the environments in the Middle Jurassic strata of southern Tunisian. The biostratigraphic and Palaeoecology studies of the Krachoua Formation undertaken from the region of Beni Kheddache are based on the ostracodfauna and charophyte flora. A Bajocian age is assigned to the upper part of the Krachoua Formation. It consists of a multispecific ostracod association dominated by the following three genera, Limnocythere, Bisulcocypris, and Theriocynoecum which reflect appropriate palaeoecological conditions with a salinity decrease. This is due to the influx and installation of a freshwater pond occasionally developed and enhanced by humid climate coupled to a sea level fall. The occurrence of these species towards the top of Krachoua Formation is synchronous with the increase of silt and clay associated to vertebrate bones reflecting a regressive tendency within a transgressive/regressive sedimentary sequence within a Middle Jurassic long-term regressive cycle.