Crassatella baudeti (Coquand, 1862) du Cénomanien de Batna (NE algérien) : paléobiogéographie, paléoécologie et biostratigraphie

The lower Cenomanian strata from the Batna region (NE Algeria) constitute the richest and most diversified deposits in terms of macro-invertebrates, mainly dominated by bivalves both in terms of specimens and taxa. Among them, Crassatellidae are restricted to the lower Cenomanian stratigraphical levels. They are represented by the single species Crassatella baudeti. The species is easily distinguished by its flattened boat anchor shape and quite strong commarginal lamellae, and is very abundant. It is present in levels ranging from Sharpeiceras schlueteri Subzone to Cunningtoniceras inerme Zone. The species is, therefore, a good marker of the last levels of the lower Cenomanian and the beginning of the midlle Cenomanian. A precise palaeontological description and an environmental discussion were conducted. Thus, Cr. baudeti would be indicative of a shallow environment, with cold but calm waters, normal salinity and moderately soft substrate. Recorded exclusively from the Cenomanian of a few Tethys localities, the exclusive presence of Cr. baudeti reflects a specific thermal gradient and climatic zonation.