Cenomanian (Upper Cretaceous) bivalves from the Hameimat Massifs, north of Tebessa, Algeria: Systematics, biostratigraphy, palaeoecological and taphonomical remarks

Abstract

In the eastern Saharan Atlas, particularly in the northern area of Tebessa Province (NE Algeria), the widely outcropping Cenomanian strata display a highly diversified macrofauna, among which bivalves are prominently represented. Twenty-eight bivalve species are here reported for the first time from the Cenomanian of Hameimat Massifs. Based on the stratigraphic distribution of these bivalves, five bivalve zones were recognized, i.e., Costagyra olisiponensis - Gyrostrea delettrei, Rhynchostreon suborbiculatum - Exogyra conica, Ceratostreon flabellatum, Ilymatogyra africana, and Pycnodonte vesicularis vesiculosa - Rastellum carinatum zones. Correlation to the ammonite biozones of the same region as follows: the Costagyra olisiponensis - Gyrostrea delettrei and the Rhynchostreon suborbiculatum - Exogyra conica zones occur respectively in the Sharpeiceras schlueteri and Mantelliceras saxbii subzones of the lower Cenomanian Mantelliceras mantelli Zone. The Ceratostreon flabellatum Zone is correlated with the middle Cenomanian Acanthoceras rhotomagense Zone. The Ilymatogyra africana Zone is correlated with the upper Cenomanian Calycoceras naviculare and the Metoicoceras geslinianum zones. Finally, the Pycnodonte vesicularis vesiculosa - Rastellum carinatum Zone represents the uppermost Cenomanian. Detailed analysis of biometrical and morphological features of these bivalve specimens provides the most reliable tool within the scope of palaeo-environmental reconstitution and the many palaeo-ecological variables that had driven the development and distribution of these macro-invertebrates. Comparison of these new data to those of adjacent south Tethyian areas supports the homogeneity of the Cenomanian bivalve faunas. Such an affinity underlines more vividly the favorable marine communications and currents driving the geographic dispersal of these bivalves during the Cenomanian.