Cenomanian-Turonian roveacrinid microfacies assemblages (Crinoidea, Roveacrinida) from the Tinrhert area (SE Algeria)

摘要

In the eastern part of the saharan platform, the Cenomanian-Turonian marine deposits are lying conformably on the red detrital sediments of the so-called Infra-Cenomanian series. In the Hamada de Tinrhert (SE Algeria), the Cretaceous ledges are displaying over great distances a fine-detailed log of the upper Cenomanian-lower Turonian carbonates overlying the lower-middle Cenomanian red-and-greenish gypsum clays. Two sections, Bordj Omar Driss and Oued Takouazet, were thoroughly analyzed to define more precisely the stratigraphical position of the Cenomanian-Turonian boundary (C/TB) in this area. Microfacies analysis of indurated carbonates documented the constant occurrence of roveacrinidal sections on both sides of the Cenomanian-Turonian boundary. Though none of the identified taxa allows to characterize specifically which side of the C/T boundary, their quantitative fluctuations are consistent with those already documented in neighbouring areas and farther beyond. An especially rich and rather constant level, at the top of the coeval Plenus Zone (belemnite biozonation, Boreal realm), occurs close to the Heterohelix event. This conspicuous level provides a supplementary proximity proxy for the Cenomanian-Turonian boundary that should be later on confirmed by the associated ammonites and correlated with the standard reference zones. (C) 2016 Elsevier Masson SAS. All rights reserved.