Litho-, biostratigraphy and sedimentological framework of the ‘mid’-Cretaceous crinoid-rich facies of the southern Aures Range (eastern Algeria)

Abstract

Field description and laboratory analysis of a nicely documented section exposing ‘mid’-Cretaceous fossiliferous deposits led to the first litho- and biostratigraphic frame for the southern part of the Aures Range (eastern Algeria) presented herein. Its median geographical position between the Sahara and the Tell domain provided us with biostratigraphical data (ammonites, associated macrofossils and microfaunas) to draw interesting insights for regional correlations, and with valuable ambient indices for a better palaeoenvironmental reconstitution along the South Tethysian margin. The investigated strata, ranging from the upper Albian to the lowermost Turonian, consist of the following formations: the Tighanimine Formation, the Arris Formation (lower and upper members) and the Adhari Formation (lower and upper members). The collected faunas allow the recognition of a mixed upper middle to lower upper Albian assemblage and three distinctive Cenomanian ammonite biozones (Mantelliceras mantelli, Acanthoceras rhotomagense and Neolobites vibrayeanus zones). Microscopic analysis had resulted in the recognition of ten microfacies types (MT 1 to MT 10) that are described in terms of depositional environments and grouped into three main facies types: (i) deep-water outer platform and toe-of-slope/distal slope facies zone, (ii) shallow subtidal, open-marine/restricted, mid-inner platform facies zone and (iii) deep-water basin, pelagic facies zone. Microfacies analysis was used to provide valuable data for marine setting reconstruction and correlation to adjacent areas. Sequential stratigraphy analysis led to distinguishing four third-order depositional sequences grouped into two mega-sequences (I and II) and correlated to the standard sea-level chart.