Taxonomy, palaeoecology and palaeobiogeography of upper Cenomanian (Upper Cretaceous) oysters and plicatulids from southern Algeria

Abstract

ABSTRACT Palaeontological investigation of four lithostratigraphic sections documenting the upper Cenomanian shallow marine carbonates of three palaeogeographic domains of southern Algeria (western Saharan Atlas, Guir Basin and Tinrhert Hamada) has produced a comprehensive collection of large bivalve assemblages for taxonomic purposes. A first inventory list of late Cenomanian oysters and plicatulids from southern Algeria is now available and consists of 15 taxa as follows: Lopha syphax, Ostreidae gen. et sp. indet., Curvostrea rouvillei, Flemingostreidae gen. et sp. indet., Costagyra olisiponensis, Amphidonta obliquata, Ceratostreon flabellatum, Ilymatogyra africana, Rhynchostreon suborbiculatum, Gyrostrea delettrei, Gyrostrea sp. indet., Pycnodonte (Phygraea) vesicularis vesiculosa, Plicatula (Plicatula.) auressensis, Plicatula (Plicatula) batnensis, and Chondrodonta? sp. indet. These taxa build five distinctive oyster-facies patterns, all purportedly recognisable in the field for stratigraphic assignment and regional correlation. Scarce sclerobiontic assemblage (borings: Entobia, Gastrochaenolites and Oichnus; and epibionts: juvenile oysters, serpulid tubes and Berenicean-type bryozoa) observed within these oyster shell assemblages is also identified, briefly described and adressed. This first taxonomic analysis highlights three main palaeogeographic components within these oyster- and plicatuloid-assemblages: endemic Mediterranean, Tethyan-Atlantic and cosmopolitan taxa. Moreover, the present study on these late Cenomanian oyster assemblages provides a first inventory list and stratigraphical baseline data towards further datation and correlation at the regional scale.