Cretaceous conchostracans from Potiguar Basin (northeast Brazil): relationships with West African conchostracan faunas and palaeoecological inferences

Abstract

Many fossil groups have been used in biochronostratigraphic and palaeoenvironmental analyses in order to understand the geological evolution of the Potiguar Basin, northeast Brazil. The present record of conchostracans (Conchostraca, Branchiopoda) adds to the diversity of fossil groups known to have lived in the area. Two distinct conchostracan faunas have been recovered from different stratigraphic levels in the basin. The first was encountered in cores of onshore lacustrine shales of the Pendência Formation (Lower Cretaceous). The second was found in exposures of marls within the Jandaıra Formation (Upper Cretaceous). Both are monospecific faunas belonging to the families Cyzicidae (Cyzicus mawsoni) and Limnadiidae (Estheriina astartoides). Both species are well preserved and normally show the two articulated valves. Conchostracans belonging to these families are common in Gondwanan basins. The Lower Cretaceous associations are very similar to coeval assemblages of West African basins (e.g., Cameroon, Congo and Gabon). Conchostracans are common in ephemeral freshwater ponds of hot, alkaline waters; they can even occur in brackish waters of coastal lagoons and tidally-influenced zones. This is presumed to be the life environment of the Late Cretaceous conchostracans in the Potiguar Basin.