Depositional environments, sea-level history and palaeobiogeography of the late Campanian-Maastrichtian on the Calabar flank, SE Nigeria

Abstract

Campanian-Maastrichtian palaeoenvironments and seal-level history on the Calabar Flank are interpreted by recognising palynofacies based on statistical and morphological variations in organic-walled microplankton, mainly dinoflagellates and miospores. A holomarine palynofacies defining an inner-neritic depositional environment is characterized by > 80% dinoflagellates, mainly spiniferate cysts with short, simple to complexly hooked or barbed processes. Fluvio-marine palynofacies corresponding to a littoral setting shows close abundance percentages of dinoflagellates and miospore elements. Both spiniferate and peridinioid cysts with short, long and simple processes occur abundantly and the miospore elements are dominated by mangrove-type species. A non-marine palynofacies representing a fresh-water environment is dominated by miospores of hinterland affinities. Few peridinioid cysts with long processes are present. Sedimentation and palynofacies disposition was mainly controlled by eustatic sea level fluctuations. Resolution of palynofacies, in relation to outcrop data, presents two depositional cycles, each exhibiting trangressive, highstand and lowstand systems tract deposits. The boundary between the two cycles is marked by an abrupt change from non-marine to holomarine palynofacies. These cycles, dated as late Campanian-mid Maastrichtian and late Maastrichtian, relate favourably with the 75 Ma and 71 Ma depositional sequences recorded on the Global Cycle Chart.