Early Cretaceous climate in North Africa: Insights from the calcareous nannofossils in the atlantic passive margin of Morocco

Abstract

The Early Cretaceous was a time of marked changes in global climate and carbon cycle. To reconstruct the paleoclimate in North Africa, four well-dated stratigraphic sections in the Atlantic passive margin of Morocco (Essaouira-Agadir Basin) were investigated. Calcareous nannofossil assemblages were used as indicators for medium-term climatic fluctuations. The spatiotemporal changes of key taxa, nannofossil assemblages, and the Temperature and Nutrient Indices (TI and NI) were used to reconstruct the paleoclimate. Nonmetric Multidimensional Scaling and permutational analysis of variance (PERMANOVA) indicated that only early Albian assemblage was significantly different from Barremian and Aptian ones. A steady but gradual decrease in sea surface temperature and increase in nutrients and diversity from the Barremian to the early Albian was observed. The opening of the Atlantic Ocean between Africa and South America has allowed the intrusion of cold waters and higher latitudinal taxa, where warm oligotrophic Aptian times were followed by a cool eutrophic condition in the Albian. The sea-level highstand in the Early Albian may have increased water circulation and intrusion of the upwelling induced, nutrients-rich cold-water, where surface water fertility increased significantly. Consequently, nannofossil diversity increased.