Foraminiferal response to sea level change, organic flux and oxygen deficiency in the Cenomanian of the Tarfaya Basin, southern Morocco

Abstract

The “Mohammed Plage” coastal section and well S13 in the Tarfaya Basin (southern Morocco) are key sections to investigate the subsidence of the basin and the Cenomanian eustatic sea level history. Results from a canonical correspondence analysis (CCA), based on benthic foraminiferal assemblage counts and additional proxies (percent planktic foraminifera, planktic foraminifera morphogroups, total organic carbon content (TOC)) show a general deepening trend for the investigated sections. The most important factor identified in the ordination of species and samples is water depth. The CCA identifies Bolivina anambra, Globulina lacrima, Lenticulina spissocostata and Spiroplactammina sp. as typical “shallow-water species”, Praebulimina nannina, Gavelinella dakotensis, Gavelinella sp., Saccammina alexanderi and Valvulineria lenticula as “deep-water species”, and Gabonita levis, Gabonita obesa, Neobulimina albertensis, Lingulogavelinella asterigerinoides, Lenticulina gaultina, Haplophragmoides gigas, Haplophragmoides bauchensis and Trochammina taylorana as unrestricted or intermediate species. The temporal succession of benthic foraminiferal assemblages indicates repeated periods of shallowing within the general deepening trend, in particular within the lower portion of the sections ( Rotalipora brotzeni and R. reicheli planktic foraminiferal zones). Restricted assemblages occurred when intensification of the oxygen minimum zone inhibited a diverse benthic community. Abundant high organic flux indicators at the base of the “Mohammed Plage” section indicate that an upwelling cell off northwest Africa was already active during the early Cenomanian.