Cenomanian marine sedimentation has been studied in sediments from the Tarfaya Basin, Southern Morocco. A continuous section of just under ten metres in length, composed from overlapping slabs of limestone, was cut from a disused quarry near the town of Tarfaya. Cutting and polishing the rock and then scanning it provided a digital record of sediment colour variation. Carbonate, organic carbon and calcareous nannofossils were studied at intervals throughout the section. Time series analysis was carried out on the sediment colour data but revealed no significant cyclicity at the sub-Milankovitch time scale. Combined results from variations in sediment colour, carbonate, organic carbon and calcareous nannofossils hint at the existence of different productivity regimes. Two productivity regimes are interpreted to alternate on a Milankovitch time scale. Regime 1 is characterised by extreme productivity induced by very strong upwelling conditions. It is characterised by dark coloured sediment, a high percentage of organic carbon, low nannofossil diversity and an abundance of the species Eprolithus floralis. Regime 2 is characterised by a less extreme environment and provides evidence for moderate to high productivity under coastal upwelling conditions. It is characterised by light coloured sediment, a lower percentage of organic carbon and a more diverse nannofossil assemblage. In particular Sollasites horticus and Tranolithus spp. become important, while E. floralis decreases in abundance. The change in intensity of oceanic upwelling required to produce these two different productivity regimes is likely to have been controlled by the strength of the trade winds. Few places in the world exhibit such extreme upwelling conditions today. One possible explanation is that the trade wind intensity during the Cenomanian greenhouse conditions was much stronger than Holocene trade winds and that these sediments were deposited during a climatic extreme
