An integrated stratigraphic framework for the uppermost jurassic to Lower Cretaceous interval of the Essaouira-Agadir Basin (Moroccan Atlantic margin) based on ammonites, calcareous nannofossils and calpionellids

Abstract

The extensive exposures of Mesozoic rocks along the Atlantic Moroccan margin can offer the best and the most continuous record of Mesozoic sediments and Upper Jurassic – Lower Cretaceous deposits along the Atlantic margin. This study reports the results of high resolution sampling and sedimentary logging of key outcrops to allow for ammonite, calpionellid and nannofossil biostratigraphy, in order to build a new integrated biostratigraphic chart for the uppermost Tithonian to the lowermost upper Barremian. This has been correlated to the offshore record (DSDP Sites 370/416A), which has also been redated using newly described calcareous nannofossil assemblages that confirm a thick and previously undescribed upper Tithonian through Berriasian succession.

Calpionellid assemblages, although sparse, show affinities to the Mediterranean Tethys assemblages. Ammonites also show affinities to the Mediterranean Tethys taxa, but the identification of two new species points to periods of endemism during the lower Hauterivian. Calcareous nannofossils show varied affinities; to the North Atlantic Tethys and Mediterranean Tethyan Realms, the Cental Atlantic and short, but distinct cold-water Boreal Realm exchanges during the Berriasian, lower Valanginian and upper Hauterivian which have necessitated the development of a local EAB nannofossil zonation. The faunal affinities, local morphological variations and periods of faunal endemism are attributed to relative sea level changes which influenced the connection between the Essaouira-Agadir Basin (EAB), Central Atlantic and the western Tethyan Realm.

A major sedimentary hiatus in the middle part of the Berriasian is recognised in the studied sections based on the biostratigraphy. This is interpreted to record a middle Berriasian unconformity that can be correlated both regionally and globally, due to an important period of tectonic activity associated with the break-up stage of the Atlantic.

This new biostratigraphy builds on recent published studies that have focused on a high resolution integrated stratigraphic framework for the upper Barremian - lower Albian interval (Lower Cretaceous) in the Essaouira-Agadir Basin of Morocco.