Integrated stratigraphy of the latest Barremian-early Albian interval in the western part of the Tethyan margin: new data from the Essaouira-Agadir Basin (Western Morocco)

The Essaouira-Agadir Basin (EAB, Morocco) presents numerous and well-exposed outcrops of the Lower Cretaceous series. Here we present an integrated stratigraphic framework for the latest Barremian-early Albian, and for the western Tethys based on i) the identification of sedimentary discontinuities, ii) the establishment of a high-resolution ammonite and calcareous nannofossil biozonation, and iii) a carbon isotope record. Various sedimentary discontinuities corresponding to erosive surfaces were recognized within these deposits. Most of these surfaces are correlated within the EAB, and correspond to drops in sea level. The distribution of ammonite assemblages was calibrated with the standard Mediterranean zonation. Several ammonite index-species have been identified, in particular for the early Aptian and earliest late Aptian. This was crucial because the lower series are dominated by condensed sedimentation and temporal hiatuses. Most of the uppermost Barremian to lower Albian ammonite standard zones have been recognized. Four new and reliable calcareous nannofossil bioevents have been identified in the late Aptian allowing to revise the NC7 Zone. The taxonomic criteria used to define species markers of both NC8A and NC8B subzones have been specified, thereby improving the calibration of these subzones with ammonite biozones. The delta C-13(carb) values from whole rock samples decrease from the late Aptian to the early Albian. The new biostratigraphic and chemostratigraphic scheme for the EAB allowed rather good correlations between sections from southern and northern Tethyan margins.

Automated summary

This study presents an integrated stratigraphic framework for the Lower Cretaceous series in the Essaouira-Agadir Basin, Morocco, based on sedimentary discontinuity identification, high-resolution ammonite and calcareous nannofossil biozonation, and carbon isotope record. The study identifies various sedimentary discontinuities and establishes correlations between sections in southern and northern Tethyan margins. Additionally, new calcareous nannofossil bioevents and ammonite index-species have been identified, improving the biostratigraphic framework for the region.