Palynostratigraphy and paleoenvironment of Upper Cretaceous sedimentary deposits from the Tarfaya-Laayoune-Boujdour-Dakhla Basin, southwestern Morocco

Abstract

Palynological investigations were carried out on Upper Cretaceous sediments from the three onshore sections, Tah, Amma Fatma and Oum Dbaa of the Tarfaya-Laayoune-Boujdour-Dakhla Basin, southwestern Morocco. 64 samples were collected for this palynological study, which yielded a very rich, diverse and well-preserved palynological content, including sporomorphs, prasinophytes, acritarchs, foraminiferal test linings and colonial fresh-water algae, dominated by dinoflagellate cysts comprising 141 species. The dinoflagellate cyst stratigraphic marker events used for the biostratigraphic interpretations include the first and last occurrences of stratigraphic marker species. The dinoflagellate cyst biostratigraphy allowed to assign the Amma Fatma section to the lower Turonian and the Tah section to the upper Campanian. The Oum Dbaa section is revised in detail and re-assigned to the upper Campanian–lowermost Maastrichtian. Analyses of the relative abundances of marine palynomorphs (mainly dinoflagellate cysts), as well as those of the palynofacies (amorphous organic matter, phytoclasts and palynomorphs) indicate two depositional settings alternating between a proximal inner shelf under suboxic-anoxic conditions and an outer neritic environment under dysoxic-anoxic conditions.