Distribution of Dinoflagellate cyst assemblages and palynofacies in the Upper Cretaceous deposits from the neritic Bou Lila section, External Rif (northwestern Morocco): Implications for the age, biostratigraphic correlations and paleoenviromental reconstructions

Abstract

As a part of our palynological investigations of the Upper Cretaceous deposits from the Rif Chain, the present study of the dinoflagellate cyst assemblage distribution and palynofacies was carried out in the Bou Lila section, located northeast of the city of Ksar El-Kébir (External Rif, northwestern Morocco). The study focused on the age refinement and interpretation of paleoenvironmental conditions within the basin during the sediment deposition. The analyzed samples are rich in palynomorphs, formed essentially of diverse and well-preserved dinoflagellate cysts, which are associated with phytoclasts and rare microforaminiferal test linings, spores, pollen grains and algae.The Bou Lila section is assigned to the late Campanian, based on dinoflagellate cyst taxa, whose first appearance datums (FADs) or last appearance datums (LADs) are markers of the late Campanian. These taxa include Areoligera coronata, Areoligera senonensis, Cerodiniuum diebelii, Chatangiella? robusta, Cribroperidinium wilsonii subsp. wilsonii, Impagidinium rigidaseptatum, Odontochtina operculata, Odontochitina costata, Palynodinium grallator, Raetiaedinium belgicum, Rigaudella appenninica, Trichodinium castanea subsp. castanea, Trigonopyxidia ginella, Trithyrodinium evittii, Trithyrodinum suspectum, Xenascus ceratioides and Xenascus wetzelii. The high diversity of the dinoflagellate cyst taxa made it possible to correlate the Bou Lila section with biostratigraphically well-calibrated upper Campanian sequences from several Tethyan and also Boreal sites, including the type Campanian area and the GSSP for the base of the Maastrichtian in southwestern France and the type Maastrichtian area in Limburg.The fluctuations in the relative abundances of the selected dinoflagellate cyst groups and other quantitative palynological parameters allow a recognition of three paleoecological zones. They indicate a gradual passage from an inner neritic setting, with high productivity conditions in the most basal part of the section, to a stable outer neritic setting in the upper part of the section.The palynofacies analyses are in general agreement with the dinoflagellate cyst results, indicating a passage from a proximal depositional environment in the lowermost part of the section to a distal depositional environment in the uppermost part of the section. The dinoflagellate cyst assemblage indicates a subtropical to temperate setting, with the presence of the northern high-latitude cold-water species Palynodinium grallator, suggesting a short cooling episode or also conditions of water stratification during the late Campanian.