Dinoflagellate cyst evidence for the age, palaeoenvironment and paleoclimate of a new Cretaceous–Paleogene (K/Pg) boundary section at the Bou Angueur syncline, Middle Atlas, Morocco

Abstract

In this paper, we present results of a palynological analysis of the phosphate succession from the northern flank of the Bou Angueur syncline in the Middle Atlas (central Morocco). The studied interval yielded a well-preserved and diverse palynological content, dominated by dinoflagellate cysts (dinocysts), allowing a detailed taxonomic study of dinocyst and a new biostratigraphic dating of the section. The studied section is assigned to the upper Maastrichtian–Danian interval. A new, relatively complete K/Pg boundary transition was recognized. The succession at the Bou Angueur syncline was compared to Tethyan K/Pg boundary sections, such as the K/Pg boundary Global Stratotype Section and Point (GSSP) at El Kef (NW Tunisia) and Ouled Hadou section (NE Morocco). The dinocyst marker events used for the identification of the late Maastrichtian include the first occurrences of Cordosphaeridium inodes subsp. inodes, Deflandrea galeata and Glaphyrocysta perforata and those used for the early Danian include the first occurrences of Carpatella cornuta, Cassidium fragile, Danea californica, Lanternosphaeridium reinhardtii and Senoniasphaera inornata.The organic-walled dinocyst-producing dinoflagellates did not undergo the K/Pg mass extinction resulting from a large meteoritic impact. They enable us to interpret the environmental and climatic changes in the earliest Danian, while calcareous microfossils could not, since they are partially or completely extinct. We thus describe seven palynological assemblages, reflecting paleoenvironmental and paleoclimatic changes, inferred from changes in relevant ecological parameters, including changes in the relative abundance of selected dinocyst groups, often used as paleoenvironmental indicators. An inner to middle neritic marine environments alternated with several short phases of more offshore conditions is deduced for the late Maastrichtian and earliest Danian and an open outer neritic marine environment during a transgressive regime in the latest Danian. Several dinocyst events were recognized in the studied interval, among which remarkable blooms of tropical warm-water and high-latitude cold-water dinocyst taxa are interpreted herein as ecological responses, related to global climatic changes, including a global warming episode during the late Maastrichtian and the well-known brief global cooling following the K/Pg boundary Chicxulub impact.