Résumé
At the end of the Cretaceous Period, a large asteroid struck the Earth and formed the Chicxulub impact crater in the Yucatan Peninsula, Mexico. In 2016, International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled into the buried peak ring of the crater, recovering a marine Paleocene to lower Eocene post-impact section deposited on top of the impact breccia. Palynological analysis of 195 samples from the post-impact section has yielded the first pre-Holocene palynological record from inside the Chicxulub crater. The pollen and plant spore assemblage has been fully described, including one new genus and five new species of angiosperm pollen. Dinoflagellate cysts from the K/Pg (Cretaceous/Paleogene) transitional unit, likely deposited within a few years after the impact event, include several probably reworked Maastrichtian specimens, as well as possible in situ early Paleocene cysts. The Paleocene-Eocene Thermal Maximum (PETM) has been identified in the Site M0077 core based on biostratigraphy and a negative carbon isotope excursion. Geochemical and microfossil evidence indicates extremely high sea surface temperatures of approximately 38 degrees C, increased terrestrial input, salinity stratification, and bottom water anoxia. Palynomorph concentrations increase in the PETM, with an acme of the dinoflagellate genus Apectodinium in the lower PETM section, and a diverse pollen assemblage derived from a lowland tropical shrubby forest, likely originating from exposed portions of the Yucatan Peninsula to the south. A second spike in palynomorph concentrations occurs upsection of the PETM layer in a laminated dark shale, interpreted to represent another early Eocene hyperthermal event, possibly ETM-3, during the Early Eocene Climatic Optimum (EECO).