Degree

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

Document Type

Dissertation

Abstract

At the end of the Cretaceous Period, a large bolide impacted the Earth and formed the Chicxulub impact crater in the Yucatán Peninsula, Mexico. In 2016, International Ocean Discovery Program (IODP) Expedition 364 Site M0077 drilled into the buried peak ring of the crater, recovering a marine Paleocene to early 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 vegetational record from inside the Chicxulub impact crater and the first palynological record of the recovery of life following the end-Cretaceous mass extinction from inside the Chicxulub impact crater. The pollen and plant spore assemblage has been fully described, including one new genus (Scabrastephanoporites) and five new species (Brosipollis reticulatus, Echimonocolpites chicxulubensis, Psilastephanocolporites hammenii, Scabrastephanoporites variabilis, and Striatopollis grahamii) of angiosperm pollen. Dinoflagellate cysts from the K/Pg (Cretaceous/Paleogene) transitional unit, likely deposited within six years of the impact event, include several probably reworked Maastrichtian specimens, as well as possible in situ early Paleocene dinoflagellate cysts. The oldest terrestrial palynomorphs, two specimens of Deltoidospora, were not observed until at least 200,000 years after the impact. The PETM has been identified in the Site M0077 core based on biostratigraphy and a negative carbon isotope excursion. Geochemical and microfossil evidence indicates sea surface temperatures of ~38 °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 from exposed portions of the Yucatán Peninsula to the south. A second spike in palynomorph concentrations occurs upsection of the PETM in a laminated dark shale, possibly representing the early Eocene hyperthermal event ETM3. Pollen and plant spore concentrations generally increase in sediments deposited during and shortly after the Early Eocene Climatic Optimum (EECO), consistent with infilling and shallowing of the crater basin during the early Paleogene. The EECO pollen and plant spore assemblages indicate a continuously present shrubby lowland tropical forest, with Malvacipollis, Bombacacidites, Brosipollis, and Crudia type pollen.

Committee Chair

Warny, Sophie

Available for download on Monday, May 08, 2023

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