Anatomy of cretaceous isolated carboante platforms of the western Gulf of Mexico

Abstract

Shallow-water carbonate platforms are ecosystems sensitive to changes in the ocean-atmosphere dynamics. Their stratal architecture, dominant biota, and vertical and lateral facies distributions are largely controlled by eustatic sea-level fluctuations, evolutionary state of biota, and climatic and oceanographic conditions. During the mid-Cretaceous (Aptian-Cenomanian) of the western Gulf of Mexico, a series of isolated and land-attached platforms developed on topographically high basement structures and continental shelves, hosting diverse marine ecosystems for over 30 million years. Their ultimate demise coincided with a series of extreme episodes of global environmental change, widespread ocean anoxia, and elevated CO₂ levels in the mid-Cretaceous. Considerable research efforts have been directed to understand the temporal architectural arrangements of facies and construct sequence-stratigraphic frameworks for the largest platforms in the western Gulf of Mexico region (i.e., Texas, Comanche, and northern Mexico-Coahuila). In contrast, small isolated platforms in central Mexico have received much less attention, despite their potential to provide a more complete picture of the regional palaeoceanographic and paleoclimatic conditions. This field-based study explores one of these isolated carbonate platforms in central Mexico, the El Doctor platform, investigating the eustatic and oceanographic conditions that governed its development. This dissertation establishes a shelf-to-basin depositional framework that serves as a type-locality for Cretaceous isolated carbonate platforms of the Western Gulf of Mexico. The study assesses depositional environments on the shelf, slope, and basin linked to a sequence stratigraphic framework tied to other regional and global time-equivalent carbonate platforms. Three composite sequences are presented in this study, which record platform-wide morphological evolution followed by progressive drowning and carbonate factory shutdown near the Albian-Cenomanian boundary coinciding with the onset of Ocean Anoxic Event 1d. The resulting stratigraphic framework sheds new light on the spatiotemporal variability in platform and slope development and demise, highlighting asynchronicity and regionally variable responses to global oceanographic and eustatic drivers around the Gulf of Mexico basin and greater Tethys realm

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