Paleoecologic and paleoceanographic reassessment of intrashelf basin formation:Iichnology, depositional environment, and sequence stratigraphy of the Upper Albian Maverick Basin, south Texas

Abstract

Cretaceous intrashelf basins, isolated depressions situated on the interior of carbonate shelves, contain some of the most prolific hydrocarbon-producing fields globally, e.g., the Bab and Shilaif intrashelf basins in the Middle East. Their origin is enigmatic, but most evidence points to the role of carbonate factory shutdown in regions of low oxygenation, surrounded by healthy well-oxygenated carbonate factory production. Despite the importance of trace fossil evidence to understanding the benthic oxygenation condition in the sedimentary environment, our knowledge in oxygen-deficient biofacies primarily comes from modern oceans, and ancient examples are rare, nearly exclusively established on the epicontinental seas. Extending the ichnologic dataset documenting trace fossil assemblages in the intrashelf basin setting is essential to a better understanding of the evolving carbonate factory and the governing environmental factors that eventually shaped the epeiric seas’ topography in a greenhouse climate. The Upper Albian Maverick Intrashelf Basin stratigraphic record in south Texas with exceptional outcrops and a unique suite of shallow cores provides an opportunity to better characterize endobenthic communities and understand the paleoecologic and paleoceanographic conditions along with the evolving ocean water chemistry through a short-lived environmental crisis. This study aims to integrate ichnologic and sedimentological signatures to define the paleoecological and paleoceanographic conditions under which this classic Cretaceous intrashelf basin formed. This study provides the first example on oceanic anoxia and oxygen-constrained trace fossil assemblages in an intrashelf basin lacking modern analogs and serves as an update on such basin settings since relevant studies were most abundant in the ’90s.