(1) University of Alabama, Tuscaloosa, AL
ABSTRACT: Lower Cretaceous Microbial Deposits, Northeastern Gulf of Mexico
Up to the recent past the role of microbialites in Phanerozoic reefs has been underappreciated. In particular, classifications and paleoenvironmental reconstructions of Cretaceous microbialites are missing. Recently microbial organisms have been discovered to play an important role in carbonate deposition in different geologic times. Microbial structures investigated in the Lower Cretaceous of the northeastern Gulf of Mexico include peloidal, alveolar, laminated, micritic massive, and micritic irregular microstructures and oncolitic, patchy, micritic massive, and laminated mesostructures. The algae Bacinella irregularis/Lithocodium aggregatum and Pseudolithothamnium album, cyanobacteria, and undifferentiated bacteria are recognized as the principal builders of microbial boundstones. Microbial boundstone occurs in most of the interpreted depositional settings, mainly high-energy and secondarily low-energy environments, such as middle-shelf, back-reef, shelf-edge, and slope settings. Lower Cretaceous microbial organisms contributed significantly to stabilize organic build-ups in high-energy shelf environments. Shelf-edge lithofacies are represented by rudist and microbial boundstones in the southeastern part of the study area and by carbonate sand banks and microbial boundstones in the northwestern part of the study area.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.