High-Resolution Cyclostratigraphy of the Albian Coahuila Carbonate Platform (NE Mexico): An Outcrop-enhanced Chronostratigraphic Resolution for the Cretaceous of the Circum-Gulf of Mexico

Christoph Lehmann, David A. Osleger, Isabel P. Montanez

Cretaceous carbonate platforms of the circum-Gulf of Mexico, including the Edwards/Stuart City Trend and the Florida, Yucatan, Tuxpan and Valles platforms are well documented based primarily on seismic stratigraphy and well-log data. However, seismic stratigraphic interpretations typically only reflect second-order or third-order sequence architecture, and well logs often fail to recognize all fifth-order parasequences. A higher degree of resolution is established in outcrops of the Albian Coahuila carbonate platform of NE Mexico that recognizes fifth-order parasequences, parasequence sets and sequence-bounding unconformities.

The Albian Coahuila carbonate platform consists of lagoonal dolomites and evaporites (Acatita Fm.), shelf-margin grainstones (Aurora Fm.) and deep-platform lime-mudstones (Upper Tamaulipas Fm.). The Coahuila carbonates represent a genetic unit, bounded above and below by deep-water lithofacies representing drowning events that are recognized globally. Up to 140 meter-scale peritidal parasequences are exposed in a 400 to 600 m thick interval deposited between the shelf-margin grainstone shoal and the evaporitic lagoon. Meter-scale parasequences are composed of a basal skeletal-peloidal grainstone, fining and shallowing-upward into a dolomitized fenestral mudstone or tidal-flat laminite. The individual parasequences are interpreted to represent high-frequency accommodation events rather than autocyclically-generated units. Parasequences within a parasequence set thin and shallow upward; the overlying parasequence set exhibits a thick basal parasequence composed of deeper water facies, suggesting abrupt flooding. At least eight parasequence sets can be correlated across four platform-margin sections and are most likely controlled by fourth-order changes in accommodation space. The parasequence sets form a pattern of long-term decrease in accommodation culminating in a sequence-bounding unconformity (mid-Albian) overlain by a long-term increase in accommodation grading upward into deep-water lithofacies (later Albian).

Several similarities and differences can be recognized between the Coahuila and coeval carbonate platforms rimming the Gulf of Mexico. Most platforms were generally progradational during the Albian. The margins of most platforms rimming the Gulf are characterized by rudist buildups and steep slopes. In contrast, the Coahuila carbonate platform is rimmed by a high-energy grainstone shoal and gentle slopes toward the deep platform. The exposure breccias that form a sequence-bounding unconformity and the accommodation signal derived from stacking patterns of parasequences may be useful for Gulf-wide correlation that may enhance our chronostratigraphic resolution beyond that provided by biostratigraphy.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995