Abstract: High-Resolution Cyclostratigraphy and Sequence Stratigraphy of the Albian Coahuila Carbonate Platform (NE Mexico): Tracing Systems Tracts and Sequences Across the Platform
Christoph Lehmann, David A. Osleger, Isabel P. Montanez
The Coahuila carbonate platform is coeval with the Lower Cretaceous Edwards/Stuart City Trend of Texas and the Tuxpan and Valles platforms of Mexico and consists of lagoonal dolomites and evaporites (Acatita Fm.), shelf-margin grainstones (Aurora Fm.) and deep-platform lime mudstones (Upper Tamaulipas Fm.). These carbonates range in thickness from 150 to 1000 m and represent a genetic unit, bounded above and below by deep-water lithofacies representing globally recognized drowning events. Up to 140 meter-scale peritidal parasequences are exposed in a 400 to 600 m thick interval deposited between a shelf-margin grainstone shoal and an interior evaporitic lagoon. Meter-scale parasequences are asymmetric hemicycles composed of a basal skeletal-peloidal grainstone, fining and shallowing-upward into a dolomitized fenestral mudstone or tidal-flat laminite. Individual parasequences are interpreted to represent high-frequency accommodation events superimposed on a longer-term accommodation signal. A parasequence set typically consists of 5 to 8 parasequences that thin and shallow upward. The overlying parasequence set exhibits a thick basal parasequence composed of deeper water facies, suggesting abrupt flooding. These parasequence sets are the building blocks of systems tracts which can be correlated across the platform.
Several scales of changes in accommodation space can be shown graphically on Fischer plots which indicate that the parasequence sets form a pattern of long-term decrease and increase in accommodation, eventually grading upward into deep-water lithofacies of the Cuesta del Cura Fm. (latest Albian). The parasequence stacking patterns reveal at least three Type II sequences which can be correlated from the evaporitic lagoon across the platform-margin into the pelagic to hemipelagic portions of the platform. These are interpreted to have been likely controlled by third-order changes in accommodation space. The accommodation signal derived from stacking patterns of parasequences and their grouping into larger-scale sequences may be useful for Gulf-wide and worldwide correlations that may e hance our chronostratigraphic resolution beyond that provided by biostratigraphy.
AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France