--> Abstract: Shelf-Edge to Deep Water Carbonate Transition, Middle Cretaceous Aurora Formation, Northeastern Mexico, by C. Lehmann, D. A. Osleger, and I. P. Montanez; #90987 (1993).

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LEHMANN, CHRISTOPH, D. A. OSLEGER, and ISABEL P. MONTANEZ, Univ. of California, Department of Earth Sciences, Riverside, CA

ABSTRACT: Shelf-Edge to Deep Water Carbonate Transition, Middle Cretaceous Aurora Formation, Northeastern Mexico

The Aurora Formation and its basinal facies equivalent, the Upper Tamaulipas Formation of northeastern Mexico correlate with the Glen Rose/Stuart City trend in south Texas and the El Abra/Tamabra complex in south and east-central Mexico. These coeval carbonates developed on a differentially subsiding passive margin associated with the opening of the Gulf of Mexico. Ten sections of the Aurora and Upper Tamaulipas, totalling 4000 m, have been logged in detail to show lateral facies relationships across an outer shelf to deep water transition.

Deep water lithofacies of the Upper Tamaulipas are characterized by muddy peloidal calciturbidites, massively-bedded mudflow deposits, and regularly-spaced firmgrounds. A spectacular exposure of shallow water equivalents within the Aurora Formation shows stratal geometries across the outer shelf to deeper ramp transition. Sigmoidal clinoforms composed of massively-bedded grainstones and intercalated rudist thickets prograde southward and downlap onto horizontally-bedded mudstones and foraminiferal wackestones. The prograding clinoforms are overlain by partially dolomitized peritidal cycles that thin upward and culminate in a laterally-extensive paleokarst. The karst breccia is 3 to 10 m thick and is composed of angular clasts of tidal-flat laminites and mudstones (up to 1 m across) su rounded by a sandy, dolomitic matrix. This major sequence boundary can be traced across the platform edge and manifests a major relative sea level fall in Albian time. Overlying lithofacies consist of foraminiferal wackestones and rudist thickets that pass upward into deeper water mudstones, culminating in complete drowning by laminated siliciclastics of the Cuesta del Cura Formation.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.