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Abstract: Cyclostratigraphic and Ichnofacies Analysis of the Upper Albian Salmon Peak Formation, Maverick Basin, Texas

Laura C. Zahm, Charles Kerans, James L. Wilson

The Upper Albian Salmon Peak Formation is a hemipelagic intrashelf basin deposit positioned landward of the main Stuart City Reef trend and surrounded to the landward (north and west) edge by high-energy carbonate ramp margin facies of Devil's River Limestone. The International Boundary and Water Commission core ID-22 from Val Verde County, near Del Rio, Texas contains a continuously cored record of Salmon Peak deposition. The Salmon Peak formation is overlain by Del Rio Shale and underlain by McKnight Formation. The top of this unit corresponds approximately to Albian/Cenomanian boundary. Integrated biostratigraphic, sedimentologic, and time-series analysis of this core allows refinement of both biostratigraphic and cyclostratigraphic histories of this upper Albian carbo ate platform-to-basin system.

The 400 ft thick Salmon Peak Formation is subdivided into (1) massive pelloidal coarse wackestone to grainstone, (2) structureless mudstone, (3) sparse Skolithos burrowed mudstone to wackestone, (4) Thalassinoides or Planolites--like burrowed organic-rich mudstone to wackestone, and (5) dark laminated organic-rich foram-bearing mudstone. A three-fold compound cycle hierarchy is recognized in the ID-22 core. Facies 1-3-4 and 2-3-4 high-frequency cycles alternate with more organic-rich, starved 3-4-5 high-frequency cycles to define intermediate-scale cyclicity. Long-term stacking records a lower asymmetric retrogradational-progradational cycle (middle McKnight through lower Salmon Peak) and upper cycle dominated by retrogradation and decreased oxygenation in t e Maverick Basin.

Micropaleontologic analysis of facies (5) shows fluctuations in abundance and diversity of planktic and benthic foraminifera which allows identification of a maximum flooding surface followed by shelf margin progradation. Time series analysis places observed lithofacies and biofacies cycles in a chronostratigraphic framework that will aid in ongoing shelf-to-basin correlations.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana