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Cyclostratigraphic and Ichnofacies Analysis of the Upper Albian Salmon Peak Formation, Maverick
Laura C. Zahm (1), Charles Kerans (2), James L. Wilson (3)
The Upper Albian Salmon Peak Formation consists of hemipelagic intrashelf basin deposits positioned behind the main Stuart City Reef trend and surrounded landward (north and west) by high-energy carbonate ramp margin facies of the Devils River Limestone. The Salmon Peak Formation is overlain by Del Rio Shale and underlain by McKnight Formation. The top of the Salmon Peak Formation corresponds approximately to the Albian/Cenomanian boundary. The Salmon Peak is continuously cored in the International Boundary and Water Commission core ID-22 from Val Verde County, near Del Rio, Texas. Integrated biostratigraphic, sedimentologic, and time-series analysis of this core allows refinement of both biostratigraphic and cyclostratigraphic histories of this Upper Albian carbonate platform-to-basin system.
The 116 meter (380 feet) thick Salmon Peak Formation is subdivided into: (1) structureless mudstone, (2) sparse Skolithos burrowed mudstone to wackestone, (3) Thalassinoides or Planolites-like burrowed organic-rich mudstone to wackestone, (4) dark laminated organic-rich foraminifera-bearing mudstone, and (5) massive coarse pelletal wackestone to grainstone. A three-fold compound cycle hierarchy is recognized in the ID-22 core. Facies 1-2-3 and 2-3-5 high-frequency cycles alternate with more organic-rich, starved 2-3-4 high-frequency cycles to define intermediate-scale cyclicity. Large-scale cyclicity is defined by a lower asymmetric retrogradational-progradational stacking of high-frequency cycles (middle McKnight through lower Salmon Peak) and an upper package dominated by retrogradation and decreased oxygenation in the Maverick Basin.
Micropaleontologic analysis of facies (4) 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 shelf-to-basin correlations.
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