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Nyman, Stephanie1 
(1) University of Texas at Dallas, Richardson, TX

ABSTRACT: Provenance and Diagenesis of the Cretaceous Wall Creek Sandstone, Frontier Formation, Powder River Basin, Wyoming

    A detailed petrographic analysis of fifty thin sections from the Wall Creek Sandstone Member of the Frontier Formation, was performed to determine provenance and diagenetic history. Petrologic and geochemical evidence supports the hypothesis that the Wall Creek is an asymmetric wave influenced delta. Well sorted, fine grained sandstone with little detrital clay occur near the interpreted updrift side of the delta. The downdrift side, within more fluvial-dominated facies, shows less mature, very fine grained sandstone with more abundant detrital clay. 
    Wall Creek sandstones are lithic arkoses and feldspathic litharenites with abundant volcanic rock fragments, indicating primary deposition of relatively immature sediments. Detrital grain types are the same throughout the study area; however, overall framework grain composition, textures, and clay types differ between each location, reflecting changing depositional processes in different parts of the delta system. 
    Major cements are kaolinite and calcite. Minus cement porosity is low. Values of calcite isotopes for 18OPDB range between -8.5 to -12.2 and 13CPDB values from -1.8 to -9.08. The geometric relationship between calcite and kaolinite, isotope values, and low- porosity prior to calcite cementation all suggest calcite was formed late. 
    Maximum burial depth of the Wall Creek sandstone reached approximately 1.3 kilometers with maximum temperature of approximately 50oC. Isotope data for calcite cement suggest precipitation from mixed marine and meteoric pore waters and both organic and marine carbon source. Abundant skeletal fragments and lesser amounts of organic material occur throughout the Wall Creek indicating carbonate cements were derived in-situ. 



AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.