Integrated Analysis of the Upper Jurassic Bossier Deltaic Complex, East Texas
John B. Wagner, Pierre A. Zippi, Larry L. Brooks, Tom D. Sheffield, Mark A. Dablain, Kimberly M. Stevens, 2013. "Integrated Analysis of the Upper Jurassic Bossier Deltaic Complex, East Texas", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
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The sandstones encased within the Bossier Shale Member of the Cotton Valley Sandstone in East Texas are subdivided into three genetically related stratigraphic cycles. The lower deltaic cycle is a seaward stepping unit that becomes reworked as a result of delta switching. The upper two cycles are aggradational to progradational units in which facies range from prodelta to delta-front to distributary channel deposits.
Previous interpretations have ranged from submarine-fan to braided river with individual cycles are interpreted to be bounded by regionally extensive marine flooding surfaces. Detailed sedimentologic, petrologic, and biostratigraphic analysis of cores, well-cuttings, and well-logs, however, indicate that the stacking pattern of the Bossier deltaic complex is controlled by autocyclic lobe-switching as a result of varying sediment supply (overall increase) associated with the large Cotton Valley fluvial system. In particular, detailed biostratigraphic analysis (palynology and kerogen) suggests that bounding shale intervals and “flooding surfaces” exhibit a high terrigenous/marginal marine signature. True marine flooding events are associated only with the source-rock shales in the underlying lower Bossier Shale interval. Additionally, the abundance of distributary channels associated with all cycles suggests the entire Bossier Sandstone section is a river-dominated system subordinately influenced by marine processes.
Rock physics and seismic modeling of the Bossier sands have demonstrated a seismic response strongly dominated by large acoustic impedance contrasts associated with porous sandstones, low porosity siltstones and over-pressured shales. Depositional and sedimentologic characteristics of the Bossier sands are similar to those of modern fluvial-dominated deltaic systems undergoing processes of delta-switching and abandonment, such as the Mississippi River Delta.