--> Abstract: Stratigraphic Hierarchy of Organic Carbon-Rich Siltstones in Deep-Water Facies, Brushy Canyon Formation (Guadalupian), Delaware Basin, Texas, by J. M. Armentrout and K. E. Peters; #90933 (1998).

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Abstract: Stratigraphic Hierarchy of Organic Carbon-Rich Siltstones in Deep-Water Facies, Brushy Canyon Formation (Guadalupian), Delaware Basin, Texas

Armentrout, John M. and Ken E Peters - Mobil Technology Co.;Bradley B. Sageman and Adam E Murphy - Northwestern University; andMichael H. Gardner - Colorado School of Mines

Sequence stratigraphy provides a hierarchical system for organizing and analyzing depositional cyclicity. The distribution of organic carbon within a sequence stratigraphic framework is examined to determine the primary factors controlling total organic carbon content and hydrocarbon yield potential.

The studied section includes the Pipeline Shale, Brushy Canyon Formation and the lower Cherry Canyon Formation of the Permian Delaware Mountain Group (Fig. 1). These strata represent one 3rd-order (Brushy Canyon Formation upward to the genetic top), siliciclastic genetic sequence deposited as a deep-water gravity-flow system along a passive margin (Gardner, 1992). Depositional cycles of 4th- (lower, middle and upper members) and 5th-order (individual coarsening upward cycles) scale are identified within a 450 meter thick section. Throughout its thickness the Brushy Canyon Formation contains organic carbon-rich siltstone beds. These units have been interpreted as suspension fallout deposits representing cycle bounding condensed sections, and form widely traceable marker beds in the outcrop belt. Two-hundred ten samples were collected, one from each slightly brown to black fine-grained bed. Each sample was split and sent for analysis: one split to Northwestern University for analysis using a Fisons NA 1500 elemental analyzer; the second split to the Institut Francais du Petrole for analysis on Rock-Eval 6. Measured values of total organic carbon (TOC) from each lab compare favorably.

Patterns of increasing and decreasing TOC and Hydrogen Index (HI) values parallel each other (Fig. 2). Enrichment and yield potential increases toward the flooding surface capping each order of cyclicity. Measured values for 5th-order flooding surfaces range from 1.0 to 3.2% TOC and 100 to 300 HI; for 4th-order flooding surfaces from 2.5 to 3.5% TOC and 200 to 300 HI; and for 3rd-order flooding surfaces from 3.5 to 4.5% TOC and 250 to 300 HI. Maximum values of TOC = 4.5% and HI >300 occur within a three meter thick organic-rich interval at the 3rd-order flooding surface (genetic top of Brushy Canyon sequence).

Preliminary data suggest that quantity and quality of preserved organic matter is controlled by changes in bulk sedimentation rate (dilution versus condensation), as well as the balance between burial/preservation of organic matter versus degradation on the seafloor during times of sediment starvation.

Gardner, M.H., 1992, Sequence stratigraphy and eolian-derived turbidites: Patterns of deep-water sedimentation along an arid carbonate platform, Permian (Guadalupian) Delaware Mountain Group, West Texas, in Murk, D.H., and Curran, B.C., eds, Permian Basin Exploration and Production Strategies: Applications of Sequence Stratigraphic and Reservoir Characterization Concepts: West Texas Geological Society Publication 92-91, p. 7-12.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil