Organic and Authigenic Mineral Geochemistry of the Permian Delaware Mountain Group, West Texas: Implications for the Chemical Evolution Of Pore Fluids
Phillip D. Hays, Suzette D. Walling, Thomas T. Tieh, 1996. "Organic and Authigenic Mineral Geochemistry of the Permian Delaware Mountain Group, West Texas: Implications for the Chemical Evolution Of Pore Fluids", Siliciclastic Diagenesis and Fluid Flow: Concepts and Applications, Laura J. Crossey, Robert Loucks, Matthew W. Totten, Peter A Scholle
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Aqueous species derived from first-order degradative reaction of organic material can modify Eh and pH conditions in the late burial environment, regulate solubility of minerals and dissolved constituents in the rock/water system and release organically bound metals imo pore water as thermal stress associated with burial progresses. This study evaluates the role of organic matter alteration in Controlling late burial diagenetic processes in the Delaware Mountain Group, a sequence of rocks that presents a unique opportunity for the study of coupled organic-inorganic diagenesis. The Delaware Mountain Group lies within the Permian Basin of west Texas and southern New Mexico and includes, in descending order, the Bell Canyon, Cherry Canyon and Brushy Canyon Formations. Characterization of mineral and organic geochemistry and study of natural geochemical tracers in the Delaware Mountain Group provide evidence of the organic drive for diagenetic processes in these rocks. Delaware Mountain Group siltstone organic matter is of a sufficient abundance, of suitable type and of a sufficiently advanced state of thermal maturity to have had the potential to generate organic acids and other thermogenic products capable of controlling pore-fluid chemistry and impacting diagenetic processes. The organic matter has yielded fluids associated with thermal stress; geochemical fossil and stable isotope correlation of siltstone organic matter with oii in Delaware Mountain Group sandstone reservoirs shows that the sillstones were the source of much of the oil. Mineralogic evidence of the role that organically-derived Compounds played in late diagenetic processes includes the presence of abundant authigenic titanium oxides in these sandstones. The formation of authigenic titanium oxides indicates that titanium mobility was elevated by formation of organometallic titanium complexes—the only natural mechanism for enhancing titanium solubility. Finally, natural isotopic (carbon isotopes) and inorganic tracers (Mn, Zn, Ni, Co, V and Cr) establish a source/sink relation between the organic matter in the siltstones and authigenic minerals in the sandstones. The relation is manifest in the isotopic and minor element content of late stage authigenic products that formed in pore fluids whose chemistry was controlled by organic malter degradation. The various lines of evidence indicate that fluids carrying the products of organic matter degradation moved from the organic-rich siltstones into the sandstones where authigenic products formed and preserved a record of ambient pore-water chemistry.
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Siliciclastic Diagenesis and Fluid Flow: Concepts and Applications
Research in the area of siliciclastic diagenesis has historically incorporated advances in related disciplines such as petrography and petrophysics, mineralogy, geochemistry, organic geochemistry, stratigraphy and basin analysis, and more recently, fluid flow. While the collection of papers in this publication covers a broad range of topics, an underlying theme is the importance of fluid flow in diagenetic processes. The mineralogy, texture and geochemistry of authigenic minerals provide constraints for fluid flow models, while formation waters provide modern snapshots of pore fluid evolution. Separated into two sections (Part I: Concepts and Part II: Applications), conceptual and practical applications are both represented.