Carbon Dioxide and Organic Acids: Their Role in Porosity Enhancement and Cementation, Paleogene of the Texas Gulf Coast
Published:January 01, 1985
Paul D. Lundegard, Lynton S. Land, 1985. "Carbon Dioxide and Organic Acids: Their Role in Porosity Enhancement and Cementation, Paleogene of the Texas Gulf Coast", Roles of Organic Matter in Sediment Diagenesis, Donald L. Gautier
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Carbon dioxide produced by decarboxylation of organic matter is not a dominant factor in secondary porosity development. In typical sedimentary basins it may account for a regional average of a few volume percent secondary porosity, but it is insufficient to account for all of the secondary porosity in Texas Gulf Coast sandstones.
Petrographic data indicate dissolution of a minimum of 5 volume percent feldspar from Paleogene sandstones of the Texas Gulf Coast. The amount of acid required for feldspar dissolution depends on its mineralogy and the fate of aluminum. Feldspar dissolution in Texas Gulf Coast sandstones probably requires at least 1 mole of protons for every mole of feldspar dissolved.
Carbonate dissolution, a process of debatable importance in sandstones, was probably of major significance in many Gulf Coast shales. This is indicated by the strontium isotopic composition of carbonate cements in sandstones, and the decreasing weight percent calcite in shales in some wells. Carbonate cementation in sandstones probably occurred in response to lowered CO2 solubility in upward-migrating formation water.
Considerations of the solubility of carbon dioxide and the distribution of organic acids with respect to temperature suggest that these species will be of great importance in porosity enhancement only if generated locally. Other potential sources of acid for dissolution reactions are reverse weathering reactions in shales and hydrous pyrolysis reactions between organic carbon and oxygen in H2O (including synthesis of organic acids from kerogen).
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Roles of Organic Matter in Sediment Diagenesis
This volume is the direct result of an SEPM Research Conference held in October 1983 at Lost Valley Ranch, Colorado. The goal of the volume is to bring attention of the sedimentological community the importance of interaction of organic compounds with the inorganic sedimentary system and the degree to which organic compounds drive diagenetic systems. This volume comprises 16 reports illustrative of the scope and direction of current research in sedimentological and geochemical studies of organic/inorganic interaction.