Authigenic Mineralogy Of Sandstones Intercalated With Organic Rich Mudstones Integrating Diagenesis And Burial History Of The Mesaverde Group Piceance Basin Nw Colorado

AUTHIGENIC MINERALOGY OF SANDSTONES INTERCALATED WITH ORGANIC RICH MUDSTONES INTEGRATING DIAGENESIS AND BURIAL HISTORY OF THE MESAVERDE GROUP NW COLORADO PICEANCE BASIN LAURA J Departmellf of Geology CROSSEY AND University of Nell DANIEL LARSEN Mexico Albuquerque Nell Mexico 87J 31 stratigraphically adjacent fine grained organic rich samples representing diverse de paludal and marine have been obtained from cores of the Mesaverde Group within the Piceance Basin Colorado These units have been buried to a sufficient depth that organic maturation has progressed to an advanced vitrinite reflectance values range from 1 0 to 2 2 in the study area The authigenic mineral state paragenesis and organic data are integrated with burial and thermal history modeling to place diagenetic events and hydrocarbon generation into a temporal framework Three phases of diagenesis early late and post hydrocarbon are characterized on the basis of petrography XRD and geochemistry of authigenic phases Clay mineral distributions of sandstone mudstone pairs indicate that mixed layer illite smectite dominates mudstone mineralogy although subordinate amounts of chlorite are observed in the marine interval Sandstone mineralogy also includes mixed layer clays and chlorite with the addition of kaolinite Additional aspects of sandstone diagenesis examined include feldspar albitization and dissolution and carbonate mineralogy Organic analyses indicate the presence of a type III kerogen component in all samples The paludal interval contains the most oxygen rich organic material and exhibits the highest sandstone porosities Water soluble organic compounds released from organic material as as burial progresses have been invoked agents affecting the course of mineral diagenesis in clastic sediments and sedimentary rocks Our results indicate the potential for the field evaluation of the effects of thermal maturation of organic matter on the diagenesis of closely adjacent sandstones ABSTRACT nine Twenty sets environments positional of sandstone and fluvial coastal One of the primary goals of diagenetic studies is to un operating on sedimentary materials or as they undergo progressive burial Once the processes of are known the results can be in pathways diagenesis tegrated with burial and thermal modeling to evaluate the timing of events of regional significance e g the devel opment of porosity and the production and migration of hy drocarbons A process oriented approach is essential if models are to be applied to a variety of sedimentary basins This approach has been used with great success in the eval uation of liquid hydrocarbon production from organic rich derstand the processes source Waples rocks see reviews in Demaison and Murris 1984 A similar 1985 ervoir rocks should approach applied to potential res enable prediction of spatial and tem poral porosity variations within a basin A key aspect of a process oriented approach to clastic diagenesis is the incorporation of organic maturation re actions including the generation and release of water sol uble organic compounds into diagenetic models Numer ous workers have shown experimentally and theoretically that water soluble organic compounds can have a profound effect on stability of aluminosilicates and carbonates through pH control and complexation Huang and Keller 1970 Surdam and others 1984 Crossey 1985 Kharaka and oth ers 1986 Surdam and Crossey 1987 although others question the overall importance of these effects in diage netic processes e g Lundegard and Land 1986 Lunde