Petrography, Sedimentology, Diagenesis, and Reservoir Characteristics of Some Pennsylvanian Phylloid Algal Limestones: Kansas and Utah, u.s.a. (United States)
Dawson, William Craig
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https://hdl.handle.net/2142/71132
Description
Title
Petrography, Sedimentology, Diagenesis, and Reservoir Characteristics of Some Pennsylvanian Phylloid Algal Limestones: Kansas and Utah, u.s.a. (United States)
Author(s)
Dawson, William Craig
Issue Date
1984
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Abstract
The Paola and Raytown limestone members of the Iola Formation (Missourian) of southeastern Kansas have been systematically analyzed with 1200 thin sections. These rocks contain a typical Pennsylvanian biotic assemblage of phylloid algae, bryozoans, encrusting foraminifers, fusulinids, Composita, productid brachiopods, and pelmatozoans.
Quantitative petrographic data indicate that the Iola Formation consists of 23 carbonate and one siliciclastic microfacies. Texture (mean grain size, frequency of matrix, and percentage of bioturbation) is used to arrange the microfacies in order of relative paleobathymetry. Temporal and spatial relationships of microfacies are used to interpret the depositional history of Iola carbonates. The four sedimentary models are variants of the "carbonate ramp model." Eleven subenvironments are recognizable within this context: distal deltaic, hypersaline lagoon, mound cap, bioconstructed mound, mound cap-flank, mound flank, bioclastic bar, hardground, bioaccumulated mound, upper ramp, and lower ramp. The paleoenvironmental evolution of Iola microfacies records a shallowing-upward sequence ranging from far offshore (below fair weather wave base) environments dominated by biogenic reworking to intertidal storm-dominated conditions. A phylloid algal mound within the Raytown Limestone is of mixed hydrodynamic-biogenic origin and exhibits four growth stages: (1) bioclastic (hydrodynamic buildup), (2) bioaccumulation, (3) bioconstruction, and (4) bioclastic (destructional).
Diagenesis of Iola microfacies was complex and included: marine phreatic (bioturbation, micritization, hardground genesis, and cementation), freshwater vadose (collapse brecciation and vadose silt infiltration), freshwater phreatic (moldic dissolution, cementation, and extensive neomorphism), deep burial (anhydritization, baroque dolomitization, stylolitization, and silicification), and late uplift (fracturation and cementation). Much diagenesis was microfacies specific.
Phylloid algal reservoirs in the Ismay Field, Utah are characterized by high porosity and low permeability. Most porosity results from selective dissolution of phylloid algae but abundant micropores in the micritic matrix impart a size bimodality to the pore system. Permeability may be enhanced by stylolites or microfractures.
Algal moldic pores, comparable to those in Ismay reservoirs, have been experimentally produced by fabric selective dissolution of low-Mg calcite a simulated deep burial (12,000 to 15,000 ft) pressures in the presence of circulating weakly acidic pore fluid. This indicates a potential for algal moldic porosity at depths far below established petroleum production.
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