Department of Geosciences
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Browsing Department of Geosciences by Author "Baylor University."
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Item Environmental framework, structural evolution and petroleum potential of the Cambrian Wilberns Formation West-Central Texas(1984) Poorman, Stephen Eugene; Beaver, Harold; Baylor University.The Wilberns Formation (Upper Cambrian) in the subsurface of west-central Texas is composed predominantly of sandstone units. Subsurface mapping of the Wilberns shows the sandstones to be persistent throughout most of the study area. Analyses of core samples indicate that the upper portion of the Wilberns Formation consists of a lower sandstone facies overlain by a dolomitic interval. The suite of sedimentary structures present in both facies suggests tidal flat deposition and the electric log signatures are similar to those produced by channel and tidal sand bodies. Thus, it is postulated that the Wilberns Formation was deposed on extensive tidal flats in tidal channels. The Fort Chadbourne fault system is a linear zone of deformation trending from Sutton County northward into northeastern Nolan County. This structural zone has uplifted and faulted the Wilberns Formation. The presence of en echelon faults and folds as the predominant structures along the Fort Chadbourne system suggests wrench faulting. The orientation of the faults (N-S) and folds (NE-SW) suggests that the wrench system had left lateral movement produced from compressive forces active during the Ouachita orogeny. Thin section analyses of core samples produced a general paragenetic sequence for the upper sandstone units of the Wilberns Formation consisting of at least four diagenetic stages as follows: (1) Burial and compaction leading to reduction of primary porosity and development of quartz overgrowths. (2) Precipitation of dolomite cement into remaining pore space. (3) Uplift and exposure leading to dissolution of calcareous materials, resulting in development of secondary porosity. (4) Re-burial and precipitation of hematite, pyrite and clays as pore lining and pore fill. Hydrocarbon migration probably occurred during this stage. This sequence of diagenetic events is responsible for the excellent reservoir quality of the sandstone units within the Wilberns Formation; it is found only along the Ford Chadbourne fault system.Item Hydrogeologic assessment of shallow groundwater flow systems in the Walnut Formation, Central Texas(1994) Feckley, David Lee; Baylor University.The Walnut Formation is the most clay-rich member of the limestone dominated Lower Cretaceous rocks of central Texas. Due to this clayey nature, the Walnut Formation is a natural target for landfills in this region. Shallow groundwater flow systems present within the Walnut Formation provide baseflow to streams which transect the Walnut outcrop belt in Central Texas. Three sites within the outcrop belt of the Walnut Formation were investigated. The Walnut flow systems are geomorphically and stratigraphically controlled, and recharge zones are influenced by the geomorphic history and subsequent soil formation. Discharge zones are controlled by seasonal influences, stratigraphy, and geomorphic position. Field observations indicated saturated zones in the near surface Walnut Formation may produce hydraulic heads above ground elevation. These saturated zones, within the weathered depth of the Walnut Formation, discharge to main streams by tributary discharge and spring flow. Conceptual models of the flow systems were constructed following field observations, hydrogeolgic testing (slug tests and pumping tests), geochemical analyses, and hydrograph analysis and interpretation. Regionally, the Walnut flow systems relate to the condition of the underlying Paluxy Formation (a minor aquifer). Flow systems of the Walnut Formation are important from a regional perspective due to the potential of non-point source contamination to surface waters by landuse practices on the Walnut outcrop area.Item Paleoenvironmental Variability across the Cretaceous-Tertiary Boundary in the Alberta Foreland Basin, as Interpreted from Fluvial Deposits and Paleosols, Red Deer River Valley, Alberta, Canada(2002) Forkner, Robert Murchison; Nordt, Lee C.; Baylor University.The integration of sedimentological, paleotectonic and paleopedogenic data across the Cretaceous-Tertiary (KT) boundary of south-central Alberta indicates fluvial aggradation and variability of paleosol morphology in response to foreland orogenesis. The depositional history records an evolution from amalgamated, multi-story, braided sand bodies to accretionary, single-story, overbank-prone meandering deposits. The distribution of paleosols throughout the section is also cyclic. Immature, well-drained paleosols are associated with the braided deposits, whereas mature, poorly-drained paleosols are interbedded with the meandering deposits. Two large-scale aggradational fluvial cycles are observed within the study interval and are interpreted to record variations in sediment supply and tilt of the depositional profile associated with foreland tectonism. Orogenic pulses are reflected in outcrop by amalgamated fluvial deposits interbedded with immature paleosols. Waning orogenesis is characterized by reduced fluvial sedimentation rates and an increase in the number of mature paleosols. Orogenic quiescence is associated with an increase in channel sinuosity, and poorly drained, gleyed, coal-capped paleosols. The KT boundary is located three meters above the tectono-stratigraphic transition from amalgamated, braided fluvial systems with well-drained paleosols to accretionary, meandering fluvial systems with poorly-drained paleosols. A gradual shift towards a more poorly-drained paleosol morphologies and increasingly accretionary fluvial styles suggests that the KT event was not the cause of increasingly cool and wet conditions across the boundary, but that the boundary lies at the inflection point between a well-drained to poorly-drained depositional cycle.Item The Significance of the Waco Mammoth Site to Central Texas Pleistocene History(2013-04-09) Naryshkin, George F.; Hayward, O. T.; Bonem, Rena Mae.; Geology.; Baylor University.A fossil assemblage consisting of three fragments of the lower jaw of Alligator mississippiensis and of articulated skeletal material of five individual specimens of Mammuthus columbi occurs in point bar deposits of the second terrace of the Brazos River, in Steinbeck Bend, Waco, Texas (Waco West Quadrangle 1/24:000). Correlation of the sequence of gravels, sands and clays with those in the Trinity River indicates Sangamon age or approximately 37,000 years B.P. Reconstruction of the paleoclimatic frost line north of the site, suggests a warmer climate than exists today in the area. Ecologically, the Waco Mammoth Site indicates a homogeneous climate in Central Texas during the Sangamon, that allowed Mammuthus columbi and Alligator mississippiensis to migrate throughout this area. Examination of the teeth and tusks revealed the sex and age of each individual and from this, the social structure of the community was determined. This showed no similarity to any social structure of the African elephant, suggesting a non-catastrophic cause of death. The high degree of articulation indicated that the mammoths either floated to the point bar shortly after their death, or died in situ. The large percentage of old males at the site suggested that killing by ancient man (similar to modern poaching practices on the African continent) may have been the cause of death of the mammoths. Kill sites of the Sangamon Age on the Trinity River in Dallas and ton counties suggest the Waco Mammoth Site could be a product of normal fluvial burial following human kill. No artifacts nor any other signs of ancient man have been at the site, supporting the "floatation to point bar" hypothesis. However, of mammoth material in this region suggests the widespread practice of mammoth killing by ancient man as early as 37,000 B. P.Item Subsurface Stratigraphy of the Strawn and Canyon Groups of west central Texas, Concho and Menard counties(1983) Woodard, Jan N.; Grayson, Robert; Parker, Don; Baylor University.Carbonate rock units of the upper Strawn Group (Desmoinesian) developed on the western flanks of the Llano uplift on a positive topographic platform, the Concho shelf. Late Mississippian and early Pennsylvanian orogenic uplifts along the Texas craton exposed the Ordovician Ellenburger Group carbonate rocks to extensive erosion and provided the paleotopographic unconformity upon which these cyclic limestones and shales were distributed. Orogenic activity related to the advancing Ouachita Fold Belt occurred synchronously with late Strawn deposition. The rising Ouachita orogenic belt initiated a fluvial-deltaic depositional complex that prograded over a slowly subsiding carbonate shelf. In early Canyon time (Missourian) deformation along the Ouachita Fold Belt decreased in intensity and a more stable carbonate platform environment was reestablished on the shelf. Cycles of marine and prodeltaic shales capped by algal limestones characterize the Canyon Group. Paleotopographic variations in the lower Canyon indicate early Missourian tectonic movement in the Ellenburger limestones. In contrast, the wedge-shape geometry of the upper Canyon carbonate units suggest shoreward-building carbonate banks. These banks developed over very porous, water-saturated prodelta shales and gained thickness as accumulating carbonates compressed the unconsolidated distal muds.