Browsing by Subject "Geology."
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Item Analysis of calcite-filled faults in carbonate strata, balcones trend near Waco, Texas.(2011-09-14) Secrest, Stephen H.; Cronin, Vincent S.; Geology.; Baylor University. Dept. of Geology.Five normal faults exposed in the Lehigh Quarry near Waco, Texas, were analyzed. The mechanical stratigraphy of the quarry ranges from relatively strong chalk to marly chalk to chalky marl to relatively weak marl. Higher clay content yields weaker rock. The dip angle of the normal faults varies with rock strength, with steeper dips across the stronger strata. Carbon stable isotopes in 174 samples indicate that the water from which the calcite precipitated is formation water and not meteoric water, while oxygen isotopes indicate that precipitation of secondary calcite in the fault cores occurred between 48° and 110°C. Mechanical twins in macrospar calcite indicate shear stress slightly more than 5-15 MPa, and deformation temperature of <170°C. The microspar fabric includes thin veinlets of secondary calcite and host lithons of cemented chalk wallrock whose orientation relative to the domain boundaries can be used as a shear-sense indicator.Item Climatic and human influences on Holocene alluvial history and paleoenvironment of the middle Delaware River Valley, USA.(2012-11-29) Stinchcomb, Gary E.; Driese, Steven G.; Nordt, Lee C.; Geology.; Baylor University. Dept. of Geology.The potential for future prolonged drought episodes in the Northeastern USA is alarming given that a humid climate currently provides water to +50 million people in the northeast, USA. Hydro-climatic projections are hampered by a lack of regionally-based paleoenvironmental reconstructions. The middle Delaware River Valley provides a unique opportunity to expand the Holocene alluvial history and paleoenvironment for the northeast, USA. Thirty-six soil profile descriptions, 332 grain size analyses, and 82 14C ages from trenches and auger borings show that similar alluvial landforms within the river valley have different formation histories and depict a valley that has experienced middle to late Holocene floodplain and terrace reworking. Despite erosion, secular changes in buried soil and sediment properties are closely associated with climate change and land-use. A Holocene time-series was constructed using 149 δ13Csom values from alluvial terrace profiles. There is good agreement between increasing δ13Csom and Panicoideae phytolith concentrations, suggesting that variations in C4 biomass are a contributor to changes in the soil δ13C. A measurement error deconvolution curve over time reveals two isotope stages (II and I), with nine sub-stages exhibiting variations in average δ13Csom (%C4). Stage II, ~10.7-4.3 ka, shows above average δ13Csom (increase %C4) values with evidence of an early Holocene warm/dry interval (sub-stage IIb, 9.8-8.3 ka) that coincides with rapid warming and cool/dry abrupt climate change. Sub-stage IId, 7.0-4.3 ka, is an above average δ13Csom (increase %C4) interval associated with the mid-Holocene warm/dry Hypsithermal. The Stage II-I shift at 4.3 ka documents a transition toward below average δ13Csom (decrease %C4) values, coinciding with decreasing insolation and moisture budget reorganization. Sub-stages Ib and Id (above average %C4) coincide with the first documented occurrence of maize in northeastern USA and population increase during the Late Woodland. These associations suggest that humans influenced δ13Csom during the late Holocene. The influence of land-use is further corroborated by a regionally extensive anthropogenic sedimentation event documented throughout eastern North America, pre-Colonial sediment (PCS) circa: A.D. 1,100–1,600. These data demonstrate that combined prehistoric land-use and climate change impacted eastern North American floodplains several hundred years prior to the onset of European Settlement.Item Field, micromorphologic and geochemical study of modern and ancient soils from Riesel, Texas and Rusinga Island, Lake Victoria, Kenya.(2014-06-11) Michel, Lauren Ashley.; Driese, Steven G.; Peppe, Daniel J.; Geology.; Baylor University. Dept. of Geology.Paleosol are utilized to reconstruct paleoclimate and paleoenvironment by paleopedologists. However, paleopedologists must constrain for all of the state factors that create a soil before paleoclimate or paleoenvironment can be assessed. Study of a modern catena in Riesel, TX shows that landscape position, parent material and time have important implications for pedogenesis. Soils with a limestone parent material component that form on ridge crests-side slopes may include marine bedrock within their pedogenic calcite nodules, because soil erosion rates exceed soil-production rates. Conversely, soils that form on toe slopes have a longer period of soil duration and formation, and more complete weathering of the parent material occurs. These soils have pedogenic carbonate nodules that reflect an admixture of CO₂ from the atmosphere and soil-derived CO₂. Since the initial discovery of Proconsul, Rusinga Island has been one of the most important Early Miocene fossil localities in East Africa, with vertebrate, invertebrate, and plant fossils recovered. Because environment is a catalyst for evolutionary adaptation, scientists have attempted to determine the paleoenvironment in which Proconsul lived. However, paleoenvironmental reconstructions have lead to conflicting results, with interpretations ranging from open grassland/parkland to closed-canopy rainforests. Recent revised stratigraphy, coupled with new paleomagnetic data and age dates, allows for a unique opportunity to reconstruct paleoenvironment for a time-slice of Miocene strata on Rusinga Island that contains both Pronconsul and the catarrhine Dendropithecus, among other vertebrate fossils. Paleopedological study has indicated the existence of a forest ecosystem developed on a landscape that received frequent inputs of sediment reworked from volcaniclastic materials. Global Positioning System mapping of fossil tree stump casts has allowed for modern forestry metrics to be applied whereas description of root cast density and structure, and paleosol descriptions have provided insight for below-ground processes. Although traditional paleosol-based proxies fail because of the lack of time for pedogenic development, paleobotanical proxies applied to fossil leaves in the overlying sandstone are able to constrain mean annual temperature and mean annual precipitation. Using this multi proxy approach, a higher-resolution picture has emerged that ties Proconsul definitively to a multistoried, closed-canopy, tropical seasonal forest that was probably relatively wet, and hot.Item Geology of the Late Pleistocene artifact-bearing Wasiriya Beds at the Nyamita locality, Rusinga Island, Kenya.(2011-12-19) Van Plantinga, Alexander A.; Peppe, Daniel J.; Geology.; Baylor University. Dept. of Geology.This study investigated the sedimentology and stratigraphy of the Late Pleistocene Wasiriya Beds at the Nyamita locality on Rusinga Island, Kenya in northeastern Lake Victoria. Little is yet known about this region during the Pleistocene. This study provides geological context for archaeological research of the stone artifacts in the Wasiriya Beds, for the paleontological work on the fauna of these beds, and for other paleoenvironmental research in these beds. A robust tephrostratigraphic framework was established using diverse statistical methods. Radiocarbon dates confirm a Late Pleistocene age for these deposits. A valley-drainage model was integrated with a facies model to infer their paleoenvironmental history. Sediments suggest a generally sharply alternating wet and dry seasonality. Geological evidence does not suggest that the Lake Victoria region was especially arid just prior to the Last Glacial Maximum. Additional data from the lower Wasiriya Beds could elaborate on their paleoenvironmental significance.Item The Jurassic Norphlet Formation of the deep-water Eastern Gulf of Mexico : a sedimentologic investigation of aeolian facies, their reservoir characteristics, and their depositional history.(2011-01-05T19:38:11Z) Douglas, Scott W., 1986-; Dworkin, Steven I.; Geology.; Baylor University. Dept. of Geology.This study defined the sedimentary facies, reservoir architecture, and depositional history of the Jurassic aeolian Norphlet Formation in the deep-water Eastern Gulf of Mexico. Seven depositional facies were identified and grouped into four facies associations, three of which being primary aeolian facies: 1) Grainflow, exhibiting the highest permeability and dip angles; 2) Wind-Ripple, exhibiting moderate permeability and dip angles; and 3) Wet Interdune, exhibiting the lowest permeability and dip angles. Associated extradunal fluvial facies were identified in the lower Norphlet interval. All facies displayed heterogeneous attributes of porosity and permeability. Permeability has been reduced by various diagenetic cements in the Norphlet. Stratigraphically equivalent aeolian stabilization surfaces were identified within the Norphlet. The reconstructed Norphlet depositional model demonstrates a relatively dry, mature, northwestward migrating aeolian erg with the Middle Ground Arch highland sediment source to the east, and presumably an ancestral Gulf of Mexico to the west.Item Seismo-lineament analysis of selected earthquakes in the Tahoe-Truckee area, California and Nevada.(2012-08-08) Lindsay, Ryan D.; Cronin, Vincent S.; Geology.; Baylor University. Dept. of Geology.Focal mechanism solutions from 29 M≥3 earthquakes recorded between 1966 and late 2009 in the Tahoe-Truckee area, California and Nevada, were used to establish a preliminary spatial correlation between these earthquakes and faults. In previous studies, only the 1966 Truckee earthquake (M 6) had been correlated with a fault: the Dog Valley fault. The most recent events on other Quaternary faults in the area were previously attributed to the mid-Holocene to Pleistocene. In this study, preliminary spatial correlation has been described between one or more earthquakes and the Dog Valley fault zone, Polaris fault, West Tahoe fault, North Tahoe fault, Incline Village fault and the hypothetical Agate Bay fault. Two additional trends are defined by seismo-lineaments and geomorphic indicators of possible faulting, and might encompass previously unrecognized seismogenic faults. This area is subject to earthquakes on north-striking east-dipping normal faults, northwest-striking dextral faults and their conjugates -- northeast-striking sinistral faults.Item Spatial correlation of earthquakes with two known and two suspected seismogenic faults, north Tahoe-Truckee area, California.(2014-06-11) Reed, Tyler H.; Cronin, Vincent S.; Geology.; Baylor University. Dept. of Geology.The Seismo-Lineament Analysis Method (SLAM) is used with relocated hypocenters and revised focal mechanisms from 29 M≥3 earthquakes reported in the north Tahoe-Truckee area, California, to spatially correlate earthquakes with the Dog Valley fault zone, the Polaris fault, and two trends that exhibit geomorphic evidence of faulting: the Martis Creek and Prosser Creek trends. These faults and trends are orthogonal-to-conjugate to each other, and are proximate to reservoirs and dam structures whose failure might impact downstream communities along the Truckee River, including Reno. Earthquakes were spatially associated with the two faults and with the Martis Creek and Prosser Creek trends, which are inferred to have developed along seismogenic faults. Horizontal infinitesimal strain analysis of GPS velocity data indicates slow clockwise crustal rotation and NW translation consistent with right-lateral shear in the northern Walker Lane, as well as maximum horizontal extension oriented ENE-WSW consistent with average T-axis orientations from focal mechanisms.