Department of Geology

Lithofacies heterogeneity, fluvial style variations, and floodplain vegetation distributions : deposition and diagenesis of the Chinle Formation at Petrified Forest National Park, Arizona.

Wed, 15 May 2013 00:00:00 GMT

Lithofacies heterogeneity, fluvial style variations, and floodplain vegetation distributions : deposition and diagenesis of the Chinle Formation at Petrified Forest National Park, Arizona. Trendell, Aislyn M. The Upper Triassic Chinle Formation in the Petrified Forest National Park (PFNP) was evaluated using sedimentologic, stratigraphic, paleopedologic and petrographic criteria. The study interval, which includes the Blue Mesa Member and overlying Sonsela Member, consists of paleosol-bearing alluvial strata whose characteristics vary markedly. The Sonsela Member is a fining upward succession that contains a higher proportion of coarse and conglomeratic sandstones than the Blue Mesa. Evidence is presented that suggests that the Sonsela was deposited within a mixed-load fluvial system that was influenced by tectonism. Sonsela sandstones have undergone an almost complete diagenetic loss of porosity due to the precipitation of authigenic clays that likely occurred at or immediately after burial and contemporaneous with the silicification of fossil logs in channel deposits. The study succession from the Blue Mesa Member to the Sonsela Member records a progressive up-section increase in grain size, increase in channel depth and width, increase in lateral and vertical connectivity of channel deposits, decrease in overbank preservation and crevasse-splay and/or sheetflood deposition, and increase in paleosol/ overbank drainage. Mean annual precipitation remained stable throughout deposition of the succession despite changing paleosol drainage. These features and an upsection decreasing sandstone mineralogic maturity are consistent with deposition within a progradational large fluvial fan system. Sediment accumulation rates within the study interval suggest decreased subsidence within the upper Blue Mesa Member that may have promoted progradation of the fluvial fan system. The Sonsela Member contains few paleobotanical fossils other than abundant silicified conifer logs within channel sandstones and, as such, its ecosystem is poorly understood. Sonsela paleosols contain fossilized root traces that provide information regarding plant size and densities. Paleosol maturity suggests that the Sonsela fluvial system experienced high rates of lateral migration and cannibalization of overbank sediments. Fossilized root characteristics suggest that small-stature plants were living on channel-proximal paleosols while distal floodplain paleosols may have hosted herbaceous understory, small-stature shrubby and fewer arborescent plants. There is little evidence to suggest that Sonsela paleosols hosted a dense coniferous forest and conifer logs may have been sourced from uplands. Rhizohalos within the Sonsela Member appear diagenetic.

Reservoir assessment of late Devonian Kakisa Formation, northeastern British Columbia, Canada.

Wed, 15 May 2013 00:00:00 GMT

Reservoir assessment of late Devonian Kakisa Formation, northeastern British Columbia, Canada. Jones, Kelly N. The Late Devonian Kakisa Formation of northeastern British Columbia, Canada is a high energy, aggradational, discontinuous carbonate bank complex that is composed of three distinct allocycles designated the “Upper”, “Middle”, and “Lower” Kakisa. The study region includes a 5500 square mile area across which the Kakisa was evaluated in regards to the nature and distribution of facies and their relationship to reservoir quality and its spatial distribution. Data integrated into the study include detailed core descriptions for seven wells, and well logs from 116 wells correlated within a grid of 37 cross sections. Gamma ray logs are particularly useful in characterizing petrofacies that are interpreted to have accumulated within low energy, “off-bank” (relatively higher gamma ray activity and lower reservoir quality) and high energy, “on-bank” (relatively lower gamma ray activity and higher reservoir quality) marine settings. The potentially gas-charged reservoir is only associated with “on-bank” stromatoporoid reef complexes observed within the Upper and Middle Kakisa. Reservoir bodies are isolated within the eastern portion of the study area, and coincide with north-trending, high-energy "on-bank" deposits.

Interaction between floodplain groundwater and a constructed wetland, north Central Texas.

Wed, 15 May 2013 00:00:00 GMT

Interaction between floodplain groundwater and a constructed wetland, north Central Texas. Foss, Laura K. The primary goal of this study was to investigate the groundwater conditions and the potential for interaction between groundwater and surface water at the East Fork Wetland Project. In order to prepare for that investigation, a study of the water budget was conducted to gain an understanding of the wetland system as a surface water system. Infiltration became both a term in the water budget and also a measurable aspect of interaction between groundwater and surface water. The water budget was found to balance in confined timeframes, but discrepancies compounded as the timeframe was extended. Groundwater was found to have a west to east gradient and the subsurface investigation indicated discontinuous lenses of more permeable (sandy) materials than the clays typical of the floodplain. Interaction between groundwater and surface water is supported by water chemistry analysis, evidence of groundwater recharge, and seepage events measured in the field.

Age, genesis, and archaeological geology of the sandy mantle on the Gulf Coastal Plain of Texas.

Wed, 15 May 2013 00:00:00 GMT

Age, genesis, and archaeological geology of the sandy mantle on the Gulf Coastal Plain of Texas. Ahr, Steven Wayne, 1970- Alfisols exhibiting strong textural contrasts between sandy A-E horizons (sandy mantle) and clayey Bt horizons on the Gulf Coastal Plain have invoked debate among pedologists, geologists, and archaeologists about parent material uniformity, the age and origin of the sandy mantle, and the scientific value of buried archaeological sites. This dissertation addresses these issues, as well as climate-related variability in the mass-balance of soil constituents, across a 700-mm mean annual precipitation (MAP) gradient. Five Alfisol pedons located on upland summit settings of the Gulf Coastal Plain of Texas were sampled, described, and analyzed. Depth trends in clay-free particle-size classes and Ti and Zr failed to reveal lithologic discontinuities in each pedon, suggesting that the A-E and Bt horizons are genetically related and the textural contrasts resulted from pedogenic, rather than depositional, processes. Thus, any buried archaeological materials would have moved down the profile under the influence of bioturbation and gravity. Optical dating of the soil profiles illustrates complex age structures. Mixing in the A-E horizons effects apparent OSL ages <10,000 years due to admixture of recently and partially bleached quartz grains. Decreased mixing occurs within Bt horizons, and ages increase systematically with depth. Pedogenic weathering alters 40K, U and Th content and environmental dose rates, with concomitant changes in OSL ages. Apparent maximum age calculations from the probable oldest equivalent dose group in soil parent materials suggest the soils began weathering at least by 90-112 ka, and 40-62 ka, which greatly precedes human entry into North America. Mass-balance trends revealed nearly 100% weathering losses of Ca, Mg, Na, Al, and Fe from the A-E horizons, with redistributions and variable gains in Bt horizons. Elemental flux is positively correlated with net mass flux of fine clay and MAP, likely due to increased weathering-related concentrations of negatively-charged clay particles in higher-MAP soils, which facilitate cation adorption and retention. This has implications for predicting pedogenic response to global climate change and for estimating important soil properties in Alfisol-like paleosols in the geologic record.