Dissertations / Theses on the topic 'Geology and the Environment'

The role of insolation as an instigator for crack initiation in rock is still a continuously perplexing topic. An immense amount of data has been collected on the influence of insolation on cracking—however, ongoing questions arise regarding the role this process plays in physical weathering. A study conducted by Dr. Martha Cary Eppes (2016) focused on the role of insolation in the initiation of cracking on a granite boulder in a temperate climate (North Carolina, USA), where 11 months of continuously recorded acoustic emissions (AE) data were used as a proxy for cracking. When these data were compared with simultaneously collected climate and rock surface data, it was found that insolation is a preliminary and contributing factor of crack initiation. However, this comprehensive data set was only representative of one climate zone—therefore, it was necessary to evaluate this relationship in other climates to support these conclusions. The following is a comparative study involving a similar granite boulder placed for an unprecedented three-year period in a semi-arid climate (New Mexico, USA). Utilizing the instrumentation of the Eppes 2016 study, acoustic emission sensors, strain gages, thermocouples, moisture sensors, and a site-located scientific weather station were deployed and monitored. During the 3-year study, 303,912 AE events (avg. 101,304 per year) occurred over a total 14,853 individual minutes over 713 days. A total 212,856 events occurred between 12:58 p.m. and 9:04 p.m. accounting for 70% of the overall deployment period. Comparable to the results of the Eppes 2016 study, high-event days (≥ 50 events) accounted for 98% of total events. Both boulders experienced the majority of events in the northern hemisphere and eastern position of the rock and no trends were indicated concerning the timing of events with precipitation. The results of this study 1) support the hypotheses that diurnal insolation contributes to the initiation and continuation of physical rock weathering and cracking whether alone or combined with temperature variations, and 2) suggest that this is characteristic of variable global locations, climates, and rock types.

Magnetic susceptibility has been used as an effective tool for affordable, rapid, and highly sensitive measurements that provide information about the compositional changes of mineral materials in rocks and soils. It has been demonstrated that a relationship between heavy metal concentrations, pollution, and magnetic susceptibility exists. The objective of this study is to use magnetic susceptibility as a method for the detection of the anthropogenic impact on the environment within Baton Rouge, Louisiana. Based on preliminary results from a previous study, we investigated a 100 square mile area, covering a variety of environmental settings, including urban areas and industrialized parts of the inner city. At each site, 20 magnetic susceptibility readings were taken and discrete surface and subsurface samples were collected for subsequent laboratory analysis.

Contour maps and histograms of magnetic susceptibility values indicate a close correlation between environmental setting and the intensity of magnetic susceptibility. Magnetic susceptibly increases within urban and industrialized areas compared to rural areas within the area of investigation. Enhanced susceptibility was observed in the industrialized areas in all magnetic parameters, including susceptibility maps of field measurements, discrete samples, and isothermal remanent magnetization. The field susceptibility data display a stronger correlation compared to the discrete sample analysis because of the statistically significant amount of data collected at each site. There is no apparent correlation between magnetic susceptibility and lithology/soil type in this area. Acquisition curves of the isothermal remnant magnetization indicate the presence of both high- and low coercivity minerals, probably magnetite with a small amount of hematite or goethite as the carriers of magnetic remanence.

The Pine Prairie Field is situated on a salt dome in northern Evangeline Parish, located in south-central Louisiana. Pine Prairie contains the only known Cook Mountain Formation hydrocarbon reservoir in Louisiana. Operators have targeted and produced hydrocarbons from the Cook Mountain reservoir in eight wells at the Pine Prairie Field. The source and origin of the Cook Mountain’s reservoir properties are unknown. The objective of this study is to determine the origin of the Cook Mountain Formation’s reservoir properties by identifying the processes associated with the formation of a Cook Mountain Reservoir. There are two carbonate outcrops at the surface expression of the Pine Prairie Dome. Samples were taken and thin sections made to determine the relationship, if any, to the Cook Mountain Formation. Thin section analysis of the carbonate outcrop was used to gain a better understanding of the depositional setting present at Pine Prairie Field. Well log, seismic, and production data were integrated to determine that, in all instances, commercial Cook Mountain production is associated with fault zones. The passage of acidic, diagenetic fluids through Cook Mountain fault zones generated areas of vuggy porosity proximal to Cook Mountain faulting. Further, fluctuations in short-term pressure gradients associated with salt diapirism resulted in the vertical migration of hydrocarbons via fault zones. In the Pine Prairie Field, fault seal breakdown occurs in Sparta and Wilcox Reservoirs, subsequently charging the Cook Mountain fault zone. Early hydrocarbon charge from the underlying Wilcox and Sparta Reservoirs prevented additional diagenesis, preserving secondary porosity in areas of Cook Mountain faulting.

The need for an expedient and economical field method for identifying the upper boundary of the capillary fringe (CF) led to an investigation of the clay-rich surficial units of two sites in New Iberia, Louisiana. Tension-sensing instruments capable of indirectly measuring water content were installed to monitor changing subsurface conditions throughout the vadose zone in response to water table fluctuation and rainfall. Tension measurements of 10 kPa and 33 kPa, correlated with the agricultural concept of field capacity by previous studies, functioned as indicators of two possible upper capillary fringe surfaces. Interpreted tension boundaries were plotted at depth to outline temporal changes in capillary fringe thicknesses, which ranged from approximately 1–5 ft depending on rainfall rates.

A comparison of gravimetric water content profiles with interpreted tension boundaries suggested that CF thickness was heavily influenced by the presence and composition of surficial fill, root systems, and the depth of the shallow water table. Collected tension and water content measurements were plotted as water retention points onto a series of estimated soil water retention curves (SWRCs). The hysteretic nature of soil-water retention relationships of the clay-rich media, evidenced by several examples of near equivalent water contents corresponding to vastly different tension measurements, and vice versa, illustrated the potential errors in basing capillary fringe thickness solely on tension measurements. While tension measurements did prove useful in recording variable conditions in the vadose zone, further research into accounting for hysteresis is required before tension boundaries can be employed in capillary fringe surface identification.

Magnetic susceptibility is a property that can be used to effectively determine the compositional changes of mineral materials in soil. The objective of this study is to detect the presence of magnetic particles related to the migration of fly ash from a nearby coal-burning power plant over parts of Pointe Coupee Parish, LA. This is based on the idea that the fly ash that is released into the atmosphere during the coal burning process contains heavy metals and magnetic particles in the form of ferrospheres, which can be used to trace back to the source. Maps of the top and sub soil were generated to differentiate the magnetic susceptibility values of the heavy metals potentially attributed to the migration and settling of fly ash onto the surface from any pre-existing or naturally occurring heavy metals in the sub soil. A 60 km² area in Pointe Coupee Parish was investigated in approximately 0.5 km² subsets.

At each site, a minimum of 20 magnetic susceptibility measurements were obtained using a field probe along with discrete surface and subsurface samples collected for subsequent laboratory analysis. Samples of fly ash obtained directly from the source were also analyzed to verify the field and laboratory analysis. Contour maps representing the spatial distribution of the fly ash along with histograms of magnetic susceptibility values, reflective light microscope, and chemical analysis indicate a correlation between the proximity to the power plant and the predominant wind direction. Acquisition curves of the isothermal remanent magnetization demonstrate the presence of predominantly low coercivity minerals (magnetite) with a small amount of a high-coercivity phase. The microstructure of the magnetic fractions of the fly ash along with select top and sub soil samples were observed using a reflective light microscope for identifying and confirming the presence of ferrospheres associated with fly ash.

This study examines the natural background concentrations of arsenic in the soils of southwest Oregon, using new samples in addition to data collected from previous theses (Khandoker, 1997 and Douglas, 1999). The original 213 samples were run by ICP-AES with a reporting limit of 20 ppm, and only three samples had detected values. The original samples were tested again (2013) at a lower reporting limit of 0.2 ppm by ICP-MS, as were 42 new samples (2013), to better ascertain the natural levels of arsenic in undisturbed soils. The aim is to add to the existing DEQ data set, which has been used to establish new regulatory levels based on natural levels in the environment that are both safer and more economically viable than the former risk-based remediation levels (DEQ, 2013).

The maximum and mean concentrations, respectively, for each province (with high formation map unit) are 85.4 and 21.99 ppm for South Willamette Valley (Tfee), 45.4 and 5.42 ppm for the Klamath Mountains (Jub), 11.9 and 2.76 ppm for the Cascade Range (Tbaa), 10.6 and 5.15 ppm for the Coast Range (Ty), 2.32 and 1.29 ppm for the Basin and Range (Qba) and 1.5 and 1.20 ppm for the High Lava Plains (Tmv).

In addition, the distribution and variance of arsenic in the A and B soil horizons is assessed in this study by comparing deviation at a single site, and also by comparing A and B horizons of 119 PSU sites. One of 18 new sites sampled for this study (distinguished with the HH prefix), site HH11, was randomly chosen to evaluate differences at a single location. Site HH11 is an Inceptisol soil above volcanic rock (KJdv map unit) located at 275 meters elevation in Douglas County within the Klamath province. Five samples were taken from the A and from the B horizons at site HH11. The means and standard deviations were 3.74 ± 0.44 for the A horizon and 4.53 ± 0.39 for the B horizon. The consistency and low deviation within each horizon indicate that a single sample within a horizon is a good representative of that horizon and supports the field methodology used in this study of taking only one sample in the A horizon and one sample in the B horizon.

Wilcoxon Rank-Sum test determined that A and B horizons for the 119 sites that had data for both the A and B horizons were not statistically different (p-value 0.76). Arsenic concentration is not associated with a particular horizon for these sites. However, differentiation between soil horizons increases with age (Birkeland, 1999), as does accumulation of the iron oxides and sulfide minerals on clay surfaces (McLaren et al., 2006) which concentrate in the B horizon. These associations warrant further study to see how they relate to arsenic level, soil development and age in Oregon soils.

Lastly, this study statistically examines six potentially important environmental predictors of naturally occurring arsenic in southwestern Oregon: site elevation, geomorphic province, mapped rock type and age, and sample soil order and color (redness). A Classification and Regression Tree Model (CART) determined soil order, elevation and rock type to be of significant importance in determining arsenic concentrations in the natural environment. According to the regression tree, arsenic concentrations are greater within Alfisol and Ultisol/Alfisol and Vertisol soil orders, at lower elevations below 1,207 meters, and within soils from sedimentary, mixed volcanic/sedimentary and unconsolidated rock types.

Submarine-fan deposits form the largest sediment accumulations on Earth and host significant reservoirs for hydrocarbons. While many studies of ancient fan deposits qualitatively describe lateral architectural variability (e.g., axis-to-fringe, proximal-to-distal), these relationships are rarely quantified. In order to enable comparison of key relationships that control the lateral architecture of submarine depositional environments, I digitized published bed-scale outcrop correlation panels from five different environments (channel, levee, lobe, channel-lobe-transition-zone, basin plain). Measured architectural parameters (bed thickness, bed thinning rates, lateral correlation distance, net-to-gross) provide a quantitative framework to compare facies architecture between environments. The results show that sandstone and/or mudstone bed thickness alone or net-to-gross do not reliably differentiate between environments. However, environments are distinguishable using a combination of thinning rate, bed thickness, and correlation distance. For example, channel deposits generally display thicker sandstone beds than mudstone beds whereas levees display the opposite trend. Lobe deposits display the most variability in all parameters, and thus would be the most difficult to identify in the subsurface. I sub-classified lobe deposits to provide a more detailed analysis into unconfined, semiconfined and confined settings. However, the results for semiconfined lobes indicate that the degree of lobe confinement and subenvironment is not easily interpretable at the outcrop scale. This uncertainty could be partially caused by subjectivity of qualitative interpretations of environment, which demonstrates the need for more quantitative studies of bed-scale heterogeneity. These results can be used to constrain forward stratigraphic models and reservoir models of submarine lobe deposits as well as other submarine depositional environments.

This work is paired with a case study to refine the depositional environment of submarine lobe strata of the Upper Cretaceous Point Loma Formation at Cabrillo National Monument near San Diego, California. These fine-grained turbidites have been interpreted as distal submarine lobe deposits. The strike-oriented, laterally-extensive exposure offers a rare opportunity to observe bed-scale architecture and facies changes in turbidites over 1 km lateral distance. Beds show subtle compensation, likely related to evolving seafloor topography, while lobe elements show drastic compensation. This indicates more hierarchical method of compensational stacking as the degree of bed compensation is small compared to the degree of element compensation. Thinning rates and bed thicknesses are not statistically different between lobe elements. This signifies that the lateral exposure is necessary to distinguish lobe elements and it would be extremely difficult to accurately interpret elements in the subsurface using 1D data (e.g., core). The grain size, mudstone to sandstone bed thicknesses, element/bed compensation, and lack of erosion observed in the Cabrillo National Monument exposures of the Point Loma Formation are most similar to values of semiconfined lobe deposits; hence, I reinterpret that these exposures occupy a more medial position, perhaps with some degree of confinement.

Changes in the concentration of atmospheric carbon dioxide (pCO2) affect global climate. Accurate determination of paleo-pCO2 can therefore provide information on the response of climate to changing pCO2. Such pCO2 proxies have been developed from a variety of terrestrial (e.g., plant stomata, paleosol carbonate, and liverworts) and marine (e.g., alkenones and boron) substrates. However, these proxies show a wide range of values and uncertainty throughout the Cenozoic and especially for the early Paleogene (53-63 mya). Here, I demonstrate the use of the carbon isotope composition of n-alkanes extracted from C3 plant waxes as an accurate recorder of changes in atmospheric chemistry. My results show that the uncertainty and range of pCO2 estimates determined using this new proxy are similar to other proxies. Because n-alkanes are abundant, chemically resistant, and not subject to degradation, this proxy represents an excellent opportunity to reconstruct pCO2 across the last 400 Myr of Earth history. By examining across 4 different chain lengths (n-27, n-29, n- 31, and n-33), I find that only n-29 and n-31 show clear changes in carbon isotope discrimination in response to changes pCO2, whereas chain-lengths n-27 and n-31 did not show any significant response. Using chain lengths n-29 and n-31, I calculate early Paleogene pCO2 = 566 ? 190 and 469 ? 165 ppmv (median ? 1?), respectively. These results demonstrate that n-alkanes can serve as a potential pCO2 proxy across geologic timescales.