http://hdl.handle.net/2027.42/13913 2013-05-19T09:00:20Z http://hdl.handle.net/2027.42/97759 The Morphology of Etched and Unetched Ion Tracks in Apatite as a Function of Orientation and Thermal Annealling Pray, John McLain Apatite samples from Durango, Mexico, and Otter Lake, Canada, have been irradiated in different orientations with 185 MeV Xe, 284 MeV Au, and 2.2 GeV Au ions in order to simulate spontaneous fission track formation as a function of annealing temperature, etching time, apatite chemistry, and the orientation of the track relative to the apatite structure. We have characterized the unetched tracks using small angle x-ray scattering and atomic force microscopy and the etched tracks using optical microscopy. Apatite is commonly used in fission track dating, and the data presented here have implications for the use the dating parameter Dpar, used to assess kinetic annealing rates in apatite. Dpar is based on the diameter of an “etch figure,” or an etched fission track at its intersection with the (10-10) face, measured parallel to the c-axis. The Dpar values are proportional to the annealing rate. Larger Dpar values indicate slower annealing kinetics. Dpar measurements of natural apatite have been used to calibrate track-length reduction rates, against which observed track lengths can be evaluated to extract information regarding the thermal history of apatite, such as residence time below 100 °C, as well as the cooling rate. We observed that etch figures show systematic reductions in diameter with increasing annealing temperature for isochronal heating experiments. This decrease is accompanied by increased variation in diameter, with standard deviations as high as 40% of the mean. This reduction in mean diameter and increase in variability occurs gradually as a function of increasing temperature in the 320-360 °C range, with an accelerated rate in the range 360-400 °C. Extrapolated to geological time and temperature scales, this variation explains the variability reported in the literature for Dpar measurements on natural apatite, because fission tracks in natural apatite are of different ages and have experienced different amounts of annealing. The decrease in etch figure diameter, however, is proportional to track length decrease during annealing. While the relation between track length and etch figure diameter presented here is simplified, it suggests that the nature of the relation between etch figure diameter and track length is straightforward and that more accurate models of track annealing could be developed. Such models could then be used to correct anomalously low Dpar values measured in natural apatite by comparison with track length. Also incorporated into this model is the formation of local zones of complete annealing along the track length. These zones have been described as crystalline“gaps” by Green et al. (1986). Since gap formation can occur at random points along the track length, increased variability in track lengths is expected, explaining the increased variation in etch figure diameters at higher annealing temperatures. The relative sizes of etch figures between Otter Lake and Durango apatite have been compared by calculation of percent differences (difference in diameter/average of both diameters) for different orientations. A two-fold greater percent difference was observed between (10-11) etch figures than between (10-10) etch figures measured for Dpar determination. Since kinetic proxy measurements compare relative lengths of etch figures among different apatite grains, the comparison of etch figures on the (10-11) growth face in addition to the (10-10) growth face may significantly increase the resolution of kinetic proxies used in fission track dating. Latent (i.e., unetched) tracks were observed using atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). “Hillocks” resulting from irradiation are reported on the surface of unetched apatite. Hillocks have diameters in the range 15-30 nm and heights in the range 3-7 nm, and size dimensions show a systematic dependence on apatite composition and orientation. This dependence is confirmed by SAXS measurements. In addition, etch figure sizes show a similar trend as latent tracks, suggesting that damage production and etching are controlled by similar crystallographic parameters. Lastly, development of microscopic streaks was observed on surfaces of apatite heated to temperatures above the track-annealing threshold and subsequently etched. These features are approximately 2-20 µm in length, and their origin is unknown. Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology, Department of Earth and Environmental Sciences 2012-09-05T00:00:00Z http://hdl.handle.net/2027.42/97758 Characterization of the Interactions between Shale Cementation and Fracture Pump Resistance, and the Subsequent Contributions to Air Emissions from Eagleford Shale Hydraulic Fracturing Operations Presley, Kathleen Natural gas is the fastest growing primary energy fuel, with demand increasimg more rapidly than any other energy source. With advances in horizontal drilling and hydraulic fracturing, shale formations have become an economically viable source for oil and natural gas. The Texas’ Eagleford shale has long been known as the source rock for Austin Chalk and the giant East Texas field, and is now being considered as a formidable self-sourced oil and gas reservoir with increasing economical potential to extract the shale’s oil and gas. However, the reservoir itself is not vertically homogenous between the upper and lower members. During hydraulic fracturing, the differences in petrofacies cause the fracturing engine pumps to work at higher load factors in 2 the more tightly cemented, clay-rich, layers. Fracture pump engines operate at ten to twelve percent higher load factor when fracturing shale gas formations without carbonate intersititial layering. As fracturing pump engines operate at a load factor higher than forty percent, the engines consume exponentially increasing amounts of diesel fuel. The augmentation of fuel consumption generates higher emissions of nitrous oxide, carbon dioxide and carbon monoxide. Calculations performed using industry and regulatory air emissions modeling scenarios reveals that emissions are most affected by load factor resulting from formational cementation, and not engine horsepower, repetitions per minute, or hours in operation. Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology or Earth and Environmental Sciences, Department of Earth and Environmental Sciences 2013-01-16T00:00:00Z http://hdl.handle.net/2027.42/97757 No Evidence for a Deglacial Intermediate Water Δ14C Anomaly in the Southwest Atlantic Sortor, Rachel The last deglaciation was characterized by an increase in atmospheric pCO2 and decrease in atmospheric radiocarbon activity. One hypothesis is that these changes were due to out-gassing of 14C-depleted carbon from the abyssal ocean. Reconstructions of foraminiferal Δ14C from the eastern tropical Pacific, Arabian Sea, and high latitude North Atlantic show that severe depletions in 14C occurred at intermediate water depths during the last deglaciation. It has been suggested that 14C-depleted water from the abyss upwelled in the Southern Ocean and was then carried by Antarctic Intermediate Water (AAIW) to these sites. However, locations in the South Pacific in the direct path of modern-day AAIW do not exhibit the Δ14C excursion and therefore cast doubt upon the AAIW mechanism (De Pol-Holz et al., 2010; Rose et al., 2010). Here we evaluate whether or not a deglacial 14C anomaly occurred at intermediate depths in the Southwest Atlantic. We find that the deglacial benthic Δ14C trend at our site is similar to the atmospheric Δ14C trend. Our results are also largely consistent with results from U/Th-dated corals at shallower water depths on the Brazil Margin (Mangini et al., 2010). We find no evidence in the southwestern Atlantic of a ~300‰decrease in intermediate water Δ14C from 18 to 14 kyr BP like that observed in the eastern tropical Pacific (Marchitto et al., 2007). When our results are paired with those from the South Pacific, it appears AAIW did not carry a highly 14C-depleted signal during the deglaciation. Another source of carbon is apparently required to explain the intermediate-depth Δ14C anomalies in the North Atlantic, Indian, and Pacific Oceans. Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology, Department of Earth and Environmental Sciences 2012-05-29T00:00:00Z http://hdl.handle.net/2027.42/97756 A New Paleothermometer for Forest Paleosols and its Implications for Cenozoic Climate Gallagher, Timothy Climate is a primary control on the chemical composition of paleosols, making them a potentially extensive archive applicable to problems ranging from paleoclimate reconstruction to paleoaltimetry. However, the development of an effective, widely-applicable paleosol temperature proxy has remained elusive. This is attributable to the fact that various soil orders behave differently due to their respective physical and chemical properties. Therefore, by focusing on an individual order or a subset of the twelve soil orders whose members exhibit similar process behavior, a better constrained paleothermometer can be constructed. Soil chemistry data were compiled for 158 modern soils in order to derive a new paleosol paleothermometry relationship between mean annual temperature and a paleosol weathering index (PWI) that is based on the relative loss of major cations (Na, Mg, K, Ca) from soil B horizons. The new paleothermometer can be applied to clay-rich paleosols that originally formed under forest vegetation, including Inceptisols, Alfisols, and Ultisols, and halves the uncertainty relative to previous approaches. A case study using Cenozoic paleosols from Oregon shows that paleotemperatures produced with this new proxy compare favorably with paleobotanical temperature estimates. Global climatic events are also evident in the Oregon paleosol record, 1 of 28 including a 2.8 °C drop across the Eocene-Oligocene transition comparable to marine records, and a Neogene peak temperature during the Mid-Miocene Climatic Optimum. Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology, Department of Earth and Environmental Sciences 2013-05-17T00:00:00Z