Collection Description

The Department of Geological Sciences has a long-standing Senior Thesis research option for the B.S. Degree which involves a written thesis, and a public oral presentation done under the supervision of a faculty member. These independent research projects typically involve field work and laboratory analyses of samples, but can also include laboratory-based experimental projects, numerical modeling of geologic phenomena and literature reviews. Senior theses are kept in the permanent collection of the Malcolm A. Love Library on the SDSU campus.

Authors hold full copyright ownership of their original works. Please contact the repository manager at digital@sdsu.edu for any further questions.

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Assessing the precision and accuracy of trace element analysis in the geochemical labratory, San Diego State University
In 1999, A.L. Fortin studied a weathering profile in the large-biotite facies of the Cretaceous La Posta Pluton. The weathering profile was subdivided into horizons R, C, and A. A suite of samples from each horizon was analyzed for trace elements using standard XRF methods at the GeoAnalytical Laboratory of Washington State University. A similar suite of samples from the same location was collected in Spring 2002 as part of a larger study focused on assessing chemical patterns associated with weathering in different microclimatic belts of the Peninsular Ranges. For this study, 5 samples from the R horizon, 4 from the C horizon, and 7 from the A horizon were analyzed using a newly installed XRF instrument and a newly established pressed-powder technique at SDSU. Five replicates of powder derived from one specimen collected from the R horizon were used to assess the precision of the new XRF procedures and instrument at SDSU. The results of replicate analyses indicate the following precisions, expressed as the 95% confidence interval about the mean, for 8 trace elements analyzed during this study. Zr =± 5.2, Sr =± 1.8, Ba =± 10.2, Rb =± 1. 1, Y = ± 0.7, Sc = ±1. 1, Th =± 0.0 (5 replicates reproduced the value of 6 ppm), Ni = ±1.5. Unfortunately, the USGS does not currently know how many samples went into compiling the recommended composition of G-2, the standard that is close to the composition of samples analyzed during this study. However, they do report the lcr uncertainty. The expected values and lcr uncertainties for G-2 are Zr = 309 ± 35, Sr = 478±2,Ba = 1882±23,Rb = 170±3, Y = 11 ±2, Sc = 3.5 ±0.4, Th = 24.7±2,Ni = 0 ± 0.0. Results obtained during this study indicate the following trace element composition and lcr uncertainties for G-2: Zr = 307.8 ± 4.1, Sr = 480.5 ± 1.4, Ba =1875.1 ± 8.2, Rb = 172.6±0.9,Y = 11.1 ± 0.5, Sc = 4.4 ± 0.9, Th = 23.5 ± 0.0, Ni = 0 ± 0.0. As a final check of the precision of the newly established methods and instrument, a comparison of the results obtained by Fortin from WSU and those obtained during this study were made. These results indicate that data obtained from the SDSU lab are comparable to those obtained from the WSU laboratory. Hence, the laboratory at SDSU appears to provide precise and relatively accurate trace element analysis., San Diego State University
Assessing the presence of pulverization textures along the Buck Ridge Fault, NE of Anza, California: A reconnaissance study
Pulverized rocks have been identified in meteorite impacts and occur along crustal scale faults primarily in igneous and metamorphic rocks (Dor et al., 2006; Mitchell et al., 2011; Aben et al. 2016). In addition, they occur to a lesser extent in both clastic and carbonate sedimentary rocks (Dor et al., 2009; Aben et al., 2017). They also have been identified in meteorite impacts (Key and Schultz, 2011). In the field, a rock is considered pulverized if all the crystals in a hand sample yield a powdery rock–flour texture when pressed by hand (Dor et al., 2006). Under the microscope this unique texture resembles a jig-saw puzzle, and is characterized by sub-grain fracturing of wallrock to the micron to tens of microns scale with little to no grain rotation or evidence of shear. Along the Clark segment of the San Jacinto Fault, pulverized rocks occur in 10-15 m wide damage zones. In such settings, pulverized rocks occur dominantly as leucocratic igneous material within high grade paragneisses (Peppard et al., 2018). In contrast, pulverized rocks have not been identified along other segments of the San Jacinto fault zone, as for example the Buck Ridge or Coyote Creek faults. Hence, I undertook a reconnaissance study aimed at assessing the presence or absence of pulverized rocks along the Buck Ridge fault. The Buck Ridge fault lies north of the Clark strand, and merges with the Clark NE of Anza (Figure 1). It transects high-grade metamorphic rocks of the pre-mid Cretaceous Burnt Valley Complex and Pleistocene alluvial sediments of the Bautista Formation. This paper will document: (1) the characteristic properties of alluvial sandstones of the Bautista Formation outside the Buck Ridge fault zone, (2) how those properties are modified within the fault zone, outside the Buck Ridge fault zone, (2) how those properties are modified within the fault zone, pulverization process. The results of work reported here suggest that pulverization, at the grain scale, is restricted to a broad ~25 meter thick zone of damaged rock along the Buck Ridge fault, and to the growing body of data supporting the idea that pulverization is another key signature of seismogenically active faults., San Diego State University
Assessing the role of element mobility within the structural aureole of the la posta, Peninsular Ranges, Southern California
The 95 Ma La Posta pluton represents the largest pluton mapped within the Peninsular Ranges batholith, southern California. It intrudes a wide variety of rocks, including the Late Jurassic Cuyamaca Reservoir gneiss. In order to assess element mobility/immobility patterns within the structural aureole of the La Posta pluton, nine samples of the Cuyamaca Reservoir gneiss were collected from outside of the structural aureole and four samples were collected from within the structural aureole. Each sample was analyzed for major elements and was studied previously by C. N. Thomson as part of here Masters thesis at San Diego State University. Because of the constant-sum format of geochemical data, they are not useful m their conventional form for assessmg the chemical changes attending the metamorphic transformation of rocks outside and inside the structural aureole of the La Posta pluton. Hence, major element data were first transformed to a continuous variable format via a log10 transformation utilizing Ti as an immobile normalizing factor. Standard descriptive statistics were then calculated, and the differences m means and associated 95 % confidence limits were determined. The hypothesis, H0 : µ0-uj = 0 was tested utilizing the student-t test. The results of the student-t test indicated that all major elements, with the exception of MgO and K20, are depleted within the structural aureole of the La Posta pluton. Such a conclusion can be explained as the result of (1) metasomatic changes associated with the development of the structural aureole, and/or (2) by chemical changes associated with mineralogical differences m the protolith of the Cuyamaca Reservoir gneiss. However, the gneissosity charateristic of the Cuyamaca Reservoir gneiss is more intensely developed within the structural aureole than in areas that were beyond the influence of the La Posta pluton. Thus, though my study is limited in context, I conclude that the calculated differences in the mean compositions of the Cuyamaca Reservoir gneiss most likely reflect poorly understood mass exchange and/or volume loss processes operating within the aureole during the emplacement of the La Posta pluton., San Diego State University
Assessing ß and the power of the Student's t test: Implications for elemental mass change during the Barrovian metamorphism of the Devonian Littleton Formation, New Hampshire.
There are currently two widely opposing interpretations of how Barrovian metamorphism affected elemental mass in the Littleton Formation, New Hampshire. Shaw (1954, 1956) and Moss and others (1995, 1996) argued that no elemental mass, other than volatile phases, changed during prograde metamorphism of mudstones in the Littleton Formation. In contrast, Ague (1994, 1996) concluded that an apparent loss of silica mass may have accompanied prograde metamorphism. Shaw (1954, 1956), Ague (1996) and Moss and others (1995, 1996) in their statistical treatment of the chemistry of the Littleton Formation controlled for Type I errors setting a.=().05 as the probability of rejecting the null hypothesis, H0, that no elemental mass change occurred during metamorphism, when it is true. In setting a. to 0.05 these authors were willing to take the chance that they might be wrong 5 times out of a 100 if they rejected H0• However, none of the above authors considered Type II errors, which would have involved controlling for ß, the probability of accepting H0 when it is false. Thus conclusions based on accepting H0 may have been in error. An analysis of Type II errors showed that acceptance of H0 carries with it an unacceptably high risk of being in error. Specifically for the chemical data derived from the Littleton Formation analysis of Type II errors shows that the Student's t test provides little guidance as to the question of whether or not elemental mass for Si, Ti, Fe, Mg, K, Na, P, Ba, Ga, Zn, Th, Nb, Y, Hf, Ta, U, Rb, La, Ce, Nd, Sm, Eu, Gd, Tb, Yb, Lu, Sc, As, B, Br, Co, Se, or Sn changed during medium-grade metamorphism or whether or not elemental mass for Si, Ti, Fe, Mg, K, Na, P, Ni, Cr, V, Ba, Zr, Ga, Zn, Th, Nb, Y, Hf, Ta, U, Rb, Cs, La, Ce, Nd, Sm, Eu, Gd, Tb, Yb, Lu, Sc, As, B, Br, Co, Se, or Sn changed during high-grade metamorphism. Thus, much of the controversy over whether or not silica mass changed during metamorphism of the Littleton Formation may have stemmed from an incomplete understanding of how Type II errors affected acceptance or rejection of H0. In short, the controversy over the Littleton Formation is an excellent example of why geologists should not indiscriminately apply the Student's t test without first controlling for ß., San Diego State University
Assessment of 20 liter nalgene HDPE carboys for the use of USGS oil well produced water sampling
California State Senate Bill 4 of 2013 mandated the State Water Board design and implement groundwater monitoring programs to assess and track the potential interactions between well stimulation methods used to increase oil/gas reservoir permeability and groundwater resources. The USGS was contracted to provide unbiased water chemistry data for groundwater adjacent oil fields and produced water from oil wells. USGS standard sampling procedure requires the use of twenty liter Nalgene carboys to collect produced water at the well head for later processing once the water phase has separated from the oil phase. These carboys are made from High-density polyethylene (HDPE) which is a polyethylene thermoplastic made from petroleum. Within steam flooded oil fields the temperature of the produced water can approach 100 C. The extreme temperatures increase the likelihood of low weight molecular acids (LWOAs) or volatile organic acids (VOCs) desorbing from the HDPE carboy contaminating the sample water. In the experiment nitrogen purged certified organic free blank water was used to simulate produced water. Two Nalgene carboys were filled with blank water: one containing boiled blank water and another containing ambient blank water The carboys were sampled for both LWOAs and VOCs at four separate times starting immediately and ending 90 minutes after the boiling blank water was added, in accordance with USGS procedure. In order to rule out other sources of contamination, a source solution blank for each analyte was also collected. The LWOA samples were then frozen to -60 degrees and shipped on dry ice for analysis, and the VOC’s were collected and placed into refrigerated storage then sent on ice to the lab for analysis. It was discovered that virtually no LWOAs and VOCs were found in any of the samples that were taken from the carboy, regardless of the water temperature or exposure duration. The only exception was the VOC Toluene, a known lab contaminant. Since the concentration in the source solution blanks and the experimental samples were within one order of magnitude it is likely the source of the Toluene was either from the blank water itself or contaminated analyzing lab equipment. In the experiment nitrogen purged certified organic free blank water was used to simulate produced water. Two Nalgene carboys were filled with blank water: one containing boiled blank water and another containing ambient blank water The carboys were sampled for both LWOAs and VOCs at four separate times starting immediately and ending 90 minutes after the boiling blank water was added, in accordance with USGS procedure. In order to rule out other sources of contamination, a source solution blank for each analyte was also collected. The LWOA samples were then frozen to -60 degrees and shipped on dry ice for analysis, and the VOC’s were collected and placed into refrigerated storage then sent on ice to the lab for analysis. It was discovered that virtually no LWOAs and VOCs were found in any of the samples that were taken from the carboy, regardless of the water temperature or exposure duration. The only exception was the VOC Toluene, a known lab contaminant. Since the concentration in the source solution blanks and the experimental samples were within one order of magnitude it is likely the source of the Toluene was either from the blank water itself or contaminated analyzing lab equipment., San Diego State University
Atterberg limits analysis of Black's Beach Landslide 1982
On January 29, 1982 a deep-seated landslide occurred on the coastal bluffs, south of the glider port, in Torrey Pines City Beach. The landslide resulted in the movement of 1.4 million cubic meters of landslide debris. The basal rupture was believed to have occurred at an elevation of approximately 140 feet (depth of 195') within the upper few meters of Ardath Shale. This basal rupture occurredapproximately 90 to 100 feet below the rupture surface of previously recorded landslides. A detailed study of the bluffs at and adjacent to Black's Beach was performed by the San Diego City Parks and Recreation Department as part of general planning for Torrey Pines City Park. The study included a field-mapping program and analysis of stereo-pair aerial photographs. The purpose of their investigation was to map general geologic conditions and prepare a map showing areas of potential danger to the public (Vanderhurst, McCarthy, Hannan 1982). The largest landslides that have occurred in the area of study (Figure 1) are coherent block-glide landslides (Figure 2). This type of landslide is made possible by the presence of a medium of low shear strength, within which slip (basal) surfaces can develop at the sole of slides. Block-glide landslides are characterized by a lack of internal fracturing within the translated blocks. The purpose of this investigation is to use analyses of Atterberg Limits to locate beds/planes of possible weakness, low shear strength, and/or high plasticity within the landslide-prone bluffs., San Diego State University
Blair Valley tonalite; An East-West Magmatic Connection
The Blair Valley tonalite outcrops just north of the La Posta pluton in the eastern zone of the Peninsular Ranges batholith (PRB). It is a 4-km long elongate body of rock that shows strong and steeply dipping foliation as compared to the relatively undeformed hornblende-biotite facies of the La Posta pluton. AU-Pb zircon age of93Ma was determined on a Blair Valley tonalite sample, which makes it essentially the same age as the 94Ma La Posta pluton. Petrographic studies of the Blair Valley tonalite show that it is primarily made up of plagioclase-quartz-biotite-hornblende with minor amounts of sphene-epidote-chlorite and oxide minerals. Comparison between previous petrographic studies of the hornblende-biotite facies of the La Posta pluton and the Blair Valley tonalite show that they are petrographically the same. Geochemical data further suggests that the Blair Valley tonalite is part of the La Posta pluton or at least a La Posta-type pluton. Variation diagrams of nearly all major element data show that the Blair Valley tonalite lies within the same linear trend as that displayed by the La Posta tonalite. An interesting relationship between the Blair Valley tonalite and the La Posta pluton is observed in trace element variation diagrams. In a strontium-silica variation diagram five of the eight samples analyzed plot away at an almost perpendicular angle to the main La Posta trend. A similar yet less obvious pattern is observed with zirconium and rubidium variation diagrams. This pattern suggests that some mixing may have occurred between the La Posta pluton and some other magmatic body. A variation diagram showing all of the PRB geochemical data along with that of the Blair Valley tonalite shows the Blair Valley tonalite merging into the field of older western zone tonalites. This suggests that the Blair Valley tonalite may represent a magmatic mix between the older western zone tonalites and the younger eastern La Posta pluton. Could this relationship represent an east-west magmatic connection in the Peninsular Ranges batholith?, San Diego State University
Bulk Density of the Julian Schist
San Diego State University
Bulk densities of surface rocks in the San Diego metropolitan area
The San Diego area has abundant sedimentary rocks exposed at the surface. Fourteen samples of relatively unweathered sedimentary rocks were collected in order to measure their bulk densities, which is useful in gravity surveys. Bulk densities were obtained using a wax-coated, water-immersion technique. The sample ages range from Quaternary to Cretaceous and the lithologies consist of sandstone and mudstone. The sandstone grain size ranges from very fine to coarse, the roundness from angular to subrounded, and the sorting from poor to well. Most are cemented by calcite, but iron oxides and/or iron oxyhydroxides cement a few and the cement in the others is unknown. The densities of the samples range from 1.75 to 2.35 gm/cc. This range in density is probably due to differences in porosity. On the basis of this assumption, the calculated porosity ranges from 16% to 56%. Samples with angular grains are denser than those with subangular grains, but these are less dense than rocks with subrounded grains. Density shows a general increase from well to poorly sorted rocks. This is typical because the poorer sorting allows smaller grains to fill pore spaces between the larger grains, therefore increasing the density. The density increases slightly from rocks with unknown cement to calcite-cemented rocks. Normally, with increasing geologic time, density increases because of diagenesis. However, the rocks do not show any correlation between density and age. Theoretically, there is no correlation between grain size and density and these samples show none., San Diego State University
Calibrating the onset of weathering in saprock: An initial step
Saprock is that part of the regolith in which more than 20% of the weatherable minerals are chemically or texturally altered. In the Peninsular Ranges of southern California, saprock is a ubiquitous feature of the landscape where remnants of the plutonic bedrock from which it was derived are preserved as corestones beneath the land surface, or as tors extending above it. Though the timing of formation of saprock is problematical, published rock-varnish microlaminations and cosmogenic 36Cl studies suggest that it may, at least locally, be older than 10,500 years and in some cases older than 21,000 years. Hence, it may have originated during the Pleistocene. If so, then temperatures were likely cooler and precipitation was likely much greater during its early formative years. At a site located near Japatul (N32o45’39.89” latitude, W116o40’47.14” longitude), I collected from a single corestone, 4 samples, and from the enclosing saprock 3 large blocks. Thin section observations indicate that the tonalite is comprised of plagioclase, quartz, biotite, and hornblende. Notable is the absence of K-feldspar. Each collected sample was analyzed for its major element chemistry, and bulk and grain density. Using non-central principal component analysis, a linear compositional trend was calculated from p(A)-p(CN)-p(K) compositions derived from the analyzed saprock and corestone samples. In p(A)-p(CN)-p(K) space, the resulting trend extends from the geometric mean of the corestone samples upward through the cluster of saprock samples and then towards the p(A) apex. Principal component 1 explains 94% of the variability of the plotted samples about the linear compositional trend. I then calculated the scale invariant weathering intensity factor, ti for each saprock sample, xi, by orthogonal projection onto the calculated linear trend. For this projection, I used the inner product ti = (xi ⊕ a-1, p)a, where a is the geometric mean of the corestone samples, and p is the perturbation vector derived from the eigen vectors for principal component 1. The average and 95% confidence interval for the t values derived from the saprock samples is 0.12 ± 0.04. The orientation of the linear compositional trend suggests that the production of the saprock from the corestone involved the loss of Ca, Na, and K in approximately equal amounts. In order to test this interpretation I utilized mass balance arguments, and calculated the changes in elemental mass with Al as the framework element. The results of this part of my study indicated that 14 ± 9% of the mass of Ca, 15 ± 2% of the mass of Na, and 14 +10/-9% of the mass of K was lost during the conversion of corestone to saprock. Such observations imply that at the study site plagioclase and biotite (the only mineral in the tonalite containing appreciable K) are weathering at similar rates. In short, in the Peninsular Ranges of southern California, t-values of ~0.1 may indicate that within the regolith fluids have become sufficiently acidic to leach and remove Ca, Na, and K. Work discussed here thus represents the initial step in calibrating the scale invariant weathering intensity factor, t, for tonalitic plutonic rocks in the Peninsular Ranges. Clearly, much work remains to be done., San Diego State University
Campo water budget
A water budget analysis of a portion of the Campo Indian Reservation in southeastern San Diego County was completed for the 1992-1993 year. The objective of this analysis was to determine the specific yield of the study area. Data was collected from local agencies as well as from various reports produced by Golder Associates and Dames and Moore. The computer program Surfer was used to generate contour maps and to determine water volume changes. The program Recharg3 was used to determine monthly recharge values. Excel spreadsheets were created to calculate the water budget and values of specific yield. The water budget was calculated on a monthly basis, a 3-month running average, and on a yearly basis. Calculated specific yield ranged from a low of0.029 to a high of 0.270. Negative specific yield values resulted from the monthly and the 3-month running average. Negative specific yield results indicate that the water budget equation is incorrectly calculating change in volume, likely due to a lag time between recharge and water level response. It was, however, possible to determine non­negative specific yields on a yearly basis for the 1992-1993 year. Specific yields for a year were calculated using maximum runoffs of 15, 20, and 25% in recharge calculations. Specific yields for the year water budget ranged from 0.075 to 0.092 (25% and 15% maximum runoff, respectively)., San Diego State University
Cenozoic faulting on Isla Cerralvo, Baja California Sur, Mexico
The rifting of Baja California away from mainland Mexico began in the late Miocene­ Pliocene when the Pacific-North American plate boundary moved east into the Gulf of California. This plate boundary jump attached the Baja California Peninsula to the Pacific Plate and initiated opening of the Gulf The patterns of faulting, basement denudation, and rift basin evolution preserved on both sides of the Gulf represent the primary record of rifting and are the basis for evaluating different dynamical models for rifting. Isla Cerralvo is located in the lower Gulf of California region just east of La Paz on the Baja California part of the rift margin. It represents the last exposure of land at the edge of the Gulf rift. The island is dominated by Cretaceous granodiorite plutons intruded into quartzofeldspathic schist. Cenozoic normal faults bound the west side of the island and strike ~N20W parallel to the coastline. In the west-central part of the island a down-to-the-west normal fault (La Gringa Fault) was mapped which places a Pliocene(?) fossiliferous sandstone­limestone hanging wall sequence on footwall granodiorite and amphibolite facies schist. Along the southwest coast of the island a higher angle normal fault (Punta Sur fault) paralleling the coast places Pliocene(?) limestone/sandstone terrace deposits and underlying greenschist facies metasedimentary rock against amphibolite facies schist and metaplutonic rock. Recent apatite fission track thermochronology from Isla Cerralvo (Kohn et al., in preparation) yield young cooling ages from Cretaceous basement on the west side of the island ( ~ 7-8 Ma) and much older ages from the east side of the island (~54 Ma). The apatite data reflects a strong contrast in denudation across the island and are consistent with eastwards block tilting of the island in conjunction with mid-Miocene footwall uplift along the La Gringa Fault. Strike and dip of foliation in schist and metaplutonic rock in footwall rocks along the west side of the island consistently strike ~N20°W parallel to the trend of Cenozoic faulting suggesting transposition of fabrics. The thermochronology and structural data suggest that down-to-the-west normal faulting on the west side of Isla Cerralvo may have accommodated substantial dip slip separation. The La Gringa and Punta Sur faults on Isla Cerralvo may correlate to west vergent normal faults along the west side of the Sierra La Gata on mainland Baja across the Cerralvo channel to the south. The La Gringa, Punta Sur and La Gata thus may comprise a single integrated west vergent fault system. The west vergent character of this system contrasts with down-to-the-east vergence along the San Jose del Cabo fault farther south which accommodated ~5-7 kilometers of dip slip separation. The regional pattern of normal faulting along this segment of the Baja California rift margin is consistent with along strike vergence reversal of structures, as documented in the East African Rift zone extensional province and elsewhere., San Diego State University

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