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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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Phase I assessments of naturally occurring asbestos; a case study in El Dorado County
One of the significant geologic problems a registered geologist must learn to identify and mitigate is the geologic hazard of naturally-occurring asbestos. In regions of California underlain by serpentine rocks, chrysotile and often actinolite asbestiform fibers are commonly present in the bedrock at Sites under development. The environmental assessment of the Site, which is usually conducted by a registered geologist, produces guidelines, which are subsequently recommended to the contractor/developer for mitigating the potential risks that are generated geologically. Naturally-occurring asbestosis a potential geologic risk which is highly regulated through standards set by multiple Federal, State, and local regulatory organizations. These standards are set to protect the workers and the public during and after development. This report details the geologic and regulatory background of naturally-occurring asbestos, and outlines, as a case study, the procedure commonly used for documenting, verifying, and then dealing with the presence of asbestos at a project Site., San Diego State University
Physical and chemical properties of the Winterhaen Metavolcanic Member: Implications for igneous petrogenesis
Lying in southeastern California between Indian Pass and Picacho State Recreation Area is the ~440 m thick, Jurassic Winterhaven Formation. This unit has been metamorphosed to chlorite-grade greenschist facies and can be divided into a lower metavolcanic member and an upper metasedimentary member. The Winterhaven Metavolcanic Member can be subdivided on the basis of texture into coarse grained (Group 1) and fine grained (Group 2) variants. Group 1 samples are found only east of Little Picacho Wash, while west of this divide 8 out of 10 samples belong to Group 2, while the remaining 2 belong to Group 1. The spatial variation in grain size suggests that lava within the Winterhaven may have flowed east to west. In this study, the physical and chemical properties of each major textural variant were evaluated. The LREE and HREE depletion patterns for both groups indicate small degrees of partial melting within the garnet-stability field. The consistency of the REE distribution patterns suggests that all samples came from the same general source. The REE distribution patterns of the Winterhaven Metavolcanic Member and Miocene Quechan volcanics are almost identical, both exhibiting LREE enrichment and HREE depletion patterns. However, samples of the Winterhaven Formation consistently plot above those analyzed from the Quechan volcanics. Such a relationship suggests that the subcontinental crustal mantle may have been depleted in the REE during the petrogenesis of the Winterhaven Formation or the Quechan volcanics involved a lower degree of partial melting during their petrogenesis., San Diego State University
Physical properties and clay mineralogy of the northern imbricate, Copper Basin Fault, SE California
Located south of Picacho State Recreation Area is the Copper Basin fault. The fault generally strikes ~EW and dips 56° S placing Jurassic (~161 Ma) gneiss over ~25 Ma Quechan volcanics. As it is traced westward, it breaks up into at least two imbricates. Here I focus on the most northward imbricate. At the study location, the fault zone of the hanging wall of the northern imbricate can be subdivided into a fault core and damage zone. Fragmentation and grain size comminution increases toward the fault core, and through three distinctive textural zones of the damage zone. The latter features are referred to, from outermost to the fault core, as damage zones 1, 2, and 3. Grain density systematically decreases toward the fault core, while bulk density remains relatively constant throughout the fault zone. Similar to grain density, porosity also decreases toward the fault core. Three samples were evaluated for their clay mineralogy. The < 2 micron fraction analyzed from damage zone 2 is composed of montmorillonitic smectite. In contrast, the < 2 micron fraction evaluated from the innermost part of damage zone 3 is composed of montmorillonitic smectite and calcite. A sample analyzed from the fault core contained significant amounts of calcite and montmorillonitic smectite. In addition, the sample from the fault core also contained mixed-layer illite/smectite (I/S) with 10% illite. These data as a whole, suggest that fluids were focused through the fault core relative to the adjacent damage zone, and implies that significant mass redistribution may have occurred within the core., San Diego State University
Physical significance of the TAR parameter alpha
A preliminary study of the properties of the TAR parameter alpha was done to attempt to determine the dependence of alpha on physical properties of the marine section it operates on. A certain correlation was found between alpha and water depth. Correlations were also found between alpha and the depth of basement. Thus it was found that alpha varies inversely with water depth because of the increase in sedimentary section, or depth of basement, seaward. An inverse relationship holds down the continental slope since the section is thinning here. On offshore cross-sections studied, alpha also varied inversely as to the two way time to the depth of basement. This variance of alpha with the length of sedimentary data on records was attributed to properties of the GAGC system. Shorter sections cause the GAGC to level off earlier and thus vary the time at which T2 occurs. With T2 occurring at earlier times on shorter sections, the interval T2-T1 decreases, thereby increasing the value of alpha., San Diego State University
Point counting scanned chemically-stained slabs and thin sections: are results statistically similar?
In order to assess whether or not point counting scanned images of chemically stained rock slabs was a reliable method for determining the modal mineralogy of a rock specimen, nine samples of the Oriflamme Canyon granodiorite were collected from a single outcrop. From each specimen an ~2-3 cm thick slab was cut. One side of the slab was polished to a smooth surface using a 600 grit polishing compound. This surface was then etched in hydroflouric acid, and then was stained to distinguish k-feldspar from plagioclase. In order to prevent deterioration a clear silicone coat was applied to the stained surface.An image of the silcone coated surface was then scanned into a digital image file at 400 dpi using Adobe Photoshop. A 0.25 cm by 0.25 cm grid was superimposed on the scanned image, and 200 points were counted in each image. Points were assigned plagioclase, k-feldspar, quartz, or biotite. Unfortunately, in 7 specimens the staining procedure produced in some areas a blurring of the yellow and pink colors used to distinguish k-feldspar from plagioclase respectivly. As a result of this problem, distinguishing plagioclase from k-feldspar based on color everywhere in the image of the stained slab became impractical. Hence, plagioclase and k-feldspar were combined into a single feldspar category. The results of point counting the 9 stained slabs yielded an average composition of 21 % quartz, 61 % feldspar, and 18% biotite. Mr. P. Jeffers counted 200 points in unstained thin sections made from each of the 9 samples from which slabs were cut. He assigned points to quartz, feldspar, or biotite. The results of his work indicated an average composition of 17% quartz, 70% feldspar, and 14% biotite. In order to assess whether or not his results are statistically different from those obtained from point counting images of stained slabs I used the difference in means Student's t test. My null hypothesis, H0, was that there is no difference in the means determined from the two different methods used during this study (i.e., X1 -X2 = o ). My alternative hypothesis, Ha, was that the two means were not equal (i.e., X1 - 'F' O ). Assuming equal variances, the 95% confidence interval for the difference in means for quartz, feldspar, and biotite was calculated. If this interval included zero, then I concluded that there was enough statistical evidence to reject H0• The results of the statistical work indicated that there is not enough evidence to reject H0 in favor of Ha for quartz and biotite. However, the data also indicate that Ho should be rejected in favor of Ha for feldspar. Though this result is difficult to interpret, it may simply be due to the difficulty of distinguishing untwined feldspar from quartz in unstained thin sections. Though there is clearly a need for more work on the subject of this thesis, the results of my work point to the potential usefulness of point counting scanned images to determine the modal compositions of rock specimens., San Diego State University
Polyphase deformation of an early Paleozoic seamount
Petrological and geochemical work indicates that the post­Cambrian and pre-Upper Devonian Bullpen Lake sequence represents a fault-bounded fragment of a seamount or ocean island. However, the structural framework of the Bullpen Lake sequence 1s not well known. Hence, a detailed structural investigation was undertaken. The results of detailed mapping indicate that the Bullpen Lake sequence was involved in two phases of deformation. During D1, a single northwest striking and northeast dipping reverse fault formed in association with a set of closed westward verging asymmetric folds (i.e., F1). Northwest striking and northeast dipping S1 cleavage parallels the axial surfaces of F 1 folds, and is locally well developed. NE trending F2 folds and crenulations (S2) deform D1 structures and are the result of D2 deformation. D 1 structures probably formed pnor to the deposition of the unconformably overlying Upper Devonian Grizzly and Sierra Buttes Formations. These formations form a north-striking homocline that dips about 45° to the northeast. Restoring the Grizzly and Sierra Buttes Formations to the horizontal results in F1 folds with 30° NE dips and D1 reverse faults with 15°NE dips. Such a result is consistent with the idea that the Bullpen Lake sequence was accreted as part of a large subduction complex sometime during the early Paleozoic. D 2 structures are not well understood at this time. However, they appear to be spatially related to the contact metamorphic aureole of the Emigrant Gap composite pluton, and thus may have been produced during its emplacement in the Middle Jurassic., San Diego State University
Potassic olivine basalt of the Alverson Formation, Superstition Mountain, Imperial County, California
Miocene volcanic rocks interbedded with nonmarine fluvial deposits are present at scattered localities in the western Salton Trough region. At Superstition Mountain the volcanic rocks are mapped as Alverson Formation and comprise an approximately 70 meter thick section of ~5-7 separate olivine basalt flows interbedded with the Split Mountain Formation. Individual flows are massive and platy, fractured in the lower part with strongly amygdaloidal flow tops. Samples were collected from the basal parts of all of the flows for petrolographic and whole rock X-ray fluorescence determination of major and trace element concentrations. The rocks are porphyritic olivine basalt with euhedral olivine microphenocrysts and holocrystalline plagioclase-pyroxene-Fe-Ti oxide groundmass. The alteration of the rocks is quite variable from very fresh rock with virtually 100% fresh olivine to rocks where the olivine has been completely replaced by secondary minerals. These rocks are mildly alkalic, high potassic basalts that fall into a rare series of basalt called shoshonite. These highly potassic rocks reflect unusual mantle compositions related to the tectonic plate reorganization from subduction to the establishment of the San Andreas Fault system during the Miocene., San Diego State University
Precision and accuracy of major element XRF data, geochemistry laboratory, San Diego State University
In the spring of 2002, a new XRF instrument was installed, and a new sample preparation technique was established in the Geochemical Laboratory at San Diego State University (SDSU). Precisions and accuracy of data obtained from the new instrument and sample preparation technique are herein documented. Five replicates of a powder derived from one of sample collected from the C horizon of a weathering profile developed on the Cretaceous La Posta pluton were analyzed. The results of these replicates indicate that precisions of the sample preparation procedure, expressed as the 95% confidence interval about the mean, for each major element is as follows: SiO2 = ± 0.21, AhO3 = ± 0.05, TiO2 = ± 0.003, Fe2O3 = ± 0.01, CaO = ± 0.01, NaO = ± 0.01, K2O = ± 0.005, MgO = ± 0.009, MnO = ± 0.0004, P2O5 = ± 0.0007. The precision of the new instrument was determined by how well values were reproduced during a 10 day period. These results are as follows: SiO2 = ± 0.06, AhO3 = ± 0.02, TiO2 = ± 0.001, Fe2O3 = ± 0.004, CaO = ± 0.005, NaO = ± 0.005, K2O = ± 0.002, MgO = ± 0.002, MnO = ± 0.0002, P2O5 = ± 0.0003. Using these estimates for precision, analysis of GSP-1, a commonly used standard for granodiorite, resulted in the the following estimate of its composition: SiO2 = 67.53 ± 0.06, AhO3 = 15.1 ± 0.02, TiO2 = 0.66 ± 0.001, Fe2O3 = 4.28 ± 0.004, CaO = 2.01 ± 0.005, NaO = 2.74 ± 0.005, K2O = 5.52 ± 0.002, MgO = 0.97 ± 0.002, MnO = 0.04 ± 0.0001, P2O5 = 0.28 ± 0.0003. These values are close or overlap with the expected values of SiO2 = 67.22 ± 0.04, AhO3 = 15.1 ± 0.05, TiO2 = 0.65 ± 0.005, Fe2O3 = 4.29 ± 0.02, Cao = 2.07 ± 0.007, NaO = 2.8 ± 0.02, K2O = 5.51 ± 0.01, MgO = 0.96 ± 0.01, MnO = 0.04 ± 0.001, P2O5 = 0.28 ± 0.004. The results ofmy study therefore suggest that data derived from the laboratory at SDSU are precise and relatively accurate., San Diego State University
Predation patterns of two predatory gastropods: muricidae and naticidae
Analysis of predation in modern forms can serve to elucidate past instances of predation in the fossil record. Comparisons of predation by modern muricid and naticid gastropods can reveal ecological patterns of prey selection in these groups. Unlike other forms of predation, drilling predation leaves evidence in the fossil record. Muricids and naticids feed on other shelled mollusks by boring holes with their radulae. Muricid and naticid drill holes are distinguishable. The purpose of this study is to analyze patterns of drill­holes in prey species between muricids and naticids, and make inferences concerning prey selection in both groups. Assumptions by previous researchers that naticids and muricids do not interact are largely based on the difference in environmental preference and prey selection. The observation that naticids and muricids prey upon each other indicates that they do sometimes share environment. Several marine gastropods sampled from Torrey Pines Beach, San Diego, California were analyzed to observe differences in prey selection between Muricidae and Naticidae. Approximately 400 specimens representing various conid, olivid, and muricid prey were examined for muricid and naticid drill holes. All specimens were studied post-mortem. Drill holes were classified into two categories: successful drilling by muricids or naticids. Counts of each type were analyzed using Chi-square tests to determine significant distinctions in prey selection between prey species and prey morphology. The chi-square results revealed that muricids attacked Oliva more than would be expected under a random model and that Oliva was the only gastropod prey regularly attacked by both muricid and naticid. A morphometric comparison of shape coordinates of Oliva, using the triangulation method, scales specimens to a 1:1 axis. A Hotelling's T-squared test displayed a marginal significance (p=0.062) in the difference in morphology of Oliva preferred by the two predatory gastropods. Although naticids and muricids occasionally take the same prey, the morphology of the prey is significantly different depending upon the predator. The predators aren't interacting competitively, yet they are sometimes found in the same environment. Muricids and naticids interact by preying on one other although they do not have a significant preference for the other predator., San Diego State University
Prior knowledge of earth sciences and earthquakes: a study of k-12 teachers
Since the adoption of the 1998 California State Science Standards, K-12 teachers are now required to teach geology in the classroom, which is often a completely new subject to the teachers and kids. A study was conducted to asess how much prior knowledge teachers possess about Earth Sciences and earthquakes in particular. A survey was administered to 68 K-12 teachers questioning them about earthquakes and Earth Science related topics to expose the levels of scientific sophistication in their geoscience knowledge on this subject. It contained 9 short answer questions, and a section about personal experiences teaching Earth Sciences. The data suggested that teachers hold some scientific knowledge but the majority needs more professional development, as indicated by the low average test score of 48% for the 9 questions. When asked for an explanation of what causes earthquakes typical findings were subjects with low scores identified relevant scientific vocabulary but were unable to define the terms. As the sophistication of open-ended answers increased, the answers scored higher on our rubric. Most teachers scored 3 or below on the open ended questions, with only approximately 15% of our subjects showing sophisticated knowledge. Possible reasons for these poor scores are that 75% of teachers have never taught a unit on earthquakes before, and only 46% of teachers regularly teach earth sciences in the classroom. The results of this study can help us better focus on the need to educate teachers and improve their ability to teach in the classroom., San Diego State University
Provenance analysis of Cenomanian valle conglomerates, Northern Vizcaino Peninsula, Baja California Sur, Mexico
Cretaceous marine forearc basin strata exposed in the northwestern Vizcaino Peninsula of west-central Baja California record an abrupt change in paleogeography at -99 Ma, close to the Albian-Cenomanian boundary. The Albian Los Cbapunes Formation comprises turbiditic mudstone and minor sandstone interpreted as deep marine basin-plain deposits. These rocks are overlain disconformably by early to mid-Cenomanian boulder-cobble conglomerates with interbedded sandstone turbites that records active faulting and uplift. Large clast sizes (abundant meter-sized clasts), angularity of matrix granules, fluid escape structures in sandstone, and slumping in thin-bedded intervals indicate derivation from a proximal source to the north and slumping in thin-bedded intervals indicate dervation from a proximal source to the north and rapid deposition on submarine slopes. Volcanic rocks make up -84% of the clast population with no major variability detected at 5 sites where counts were made. The volcanics are mainly intermediate to silicic composition. Potassium-feldspar rich granitoids make up most of the remainder of the clasts with subordinant sedimentary and metamorphic clasts including quartzite. Magnetic susceptibility values of 499 granitoid clasts measured with a Geoinstruments JH-8 susceptibility meter vary widely over four orders of magnitude; these values are consistent with a mixed western/eastern zone Peninsular Ranges batholith source, and a potential unknown source. A biotite granodiorite clast yielded a concordant 135-140 Ma zircon U/Pb crystallization age. The zircon age and the dominance of K-rich graoitoids, are inconsistent with a PRB source for the Cenomanian conglomerates. The Vizcaino arc and ophiolite basement is also a possible source area, but the presence of K-rich granitoids and quartzites clasts are also inconsistent with the local basement lithologies., San Diego State University
Provenance and tectonic implications of greenstone clasts in Eocene (?) conglomerates, Picacho State Recreation Area, SE California
A. Yin proposed that the Chocolate Mountain anticlinorium formed ~65-50 Ma as a fault-bend fold lying above the low angle trajectory of the subducting Farallon plate. In contrast, C. Jacobson and colleagues based on thermochronological data have argued that the anticlinorium can be no older than about 24 Ma. This latter interpretation is supported by recent provenance studies by G.H. Girty and students at San Diego State University that indicate the Chocolate Mountain anticlinorium was growing during the early to middle Miocene. However, little work has been undertaken regarding probable Eocene(?) gravels unconformably overlying the Jurassic Winterhaven Formation, and stratigraphically underlying the OligoceneQuechan volcanics. These gravels contain abundant rounded pebble- and cobble-sized clasts of metavolcanic rock that superficially resemble rocks in the Winterhaven Formation. The purpose of this thesis is to assess whether or not the Eocene (?) gravels were deposited during initial growth of the Chocolate Mountains anticlinorium, or alternatively were derived from a more distant source. In order to build a geochemical database of possible metavolcanic source rocks in the Winterhaven Formation, I first collected and chemically analyzed a suite of 14 representative samples from the Winterhaven Formation, and then collected and analyzed a suite of 8 volcanic (greenstone) clasts from the Eocene(?) gravels. All samples were analyzed for major and trace elements using standard XRF procedures. Thin section study revealed that all samples have been metamorphosed to the greenschist facies. Hence, the Ti02/Zr versus NbN magma series discrimination diagram was used toclassify each analyzed specimen. The results of this phase of my work indicated that the metavolcanic rocks in the Winterhaven Formation vary from basalt to basalt-andesite to trachyte. On a bivariate plot of [Fe2O3 + MgO] versus Sc, analyzed samples from the Winterhaven Formation form a crude linear array with basaltic specimens consistently having the highest Sc and [Fe2O3 + MgO] values and trachytes the lowest, while samples of basalt-andesite form an intermediate variety. Such trends suggest that the suite of analyzed samples from the Winterhaven Formation may represent a related series derived from a common magma through crystal fractionation of a mafic phase such as amphibole and/or pyroxene. In contrast to samples from the Winterhaven Formation, the seven greenstone clasts plot about the boundary separating basalt and andesite on the TiO2/Zr versus Nb/Y magma series discrimination diagram, and one sample plots well within the basalt­andesite field. For a given Sc value, the greenstone clasts display higher [Fe2Q3 + MgO] values than do samples analyzed form the Winterhaven Formation. These data suggest that the greenstone clasts in the Eocene (?) gravels were not derived from the Winterhaven Formation, and imply further that they may have been derived from a distant source. In short, the Chocolate Mountains anticlinoriurn was not a significant feature at the Earth's surface during their deposition., San Diego State University