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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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Directivity effect and surface wave comparison of a Hawaii shallow megathrust earthquake
The directivity of an earthquake characterizes the most severe propagation direction of fault rupture. Surface waves are an indication of directivity as they maintain their energy longer than body waves. Using IRIS client station data, surface waves can be plotted with respect to azimuth. This method determines in what direction the surface waves were the strongest, and therefore describes directivity of any specific rupture event. The focus of this project is to determine the directivity of the Mw6.9 shallow thrust earthquake that occurred on May 4, 2018. This earthquake ruptured as a result of volcanic activity at Kilauea volcano and caused a tsunami of 40cm. Shallow thrust earthquakes in Hawaii occur on the basal décollement between the volcano pile and the oceanic crust. These shallow earthquakes occur due to volcanic activity and fault rupture, while deep mantle earthquakes occur due to mass and temperature changes of volcanoes above the mantle. Deep earthquakes have less surface wave energy than those with a shallow depth. It is possible to show this relationship by comparing the surface wave amplitudes for a shallow and a deep rupture event. Thus, comparing the Mw6.9 shallow rupture with a Mw4.9 deep mantle rupture will further demonstration this relationship., San Diego State University
Discovery of quartzites in Cenomanian Valle group conglomerates, Northern Vizcaino Peninsula, Baja California Sur, Meixco
Cenomanian boulder-cobble conglomerate comprises a volumetrically important part of the Valle Group in the northern Vizcaino Peninsula of Baja California Sur. Provenance study of conglomerate clasts yields information about the nature of highland source regions that supplied the detritus. The conglomerates are part of a deep marine sequence of turbiditic deposits that prograded across a basin and plain mudstone-sandstone sequence. The conglomerate clast population is dominated by volcanic and plutonic rocks. Quartzite clasts are a distinctive minor component that make up less than 1% of the clast population. A polarizing microscope was used to characterize eight different quartzite clasts collected from three widely spaced localities. Five of the eight samples have well-preserved sedimentary textures characterized by very well­rounded, moderately to well-sorted, silica cemented quartz grains that comprise nearly 100% of the framework. Quartz exhibits variable degrees of undulose extinction. Very well-rounded detrital zircon and tourmaline are minor components. The remaining three samples are characterized by strongly recrystallized granoblastic quartz fabrics, but very well-rounded detrital zircon and tourmaline indicate a sedimentary origin. Detrital zircon and tourmaline from one sample were studied with a scanning electron microscope to examine surface morphology. The documented presence of mature quartzarenite sandstone clasts in the Valle Group Cenomanian conglomerates requires a continental provenance. Potential sources are prebatholithic wall rocks of the Peninsular Ranges batholith or cratonal sedimentary sequences farther to the east., San Diego State University
Displacement history and affinity of the Truckhaven Fault, Imperial County California - Is this fault part of the West Salton Detachment fault zone or the San Jacinto fault zone?
The Rainbow Rock Quarry is part of the footwall of the Truckhaven Fault and has been a gold and silver mining prospect for over one hundred years. It is situated along the north edge of Wonderstone Wash in the northwestern Seventeen Palms USGS 7.5 minute quadrangle, located in the southeastern section of the active San Andreas Fault system. This region is characterized by seismic activity, continental rifting, volcanism, hydrothermal alteration, rapid sedimentation and active precious metal deposition. The Truckhaven Fault zone strikes ~N65°E and separates a Cretaceous quartz monzonite footwall from Plio-Pleistocene Canebrake Conglomerate and Palm Spring Formation in the hanging wall. Well-developed slickenlines at one locality document sinistral normal slip on the Truckhaven Fault. The fault zone dips southeast and hosts sites of alteration mostly in hanging wall rocks, including gold and silver mineralization and argillization. To the southwest of Rainbow Rock is the source of Wonderstone Wash. The goal of this project was to conduct a field investigation of the area where the Truckhaven Fault strikes into the West Salton Detachment and determine the relationship between these two faults. Several exposures of hydrothermal alteration were observed in this area in addition to reverse faulting and metamorphic amphibolite rocks were studied in thin section to better understand the rocks that may represent the footwall of the West Salton Detachment. By illustrating the architecture of these two faults, we hope to understand the kinematics during their activity, in order to question whether they remain active, or accommodation has been relieved by the San Jacinto Fault system., San Diego State University
Distribution of fine-grained sediments and subsidence in Borrego Valley
By analyzing well logs from 50 locations throughout Borrego Valley, a high percentage of fines were found to be widely distributed in the upper central portion of the valley. In a previous study, ground surface changes of Borrego Valley were observed by lnSAR and found not to be correlated to groundwater level change (Pickard and Mellors, 2005). In this study, well-log fine-grained sediment distributions were used to find any association between areas of subsidence and the amount of fines. It was observed that well locations with high percentages of fines, ranging from 20-87%, corresponded to areas of increasing subsidence at a rate of0.2 cm/yr to 0.4 cm/yr throughout the valley. Clay content was also found to be concentrated in the central portion of the valley, which is characteristic of alluvial fan depositional environments. Well log data and associated cross sections showed that clay content did increase with depths of up to -200 feet below sea level towards the southeastern portion of the study area. Areas that showed lower percentages of clays correlated to areas with less subsidence. In contrast, the areas that contained high values of clay content and were not in vicinity of subsidence, as observed by lnSAR, primarily had clays in the lower portion of the aquifer, which would not be dewatered by the dropping water table., San Diego State University
Distribution of tracer in injection boreholes in a heterogeneous aquifer
The distribution of dye tracer immediately after injection into a heterogeneous aquifer under pumping and non-pumping conditions was studied. The tests were conducted on an alluvial aquifer adjacent to the Sweetwater River in Bonita, CA. Borehole induction and geologic logging show the site to be vertically heterogeneous. The upper 28 ft of the aquifer consists of sands overlying a 3 ft thick clay layer. Below this clay layer, there are more sands with gravel layers at 52-54 ft and 60-64 ft. Two injection pulses occurred under pumping conditions. The production well was pumped at a constant rate of 148 gpm. In the first tracer injection under pumping conditions, iodide was injected into MW2A and MW2B, while rhodamine WT was injected into MW2A. In the second tracer injection under pumping conditions, fluorescein and rhodamine WT was injected into MW2B, while rhodamine WT was injected into MW2A. Under non-pumping conditions, rhodamine WT was injected into both MW2A and MW2B. It was seen that a distinct vertical stratification of the tracers occurred under pumping conditions, which is related to the natural gradient and higher flow rate though the most permeable layer in each borehole. Under non-pumping conditions, this distinct stratification did not occur, and no trends of tracer distribution within a borehole was observed. The fundamental implication of this study emphasizes the importance of measuring tracer concentration at several depths within a borehole during a tracer test., San Diego State University
Do the QFL and chemical-based provenance-discrimination models yield internally consistent results when applied to sandstone turbidites and associated mudstones
The post-Cambrian and pre-Upper Devonian Shoo Fly Complex 1s interpreted to contain the remnants of an early to middle Paleozoic subduction system. It contains the Culbertson Lake allochthon, which inturn includes the sandstone and mudstone dominated Poison Canyon and Red Hill units. Quartz-rich (>80% Q) sandstone samples from the Poison Canyon and the Red Hill units were collected and point counted by previous investigators. This and other work indicated that sand-sized detritus within the Shoo Fly Complex was derived from a transitional to continental interior provenance. In order to assess whether or not the chemically-based provenance discrimination model yields results which are internally consistent with the more conventional QFL or petrologically-based discrimination model, 21 mudstone samples were collected and analyzed for major, trace and rare earth elements (REE). Samples from both the Poison Canyon and Red Hill units have Al2°-3/Ti()z values ranging between ~ 18 and ~24, mean Th/U values that are greater than 3.8, and REE patterns characterized by LREE enrichment, negative Eu anomalies, and slightly fractionated HREE patterns. These results are consistent with a source region dominated by old upper continental crust. Thus, the results of this study indicate that both the chemically- and petrologically-based proven ance­discrimination models yield similar interpretations for the source of siliciclastic detritus in the Poison Canyon and Red Hill units. Such a conclusion strengthens the belief that both models generally produce reliable results. However, more work focused on identifying the similarities and dissimilarities in source-rock interpretation produced by the two provenance-discrimination models is clearly needed. Our work has just begun., San Diego State University
Effects of weathering and erosion on magnetic susceptibility of fresh plutonic rock: Cowles Mountain, San Diego
The purpose of this study is to investigate the effects of weathering and erosion on the magnetic susceptibility of fresh plutonic rocks exposed on Cowles Mountain in San Diego, California. Fresh granite outcrops from 17 widely distributed locations within an ~5 km2 area yield consistent in situ magnetic susceptibility values with an average reading of 3027 x 1 o-5. Ten outcrops of weathered granite, which typically have weathering rinds
Effects of weathering on oxide mineralogy and magnetic susceptibility in granite basement outcrops, Cowles Mountain, San Diego
Thin-section petrography shows that plutonic rock that makes up the main part of Cowles Mountain is medium-grained hypidiomorphic hornblende monzogranite. In situ field measurements of magnetic susceptibility for apparently fresh monzogranite outcrops yield values from 17 widely distributed sites that average 3027 x 10-5. Magnetic susceptibility measurements at several of the sites however exhibit great variation; for example at one site, values over an area of ~20 m2 range from -400 x 10-5 up to ~5000 x 10-5. Thin section examination of two samples collected three meters apart with high and low readings, respectively, demonstrate that the great variation in magnetic susceptibility is independent of modal abundance of opaque oxides in the rock. X-ray diffraction analysis of opaque oxides collected with a hand magnet from these two rocks reveal however that the sample with the high magnetic susceptibility reading contains nearly pure magnetite, while the low reading sample contains hematite in addition to magnetite. The difference in opaque oxide mineralogy for these two samples is not detectable in thin section analysis by transmitted light. Results from this study suggest that significant variation in magnetic susceptibility from apparently fresh outcrops may be due to subtle effects of weathering and oxidation of magnetite. Magnetic susceptibility data from weathered outcrops of monzogranite on Cowles Mountain and from locally derived coarse sand on steep slopes of the mountain yield lower average values of 1873 x 10-5 and 638 x 10-5, respectively, which is consistent with progressive lowering of magnetic susceptibility as a result of oxidation of magnetite., San Diego State University
Eolian strata of Holocene Lake Cahuilla analyzed by modified latex peels, Carrizo Wash, Anza-Borrego Desert, California
Bedforms, unconsolidated sediment, and sedimentary rocks of eolian and subaqueous origin have been studied, documented, and compared extensively using photographic methods for decades. With the development and availability of high quality digital cameras, documenting such sedimentary features in the field using photography is but one way of collecting usable data. The obvious limitation of photographic data is the inability to further study these sedimentary features under a stereoscopic microscope. The purpose and goal of this study are to document the occurrence and describe the grain texture and fine structure of eolian ripple-strata that had been deposited near the shoreline of Holocene Lake Cahuilla and are now exposed at Carrizo Wash, Anza-Borrego Desert, southern California. Casts of the two kinds of strata were taken in the field by using a modified latex peel method so that peels could be further studied in a lab. Materials experimented with for making peels in the field included door screen, liquid latex, silicone gel, and cheesecloth; latex paint and natural burlap are readily available, inexpensive, and worked best. Sedimentary structures captured by the modified latex peels include: wind-ripple strata, and indeterminate laminations, convoluted by seismic shaking in a hydroplastic state. The peels were transported easily to the lab and examined with a stereoscopic microscope. In the original study design, the collecting of modified peels was intended for tidal cross-strata in the Eocene Torrey Sandstone for contrasting with eolian cross-strata associated with Pleistocene beach ridge deposits, both exposed in San Diego County, California, and with eolian strata at Carrizo Wash. However, neither the smooth, indurated exposures of Torrey Sandstone nor the poorly exposed Pleistocene eolian cross-strata lent themselves to sampling by peels. Successful observations of the peels from Carrizo Wash show thin, parallel, upward-coarsening laminations of very fine- to fine-grained sand of wind-ripple origin., San Diego State University
Erroneous contact between the two-pyroxene diorite through granodiorite and hornblende-biotite granodiorite units of the emigrant gap composite pluton corrected through detailed mapping, petrography, and geochemistry
The Middle Jurassic Emigrant Gap composite pluton is subdivided into peridotite, gabbro, two-pyroxene diorite through granodiorite, and hornblende-biotite granodiorite units. In a recent map accepted for publication by the U.S. Geological Survey, R. A. Schweickert and colleagues show a contact separating the two latter units in the northwesternmost part of the pluton. However, previous reconissance work by Kevin Bryan (San Diego State University), indicated that this contact may have been erroneously located. In order to assess this possibility I remapped and sam pied the area of the contact proposed by R. A. Schweickert and colleagues. The results of my work indicate that the area is completely underlain by hornblende-biotite granodiorite which is geochemically and petrologically indistinguishable from other samples analyzed from the hornblende-biotite granodiorite unit. Thus, my work indicates that the contact proposed by Schweickert and co-workers is erroneously placed, and in fact should be located where previously mapped by Kevin Bryan as part of his senior thesis project at San Diego State University., San Diego State University
Estimating elemental mass changes during the conversion of corestones to saprock: Implications for the mobility and fraction of REE in the Mediterranean (hot summer) climate
When precipitation ranges from about 50-80 cm/year to ~200 cm/year, the REE are commonly mobilized and fractionated within the regolith. However, little if any work has been done on how the REE are affected by the conversion of corestone to saprock in a relatively dry climate like that of the Peninsular Ranges, southern California. Here, we document for the first time, the REE mobility patterns that accommodated the transformation of corestone to saprock at two sites within the Peninsular Ranges, all lying within a Mediterranean (hot summer) climate. The two sites are informally referred to as Yucca-Perris and Motte Rimrock. At both sites precipitation and average annual temperature vary from 20.8 cm/year and 10.3° – 25.5° C. Corestones at the two study sites are composed of hypidiomorphic equigranular tonalite. In adjacent saprocks, plutonic textures are disrupted by an array of cracks, and a thin film of light-brown translocated clay material lies along their walls. During point counting between ~2% to ~11% of points landing on plagioclase at both sites were counted as clay alteration. XRD study shows that the <2 micron fraction at Yucca-Perris is dominated by illite, kaolinite, and smectite. In contrast, the < 2 micron fraction at Motte Rimrock is dominated by illite, kaolinite, and vermiculite. REE distributions derived from both corestone and saprock samples from each of the two sites cluster on chondrite-normalized plots. This result suggests that the REE have not been greatly affected during the conversion of corestone to saprock. In order to assess the statistically validity of this and other interpretations mentioned above we calculated the elemental mass changes at each site utilizing Ti as a reference frame element. The results of this part of our study showed that there were no detectable changes in elemental mass for the 10 major elements analyzed during this study at Yucca-Perris. In contrast, there was a statistically significant loss of Ca, Na, and K mass at Motte Rimrock. With the exception of a nominal statistically significant gain in the mass of La at Yucca-Perris, changes in the masses of the 14 REE at the two sites are not otherwise statistically significant at the 95% confidence level. Similar results were obtained using Zr as a reference frame. Hence, the results of this study suggest that within Mediterranean (hot summer) climates, the REE are not generally mobilized or fractionated during the conversion of corestone to saprock, a major process involved in the formation of the regolith., San Diego State University
Estimating ß and power for the student's-t test: implications for calculating mass changes in contact metamorphic aureoles - part I: major and some trace elements
Introductory and background material presented in this thesis were written jointly by Khrista M. Garrison, Laura M. Bradbury, and Gary H. Girty. Estimates and discussions of ß and power for Si, Ti, Fe, Mn, Ca, Mg, K, Na, P, Ni, Cr, V, Ba, Zr, Ga, Zn, Th, and Nb are included in the thesis by Garrison. Estimates and discussions of ß and power for Y, Hf, Ta, U, Pb, Rb, Cs, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm. Yb, and Lu can be found in the thesis by Bradbury. All ß and power were made utilizing the SOLO Power Analysis software package produced by BMDP Statistical Software. Inc.. The accuracy of the used in SOLO Power Analysis was verified by checking its output against values calculating utilizing the numerical integration routines in Mathematica. The general algorithm that was used to estimate ß and power is discussed in the section entitled Procedures for Estimating ß And Power. Appendix I is a listing of all chemical data used in the calculations of ß and power. Appendix II provides a brief description of analytical procedures and precessions of chemical analyses used during this study., San Diego State University

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