We've Moved!

Visit SDSU’s new digital collections website at https://digitalcollections.sdsu.edu

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.

Back to top


On the potential for catastrophic flooding in the Salton Trough, California
The Salton Trough includes the largest expanse of dry land below sea level in the Western Hemisphere. Within the last five million years, the Salton Trough has been occupied by intermittent shallow marine seas, as well as brackish to freshwater lakes. The latter was formed as a result of the Colorado River delta prograding westward across the southern end of the Salton Trough, effectively separating it from the Gulf of California. This barrier still exists today, acting as a natural earthen dam between the Gulf and the Trough. During canal construction in 1905-1907, Colorado River floods resulted in the accidental formation of the Salton Sea. Presently, the flow from the Colorado River is under the control of a system of dams, canals, gates and channels. A delicate balance between the works of man and nature protects the region from being inun­dated. However, active tectonics in this region could potentially undermine both the work of humans and nature. Three scenarios considered in this study on modern-day catastrophic flooding in the Salton Trough are: 1) Marine transgression resulting from the failure of the Colorado River delta during a catastrophic earthquake. 2) Freshwater inundation of the Salton Trough resulting from the disruption of the Colorado River distributary channels and canals. 3) Marine transgression resulting from continuing subsidence of the Salton Trough due to sea-floor spreading in the Gulf of California., San Diego State University
Paleodepth reconstruction through the Pennsylvanian Finis Shale of Texas: Insights from brachiopod oxygen isotopes
The Upper Pennsylvanian Finis Shale occurs within the Graham Formation of the Cisco Group and represents a mud-dominated environment along the eastern shelves of the subequatorial Midland Basin (Pierce et al., 2010). In a representative section of the Finis Shale, Forcino et al. (2010) documented a fundamental decrease in the abundance and biomass of the dominant species of brachiopod, Crurythris, within the faunal assemblage midway through the section. For this study, oxygen-isotope (δ18O) variations within the well-preserved calcite valves of Crurythris specimens were used to assess potential changes in paleodepth via (1) changes in ambient bottom water temperature (e.g., shallower waters being warmer) and seawater δ18O (e.g., shallower water being potentially more influenced by isotopically-light freshwater input). Fourteen similarly sized and presumably similarly aged whole specimens that showed minimal surface recrystallization were selected from a broader sample population of thin-sectioned specimens. The interior shell material of the selected specimens were microsampled using a Micromill and analyzed on a Micromass PRISM dual-inlet mass spectrometer. For five of the 14 specimens, sufficient shell material existed to sample their umbo and commissure regions separately to assess intraspecimen variability. For four of the five umbo-commissure-sampled specimens, δ18O was higher in the commissure than umbo. The weighted averages for each of these specimens were then calculated to allow comparison to the remaining “whole-shell” specimens. Stratigraphically, the sample population shows a weak up-section trend of decreasing δ18O. This δ18O decrease is consistent with two potential up-section environmental scenarios: increasing temperature and fresh water input. In turn, both of these scenarios are consistent with a sea-level regression through the section. Additional analyses at higher stratigraphic resolution are warranted to test these exploratory results and tentative interpretations., San Diego State University
Paleoecology of a Pleistocene mollusc assemblage from Tourmaline Canyon
A Pleistocene mollusc assemblage of approximately 30 species was collected from a basal conglomerate in the Bay Point Formation at Tourmaline Canyon, San Diego, California. The total assemblage appears to be composed of four different components; a rocky shore in­tertidal life assemblage, material derived from a bay or estuarine environment, material derived from deeper water offshore, and mater­ial reworked from the underlying San Diego Formation. Correlation is made with UCLA loc­ality 3605 by similarity of fossil assemblage and terrace level., San Diego State University
Paleoecology of an early Pleistocene fauna of the San Diego Formation
Early Pleistocene deposits on the south slope of Mount Soledad have yielded a fauna of 20 species, mostly mollusks, which represent a littoral-sublittoral, partially protected embayment. Water temperatures were probably as much as 8° cooler than at present. The fauna is probably temporally equivalent to the Timms Point silt of the Palos Verdes Hills and the upper part of the Pico Formation of the Ventura basin., San Diego State University
Paleoenvironment in a portion of the Del Mar formation
The Del Mar formation was studied in three outcrops along the coast of San Diego County between Torrey Pines State Park and the mouth of the San Dieguito Valley. The rock consist of sandstones, siltstones, and silty shales with a great deal of lateral variation. The sandstones and siltstones consist mostly of quartz and rock fragments. The shales commonly contain pyrite, marcasite, and sulfur-rich coal indicating a reducing environment, which is usually related to a humid climate. The fauna in the rocks contains twenty-one species of molluscs, none of which are alive today. Six of these species are considered brackish-water indicators. The environmental information for the other fossils is based on characteristics of the genera. They indicate a sandy to muddy environment at a depth of about sixty feet or less., San Diego State University
Paleoenvironmental and paleogeomorphological implications of the combined Delmar-Ardath Middle Eocene pollen and spore flora (Delmar formation and Ardath Shale of the La Jolla Group), San Diego, California
The Delmar formation-Ardath Shale combined pollen assemblage yields a climatic determination, for the middle Eocene San Diego Embayment, of "Aw" for the coast and immediate interior and "Caw" for the interior uplands. The minimum average elevation of the Caw site was about 620 m (2,000 feet) above sea level. The mean annual temperature of the coast was probably 25°C, with the coldest month averaging above 13°C. The uplands' climate was similar to that of the coast in the summer, but the coldest month averaged closer to 0°C. Rainfall was at least 100 cm annually and was concentrated mainly in the summer. A well-drained, xerophytic microenvironment on the barrier beach (Torry sandstone to be) may have harbored drought tolerant plants like Ephedra. The Eocene Delmar lagoon was well isolated from the marine environment, and probably received most of its contained pollen and spores from a distributary channel of the same large river that deposited the extensive, terrestrial Eocene conglomerates of the San Diego area. Evidence of some communication between the sea and the lagoon is indicated by the exhumed tidal scour channel preserved at the Delmar sample locality (refer to stereograms at the end of this report). The tidal orifice migrated down the barrier beach after its erosive currents had cut a channel into the soft lagoonal muds. The resulting isolated depression in the lagoon recieved much organic matter, which ultimately became the pollen-rick, locally developed, lignitic siltstone bed which is exposed today at the sample site., San Diego State University
Paleontology of a late Pleistocene marine terrace, Tecolote Creek, San Diego County, California
A late Pleistocene terrace deposit at Tecolote Creek, San Diego County, California, has yielded 25 species of marine mollusks. The composition of the fauna suggest a semi-protected shallow water assemblage of a bay-estuary environment. The minimum hydro-temperature during late Pleistocene may have been as much as 6° warmer than at present off the San Diego coast., San Diego State University
Paleopathological analysis of perforations on ammonite specimens (Placenticeras meeki) found in the Bearpaw Formation (Campanian) of Canada
There has been much debate over the possible causes of perforations often seen on ammonite shells. Some scientists have claimed that they were signs of a predator attack, while others maintain that limpet home scars combined with sediment loading diagenesis were a more likely cause. This project contributes to this ongoing debate via study of two Placenticeras meeki shells on display at the Roynon Museum of Earth Science and Paleontology and several fossil cephalopods and limpets at the San Diego Natural History Museum. The research has ultimately called the limpet hypothesis into question, and the predation hypothesis has been deemed the more probable explanation. Several different genera of Cretaceous sea predators were examined as possible culprits, with Prognathodon being identified as the most probable predator causing the Placenticeras perforations. Evidence of both predation and scavenging are also explored on both of the Roynon Museum ammonites, as well as further implications into mosasaur predator-prey interactions., San Diego State University
Paleoseismic investigation of the Newport-Inglewood fault zone in Orange County, Southern California with cone penetrometer tests
This project investigated the use of cone penetrometer test (CPT) data in the paleoseismic study of the Newport-Inglewood fault zone (NIFZ) in Orange County. Southern California. Existing paleoseismic techniques, such as trenching, can be very difficult or impractical in low lying areas with shallow ground water. CIT can be used to determine the properties of a soil and to profile the subsurface geology. The goals of this project were to correlate stratigraphy with existing CIT and boring data. These data would then be used to locate faults, and interpret the seismic history at this site. The CPT results show that units can be correlated and vertical displacement across faults can be measured. The results also show that with closer spacing of cone penetrometer tests better results can be obtained. This project was successful in meeting the preliminary goals and demonstrates that CPT borings can be a useful paleoseismic tool., San Diego State University
Partial melting analysis of gabbroic source rock Los Pinos Mountain, San Diego County, California
The Los Pines gabbro is located about 60 km east of San Diego, California and has a K-Ar cooling age of 143 Ma with Ar-Ar integrated ages of 115 Ma and 111 Ma. Field relationships indicate that the gabbros have been intruded by younger rocks of tonalitic composition with ages ranging from 108 Ma to 102 Ma. A geochemical modeling analysis was performed to determine if the tonalites could have been produced by partial melting of a gabbroic source rock similar to Los Pines gabbro. The gabbroic source rock was modeled in a spreadsheet program, using the batch melting equation, to see if it produce rare earth element (REE) patterns within the tonalite compositional range. The parameters established by the REE modeling were tested by modeling other trace elements (i.e., Rb, Sr, Ni, Cr, Ba, Zr, Y) to see if their content fell within one standard deviation (1 cr) of the tonalite trace element content. Modeling showed that it is possible to produce a tonalitic composition by partially melting 5% to 30% of the gabbroic source rock. The trace element model results agreed with those of the REE models suggesting that the tonalites near Los Pines Mountain could have been produced by partial melting of a source rock similar to the Los Pines gabbro., San Diego State University
Petrochemistry of the Jacumba volcanics at Devils Canyon, west of Ocotillo, California
In the Jacumba area of Southern California there is an outcrop of volcanic rocks referred to herein as the Devil’s Canyon Exposure (DCE). This outcrop is part of the Miocene-age Jacumba Volcanics, consistent in age with other volcanic rocks found throughout the southern California borderland. However, the Jacumba volcanics differ from the borderland rocks in a number of important ways. Past research has proposed the theory of a slab window as the mechanism for melt generation for these Miocene rocks. Though the DCE specifically has never before been studied, samples from the Jacumba and Alverson volcanics from previous studies demonstrate that several of these lavas are andesitic, with Sr/Y ratios greater than 30, and Y concentrations <15 ppm. These characteristics define these lavas as adakites which are believed to be derived from the melting of a mafic (basalt/gabbro/eclogite) source, perhaps derived from the melting of oceanic crust. Sixteen samples were collected from the DCE area. Seven of the samples were used to create thin sections for petrologic study. All sixteen samples were used to create both pressed pellets for trace element analysis and glass pellets for major element analysis using X-Ray Fluorescence (XRF) spectrometry. The data was then analyzed using geochemical plots and diagrams. Most of the DCE samples display Sr/Y ratios that fall into the lower portion of the adakite field. The DCE samples are calc-alkaline rocks of a bimodal assemblage with four basaltic to basaltic andesite dikes and more evolved rocks of high-silica andesite and dacite. Looking exclusively at the DCE samples, both the mafic dikes and the more evolved rocks show similar patterns on normalized trace-element plots. The DCE samples also display a clear Nb trough and Pb peak as well as an enrichment of Large Ion Lithophile Elements (LILEs) compared to High Field Strength Elements (HFSEs). When compared with the high-Mg andesites, the DCE samples have lower concentrations of both K2O (LILE) and Zr (HFSE). Theories describing the derivation of the DCE samples must address both the high Sr/Y adakite signature as well as the calc-alkaline character of the rocks. The Sr/Y ratios can likely be attributed to low Y retained in garnet or amphibole, and high Sr derived from melting of a mafic source (without subsequent plagioclase fractionation). Calc-alkaline rocks are thought to be associated with a primary basalt derived from melting of a mantle source that was previously enriched in LILEs by a hydrous fluid phase. In order to explain both of these features, there could be several potential scenarios including: (1) the melting of an amphibole-rich oceanic slab, (2) the mixing of slab melts with melts from a previously hydrated mantle wedge, or (3) the melting of an amphibole-bearing lower crust beneath Peninsula Ranges Batholith., San Diego State University
Petrogenesis of a weathering profile, Peninsular Ranges, Southern California
As part of a larger study aimed at documenting the precision and accuracy of data derived from the new GeoChemical Laboratory at San Diego State University, seven samples were collected from the A, 4 from the C, and 5 from the R horizons of a weathering profile developed on a Cretaceous granodiorite. At the collection site, mean annual precipitation is between ~ 15 and ~ 20 inches, and mean annual air temperatures are between ~ 13° - ~ 15° C. On A-CN-K ternary plots, chemical data cluster with some tendency for specimens from the A horizon to plot slightly above samples from the R and C horizons. Such a relationship implies that Na and Ca may have been preferentially removed during development of the A horizon. On an A-CNK-FM plot samples cluster with the positions of samples from the different horizons overlapping significantly. Hence, A-CN-K and A-CNK-FM data are consistent with earlier petrologic work that indicated that plagioclase was preferentially attacked during development of the A horizon, but that in general the intensity of chemical weathering was not great. Mass balance arguments suggest that at the 95% confidence level, less than about 12% of the original elemental mass of Fe, Ca, Mg, Na, and Sr were removed while P and Ba lost ~23% and ~20% of their original masses. In contrast, both Ni and Zr mass were added. These variations translate into an overall change in bulk mass of-2.1 grams(+/- 1.0 grams)/100 grams., San Diego State University