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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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Flow-emplacement features of the North-Central Pisgah Crater Lava Field, Mojave Desert, California
The Pisgah Crater and its associated lava flow field are located in the Mojave Desert. Flow-emplacement features characterize the lava flow field. Flow fronts within the field are denoted with numerous breakouts and at least one monoclinal flexure with a height of 7.3 m. Many lava tubes in various sizes protrude away from the crater. The surface of many flows contain rootless vents in the form of hornitos and spatter cones. Their characteristics show the mechanism in which the Pisgah lavas were emplaced; therefore, these flow-emplacement features, as well as the crater itself, give insight into the nature of the eruption., San Diego State University
Fluvial sediment record as climate indicator in Southern California
Coastal environments of San Diego are influenced by sediment processes where sediment is delivered to the coast by a combination of river systems and cliff erosion. Changes to coastal systems due to human modifications (e.g., dams, urbanization) and anthropogenic climate change have altered natural systems of sediment dispersal and models of future climate change show impacts to the coast continuing and even accelerating in the future. Our ability to predict those impacts and implement management strategies to adapt to change could be aided by a better understanding of how coastal systems have responded to similar changes in the past. To assess past influence of climatic factors on fluvial deposition into lagoonal and deltaic environments in San Diego, a suite of vibracores were collected from Agua Hedionda Lagoon in Carlsbad and Fiesta Island in Mission Bay, which represents ancient San Diego River Delta deposits. The vibracores were logged for sediment properties including grain size, color, organic/fossil content, and structures. The cores from Agua Hedionda Lagoon were mostly fine-grained, dark, cohesive deposits with evidence of bioturbation and limited preservation of thin undisturbed layers. The cores from the ancient San Diego River delta captured more detailed stratigraphy with several changes in lithology. The cores were predominantly silty-sand, but several coarser layers were also observed. Samples from selected depths were analyzed by laser particle size analyzer to quantify variation in sediment grain size within these layers. Results were used to assess the evolution of the fluvial depositional environment, which may be related to changes in regional climatic conditions. Fine-grained layers are interpreted to be indicative of dry periods with low sedimentation rates and relatively low-energy depositional conditions. Coarser sands, which are associated with higher energy environments, are inferred to be flood deposits during increased precipitation. Nevertheless, the highly variable geomorphology of a delta has a large influence on sediment accumulation and composition, and the observed changes could reflect changing delta sub-environments, rather than precipitation rates. Further detailed analysis of the cores should include radiocarbon dating for determination of sedimentation rates and comparison with historic storm/flood events and an analysis of mineralogy present within the sediments. These additional data could help refine our understanding of the controls on sediment deposition in coastal San Diego environments., San Diego State University
Fossil assemblages of Isla Cerralvo, Baja California Sur
Field survey of Isla Cerralvo in Baja California Sur reveals the presence of invertebrate fossils weathering from an unnamed marine sedimentary formation presumed. The fossils occur in Pliocene (?) conglomerate, sandstone and fossiliferous calcarenite sedimentary rocks exposed in the hanging wall of the La Gringa normal fault along the west-central coast of the island (Montrella et al., 2003). Flat-lying Pliocene(?) fossiliferous limestone/sandstone terrace deposits are also located at the south end of the island at Punta Montana and Punta Sur. A preliminary paleontological survey of the fossils from the La Gringa fault locality reveals the presence of at least two different bivalves. These were identified by Scott Rugh from the San Diego Natural History Museum as Ostrea fisheri and Argopecten sp. The first fossil, Ostrea fisheri, has been described from Upper Pleistocene rocky shoreline fossil assemblages at Bahia Santa Ines farther north in the Gulf of California where they are overlain by deposits correlated to oxygen isotope substage 5e which is about 125,000 years ago (Libby and Johnson, 1997). The Argopecten sp. resemble abeietis abbotti which occurs in the Broadway faunal horizon in San Diego area where it is dated at around 500,000 years old (Rugh, personnel communication, 2005). Good preservation of the bivalves is also consistent with a Pleistocene age. These tentatively identified fossils indicate that the La Gringa fault on Isla Cerralvo may be an active fault. More work is necessary to check this possibility., San Diego State University
Functional anatomy and paleoecology of a North American canid in the late Oligocene (Mammalia: Carnivora)
During the last 40 my canid species have appeared and radiated throughout North America. Throughout this evolutionary history there have been three subfamilies of Canidae: Hesperocyoninae, Borophaginae, and Caninae. Extinct canid skeletal remains can be found within the Otay formation’s gritstone and sandstone-mudstone members of San Diego County, California. The Otay formation dates within the Late Oligocene, Early Arikareean and carries fossils between 30-28mya. During this time basal species of each subfamily coexisted: Hesperocyon, Archaeocyon, and Leptocyon, respectively. While in-tact postcranial skeletal remains are rare, specimens SDNHM 111027, SDNHM 73132, and ACC 12 from the San Diego Natural History Museum consist of articulated limb bones, while SDNHM 111027 and ACC12 also include their partial cranium with subsequent dentition. This dentition was used to classify these specimens as Archaeocyon. Once identified, the locomotion and hunting behavior of Archaeocyon was determined through limb bone and body weight morphologic analyses. Morphometric data suggests Archaeocyon displayed evolutionary adaptations for scansorial, terrestrial, and semi-fossorial locomotion behavior which could be related to the expansion of grasslands occurring in the Late Oligocene. Predatory behavior from the morphology suggests these canids ambushed their prey as well as being adapted for pounce-pursuit hunting behavior., San Diego State University
Functional morphology of productid spines
San Diego State University
Further resolution of past earthquake surface ruptures at carrizo wash, southern San Jacinto Fault, Imperial Valley, California: The devil is in the deposits
Prior paleoseismic work at Carrizo Wash along the Superstition Mountain strand of the San Jacinto fault demonstrated recurrent late Holocene faulting. However, an erosional unconformity in the initial excavations likely removed evidence for some past events, and correlations to nearby sites were problematic because of mismatches in the number of recognized lake units. In this study, I excavated new trenches beyond the affects of the erosional channel and found evidence for an additional event. I also found clear evidence for an additional delta­lake sequence that was not present in the original exposures. These observations confirm the suspected correlation of earthquake events across multiple fault segments, as well as redefine the regional correlation of highstands for the ancient Lake Cahuilla in the western Salton Trough., San Diego State University
General geology of San Felipe, Baja California Mexico
This report, done as course work for Geology 198 at San Diego State College, presents the general geology of a 14 square mile area north of the town of San Felipe, Baja California Mexico, approximately 31° 2' north latitude and 115° 10' west longitude. The rocks of the area are complexly folded Mesozoic metaquartzites, limestones, and slates; cretaceous quartz, orthoclase diorites which have intruded the area as several distinct bodies, and Plio-Plastocene shallow-water marine sedimentary rocks. The sedimentary sequence has been thermally meta­morphosed by the plutons to the epizonal or low mesozonal grade., San Diego State University
General geology of the orbicular diorite Near Pine Valley, California
Orbicule-bearing plutonic rocks are exposed approx­imately four miles southeast of Pine Valley, San Diego County, California. Three principal rock unite, a gabbro, a granodiorite, and a tonalite are exposed in this area; the tonalite is the youngest, the granodiorite next youngest, with the gabbro being the oldest. The orbicules were mapped as part or the gabbro body by Merriam (1958) but present study shows them to be associated with an early, more basic phase of the granodiorite. The orblcules range from two to fifteen inches in diameter with some being spherical and some elongate. They have a dis­tinct concentric, structure and are made up of alternately mafic-rich and felsic-rich cores with more coarsely crystalline cores. Some comb-layering associated with the orbicules suggests that the orbicules formed around xenoliths in a moving aqueous fluid (Moore and Lockwood, 1973)., San Diego State University
Geochemical analysis of arc to rift transitional volcanism of the Boleo Copper District: Santa Rosalia, Baja California Sur, Mexico
This study examines major and trace element volcanic geochemistry of the volcanic rocks of the Santa Rosalía basin, in the Gulf of California (Mexico), as part of the Baja Basins NSF-REU (National Science Foundation-Research Experience for Undergraduates) project. Recent work in the in the area by Conly (2005) proposes the presence of post-subduction volcanics that would record the transition from arc to rift volcanism, as Baja was wrenched away from mainland Mexico in the late Miocene. However, due to the unreliability of K/Ar dates and absence of sample locations, this study re-examines the major and trace element geochemistry to see if this transition was indeed present. METHODS: We mapped of the volcanic rocks in detail and determining their major and trace element geochemistry, analyzed at Washington State University, in preparation for (pending) detailed U-Pb zircon and 40Ar/39Ar geochronological work as well as isotopic analysis. RESULTS: Our preliminary study of major and trace element geochemistry of 22 samples from 18 separate map unit showed calc-alkaline trends of fractional crystallization, consistent with arc-related magmatism. Sample compositions include basalt, basaltic trachyandesite, basaltic andesite, andesite, trachyandesite, dacite, and rhyolite and include lavas, lava domes, intrusions, block-and-ash flow tuffs, ignimbrites, and pyroclastic fall deposits. DISCUSSION: Two separate chemical groups formed within the data, which coincided with their geographic occurrence in either the north or south sub-basin. Rocks from the southern sub-basin were slightly more mafic and showed depletions in LREE and enrichments in HREE when samples are normalized to chondrites. When plotted on a La/Sm vs La plot, trends indicate variable degrees of partial melting from a similar magmatic source. Based on the similarities between the two groups and consistent arc signatures of Nb-Ta-Ti depletions, we feel that there is no chemical indication of rifting in these rocks. Since there are no direct stratigraphic controls between the two groups, there is no way to assume age relationships until new geochronology dates come in., San Diego State University
Geochemical analysis of la posta soil profile #2: is plagioclase degraded during pedogensis in an arid climate
La Posta Soil Profile #2 developed on a small area underlain by the small-biotite facies of the Cretaceous La Posta pluton within an arid climatic belt. Within La Posta Soil Profile #2, R, C, and A weathering horizons are apparent. Five samples for chemical analysis were collected from each horizon. On the A-CN-K ternary diagram, resulting data form a crude linear trend sub-parallel to the A-CN join. Moreover, data from the A­horizon consistently plot above data derived from R and C, and closer to the A apex. On the A-CNK-FM ternary diagram data form a crude linear trend directed toward the A-FM join, and away from the CNK apex. Again data from the A-horizon plot away from data from Rand C, and closer to the A-FM join. Bivariate plots of Sr, Ca, and Na show that these elements are depleted in the A-horizon relative to horizons Rand C. All three elements are common to plagioclase. Data discussed above indicate that plagioclase is being degraded and removed from the A-horizon during its development., San Diego State University

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