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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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Provenance determinations by geochemical methods, lower Paleozoic Shoo Fly Complex, Northern Sierra Nevada, California
Petrological and geochemical data from interstratified sandstones, argillites and radiolarian cherts of the post-Cambrian to pre-Late Devonian Shoo Fly Complex indicate that the provenance of the sediments deposited there was multifarious. Sandstone point-count data suggest that the provenance had both subduction complex and continental related sources. Trace and rare earth element data from the cherts suggest magmatic arc and alkalic basalt influences. Major, trace and rare earth element provenance discrimination plots of argillite samples overwhelmingly argue for a passive margin source. A number of conflicting theories and models are expounded as to the significance and setting of the complex. In light of the geochemical data presented here, as well as sedimentological, structural and stratigraphical data derived from detailed field work, the trench associated with the Lesser Antilles volcanic arc is thought to be a good analogue to the depositional and tectonic setting of the Shoo Fly Complex., San Diego State University
Provenance of Upper Cretaceous La Bocana Roja and Punta Baja formations as expressed by magnetic susceptibility
Magnetic susceptibility is a technique useful for differentiation of magnetite-rich sandstones from those deplete in magnetite. Analyses of fluvial sandstones of the Upper cretaceous La Bocana Roja Formation near El Rosario, Baja California, yielded susceptibility values ranging from 50 X 10􀀨 to 700 x 10s, averaging 320 X 10􀀫 SI units. These values indicate that the sandstone is rich in magnetite, and the values are similar to those of the magnetite-rich western zone of today's Peninsular Ranges batholith. The submarine canyon sandstones of the overlying Upper Cretaceous (Campanian) Punta Baja Formation show an order of magnitude drop in magnetic susceptibility. These values range from 5 X 10􀀱 to 50 X lOs, averaging 20 X l􀀶s SI units. The difference in susceptibilities suggests a change in provenance; the values for the Punta Baja Formation resemble the present-day values of the eastern, ilmenite-rich zone of the Peninsular Ranges batholith., San Diego State University
REE, Th, and Sc evidence for the depositional setting and source rock characteristics of the Toms Creek chert, Sierra Nevada, California
The Shoo Fly Complex is the remnant of an early Paleozoic subduction complex. The Toms Creek chert, a chlorite-grade greenschist facies unit, located within the Shoo Fly Complex, consists of -10 m of interstratified chert and argillite. Rare earth element (REE) data derived from 9 samples form relatively flat patterns with small positive Eu anomalies when normalized to post-Archean average Australian shale (PAAS). These REE patterns are grossly similar to those displayed by modern-day andesites from the Sunda arc. On a La-Th-Sc ternary diagram, data plot from -70% Sc toward -70% La and fall mainly within the magmatic arc related field though some samples spread into the passive margin field. On an A-CN-K ternary diagram, data cluster near island arc andesite and spread along a weathering trend toward the average composition of illite/muscovite, suggesting a predominance of andesitic island arc material, with variable proportions of moderately to extensively weathered differentiated continental crust particulate matter. Data presented here are consistent with the results of previous petrological and geochemical studies conducted in the Shoo Fly Complex and indicate the Toms Creek chert was deposited on the margin of an oceanic plate adjacent to an andesitic island arc., San Diego State University
Reconnaisance noble gas study of three groundwater systems in the lower Okavango Delta, Botswana: Implications for groundwater dating
The Okavango Delta in Botswana, Africa has a unique hydrological setting. The massive geologic feature termed the Okavango "Delta" is actually a low gradient alluvial fan system spread out over 65,000 km2. This fan is subject to annual flood events from the discharge of the Okavango River. In this semi-arid environment, surface water volume is decreased by 98% from surface inflow at the head of the fan to surface outflow, over 200 km away, near the town of Maun. With increasing population, the need for sustainable water is unyielding. This has prompted the exploration of groundwater systems in the region. Three river valleys near Maun were chosen for the purpose of groundwater chronological studies using noble gases. Two of the river valleys have experienced recent surface flooding, which is the primary recharge mechanism of the region. The third system, which has not received surface flooding for the past 13 years, is the main groundwater supply to Maun. The groundwater systems of the Thamalakane, Boro, and Shashe river valleys are evaluated using helium isotopes and abundances. The 4He concentrations within the study area are found to be in excess of the solubility equilibrium with the atmosphere (4Hemeasured > 4Heair), implying subsurface radiogenic production of 4He. Corrections for air-derived helium are made using measured neon concentrations, which are assumed to have no subsurface production. Simple age calculations are then made using estimated values of U and Th concentrations in the aquifer rocks, their bulk density (p) and porosity (cj>), and the corrected 4He concentrations. The helium-derived ages are compared to age estimations made using Darcy's Law and based on the hydraulic properties of the aquifer systems. In general, the helium-derived ages range from 1 to 2 orders of magnitude greater than the hydraulic ages. Many critical assumptions are made with regard to the variables in the age equations (both for helium and hydraulic), such as: (l) a homogenous distribution of: U and Th, effective porosity, and bulk density; (2) a constant hydraulic gradient and hydraulic conductivity; and (3) a relatively good approximation of the recharge areas (distance away from recharge zones). In the Thamalakane system, helium is found to be highly scattered and does not show an expected trend. The Boro system has only two sampling boreholes, which do not conform to predicted values. The Shashe system has the best helium data and the most samples taken from one aquifer (the middle semi-confined aquifer). The helium concentrations increase down gradient from the recharge area and have a nearly constant slope. Helium derived ages in the Shashe Valley are greater than the expected hydraulic ages by a factor of 10. The age difference can be explained in terms of a crustal flux of helium degassing from the underlying basement rocks. This crustal flux, termed the solution rate factor, effectively reduces the apparent age of the groundwater by taking into account the basement lux and the distance from the borehole screen to the bottom of the aquifer. The solution rate factor often reduces the apparent age up to 3 orders of magnitude. Helium can and has been used to help characterize aquifers. Unfortunately the lack of quantitative measurements in the region prevents the complete characterization of these systems. Future studies in the area should focus towards obtaining more samples along the various valleys, and collecting the samples in specific aquifers. Measurements of 14C as well as U and Th, bulk density, porosity, and other hydraulic parameters need to be addressed., San Diego State University
Reconnaissance geochemistry of the early Jurassic Sailor Canyon formation: Implications for paleotectonic setting and the use of trace element provenance-discrimination diagrams
The Lower Jurassic Sailor Canyon Formation crops out north of Interstate 80 In the northern Sierra Nevada of California. It consists of several kilometers of mostly tuffaceous sandstone turbldltes and arglllltes. Most turbldltes display either Tbc or Tbcd Bouma turbldlte Intervals, and thus were probably deposited In a marine basin a I setting. Trace element data d erlved from tuffaceous sandstones when plotted on the La-Th-Zr/10 and La-Th-Sc provenance-discrimination diagrams of M. R. Bhatia and K.A.W. Crook plot In or near the field characterslstlc of sediment derived from Island arcs composed of Intermediate composition volcanic material. Such an Interpretation is also Indicated by La versus Th and Ti/Zr versus La/Sc relationships, as well as by chondrlte-normallzed rare earth element data. Thus, data and observations made during this study support paleotectonlc models which portray the Saller Canyon Formation as being deposited In a forearc basin which had developed along the leading edge of North American during the Early Jurassic., San Diego State University
Reconnaissance geology of the southeastern Sierra De Pintas, Baja California
The Sierra de Pintas Mountains located on the west coast of the Gulf of Baja California about 10 kilometers south of Mexicali, are an impressive exposure of pyroclastic rock of Cretaceous and Tertiary age. The area mapped contains both the Cretaceous Montezuma Formation (new name) and the Tertiary Sierra de Pintas Formation (new Name), which together make up a stratigraphic thickness of nearly 4,000 feet of pyroclastic rock. The area is highly faulted, with several major faults and smaller faults which form horsts and grabens along the edges of the Sierra de Pintas., San Diego State University
Reconnaissance magnetic survey of the San Pedro Martir Fault and medial structure in Valle Chico, Baja California
A survey consisting of four traverses was run with a proton precession magnetometer in Valle Chico approximately 50 miles SW of San Felipe. Running along the axis of the valley is the southward extension of the San Felipe fault, here apparently pulling apart with neither strike-slip nor vertical motion. The purpose of this study was to traverse the San Pedro Martir fault and the medial fault to determine if the fault structure is expressed in the magnetics, and if so the nature of the faulting. Three traverses across the San Pedro Martir Fault, two traverses located where the fault scarps are highly visible, a third where the fault is covered by recent alluvium. The fourth line of the survey crosses the structure in the center of the valley. Gologic models of the study area were constructed so that they would produce magnetic profiles similar to those obtained in the study and at the same time be geologically plausable. A likely model for the area of the San Pedro Martir fault is on of a magnetically susceptible volcanic flow, surrounded by relatively non-susceptible metamorphic and granitic rocks, that has been broken by the step faulting. The lack of an anomaly in profile D indicates that any subsurface structure is not associated with a lateral magnetic susceptiblity difference., San Diego State University
Reconnaissance whole rock X-ray fluorescence analysis of samples from Islas Los Coronados, Baja California Mexico
The Islas Los Coronados are a small archipelago comprised of three islands (North, Middle and South) and one islet just off the coast of Baja California, a mere 15 miles south from Point Loma located in Mexican waters. The islands are steep and difficult to access. Gordon Gastil visited the island in October of 1969 to conduct a geologic reconnaissance of the islands and collected a series of samples for analysis. One of the outstanding questions regarding the island geology is the affinity of a ~200 meter thick homoclinally dipping series of sandstone, siltstone and conglomerate that makes up North Island. Gastil in a correspondence to Ned Allison dated October 13, 1969 was of the opinion these are correlative to Upper Cretaceous non-marine analogous to the El Gallo Formation near El Rosario in Baja California, part of the Rosario Group of southern and Baja California. This study provides the first ever geochemical analyses from Islas Los Coronados in Baja California, Mexico. Whole rock major and trace element concentrations were determined by X-ray fluorescence spectrometry. Three North Island sandstone/siltstone samples have ~66-71 wt% SiO2. The composition of these samples is compared to Upper Cretaceous quartzofeldspathic Great Valley Group sandstone compositions reported by Surpless (2014). The overall compositional similarity of Great Valley Group sandstone to North Island sandstone in terms of both major and trace elements is consistent with Gastil’s hypothesized Upper Cretaceous age assignment for North Island. Volcanic clasts from Middle and South Islands are subalkaline basalt or basaltic andesite with high Cr, Ni, Cu, Zn. A cobble from a San Onofre breccia collected near Smuggler’s Cove on South Island is a rhyolite., San Diego State University
Reconstructing coastal events recorded in ancient San Diego River delta deposits
Coastal environments and ecosystems of San Diego are influenced by sediment processes where sediment is delivered to the coast by a combination of river systems and cliff erosion. The amount, characteristics, and distribution of this sediment are important for patterns of coastal habitat distribution and sandy beach replenishment. Changes to coastal systems due to human modifications (e.g., dams, urbanization) and anthropogenic climate change have altered natural systems of sediment dispersal. 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. Using a vibracore system we collected 6 sediment cores from San Diego River delta deposits located beneath Fiesta Island in Mission Bay, San Diego. These sediment cores captured stratigraphy that could be associated with both short-term single day events, and relatively long-term changes to the drainage basin. The westernmost of the cores contained detailed stratigraphy and was sampled for grain size analysis and radiocarbon dating. In total, 30 samples were taken along the 272 cm core and analyzed for grainsize using a laser particle size analyzer. Five samples were taken for radiocarbon dating at the UC Irvine W.M. Keck Carbon Cycle Accelerator Mass Spectrometry laboratory. Based on lithology, three distinct units were identified. The lower unit is 49cm thick and consists of fine-grained sand with interbedded laminations, interpreted to be deposited in a tidally dominated environment. The middle unit is 165 cm thick and contains undifferentiated silty sand, characterized by darker sediments with a higher organic content. This unit is interpreted to represent deposition in wetland or marsh environments. The upper unit is similar in grain size and contains similar laminated bedding seen in the lower unit, and is also interpreted as tidally influenced. Within the upper unit there is an ~7 cm coarse sand layer with an oxidized middle portion and crossbedding, interpreted as a single event caused by a large storm or flood. Radiocarbon analysis provided a 95.4% probability that the contact between the lower and middle units occurred between 315 and 1675AD and a 95.4% probability that the contact between the middle and upper units occurred between 1766 and 1956AD. With more radiocarbon samples, we could improve the age model and obtain a much more in depth understanding of how often the San Diego River has fluctuated in the past, as well as get a better insight into how the climate of Southern California has changed in the late Holocene., San Diego State University
Reconstructing the South Atlantic carbonate compensation depth from the early Eocene to late Miocene: comparing local to global reconstructions
The Carbonate Compensation Depth (CCD) is defined as the depth below which the CaCO3 content of surface sediments is less than 20 wt% due to dissolution. The CCD varies in its position over time due to changes in sea level, LCO2, and the weathering supply and burial removal of [Ca] and [CO{] ions. Regional CCD variations can be reconstructed from suites of Ocean Drilling Program (ODP) sediment cores of known age and paleodepth. The goal of this project was to determine Late Miocene to Early Eocene stratigraphic variations in wt% CaCO3 at ODP South Atlantic Site 1267 on Walvis Ridge, and compare this local high-resolution reconstruction of paleoCCD variations to more global low-resolution reconstructions. For each core sample, a dry powered split of knov\-'.n mass was acidified with a known volume of 0.5 M HNO3 solution to dissolve all carbonate, the resultant solution was analyzed by ICP-OES to determine [Ca], [Mg], and [Sr], and the given sediment mass, acid volume, and [Ca] were used to estimate wt% CaCO3. This ICP-OES-based method to calculate wt% CaCO3 was found to work as well as the standard carbonate-coulometry-based method. The Site 1267 magnetobiostratigraphic age-model was used to convert wt% CaCO3 data from the depth-domain to the time-domain, and the crustal age-depth relationship was applied to estimate Site 1267 paleodepths throughout the study interval. The sample population showed a significant and strong correlation between ICP-OES-determined wt% CaCO3 values and ship-board-determined natural gamma ray (NGR) counts, and this correlation was applied to the 2.5-cm-resolution NGR record to produce a high-resolution ( 103 yr) synthetic record of wt% CaCO3. Integration of sediment, time, and paleodepth data allowed determination of whether the paleoCCD was deeper or shallower than Site 1267's paleodepth through time. The Site 1267 record shows good general agreement with previous low-resolution(> 105"6 yr) paleoCCD reconstructions, correlates relatively well with eustatic sea level fluctuations. This approach can be applied to shallower and deeper ODP Leg 208 drill sites on Walvis Ridge to provide additional constraints on the regional history of the paleoCCD in the South Atlantic., San Diego State University
Right-lateral faulting of Santa Catalina Island: California
Santa Catalina Island is located within the California continental borderland, a geomorphic province whose origin has long been attributed to faulting within the San Andreas strike-slip system. The presence of such strike-slip faults has largely been inferred based on the topography of the ocean floor and on the presence of active seismicity on many of the apparent fault features. A strike-slip fault of significant size is present on one of the islands within the borderland (Santa Cruz), but most actual rock exposures on the other islands do not demonstrate the presence of major strike-slip faults. Study of a variety of remote sensing images and field work on Santa Catalina Island indicators of strike-slip faulting are present. Geomorphic evidence in the form of a unique drainage pattern, truncated ridges, faults and rock unit correlations all provide evidence for strike- faulting on the island., San Diego State University