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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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Characterization of seafloor sediment and morphology offshore from the Northern Channel Islands, California
New high-resolution multibeam bathymetry and acoustic backscatter data were collected and processed along with previously collected CHIRP data from the shelf offshore the Northern Channel Islands, California. These display patterns of sediment distribution, tectonic deformation, seafloor geomorphology, and lithology. The combination of these datasets will help to identify changes in seafloor lithology, for example between rock, gravelly-muddy sand, muddy sand, and mud. Results can be used for numerous studies, including applications to mapping of submerged archaeological resources and benthic habitat distribution. The four Northern Channel Islands were once a unified landmass known as ‘Santarosae’ during the last glacial maximum when global sea level was approximately 120 meters lower than today. The presence of numerous paleocoastal archeological sites on the modern islands suggests that similar sites may exist on the submerged shelf. Mapping seafloor and sub-seafloor geology can identify paleolandforms that may have provided resources and been occupied by early people living on Santarosae. Between Santa Cruz and Santa Rosa Islands, folded beds of Monterey Shale are truncated by a strong acoustic reflector interpreted to be the transgressive surface created by sea level rise since the last glacial maximum. To the north of Santa Rosa Island, there is a continuous trend of volcanic rocks observed both at the seafloor and buried below marine sediment. Sediment thickness above the transgressive surface and volcanic bedrock varies widely across the survey area due to differences in tectonic and hydrographic influences. Understanding these structural and hydrographic controls of the seafloor morphology will improve predictive modeling of submerged archaeological sites for better resource management., San Diego State University
Characterization of the geomorphology along the agua blanca fault, Santo Tomas Valley
Slip per event and earthquake recurrence interval data for the Agua Blanca fault has previously been estimated based only on empirical evidence. Direct field evidence of lateral offsets and detailed geomorphology has not been examined along the entire fault length. This study mapped previously unmapped geomorphology of the western section of the Agua Blanca fault in Valle Santo Tomas. Evidence of active faulting along the valley is presented here. A 2.4 m fresh offset channel along the ~35km western section appears to be a result of only the most recent surface rupture, suggesting a slip per event of 2.4 m. Combined with the known 4-6mm/yr slip rate, this estimate of slip suggests an earthquake interval of 400-600 years. A 35 km surface rupture length is inconsistent with 2.4 meters of displacement in a single event, casting doubt on the previously published surface rupture behavior of the fault. According to field observations and calculations using the regression of Wells and Coppersmith, the Agua Blanca fault may rupture as much as 85 km of its length, producing earthquakes in the range of M7 .1 - 7.4. With an earthquake interval of possibly 400 years and an estimated time lapse of 350 years since its last surface rupture, the Agua Blanca fault may be accumulating sufficient strain for a destructive earthquake., San Diego State University
Chemical and hydrologic investigation of the intermediate aquifer in Harper Lake Basin, San Bernardino County, California
Harper (Dry) Lake Basin is part of the Centro Sub-area of the of the Mojave Water Agency area in the central Mojave Desert region of California. This project is a groundwater study of part of the basin conducted in conjunction with Ninyo & Moore, a local geotechnical and environmental consulting firm, who was contracted to evaluate groundwater resources and water quality in the area. This area has been the site of ranches, farms and agriculture since the early 20th century. Chemical and hydrologic data were collected over a nine-month period from six wells on the property to determine reliability for domestic use. All six wells were all drilled to a depth of ~220 feet into a confined aquifer within Quaternary alluvium. A perched aquifer, separated by a 50 ft low permeability clay aquitard, lies above the aforementioned aquifer, while the fractured Black Mountain Basalt aquifer acts as the deep aquifer. The focus of this study is the condition of the intermediate aquifer. Groundwater flow in the region based on water table heights is from southeast to northwest, parallel to regional faults and the Harper Lake shoreline. Chemical analyses of water from shallow groundwater wells were also incorporated into this study. Major cations and anions as well as arsenic, nitrate, and other key element concentrations were monitored for inherent water quality. Piper diagrams and charts were then created for interpretation of those concentrations in relation to Environmental Protection Agency (EPA) and California Department of Public Health Standards. Average total dissolved solids (TDS) from the intermediate aquifer were quite variable but in general the water is brackish to highly brackish. Systematic spatial variation was also found in major anions in the intermediate aquifer trending from south to north. Average concentrations for arsenic, boron, and nitrate exceeded EPA standards for a number of wells during the months of observation; however hexavalent chromium, known to be present in the groundwater 10 miles to the southeast has not tested positive in any of the wells at this site. Water levels were measured to calculate direction of flow., San Diego State University
Chemical weathering of volcanic protolith to bauxite ore: A geochemical analysis using major element compositional data
The Palau Archipelago is the only emergent feature on the Kyushu-Palau Ridge. The islands are composed of volcanic rocks that plot within the tholeiite series ranging from basalt to dacite. Extreme chemical weathering due to a tropical climate has led to areas of bauxite formation, the primary ore of Aluminum. This study attempts to describe major element compositional changes between the volcanic parent rock (protolith) and the altered material (bauxite) in response to in situ chemical weathering using statistical modeling and geochemical analysis. A linear compositional model was found to fit 99.95% of the variation in the major element data. Titanium was identified as an immobile element and used to conduct mass balance calculations. Consistent with the extreme climate of the sample location, leaching (mass loss) was observed for the following minerals: SiO2 96%, CaO 100%, MgO 98%, K2O 99%, Na2O 100%, MnO 90% and P2O5 53%. The only elements with observed increases in bulk mass were Al2O3 166%, Fe2O3 5%. A greater increase of Aluminum was seen in the nodular samples then was seen in the bauxite ore., San Diego State University
Chemical, clay mineralogical, and petrological characteristics of erosional exhumed saprock derived from a 125 Ma granite south of Temecula, California
The study site, located near the top of an ~20° – 30° E-SE dipping slope underlain by ~125 Ma granite, consists of a large mushroom-shaped corestone, ~4 m in width and extending ~3 m above the land surface. Such geometry implies that as much as 3 m of regolith was removed during erosional exhumation of the corestone. Twelve samples collected from the granitic corestone and 12 from the adjacent saprock were analyzed for their major element chemistry. In addition, the clay mineralogy of the < 2 μm fraction separated from representative saprock samples was evaluated by standard XRD procedures. Following conversion to molar A, CN, and K concentrations, non-central principal component analysis revealed that principal component 1 explained 94.6% of the variance of saprock data about a calculated compositional linear trend. In A-CN-K ternary space, the perturbation vector derived from eigen vectors associated with principial component 1 directed the compositional linear trend away from the CN apex and toward the A-K join, and thus suggested that formation of the saprock involved a loss of Ca and Na mass. Given that these elements are largely held within the crystal lattice of plagioclase, the above data suggest leaching of plagioclase during transformation of granitic basement to saprock. MgO passed statistical tests for immobility, and was used as a reference framework in mass balance calculations. Results supported the above interpretations, indicating a 37% loss in Ca and a 32% loss in Na mass. Such losses also are supported by thin section work which shows that plagioclase has been extensively converted to clay, and XRD work which shows that the < 2 μm fraction is dominated by kaolinite and minor vermiculite. In addition, a 14% loss in Mn mass likely reflects leaching from biotite. In contrast to the above losses in elemental mass, gains of 18% Al, 38% Fe, and 36% Ti mass are statistically significant. Thin section work revealed that the saprock crack system is lined with a yellowish-brown clay mineral that is likely kaolinite (Al2Si2O5(OH)4). The Si:Al ratio in kaolinite is 2:1. Hence, depending on the volume of kaolinite lining the crack system, an increase in Si mass also should be evident. Relative to the overall change in bulk mass, an 18% increase in Al mass translates into an increase of ~2.5 grams of Al2O3 per 100 grams of granodiorite. Thus, if 2.5 grams of Al2O3 were added, then ~5 grams of SiO2 are required to balance that needed in kaolinite. Unfortunately, the volume of kaolinite lining the crack system is small, and the gain of 10% (+12%/-11%) Si mass, though statistically insignificant, translates into an addition of ~7.9 grams of SiO2. Though more work is required, the above data are consistent with the idea that within the erosional removed 3 m thick section of regolith, particles of kaolinite, along with ions of Fe and Ti were eluviated, and then transferred downward where they were illuviated, exchanged, or adsorbed onto the walls of the saprock crack system., San Diego State University
Chloride and nitrate distributions in unsaturated alluvium, near Joshua Tree, California
Groundwater pumping is the sole source of water supply in the Joshua Tree groundwater sub-basin in the southwestern part of the Mojave Desert; miles from Los Angeles, California. As a result of groundwater pumping for public supply in excess of recharge, water levels in the area have declined more than 50 feet since the 1950’s. The Joshua Basin Water District (JBWD) is concerned about the long-term sustainability of the aquifer and is contemplating managed aquifer recharge using water imported from northern California. The United States Geological Survey (USGS) has completed test drilling and instrumentation in the 400 foot thick unsaturated zone at a proposed site near the community of Joshua Trees. Drill cuttings were collected at 1-foot intervals using the Overburden Drilling Exploration method (ODEX). The method uses air rather than water as a drilling fluid. Extraction and analysis of chloride nitrate, and other soluble anions from selected cuttings of unsaturated alluvium in the Mojave Desert, near Joshua Tree, California was done to determine the accumulation of the soluble salts at the proposed recharge site. The drill cuttings were oven-dried, sieved sediment of different depths, hydrated with water and shaken overnight to extract the soluble salts. The resulting extract was filtered through a 0.45 micrometer pore-sized filter prior to analysis by ion chromatography for soluble anions. The mass of chloride and nitrate in the unsaturated zone is used to estimate the time since recharge and the long-term downward water flux of the arid area. Data from this work were compared with previous data to estimate precision and accuracy of the technique. The previous data of the studied area show that it has been 10,000 to 12,000 years since recharge. The data from this study has showed similar results in that the last time the area saw recharge was 8,000 to 9,000 years., San Diego State University
Clast counting and magnetic susceptibility screening in the cabrillo formation, San Diego California: indications of stratigraphic variation and provenance
Clast counting of Maastrichtian Cabrillo Formation conglomerates between Bird Rock and Tourmaline Beach in San Diego, California defines distinctly different clast populations above and below a 20 m thick mudstone/turbidite interval in the middle of the section. Comparing lower and upper conglomerate means, proportions of volcanic clasts increase from 51.2 to 66.5% upsection, while metamorphic clast proportions decrease from 31.5 to 18.5%. Quartzites compose 86% of metamorphic clasts. The proportion of plutonic clasts in the section remains consistent throughout at 16.2%. Chi­square hypothesis testing confirms a statistical difference between upper and lower conglomerates. Monzogranites and garnet-muscovite leucogranites are abundant in the section while granitoids with rapakivi texture are a minor but widespread component. Previous workers have assumed a fully local Peninsular Ranges batholith provenance for the Cabrillo Formation. However, potassic and peraluminous granitoids are over-represented in the coastal conglomerates compared to the mainly tonalitic Peninsular Ranges batholith. The atypical granitoids, as well as abundant quartzite suggest that exotic sources may have supplied detritus to the Cabrillo Formation. Alternatively, the unusual granites may represent a lag deposit due to their superior durability compared with more calcic plutonics. In-situ magnetic susceptibility screening of plutonic clasts indicates 71.5% are consistent with an eastern-zone Peninsular Ranges batholith derivation. These measurements generally support an episode of uplift in the eastern Peninsular Ranges batholith in the Late Cretaceous proposed by others. The magnetic susceptibility data show no variation in granitoid provenance upsection., San Diego State University
Clast counts and magnetic susceptibility in the Cabrillo formation, San Diego, California
The Cabrillo Formation represents an inner-submarine fan valley underlain conformably by the Point Loma Formation. Together the two formations formed as a westward­prograding submarine fan. Its provenance is thought to be the Peninsular Ranges batholith and metamorphic rock formations plus the Santiago Peak Volcanics. Counting clast lithologies can help to prove or disprove these sources. Clast counting of Cabrillo Formation conglomerate beds behind the San Diego Sewage Treatment Plant on Point Loma shows similar clasts in the lower and middle levels of the formation: volcanic clasts 51 vs. 46%, plutonic clasts are 18 vs. 24%, and metamorphic clasts at 28% vs. 23% respectively. All of the sedimentary clasts are rip-up clasts from the underlying mudstone. In situ magnetic susceptibility readings of all counted clasts at the two sites show that 86% of the clasts have less than 21 X 10-5 SI units, and 95% of the clasts have less than 100 X 10-5 SI units. High readings were found in aphanitic volcanics, dacites and some scarce quartz diorites. These primarily non-magnetic clasts match with values found today in the eastern-zone of the Peninsular Ranges batholith, helping to support other evidence that interprets an intense uplift in the eastern Peninsular Ranges., San Diego State University
Clay mineral analysis of a mudstone facies: Jurassic Curtis Formation, East-central Utah
The Curtis Formation, a lithostratigraphic unit of the San Rafael Group of east-central Utah, was deposited mainly by tide- and wave-currents in a nearshore shelf depositional system during Late Jurassic time. In the lowermost 6 to 8 meters (20 to 26 feet) of the Curtis lies a mudstone facies, for which an analysis for composition and origin of clay minerals has not been done. A week was spent systemically collecting samples at four locations. Three are along the western San Rafael Swell (Sid and Charley, Horn Silver Gulch, and South Sand Bench at I-70), and one is on the east side of the Swell (San Rafael Swell East). Samples were collected at half meter intervals from just above the J-3 regional unconformity on the underlying Entrada Sandstone up to where the facies become silty and sandy. Because the samples are cemented with calcium carbonate, they were disaggregated with acetic acid to yield an insoluble residue of less than 4 μm (0.004 mm) silt- and clay-sized particles. Silt-sized grains separated from clay-sized grains in a settling tube over a two-hour period. The clay-liquid suspension was drawn with a syphon tube, smeared on glass slides, and allowed to dry. Each of the clay smears was then further prepared for four different analyses on an X-ray diffractometer: 1) untreated, 2) glycolated with ethylene glycol, 3) heat treated to 4000 C, and 4) heat treated to 550o C. Substances identified are the clay minerals smectite, illite, and chlorite, plus the non-clay minerals quartz and the zeolite phillipsite. The 3 clay minerals are detrital and were formed by chemical weathering of minerals in a parent rock. Sparse andesitic rock fragments in conglomeratic units within the mudstone facies together with the presence of the zeolite mineral phillipsite suggest that smectite probably formed from the chemical weathering of volcanic materials. Illite and chlorite clays could not have originated at the expense of smectite during burial diagenesis because the relative abundance of smectite increases while illite decreases upward stratigraphically, and chlorite abundance is uniform throughout the mudstone facies. Chlorite clays probably formed by the of Illite to smectite as weathering conditions shifted from cooler and drier to warmer and humid over time weathering of minerals in either volcanic or metamorphic rocks. The decrease in the illite to smectite ratio from the base to top of the mudstone facies can be explained by the chemical alteration., San Diego State University
Clay mineral investigation of the Delmar Formation
The Delmar Formation is believed to have a lagoonal depositional environment, because of facies relationships and paleoecological studies. This type of environment is protected from normal littoral processes by the barrier islands (Torrey Sandstone). The areas in and around tidal inlets, however, have relatively higher energy conditions. The lithology is predominately dusky-yellowish-green sandy mudstone interbedded with yellowish gray, medium to coarse-grained sandstone. Coal and fossil wood fragments are common. Fifty samples were taken from vertical channels dug at six locations - three along the coast and three inland. The clay­sized fraction (less than 2 microns) was extracted, and then analyzed using X-ray diffraction techniques. The diffractograms show kaolinite, smectite, vermiculite, illite, chlorite, and mixed-layer minerals. The expandable clays, smectite and vermiculite, dominate each sample. Kaolinite is present in every sample. illite varies laterally; it was not detected at the sample site in San Dieguito Valley, and at the sample site along the coast just south of Del Mar. The thin claystone beds contain 57% expandable clay minerals. Vertical variations in clay mineralogy are grossly similar in the exposures that were sampled. The variations approach the accuracy of the data. Variations that do occur could be attributed to current patterns in the lagoon and/or source area., San Diego State University
Coastal processes and characterization of beach sands along the Capistrano littoral subcell, Southern Orange County, California
The distribution and characterization of sands along the coast of Southern California have several important consequences. They have a large impact on coastal development such as residential structures on the beach or sea cliffs and on coastal structures such as harbors and breakwaters. Our study was undertaken in southern Orange County, a region with high erosion rates and much coastal development. In particular, we studied the beaches from Dana Strands southward to Lower Trestles including the sea cliffs and the creeks that feed sediment onto these beaches. Using the methods of statistical analysis of grain size distributions, plus observations on grain shape, beach orientation, and mineral trends allow us to understand the southward movement of sand along these beaches and the relative contributions by littoral drift, creeks, and the sea cliffs. Our results show distinct boundaries of a littoral cell at Dana Point in the north and San Mateo Point in the south. We also see a general trend of southward fining of grain sizes in the swash zones within the Capistrano subcell and a coarsening of backshore grain sizes southward within the cell., San Diego State University
Coastal processes and characterization of beach sands in the Capistrano littoral subcell Southern Orange County, California
The distribution and characterization of sands along the coast of southern California affects resi­dential, commercial, and other coastal structures such as harbors and breakwaters. This study of sands took place in southern Orange County, a region of high erosion and significant coastal development. In particular the shoreline from Dana Strands southward to Lower Trestles, including the cliffs and creeks feed sediment to these coastal beaches. Statistical analyses of grain size distribution (mean, mode, sorting, skewness, and kurtosis) and mineral trends at these beaches are used to understand the direction of sediment transport and the relative contributions form the littoral drift, creeks, and sea cliffs to the beach sediments. The results show a predominant north to south littoral drift direction during the late winter and spring months, with distinct littoral cell boundaries at Dana Point in the north and at San Mateo Point in the south. The swash zone sediments fine to the south within the cell, while the backshore sediments (where they exist) coarsen to the south because of cliff and creek con­tributions. The non-resistant sandstone sea cliffs in southern San Clemente are an important source for local beach sands, but this reduces the integrity of the cliffs that are vital to the stability of resi­dential structures., San Diego State University