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Collection Description

Collection of student theses and dissertations from as early as 1939, but mainly from 2010 to present.

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"Middle" Cretaceous metasedimentary rocks of La Olvidada northeastern Baja California, Mexico
Plate 1. Geologic map of the metasedimentary rocks of La Olvidada and vicinity. Plate 2.Columnar section of the metasedimentary rocks of La Olvidada., Recent field mapping near La Olvidada barite prospect, at the 30th parallel in northeastern Baja California, has delimited a 125 square km exposure of medial Cretaceous (Barremanian-Turonian), pre-batholithic, upper greenschist to lower amphibolite metasedimentary rocks. These rocks, collectively referred to as the metasedimentary rocks of La Olvidada, are exposed in a seven km thick section characterized by northwest-striking bedding and foliation, steep northeasterly dips, and isoclinal folding. This section consists of an unconformable basal sequence of quartz-rich metaconglomerate, metaquartzite, phyllite, and marble overlain by rhythmically interbedded and laminated flysch-like carbonaceous metachert and quartz-mica phyllite. The basal sequence is interpreted to have been conglomerate, sandstone, and limestone deposited on a subsiding continental shelf, whereas the flysch-like rocks are interpreted as pelagic bedded chert and turbidite sandstone deposited predominantly in the basin plain facies. A lens of metaconglomerate, metaquartzite, and minor metaandesite enveloped by flysch-like rocks is also exposed in the section. These rocks are interpreted as conglomerate and calcareous sandstone deposited in a channelized facies of a submarine fan or flank talus deposited adjacent to a basin floor high. Andesite was probably erupted from local submarine vents. Clastic provenance and paleocurrent evidence imply that a cratonal source terrane was situated southwest of the depositional basin. The metasedimentary rocks of La Olvidada crop out continentward of Aptian-Albian age metavolcanic rocks (Alisitos Formation) which have been interpreted as a fossil volcanic arc. This tectonic geometry suggests that the rocks of La Olvidada were deposited in a back-arc setting. An alternate hypothesis explains the present position of the arc by Late Cretaceous northwest translation, which dislocated a segment of a western mainland Mexico arc (Sonoran) and placed it seaward of the rocks of La Olvidada., San Diego State University
500 year rupture history of the Imperial fault at the international border through analysis of faulted Lake Cahuilla sediments, carbon-14 data, and climate data
We excavated a trench across a sag pond created by a 30 m-wide releasing step along the Imperial fault 1.4 km north of the U.S.-Mexico international border to test earthquake recurrence models. The stratigraphy at the site exhibits distinct pulses of lacustrine and deltaic deposition with localized zones and layers of well-sorted sand deposits interpreted as the result of liquefaction. Evidence for five events is observed in the upper 3.5 m of stratigraphy, which corresponds to deposition from three full lake episodes over the past 400-550 years. Age control is by 14C dating of detrital charcoal from the trenches and correlation to the well-constrained regional chronologic model of Lake Cahuilla. Evidence for events is based on production of accommodation space and associated growth strata, upward fault terminations and fissures, massive liquefaction in the form of sand dike intrusions and sand blow deposits, and significant vertical offset in the step-over area. The two most recent events appear to be significantly larger than the earlier two events based on event-by-event palinspastic reconstruction and correlation to previous trenching studies. Six meters of strike slip passed through the sag in the 1940 Imperial Valley earthquake. The penultimate event produced nearly identical vertical displacement as in the 1940 earthquake, implying that it was also large and likely slipped about 6 m. In contrast, events 3 and 4 produced little vertical displacement from which we infer that displacement in these earthquakes was small at our site. We interpret these as moderate 1979-type earthquakes and that the southern end of these ruptures was likely close to our site. Event 5 is interpreted to be large based on its expression in nearby trenches; our trenches were not deep enough to capture the vertical separation for this event. Together, if each event interpreted as large experienced a similar amount of displacement as in 1940, this implies something on the order of 18 m of displacement in the past 400-550 years, yielding a slip rate of 32-45 mm/yr. This rate is indistinguishable from all geodetically-inferred rates for the Imperial fault and implies that most of the plate motion is accommodated by the Imperial fault at the international border. The CD-ROM, an appendix to the thesis, is available for viewing at the Media Center of the San Diego State University (SDSU) Library., San Diego State University
A 7000 year record of paleoearthquakes on the central Garlock fault, near El Paso Peaks, California
A trench excavated across the central Garlock fault, on a small playa near the El Paso Mountains, has revealed a remarkable record of paleoearthquakes. The trench contains event evidence in the form of buried fissures and scarps for six well-resolved earthquakes, designated as events W, U, R, Q, K, and F, within the last 7000 years. The trench and auxiliary exposures that we excavated did not reveal evidence for three poorly-resolved events reported in a previous study and in some cases, we provided alternative interpretations for what was previously observed. Additionally, one paleoearthquake identified in the previous study and thought to be a well-resolved event in the original trench was misinterpreted and is not an event. The multiple exposures allow us a qualitative measure of our interpretation uncertainties, and we believe that our event record is not over-interpreted, although it may be under-interpreted. Radiocarbon dates of detrital charcoal, combined with a technique of interpolating the event ages with sedimentation rates, provide constraints on the timing of faulting events. The most recent earthquake, event W, occurred between A.D. 1450-1640, with a preferred age of A.D. 1530. The penultimate event occurred between A.D. 560-800 and has a preferred age of A.D. 680. Event R has a preferred age of A.D. 325, and occurred between A.D. 225-450. Event Q, which has a preferred age of A.D. 100 and occurred between 40 B.C. - A.D. 240, appears to have more vertical deformation associated with it, indicating it may have been larger event. Event K, which occurred after 3490 B.C. and before 2910 B.C. has a preferred age of 3120 B.C. The oldest identified paleoearthquake, event F, occurred between 5320-4050 B.C., with a preferred age of 4880 B.C. The event ages indicate that earthquake recurrence is highly irregular at the El Paso Peaks site, with individual intervals ranging from as little as 225 years to as much as 3220 years. This suggests that the central Garlock fault follows a Poissonian model of recurrence behavior rather than quasi-periodic behavior. Our analysis shows that, while the irregular recurrence may be an artifact of the geologic evolution of the trench site, there may exist a more fundamental physical process underlying the behavior of the central Garlock fault. This poorly understood process may be related to the temporal and spatial clustering of earthquakes observed for faults in the Eastern California Shear Zone., San Diego State University
A Bridgerian age flora from Del Mar, California
A small but well-preserved transported assemblage of plant fossils collected from the middle Eocene Torrey Sandstone at Del Mar, California, provides, for the first time, an accurate picture of local climate and vegetation 49 to 50 Ma. The flora includes taxa from estuarine, riparian, and coastal lowland habitats of a paratropical broadleaf forest. Living taxa similar to Torrey flora species inhabit warm temperate to paratropical forests of southeastern China, Mexico, and the southeastern United States. The taxonomic composition and foliar physiognomy of Torrey flora fossils indicate a warm (20 C mean annual temperature), equable (less than 8 C mean annual temperature range), frostless climate, with annual rainfall of between 120 and 150 cm, concentrated during the months of April through September. These conclusions suggest that although a climatic drying trend was well established in western North America as early as 50 Ma, conditions remained mesic in the coastal San Diego region. The occurrence of tropical taxa including Tabernaemontana and Eugenia americana in the Torrey flora indicate that the mean annual temperature of the San Diego area had increased between early and middle Eocene time., San Diego State University
A comparative analysis of interpolation techniques for estimating transmissivities in San Antonio Creek Valley, Santa Barbara County, California
Defining the spatial distribution of hydrologic data is an important aspect in many water-resources investigations. Estimating values of a particular parameter in areas where no known data exist may be accomplished by employing an interpolation technique. Several techniques are available, each producing results of varying degrees of accuracy. Six interpolation techniques were compared in this study for estimating the transmissivity distribution for San Antonio Creek valley in Santa Barbara County, California. The interpolation techniques considered in this study were nearest neighbor, inverse distance squared weighting, least squares, Laplace, Laplace plus splines and kriging. The basis of comparison was a transmissivity distribution produced by a calibrated two-dimensional steady-state ground-water flow model. A hypothetical fault was introduced to determine the accuracy of each method when a discontinuity exists. Methods of analysis included verification of ten known values suppressed and subsequently estimated by each technique and whole-dataset analysis. The verification procedure included an error analysis, use of scatterplots and simple regression. Scatterplots and simple regression were also used in the whole-dataset analysis, as well as a qualitative analysis consisting of comparisons of transmissivity distribution, contours of the difference between real and estimated transmissivities and contoured water-level elevations generated by using each estimated and the real transmissivity distribution in the model. The error analysis for the verification data indicated that Laplace plus splines had the best overall average error, 67 percent. Kriging interpolation produced the most estimates with errors less than ten percent, an arbitrary criterion of acceptability. However, other kriged values had errors much higher than those of Laplace plus splines. Scatterplots showed that least squares produced the best fit about the real equals estimated line with Laplace plus splines also producing a good fit. Nearest neighbor interpolation produced the worst plot, with much scatter about the real equals estimated line. Simple regression analysis indicated the Laplace plus splines had the highest correlation coefficient and coefficient of determination and lowest sum of squared deviations and standard deviation about the regression line. Least squares interpolation produced results similar to those of Laplace plus splines. Nearest neighbor produced the worst results. Scatterplots for whole datasets for both the with- and without-fault data showed that Laplace plus splines provided the best fit about the real equals estimated line. Laplace interpolation also produced a good fit. In this case, however, least squares produced the worst fit, with many outliers. In general, simple regression for whole datasets supported the scatterplot analysis. For the without-fault case, Laplace plus splines produced the highest correlation coefficient and coefficient of determination and lowest sum of squared deviations and standard deviation about the regression line. Laplace interpolation, however, produced slightly better values for the with-fault case. Least squares provided the worst results. The qualitative analysis provided similar results. Laplace plus splines and Laplace interpolation techniques produced the most accurate results in estimating transmissivity values in the San Antonio Creek valley. Kriging, inverse distance squared weighting and nearest neighbor can produce satisfactory results when data are abundant and uniform. Least squares interpolation has a tendency to produce values that increase without limit near the basin boundary., San Diego State University
A comparative study of Holocene sand and Cretaceous sandstone derived from the Peninsular Ranges, California and Baja California Norte, Mexico: Evidence for deep dissection of the Peninsular Ranges magmatic arc
Detailed modal data on the composition of Holocene sand derived from pre-Tertiary rocks of the Peninsular Ranges are used to independently test previously proposed provenance-discrimination models, and are also compared to data for sandstones from the Late Cretaceous Point Loma Formation. The results of this study indicate that detritus in sandstones from the Point Loma Formation was derived from the deeply dissected plutonic/metamorphic roots of the Peninsular Ranges magmatic arc. This conclusion is significant because it implies that parts of the Peninsular Ranges magmatic arc were uplifted, deeply dissected, and nearly stripped clean of their volcanic cover by Late Cretaceous time. There is little evidence in the San Diego area for the volcanic detritus that was presumably derived from the denudation of the Peninsular Ranges magmatic arc. This apparent paradox may imply that: (1) the Peninsular Ranges magmatic arc system was unlike modern arc systems and lacked an extensive volcanic cover; or, (2) the volcanic debris derived from the erosion of the volcanic cover is hidden beneath the Pacific Ocean, or was tectonically removed., San Diego State University
A critical examination and evaluation of the structure and stratigraphy in the downtown San Diego area, California
A trench was excavated, logged, and interpreted across projections of the Rose Canyon Fault Zone in the downtown area of San Diego, California. The trench traversed 930 m (3150 ft), crossing mapped projections of the Coronado, Old Town, Rose Canyon, and San Diego Bay faults. In examining the trench exposures, a normal fault, with an apparent strike-slip component, termed the San Diego Fault, was observed on Broadway between Front Street and First Avenue in downtown San Diego. The San Diego Fault strikes N5°W, dips 60°-70°E and has a vertical separation of 10 m (33 ft) based on faunal and stratigraphic correlations within sediments that have been dated to be 360,000 to 560,000 ± 75,000 years old using amino acid racemization techniques. A paleosol that has subsequently developed on these sediments has been vertically offset a minimum of 60 cm (24 in.) and has been estimated to be 75,000 to 128,000 years old based on its pedogenic development. A 20,000-year old palesol overlies the fault and displays no evidence of offset. The San Diego Fault appears to be contemporary with the extensional stress environment found within the San Diego area. There was no readily discernible evidence of faulting elsewhere in the trench, suggesting that the major north-south faults projected through the downtown area do not offset Middle to Upper Pleistocene sedimentary rocks., San Diego State University
A detrital heavy mineral provenance study of Upper Cretaceous fore-arc strata, northern Peninsular Ranges, Southern California
San Diego State University, Provenance analyses of detrital minerals in sedimentary basins allow geologists to determine the characteristics of ancient highlands that are now eroded away and inaccessible to direct study. The purpose of this study is to apply techniques of provenance analysis to Upper Cretaceous forearc basin strata in San Diego and the Santa Ana Mountains. These strata were deposited adjacent to and locally onlap crystalline basement of the deeply denuded Peninsular Ranges batholith (PRB), the presumed source of forearc basin sediment. The PRB is divided into western and eastern zones based on distinct asymmetrical characteristics in the plutonic rocks that reflect transverse spatial variation across the batholith. The Cretaceous sediment characteristics of the fore-arc basin can be compared to the plutonic rocks to spatially resolve sources within the PRB. Most detrital sediment provenance studies utilize the framework mineral grains of sandstone such as feldspar and quartz. This study focuses on the heavy minerals to support previous studies that have shown the Upper Cretaceous sediments in the fore-arc basin were derived from the PRB as well as to narrow the provenance for most of the Upper Cretaceous sediments to the eastern zone of the batholith. Analytical methods selected for this detrital sandstone heavy mineral investigation include: in situ measurements of magnetic susceptibility, point counting of heavy mineral separates, X-ray diffraction (XRD) analysis of Fe-Ti oxide minerals, 87Sr/86Sr isotopic analysis of detrital apatite grains, and scanning electron microscope examination of selected mineral grains. Analysis was performed on sandstone samples from the Trabuco, Ladd, and Williams Formations of the Santa Ana Mountains and Lusardi, Point Loma, and Cabrillo Formations of the San Diego Embayment. The mineralogy of the Trabuco and Lusardi Formations at the base of the sections studied indicates a western zone PRB source for detritus. These formations are at least in part red-beds deposited in subaerial environments. The provenance of overlying formations demonstrate a predominantly eastern zone PRB source with sediments deposited in marine diagenetic conditions that allowed unstable minerals to survive. The fore-arc basin minerals and their condition indicate the distance from source to the sedimentary basin was relatively short. Batholithic source rocks had a partial cratonic signature based on 87Sr/86Sr apatite ratios, and were of an acidic igneous composition. Upsection shifts in provenance characteristics indicate progressive headward erosion of drainage basins into the denuding batholith during the deposition of the Point Loma and Williams Formations.
A geochemical and isotopic study of the youngest lavas from the islands of Upolu and Savai'i, Samoa
We report major and trace element abundances and Hf, Pb, and Nd isotopic ratios for eight of the youngest rejuvenation stage lavas from the Samoan Islands of Upolu and Savai'i. The extensive and voluminous amount of rejuvenation stage volcanism on the Samoan islands, especially on the islands of Savai'i and Upolu, has made these islands key in the understanding of rejuvenation magmatism. The six lavas from Upolu are basanites, whereas the two lavas from Savai'i are alkali basalts. With the exception of one basanite with 7.4 wt. % MgO, all of the samples are relatively primitive (MgO = 10.5 to 12.2 wt. %) and show little evidence of fractionation beyond olivine control. However, variations in major element abundances at a given MgO value indicate changes in the parental melt composition. This interpretation is confirmed by wide variations in ratios of incompatible trace elements (e.g., Nb/La or Ce/Yb). On a primitive mantle normalized trace element diagram, the lavas have relatively constant, low abundances of heavy rare-earth elements (e.g., Yb) due to the presence of residual garnet in the mantle source region. The _Nd (-0.26 to +2.93) and εHf (+3.82 to +7.17) values, and Pb isotope ratios (e.g., ___Pb/___Pb = 18.57-18.88) vary significantly but plot within the range of published data for rejuvenation stage lavas from these islands. On a plot of εNd vs. ___Pb/___Pb, the new Upolu and Savai'i analyses make a distinctive positive correlation that overlaps with previous analyses of rejuvenation stage lavas from these islands. Interestingly, this trend is distinct from the ones defined by many of the purported Upolu and Savai'i shield stage lavas. These data will help to better understand the origin of rejuvenation stage magmatism., San Diego State University
A geochemical evaluation of enhanced in-situ bioremediation of chlorinated ethenes in groundwater
Includes bibliographical references (page 51), Sites impacted with chlorinated solvents present unique technical challenges when compared to most other groundwater contaminants. Chlorinated volatile organic compounds (CVOCs) such as such as tetrachloroethene (PCE), trichloroethene (TCE), or 1,1,1- trichloroethane (1,1,1-TCA) generally do not degrade naturally in the environment. Therefore, more aggressive source depletion methods such as enhanced in-situ bioremediation (EISB) may be implemented to treat the groundwater plume. EISB involves injection of an electron donor to promote reducing conditions followed by inoculation of groundwater with dechlorinating bacteria. When conditions are favorable, the dechlorinating bacteria sequentially remove chlorine ions from the chlorinated solvent compound until an innocuous end product is produced. This process creates unique and dramatic changes in the natural geochemistry of the aquifer system. A CVOC-impacted site located at Naval Air Station North Island (NASNI) was used as a test case for this study. NASNI is an active military base located adjacent to the City of Coronado in San Diego County, California. The site, or Operable Unit 24 (OU 24), is a chlorinated solvent groundwater plume which may have originated from an acid waste pump station associated with a historic industrial waste pipeline. The purpose of this study was to evaluate the geochemical changes that occur during EISB and how they relate to the effectiveness of remediation. An evaluation of the redox conditions present in groundwater and the observed reduction in CVOC concentrations was used to evaluate the effectiveness of EISB. In addition, geochemical modeling was performed to develop an understanding of the effect of redox conditions on observed dissolved inorganic constituent concentrations due to precipitation or dissolution of minerals present in the aquifer. Based on the results of the geochemical evaluation, groundwater generally became more reducing and VOC concentrations decreased following implementation of EISB. In addition, minerals containing Fe, Mn, and SO4 were sensitive to redox transformations. Conversely, Ca, Mg, Na, and some Mn-containing minerals were not sensitive to redox conditions. Reduced minerals FeS, FeS2, and H2S have the potential to precipitate and oxidized Fe and Mn minerals have the potential to dissolve as groundwater becomes more reducing. This can create problems with groundwater treatment systems that expose groundwater to oxygen. When reduced groundwater containing high concentrations of dissolved Fe and Mn is exposed to oxygen, the Fe and Mn hydroxide minerals will precipitate and may foul remediation equipment. Additionally, redox transformations can potentially mobilize toxic metals such as arsenic, chromium, lead, and mercury through oxidation and reduction processes., San Diego State University
A geochemical reconnaissance of thermal waters along portions of the San Jacinto and San Andreas fault zones, Southern California
Twenty-three warm spring wells from six different areas were sampled along parts of the San Jacinto and San Andreas fault zones. An additional 51 well water analyses in the studied areas were obtained from other sources. The waters were analysed for 15 different elements plus Si02 to determine: 1) if near surface mixing with local cold ground water occurs, 2) reservoir temperatures, 3) estimated depth of circulation of thermal waters, 4) water-rock reactions at depth, and 5) relationships between springs. Tritium samples were taken at each of the six areas and indicate no mixing between the ascending thermal waters and cold ground waters except for Arrowhead Springs, which was found to have a 13.5% component of cold water. Surface temperatures of the warm springs and wells range from 29°C to 85°C. Estimated reservoir temperatures vary from 48°C at Ocotillo Wells to 120°C at San Bernardino. Depth of circulation in these two areas are 0.9 km and 3.3 km, respectively, with the four other areas having intermediate values. Two of the four warm springs are sodium carbonate dominated due to water-rock reactions with originally calcium carbonate ground waters. The other two warm springs are sodium sulfate dominated and appear to be oxidized from originally sodium carbonate springs. The warm wells fall into two categories: calcium bicarbonate and sodium-calcium sulfate-chloride dominated. The different chemistries can be explained on the basis of the original recharge water and various mechanical and chemical reactions., San Diego State University