Matching Items (39)
Description
The historic Cacachilas mining district is located in Baja California Sur, approximately 20 kilometers east of La Paz, and has a series of gold- and silver-hosted veins, faults, and shear zones within Cretaceous granodioritic plutons. The remote geographic location and past political events within Mexico left the district essentially unexplored after the late 1800s, when the Mexican Revolution began. More recent discovery of gold deposits along the Baja peninsula instigated a renewed interest in mineralization in the Sierra Cacachilas. The area lacks detailed previous geologic data, so this study focused on characterizing the controls of mineralization and the locations of mineralized trends of deposits within the northeastern Sierra Cacachilas, with a goal toward helping assess economic viability of the deposits. I mapped surficial geologic data, such as outcrop locations, alteration assemblages, limonite intensities, and structural measurements. I then synthesized these into geologic maps and cross sections. I combined field data with geochemical assays and structural plots to better characterize individual historic district trends and newly located trends to understand the distribution of mineralization at surface and at depth. Lastly, I synthesized geology of the Sierra Cacachilas with other gold and silver deposits located in the southern Baja peninsula to better characterize the mineralization and deposit style of the Cacachilas district.
Mineralization in the northeastern Sierra Cacachilas is mainly restricted to steeply dipping quartz veins, faults, and brittle-ductile shear zones that trend generally northeast. Some veins are en-echelon within the mineralized zones, implying some lateral movement along the zones. Veins are dominated by milky to clear quartz with trace sulfides, abundant limonite (after sulfides), and local open-space textures. Mineralization is interpreted to be intermediate between classic epithermal and mesothermal veins. Within mineralized trends and commonly associated with mineralization are greisen-like zones that are defined by intense sericitic to muscovitic overprint, trend northeast, and are with or without sulfides. The intensity of sulfide abundance and limonitic alteration after sulfides within and near mineralized zones is overall a good guide to mineralization. Based on past reports and on my recent studies, the Cacachilas district has very promising potential for relatively small, high-grade deposits.
Mineralization in the northeastern Sierra Cacachilas is mainly restricted to steeply dipping quartz veins, faults, and brittle-ductile shear zones that trend generally northeast. Some veins are en-echelon within the mineralized zones, implying some lateral movement along the zones. Veins are dominated by milky to clear quartz with trace sulfides, abundant limonite (after sulfides), and local open-space textures. Mineralization is interpreted to be intermediate between classic epithermal and mesothermal veins. Within mineralized trends and commonly associated with mineralization are greisen-like zones that are defined by intense sericitic to muscovitic overprint, trend northeast, and are with or without sulfides. The intensity of sulfide abundance and limonitic alteration after sulfides within and near mineralized zones is overall a good guide to mineralization. Based on past reports and on my recent studies, the Cacachilas district has very promising potential for relatively small, high-grade deposits.
ContributorsSeverson, Allison Rose (Author) / Reynolds, Stephen J. (Thesis advisor) / Semken, Steven (Committee member) / Burt, Donald (Committee member) / Arizona State University (Publisher)
Created2015
Description
Amazonia, inhabited and investigated for millennia, continues to astonish scientists with its cultural and natural diversity. Although Amazonia is rapidly changing, its vast and varied landscape still contains a complex natural pharmacopeia. The Amazonian tribes have accrued valuable environmental and geological knowledge that can be studied. This dissertation demonstrates that Indigenous Knowledge considered alongside Western Science can enhance our understanding of the relationship of people to geological materials and hydrological resources, and reveal mineral medicines with practical applications.
I used methods from anthropology and geology to explore the geological knowledge of the Uitoto, a tribe of the Colombian Amazon. The Uitoto use two metaphors to describe Earth systems: 1. the earth is a body, and 2. the Amazon is a tree. I found that they classify surface-water systems according to observable characteristics and use mineral clays to treat various maladies. I argue that Uitoto knowledge about Amazonian mineral resources and surface water is practical, empirically–based and, in many cases, more nuanced than mainstream scientific knowledge.
I studied the mode of action of a natural antibacterial clay from the Colombian Amazon (AMZ) to discover whether the Uitoto’s claims about the clay’s medicinal values was verifiable using the methods of Western Science. Natural antibacterial clays can inhibit the growth of human pathogens. Methods from microbiology and geochemistry were combined to evaluate the mineral-microbe interactions that inhibit growth of model Gram-negative (Escherichia coli) and Gram-positive (Bacillus subtilis) bacteria. The AMZ antibacterial clay contains 45 % kaolinites and 30 % smectites. Its high surface area maintains an acidic environment (pH 4.5) and releases high concentrations of aluminum. Aluminum accumulates in the outer membrane of E. coli by binding to phospholipids. Furthermore, the membrane’s permeability increases due to synergistic effects between aluminum and transition metals released from the AMZ (i.e. Fe, Cu). The changes in the membrane may compromise its function as a barrier. Understanding the antibacterial mechanism of AMZ is key for its safe use as a natural product. These findings can help us harness the capabilities of antibacterial clays more efficiently.
Lastly, I integrated the results of this work in place-based, cross-cultural educational materials tailored for the tribal schools in the Colombian Amazon. The design of the units was informed by principles of curriculum design and successful pedagogic approaches for Native American students. The purpose of these educational materials is to return the results of research, enhance learning and participation of indigenous peoples in geosciences, and respond to the multicultural and plurilingual educational needs in countries such as Colombia.
I used methods from anthropology and geology to explore the geological knowledge of the Uitoto, a tribe of the Colombian Amazon. The Uitoto use two metaphors to describe Earth systems: 1. the earth is a body, and 2. the Amazon is a tree. I found that they classify surface-water systems according to observable characteristics and use mineral clays to treat various maladies. I argue that Uitoto knowledge about Amazonian mineral resources and surface water is practical, empirically–based and, in many cases, more nuanced than mainstream scientific knowledge.
I studied the mode of action of a natural antibacterial clay from the Colombian Amazon (AMZ) to discover whether the Uitoto’s claims about the clay’s medicinal values was verifiable using the methods of Western Science. Natural antibacterial clays can inhibit the growth of human pathogens. Methods from microbiology and geochemistry were combined to evaluate the mineral-microbe interactions that inhibit growth of model Gram-negative (Escherichia coli) and Gram-positive (Bacillus subtilis) bacteria. The AMZ antibacterial clay contains 45 % kaolinites and 30 % smectites. Its high surface area maintains an acidic environment (pH 4.5) and releases high concentrations of aluminum. Aluminum accumulates in the outer membrane of E. coli by binding to phospholipids. Furthermore, the membrane’s permeability increases due to synergistic effects between aluminum and transition metals released from the AMZ (i.e. Fe, Cu). The changes in the membrane may compromise its function as a barrier. Understanding the antibacterial mechanism of AMZ is key for its safe use as a natural product. These findings can help us harness the capabilities of antibacterial clays more efficiently.
Lastly, I integrated the results of this work in place-based, cross-cultural educational materials tailored for the tribal schools in the Colombian Amazon. The design of the units was informed by principles of curriculum design and successful pedagogic approaches for Native American students. The purpose of these educational materials is to return the results of research, enhance learning and participation of indigenous peoples in geosciences, and respond to the multicultural and plurilingual educational needs in countries such as Colombia.
ContributorsLondoño Arias, Sandra Carolina (Author) / Williams, Lynda B (Thesis advisor) / Semken, Steven (Thesis advisor) / Brandt, Elizabeth A. (Committee member) / Hartnett, Hilairy H (Committee member) / Raymond, Jason (Committee member) / Arizona State University (Publisher)
Created2016
Description
The search for life on Mars is a major NASA priority. A Mars Sample Return
(MSR) mission, Mars 2020, will be NASA's next step towards this goal, carrying an instrument suite that can identify samples containing potential biosignatures. Those samples will be later returned to Earth for detailed analysis. This dissertation is intended to inform strategies for fossil biosignature detection in Mars analog samples targeted for their high biosignature preservation potential (BPP) using in situ rover-based instruments. In chapter 2, I assessed the diagenesis and BPP of one relevant analog habitable Martian environment: a playa evaporite sequence within the Verde Formation, Arizona. Coupling outcrop-scale observations with laboratory analyses, results revealed four diagenetic pathways, each with distinct impacts on BPP. When MSR occurs, the sample mass returned will be restricted, highlighting the importance of developing instruments that can select the most promising samples for MSR. Raman spectroscopy is one favored technique for this purpose. Three Raman instruments will be sent onboard two upcoming Mars rover missions for the first time. In chapters 3-4, I investigated the challenges of Raman to identify samples for MSR. I examined two Raman systems, each optimized in a different way to mitigate a major problem commonly suffered by Raman instruments: background fluorescence. In Chapter 3, I focused on visible laser excitation wavelength (532 nm) gated (or time-resolved Raman, TRR) spectroscopy. Results showed occasional improvement over conventional Raman for mitigating fluorescence in samples. It was hypothesized that results were wavelength-dependent and that greater fluorescence reduction was possible with UV laser excitation. In Chapter 4, I tested this hypothesis with a time-resolved UV (266 nm) gated Raman and UV fluorescence spectroscopy capability. I acquired Raman and fluorescence data sets on samples and showed that the UV system enabled identifications of minerals and biosignatures in samples with high confidence. The results obtained in this dissertation may inform approaches for MSR by: (1) refining models for biosignature preservation in habitable Mars environments; (2) improving sample selection and caching strategies, which may increase the success of Earth-based biogenicity studies; and (3) informing the development of Raman instruments for upcoming rover-based missions.
(MSR) mission, Mars 2020, will be NASA's next step towards this goal, carrying an instrument suite that can identify samples containing potential biosignatures. Those samples will be later returned to Earth for detailed analysis. This dissertation is intended to inform strategies for fossil biosignature detection in Mars analog samples targeted for their high biosignature preservation potential (BPP) using in situ rover-based instruments. In chapter 2, I assessed the diagenesis and BPP of one relevant analog habitable Martian environment: a playa evaporite sequence within the Verde Formation, Arizona. Coupling outcrop-scale observations with laboratory analyses, results revealed four diagenetic pathways, each with distinct impacts on BPP. When MSR occurs, the sample mass returned will be restricted, highlighting the importance of developing instruments that can select the most promising samples for MSR. Raman spectroscopy is one favored technique for this purpose. Three Raman instruments will be sent onboard two upcoming Mars rover missions for the first time. In chapters 3-4, I investigated the challenges of Raman to identify samples for MSR. I examined two Raman systems, each optimized in a different way to mitigate a major problem commonly suffered by Raman instruments: background fluorescence. In Chapter 3, I focused on visible laser excitation wavelength (532 nm) gated (or time-resolved Raman, TRR) spectroscopy. Results showed occasional improvement over conventional Raman for mitigating fluorescence in samples. It was hypothesized that results were wavelength-dependent and that greater fluorescence reduction was possible with UV laser excitation. In Chapter 4, I tested this hypothesis with a time-resolved UV (266 nm) gated Raman and UV fluorescence spectroscopy capability. I acquired Raman and fluorescence data sets on samples and showed that the UV system enabled identifications of minerals and biosignatures in samples with high confidence. The results obtained in this dissertation may inform approaches for MSR by: (1) refining models for biosignature preservation in habitable Mars environments; (2) improving sample selection and caching strategies, which may increase the success of Earth-based biogenicity studies; and (3) informing the development of Raman instruments for upcoming rover-based missions.
ContributorsShkolyar, Svetlana (Author) / Farmer, Jack (Thesis advisor) / Semken, Steven (Committee member) / Sharp, Thomas (Committee member) / Shim, Sang-Heon Dan (Committee member) / Youngbull, Aaron Cody (Committee member) / Arizona State University (Publisher)
Created2016
Description
For this dissertation, three separate papers explore the study areas of the western Grand Canyon, the Grand Staircase (as related to Grand Canyon) and Desolation Canyon on the Green River in Utah.
In western Grand Canyon, I use comparative geomorphology between the Grand Canyon and the Grand Wash Cliffs (GWC). We propose the onset of erosion of the GWC is caused by slip on the Grand Wash Fault that formed between 18 and 12 million years ago. Hillslope angle and channel steepness are higher in Grand Canyon than along the Grand Wash Cliffs despite similar rock types, climate and base level fall magnitude. These experimental controls allow inference that the Grand Canyon is younger and eroding at a faster rate than the Grand Wash Cliffs.
The Grand Staircase is the headwaters of some of the streams that flow into Grand Canyon. A space-for-time substitution of erosion rates, supported by landscape simulations, implies that the Grand Canyon is the result of an increase in base level fall rate, with the older, slower base level fall rate preserved in the Grand Staircase. Our data and analyses also support a younger, ~6-million-year estimate of the age of Grand Canyon that is likely related to the integration of the Colorado River from the Colorado Plateau to the Basin and Range. Complicated cliff-band erosion and its effect on cosmogenic erosion rates are also explored, guiding interpretation of isotopic data in landscapes with stratigraphic variation in quartz and rock strength.
Several hypotheses for the erosion of Desolation Canyon are tested and refuted, leaving one plausible conclusion. I infer that the Uinta Basin north of Desolation Canyon is eroding slowly and that its form represents a slow, stable base level fall rate. Downstream of Desolation Canyon, the Colorado River is inferred to have established itself in the exhumed region of Canyonlands and to have incised to near modern depths prior to the integration of the Green River and the production of relief in Desolation Canyon. Analysis of incision and erosion rates in the region suggests integration is relatively recent.
In western Grand Canyon, I use comparative geomorphology between the Grand Canyon and the Grand Wash Cliffs (GWC). We propose the onset of erosion of the GWC is caused by slip on the Grand Wash Fault that formed between 18 and 12 million years ago. Hillslope angle and channel steepness are higher in Grand Canyon than along the Grand Wash Cliffs despite similar rock types, climate and base level fall magnitude. These experimental controls allow inference that the Grand Canyon is younger and eroding at a faster rate than the Grand Wash Cliffs.
The Grand Staircase is the headwaters of some of the streams that flow into Grand Canyon. A space-for-time substitution of erosion rates, supported by landscape simulations, implies that the Grand Canyon is the result of an increase in base level fall rate, with the older, slower base level fall rate preserved in the Grand Staircase. Our data and analyses also support a younger, ~6-million-year estimate of the age of Grand Canyon that is likely related to the integration of the Colorado River from the Colorado Plateau to the Basin and Range. Complicated cliff-band erosion and its effect on cosmogenic erosion rates are also explored, guiding interpretation of isotopic data in landscapes with stratigraphic variation in quartz and rock strength.
Several hypotheses for the erosion of Desolation Canyon are tested and refuted, leaving one plausible conclusion. I infer that the Uinta Basin north of Desolation Canyon is eroding slowly and that its form represents a slow, stable base level fall rate. Downstream of Desolation Canyon, the Colorado River is inferred to have established itself in the exhumed region of Canyonlands and to have incised to near modern depths prior to the integration of the Green River and the production of relief in Desolation Canyon. Analysis of incision and erosion rates in the region suggests integration is relatively recent.
ContributorsDarling, Andrew Lee (Author) / Whipple, Kelin (Thesis advisor) / Semken, Steven (Committee member) / Arrowsmith, Ramon (Committee member) / DeVecchio, Duane (Committee member) / Heimsath, Arjun (Committee member) / Arizona State University (Publisher)
Created2016
Description
ABSTRACT The accretion of juvenile island-arc lithosphere by convergent tectonism during the Paleoproterozoic, in conjunction with felsic volcanism, resulted in the assembly, ductile to partial brittle deformation, uplift, and northwest-directed thrusting of rocks in the McDowell Mountains region and adjacent areas in the Mazatzal Orogenic belt. Utilizing lithologic characteristics and petrographic analysis of the Proterozoic bedrock, a correlation to the Alder series was established, revising the stratigraphic sequences described by earlier works. The central fold belt, composed of an open, asymmetric syncline and an overturned, isoclinal anticline, is cut by an axial-plane parallel reactivated thrust zone that is intruded by a deformed Paleoproterozoic mafic dike. Finite strain analyses of fold geometries, shear fabrics, foliations, fold vergence, and strained clasts point to Paleoproterozoic northwest-directed thrusting associated with the Mazatzal orogen at approximately 1650 million years ago. Previous studies constrained the regional P-T conditions to at least the upper andalusite-kyanite boundary at peak metamorphic conditions, which ranged from 4-6 kilobars and 350-450⁰ Celsius, although the plasticity of deformation in a large anticlinal core suggests that this represents the low end of the P-T conditions. Subsequent to deformation, the rocks were intruded by several granitoid plutons, likely of Mesoproterozoic age (1300-1400 Ma). A detailed analysis of Proterozoic strain solidly places the structure of the McDowell Mountains within the confines of the Mazatzal Orogeny, pending any contradictory geochronological data.
ContributorsVance, Brad (Author) / Reynolds, Stephen J. (Thesis advisor) / Semken, Steven (Committee member) / Stump, Edmund (Committee member) / Arizona State University (Publisher)
Created2012
Description
Previous studies have shown that adequate content knowledge is a necessary, but not sufficient, requirement for affective teaching. While legislation requests teachers to be "highly qualified" in a subject area, such as physics, many teachers are frequently asked to teach in an area when they are not certified through a teaching license to do so. This study uses mixed methods to examine the knowledge of beginning physics teachers. Through semi-structured interviews, classroom observations, and concept maps, the pedagogical content knowledge, subject matter knowledge, and practices of three groups of beginning secondary physics teachers were explored. Data were analyzed qualitatively using cases and quantitatively using descriptive statistics and t-tests, the results of which were combined during the interpretation phase of the research process. The study indicated that, over the first two years of teaching, the in-field group of teachers showed stronger physics content knowledge, a consideration for student difficulties with physics topics, and a positive shift in pedagogical content knowledge impacted by working with students, as compared to the rest of the teachers in the study. This research has implications in the development of secondary physics teachers and in the field of physics education research. Specifically, this research has implications in the physics content support for beginning secondary science teachers, the novice/expert research in physics education research, and the pedagogical preparation of undergraduate students, graduate students, and faculty in physics.
ContributorsNeakrase, Jennifer Jean (Author) / Luft, Julie (Thesis advisor) / Semken, Steven (Committee member) / Culbertson, Robert (Committee member) / Green, Samuel (Committee member) / Clark, Douglas (Committee member) / Arizona State University (Publisher)
Created2010
Description
Blue Mound State Park, located in the state of Wisconsin (USA), is host to a topographic anomaly known as Blue Mound. This mound is the western of the two mounds that make up the park, and it marks the highest elevation in southern Wisconsin. Unlike its eastern sibling, Blue Mound possesses an unusual chert cap that may have protected it from erosion, thus preserving its stratigraphic integrity. Although Blue Mound's unique chert armor was noted in 1927 by the Wisconsin Geological and Natural History Survey, no published work has satisfactorily explained its origin. As little was known about the formation of cherts until the mid-to-late 1900s, the Blue Mound cap was classified merely as a Silurian dolostone into which chert had somehow become integrated (Steidtmann). However, the published observations of the Blue Mound chert do not necessarily match with the classification granted by the Wisconsin Geological and Natural History Survey, nor were any convincing interpretations offered regarding the presence of the chert. Since 1927, significant progress in the field of sedimentology has been achieved. There now exists knowledge that may fill the gaps between observation and interpretation in the Blue Mound survey. The observations in the 1927 bulletin correspond with modern notions of a paleokarst chert breccia, which forms a chert rubble or residuum. A chert breccia is formed when existing clasts, or pieces, of chert become cemented together by further chert deposition (Kolodny, Chaussidon and Katz). This can form large boulders of chert rubble that resist erosion. Accumulation of chert rubble has been documented to form along old weathering surfaces as an insoluble residue in environments similar to Blue Mound (Kolodny, Chaussidon and Katz). The purpose of this investigation was to verify the observations within the 1927 survey of the Blue Mound chert, and determine through field observations and sample study if the Blue Mound chert fits the model of a paleokarst chert breccia.
ContributorsGalarowicz, Calley (Author) / Knauth, Paul (Thesis director) / Semken, Steven (Committee member) / Martin, Thomas (Committee member) / Barrett, The Honors College (Contributor) / School of Earth and Space Exploration (Contributor)
Created2013-05
Description
The goal of the first study was to characterize the Miocene arkosic conglomerate in the Goldfield Mountains to determine the paleocurrent direction and source of the cobbles. This conglomerate is tilted to the northeast and unconformably overlies Proterozoic basement. Imbrication measurements are scattered but suggest the direction of paleoflow was toward the northwest and northeast, which suggests the cobbles were sourced from the southeast and southwest. The abundance of Dripping Spring Quartzite and the presence of Barnes Conglomerate in the cobbles, suggests an Apache Group source. In addition, south-southeast of the map area, there are several rock units composed of the same material as cobbles within the arkosic conglomerate. The arkosic conglomerate was likely deposited during onset of mid-Cenozoic extension, where the resulting highlands could provide a nearby source for the cobbles. This nearby source is interpreted to be south-southeast of the study area. A second study examined the effectiveness of course reform conducted on an introductory undergraduate course sequence. Questions of this study included: (1) How does the curriculum cater to a student population with diverse goals? (2) How do reformed courses add educational value as perceived by the student? (3) How does the redesigned curriculum and the instructional strategies, as implemented, address the goals of the reform?
The curriculum addressed the goals of the reform by (1) creating more opportunities for students to gain the skills relevant to their future goals, (2) having students utilize big data to make observations, interpretations, and predictions, (3) engaging students in scientific collaboration through group work and discussion, (4) giving students the opportunity to utilize computer programs that apply across various subjects and fields (i.e. Excel, MS Word, ArcGIS), and (5) requiring students to conduct original research to solve a problem and present their results orally and in written form. These redesign efforts were successful in meeting the objectives, and majority of the student participants reported one or more of the reformed experiences were valuable to their education and future goals. An understanding of teaching methods and educational values held by undergraduate students within the School of Earth and Space Exploration can be adapted and applied across subjects.
ContributorsAccetta, Danielle (Author) / Reynolds, Stephen J (Thesis advisor) / Johnson, Julia K (Committee member) / Semken, Steven (Committee member) / Arizona State University (Publisher)
Created2021
Description
Lithium (Li) is a trace element in kerogen, but the content and isotopic distribution (δ7Li) in kerogen has not previously been quantified. Furthermore, kerogen has been overlooked as a potential source of Li to sedimentary porefluids and buried sediments. Thus, knowing the content and isotopic composition of Li derived from kerogen may have implications for research focused on the Li-isotopes of buried sediments (e.g., evaluating paleoclimate variations using marine carbonates).The objective of this work is to better understand the role of kerogen in the Li geochemical cycle. The research approach consisted of 1) developing reference materials and methodologies to measure the Li-contents and δ7Li of kerogen in-situ by Secondary Ion Mass Spectrometry, 2) surveying the Li-contents and δ7Li of kerogen bearing rocks from different depositional and diagenetic environments and 3) quantifying the Li-content and δ7Li variations in kerogen empirically in a field study and 4) experimentally through hydrous pyrolysis.
A survey of δ7Li of coals from depositional basins across the USA showed that thermally immature coals have light δ7Li values (–20 to – 10‰) compared to typical terrestrial materials (> –10‰) and the δ7Li of coal increases with burial temperature suggesting that 6Li is preferentially released from kerogen to porefluids during hydrocarbon generation. A field study was conducted on two Cretaceous coal seams in Colorado (USA) intruded by dikes (mafic and felsic) creating a temperature gradient from the intrusives into the country rock. Results showed that δ7Li values of the unmetamorphosed vitrinite macerals were up to 37‰ lighter than vitrinite macerals and coke within the contact metamorphosed coal.
To understand the significance of Li derived from kerogen during burial diagenesis, hydrous pyrolysis experiments of three coals were conducted. Results showed that Li is released from kerogen during hydrocarbon generation and could increase sedimentary porefluid Li-contents up to ~100 mg/L. The δ7Li of coals becomes heavier with increased temperature except where authigenic silicates may compete for the released Li. These results indicate that kerogen is a significant source of isotopically light Li to diagenetic fluids and is an important contributor to the global geochemical cycle.
ContributorsTeichert, Zebadiah (Author) / Williams, Lynda B. (Thesis advisor) / Bose, Maitrayee (Thesis advisor) / Hervig, Richard (Committee member) / Semken, Steven (Committee member) / Shock, Everett (Committee member) / Arizona State University (Publisher)
Created2022
Description
The Pennsylvanian and Permian sedimentary units of the American Southwest hold valuable records of a significant major tectonic event that formed the Ancestral Rocky Mountains and associated basins, such as the Paradox and Pedregosa Basins. These mountains exposed Precambrian crystalline rocks, contributing debris into the basins, forming predominantly reddish sedimentary sequences, such as the Supai Group of Grand Canyon, and the Abo Formation and Yeso Group of New Mexico. Previous studies have indicated that components of these sedimentary sequences were derived from regions outside the Southwest, such as the Appalachian Mountains of that time.Central New Mexico contains well-exposed sequences of Pennsylvanian and Permian sedimentary units with extensively studied biostratigraphy. Tight palaeontologic age constraints from these sequences provide an opportunity to examine variations over time of the relative contribution of sediment derived from the nearby Ancestral Rocky Mountains versus sediment of more distal origins.
This study utilizes the laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) approach to U-Pb dating of detrital zircons found within the Pennsylvanian and Permian sequences of central New Mexico, to evaluate changes in potential source regions and sediment transport over time, and to contribute insights to the existing tectonic and sedimentary record of the area during the Pennsylvanian and Permian periods. The findings reveal the Pennsylvanian units were dominated by locally derived sediment, characterized by zircon ages ranging from 1400 to 1800 Ma, whereas Permian units record a substantial influx of distally derived grains with zircon ages ranging from approximately ~270 Ma to 1300 Ma. This indicates that the Ancestral Rockies were the dominant sedimentary sources during the Pennsylvanian but became subdued enough in the Permian to allow the sedimentary basins to capture exotic grains derived from distant regions in North America. These findings contribute valuable insights to the tectonic and sedimentary history of central New Mexico during the Pennsylvanian and Permian periods, shedding light on the evolution of the Ancestral Rockies and the influences of distant sediment sources on the region's depositional patterns.
ContributorsAigner, Michelle (Author) / Reynolds, Stephen J (Thesis advisor) / Hodges, Kip V (Committee member) / Semken, Steven (Committee member) / Arizona State University (Publisher)
Created2023