Browsing by Department "Geology And Geophysics"

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Clumped Isotope Reordering Kinetics in Carbonate Minerals: The key to accurate ocean paleotemperatures and basin thermal histories
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/225; National Science Foundation
One of the most exciting new ideas in geochemistry is to measure two rare isotopes in calcium carbonate instead of just one and "clump" them together. This provides a new and powerful tool to study the temperature of ancient oceans and sediments and will help scientists looking at climate change, plate tectonics, and petroleum exploration. This study will help identify the calcium carbonate minerals most likely to preserve ancient temperatures. It will also provide the chemical information needed to use two minerals at the same time to better estimate the temperature history of the rocks. This project will develop this new tool by connecting atom-level processes with observed chemical reactions. The study will improve temperature estimates of ancient oceans and the temperature history of rocks related to petroleum reservoirs. The project will train graduate and undergraduate students and will add a new section of a capstone undergraduate course that will introduce seniors to the field. The project will also engage chemistry graduate and undergraduate students from underrepresented minority groups One of the most exciting developments in geochemistry in the 21st century is the ability to measure the relative abundance of molecules with two rare isotopes ("clumped isotopes") in calcium carbonate minerals (e.g., calcite) and apply this technique to reveal the temperatures of ancient oceans or the burial temperatures of sediments now exposed at the surface. A major complication in clumped isotope paleothermometry however is reequilibration (reordering) of the signatures at elevated temperatures (>100oC) on million-year timescales. While complicating paleoclimate studies, this reordering provides great potential for measuring rates of burial, uplift, and exhumation of geologic formations, but only if the rates (kinetics) of reordering are well understood. Currently, only the reordering kinetics of the mineral calcite (CaCO3) has been studied in detail. To address this knowledge gap, experiments will be conducted in which different minerals are heated and the rate at which they reorder is measured. The mechanisms of clumped isotope reordering will be examined at an atomistic level using a range of sophisticated chemical techniques such as programmable heated-stage synchrotron X-ray diffraction, total scattering, Raman spectroscopy, and scanning transmission X-ray microscopy, in conjunction with advanced models for atomic bonding. Correlating atomic characteristics with kinetic parameters and mineralogical characterization will allow determination of detailed equations governing the rates of reordering in a variety of carbonate minerals. The project will train graduate and undergraduate students and will add a new section of a capstone undergraduate course that will introduce seniors to the field. The project will also engage chemistry graduate and undergraduate students from underrepresented minority groups This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Clumped Isotope Reordering Kinetics in Carbonate Minerals: The key to accurate ocean paleotemperatures and basin thermal histories
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/225; National Science Foundation
One of the most exciting new ideas in geochemistry is to measure two rare isotopes in calcium carbonate instead of just one and "clump" them together. This provides a new and powerful tool to study the temperature of ancient oceans and sediments and will help scientists looking at climate change, plate tectonics, and petroleum exploration. This study will help identify the calcium carbonate minerals most likely to preserve ancient temperatures. It will also provide the chemical information needed to use two minerals at the same time to better estimate the temperature history of the rocks. This project will develop this new tool by connecting atom-level processes with observed chemical reactions. The study will improve temperature estimates of ancient oceans and the temperature history of rocks related to petroleum reservoirs. The project will train graduate and undergraduate students and will add a new section of a capstone undergraduate course that will introduce seniors to the field. The project will also engage chemistry graduate and undergraduate students from underrepresented minority groups One of the most exciting developments in geochemistry in the 21st century is the ability to measure the relative abundance of molecules with two rare isotopes ("clumped isotopes") in calcium carbonate minerals (e.g., calcite) and apply this technique to reveal the temperatures of ancient oceans or the burial temperatures of sediments now exposed at the surface. A major complication in clumped isotope paleothermometry however is reequilibration (reordering) of the signatures at elevated temperatures (>100oC) on million-year timescales. While complicating paleoclimate studies, this reordering provides great potential for measuring rates of burial, uplift, and exhumation of geologic formations, but only if the rates (kinetics) of reordering are well understood. Currently, only the reordering kinetics of the mineral calcite (CaCO3) has been studied in detail. To address this knowledge gap, experiments will be conducted in which different minerals are heated and the rate at which they reorder is measured. The mechanisms of clumped isotope reordering will be examined at an atomistic level using a range of sophisticated chemical techniques such as programmable heated-stage synchrotron X-ray diffraction, total scattering, Raman spectroscopy, and scanning transmission X-ray microscopy, in conjunction with advanced models for atomic bonding. Correlating atomic characteristics with kinetic parameters and mineralogical characterization will allow determination of detailed equations governing the rates of reordering in a variety of carbonate minerals. The project will train graduate and undergraduate students and will add a new section of a capstone undergraduate course that will introduce seniors to the field. The project will also engage chemistry graduate and undergraduate students from underrepresented minority groups This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Collaborative Research: Linking Atmospheric CO2 to Millennial Changes in Atmospheric and Oceanic Circulation in the Eastern Equatorial Pacific Ocean over the Past 100 kyr
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/205; National Science Foundation
To understand future climate change, we must know how climate varied in the past. One of the biggest unknowns about past climate is the origin of atmospheric carbon dioxide (CO2) variability over global warm-cold cycles. This project will address potential causes of the varying atmospheric carbon dioxide by focusing on changes in the efficiency of fertilization of the surface ocean, and how, and if, that is related to changes in the deep-ocean. Furthermore, the research will investigate both the "how" of varying carbon dioxide with the "where", namely the Eastern Equatorial Pacific (EEP), an important region of the world ocean where, today, significant CO2 is exhaled to the atmosphere and the greatest rates of phytoplankton growth are found. The project will contribute to an improved understanding of global climate change and important Earth systems connected to the tropical Pacific Ocean. On the broadest of levels, understanding the past dynamics of Earth's carbon cycle is of fundamental importance to inform and guide societal policy-making in an increasing CO2 world. The project will support the educational and professional development of graduate and undergraduate students and results will be incorporated into the curriculum of undergraduate and graduate classes. In addition, a series of YouTube videos will be developed that are aimed at communicating the importance of how past climate variability informs us about climate's future variability and its potential impact on our lives. The project seeks to answer questions related to: 1) where and how atmospheric carbon dioxide was sequestered from the atmosphere, or ventilated from the ocean, on millennial timescales, and 2) how these carbon dynamics are related to both changes in atmospheric and oceanic circulation over the last glacial period and into the deglacial and Holocene. To address these objectives, an integrated suite of multiple proxies will be measured in two high accumulation rate sediment cores previously collected from the EEP. These proxies include: authigenic uranium as a proxy for bottom water oxygenation and radiocarbon ages of benthic foraminifera as a proxy for changes in the age of deep water in the EEP, 231Pa/230Th ratios and excess Ba fluxes as proxies for productivity, excess 230Th-derived 232Th flux as a proxy for dust flux, B/Ca ratios in planktonic foraminifera as a proxy for carbonate ion concentration of surface water, and Nd and Pb isotope ratios as a proxy for the provenance of the dust source of the detrital component of the sediment and, therefore, an index of Intertropical Convergence Zone migration. By investigating the storage of a respired carbon pool in the deep ocean during cold periods of the last glacial period (i.e., from ~71,000 to 14,000 years ago), in conjunction with probing how this storage relates to changes in export production and potential iron fertilization, the research will shed light on the mechanistic links between ocean (stratification/ventilation) and atmospheric (wind belt shifts) circulation and the modification of atmospheric CO2 levels. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Collaborative Research: Linking Atmospheric CO2 to Millennial Changes in Atmospheric and Oceanic Circulation in the Eastern Equatorial Pacific Ocean over the Past 100 kyr
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/205; National Science Foundation
To understand future climate change, we must know how climate varied in the past. One of the biggest unknowns about past climate is the origin of atmospheric carbon dioxide (CO2) variability over global warm-cold cycles. This project will address potential causes of the varying atmospheric carbon dioxide by focusing on changes in the efficiency of fertilization of the surface ocean, and how, and if, that is related to changes in the deep-ocean. Furthermore, the research will investigate both the "how" of varying carbon dioxide with the "where", namely the Eastern Equatorial Pacific (EEP), an important region of the world ocean where, today, significant CO2 is exhaled to the atmosphere and the greatest rates of phytoplankton growth are found. The project will contribute to an improved understanding of global climate change and important Earth systems connected to the tropical Pacific Ocean. On the broadest of levels, understanding the past dynamics of Earth's carbon cycle is of fundamental importance to inform and guide societal policy-making in an increasing CO2 world. The project will support the educational and professional development of graduate and undergraduate students and results will be incorporated into the curriculum of undergraduate and graduate classes. In addition, a series of YouTube videos will be developed that are aimed at communicating the importance of how past climate variability informs us about climate's future variability and its potential impact on our lives. The project seeks to answer questions related to: 1) where and how atmospheric carbon dioxide was sequestered from the atmosphere, or ventilated from the ocean, on millennial timescales, and 2) how these carbon dynamics are related to both changes in atmospheric and oceanic circulation over the last glacial period and into the deglacial and Holocene. To address these objectives, an integrated suite of multiple proxies will be measured in two high accumulation rate sediment cores previously collected from the EEP. These proxies include: authigenic uranium as a proxy for bottom water oxygenation and radiocarbon ages of benthic foraminifera as a proxy for changes in the age of deep water in the EEP, 231Pa/230Th ratios and excess Ba fluxes as proxies for productivity, excess 230Th-derived 232Th flux as a proxy for dust flux, B/Ca ratios in planktonic foraminifera as a proxy for carbonate ion concentration of surface water, and Nd and Pb isotope ratios as a proxy for the provenance of the dust source of the detrital component of the sediment and, therefore, an index of Intertropical Convergence Zone migration. By investigating the storage of a respired carbon pool in the deep ocean during cold periods of the last glacial period (i.e., from ~71,000 to 14,000 years ago), in conjunction with probing how this storage relates to changes in export production and potential iron fertilization, the research will shed light on the mechanistic links between ocean (stratification/ventilation) and atmospheric (wind belt shifts) circulation and the modification of atmospheric CO2 levels. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria
Collaborative Research: Magnesite Deformation and Potential Roles in the Slip and Seismicity of Subduction Zones
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/402; National Science Foundation
Intermediate (70-300 km depth) and deep (300-700 km depth) focus earthquakes of great magnitudes are common in subduction zones. Though many ideas have been advanced, the cause of earthquakes at these depths remains as one of the most significant unresolved problems in the earth sciences. Researchers from University of Akron, Texas A&M University, and Brown University are exploring a new mechanism that might explain these enigmatic events: magnesite, a magnesium carbonate commonly observed in altered basalts and peridotite (primary constituents of the subducting plates), could initiate deep focus earthquakes. In this project, the research team is carrying out laboratory experiments in which magnesite is deformed under very high pressure and temperature conditions. Their recent experimental work demonstrated that magnesite is considerably weaker than peridotite, which indicates that veins of magnesite could act as nucleation points for earthquakes. In this project, they will experimentally investigate how two fundamental parameters, grain size and pressure, affect the strength of magnesite and incorporate the results in a computational model of earthquake nucleation. The project would advance desired societal outcomes by potentially shedding light on the causes of earthquakes and providing research experiences for undergraduate and graduate students. The grain-size sensitivity of diffusion creep and the pressure sensitivity of magnesite deformation mechanisms in all three creep regimes (diffusion, dislocation and low-temperature plasticity) need to be quantified in order to apply experimental flow laws to models of creep and shear instability. These parameters are critical considering that diffusion creep is the dominant deformation mechanism in magnesite at many natural conditions and may cause strain localization and possibly seismicity at high pressure in subducting slabs. In this project, the research team will: (1) quantify the grain-size sensitivity of magnesite strength when deforming by diffusion creep and limited plasticity mechanisms; (2) determine the pressure sensitivity of magnesite deformation mechanisms; and (3) model dynamic slip by ductile instabilities in magnesite, applying the shear-heating model. Hydrostatic experiments will be performed to investigate the grain growth kinetics of magnesite. Deformation experiments with different grain sizes over a wide range of pressures will be carried out to determine the grain size and pressure sensitivities of magnesite deformation mechanisms, as identified by scanning and transmission electron microscopy. This will be achieved using state-of-the-art high-pressure deformation apparatuses, such as the D-DIA coupled with X-ray synchrotron radiation for in-situ strain and stress measurements. The results will allow accurate determination of the rheology of magnesite, evaluation of its effects on the bulk rheology of subducting slabs, and prediction of conditions for shear instability where carbonates are subducted.
EarthCube Data Infrastructure: Collaborative Proposal: A unified experimental-natural digital data system for analysis of rock microstructures
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/381; National Science Foundation
When viewed at the micro-scale, rocks reveal structures that help to interpret the processes and forces responsible for their formation. These microstructures help to explain phenomena that occur at the scale of mountains and tectonic plates. Interpretation of microstructures formed in nature during deformation is aided by comparison with those formed during experiments, under known conditions of pressure, temperature, stress, strain and strain rate, and experimental rock deformation benefits from the ground truth offered through comparison with rocks deformed in nature. However, the ability to search for relevant naturally or experimentally deformed microstructures is hindered by the lack of any database that contains these data. The researchers collaborating on this project will develop a single digital data system for rock microstructures to facilitate the critical interaction between and among the communities that study naturally and experimentally deformed rocks. To aid in the comparison of microstructures formed in nature and experiment, the researchers will link to commonly used analytical tools and develop a pilot project for automatic comparison of microstructures using machine learning. Rock microstructures relate processes at the microscopic scale to phenomena at the outcrop, orogen, and plate scales and reveal the relationships among stress, strain, and strain rate. Quantitative rheological information is obtained through linked studies of naturally formed microstructures with those created during rock deformation experiments under known conditions. The project will develop a single digital data system for both naturally and experimentally deformed rock microstructure data to facilitate comparison of microstructures from different environments. A linked data system will facilitate interaction between practitioners of experimental deformation, those studying natural deformation and the cyberscience community. The data system will leverage the StraboSpot data system currently under development in Structural Geology and Tectonics. To develop this system requires: 1) Modification of the StraboSpot data system to accept microstructural data from both naturally and experimentally deformed rocks; and 2) Linking the microstructural data to its geologic context ? either in nature, or its experimental data/parameters. The researchers will engage the rock deformation community with the goal of establishing data standards and protocols for data collection, and integrate our work with ongoing efforts to establish protocols and techniques for automated metadata collection and digital data storage. To analyze the microstructures studied and/or generated by these communities, we will ensure StraboSpot data output is compatible with commonly used microstructural tools. They will develop a pilot project for comparing and analyzing microstructures from different environments using machine-learning
EarthScope SAFOD Management Office for Physical Samples
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/641; National Science Foundation
The funding award supports the San Andreas Fault Observatory at Depth (SAFOD) Office for Management of Physical Samples at Texas A&M University in College Station, Texas, from October 2013 to September 2016. The functions of the office include managing the curation and long-term storage of the SAFOD physical samples at the IODP Gulf Coast Repository (GCR) of Texas A&M University, cutting and distributing sub-samples awarded to scientists, maintaining a digital archive of sampling history and publications resulting from study of the physical samples, working to increase the diversity of researchers participating in sample characterizations, and fostering integration of SAFOD results with those of the broader scientific community studying earthquake mechanics. The management office works with three committees charged with reviewing policies and maintaining effective operations necessary to meet commitments to the Principal Investigator (PI) user community, specifically the SAFOD Advisory Committee (SAC), the SAFOD Core Sample Working Group (CoSWoG), and the SAFOD Sample Committee (SSC). The primary objectives of the management office are to preserve the SAFOD samples in cold storage lockers and to facilitate continuing use of the samples for independent PI-driven geoscience research. As part of the management office activities, a Web-based mapping and sample request tool, the Core Viewer, is maintained and updated annually for communicating sample request and sample award information to the scientific community. This is the primary tool for recording, reviewing, and executing sample distributions to scientists. The San Andreas Fault Observatory at Depth (SAFOD) is one of the major research facilities of EarthScope and provides for the study and direct monitoring of the physical and chemical processes that control fault creep and earthquake rupture in an active plate-boundary fault zone. The most significant achievements of SAFOD to date are the successful scientific drilling across the San Andreas Fault at ~3 km depth, initiating an in situ geological and geophysical characterization of the fault zone, and the successful collection of valuable core and other physical samples from across the active components of the fault. The samples form the basis of ongoing laboratory investigations using a variety of technologies and approaches to address fundamental questions of earthquake mechanics. These studies are transforming our understanding of faulting processes and ultimately will advance modeling and monitoring of seismogenic faults, and earthquake hazard mitigation. The physical sample collection of SAFOD is truly exceptional and of great scientific value. The collection is the direct result of over 15 years of careful planning and completion of a multi-phase, complex drilling project. The samples provide a window to the active processes operating in a major active plate-boundary fault at seismogenic depths. The data and interpretations that result from the scientific analysis of these unique samples establish an important baseline for comparison with other drilled fault zones and with geological observations of exhumed faults. Because of their unique characteristics, the SAFOD samples are in high demand by researchers worldwide; no other active seismogenic fault zone drilling program is set up to provide samples to a large number of researchers for continued scientific discovery. In addition to sample curation and distribution, the SAFOD sample facility provides valuable materials for education and outreach, and promotes the sharing of scientific data internationally. Efficient and thoughtful management of this resource is facilitiating scientific investigations. The research projects from this project ultimately will benefit society through improved earthquake hazard mitigation.
Experimental Investigations On The Deformation Behavior Of Sediment In The Shallow Region Of The Nankai, North Sumatra, And Aleutian Subduction Zones
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/396; National Science Foundation
The main objective of the work is to characterize the physical properties of sediments at subduction zones. Experiments on sediments from the Nankai Trough and the Sumatra and Aleutians Trench will be conducted at the rock mechanics laboratory at Texas A&M University. The experiments will be run at high pressure and temperature conditions to simulate the conditions that the sediments encounter as they are carried deep into the earth as one tectonic plate plunges beneath another. The project results will aid in understanding slip on faults and the potential for tsunami generation at subduction zones worldwide. This project will support an early-career female researcher as a GeoPRISMS post-doctoral fellow. This research aims to understand deformation behavior in the shallow portion of subduction zones where greater displacement and ground deformation can occur in response to megathrust earthquake ruptures. This project will address key fundamental questions about whether the shallow near-trench portion of a subduction zone is locked and accumulating strain or fully creeping. Consolidation and creep experiments will be conducted at elevated pressures and temperatures and at a range of strain rates on sediment samples from three different subduction systems - Nankai Trough, Sumatra, and Aleutian subduction zones. The research goals of the project are to 1) characterize the elastic, plastic, and viscous deformation behaviors as a function of pressure, temperature, strain rate, and sediment lithology and 2) assess the potential for strain accumulation and co-seismic slip rupture propagation in the shallow near-trench regions of subduction zones. The project will advance knowledge of strain accumulation, fault coupling, and slip behavior at subduction zones.
X-Ray Florescence (XRF) Technologies For Biosignature Screening In Aeolian Environments
Geology And Geophysics; TAMU; https://hdl.handle.net/20.500.14641/502; NASA-Washington
The overarching research goal driving this study is to understand the influence of planetary surface sedimentary processes on biosignature preservation. We explore this goal by studying the influence of physical processes on the preservation of geochemical biosignatures in aeolian environments. Our study tests two primary hypotheses. (1) We hypothesize that microbial crusts in wet aeolian environments develop elemental compositions distinct from interstratified sediment through physical sorting and accumulation of silt-sized heavy mineral grains and bio/chemical concentration of nutrients and cements. (2) We further hypothesize that eroded microbial crust chips retain coupled elemental enrichments associated with crust growth, but enrichments become decoupled into separate size fractions and physically separated into different modes of aeolian transport during progressive disaggregation. To test our hypotheses, we proposed a three-year field and laboratory study that includes using a ?(micro)XRF testbed to simulate PIXL instrument analyses planned for the Mars 2020 mission. We identify the geomorphic and stratigraphic distribution of microbial and associated elemental material in aeolian environments and analyze the material using imaging ?XRF technology. Our modern aeolian field site is at Padre Island National Sea Shore (PAIS), Texas, and our ancient aeolian field site is within the Jurassic Entrada formation near Canyonlands National Park, Utah. Both field sites are wet aeolian systems with microbial material present at Padre Island and microbial textures present within the Entrada formation.