Geology

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    Active Seismic Exploration of Planetary Subsurfaces via Compressive Sensing
    (2025) Wang, Jingchuan; Schmerr, Nicholas; Lekic, Vedran
    The software supports the following study: We present a method for improving seismic data collection on planetary surfaces such as the Moon and Mars. This approach is based on recent advances in compressive sensing technology to reduce the number of data collection points required compared to conventional methods without sacrificing the quality of the resulting subsurface images. We demonstrate its effectiveness using both synthetic and field data from locations with similarities to planetary surface environments. The method is then applied to reanalyze seismic data collected by the crew of the Apollo 14 and 16 missions. Our study has implications for mission planning, as this method can make space missions more efficient by reducing the equipment and time to collect geophysical data on planetary surfaces. It also makes it possible to reconstruct missing or damaged data, improving the quality of imagery and enhancing our understanding of the interior of other worlds.
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    GEOMORPHIC AND HYDROLOGIC CHARACTERISTICS OF SMALL URBANIZED TRIBUTARIES TO A FALL ZONE STREAM
    (2024) Harris, John Allen; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Many rivers along the Atlantic Coast contain major knickpoints, which define the Fall Zone. These often-urbanized rivers straddle multiple physiographic regions with spatial variations in lithology, topography, and hydrology. This research evaluates the effects of mainstem channel incision and urbanization on channel and catchment morphology, bed substrate mobility, catchment water storage dynamics, and hydrologic response in tributaries of the Northwest Branch of the Anacostia River above and below the Fall Zone knickpoint. Topographic analyses show that differential incision below the mainstem knickpoint has initiated steep secondary channels incised into bedrock. Measurements at representative reaches show that bankfull shear stress exceeds critical shear stress in these newly initiated tributaries, resulting in erosive channels outside of threshold conditions. Increased urban runoff introduced at storm drain outfalls maintains these non-steady state conditions. Geophysical surveys reveal that regolith depth for water storage capacity is primarily below the flatter ridgetops of the tributary catchments, where development is concentrated. The secondary tributaries cannot access these upland storage zones, and thus have limited infiltration and recharge capacity. I installed streamgages in the tributaries and constructed catchment water balances to study storage dynamics and hydrologic response. Hydrologic consequences of urbanizing the steep secondary tributaries include flashy, elevated stormflows, greater total runoff, and reduced baseflows that are not maintained during drought periods. The combination of steep channels, thin regolith, and urban overprint limits infiltration to moderate storm responses and recharge storage. These effects were not seen in non-urbanized secondary tributaries, urbanized tributaries above the knickpoint, or the forested reference streams above the Fall Zone. These findings define the geomorphic adjustment of tributaries to differential mainstem incision and explore the hydrologic impacts of urbanizing small steep catchments with limited effective storage capacity. Supplementary files:S1: Table with the location, drainage area, stream gradient, bankfull hydraulic values, and grain size values at each Northwest Branch tributary and reference reach used in the study. S2: Spreadsheet with the water level logger gage height values collected at 5-minute intervals from April 2023-March 2024 and calculated discharge from the Northwest Branch tributary streamgages. S3: Spreadsheet with the monthly water balance values for the Northwest Branch tributary catchments and reference watersheds from April 2023-March 2024. S4: Table with the depth to bedrock values and corresponding slope angles measured from the seismic profiles and LiDAR-derived digital elevation models.
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    USING BAYESIAN ELECTRICAL RESISTIVITY INVERSION TO REVEAL HILLSLOPE DRY-UP PROCESS IN A MEDITERRANEAN CLIMATE
    (2024) Shahid, Saffat; Huang, Mong-Han; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Hydrologic dynamics in hillslopes is essential for comprehending the processes that shape landscape evolution and sustain the Earth’s critical zone. Electrical resistivity (ER) is considered as one of the best geophysical methods to observe these dynamics due to its sensitivity to subsurface water content. To understand hillslope water dynamics and mitigating the risks of slope instability caused by extreme weather events, we studied how subsurface hydrological processes are being influenced by variations in vegetation type across different aspects of hillslopes. Thus, how accurately ER can quantify the dry-up process during the growing season on hillslopes becomes critical, particularly in regions with distinct dry summers and wet winters (i.e. Mediterranean climates). The Blue Oaks Ranch Reserve (BORR) in Central California provides an ideal location for this study due to its consistent ridge-valley systems, which well represents the regional climatic and topographic conditions. Previous work at BORR used active source seismic refraction (SR) to constrain subsurface structure. To additionally investigate moisture content in regolith, we conduct ER surveys with Schlumberger and Dipole-Dipole configurations to invert for resistivity using Transdimensional Hierarchical Bayesian (THB) inversion framework with reversible-jump Markov Chain Monte Carlo (THB rj-MCMC). We also performed 2D synthetic tests to evaluate how well THB can recover a synthetic model with imposed data uncertainty. The results indicate that Schlumberger outperforms Dipole-Dipole in the THB rj-MCMC inversion. However, these results also reveal limited depth resolution to ~10 m depth using current ERT configurations. Finally, we adopt the THB approach for a series of ER surveys at BORR between June and September 2023. The findings suggest a distinct increase in resistivity on the North-facing slope during growing seasons, indicating reduced moisture content particularly in areas with presences of oak trees as they draw water from deep regolith. On the South-facing slope, resistivity remained stable due to the dominance of grass that lacks deep roots for consuming deep moisture. Our resistivity results show that vegetation type particularly trees play a critical role in regolith moisture distribution. To compare and correlate changes in resistivity over dry periods, we analyzed soil probe data previously collected at the site. The correlation suggested that increases in resistivity are related to decreases in volumetric moisture content. Additionally, we compared ERT data with seismic survey data to better understand changes in subsurface properties like porosity and saturation along depth, as ERT and seismic velocity is sensitive to moisture content and material porosity.
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    QUANTIFICATION OF MELT DISTRIBUTION, MELT CONNECTIVITY, AND ANISOTROPIC PERMEABILITY OF DEFORMED PARTIALLY MOLTEN ROCKS USING X-RAY MICROTOMOGRAPHY
    (2024) Bader, James Alexander; Zhu, Wenlu; Montesi, Laurent G.J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Volcanic activity plays a dominant role in shaping the surface of Earth and other planets. For example, Earth’s ocean floor is created by volcanic activity at mid-ocean ridges. There, magma is sourced from a ~60 km deep, ~100 km wide region of the mantle, from which partial rock ascends and erupts along narrow ridges that run along the middle of Earth’s oceans. Volcanic activity at mid-ocean ridges, the strength of Earth’s mantle, and the geochemical composition of volcanic rocks and ocean water are all influenced by how the melt is distributed in partially molten rocks, and how easily it can flow through the partially molten mantle beneath these ridges. In particular, it is often assumed that most of the melt ascends through isolated channels that direct it towards the mid-ocean ridges, making melt transport localized and anisotropic. A possible origin of these channels is the differential stress induced by upwelling mantle material beneath the ridge, which has been shown in laboratory experiments to localize melt into planar regions named “melt-rich bands.” To date, the development and characteristics of melt-rich bands have been studied principally using theoretical models and two-dimensional (2D) images of sheared partially molten rocks. There has been little experimental research using 3D techniques until now. This thesis uses 3D images of sheared partially molten rocks created in the laboratory, obtained using high-resolution x-ray microtomography (X-ray µCT), to investigate how the distribution of melt, its orientation, its connectivity, and its ability to flow through the rocks changes when stress is applied. This study shows how melt connectivity and, therefore, rock permeability changes as melt changes from being dispersed through a partially molten rock to being localized on well-developed melt-rich bands. This work shows that melt forms melt volumes that are preferentially elongated within the plane of melt-rich bands even before these bands form. This discovery emphasizes the importance of permeability anisotropy at all stages of melt-rich band development. We also measured permeability and melt connectivity at all scales, both inside and outside melt-rich bands. Our results show that melt can hardly flow perpendicular to melt-rich bands over distances larger than a few grains. Additionally, the permeability along the melt-rich bands is also reduced by half compared to that in a partially molten rock that is not subjected to differential stress. This research quantifies the uneven distribution of permeability in a sheared, partially molten rock. It also proposes a scheme to average local permeability estimates, helping us understand and quantify how melt travels along melt-rich bands at various scales. These findings provide valuable insights into how magma flows in the Earth’s mantle, especially at active plate boundaries like mid-ocean ridges. Overall, this research provides the first experimental constraints, based on 3D microtomography images, on the melt network and how melt flows in the presence of stress in partially molten rocks.
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    Dataset for Constraining Wetland and Landfill Methane Emission Signatures Through Atmospheric Methane Clumped Isotopologue Measurements" [Paper #2024JG008249-T]
    (2025) Sun, Jiayang; Farquhar, James
    From Primary Paper: Microbial methane emissions are associated with a wide range of isotopic signatures, providing information about the sources and sinks of methane. Methods of directly sampling methane from environments such as wetlands may fail to capture the temporal and spatial variations in emissions at a specific site and time. The Keeling plot method is commonly used to infer the overarching isotopic signatures of methane sources. In this study, we have expanded the application of the Keeling plot from conventional stable isotope ratios to include novel clumped isotopologue compositions of methane. This advancement aims to provide more robust constraints on regional methane emission signatures. We analyzed methane isotopologue compositions from air samples collected above wetlands and landfills across Maryland, USA, and determined the endmember compositions for background air, wetland, and landfill sources. Our findings indicate that the isotopologue compositions of methane from regional wetland emissions exhibit seasonal variations — δ13C and δD values become less positive as winter approaches, reflecting changes in methane oxidation and production rates. The continuous monitoring of air methane isotopologue signatures will deepen our understanding of the seasonal patterns in methane emissions and contribute to refining the global methane budget, as valuable insights can be extracted from these measurements.
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    GEOCHEMICAL INDICATORS OF REDOX AND WEATHERING ACROSS THE EDIACARAN-CAMBRIAN TRANSITION IN SIBERIA
    (2024) Doerrler, Andrew; Kaufman, Alan Jay; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The transition between the Ediacaran and Cambrian periods witnessed the fall of the enigmatic Ediacara biota. The cause of their extinction is poorly understood, but the timing broadly coincides with a significant negative ẟ13C anomaly, the BAsal Cambrian Carbon isotope Excursion (BACE). These macroscopic organisms were likely tolerant of anoxic conditions, so oceanic oxidation may have been a kill mechanism. This study utilizes uranium isotopes, sulfur isotopes, and cerium anomalies to understand oceanic redox conditions from two BACE sections in Siberia, as well as lithium isotopes to constrain weathering intensity. Reconstruction of seawater ẟ238U values from equivalent evaporite and carbonate-dominated successions indicate a notable increase in oxygen during the event supporting the oxidation hypothesis. Global sea level fall and evaporite formation suggest that seawater salinity increased dramatically along continental margins, which may provide an alternative osmotic kill mechanism for the softbodied Ediacaran biota. Support for the salinity hypothesis comes from profound ẟ7Li and ẟ34S compositions of carbonate and pyrite, respectively, which arguably resulted from the distillation of lithium and sulfate from seawater into evaporite-rich lithologies.
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    GEODES San Francisco Volcanic Field Geochemical Sampling
    (2023) Shubham, Sourabh; Farcy, Benjamin; Wright, Shawn; Schmerr, Nicholas; Whelley, Patrick
    In August of 2023, the NASA SSERVI GEODES team conducted a field expedition in the San Francisco Volcanic Field, northern Arizona. The field expedition had a geochemical component, with the objective of characterizing the lithological and geochemical diversity across key volcanic features. Using handheld XRF and VNIR spectrometers, field data and rock samples were collected from O'Leary Peak, Elden Mountain, Schultz Peak, SP Crater, and the Lava River Cave. Sampling strategies included targeting visually distinct lithologies and calibrating instruments with geochemical standards to ensure data accuracy. Preliminary analyses reveal diverse compositions, including rhyolites, basalts, and intermediate magmas. The collected samples will undergo detailed laboratory geochemical analysis to enhance understanding of volcanic processes and evolution in this region.
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    Integrated Geochemical Studies of the Shuram Excursion in Siberia and South China
    (2024) Pedersen, Matthew; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Ediacaran Period Shuram Excursion (SE) is a globally-distributed and highly controversial phenomenon where over millions of years, sedimentary carbonates record δ13C values of -10‰ and lower. This carbon cycle anomaly may reflect disequilibrium in the world’s oceans, driven by the oxidation of a large pool of dissolved organic carbon (DOC), with the oxidants sourced from the intense weathering of the continents, forcing major changes to ocean chemistry through the ventilation of the deep ocean, evidenced by a positive shift in carbonate uranium isotope values, and invoking the onset of early animal biomineralization. This study utilizes high-resolution carbonate Li isotopes from two SE-successions, U isotopes, REE abundances and Ce anomalies which reveal the dynamic interplay between intensified continental weathering associated with tectonic reconfiguration and the subsequent environmental and ecological response that may have been amplified by the ecosystem-engineering abilities of a newly discovered sponge-grade animal.
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    A Better Understanding of Atmospheric Methane Sources Using 13CH3D and 12CH2D2 Clumped Isotopes
    (2024-09) Haghnegahdar, Mojhgan A.
    We evaluate the use of clumped isotopes of methane (CH4) to fingerprint local atmospheric sources of methane. We focus on a regenerative stormwater conveyance (RSC) stream wetland site running through the University of Maryland campus, which emits methane due to its engineering. Air samples in the RSC were collected at different heights above the surface and at different times of the day including both early in the morning, after methane accumulated below the nocturnal boundary layer, and late in the afternoon when convection mixed air to the cloud layer. Measured Δ12CH2D2 values of air samples record mixing between locally produced methane with low D/H and ambient air. The Δ12CH2D2 of the near surface air collected at the RSC during the early morning ranges from ~+23‰ to ~+35‰ which is lower than the ~+50‰ values of tropospheric air. Mixing between background air (with Δ12CH2D2 ~+50‰) and methane captured from chamber and bubble samples, as well as produced in incubation (all with negative Δ12CH2D2), explains the observed values of Δ12CH2D2 and Δ13CH3D of near surface RSC air samples. The effect of mixing with biogenic sources on Δ13CH3D is much smaller. The findings demonstrate how methane isotopologues can be used as a tool not only to fingerprint local contributions to these greenhouse gas emissions but also to identify sources of near-surface methane hot spots.
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    Snowfall Replenishes Groundwater Loss in the Great Basin of the Western United States, but Cannot Compensate for Increasing Aridification
    (Wiley, 2024-03-20) Hall, Dorothy K.; Loomis, Bryant D.; DiGirolamo, Nicolo E.; Forman, Barton A.
    There has been an acceleration of groundwater loss in the Great Basin (GB) of the western U.S. as determined from total water storage (TWS) measurements from the GRACE/FO satellite missions. From 2002 to 2023, there was a loss of TWS in the GB of ∼68.7 km3 which is more than six times the current volume of the Lake Mead Reservoir. In this arid/semi-arid region, groundwater is the primary factor contributing to the decade-scale decline in TWS. Stronger declining trends are found in the western versus the eastern GB. Snow loading is the major cause of seasonal fluctuations of TWS in the GB. Despite annual replenishment of groundwater by snow, the downward trend persists even in notable snow years. Likely causes include declining snow mass, upstream water diversions and increased evaporation/sublimation due to increasing temperatures. Dire consequences for humans and wildlife are associated with this large loss of groundwater.