Department of Geological Sciences and Geological Engineering Faculty Publications

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    Simulations of Landslide Wave Generation and Propagation Using the Particle Finite Element Method
    (Wiley, 2020-06-03) Mulligan, Ryan P.; Franci, A.; Celigueta, M. A.; Take, W. Andy
    In this study, the impulse waves generated by highly mobile slides in large-scale flume experiments are reproduced numerically with the Particle Finite Element Method (PFEM). The numerical technique combines a Lagrangian finite element solution with an efficient remeshing algorithm and is capable of accurately tracking the evolving fluid free-surface and velocity distribution in highly unsteady flows. The slide material is water, which represents an avalanche or debris flow with high mobility, and the reservoir depth is varied, thereby achieving a range of different near-field wave conditions from breaking waves to near-solitary waves. In situ experimental observations of fluid velocity and water surface levels are obtained using high-speed digital cameras, acoustic sensors, and capacitance wave probes, and the data are used to analyze the accuracy of the PFEM predictions. The two-dimensional numerical model shows the capability of holistically reproducing the entire problem from landslide motion, to impact with water, to wave generation, propagation, and runup. Very good agreement with the experimental observations are obtained, in terms of landslide velocity and thickness, wave time series, maximum wave amplitude, wave speed, and wave shape. In a broad perspective, the results demonstrate the potential of this numerical method for predicting outcomes of interacting multi-hazard scenarios, such as landslides triggered by loss of slope stability and the generation of tsunami.
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    Indian Plate Structural Inheritance in the Himalayan Foreland Basin, Nepal
    (Wiley, 2021-07-15) Duvall, Michael; Waldron, John; Godin, Laurent; Najman, Yani; Copley, Alex
    The Himalaya, the Earth's largest active orogen, produces a deep but relatively unexplored foreland basin by loading the Indian Plate. Newly available two-dimensional seismic data (ca. 5,180 line km) spanning 900 km of the Nepali lowlands allow mapping and interpretation of several regional subsurface markers in two-way-travel time and estimated depth. Isopach maps for the major intervals allow us to interpret the interplay between basement structure, flexure, and faulting within the Ganga Basin. The Indian continental lithosphere beneath the foreland basin contains basement ridges oriented at high angles to the thrust belt. These basement structural highs and intervening depressions, tens to hundreds of kilometres wide, influenced deposition of the Precambrian Vindhyan strata and overlying Paleozoic to Mesozoic successions. The overlying Miocene to Quaternary foreland basin shows along-strike thickness variations across the basement features. Because the foreland basin sediments were mainly deposited in an alluvial plain close to sea-level, accommodation, and therefore thickness, was predominantly controlled by subsidence of the Indian Plate, providing evidence that the basement features controlled foreland basin development. Subsidence varied in time and space during Neogene basin development. When combined with flexural modelling, these observations imply that the subsidence history of the basin was controlled by inherited lateral variations in the flexural rigidity of the Indian Plate, as it was translated northward beneath the Himalayan Orogen. Basement features continue to play a role in higher levels of the thrust belt, showing that basement features in a down-going plate may produce non-cylindrical structures throughout orogen development.
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    Review of Close-Range Three-Dimensional Laser Scanning of Geological Hand Samples
    (Elsevier, 2020) Hudson, Rebecca; Faraj, Fouad; Fotopoulos, Georgia
    The morphological study of geological hand samples has a wide variety of applications in the geosciences, which is conventionally accomplished by measuring the distance between features of interest on the sample’s surface. Close-range three-dimensional (3D) laser scanners provide an opportunity to study the form and shape of geological samples in a digital environment and have been increasingly utilized in fields such as paleontology, rock mechanics, and sedimentology, with some uptake in planetary sciences and structural geology. For paleontological studies, primary applications are in quantitative analysis of fossil morphology and integration into 3D animated models for understanding species movements. In the field of rock mechanics, typical uses of 3D digital geological hand sample models include quantifying joint roughness coefficient (JRC), determining the surface roughness of rock samples, and assessing morphological changes over time due to processes such as weathering. In the field of sedimentology, such models are incorporated to characterize the shape of sediment particles and to calculate key parameters such as bulk density. This paper aims to provide a comprehensive review of established literature that includes substantial use of digital geological hand samples acquired from 3D close-range (<1m target distance) triangulation laser scanners in an effort to identify opportunities for future progress (such as global data sharing) as well as challenges specific to the nature of geological samples (e.g., translucency) and geoscientific workflows (on and off-site).
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    Glimpses of Oceanic Lithosphere of the Challenger Deep Forearc Segment in the Southernmost Marianas: The 143°E transect, 5800–4200 m
    (Wiley, 2020-06-16) Stern, Robert; Ohara, Yas; Ren, Minghua; Leybourne, Matthew; Bowers, Brent
    We studied nine samples of igneous rocks from the inner wall of the Mariana Trench above the Challenger Deep from 4150 to 6100 m depth recovered by manned submersible and ROV. Samples from two regions that bracket the Moho were studied: (i) 7 samples from a N‐S transect a few km to the west of the Shinkai Seep Field; and (ii) 2 samples from the Shinkai Seep Field. Transect samples include olivine‐2 pyroxene hornblendites, amphibole basalts, basaltic andesite, and hornblende andesite. We analyzed three transect samples for 40Ar/39Ar ages; two yielded good plateau ages of 46.5 ±0.5 Ma (hornblendite) and 46.60 ±0.15 Ma (hornblende andesite). These results combined with previously published results, indicate that this crust formed during an intense 46–47 Ma magmatic episode that occurred 5–6 my after subduction initiation. Hornblendites and hornblende basalts formed from primitive magmas, as shown by high MgO (11–21 wt%), Ni (222–885 ppm) and Cr (412–1145 ppm) contents. Electron microprobe analyses indicate that hornblende is Na‐rich (up to 3.0 wt% Na2O) and that many samples have an atypically large range in plagioclase composition (i.e. individual samples have An < 10 to An 90 plagioclase). Two subgroups can be identified: a mostly deeper depleted suite and a mostly shallower enriched suite. These results indicate that (i) the crust–mantle boundary in this region is transitional, occurring over a ~ 1.5 km interval, with interlayered peridotite and hornblendites between 5800 and 4300 m; and (b) extension to form the Challenger Deep forearc segment occurred by combined stretching of old crust and injection of young basaltic magmas. In contrast to the mostly fresh nature of transect samples, the two samples from the Shinaki Seep Field are intensely altered peridotite and basalt.
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    An Epeiric Glass Ramp: Permian Low-Latitude Neritic Siliceous Sponge Colonization and its Novel Preservation (Phosphoria Rock Complex)
    (Elsevier, 2019-11-29) Matheson, Edward; Frank, Tracy D.
    Glass ramps are shallow-marine depositional settings in which siliceous sponge meadows dominate coastal environments. They are increasingly recognized throughout the Phanerozoic and represent a biosiliceous counterpart to neritic carbonate factories. Detailed reexamination of the Permian Tosi Chert in the Bighorn Basin indicates that it records a glass ramp that extended over at least 75,000 km2. Outcrops, cores, and wireline logs are used to discriminate previously unidentified shallow subtidal to peritidal facies in its landward extent. These facies indicate that sponge meadows ranged from variably oxygenated offshore settings through low-energy, well-oxygenated, and saline shallow subtidal settings, with spicules transported into supratidal environments affected by enterolithic evaporite growth. This range of subenvironments is largely unique among glass ramps. This is the result of the Tosi's accumulation in an epicontinental sea where waves impinged offshore but frictional attenuation caused low-energy nearshore environments. As a result, the Tosi shares similarity with epeiric sea carbonate deposition and is referred to herein as an epeiric glass ramp. The low palaeolatitude of the Tosi and hot and arid desert it bordered also contributed to its uniqueness as shallow waters were warmer and more saline than higher-latitude counterparts. As a result, a minor sea-level fall at the termination of biosiliceous deposition was associated with increased lagoonal circulation and refluxing brines that caused evaporite and dolomite precipitation within the upper Tosi. Preservational attributes of the Tosi also add to the range of unique traits that can be used to reconstruct neritic biosiliceous environments. These include three disparate colours of chert (black, grey, and purple) related to the host strata and diagenetic redox conditions, early chertification that preserved sedimentary structures within nodules, and nodule shape related to bioturbation intensity. The Tosi glass ramp thus expands the known extent and context of Permian glass-ramp deposition along the western Laurentian margin and illustrates key properties that will aid future glass ramp identification.