Thesis (M.S.)-Oregon State University, 1988. / Includes bibliographical references (leaves 74-80). Also available via the Internet.

abstract: It has been hypothesized that the ~25 km Rochechouart-Chassenon impact structure (RCIS) in the NW Massif Central, France, was formed during a Late Triassic (ca. 214 Ma) terrestrial impact event that produced a catena of several large craters. Testing this hypothesis, and assessing its possible impacts on biological evolution, requires both accurate and precise dating of candidate impact structures. Like many of these structures, the age of the RCIS is controversial because geochronological datasets yield contradictory results, even when a single isotopic system is used; for example, the two most recent 40Ar/39Ar studies of RCIS yielded statistically inconsistent dates of 201 ± 2 Ma (2σ) and 214 ± 8 Ma (2σ). While the precision offered by various geochronometers used to date impact structures varies significantly, a fair way to assess the confidence scientists might have in the accuracy of an impact age is to establish whether or not multiple chronometers yield statistically indistinguishable ages when applied to that structure. With that in mind, I have applied the (U-Th)/He, U/Pb, and radiation damage chronometers to zircons separated from two different RCIS impactites. My best estimate of the zircon (U-Th)/He age of the impact event is 191.6 ± 9.1 Ma at the 95% confidence level. U/Pb zircon dates suggest that most zircons in the RCIS target rocks were not completely reset during impact, but a subset (n = 8) of zircons appear to have crystallized from the impact melt or to have been completely reset; these zircons indicate a U/Pb impact age of 202.6 ± 5.8 Ma (95% confidence level). Zircon radiation damage dates are highly variable, indicating that the RCIS event resulted only in partial annealing of pre-impact zircon in the country rock, but a small sub-population of zircons yielded a mean date of 211 ± 13 Ma (95% confidence level). These results – all statistically indistinguishable from the previously published 40Ar/39Ar date of 201 ± 2 Ma – collectively argue that the impact age was near the presently agreed upon Triassic-Jurassic boundary. This age raises the possibility that seismite and tsunamite deposits found in the present-day British Isles may be related to the RCIS. / Dissertation/Thesis / Masters Thesis Geological Sciences 2016

Lorsque de l’air est injecté à la base d’une couche de grains immergée, il traverse le système par percolation ou fracturation. Il forme ainsi plusieurs chemins qui atteignent la surface libre de la couche à des endroits différents. Nous avons réalisé l’étude expérimentale de ce processus (configuration 2D et 3D), ainsi que son analyse numérique et théorique. Dans un premier temps, nous nous sommes concentrés sur la dynamique d’invasion de l’air dans le milieu, à temps court et à temps long, lors de l’injection d’un flux d’air continu. À temps long, la taille typique de la région explorée par l’air (zone fluidifiée) peut être expliquée par un processus diffusif [1]. Nous avons également étudié l’effet de la gravité, en inclinant la cellule expérimentale. La comparaison des résultats avec des simulations numériques pour l’injection d’un volume d’air fixé permet de caractériser la morphologie de la zone d’invasion. Nous montrons que la hauteur et la largeur typique de la région explorée par l’air ne dépend pas uniquement du volume injecté, mais peut s’exprimer en fonction d’un paramètre χ sans dimension qui représente les effets relatifs de la gravité et de la capillarité [2]. Nous présenterons quelques résultats préliminaires montrant la dynamique d’évolution de la zone fluidifiée en fonction des différentsparamètres. Enfin, lorsqu’on augmente la hauteur d’eau au-dessus de la couche granulaire, l’advection et le dépôt successif des grains forment un cratère, composé de deux dunes qui croissent et s’éloignent du centre. La taille typique du cratère augmente de façon logarithmique dans le temps, indépendamment du processus d’émission du gaz [3].Références -[1] G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 83, 011302 (2011).[2] G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 83, 061302 (2011).[3] G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 79, 021301 (2009). / When air is injected at the bottom of an immersed granular layer, it crosses the system by percolating or fracturing. It thus forms several paths that reach the free surface of the layer at different locations. In this thesis, we study this process experimentally (for a three and two dimensional setup), numerically and theoretically. First, we focus on the dynamics of the air invading the medium at short and long time scale, when injecting a continuous air flow. At long time, the typical size of the region explored by the air can be accounted for by a diffusion-like process [1]. We also investigate the effect of gravity by tilting the experimental cell. We contrast the results with numerical simulations for the injection of a fixed volume of air, and characterize the morphology of the invasion zone. We show that the typical height and width of the region explored by the air does not depend on the injected volume only, but also on a dimensionless parameter χ which accounts for the relative effects of the gravity and capillarity [2]. Finally, when increasing the water height above the granular layer, successive grain advection and deposition form a crater consisting of two dunes growing and moving apart one from the other. We observe that the typical size of the crater increases logarithmically with time, independently of the gas emission process [3].References -[1] G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 83, 011302 (2011).[2] G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 83, 061302 (2011).[3] G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 79, 021301 (2009).

abstract: Establishing the timing of impact crater formation is essential to exploring the relationship between bolide impact and biological evolution, and constraining the tempo of planetary surface evolution. Unfortunately, precise and accurate impact geochronology can be challenging. Many of the rock products of impact (impactites) contain relict, pre-impact phases that may have had their isotopic systematics completely reset during the impact event, only partially reset, or not reset at all. Of the many isotopic chronometers that have been used to date impactites, the U/Pb zircon chronometer (ZrnPb) seems least susceptible to post-impact disturbances, and ZrnPb dates are typically much more precise than those obtained using other chronometers. However, the ZrnPb system is so resistant to resetting that relict zircons in impactites often yield dates that reflect the igneous or metamorphic ages of the target rocks rather than the age of the impact itself. The present study was designed to answer a simple question: is there a straightforward sample collection and analysis strategy for high-accuracy ZrnPb dating of an impact structure if the impactites collected from it may contain inherited zircons? To study this, ZrnPb dates were determined for impactites from a single crater with a well-constrained impact age: the West Clearwater Lake impact structure, located at Lake Wiyâshâkimî, Québec, Canada. The amount of ZrnPb resetting and the mechanisms responsible for resetting varied amongst the samples. Each sample characteristically contained either: newly crystallized zircons from the impact melt ("neocrystalline"), relict zircons ~50-100% reset, or, relict zircons ~0-50% reset. The variably reset relict zircons define a discordia line from ~2700 Ma to ~286 Ma – consistent with the ages of the target rock and the impact, respectively (Schmieder et al., 2015a; Simard, 2004). ZrnPb measurements from the neocrystalline zircons provided a new preferred impact age of 286.64 ± 0.35 Ma (2σ), a ~10x improvement in precision. The characteristics of the West Clearwater ZrnPb data vary between samples yet become easily interpretable as a whole, showing that efforts to measure robust, precise impact ages benefit from strategies that prioritize applying multiple analytical techniques to multiple types of impactite from the same crater. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

The Moon is the closest celestial body to us. It is also the one we know most about, the only one we have visited so far, and our constant companion. With NASA's new Artemis program and newfound interest in exploring the Moon and beyond, my proposal is to create a base on the Moon for further space exploration, scientific development and establishment of an extraterrestrial colony. Dealing with obstacles such as lack of resources, radiation and no atmosphere, my project combines different constructive strategies, such as 3D-printing, excavating and inflatable membranes, to create an environment where humans can live and thrive on the Moon. The habitat allows for performing experiments and engaging in the basic survival activities, but also creates a home in such a challenging and distant place. Creating varied layers of habitability and protection ensure for a productive and entertaining existence on our one and only satellite, paving way to further explore the Solar System.

Anomalously high groundwater salinities exist within the syn-impact sediment of the Chesapeake Bay impact crater, including an unexplained brine. This brine may be the result of phase-separation of seawater that occurred within the syn-impact sediments as underlying deformed and possibly melted basement rock cooled following impact. The 85 km wide crater has been described as a complex peak-ring crater; created 35.8 million years ago in the then submerged unconsolidated sediments of the Atlantic Coastal Plain and now completely buried by post-impact sediments. An annular trough with relatively undisturbed basement surrounds a ~38 km diameter inner basin with a peak ring and central uplift. The basement surface within the inner basin was modified by the impact and is projected to be approximately 1.6 km below sea level. Geothermometry and advective and conductive heat flow modeling was performed to characterize a possible post-impact hydrothermal system. Thermal maturity and radiogenic techniques were used to estimate the temperature history of the crater sediments. Core samples from one borehole just outside the crater, two within the annular trough, and one shallow borehole within the inner basin were examined. Numerical heat and fluid flow models were developed using a range of likely sediment parameters and basal heat flow values to determine if phase-separation temperatures were likely to have occurred, and to evaluate what affect, if any, lithostatic overpressures may have had on post-impact cooling. Geothermometry results indicate that no detectable thermal anomaly exists within the syn or post-impact sediments at these boreholes; however, no data are available within the deep inner basin where temperatures were likely to have been higher. Samples from existing boreholes suggest that sediment are organically immature and likely were never heated above ~40°C for a geologically significant period of time. These results support apatite He (U/Th) and previously published apatite fission track radiogenic ages indicating no Cenozoic resetting. Heat flow simulations indicate that a high temperature (>400°C) hydrothermal system could have existed within the inner basin and not caused any measurable effect on thermal maturity in the annular trough and shallow portion of the inner basin. Results also indicate that phase-separation could have occurred in the syn-impact sediments using reasonable estimates of basal heat flow, permeability, thermal conductivity, and porosity values, and that overpressures resulting from rapid deposition of syn-impact sediments dissipate within a few thousand years and are not an important heat transport mechanism. / Master of Science

The cairns on Gotland have been one of the most studied aspects regarding the Bronze Age on the island. Most attention has been directed to how they were built and to whom they belong. My study will focus on Ullviarrojr, which is a so-called crater cairn, and the area around the cairn. Ullviarrojr is among the few large cairns on the Island over 35 meter in diameter and the area around it show very few other archaeological remains. The closest ancient remains are around 400 metres away in an almost circle shape. By making a landscape analysis regarding the area around the cairn and an archive study I want to understand its relationship to the Bronze Age landscape. I have consulted unpublished works and made site visits and interviewed the current landowner to get an overview of if there are additional archaeological remains in the area of if remains have been destroyed and taken away. My study will provide some new information on an area that has not been examined in detail, which would help future studies to understand the cairns and the area around cairns.

Under Cooperative Agreement Number H8601010007, BARA contracted with the NPS to amend the document review with primary data from representatives of the tribes that were found to be historically and culturally affiliated with Sunset Crater Volcano, Walnut Canyon, and Wupatki National Monument. Additionally, this addendum to the affiliation study includes information about traditional uses of park resources as described by tribal representatives. This information is critical to park management and for compliance with various laws, regulations, executive orders, and policies so that park managers can better address tribal requests for continued access and use of park resources. The first purpose of this study is to amend the completed literature search with primary data collected with tribal representatives of the six ethnic groups. This data will provide contemporary validation of the literature search and contribute additional information related to tribal affiliation. The second purpose of this study is to provide primary data about past and present tribal uses of park resources. As a Traditional Use Study of park resources, this effort contributes information essential to park management as well as to compliance with a myriad of laws, regulations, executive orders, and NPS policies. The specific objectives of this study include identification of natural resources at each park that are used for traditional purposes, descriptions of the cultural importance of these resources, and, where possible, links between contemporary resource use and records of historic use.

This thesis presents the results of contemporary limnological and palaeolimnological investigations of a series of crater lakes in order to reconstruct the palaeoenvironmental history of western Uganda, East Africa. The research examines questions of spatial and temporal heterogeneity of climate changes in the context of growing human impacts on the landscape over the last millennium. Sediment records from two lakes, Nyamogusingiri and Kyasanduka within the Queen Elizabeth National Park (QENP) were investigated to look at the long term records of climate and environmental change (spanning the last c. 1000 years). Five shorter cores across a land-use gradient were retrieved to assess the impact of human activity on the palaeoenvironmental record over the last ~150 years. High-resolution (sub-decadal), multiproxy analyses of lake sediment cores based on diatoms, bulk geochemistry (C/N and δ13C) and sedimentary variables (loss-on-ignition, magnetic properties and physical properties) provide independent lines of evidence that allow the reconstruction of past climate and environmental changes. This multiproxy approach provides a powerful means to reconstruct past environments, whilst the multi-lake approach assists in the identification and separation of local (e.g. catchment-scale modifications and groundwater influences) and regional effects (e.g. climatic changes). The results of a modern limnological survey of 24 lakes were used in conjunction with diatom surface sediment samples (and corresponding water chemistry) from 64 lakes across a natural conductivity gradient in western Uganda (reflecting a regional climatic gradient of effective moisture) to explore factors controlling diatom distribution. The relationships between water chemistry and diatom distributions were explored using canonical correspondence analysis (CCA) and partial CCA. Variance partitioning indicated that conductivity accounted for a significant and independent portion of this variation. A transfer function was developed for conductivity (r2jack = 0.74). Prediction errors, estimated using jack-knifing, are low for the conductivity model (0.256 log units). The final model was applied to the core sediment data.This study highlights the potential for diatom-based quantitative palaeoenvironmental reconstructions from the crater lakes in western Uganda. Sedimentary archives from the Ugandan crater lakes can provide high-resolution, annual to sub-decadal records of environmental change. Whilst all of the lakes studied here demonstrate an individualistic response to external (e.g. climatic) drivers, the broad patterns observed in Uganda and across East Africa suggest that the crater lakes are indeed sensitive to climatic perturbations such as a dry Mediaeval Warm Period (MWP; AD 1000-1200) and a relatively drier climate during the main phase of the Little Ice Age (LIA; c. AD 1500-1800); though lake levels in western Uganda do fluctuate, with a high stand c. AD 1575-1600). The general trends support the hypothesis of an east to west (wet to dry) gradient across East Africa during the LIA, however, the relationship breaks down and is more complex towards the end of the LIA (c. AD 1700-1750) when the inferred changes in lake levels at Nyamogusingiri and Kyasanduka are synchronous with changes observed at Lakes Naivasha (Kenya) and Victoria and diverge from local lake level records (from Edward, Kasenda and Wandakara). Significant changes in the lake ecosystems have occurred over the last 50-75 years, with major shifts in diatom assemblages to benthic-dominated systems and an inferred increase in nutrient levels. These changes are coincident with large sediment influx to the lakes, perhaps as a result of increasing human activity within many of the lake catchments.

No description available.