<p> The Hueco and Mesilla Bolsons are part of the intramountain basins of the Rio Grande Rift system. These bolsons are the primary source of groundwater for the El Paso-Ciudad Juarez metropolitan area and contain faults that show evidence of repeated earthquakes during the Quaternary. The region is also associated with has low-level (M&lt;4) seismicity. The collection and analysis of precision gravity data, coupled with information from water wells, multichannel analysis of surface waves (MASW) studies and previously published seismic reflection lines, have been used to examine the structure and faulting within these bolson. This study reveals that the Hueco and Mesilla Bolsons are very different structurally. The southern Mesilla Bolson contains about 500 m of sediment. Faults are difficult to trace and have less than 50-100 m of displacement across them. The southernmost bolson contains numerous Tertiary intrusions and the thickness of Cretaceous bedrock appears to decrease from south to north, possibly delineating the edge of Laramide age deformation within the bolson. The northern Hueco Bolson contains 1800 to 2500 m of basin fill. Displacement along the East Franklin Mountains fault (EFMF), a fault with evidence for repeated earthquakes within the past 64,000 years, is about 1500 m, and displacement on intrabasin faults is 200-300 m. Several intrabasin faults appear to control the saline to freshwater contact within the bolson. The EFMF may extend over 30 km south of the end of its mapped trace at the end of the Franklin Mountains and a number of intrabasin faults also extend south into the urbanized regions of the study area. The EFMF and other basin structures appear to be offset or disrupted at the speculated edge of Laramide deformation that lies beneath the bolson. Horizontal Gradient Methods (HGM) were applied to the gravity data and were successful for tracing faults and older Laramide features within the Hueco Bolson beneath the urbanized regions of the cities. HGM were not as successful at tracing faults within the Mesilla Bolson, however they were helpful for tracing the subsurface extent of igneous intrusions including the Mt. Cristo Rey, River, Three Sisters, and the Westerner outcrops. Some of these features appear linked at depth by a series of dikes and faults. MASW data were used to determine the average shear wave velocity in the upper 30m (Vs 30) at &sim;70 sites within the Hueco Bolson. These observations were combined with similar data collected previously in Juarez to produce regional velocity and site classification maps. The results show low velocities are found close to the river within fluvial deposits with higher velocities close to the Franklin Mountains where bedrock is close to the surface and higher velocities in upland regions of northeast El Paso were soils appear to be more highly cemented. These data will be used in conjunction with information on bolson geometries to model the expected effects of strong ground motion from earthquakes in the El Paso-Ciudad Juarez region.</p>

<p> Much scientific knowledge already exists on the Cretaceous-Paleogene (K/Pg) Boundary Deposit from outcrop and shallow core near to outcrop. The significance of this study is to learn from the only deep-well core on land, from the northern Gulf of Mexico (GoM) known to preserve this deposit. This core was chosen because of its pristine (unweathered) condition. The aim was to characterize the portion of this core which was influenced by the Chicxulub Impact event 65.5 Ma to enhance the scientific knowledge of the K/Pg boundary. I hypothesized that this core represents three lithofacies: 1) pre-impact chalk, 2) mass wasting deposit and fall back material, 3) Midway Shale; and that the mass wasting deposit and fall back material were deposited as a direct result of the impact event. I tested these hypotheses by employing: 1) Macroscopic descriptions, 2) Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) of selected portions, 3) 10% HCl treatment and microscopic descriptions of the resulting insoluble portions. The findings show that the core can be divided into three main sections in ascending order: 1) a lighter carbonate, 2) a darker carbonate, and 3) a black shale. From optical and SEM analysis, I find that the microfossils and ubiquitous coccoliths found throughout the carbonate sections of this core do not exist in the core above section 2. Section 2 is mostly a Chicxulub Impact induced mass wasting deposit. In order to investigate better the non-carbonate components of the core, representative portions were treated with 10% HCl, an investigative technique not commonly applied to cores of the K/Pg boundary. Under an optical microscope ,10% HCl insoluble portions from the K/Pg boundary reveal no regularly shaped impact spherules. I find no Si-rich spherules and posit that the spherules in this core are almost entirely, Ca-rich.</p><p>

<p> This work investigates the lithospheric structure beneath the Mesozoic (~140 &ndash; ~110 Ma) Chilwa Alkaline Province (CAP) in southern Malawi and northeastern Mozambique using aeromagnetic and satellite gravity data (the World Gravity Model 2012 (WGM 2012). The CAP is a granite, syenite, nepheline syenite, and basanite province with minor intrusions of carbonatite bodies. It intrudes the Precambrian terranes of the Southern Irumide belt and the Unango complex. It is located on the northeastern margin of the Mesozoic Shire graben and on the southeastern edge of the Cenozoic Malawi rift, which is considered the southernmost segment of the Western Branch of the East African Rift System (EARS). Some of the CAP&rsquo;s intrusive bodies are clearly offset by the border normal faults of the Malawi rift. Previous petrographic, geochemical and isotopic studies have suggested that the CAP is underlain by a thinned sub-continental lithospheric mantle (SCLM) possibly due to the Mesozoic Karoo rifting event. Hence, mantle magmatic source has been favored as an origin for the CAP. However, melting of a thickened continental crust cannot be ruled out for the origin of the CAP as has been suggested for several other alkaline intrusions. In this study: (1) Edge enhancement of the aeromagnetic data showed the CAP to be defined by circular and overlapping magnetic anomalies typical of hypabyssal nested igneous ring complexes. (2) Three-dimensional (3D) Voxi modeling and magnetic susceptibility analysis of the aeromagnetic data covering selected CAP&rsquo;s intrusive bodies showed that these were emplaced at an average depth of ~ 4 km. (3) Upward continuation of the WGM 2012 Bouguer gravity anomalies suggested that the CAP was sourced from possibly deeper magma chambers now preserved as broad batholiths at ~4 km to~6 km depth. (4) Two-dimensional (2D) radially-averaged power spectral analysis of the WGM 2012 Bouguer gravity anomalies showed that the CAP is underlain by a thick crust (possibly due to mafic magmatic under-platting) where the Moho can be as deep as ~45 km. It also showed that the CAP is underlain by a relatively thin SCLM (possibly due to Mesozoic Karoo rift-related lithospheric stretching) where the asthenosphere-lithosphere boundary (LAB) can be as shallow as ~110 km. This work suggests that thinning of the SCLM might have allowed for the ascendance and decompression melting of the asthenosphere but also provided heat source (through mafic magmatic under-platting) to partially melt the lower crust to form the CAP from a mixed magma source and through caldera collapse mechanism. This model can be tested by additional geochemical and isotopic studies. This work highlights the importance of potential field data for imaging complex continental lithospheric structure. Understanding the lithospheric structure beneath the CAP is helpful in guiding future mineral exploration efforts because igneous ring complexes are important sites for the formation of economic mineralization zones.</p><p>

<p> A 6012-foot Monterey Formation succession at Chico Martinez Creek, San Joaquin basin, is characterized at high spatial resolution by spectral gamma-ray data in 2- foot increments, 5-foot lithologic descriptions, and qualitative XRD and FTIR analysis. Based on these data, the 4 Monterey members&ndash;the Gould, Devilwater, McDonald and Antelope shales&ndash;are subdivided into 7 distinctive lithofacies. New paleomagnetic data, combined with industry-provided biostratigraphy establishes a chronostratigraphic framework and allows determination of linear sediment accumulation rates. Condensed sedimentation at the onset of McDonald deposition (~14 Ma) is also observed in correlative members in the Pismo, Santa Maria and Santa Barbara basins. This regional event is associated with eustatic regression from the Mid-Miocene highstand related to formation of the East Antarctic Ice Sheet and ongoing thermotectonic basin subsidence. A surge in linear sediment accumulation rates in the siliceous upper McDonald and Antelope (~10.4 Ma) is attributed to a regional increase in diatom productivity. </p>

<p> The Paleocene-Eocene Thermal Maximum (PETM) was followed by a lesser hyperthermal event, called ETM2, at &sim;53.7 Ma (Zachos et al., 2010). The carbon isotope excursion and global temperature increases for ETM2 were approximately half those of the PETM (Stap et al., 2010). The paleohydrologic response to this event in the continental interior of western North America is less well understood than the response to PETM warming. Although ETM2 is better known from marine than continental strata, the hyperthermal has been identified from outcrops of the alluvial Willwood Formation from the Deer Creek and Gilmore Hill sections of the McCullough Peaks area in the Bighorn Basin, Wyoming (Abels et al., 2012). The presence of ETM2 in Willwood Formation strata provides a rare opportunity to examine local continental climactic and sedimentary response to this hyperthermal. </p><p> Core drilled at Gilmore Hill was described and analyzed geochemically. The core consists of paleosols formed on mudrocks that are interbedded with siltstones and sandstones. Carbon isotope analysis of carbonate nodules from paleosols in the core shows that the top of the core, below a prominent yellow sandstone, most likely records the very beginning of the carbon isotope excursion that marks ETM2 (Maibauer and Bowen, unpublished data).The rest of the CIE was likely either not recorded due to sandstone deposition or removed by erosion prior to the deposition of the sandstone. </p><p> Analysis of bulk oxides in the paleosols using the methods of Sheldon et al. (2002) and Nordt and Driese (2010b) provides quantitative estimates of precipitation through the core section. The estimates reveal drying over the &sim;15m leading up to ETM2. Red and brown paleosols, attributed to generally dry conditions, dominate the entire section below the onset of ETM2 and confirm drier conditions. In contrast, thick purple paleosols are associated with ETM2 at the Deer Creek site and suggest wetter conditions during most of the ETM2 interval. The prominent yellow sandstone at the top of the Gilmore Hill core was probably deposited during those wetter climate conditions. </p><p> The core displays distinct changes in stratigraphic architecture: the bottom &sim;100m is mudrock-dominated and the top &sim;100m is sandstone dominated. Several PETM studies have suggested that sediment coarsening in continental basins in the US and Spain developed in response to precipitation changes associated with global warming. Analysis of the Gilmore Hill core's stratigraphic architecture in conjunction with carbon isotope and precipitation data shows that the prominent sandstone in the position of ETM2 was not caused by climate change. The sandstone is the uppermost part of the sandstone-rich interval whose base underlies ETM2 by more than 50m. This study shows that the shift from mudrock- to sandstone-dominated stratigraphy at Gilmore Hill, and possibly throughout the McCullough Peaks area, was not caused by climactic change associated with ETM2. While studies of PETM sections have suggested that the hyperthermal caused sediment coarsening in several different basins including the Bighorn Basin (e.g., Schmitz and Pujalte, 2007; Smith et al., 2008b; Foreman et al., 2012), this study suggests that the lesser magnitude ETM2 did not cross the necessary threshold to provoke a sedimentological response in the Bighorn Basin.</p>

<p>Calcium bentonite deposits of the Glendon and Bucatunna formations of the Oligocene Vicksburg Group located in Smith County, Mississippi were examined to determine the depositional environment, diagenetic history and origin of the bentonite. Traditionally, calcium bentonite was considered to be the product of the weathering of volcanic ash deposits. The hypothesis tested is that the bentonite deposits are not a result of weathered volcanic ash, but are a result of weathered marl. Core samples were drilled from the Chisholm bentonite mine in Smith County and were studied using X-ray diffraction, scanning electron microscopy, and petrographic microscopy. Abundant bacteria along with nanometer-scale organic textures were found throughout and are consistently associated with bentonite, illite, and smectite. No evidence of volcanic ash was found. It appears that the calcium bentonite clays in the Glendon and Bucatunna formations of Smith County, Mississippi formed from weathering, including bacterial activity, of glauconite-bearing marl.

<p> Significant accumulations of lower Wilcox Group coals have previously been reported throughout regional reconnaissance studies in north-central Louisiana. The present study is part of a series of contiguous sub-regional studies that incorporate much higher well densities, evaluate each well log individually for coal presence, and map the structures and thicknesses of the Reynolds and the Russell coal. The thickest coal accumulations are found in paralic lagoon deposits in the northern portions of the study area within Lasalle and Rapides Parishes just south of the Angelina-Caldwell Flexure and ontop of the LaSalle Arch. No lower Wilcox Group coals were found south of Township 2N (latitude 31.100&deg; N) in this study. Lower Wilcox Group strata south of Township 2N are interpreted as a shoreline with marine conditions to the south, not suitable for coal accumulation.</p>

<p> Fluvial suspended sediment is a master variable affecting a wide range of fluvial and coastal environmental processes, and dominating the terrestrial mass flux to the oceans. Although it has long been recognized that relationships between suspended sediment concentration and discharge are not stationary in small, mountainous rivers over time scales from hours to decades, most studies continue to assume stationarity. This collection of studies directly addresses the issue of non-stationarity in the suspended sediment &ndash;discharge relationship of the Salinas River, central California, and examines the progression of abandoned channel fill sequences in the Eel River Estuary of northern California. </p><p> Preceding these studies is a methodological analysis of the pretreatment of fluvial and marsh sediments for particle size analysis. Pretreatment of sediment with hydrogen peroxide to remove organic constituents and aid deflocculation is a common component of particle size analyses of terrestrial and marine sediments. The first chapter presents the quantitatively determined effect of a range of treatment levels on particle size distribution among four sediment types representing a range of mineral/organic particle size distributions, organic content and particle characterization (charcoal or detrital plant material). </p><p> The following three chapters examine the effects of antecedent basin conditions on the suspended sediment &ndash; discharge relationship in the Salinas River. In chapter two, forty-five years of suspended sediment data from the lower Salinas and 80 years of hydrologic data were used to construct hydrologic descriptors of basin preconditioning and test the effects of these preconditions on suspended sediment behavior. Fine (diameter (<i>D</i>) &lt; 63 &mu;m) and sand sized (<i>D</i> > 63 &mu;m) sediment were found to respond differently to antecedent hydrologic conditions. Fine sediment was most sensitive to flushing flows of moderate discharge (10 &ndash; 20x mean discharge (<i>Q_mean</i>) that led to lower subsequent fine sediment concentrations, while sand concentrations were generally decreased by periods of drought and longer elapsed time since a wide range of discharges acting as maintenance flows. </p><p> Chapter three examines the interannual to decadal scale persistence of suspended sediment &ndash; discharge relationship states in the lower Salinas River, assesses the role of antecedent hydrologic conditions in controlling these patterns, and addresses their relationship to El Ni&ntilde;o Southern Oscillation (ENSO) climatic states. The decadal scale variability in suspended sediment behavior was influenced by interannual to decadal scale fluctuations in hydrologic characteristics, including: elapsed time since small (&sim; 0.1x Qmean), and moderate (&sim; 10x Qmean) threshold discharge values, the number of preceding days that low/no flow occurred, and annual water yield. El Ni&ntilde;o climatic activity was found to have little effect on decadal-scale fluctuations in the fine suspended sediment &ndash; discharge relationship due to low or no effect on the frequency of moderate to low discharge magnitudes, annual precipitation, and water yield. However, sand concentrations generally increased in El Ni&ntilde;o years due to the increased frequency of moderate to high magnitude discharge events, which generally increase sand supply. </p><p> Chapter four brings to bear the decadal scale persistence of suspended sediment - discharge behavior, the effects of antecedent hydrologic conditions, and ENSO influences on the estimation of inter-decadal scale sediment flux from the Salinas River. The longer sampling records employed in this study and incorporation of decadal scale behavior or antecedent hydrologic conditions resulted in average annual load estimates of 2.1 or 2.4 Mt, in comparison to earlier estimates of &sim; 3.3 Mt by previous researchers. El Ni&ntilde;o years dominated the sediment budget by producing on average ten times more sediment than non-El Ni&ntilde;o years. </p><p> Chapter five proposes a modification of the current generic model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. This work was based on evidence from two consecutive abandoned channel fill sequences in Ropers Slough of the lower Eel River Estuary. Planform geomorphic characteristics derived from these images were used in conjunction with sub-cm resolution stratigraphic analyses to describe the depositional environment processes and their resultant sedimentary deposits. The abandoned channel fill sequences appeared to differ due to the topographic steering of bed sediment transport and deposition previously identified in rivers experiencing only unidirectional flow, while also expressing the seasonal dichotomy of fluvial and tidal deposits.</p>

<p> New stratigraphic and geomorphic data from the Santa Maria Basin, California, suggests that the major basin-bounding Little Pine fault system has been acting in a primarily reverse offset fashion since the late Pleistocene. A series of stratigraphic columns in the Plio-Pleistocene Paso Robles Formation measured along the Little Pine fault indicate that there was episodic uplift during the latest Pleistocene. A 20-40% increase in the percent composition of resistive, Franciscan Complex-derived cherts within active drainages indicate that uplift of the San Rafael Mountain front increased rapidly since the deposition of older sediments. The shape of stream profiles created along the Little Pine fault suggest ongoing uplift associated with the central and southeastern segments of the fault, with a lesser amount of uplift occurring further northwest along the Little Pine fault. A number of ridgeline profiles were also created which exhibit significant jumps in topography near, or just northeast of the Little Pine fault, suggesting that recent uplift is responsible. The ridgeline profiles also suggest an increased rate of uplift adjacent to the central and southeastern segments of the Little Pine fault zone, in agreement with the along-strike variations in uplift suggested by the stream profiles. Stream traces were also examined for deflections as they flowed across the Little Pine fault, but most show no significant lateral offset.</p>

<p> The Waucobi Lake Beds in Owens Valley, California contain two distinct facies representing saline-alkaline and fresh water environments. The potential cause for the change in lacustrine facies is examined through geomorphic, geochemical and sedimentological analyses. An age range for the lake beds was constrained with the dating and &ldquo;fingerprinting&rdquo; of 13 tuffs throughout the Waucobi Lake Bed exposures. 40Ar/39Ar dating completed for this study provides ages of 2.63 to 2.06 Ma for tuff layers found within the lake beds, with the transition from saline-alkaline facies to fresh water facies occurring around 2.5-2.4 Ma. Regional climate during the late Pliocene-early Pleistocene is reflected by the saline-alkaline environment within Waucobi. However, the Waucobi environment deviates from regional climate after 2.5 Ma, implying that the fresh water facies represents a change in lacustrine hydrology. Given the coincidence between a prominent seismite recorded in the lake beds with the facies change, tectonic activity rather than climate is postulated as the cause for the transition in the lake environment.</p>