<p> The purpose of this study was to identify the geologic signature of paleostorm events within the mid-continent region. This research aimed to create a better understanding of the long-term geologic history of major storms and to allow for better-informed projections regarding future return periods for such storms. The study locations were Cheyenne Bottoms Wildlife Refuge, Kansas and Canton Lake, Oklahoma. To determine the geologic signature of major storms, sediment cores were taken at both locations and sampled at high resolution (3 mm) intervals for grain size analysis using a Cilas laser particle size analyzer. Downcore chronology was determined through Pb-210, Cs-137 and C-14 dating methods. Using a recent known major storm occurrence at Canton Lake, the signature created by storms in the geologic record was identified. The resulting signature was then used to identify paleostorms in the longer-term record in the Cheyenne Bottoms core. The results were also used to determine storm/climate cycles in the long-term geologic record, and to calculate true return periods for major storms. A better understanding of true return periods and possible increases in frequency or intensity of large storms is essential in the effort to mitigate future damage to infrastructure and loss of human life</p>

<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> 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>