Removal of vegetation and subsequent erosion in karst regions such as central Kentucky or southeastern Alaska often leads to increased sedimentation in karst features such as caves and dolines. This sedimentation can impact the ground water by altering flow paths and the bio-geochemistry of the karst aquifer itself. Various methodologies have been used to obtain quantitative erosion and sedimentation rates for surface areas in karst and non-karst settings, but few quantitative studies have taken place in caves. The purpose of this study is to examine the effects of timber harvesting and development upon the caves and karst of southeastern Alaska by determining the recent (post 1954) sediment accumulation rates. Cesium 137 from open-air nuclear testing was is used to determine the age of the sediments in caves, surface karst features and undisturbed areas. Sediments generated from surface land disturbances and deposited in caves and karst features since 1954 may have positive cesium activities, whereas sediments deposited in caves and karst features before 1954 (the beginning of 137Cs deposition in the environment) will have little or no cesium activity. The method was successfully tested in the main river passage of Big Bertha Cave in south-central Kentucky before fieldwork commenced in Alaska. Samples collected from sediment berms in the study areas were analyzed for 137Cs on the EG and G High Purity Germanium detector at the Western Kentucky University Applied Physics Institute for a period of 12 hours. Results from each site were obtained in terms of peak area (net counts) and then converted into international units (Bq/Kg). Vertical profiles of cesium activity were constructed for each site and a minimum sediment accumulation rate (in cm per year) calculated. This sedimentation rate represents a minimum rate of sediment accumulation since it does not take into account the removal and re deposition of sediment during flood events. The Alaskan caves and karst areas selected for this study are all within or downstream from areas of significant development and /or timber harvesting, and cesium 137 is present at all locations. Recent sedimentation rates in the sampled caves and karst of southeastern Alaska range from approximately 1.5 cm/year to over 6 cm/year, and it appears that recent timber harvesting has had a significant effect upon sedimentation in these areas.

No description available.

Unraveling the fluid-present metamorphism of schists from garnet compositions in the Black Hills, South Dakota

The Discrete Element Method (DEM) was used to model the advance of allochthonous salt sheets through differential loading. The effects of basal slope angle, initial salt thickness, sediment thickness, loading time, progradation rate, and the mechanical strength of the overburden were tested to determine their influence on the development of stratigraphic and structural relationships in the emerging salt and sediment structures. These simulations show that the advance of salt is driven by gravitational instability and sediment loading. Salt advance is greatest with high basal slopes, thick salt, weak sediments, and high sediment progradation rates. The rate of salt advance determines the angle of a subsalt sediment ramp, which influences the final geometry of the system. High angle ramps form with slow salt front advance rates and tend to form counterregional sediment geometries, while low angle ramps form with rapid salt front advance and tend to produce roho geometries.

Our study utilizes a pseudo-3D grid of 2D, depth-migrated seismic profiles in order to provide new constraints on rifting within the Deep Galicia Basin. 3D analysis shows that faults strike within 10° of north, indicating east-west directed rifting. Three distinct structural domains are identified on the east-west oriented profiles. In addition to an exhumed mantle domain, two crustal domains are distinguished by their different faulting styles and thinning. Restored crustal thickness (9-14 km) within the intracrustal fault domain (IFD) is close to the current thickness of the Galicia Bank crust (15-20 km), implying that the observed faults within the IFD were the first to form after the formation of the Galicia Bank. Restored crustal thickness within the detachment fault domain (DFD) is less than in IFD, yielding 3-5 km thickness. This suggests that the DFD either experienced an additional generation of faulting compared to the IFD, or was extended by a different mechanism, e.g. rolling-hinge-style rifting.

The Bear Lake Plateau extends north-south across the north central corner of Utah and the southeastern corner of Idaho. North Eden Creek drains westward through part of the plateau and is cross-axial across both strikes of beds and other structures in the area. The formations in the area mapped are of Triassic, Jurassic, and Tertiary age, although only Jurassic and Tertiary rocks contribute sediments to North Eden Creek. The formations consist of sandstones (Nugget) limestones (Twin Creek) and conglomerates (Wasatch). A local extrusion of basalt occurs in the southwestern part of the drainage area. Particle-size analyses of 15 samples from pits dug along North Eden Creek and its tributaries and North Eden Delta show that mean and maximum particle sizes increase downstream due to additions by tributaries and mass-wasting from the coarse-grained, highly jointed Nugget Formation flanking lower parts of the stream. Mineralogic analyses of these samples show that quartzite and chert predomi

EARTH AND ENVIRONMENTAL SCIENCE LAND USE CONTRIBUTIONS TO PHOSPHORUS LOADING IN AN IMPAIRED STREAM, MILL CREEK, TENNESSEE VENA JONES Thesis under the direction of Professor Kaye Sawyer Savage Located in Middle Tennessees Central Basin, Mill Creek is listed with EPA for water quality impairment [303(d)] from high phosphorus concentrations that affect its biogeochemical properties. Mill Creek was sampled at three locations according to land use during dry and wet weather. Imperviousness associated with land use increases downstream. Agricultural regions, MCW-A, are in the headwaters, suburban portions, MCW-B, are downstream and the lower reaches are highly urbanized and industrial, MCW-C. Water samples were filtered successively to fractions >0.65µm, 0.65>0.45µm, 0.45>0.1µm, and <0.1µm using tangential flow filtration and analyzed for total phosphorus, soluble reactive phosphate, and trace metals. Phosphate loads increased downstream. Total phosphorus and Pb increased during wet weather; other trace metals were diluted. Phosphorus was associated with fractions <0.1µm and >0.65µm. Phosphorus contributed to the stream from bedrock and soils was minor. Most contaminants associated with industry were diluted with increasing discharge; this suggests that non-point sources are inducing impairment. Increased impervious surfaces increased frequent flood peak discharge values and runoff. Urban runoff in MCW-B and MCW-C most likely increased soluble reactive phosphate concentrations in Mill Creek. Continued development will most likely contribute to higher P loads through increased runoff from impervious surfaces where overland flow has the opportunity to suspend and redistribute pollutants. The source of this P is most likely domestic during wet weather. Increased particulate phosphorus will likely increase with increased development where erosion from disturbed land surfaces is a common problem.

The Spirit Mountain batholith (SMB) is a ~250 km2 composite silicic intrusion located within the Colorado River Extensional Corridor (CREC) in southernmost Nevada. Westward tilting of 40-50º has exposed a cross section of the SMB. Piecemeal construction is indicated by zircon geochronology, field relations, and elemental geochemistry. U/Pb data (zircon SHRIMP) demonstrate a ~2 million year (17.4-15.3 Ma) history for the SMB. Individual samples contain zircons with ages that span the lifetime of the batholith, suggesting recycling of extant zircon into new magma pulses. Field relations reveal distinct magmatic episodes and suggest a common injection geometry of stacked horizontal sheeting. The largest unit of the SMB is a gradational section (from roof to depth) of high-silica leucogranite through coarse granite into foliated quartz monzonite and has a ~million year history. The 25 km2 x 2 km2 leucogranite zone was emplaced incrementally as subhorizontal sheets throughout the history of this section, suggesting repeated fractional crystallization and melt segregation events. Age data from this gradational unit show multiple zircon populations within individual samples. Subsequent distinct intrusions that cut this large unit preserve a sheeted, sill-on-sill geometry. We envision the SMB to have been a patchwork of melt-rich, melt-poor, and entirely solid zones throughout its active life. Preservation of intrusion geometries and contacts depended on the consistency of the host rock. Zircons recycled into new pulses of magma document remobilization of previously emplaced crystal mush, suggesting the mechanisms by which evidence for initial construction of the batholith became blurred.

New whole-rock Pb isotopic data combined with existing Pb, Sm-Nd, and U/Pb zircon data from the Blue Ridge and the Mid-Continent Granite Rhyolite terrane support recent suggestions that the southern and central Appalachian basement (SCAB) is exotic with respect to Laurentia. The conventional view that basement in the southern Appalachians represents juvenile Mesoproterozoic crust, the final stage of the southeastward growth of Laurentia prior to Rodinian collision, has been called into question based upon geochronological and isotopic data. Our expanded whole-rock Pb isotopic database for the Blue Ridge and the Mid-Continent Granite Rhyolite terrane, combined with existing Pb, Sm-Nd, and U/Pb zircon data, verify that SCAB is exotic to Laurentia. The 1.0-1.25 Ga Llano Uplift, 1.0-1.3 Ga Adirondacks, and 1.4-1.5 Ga Granite-Rhyolite Terrane all have Sm-Nd depleted mantle model ages (TDM) close to their U/Pb zircon ages, and are thus apparently juvenile crustal material. In addition, all have low 207Pb/204Pb (for a given 206Pb/204Pb). Conversely, most 1.0-1.2 Ga SCAB massifs have TDM ages >1.5 Ga, indicating incorporation of pre-existing crustal material with TDM ages greater that those found in juvenile rocks of eastern North America. In addition, all SCAB massifs sampled thus far have a more elevated 207Pb/204Pb (for a given 206Pb/204Pb) than any nearby juvenile Laurentian crust. The combined Pb data suggest that two isotopically distinct reservoirs are required to produce the Pb isotopic array observed for Mesoproterozoic eastern North America. One reservoir, characterized by low 207Pb/204Pb, produced juvenile crust found in the Adirondacks, Llano, and mid-continent. A second reservoir, characterized by higher 207Pb/204Pb, produced the SCAB massifs. Thus, both Sm-Nd and Pb isotopic data, perhaps the most robust indicators of crustal origin in high-grade terranes, preclude derivation of SCAB from any nearby juvenile crustal material. The clearest evidence for exotic crust in the SCAB comes from the Roan Mountain area of eastern TN-western NC (northern Mars Hill terrane). U/Pb SHRIMP ages up to 1.8 Ga for igneous rocks, detrital zircons >2.0 Ga, TDM ages >2.0 Ga, and the most elevated 207Pb/204Pb observed in eastern North America demonstrate the anomalous age (Paleoproterozoic?) and isotopic characteristics of this crustal block with respect to the surrounding basement.

Zirconium and Hf are nearly identical geochemically, and therefore most of the crust maintains near chondritic Zr/Hf ratios of ~35-40. By contrast, many high-silica rhyolites and granites have anomalously low Zr/Hf (15-30). As zircon is the primary reservoir for both Zr and Hf and preferentially incorporates Zr, crystallization of zircon controls Zr/Hf, imprinting low Zr/Hf on coexisting melt. Thus, low Zr/Hf is a unique fingerprint of effective magmatic fractionation in the crust. Age and compositional zonation in zircons provides a record of the thermal and compositional histories of magmatic systems. High Hf (low Zr/Hf) in zircon zones demonstrates growth from fractionated melt, and Ti provides an estimate of temperature of crystallization (T(TiZ)) (Watson and Harrison, 2005). Whole-rock Zr/Hf and zircon zonation in the Spirit Mountain batholith, Nevada, documents repeated fractionation and thermal fluctuations. Ratios of Zr/Hf are ~30-40 for cumulates and 18-30 for high-SiO2 granites. In zircons, Hf (and U) are inversely correlated with Ti, and concentrations indicate large fluctuations in melt composition and T(TiZ) (>100º C) for individual zircons. Such variations are consistent with field relations and ion probe zircon geochronology that indicate a million year history of repeated replenishment, fractionation, and extraction of melt from crystal mush to form the low Zr/Hf high-SiO2 zone.