GeoSymposium Abstracts
April 20-21, 2007
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Logo by Alex Roy
Abstracts for oral session
Howley, Robyn (abstract)
Yonovitz, Maureen (abstract)
Griffin, Lora (abstract)
Barrow, Wendy J. (abstract)
Arriola, Tonia (abstract)
Evans, Tricia (abstract)
Zaragoza, Shelley (abstract)
1. Arrowood, T. and Young, M., Determining the transport of the acrylamide monomer (AMD) in soil and groundwater systems
2. Artz, Z. and Simon, A., Petrology and age constraints of intrusive phases at Cortez, Lander County, Nevada: exploring the link between magmatism and carlin-type mineralization
3. Baron, A., Yu, Z., Kreamer, D. and Zhu, J., Simulation of response to rainfall events in the Virgin Rver floodplain
4. Bell, A. and Simon, A., Platinum group element mobility in silicate melts
5. Carter, J. and Simon, A., Studying fluid inclusions in the La Popa basin, Mexico as an analog to fluid migration in sediments in the gulf of Mexico
6. Chen, X., Yu, Z. and Cui, G., Research on the mechanism of eutrophication control in Taihu basin
7. Druschke, P., Hanson, A. and Wells, M., The Sheep Pass Formation, Nevada: Stratigraphic evidence for a paleogene transition and contraction to extension in the sevier hinterland
8. Griffing, C.Y., Loeschner, M.S., Vetter, L., McLaurin, B.T., and Rowland, S., Fluvial Depositional Environment of a Pleistocene Megafaunal Locality, Panaca, Nevada
9. Howell, M., Genesis of hyperarid soils of the Atacama Desert, Chile
10. Johnsen, R. and Smith, E., Evidence for dome collapse and coeval mafic-felsic volcanism in the central Mccullough Range, Nevada
11. Kayyon, L., Kinematic and timing constraints on the Sevier Fold and Thrust Belt, southern Nevada and southeastern California
12. Mercadante, J. and Rowland, S., Gregarious behavior recorded in the tracks of an early middle Jurassic Synapsid
13. Miller, N., Druschke, P. and Hanson, A., The Milk Ranch Canyon section, east-central Nevada: a neogene coarse clastic succession
14. Nie, W. and Snelson, C., A seismic reflection and refraction survey of the Arrow Canyon range and Wildcat Wash Faults
15. Pan, F., Ye, M., Yu, Z. and Zhu, J., Simulation of radionuclide transport in the heterogeneous unsaturated zone of Yucca Mountain, Nevada
16. Robins, C., Howell, M., Morton, J., Williams, A., Yonovitz, M., Buck, B. and Merkler, D., Comparative analysis of surficial geological maps and nrcs soil surveys for flood hazard assessments on alluvial fans: a case study in Ivanpah Valley, Nevada
17. Shirk, A., Exhuming the Tule Springs research project: new perspectives and technique
18. Speeter, G. and Taylor. W., Analysis of late Paleozoic contractional deformation and Cenozoic extension in green monster canyon (northern monitor range). Nye county, Nevada
19. Williams, A., Buck, B., Sun, H. and Soukup, D., Mapping of biological soil crusts in Hidden Valley national wilderness area, Nevada
20. Wooton, K. and Spell, T., Petrogenesis of extracaldera rhyolites, Yellowstone volcanic field, Wyoming: a 4th caldera cycle?
21. Yin, J., Young, M. and Yu, Z. Scaling effects on the spatial variable soil moisture in arid regions
22. Zellner, G. and Simon, A., Source of ore fluids and conditions of mineralization at bullard pass, Yavapai County, Arizona
Determining the transport of the acrylamide monomer (AMD) in soil and groundwater systems
Todd Arrowood and Michael Young
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Polyacrylamide (PAM), which is produced from a known carcinogen AMD, has been proposed to seal unlined water delivery canals in the western United States. The fate and transport of AMD is not well known. A quantification of the sorption coefficient, sorption isotherms, and understanding of AMD breakthrough in soil and water systems is necessary to determine the possible risk associated with this proposed use of PAM. Three types of soil, a sand (C33), a loam soil, and #70 and #60 engineered quartz sand were used in all the experiments. Batch experiments were conducted to determine the sorption coefficient and create a sorption isotherm for AMD. Short column (0.15 m) experiments were conducted to determine AMD breakthrough, transport, and mobility. It was determined that the sorption of AMD is instantaneous and is slightly affected by the amount of clay and silt content in the soil samples. The concentration of AMD that adsorbed onto the Loam varied from 1.6-22%. This percentage of sorption is relative to the initial concentration tested. The C33 sand and quartz sand had no statistically significant sorption. The isotherms exhibited a Freundlich fit which shows that soil has a lowering affinity for AMD adsorption with increasing concentration levels. The equation of the isotherm for AMD in the loam soil is Cs = 6.07 x 10-4 ¡À 2.32 x 10-4 Cw0.569¡À0.0631. Preliminary results from the ongoing short column tests show that AMD has a breakthrough very similar to that of the bromide tracer in both the C33 and # 60 sand. This work is sheduled to be completed by the end of March 2007. Long-column (1 m) experiments will also be conducted to determine AMD transport in collaboration with scientists examining microbial breakdown of AMD in soil systems. Numerical and predictive models will be created to simulate AMD¡¯s transport in a simulated system using HYDRUS 2-D. This work is as yet unfinished and sheduled to be completed by June 2007.
Keywords: acrylamide, polyacrilamide, transport, breakthrough curves
PETROLOGY AND AGE CONSTRAINTS OF INTRUSIVE PHASES AT CORTEZ, LANDER COUNTY, NEVADA: EXPLORING THE LINK BETWEEN MAGMATISM AND CARLIN-TYPE MINERALIZATION
Zachary Artz and Adam Simon
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
There is an ongoing debate regarding the source of fluids, metals, and heat that is required to form Carlin-type gold deposits. Fluid inclusion data from multiple Carlin-type deposits suggest that a mixture of meteoric, magmatic, and metamorphic waters may be responsible for transporting gold with subsequent ore mineralization occuring at temperatures on the order of 200¡ã C. Apatite fission tracks suggest that the paleo-geothermal gradient would be insufficient to heat ore fluids to this temperature. Therefore, it is necessary to call upon magma as another source of heat to account for the elevated fluid inclusion temperatures. This data was collected and observed in the Cortez area, located approximately 50 miles southwest of Carlin, Nevada, along the Battle Mountain-Eureka trend. It¡¯s here that the observation of numerous magmatic bodies outcropping at the surface, and dikes and sills that were intercepted by drill cores in the subsurface, makes magma a viable heat source. Examination of drill cores indicate a strong spatial relationship between the position of sills and high grade ore zones; i.e., sills up to 100 meters in thickness underlie Au-rich rock. This project will explain the possible link between magmatism and Au-mineralization, by petrographically characterizing the intrusive rocks, both at the surface and in drill cores; by constraining the timing of magmatism; and comparing this to the inferred age of Au-deposition.
Keywords: Carlin-type, magmatism, Cortez, Nevada
SIMULATION OF RESPONSE TO RAINFALL EVENTS IN THE VIRGIN RIVER FLOODPLAIN
Alexander Baron, Zhongbo Yu, David Kreamer, and Jianting Zhu
Water Resources Management, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The allocation of Southern Nevada water from Lake Mead is commonly understood to be inadequate to sustain the area¡¯s current rapid population growth. In response to this, and to the constant threat of drought in the American Southwest, local water managers are planning for increased pumping of groundwater and the possibility of a diversion of surface water in the Lower Virgin Valley. In this study a model was used to simulate hydrologic response to rainfall in the Valley's floodplain aquifer. First, the river stage was quantified at different time steps throughout a rainfall event. River stage was then used as a boundary condition for a MODFLOW model that described seepage from the river into the floodplain aquifer. This model will help water management officials to understand interactions between surface water and groundwater in a hydrologic system that is divided between the different state and local administrative entities, and which provides water for extensive reaches of phreatophytic vegetation.
Keywords: Virgin River, MODFLOW, boundary conditions
PLATINUM GROUP ELEMENT MOBILITY IN SILICATE MELTS
Aaron Bell and Adam Simon
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The solubility, partitioning, diffusive behavior of the Platinum group elements in silicate melts is poorly constrained, and has yet to be studied extensively. This project proposes to perform a series of coupled diffusion experiments to assess the diffusive behavior of Pt in a silicate melt in conjunction with a series of PGE solubility and partitioning experiments between silicate melt and aqueous fluid. The two proposed studies are inherently linked as thermodynamic and kinetic studies involving stability and inherent mobility of Pt in silicate melts. The proposed partitioning experiments are designed to evaluate the dependence of PGE solubility between coexisting silicate melt and aqueous fluid as a function of variables such as: fS2, fO2, aqueous fluid pH, melt polymerization, and melt chemistry. Additionally, the proposed diffusion experiments are designed to evaluate the diffusive behavior of Pt and Rhodium (Rh) as a function of melt redox state. The coordination capacity of various ligands (Cl, P, OH, and S) may also be evaluated from the diffusion experiment data. Variation of the fO2 will hopefully elucidate the effect of melt oxidation state on Pt speciation and mobility as a metal-ligand complex.
Keywords: diffusion, PGE, Solubility, speciation
STUDYING FLUID INCLUSIONS IN THE LA POPA BASIN, MEXICO AS AN ANALOG TO FLUID MIGRATION IN SEDIMENTS IN THE GULF OF MEXICO
Jonathan Carter and Adam Simon
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The Gulf of Mexico has large untapped reserves of petrol chemicals waiting for discovery and use that are challenging to locate owing to the poor spatial resolution of seismic data. One way to improve our understanding of seismic refraction data is to study structures in exposed sedimentary basins; i.e., basins present on dry land. The La Popa basin in northeastern Mexico serves as a natural laboratory for these types of studies as it contains similar sedimentary facies with many analogues to the inaccessible seafloor. The basin contains a number of salt welds and diapirs which act to channel petroleum-bearing fluids as the latter ascend via porous media flow and also along faults and major changes in lithology. There is evidence that the salt weld in the Devil's Anus area may have acted a conduit for petroleum-bearing fluid flow. Samples of upwelling fluids are potentially preserved as fluid inclusions inside minerals such as quartz, calcite and dolomite which precipitate from the fluids in response to changes in pressure, temperature and pH during water-rock interaction. These fluid inclusions act as time capsules, with diameters of 1 - 10 microns on average, preserving the chemical history and temperature information of the fluid at the time of mineral growth. Thus, they can help us understand the history of hydrocarbons allowing for more accurate constraints on the burial depth, temperature history, fluid compositions/interactions and the migration patterns of both fluid movements and accumulation. In this project, I am studying fluid inclusions in minerals which were collected along a transect near the Devil's Anus area adjacent to the prominent salt weld. Using fluid inclusion microthermometry, I will build a thermal model for fluid flow in the basin and also constrain the major chemical constituents of the fluids. I will present data about locations of fluid inclusions, their composition, and burial temperatures as well as useful data about the movement and presence of hydrocarbons and other paleofluids in the La Popa Basin. These data will help models which aim to enhance oil reserve discovery, oil generation data, and reservoir charge estimation.
Keywords: fluid inclusions, petroleum, oil, thermal history
RESEARCH ON THE MECHANISM OF EUTROPHICATION CONTROL IN TAIHU BASIN
Xing Chen, Zhongbo Yu, and Guangbai Cui
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
In recent years, continuing attention has been turned to the contribution of non-point sources to the water quality impairment. Water resources in Taihu basin could not meet the water demand for the large population and rapid economic development in the region. Subsequently the availability of clean water limits the sustainable development in economy and society within the basin in recent decades. This study divides the complex ecosystem in Taihu basin into 3 internally related subsystems: drainage network, lake and land. The integrated mathematical, laboratory and field approaches were used for the research in this study. Four research themes which are (1) transportation and quantification of non-point nutrient materials in the water-soil interface, (2) mechanism of pollution accumulation and transportation in the drainage network, (3) dynamics of pollution accumulation and transportation, and (4) bearing capacity of pollution burden and principles of pollution control in Taihu basin were explored in this study. The N and P transport in water-soil interface were qualified and quantified and the mechanism of algae outbreak was further understood, while the management principles such as the application of artificial wetlands or hydraulic engineering were established. The innovative idea of the combination of catchment control and district control has been created to manage the water environment. Based on this idea, the practice of implementing the district control to achieve the control objectives of the basin has produced significant improvements.
Keywords: Taihu basin, non-point pollution, eutrophication, mechanism
THE SHEEP PASS FORMATION, NEVADA: STRATIGRAPHIC EVIDENCE FOR A PALEOGENE TRANSITION AND CONTRACTION TO EXTENSION IN THE SEVIER HINTERLAND
Peter Druschke, Andrew Hanson, and Michael Wells
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The Sheep Pass Formation of east-central Nevada is a >1 km thick sequence of latest Cretaceous to Eocene alluvial/fluvial and lacustrine strata deposited within the Sevier hinterland. Our new 1:12,000 scale mapping and stratigraphic measurements of the Egan Range type section indicate that the basal member of the Sheep Pass Formation (SPF) generally occupies a narrow trough that is bounded by a series of faults cutting the Paleozoic basement. The basal conglomeratic member of the SPF may be further divided into a lower, massive, poorly bedded boulder conglomerate containing abundant megabreccia blocks of upper Paleozoic limestone and sandstone, and an upper, well organized sequence of pebble to cobble conglomerate and siltstone. The lowermost beds of the basal SPF member appear to be confined to the fault-bounded trough, while the upper beds of the basal member overlap the faults but thin dramatically or pinch-out entirely outside of the trough. Upper members of the Sheep Pass Formation overlap these faults with only minor changes in thickness. Preliminary field observations suggest that the faults bounding this trough have an older over younger sense of offset. Additionally, we have identified a younger fault that juxtaposes the SPF against upper Paleozoic rocks, and mapping to date suggests a younger over older sense of offset. Indications are that this younger fault is overlapped by the Stinking Spring conglomerate and the volcanic sequence of the Garrett Ranch Group. If these observations are correct, this would bracket the younger fault between the Bridgerian (ca 52-46 Ma) fossil assemblage of the upper Sheep Pass Formation, and our 40Ar/39Ar sanidine age of 35.43 ¡À 0.11 Ma of the basal Garrett Ranch Group tuff in Sheep Pass Canyon. This would also make the faults at the base of the SPF older than the Maastrichtian (ca. 70-65 Ma) fossil assemblage of the lower SPF. The implications are that the SPF may record a transition from contraction to extension within the Sevier hinterland during Paleogene time.
Keywords: Sheep Pass Formation, Sevier hinterland
FLUVIAL DEPOSITIONAL ENVIRONMENT OF A PLEISTOCENE MEGAFAUNAL LOCALITY, PANACA, NEVADA,
Corinne Y. Griffing, Mathew S. Loeschner, Lael Vetter, Brett T. McLaurin, and Steve Rowland
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Reconstructions of Neogene depositional environments in the Basin and Range usually focus exclusively on geomorphology. Here we present sedimentary and paleontological data for a site at the Wilkin Quarry, Panaca, Nevada. A horn core from the Pleistocene longhorn bison (Bison latifrons) was recovered from sediments within the quarry, constraining the age of the deposit to the Rancholabrean Land Mammal Age (~200 ka to 11.5 ka). This is the first reported B. latifrons occurrence in Nevada. Fragmented mammoth tusk material was also recovered, and is presumed to be from the Columbian mammoth ( Mammuthus columbi). Fine-grained sediments were screenwashed for invertebrate microfauna, but no material was identified. Plant macrofossils were recovered from finer grained sediments; macrofossil and palynological analyses are in progress. In an attempt to assess the paleoenvironment of this time interval, sedimentological data were collected by undergraduate students in a paleontology course.
A quarry face approximately 53 m long and 7 m high was photographed to evaluate alluvial facies architecture. Three stratigraphic profiles were measured to determine lithology, texture, sedimentary structures, and paleocurrent. The profiles indicate 3 to 5 fining-upward successions within a 7 m interval with cycle thicknesses of 1 to 2 m. The cycles consist of a basal, moderately to poorly sorted gravel; the upper portion of each cycle consists of a moderately to poorly sorted gravelly sand or silty sand. Paleocurrent data measured from cross-strata and clast imbrication indicate bimodal paleoflow directed to the northeast and southwest. We interpret these sedimentary packages to represent deposition in gravel bed rivers with episodic discharge. Overbank deposits are poorly preserved due to frequent channel migration and avulsion. The dominant flow direction indicated by paleocurrent data was to the southwest, which is consistent with modern local drainages. However, the northeast component of the bimodal paleocurrent distribution may represent localized sinuous reaches of the fluvial system. The topographic position of the quarry site suggests that these fluvial deposits form terraces representing an abandoned floodplain of the modern Meadow Valley Wash.
Keywords: Pleistocene, megafauna, paleocurrent
GENESIS OF HYPERARID SOILS OF THE ATACAMA DESERT, CHILE
Michael Howell
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Soils in the Atacama Desert, Chile are dominated by salt mineral assemblages that are found nowhere else on Earth. Salts are attributed to atmospheric, eolian, and groundwater origins. However, little is known regarding the pedogenic processes that control their distribution. Three sites in the Baquedano Nitrate District will be studied to better understand the genesis of these rare and exotic soils. The main goals of this study are to establish the salt mineral assemblages and their distribution within soil profiles, examine micromorphologic features and fabrics associated with these salt assemblages, compare research observations to other arid soils with an emphasis on developmental processes, and construct a theoretic model depicting the genesis of these hyperarid soils. This research will employ petrography, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM) as the main analytical techniques to supplement field descriptions / soil characterizations and accomplish the research goals. Preliminary XRD results reflect a concentration of Ca-sulfate salts in unconsolidated surface horizons with both Na-chloride and nitrate salts found at greater depths in the indurated zones of the soil profile. At two of the three sites there is also an almost pure Na-sulfate salt horizon at the transition from unconsolidated to massive horizons. Ultimately, the distribution of these salts in soil profiles will not only provide an explanation of hyperarid soil genesis, but also offer an analogue for salt assemblages / micromorphology linked to soil processes and landscape features observed in other arid soils; possibly paleosols preserved in the rock record and soils found on Mars.
Keywords: salt mineralogy, pedogenesis, micromorphology, hyperarid
EVIDENCE FOR DOME COLLAPSE AND COEVAL MAFIC-FELSIC VOLCANISM IN THE CENTRAL MCCULLOUGH RANGE, NEVADA
Racheal Johnsen and Eugene Smith
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The McCullough Range was not highly disrupted by faulting during Miocene extension and provides a unique view of a late-Tertiary volcanic field in the Northern Colorado River Extensional Corridor. Our work focused on the volcanic section lying beneath the tuff of Bridge Spring (15.2 Ma) and above Peach Springs Tuff (18.5 Ma) and identified three volcanic centers. A broad basalt-andesite cone, informally named the Cactus Hill volcano (CHV), nearly 2 km in diameter, contains a 200 m thick section of basalt and andesite flows and agglomerates. Basalt (46-52% SiO2) with olivine and clinopyroxene phenocrysts in a vitric matrix is interbedded with andesite (55-57% SiO2) containing hornblende, olivine and pyroxene. Two basalt dikes (each 2-3 m wide) cut the CHV. Intruding the CHV on its western flank are at least 8 dacite (61-64% SiO2) domes. Debris aprons associated with domes are interbedded with basalt and andesite. Dacite contains small plagioclase and occasional hornblende phenocrysts. Also present are xenocrysts and glomerocrysts of clinopyroxene and plagioclase. Located 2 km to the southwest is a dome complex (DC) composed of dacite (63-65% SiO2) with large (2-4 mm) plagioclase phenocrysts, hornblende, and glomerocrysts of plagioclase and clinopyroxene. Breccia representing dome growth and collapse crops out about the DC. The Eldorado Valley Volcano (EVV), a series of dacite domes and flows, 2.5 km west of the CHV, is the source of a 250 m thick breccia unit (Eldorado Valley breccia) that crops out between and is interbedded with rocks of the DC and CHV. Eldorado Valley breccia is a block and ash deposit (locally containing beds 1.5 m thick) containing bombs and clasts. Bombs are 10 cm to 6 m in size and are recognized by radial fractures and breadcrust surfaces. Clasts range in size from <1 cm to 3 m. Bombs and clasts are usually vitric aphanitic dacite (68% SiO2), but may include biotite and hornblende phenocrysts; all contain small clinopyroxene/plagioclase glomerocrysts. The thickness of the Eldorado Valley breccia represents both debris aprons from dome growth and deposits from partial collapse of domes. Coeval mafic-felsic volcanism in the CHV is demonstrated by the interbedding of EVV dacite breccia and CHV dacite dome debris with CHV andesite and basalt.
Keywords: volcanism, McCullough Range
KINEMATIC AND TIMING CONSTRAINTS ON THE SEVIER FOLD AND THRUST BELT, SOUTHERN NEVADA AND SOUTHEASTERN CALIFORNIA
Lisa Kayvon
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The Pachalka, Winters Pass, Chicago Pass, Wheeler Pass, and Gass Peak thrusts, located in the southern portion of the Sevier fold and thrust belt of southeastern California and southern Nevada, have been proposed to be correlative based on hanging-wall stratigraphy and structural style. These thrusts currently occur in separate mountain ranges and geochronologic studies have not been undertaken to demonstrate movement of a single composite thrust sheet. In Utah, the thrust sheets which similarly carry the Neoproterozoic clastic wedge, termed megathrust sheets, are Early Cretaceous in age. The sparse existing geochronologic constraints on the timing of thrusting of the megathrust sheets of southeastern California and southern Nevada suggests conflicting ages of Late Jurassic and late Early Cretaceous.
The objectives of this study are three fold: 1) to determine observable cross-cutting relationships between the thrust faults, shear zones, associated folds and intrusive units; 2) to determine the temperature of thrust related deformation by examining deformation mechanisms and to compare these estimates to thermochronogically-derived cooling histories; and 3) to determine the erosional signatures of the hanging walls to thrusts with ~ 5 km of stratigraphic throw by examining cooling histories. Methods to be used include field studies involving geologic mapping, measurement of mesoscopic kinematic indicators, and sample collection; petrographic analysis involving study of microscopic kinematic indicators and deformation mechanisms; U-Pb geochronology to date syntectonic intrusions and deformed mafic sills in footwall rocks; 40Ar/39Ar thermochronology on mica and K-feldspar; and low-temperature thermochronology involving fission track and (U-Th)/He dating of zircon and apatite to obtain hanging-wall cooling histories. Collectively, these approaches will allow the timing and kinematics of thrusting from the individual ranges to be better established and importantly, will allow the hypothesis of coeval motion on a single composite megathrust sheet to be tested.
Keywords: Sevier, geochronology, thermochronology, megathrusts
GREGARIOUS BEHAVIOR RECORDED IN THE TRACKS OF AN EARLY MIDDLE JURASSIC SYNAPSID
Jennifer Mercadante and Steve Rowland
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Approximately 100 individual tracks of the ichnogenus Brasilichnium occur on a single foreset surface of the early Middle Jurassic Aztec Sandstone in Valley of Fire State Park of Southern Nevada. These tracks were kindly brought to our attention by Steven and Evan Theodore. They occur in twelve subparallel trackways that traverse up the slip face of a dune. Individual trackways are up to 1.5 m long, and their bearings deviate from one another by a maximum of 26 degrees.
Some of the tracks show impressions of four distinct toes, while others show only three. Individual tracks range in length from 2.0 cm to 3.8 cm and in width from 2.2 cm to 4.1 cm. Length:width ratios range from 0.68 to 1.13. This range of ratios slightly exceeds ― but is in good agreement with ― the range reported by Reynolds (2006) for Brasilichnium in the Aztec Sandstone of the Mescal Range of eastern California.
Brasilichnium tracks are inferred to have been made by a synapsid quadruped ― perhaps a tritylodont therapsid (Loope, 2006). Brasilichnium is locally fairly common in the Navajo Sandstone, and it has also been documented in the correlative Aztec Sandstone of the Mescal Range of California. The Valley of Fire occurrence reported here is the first known occurrence of this ichnogenus in Nevada.
In all other occurrences of which we are aware, Brasilichnium occurs in solitary trackways. The presence of multiple, subparallel tracks suggests that the Brasilichnium trackmaker was, at times, highly gregarious. This may be the earliest evidence of gregarious behavior in a synapsid.
Keywords: Brasilichnium, gregarious, trackways, Aztec Sandstone
THE MILK RANCH CANYON SECTION, EAST-CENTRAL NEVADA: A NEOGENE COARSE CLASTIC SUCCESSION
Nickolas Miller, Peter Druschke, and Andrew Hanson
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The Milk Ranch Canyon (MRC) section is an informally-named, poorly described succession of coarse fluvial and alluvial sandstone and conglomerate located in the Egan Range of east-central Nevada. The MRC section rests unconformably on the Late Eocene to Oligocene Garrett Ranch Group volcanic sequence, and is capped by Late Miocene to Pliocene(?) volcanic flows and younger conglomerates of the Cave Valley Formation. The MRC section was measured at 275 m thick below a fault repeated interval. Conglomerate clast counts and paleocurrent data were obtained at regular intervals through the section, and 2 samples for LA-ICP-MS detrital zircon dating were collected from the basal and upper portion of the section. Clast counts show a dominance of carbonate (70%) and quartzite (20%) clasts with a minor contribution from the Garrett Ranch Group (10%). Paleocurrent data (N=86) indicate a transport direction toward the W/NW. Detrital zircon age spectra indicate a dominance of Miocene (ca. 24-16 Ma) zircons, with a major contribution from the Garrett Ranch Group (ca. 36-30 Ma). Lesser contributions from Jurassic (ca. 200 Ma) and Mesoproterozoic (ca. 1 Ga and 1.7 Ga) sources were identified. Provenance and paleocurrent data suggest derivation of the MRC sediments from unroofing of the southern Schell Creek Range (Mount Grafton vicinity) or additional source areas to the east. The MRC section is potentially correlative to widespread conglomerates within the Schell Creek Range, specifically the Miocene North Creek Formation, as well as the Miocene Horse Camp Formation of the northern Grant Range to the west. The MRC section forms part of an approximately 2 km thick Late Cretaceous to Neogene sedimentary and volcaniclastic succession in the southern Egan Range, which includes the Sheep Pass Formation and Garrett Ranch Group. Together these data may provide insight into the Paleogene to Neogene extensional and paleogeographic histories of east-central Nevada.
Keywords: ICP-MS detrital zircon, Egan Range, Garrett Ranch Group
A SEISMIC REFLECTION AND REFRACTION SURVEY OF THE ARROW CANYON RANGE AND WILDCAT WASH FAULTS
Wenming Nie and Catherine M. Snelson
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Two Quaternary-age faults, the Arrow Canyon Range fault (ACRF) and Wildcat Wash fault (WWF), are located in the Coyote Spring Valley, which is ~70 km away from Las Vegas, Nevada. The tips of these faults overlap and may be connected in the subsurface. There is a gap at the surface between the two faults, which is ~4.6 km long. Whether these faults are separate or connected is very crucial in estimating the seismic hazard. The paleoseismic history and structural development of the ACRF and WWF indicate that they may connect at depth. To test this hypothesis, a high-resolution seismic reflection (with 3 m station spacing) and refraction (with 10 m station spacing) survey will be performed to explore the subsurface geological structures of the ACRF and WWF. The survey will use a vibroseis source and a 144-channel Geode recording system. Two seismic cross-sections of up to 500-600 m depth will be produced by this survey, which can provide further valuable information to estimate the seismic hazard of the ACRF and WWF.
Keywords: faults, geologic map, seismic reflection, vibroseis
SIMULATION OF RADIONUCLIDE TRANSPORT IN THE HETEROGENEOUS UNSATURATED ZONE OF YUCCA MOUNTAIN, NEVADA
Feng Pan, Ming Ye, Zhongbo Yu, and Jianting Zhu
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
This study is to investigate the effects of heterogeneity of hydrologic parameters (i.e., matrix permeability and porosity) on unsaturated flow and radionuclide transport in the heterogeneous unsaturated zone (UZ) of Yucca Mountain, Nevada. The matrix permeability and porosity are treated as heterogeneous random variables. Measurements of the two hydrologic parameters, within each hydrogeological unit, are transformed to follow a normal distribution using seven transformations based on previous study. Assuming that correlation scales of permeability are the same as those of porosity, sample variograms of the transformed measurements of each unit are evaluated and fitted to spherical models. Two hundred conditional fields of permeability and porosity are generated using Sequential Gaussian Simulator (SGSIM). Monte Carlo simulations with the 200 realizations are conducted using TOUGH2 code. Mean, variances, 5% and 95% percentiles of saturation, capillary pressure, and fluxes are estimated, and the uncertainty of unsaturated flow caused by the heterogeneity of hydrolgic parameters is assessed. The effect of heterogeneity in hydrologic parameters on the reactive and conservative tracer transport is investigated in a similar manner. Uncertainty analysis indicates that predictive uncertainty caused by heterogeneity of the parameters is more significant than that of homogeneous random parameters. The results can provide important information to facilitate science-based decision-making and risk analysis for the Yucca Mountain Project.
Keywords: radionuclide transport, heterogeneity, SGSIM
Comparative analysis of surficial geological maps and nrcs soil surveys for flood hazard assessments on alluvial fans: a case study in ivanpah valley, nevada
Colin R. Robins, Michael S. Howell, Janice Morton, Amanda J. Williams, Maureen Yonovitz, Brenda Buck, and D. Merkler
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Flood hazard maps of alluvial fans in desert environments are created with the hopes of predicting debris and stream flow paths and revealing areas of especially high erosion or flood risk. Consequently, accurate flood hazard maps are essential to prevent loss of life and property during large-magnitude storms (i.e., 10-yr and 100-yr events), and, by preventing development on hazardous sites, they also minimize the need for emergency relief funds following floods.
At present, flood hazard interpretations for a given study area can differ widely depending on which soil and/or surficial geologic data are used, and how those data are incorporated into flood maps or computer models. Similarly, when different hazard interpretations exist for the same study area, it is often unclear to map users which interpretation is more accurate. Moreover, alluvial fans in arid/semi-arid climates do not behave like perennial rivers, thus models created for more humid systems are inaccurate. In recent years, researchers (e.g., Pelletier et al., 2005; House, 2005) have improved FEMA flood insurance rate maps via better integration of detailed soil and surficial geologic data, and via high-resolution modeling of stream flow on alluvial fans. Despite some integration of soils data with flood hazard criteria, NRCS soil survey map units have never been compared to FEMA or surficial geologic flood hazard units.
Broad objectives of this project are to: (1) identify differences between the NRCS soil survey and House et al.(2006) surficial geology map of the Ivanpah Valley Area, Clark County, Nevada; (2) discuss the uses and limitations of established soil and geomorphological mapping methods for flood hazard assessment; and (3) explain what those differences and limitations mean for map users. A specific goal of this study is to determine percent correlation between soil map units and geomorphological flood-hazard units using GIS analysis. This goal may reconcile differences of flood hazard interpretation for map users, and may lead to improved, applied soil-geomorphologic mapping methods in the future.
Ivanpah Valley, in southwest Nevada, is ideally suited for this study not only because it is an active landscape with classic, arid landform features and a dynamic geomorphological history, but also because it is the site for a proposed, new airport to serve Las Vegas, NV. Recently published flood hazard assessments (House et al., 2006a&b) and soil surveys (Soil Survey Staff, 2006) from Ivanpah Valley serve as illustrative starting points for comparison of soil and surficial geologic mapping.
Keywords: flood hazard assessment, soil geomorphology, mapping, GI
exhuming the tule springs research project: new perspectives and technique
Aubrey M. Shirk
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Excavation of Rancholabrean mammals from the Tule Springs locality was begun in 1933, with sporadic work continuing to 1963. However, extraction of the macrofauna was virtually suspended until recent times. The focus of earlier research was (1) to provide support for the cause of extinction at the end of the Pleistocene, which has been mainly attributed to global climate change, and (2) implications for the presence of early humans and evidence of hunting practices. At the end of the Pleistocene, many species included within the proboscidea (mammoths, mastodons), xenarthra (sloths, glyptodonts), carnivora (wolves, saber-tooth cats), perissodactyla (horses, rhinos), and artiodactyla (camels, bison) were effectively terminated. A shortage of evidence for human influence subsequently rendered the extinction a possible combination of the two processes. The purpose of this project is to re-examine previously extracted materials as well as to conduct new excavations in proximity to the Tule Springs locality contained within the Las Vegas Formation. Both the reviewed and the newly collected specimens will undergo important and essentially unperformed analyses (isotopic analysis, paleoecology, biogeography). Results will provide insight on a broad scale which will be used to form an interpretation of the ecology and biogeography of these organisms, in addition to potentially substantiating the cause for extinction.
Keywords: Pleistocene, mammals, Las Vegas Formation
ANALYSIS OF lATE pALEOZOIC CONTRACTIONAL DEFORMATION AND CENOZOIC EXTENSION IN GREEN MONSTER CANYON (NORTHERN MONITOR RANGE). NYE COUNTY, NEVADA
Garrett Speeter and Wanda Taylor
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
speeter@unlv.nevada.edu
Recent work suggests that Paleozoic shortening should be overprinted by Cenozoic extension in central Nevada. Shortening may be associated with the Antler or Sonoma Orogenies or a recently proposed Pennsylvanian shortening event. To test this hypothesis, field mapping was conducted in Green Monster Canyon, Monitor Range (central Nevada). The geologic record in this area provides evidence for at least three deformation events. Early east-trending shortening is interpreted to be caused by one of the contractional orogenies that have been overprinted by later Cenozoic extension. Cross cutting relationships and near perpendicular fault strikes are evidence for separate deformation events. Ordovician units show folding along two different axes which provides evidence for two shortening events that occurred after the deposition of Ordovician strata. The two sets of folds in Ordovician strata are interpreted to have been caused by two of the three contractional orogenies.
Keywords: Paleozoic, deformation, Cenozoic, contraction
Mapping of biological soil crusts in hidden valley national wilderness area, nevada
Amanda J. Williams, Brenda Buck, Henry Sun, and Deborah Soukup
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Though easily overlooked, biological soil crusts are critical features in many desert ecosystems, covering up to 70 percent of the landscape (Belnap 1994). These crusts are complex matrices of soil particles intermingled with algae, cyanobacteria, lichen, mosses, microfungi, and bacteria (Friedmann and Galun 1974). Microbial filaments grow in and around soil particles, fusing the surface into a desert skin that resists sediment loss (Belnap 1995). In addition, biological soil crusts function to contribute soil organic matter and nutrients, manage soil moisture, and decrease the establishment of annual weed species (Eldridge and Greene 1994). These crust are easily destroyed by off-road vehicular use, foot traffic, grazing, and horseback riding (Belnap 1995), making them key elements to protect in recreational areas.
Biological soil crusts come in a variety of forms, in terms of both species composition and surface morphology. Early succession crusts (smooth crusts) are primarily composed of cyanobacteria (Belnap et al. 2003). Later succession crusts (rougher crusts) are colonized by moss, lichen, cyanobacteria, and algal communities. While the exact age of these crusts is unknown, some estimate that the succession of these crusts may take 10s to 100s of years (Belnap et al). Crust distribution and community structure are controlled by many factors including elevation, precipitation, topography, soil texture, soil chemistry, soil depth, vascular plant competition, and disturbance (Belnap et al. 2001). However, the influence of geomorphology and surface age on crust distribution has not yet been explored.
The purpose of this study is to create a digital map illustrating the distribution of biological soil crust communities and macrovegetation communities within the Hidden Valley National Wilderness Area, Nevada, as they relate to various landscape and environmental factors, disturbance, and recovery. We plan to identify the various crust types (in terms of community structure and morphology) and relate those to geomorphology, macrovegetation structure, soil characteristics, soil water distribution, topographic influences, and disturbance. We will predict recovery rates of disturbed crusts by combining soil crust turnover rates (estimated by carbon-14 dating, a technique new to crust research), weather data, soil moisture data, and soil texture.
This area has a varied history of management and disturbance (grazing, 4X4 traffic, hiking), making it the ideal site for a study concerning disturbance. The digital mapping and the data we collect will allow us to make estimates on crust recovery, and it will assist the Bureau of Land Management in making critical land management decisions.
Keywords: biological soil crusts, mapping, geomorphology, disturbance
PETROGENESIS OF EXTRACALDERA RHYOLITES, YELLOWSTONE VOLCANIC FIELD, WYOMING: A 4TH CALDERA CYCLE?
Kathleen M. Wooton and Terry L. Spell
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Yellowstone Volcanic Field, Wyoming, is one of three large-scale caldera-forming volcanic fields in the western U.S. and has been the site of three caldera collapse events over the last ~2 Ma, erupting up to 2,500 km3 of material during a single event. Extracaldera rhyolites in the Norris-Mammoth Corridor of the Yellowstone Volcanic Field appear to be unrelated to intracaldera volcanism, resulting instead from a new crustal magma source derived from the northeastward propagation of the Yellowstone ¡°melting anomaly.¡± It was originally suggested that extracaldera rhyolites formed as small, independent crustal melt magma batches associated with basaltic magmatism north of the Yellowstone caldera. Recent work, however, indicates the extracaldera rhyolites erupted from a single, large-scale magma body. The presence of a young, distinct volcanic system north of the last Yellowstone caldera suggests that the Yellowstone Volcanic Field may be in the initial stages of a fourth caldera cycle.
The youngest extracaldera rhyolite unit, the Roaring Mountain Member, is chemically distinct from the previous extracaldera lavas, reverting to more primitive chemistries. The presence of recent 80 ka (K-Ar age) mingled lavas within the Roaring Mountain rhyolites suggests mafic magmatism persisted after the latest basalt eruptions at 209 ka. This indicates recent continued mafic magma intrusion with the potential to generate large silicic magma bodies beneath the Yellowstone Volcanic Field.
Keywords: Yellowstone, rhyolite, Roaring Mountain Member
SCALING EFFECTS ON THE SPATIAL VARIABLE SOIL MOISTURE IN ARID REGIONS
Jun Yin, Michael Young, and Zhongbo Yu
Desert Research Institute, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
Spatially variable soil moisture in arid regions plays a significant role in the sustainable development of desert ecosystems. To address the relationship between the soil moisture and the climate, the soil physical properties as well as the plants, a hydrologic model is a useful tool. However, in a distributed hydrologic model, misinterpretation of the field heterogeneity often happens when the research watershed is relatively large. Field measurements (e.g., heterogeneity of the saturated hydraulic conductivities) in many computational cells are then set aside for future study due to the restrictions of time and project budget. One way to solve this problem is to introduce the ¡°effective¡± value, which is a parameter that equivalently represents the heterogeneity in each grid cell. In the proposed study, we hypothesized that simulations of spatially distributed soil moisture (and then the simulations of the surface runoff) are scale dependent and these scale effects can be predicted by applying some certain statistical method. Therefore, the purpose of this study is firstly to develop a statistical method to ¡°upscale¡± the in-situ soil hydraulic properties to grid cells with different sizes, and secondly to derive a deterministic scaling function to build the relationship between the scale and the model simulations.
Keywords: scaling, soil, hydrological model
Source of ore fluids and conditions of mineralization at bullard pass, yavapai county, arizona
Greg Zellner and Adam Simon
Department of Geoscience, University of Nevada Las Vegas, Las Vegas, NV 89154-4010
The Harcuvar Range in central Arizona hosts mineralization that has been of economic interest for more than 100 years. Early miners exploited rich gold, silver, and copper veins throughout the range until the mid 1940¡¯s. To date, the Bullard mining district has produced 610,000 pounds of copper, 3,600 ounces of gold, and 6,000 ounces of silver according to historic mine records. Despite the long and rich history of the Harcuvar deposits, little is known about the source, timing, and mechanism of mineralization within the footwall of the Bullard detachment fault. Previous interpretations of Harcuvar mineralization suggest that basinal brines from tertiary extension are the primary source of base and precious metals (Davis and others, 1986). Although, spatial relationships of igneous and metamorphic rocks to mineralization suggest they may be a plausible source of mineralizing fluids. This study will focus on detailed field mapping along with geochemical, geochronological, fluid inclusion, and cathodluminescence analysis to constrain the conditions, paragenesis sequence, and source of ore forming fluids. By establishing a correlation between volcanic or metamorphic rocks and mineralization, a model for emplacement may be established that will aid in further exploration of the surrounding district.
Keywords: economic, mineralization
| Lilly Fong Geoscience (LFG) 104B Phone: 702-895-3262 Fax: 702-895-4064 Email: geodept@unlv.edu |
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