Graduation date: 1999

Graduation date: 1994

The interaction between climate, environments, and mammalian faunas during the late Pleistocene-Holocene has been studied intently over the last several decades. Cave deposits play an important role in our understanding of these complex interactions, but they are especially significant for our understanding of the faunal history of the Great Basin. In order to develop a deeper time perspective on mammalian faunal change, I began a project that integrated several elements necessary for identifying and interpreting biotic change in the Great Basin of the western United States. These elements included development of a framework for understanding the importance of cave deposits for the paleontological record, collection of a mammalian fauna that pre-dates the terminal Pleistocene, identification of that fauna in the midst of shifting taxonomic paradigms, and evaluation of the fauna in the context of previous regional biogeographic models. I utilized data from the FAUNMAP database to evaluate the significance of the contribution that cave deposits make to the Pleistocene mammal record. Caves do provide unique faunal data in addition to contributing a high percentage of the individual species records for late Pleistocene mammals. Fieldwork was conducted at Cathedral Cave, NV, in order to assess a fauna that was thought to predate the late Pleistocene-Holocene transition. In excess of 30,000 identifiable fossils were recovered in an excavation area that was roughly 1.5 x 2 x 0.7 m. Prior to fieldwork in 2003, age estimates for the fauna were between 750 ka to 850 ka. New chronologic analyses suggest a more recent age (≤146.02±2.584 ka to 151.2±4.4 ka) that extends the known chronologic distributions of several taxa and alters previously established biochronologic frameworks for the Pleistocene. This work also calls into question previous age assignments for portions of Smith Creek Cave. Individual faunal identifications were made using a conservative data-reliant approach in order to minimize geographic assumptions and render an independent data set useful for broad biogeographic analyses. Although the faunal data presented here do not explicitly support or refute regional biogeographic models, they do indicate that patterns of faunal change can be found even when species-level identification are not achieved.

The pollen, plant macrofossil and aquatic fossil stratigraphies from a transect of sites in the Sierra Nevada, California, were examined to deduce paleoenvironmental change since the late-Wisconsinan. Fossil pollen samples were compared to modern pollen samples from both sides of the Sierra Nevada crest. Modern samples corresponded largely to modern vegetation units, validating the use of pollen for this purpose in mountainous environments. Vegetation change during the Holocene was largely contemporaneous on both sides of the crest at elevations where lake cores and meadow sections were analysed. Deglaciation occurred by ca. 12,500 yr BP at a site on the east side, and by ca. 11,000 yr BP at a west side site. Prior to ca. 10,000 yr BP, few trees were found around the higher elevation sites. An open forest with trees characteristic of the modern Sierra Montane and Upper Montane forest grew around the mid- to high elevation sites by the early Holocene. Montane chaparral species, such as bush chinquapin, mountain mahogany and probably huckleberry oak, with sagebrush, were most abundant then. Along with lowered lake levels or absence of perennially standing water, and greater affinities to modern pollen samples from the more arid east side, these observations suggest drier conditions than today. However, by ca. 6500-5500 yr BP, effective precipitation increased, as shown by increases in subalpine conifers (mountain hemlock and red fir) and higher lake levels, and less affinities to modern samples from the east side. Modern vegetation developed at most sites within the last 2-3 millenia. Specific changes in the vegetation at this time included a reduction in upper elevational limits of mountain hemlock and red fir, with possible downslope retreat of whitebark pine, indicating greater cooling and/or wetter conditions. This is consistent with the record of wet meadow genesis as well as tree-ring and Neoglacial chronologies.

Gold mineralization in the Velvet District occurs in an eastward dipping sequence of Miocene tuffs, flows, and tuffaceous sediments on the west flank of the Trinity Range in Pershing County, Nevada. Numerous north-northeast trending normal faults extend through the district. These faults served as conduits for ascending hydrothermal fluids which deposited gold and silver along poorly defined zones of brecciation, argillic alteration, and quartz veining. Concentration of gold does not exceed a few parts per million and is highest in zones of intersecting fractures. The hydrothermal solutions which deposited the gold were the near-surface expression of a larger geothermal system. Meteoric water leached gold, silver, arsenic, antimony, and other metals from the surrounding rock as it percolated downward towards a deep heat source. The hot fluids escaped upward along fracture zones and precipitated precious metals in veins near the surface. Fluid inclusion studies indicate that the quartz veins were deposited in the temperature range 218-264°C from fluids which had salinities equivalent to 0.2-0.8 weight percent NaCl. δ¹⁸0 of quartz veins varies from -2.5 to +6.7 %, and the low values appear to define a zone of concentrated fluid flow and potential subsurface mineralization in the southeast part of the district. The lowest value, -2.5 %, indicates that the ore fluid must have been Tertiary meteoric water with δ¹⁸0 equal to -13 %. Reaction of hydrothermal fluids with wall rock produced an alteration assemblage of illite-kaolinite-quartz which underlies most of the shafts, adits, and prospect pits in the district. The illite-kaolinite-quartz assemblage is laterally gradational into a kaolinite (or dickite)-smectite-alunite-quartz assemblage which is indicative of lower temperatures. Pyrite and other sulfides are rare, but limonite and jarosite are widespread in surface outcrops. Alteration of tuffs released abundant silica which precipitated as quartz veins and discharged in hot springs at the bottom of lakes, where thick deposits of diatomaceous earth accumulated. / text

No description available.

Thesis (M.A.)--University of Nevada, Reno, 2005. / "August 2005." Online version available on the World Wide Web.

The Weepah Hills Area (Nevada) exposes exhumed metamorphic and plutonic rocks and upper-plate (supradetachment) volcano-sedimentary rocks that have experienced a complex, multi-stage deformational and depositional history. The Weepah Hills metamorphic core complex (WHMCC) is located in a region of the western Cordillera that was affected by both Miocene Basin-and-Range style E-W extension and Mio-Pliocene Walker Lane transcurrent shearing. Mio-Pliocene transcurrent deformation is transferred across a ~175 km releasing bend, known as the Mina Deflection, that kinematically links dextral strike-slip faults of the Death Valley-Fish Lake Valley with the central Walker Lane Belt. Progressive Mio-Pliocene transtension is characterized by core complex detachment faulting and younger high-angle normal faults. Timing of detachment faulting is constrained by both (U-Th)/He thermochronometry of footwall rocks and detailed chronostratigraphy of upper-plate strata to between 9-6 Ma. This age is supported by deformation recorded in the upper-plate strata that is attributed to progressive folding of the detachment associated with corrugation development. Earlier Miocene Basin-and-Range style extension is characterized by N-S trending high-angle normal faults and half-grabens that are strongly overprinted by Mio-Pliocene structures. (U-Th)/He zircon cooling ages from the detachment footwall range from ~12-20 Ma and are attributed to exhumation and unroofing related to E-W Basin-and-Range extension. New detailed sedimentological and geochronologic data show that, in contrast to previous research, the WHMCC upper-plate strata do not form a single supradetachment package, but rather three temporally distinct Miocene stratigraphic packages bounded by angular unconformities. The stratigraphic, structural, and exhumational record preserved in the WHMCC elucidates the timing of deformation and sedimentary basin evolution related to both Basin-and-Range E-W extension and Walker Lane related NW-directed transtension. / text

No description available.

No description available.