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2004

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Articles 391 - 420 of 432

Full-Text Articles in Earth Sciences

Application Of Well Log Tomography To The Dundee And Rogers City Limestones, Michigan Basin, Usa, Mellisa A. Le M. Jan 2004

Application Of Well Log Tomography To The Dundee And Rogers City Limestones, Michigan Basin, Usa, Mellisa A. Le M.

Dissertations, Master's Theses and Master's Reports - Open

The Michigan Basin is located in the upper Midwest region of the United States and is centered geographically over the Lower Peninsula of Michigan. It is filled primarily with Paleozoic carbonates and clastics, overlying Precambrian basement rocks and covered by Pleistocene glacial drift. In Michigan, more than 46,000 wells have been drilled in the basin, many producing significant quantities of oil and gas since the 1920s in addition to providing a wealth of data for subsurface visualization.

Well log tomography, formerly log-curve amplitude slicing, is a visualization method recently developed at Michigan Technological University to correlate subsurface data by utilizing …


Paranthropus Paleobiology, Paul J. Constantino, Bernard A. Wood Jan 2004

Paranthropus Paleobiology, Paul J. Constantino, Bernard A. Wood

Biological Sciences Faculty Research

No abstract provided.


Activators Of Luminescence In Speleothems As Source Of Major Mistakes In Interpretation Of Luminescent Paleoclimatic Records, Y. Y. Shopov Jan 2004

Activators Of Luminescence In Speleothems As Source Of Major Mistakes In Interpretation Of Luminescent Paleoclimatic Records, Y. Y. Shopov

International Journal of Speleology

This work summarizes the main results of the operation of the International Program “Luminescence of Cave Minerals” of the commission on Physical Chemistry and Hydrogeology of Karst of UIS of UNESCO in the field of activators of speleothem luminescence. It discusses Activators of Luminescence in Speleothems as a source of major mistakes in the interpretation of luminescent paleoclimatic records. It demonstrates the existence of 6 types of luminescence of speleothems and cave minerals in dependence of the type of the luminescence center and its incorporation in the mineral. 24 different activators of photoluminescence of speleothem calcite and 11 of aragonite …


Trace Elements In Speleothems. A Short Review Of The State Of The Art, Sophie Verheyden Jan 2004

Trace Elements In Speleothems. A Short Review Of The State Of The Art, Sophie Verheyden

International Journal of Speleology

A state of the art of the research on trace elements of speleothems is given. First studies focussed on problems such as the colour of speleothems and the aragonite problem. Insitu studies and studies oriented towards a better understanding of vadose hydrology brought new insights in the controls on trace elemental composition of speleothems. Recent studies deal with microscale analyses and annual and intra-annual chemistry changes. Further in-situ studies should be performed to further differentiate influences, such as climate, soil/weathering and local hydrology in order to better constrain possible transfer functions between the surface and a speleothem.


The Distribution Of Radon Concentration In Caves, Arrigo A. Cigna Jan 2004

The Distribution Of Radon Concentration In Caves, Arrigo A. Cigna

International Journal of Speleology

Radon concentration in caves is known to vary within an extremely wide range. Here the distribution of the average values of radon concentration is examined and a power law describing is identified, i.e. radon concentration has a fractal dimension D=1.26. This fact means that concentrations are not grouped around a mean value, a characteristic common to many other phenomena.


Sources And Cycling Of Carbonyl Sulfide In The Sargasso Sea, Gregory A. Cutter, Lynda S. Cutter, Katherine C. Filippino Jan 2004

Sources And Cycling Of Carbonyl Sulfide In The Sargasso Sea, Gregory A. Cutter, Lynda S. Cutter, Katherine C. Filippino

OES Faculty Publications

The cycling of the radiatively important gas carbonyl sulfide (OCS) was studied in surface waters of the Sargasso Sea. In August 1999, surface OCS concentrations averaged 8.6 pmol L-1, showed minor diel variations, and varied little with depth. An OCS precursor, total dissolved organic sulfur (DOS), was lowest at the surface (40 nmol L-1) and increased with depth. The photoproduction rate of OCS from in situ incubations averaged 9.6 pmol L-1 h-1, whereas dark production was 7.0 pmol L-1 h-1. Apparent quantum yields were 10-5-10-7 from 313-436 …


Analytical Intercomparison Between Flow Injection-Chemiluminescence And Flow Injection-Spectrophotometry For The Determination Of Picomolar Concentrations Of Iron In Seawater, Andrew R. Bowie, Peter N. Sedwick, Paul J. Worsfold Jan 2004

Analytical Intercomparison Between Flow Injection-Chemiluminescence And Flow Injection-Spectrophotometry For The Determination Of Picomolar Concentrations Of Iron In Seawater, Andrew R. Bowie, Peter N. Sedwick, Paul J. Worsfold

OES Faculty Publications

A lab- and ship-based analytical intercomparison of two flow injection methods for the determination of iron in seawater was conducted, using three different sets of seawater samples collected from the Southern Ocean and South Atlantic. In one exercise, iron was determined in three different size-fractions (< 0.03 &μm, < 0.4 μm, and unfiltered) in an effort to better characterize the operational nature of each analytical technique with respect to filter size. Measured Fe concentrations were in the range 0.19 to 1.19 nM using flow injection with luminol chemiluminescence detection (FI-CL), and 0.07 to 1.54 nM using flow injection with catalytic spectrophotometric detection with N, N-dimethyl-p-phenylenediamine dihydrochloride (FI-DPD). The arithmetic mean for the FI-CL method was higher (by 0.09 nM) than the FI-DPD method for dissolved (< 0.4 μm) Fe, a difference that is comparable to the analytical blanks, which were as high as 0.13 nM ( CL) and 0.09 nM (DPD). There was generally good agreement between the FI-CL determinations for the < 0.03 μm size fraction and the FI-DPD determinations for the < 0.4 μm size fraction in freshly collected samples. Differences in total-dissolvable ( unfiltered) Fe concentrations determined by the two FI methods were more variable, reflecting the added complexity associated with the analysis of partially digested particulate material in these samples. Overall, however, the FI-CL determinations were significantly (P = 0.05) lower than the FI-DPD determinations for the unfiltered samples. Our results suggest that the observed, systematic inter-method differences reflect measurement of different physicochemical fractions of Fe present in seawater, such that colloidal and/or organic iron species are better determined by the FI-CL method than the FI-DPD method. This idea is supported by our observation that inter-method differences were largest for freshly collected acidified seawater, which suggests extended storage (>6 months) of acidified samples as a possible protocol for the determination of dissolved iron in seawater.


A Holocene Record Of Changing Arctic Ocean Ice Drift Analogous To The Effects Of The Arctic Oscillation, Dennis A. Darby, Jens F. Bischof Jan 2004

A Holocene Record Of Changing Arctic Ocean Ice Drift Analogous To The Effects Of The Arctic Oscillation, Dennis A. Darby, Jens F. Bischof

OES Faculty Publications

The Arctic Oscillation (AO) controls the configuration of the Transpolar Drift (TPD). If thicker ice from the Beaufort Gyre were exported, the volume of fresh water/sea ice in the Nordic seas would significantly increase, decreasing the formation of North Atlantic deep water. This would cool large parts of the Northern Hemisphere and affect global climate. Therefore, in order to understand how the global climate system functions, it is imperative to know how the TPD changed over the last millennium or more. The provenance of grains in a sediment core located near the confluence of the TPD and the Beaufort Gyre …


Black Carbon In Estuarine And Coastal Ocean Dissolved Organic Matter, Antonio Mannino, H. Rodger Harvey Jan 2004

Black Carbon In Estuarine And Coastal Ocean Dissolved Organic Matter, Antonio Mannino, H. Rodger Harvey

OES Faculty Publications

We measured black carbon (BC) in ultrafiltered, high-molecular weight dissolved organic matter (UDOM) in surface waters of Delaware Bay, Chesapeake Bay, and the adjacent Atlantic Ocean (U.S.A.) to investigate the importance of riverine and estuarine dissolved organic matter (DOM) as a source of BC to the ocean. BC was 5-72% of UDOM-C (27 ± 17%), which corresponds to 8.9 ± 6.5% of dissolved organic carbon (DOC), with higher values in the heavily urbanized midbay region of the Delaware Estuary and lower yields in the river and coastal ocean. The spatial and seasonal distributions of BC along the salinity gradient of …


In-Situ Apparent Conductivity Measurements And Microbial Population Distribution At A Hydrocarbon-Contaminated Site, Estella A. Atekwana, D. Dale Werkema, Joseph W. Duris, Silvia Rossbach, Eliot A. Atekwana, William A. Sauck, Daniel P. Cassidy, Jay Means, Franklyn D. Legall Jan 2004

In-Situ Apparent Conductivity Measurements And Microbial Population Distribution At A Hydrocarbon-Contaminated Site, Estella A. Atekwana, D. Dale Werkema, Joseph W. Duris, Silvia Rossbach, Eliot A. Atekwana, William A. Sauck, Daniel P. Cassidy, Jay Means, Franklyn D. Legall

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

We investigated the bulk electrical conductivity and microbial population distribution in sediments at a site contaminated with light nonaqueous-phase liquid (LNAPL). The bulk conductivity was measured using in-situ vertical resistivity probes; the most probable number method was used to characterize the spatial distribution of aerobic heterotrophic and oil-degrading microbial populations. The purpose of this study was to assess if high conductivity observed at aged LNAPL-impacted sites may be related to microbial degradation of LNAPL. The results show higher bulk conductivity coincident with LNAPL-impacted zones, in contrast to geoelectrical models that predict lower conductivity in such zones. The highest bulk conductivity …


Modeling And Measuring The Dispersion Of Odors From Hog Confinements, François Béra Jan 2004

Modeling And Measuring The Dispersion Of Odors From Hog Confinements, François Béra

Dissertations and Theses @ UNI

A comparison was made between predicted and measured odor concentration downwind of two hog finishing confinements. Two Gaussian dispersion models, STINK.BAK and AERMOD, were used. The experimental cases examined odor emanating from a mechanically-ventilated facility and a curtain-sided facility during summer 2003. A field olfactometer was used to measure odor concentration. The odor concentrations served as input to STINK.BAK, which then estimated the odor emission rate from the confinement. AERMOD used this emission rate and other meteorological data to predict the peak concentration of odor around the confinement over the sampling hour. The calculated odor emission rates are slightly higher …


A Boundary Element Method For Thermo-Poroelasticity With Applications In Rock Mechanics, Qiang Zhang Jan 2004

A Boundary Element Method For Thermo-Poroelasticity With Applications In Rock Mechanics, Qiang Zhang

Theses and Dissertations

Coupled thermal and poromechanical processes play an important role in many geomechanics problems, such as borehole stability analysis and studies of initiation and propagation of hydraulic fractures. Thermal effects, as well as hydraulic effects, can greatly change the stresses and pore pressure fields around an underground opening. This is due to the fact that thermal loading induces a volumetric deformation because of thermal expansion/contraction of both the pore fluid and the rock solid. Volumetric expansion can result in significant pressurization of the pore fluid. In order to take into account the influence of temperature gradients on pore pressure and stresses, …


A Comparison Of Land Use And Nonpoint Source Pollution In The Cedar River Tributaries In Iowa, Chad Levi Fields Jan 2004

A Comparison Of Land Use And Nonpoint Source Pollution In The Cedar River Tributaries In Iowa, Chad Levi Fields

Dissertations and Theses @ UNI

A comparative water analysis on major Cedar River tributaries was conducted to determine nutrient and sediment concentration, nutrient loads, and watershed land use during the spring and summer of 2002. The Cedar River watershed is located on a primarily agricultural land, and has a drainage area of20,242 km2. The watershed extends from southern Minnesota to southeastern Iowa, where it joins the Iowa River which subsequently flows into the Mississippi River. Past studies have concluded that the Cedar River contributes much of the nutrients entering the Mississippi River and the Gulf of Mexico. These nutrients then contribute to the zone of …


Influence Of Solar Luminosity Over Geomagnetic And Climatic Cycles As Derived From Speleothems, Y. Shopov, D. Stoykova, L. Tsankov, M. Sanabria, D. Georgieva, D. Ford, L. Georgiev Jan 2004

Influence Of Solar Luminosity Over Geomagnetic And Climatic Cycles As Derived From Speleothems, Y. Shopov, D. Stoykova, L. Tsankov, M. Sanabria, D. Georgieva, D. Ford, L. Georgiev

International Journal of Speleology

We observed cycles presented in a luminescent solar insolation proxy record from a speleothem from Jewel Cave, South Dakota, US. We found cycles of orbital precession with periods of 23 and 19 ka and of obliquity of 41 ka and many others from non-orbital origin in this sample. We determined the Solar origin of the cycles with durations of 11500, 4400, 3950, 2770, 2500, 2090, 1960, 1670, 1460, 1280, 1195, 1145, 1034, 935, 835, 750 and 610 years. It was done by their detection both in proxy records of speleothem luminescence, Δ14C and the intensity of the geomagnetic …


Surface Cover Infiltration Index: A Suggested Method To Assess Infiltration Capacity For Intrinsic Vulnerability In Karstic Areas In Absence Of Quantitative Data, Levent Tezcan, Mehmet Ekmekci Jan 2004

Surface Cover Infiltration Index: A Suggested Method To Assess Infiltration Capacity For Intrinsic Vulnerability In Karstic Areas In Absence Of Quantitative Data, Levent Tezcan, Mehmet Ekmekci

International Journal of Speleology

Karst is a hydrogeological environment of importance not only for its water resources potential but also for its scenic and economic potential, thereby increasing the intensity of human impact. The uniqueness of karst in this regard stems from its high sensitivity and vulnerability to imposed pressures and its distinctive response to these pressures. Therefore, a clear definition and formulation of the concept of ‘intrinsic vulnerability’ is essential for the design of vulnerability and/or management criteria of the karstic system as a resource. In this regard, the recharge rate, the amount of water passing through the unsaturated zone into the aquifer, …


Evolution Of Golpazari-Huyuk Karst System (Bilecik-Turkey): Indications Of Morpho-Tectonic Controls, Mehmet Ekmekci, Lütfü Nazik Jan 2004

Evolution Of Golpazari-Huyuk Karst System (Bilecik-Turkey): Indications Of Morpho-Tectonic Controls, Mehmet Ekmekci, Lütfü Nazik

International Journal of Speleology

The Golpazari-Huyuk karst system is located in the Central Sakarya Basin whose geomorphologic evolution is mainly controlled by the Post-Miocene epirogenic continental rise. Drastic change in the drainage pattern and dissection of the carbonate platform were the major consequences of this tectonic movement. Rapid incision of the Sakarya river changed the position of the erosion base which consequently distorted the direction of surface and subsurface flow. The Golpazari and Huyuk plains are two topographically distinct, flat bottomed geomorphic features separated by a carbonate rock relief. The difference in elevation between these 10 km distant plains is 350 m. Morphological, geological …


Dissaggregation Modelling Of Spring Discharges, Elena Kirilova Bojilova Jan 2004

Dissaggregation Modelling Of Spring Discharges, Elena Kirilova Bojilova

International Journal of Speleology

Disaggregation models are basically divided into three main groups: temporal, spatial and temporal-spatial. The focus of this paper is the application of temporal disaggregation models to disaggregate the seasonal flow in some large time intervals to sub-seasonal flows in some shorter time intervals. Two basic models are applied: the original model of Mejia and Rousselle and the corrected extended Lin model one-stage disaggregation. The flow totals from some karstic springs are used. Data for five springs in different areas of Bulgaria for the aims of the study are executed. The synthetic data generation for the chosen spring stations for a …


Comparative Estimate Of Resistance To Drought For Selected Karstic Aquifers In Bulgaria, Tatiana Orehova Jan 2004

Comparative Estimate Of Resistance To Drought For Selected Karstic Aquifers In Bulgaria, Tatiana Orehova

International Journal of Speleology

Effective management of water resources requires adequate knowledge of groundwater system including the influence of climate variability and climate change. The drought of 1982-1994 in Bulgaria has led to important decrease of springflow and lowering of water levels. Therefore, groundwater demonstrated its vulnerability to drought. The purpose of this paper is to determine relative resistance of selected aquifers in Bulgaria to a prolonged decrease of recharge to groundwater. The drought resistance indicator has been defined for some karstic aquifers based on the method proposed in report of BRGM. The data from National Hydrogeological Network located in the National Institute of …


Paleocollapse Structures As Geological Record For Reconstruction Of Past Karst Processes During The Upper Miocene Of Mallorca Island, P. A. Robledo Ardila, J. J. Durán, L. Pomar Jan 2004

Paleocollapse Structures As Geological Record For Reconstruction Of Past Karst Processes During The Upper Miocene Of Mallorca Island, P. A. Robledo Ardila, J. J. Durán, L. Pomar

International Journal of Speleology

Paleocollapse structures and collapse breccias are one of the major features for paleokarst analysis and paleoclimate record. These are affecting the Llucmajor and Santanyí carbonate platforms. These platforms, of southern and eastern Mallorca respectively, are a good example of progradation reef platform in the western Mediterranean. The Santanyí platform is constituted of two sedimentary units, both affected by paleocollapse structures: (1) The Reef Complex attributed to the upper Tortonian-lower Messinian; (2) Santanyí Limestone attributed to the Messinian. There are abundant paleocollapse outcropping in the Reef Complex and Santanyí Limestone units. These structures have been produced by roof collapse of caverns …


The Role Of The Environmental Archaeologist In The Study And Reconstruction Of Cave Palaeoclimate, Maria Gkioni Jan 2004

The Role Of The Environmental Archaeologist In The Study And Reconstruction Of Cave Palaeoclimate, Maria Gkioni

International Journal of Speleology

Man and environment are engaged in a continuous battle to impose themselves on one another. The results are found in environmental modifications or climatic oscillations and, as far as man is concerned, in the different character of cultural remains. Man responds to environmental changes by migrating or evolving technological innovations, both of which leave important remains that the archaeologist is called on to recognise and interpret during and after an excavation. They both also reflect the sociocultural responses to climatic stress. This paper refers to a specific case study, caves, which housed man and his activities from the very early …


Hydrologic Variations Within Created And Natural Wetlands In Southeastern Virginia, Aaron Dyer Despres Jan 2004

Hydrologic Variations Within Created And Natural Wetlands In Southeastern Virginia, Aaron Dyer Despres

OES Theses and Dissertations

The hydrology of wetlands, particularly how wetland soils collect, store, and redistribute water strongly affects how wetland systems function. In created wetlands, construction processes and materials influence the hydrology and consequently, the potential for successful reestablishment of target vegetation communities. During 2002–2004, the Virginia Department of Transportation constructed large mitigation wetlands on two different Quaternary aged surfaces with very similar hydrogeomorphic conditions. The Sandy Bottom Nature Park site (SBNP) located in Hampton, VA and rests on the sandy loam Tabb Formation while the Charles City Wetland site (CCW) lies on the older and clay-rich Shirley Formation. This study documents and …


An Investigation Of Dissolved Organic Matter In A Shallow Coastal Bay Subject To Aureococcus Anophagefferens Blooms, Jean-Paul Simjouw Jan 2004

An Investigation Of Dissolved Organic Matter In A Shallow Coastal Bay Subject To Aureococcus Anophagefferens Blooms, Jean-Paul Simjouw

OES Theses and Dissertations

Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, was identified in Chincoteague Bay in 1997 and has “bloomed” there since at least 1998. Aureococcus anophagefferens is capable of using dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) substrates to support growth, and this utilization is hypothesized to give the organism a competitive advantage relative to other phytoplankton when inorganic nutrient concentrations are low or depleted. Because previous studies suggest dissolved organic matter (DOM) is important in initiating and sustaining brown tide blooms, a field study of the variations in DOC concentration and DOM composition was performed at …


Compositional And Mineralogical Relationships Between Mafic Inclusions And Host Lavas As Key To Andesite Petrogenesis At Mount Hood Volcano, Oregon, Melinda Michelle Woods Jan 2004

Compositional And Mineralogical Relationships Between Mafic Inclusions And Host Lavas As Key To Andesite Petrogenesis At Mount Hood Volcano, Oregon, Melinda Michelle Woods

Dissertations and Theses

Throughout its eruptive history, Mount Hood has produced compositionally similar calc-alkaline andesite as lava flows and domes near the summit and basaltic andesitic flows from flank vents. Found within the andesite are slightly more mafic inclusions that are compositionally similar to the host andesite (or host lavas); no inclusions were found in the flank lavas. Host lavas and inclusions have the following mineral assemblage: plag + opx ± cpx ± amp + oxides. Flank lava mineralogy is similar to the inclusions and host lavas, but since they are more mafic they contain olivine instead of amphibole. Average silica content among …


Improving Nutrient Management At Lake Joondalup, Western Australia, Through Identification Of Key Sources And Current Trajectories, Michelle Cumbers Jan 2004

Improving Nutrient Management At Lake Joondalup, Western Australia, Through Identification Of Key Sources And Current Trajectories, Michelle Cumbers

Theses : Honours

Eutrophication has become a considerable issue for managers of water bodies across Australia. Rapid urbanisation in the south-west of Western Australia is causing the eutrophication of many wetlands within the region. Lake Joondalup is a eutrophic, urban lake, located approximately 20km north of Perth city. It comprises part of the Yellagonga Regional Park, having a high conservation value. The aim of this study was to provide managers of Lake Joondalup with information on the relative importance of different nutrient sources into the lake, thus enabling the development of appropriate management strategies. Additionally, a historical examination of available water quality data …


20 Years Of Speleothem Paleoluminescence Records Of Environmental Changes: An Overview, Yavor Y. Shopov Jan 2004

20 Years Of Speleothem Paleoluminescence Records Of Environmental Changes: An Overview, Yavor Y. Shopov

International Journal of Speleology

This paper discusses advance of the research on Speleothem Paleoluminescence Records of Environmental Changes after it have been first introduced by the author 20 years ago. It is demonstrated that most of the progress in this field was made in result of the operation of the International Program “Luminescence of Cave Minerals” of the commission on Physical Chemistry and Hydrogeology of Karst of UIS of UNESCO. Potential, resolution and limitations of high resolution luminescence speleothem proxy records of Paleotemperature, Solar Insolation, Solar Luminosity, Glaciations, Sea Level advances, Past Precipitation, Plants Populations, Paleosoils, Past Karst Denudation, Chemical Pollution, Geomagnetic field and …


Cave Temperatures And Global Climatic Change, Giovanni Badino Jan 2004

Cave Temperatures And Global Climatic Change, Giovanni Badino

International Journal of Speleology

The physical processes that establish the cave temperature are briefly discussed, showing that cave temperature is generally strictly connected with the external climate. The Global Climatic changes can then influence also the underground climate. It is shown that the mountain thermal inertia causes a delay between the two climates and then a thermal unbalance between the cave and the atmosphere. As a consequence there is a net energy flux from the atmosphere to the mountain, larger than the geothermal one, which is deposited mainly in the epidermal parts of caves.


Advances In The Geology Of The Tobacco Root Mountains, Montana, And Their Implications For The History Of The Northern Wyoming Province, Tekla A. Harms, John B. Brady, H. Robert Burger, John T. Cheney Jan 2004

Advances In The Geology Of The Tobacco Root Mountains, Montana, And Their Implications For The History Of The Northern Wyoming Province, Tekla A. Harms, John B. Brady, H. Robert Burger, John T. Cheney

Geosciences: Faculty Publications

Integrated studies by Keck Geology Consortium participants have generated many new insights into the Precambrian geology of the Tobacco Root Mountains. We have clarified the tectonic setting and origin of two suites of metamorphic rocks: (1) a quartzofeldspathic gneiss complex with associated metasupracrustal rocks (the combined Indian Creek and Pony–Middle Mountain Metamorphic Suites) that originated in a continental arc setting between 3.35 and 3.2 Ga with subsequent sedimentation and (2) mafic metavolcanic rocks with intercalated metasedimentary rocks (the Spuhler Peak Metamorphic Suite) from a suprasubduction zone ophiolite or backarc basin possibly of Proterozoic age. A poorly preserved metamorphic event at …


Proterozoic Metamorphism Of The Tobacco Root Mountains, Montana, John T. Cheney, John B. Brady, Kara A. Tierney, Kathleen A. Degraff, Heidi K. Mohlman, Jessica D. Frisch, Christine E. Hatch, Michael L. Steiner, Sarah K. Carmichael, Robin G.M. Fisher, Carrie B. Tuit, Kurt J. Steffen, Pamela Cady, Josh Lowell, Leandra L. Archuleta, Jillian Hirst, Karl W. Wegmann, Brian Monteleone Jan 2004

Proterozoic Metamorphism Of The Tobacco Root Mountains, Montana, John T. Cheney, John B. Brady, Kara A. Tierney, Kathleen A. Degraff, Heidi K. Mohlman, Jessica D. Frisch, Christine E. Hatch, Michael L. Steiner, Sarah K. Carmichael, Robin G.M. Fisher, Carrie B. Tuit, Kurt J. Steffen, Pamela Cady, Josh Lowell, Leandra L. Archuleta, Jillian Hirst, Karl W. Wegmann, Brian Monteleone

Geosciences: Faculty Publications

Textures and mineral assemblages of metamorphic rocks of the Tobacco Root Mountains are consistent with metamorphism of all rocks during the Big Sky orogeny (1.77 Ga) at relatively high pressure (P >1.0 GPa) followed by differential reequilibration on a clockwise P-T path at lower pressures (0.6–0.8 GPa). The highest pressures are documented by coarse-grained kyanite and orthopyroxene in aluminous orthoamphibolites, which require P ≥ 1.0 GPa. Other higher-pressure mineral assemblages of note include kyanite + orthoamphibole and kyanite + K-feldspar. Abundant textural evidence for partial melting in pelitic and basaltic rocks includes leucosomes, very large (several cm across) porphyroblasts of …


Precambrian Meta-Ultramafic Rocks From The Tobacco Root Mountains, Montana, Kathleen E. Johnson, John B. Brady, William A. Macfarlane, Rebecca B. Thomas, Chris J. Poulsen, M. Jennifer Sincock Jan 2004

Precambrian Meta-Ultramafic Rocks From The Tobacco Root Mountains, Montana, Kathleen E. Johnson, John B. Brady, William A. Macfarlane, Rebecca B. Thomas, Chris J. Poulsen, M. Jennifer Sincock

Geosciences: Faculty Publications

Meta-ultramafic rocks occur as small (2 to 100 m long), podiform bodies in all three major Precambrian rock suites of the Tobacco Root Mountains of southwest Montana. Most samples consist of a randomly oriented, coarse-grained assemblage of orthopyroxene, olivine, and magnesiohornblende ± spinel, partially replaced by a fine-grained assemblage that may include anthophyllite, talc, cummingtonite, magnesiohornblende, chlorite, serpentine, and/ or magnetite. Blackwall reaction zones of anthophyllite, actinolite, chlorite, and/or biotite surround several of the meta-ultramafic bodies. The absence of clinopyroxene with orthopyroxene limits the metamorphic pressure-temperature history of these rocks to temperatures below ~800 °C. The presence of anthophyllite with …


Environmental Indicator Proxies From A Mid-Holocene Coral Reef, Enriquillo Valley, Dominican Republic, Gala M.M. Guerard, Lisa Greer, H. Allen Curran Jan 2004

Environmental Indicator Proxies From A Mid-Holocene Coral Reef, Enriquillo Valley, Dominican Republic, Gala M.M. Guerard, Lisa Greer, H. Allen Curran

Geosciences: Faculty Publications

No abstract provided.