Geosciences Faculty Publications and Presentations Copyright (c) 2013 Boise State University All rights reserved. http://scholarworks.boisestate.edu/geo_facpubs Recent documents in Geosciences Faculty Publications and Presentations en-us Mon, 06 May 2013 09:42:29 PDT 3600 Age Intercalibration of <sup>40</sup>Ar/<sup>39</sup>Ar Sanidine and Chemically Distinct U/Pb Zircon Populations from the Alder Creek Rhyolite Quaternary Geochronology Standard http://scholarworks.boisestate.edu/geo_facpubs/156 http://scholarworks.boisestate.edu/geo_facpubs/156 Fri, 03 May 2013 14:53:21 PDT We report results from a 40Ar/39Ar sanidine and CA-TIMS 238U/206Pb zircon dating study of eruption and crystal residence timescales of the Alder Creek Rhyolite (ACR), California, extruded during the Cobb Mountain normal-polarity subchron (C1r.2n). A 40Ar/39Ar ACR sanidine date of 1.1850 ± 0.0016 Ma (2σ external uncertainty), determined relative to the astronomically dated A1 tephra sanidine, is interpreted as the ACR eruption age. This age is supported by CA-TIMS U–Pb zircon dating, guided by LA-ICPMS trace element analyses, titanium-in-zircon (TiZR) thermometry, and cathodoluminescence (CL) imaging. Using these data, two compositionally distinct zircon populations were revealed. “Pre-ACR” Group B zircon exhibit oscillatory zoning, large positive Ce and negative Eu anomalies, high incompatible trace element contents, TiZR temperatures of 650 °C–750 °C, and Th/U disequilibrium corrected 238U/206Pb dates of 1.38–1.24 Ma. These crystals are interpreted as antecrysts inherited from earlier intrusives in the Geysers–Cobb Mountain magma source region. “ACR-related” Group A zircon, present as discrete grains and overgrowths on Group B zircon, display less intense CL with diffuse zoning, and have less pronounced positive Ce and negative Eu anomalies, lower incompatible trace element contents, higher TiZR temperatures that range up to 840 °C, and significantly younger dates. The youngest Group A dates yield a weighted mean of 1.1978 ± 0.0046 Ma (2σ, including systematic uncertainties) that is interpreted as the mean age of zircon crystallization prior to eruption. The 13 ± 5 ka offset between the 40Ar/39Ar and 238U/206Pb dates can be attributed to zircon magma residence time. Recognition of a young population of ACR zircon is consistent with the 40Ar/39Ar eruption age, which coincides with the astronomical age estimate for the Cobb Mountain subchron determined by correlating the oxygen isotope record of the giant piston core MD972143 to the La93(1,1) orbital solution. On the basis of independent radio-isotopic and orbital forcing results, we propose the refined age of 1.1850 ± 0.0016 Ma (2σ external uncertainty) for the Quaternary ACR 40Ar/39Ar sanidine standard.

]]> Tiffany A. Rivera et al. Detecting Geyser Activity with Infrasound http://scholarworks.boisestate.edu/geo_facpubs/155 http://scholarworks.boisestate.edu/geo_facpubs/155 Wed, 01 May 2013 12:17:46 PDT We monitored geyser activity in the Lower Geyser Basin (LGB) of Yellowstone National Park with dual four-element microphone arrays separated by ~ 600 m. The arrays were independently used to identify incident coherent plane wave energy, then conjoint cross beam back-azimuths from the two arrays were used to precisely locate signal sources. During a week in August 2011 we located repeating infrasound events, peaked in energy between 1 and 10 Hz, originating from at least five independent geothermal features, including the episodically erupting Great Fountain, Fountain and Kaleidoscope Geysers, as well as periodic infrasound from nearby Botryoidal and persistent sound from Firehole Spring. Although activity from nearby cone-type geysers was not detected in the infrasound band up through 50 Hz, the major fountain-type geysers (i.e., with columns greater than 10 m) could be detected at several kilometers, and two minor geysers (i.e., a few meters in eruption height) could be tracked at distances up to a few hundred meters. Detection of geyser activity was especially comprehensive at night when ambient noise was low. We conclude that infrasound monitoring of fountain-type geysers permits convenient tracking of geyser activity, episodicity, signal duration, energy content, and spectral content. These parameters enable objective statistical quantification of geyser behavior and changes over time that may be due to external forcing. Infrasonic study of geyser activity in an individual basin has great monitoring utility and can be reasonably accomplished with two or more distributed sensor arrays.

]]> Jeffrey B. Johnson et al. Regional Groundwater Flow in an Area Mapped as Continuous Permafrost, NE Alaska (USA) http://scholarworks.boisestate.edu/geo_facpubs/154 http://scholarworks.boisestate.edu/geo_facpubs/154 Wed, 24 Apr 2013 11:19:00 PDT Fundamental knowledge of groundwater systems in areas of permafrost is often lacking. The likelihood of finding good quality groundwater resources of acceptable quantities generally decreases as the areal coverage of permafrost increases. In areas of continuous permafrost, the probability of finding areas of groundwater recharge and discharge are minimal. Still, in northeastern Alaska (USA), the presence of numerous springs and associated downstream aufeis formations clearly indicates that there has to be a groundwater system with the required complementary areas of groundwater recharge and transmission. Recharge zones and transmission pathways in this area of extensive permafrost, however, are essentially unknown. This study shows that the recharge occurs on the south side of the Brooks Range in northeastern Alaska, where extensive limestone outcrops are found. The transmission zone is beneath the permafrost, with discharge occurring through the springs via taliks through the permafrost (where faults are present) and also likely at the northern edge of the permafrost along the Beaufort Sea coast.

]]> Douglas L. Kane et al. Strontium Isotope Zoning in Garnet: Implications for Metamorphic Matrix Equilibration, Geochronology and Phase Equilibrium Modelling http://scholarworks.boisestate.edu/geo_facpubs/153 http://scholarworks.boisestate.edu/geo_facpubs/153 Fri, 19 Apr 2013 15:11:12 PDT In principle, garnet growth rates may be calculated from 87Rb/86Sr and 87Sr/86Sr measurements in garnet subsamples and the surrounding rock matrix. Because of low Rb/Sr, garnet should passively record the matrix decay of 87Rb to 87Sr as a progressive increase in 87Sr/86Sr from core to rim. This concept was tested by collecting Rb-Sr data for five garnet grains from four major orogenic belts: eastern Vermont (c. 380 Ma), western New Hampshire (c. 320 Ma), southern Chile (c. 75 Ma) and northwestern Italy (c. 35 Ma). Both normal Sr isotope zoning (increasing 87Sr/86Sr from core to rim) and inverse Sr zoning (decreasing 87Sr/86Sr from core to rim) were observed. Garnet and matrix isotope data commonly yielded grossly inaccurate model ages. Incomplete Rb and Sr equilibration among matrix minerals is invoked to explain the deviations between theoretical v. measured zoning patterns and the age disparities. Initially, the reactive matrix is dominated by rapidly equilibrating Rb-rich mica, which imparts high 87Sr/86Sr values in garnet cores. Progressive participation of slower equilibrating Sr-rich plagioclase buffers or even reduces 87Sr/86Sr, possibly leading to flat or decreasing 87Sr/86Sr from garnet cores to rims. Unusually high 87Sr/86Sr in garnet in combination with bulk matrix compositions causes erroneously young apparent ages, so metamorphic ages, growth rates, and associated heating and loading rates are likely suspect. Although Rb-Sr may be the most susceptible because of the profound disparities between mica and feldspar, zircon reactivity might influence the Lu-Hf system by up to a few per cent. The Sm-Nd system seems generally immune to these effects. Pseudosection analysis and conventional garnet geochronology, which presume complete matrix equilibration during metamorphism, may require modification to account for differences between whole-rock v. reactive matrix compositions.

]]> J. Sousa et al. One Hundred Years of Isotope Geochronology, and Counting http://scholarworks.boisestate.edu/geo_facpubs/152 http://scholarworks.boisestate.edu/geo_facpubs/152 Mon, 08 Apr 2013 11:15:29 PDT In 1913, Frederick Soddy's research on the fundamentals of radioactivity led to the discovery of “isotopes.” Later that same year, Arthur Holmes published his now famous book The Age of the Earth, in which he applied this new science of radioactivity to the quantification of geologic time. Combined, these two landmark events did much to establish the field of “isotope geochronology” – the science that underpins our knowledge of the absolute age of most Earth (and extraterrestrial) materials. In celebrating the centenary, this issue brings together modern perspectives on the continually evolving field of isotope geochronology – a discipline that reflects and responds to the demands of studies ranging from the early evolution of the Solar System to our understanding of Quaternary climate change, and the 4.5 billion years in between.

]]> Daniel J. Condon et al. High-Precision Geochronology http://scholarworks.boisestate.edu/geo_facpubs/151 http://scholarworks.boisestate.edu/geo_facpubs/151 Mon, 08 Apr 2013 11:09:20 PDT High-precision geochronology is integral to testing hypotheses regarding the correlation, causes, and rates of events and processes in Earth history. Recent studies have sought to reconcile very precise, but apparently conflicting, ages for the same geological samples and events using different chronometers. Both systematic (decay constants, ages of standard materials) and geological (daughter-nuclide loss, inheritance) complexities contribute to the challenges of rock-clock calibration. Community-wide efforts to improve radioisotope geochronology have successfully mitigated many of these factors, and have brought high-precision geochronology to a threshold of unprecedented integration with stratigraphic and geochemical proxies of Earth systems dynamics.

]]> Mark D. Schmitz et al. A Latest Carboniferous Warming Spike Recorded by a Fusulinid-Rich Bioherm in Timor Leste: Implications for East Gondwana Deglaciation http://scholarworks.boisestate.edu/geo_facpubs/150 http://scholarworks.boisestate.edu/geo_facpubs/150 Wed, 03 Apr 2013 13:01:52 PDT

During the late Paleozoic and early Mesozoic Timor lay in the northern part of the north–south East Gondwana rift system along which the western margin of Australia later developed. Discovery of a latest Gzhelian bioherm in the central highlands of Timor Leste has implications for latest Carboniferous–earliest Permian climate history and deglaciation in basins further south in the rift system.

Limestone outcrop of the Maubisse Formation near the village of Kulau is recognized as a bioherm with a massive lower unit, including reef framework at the base, and a bedded grainstone upper unit. The bioherm developed on a basalt substrate in warm shallow-water, as indicated by photozoan assemblages in the massive lower unit. Foraminifera belonging to 17 genera are recorded from the bioherm. These include representatives of the families Biseriamminidae, Biwaellidae, Bradyinidae, Cornuspiridae, Lasiodiscidae, Palaeotextulariidae, Pseudotaxidae, Ozawainellidae, Schubertellidae, Schwagerinidae, Staffellidae and Textrataxidae. Twenty-one species have been referred to known types and 12 species are left in open nomenclature. The assemblage probably belongs within the uppermost Gzhelian Schwagerina robusta–Ultradaixina bosbytauensis Zone although a possible lowest Asselian correlation cannot be excluded. The bioherm is the oldest carbonate unit so far recorded from the Maubisse Formation, and the oldest sedimentary unit biostratigraphically dated in Timor.

The dominantly heterozoan composition of the skeletal component of the limestone (except for the basal photozoan assemblage) and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a paleolatitude of about 40° S. The late Pennsylvanian was a time of glaciation that in Australia is represented by a significant stratigraphic hiatus in basins to the south of Timor in the East Gondwana rift system. The development of the Kulau bioherm during the latest Gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment (alternating diamictite and mudstone) in the southern basins.

]]> Vladimir I. Davydov et al. Pre- to Synglacial Rift-Related Volcanism in the Neoproterozoic (Cryogenian) Pocatello Formation, SE Idaho: New SHRIMP and CA-ID-TIMS Constraints http://scholarworks.boisestate.edu/geo_facpubs/149 http://scholarworks.boisestate.edu/geo_facpubs/149 Thu, 28 Mar 2013 10:51:03 PDT

Volcanic and diamictite-bearing strata of the Neoproterozoic Pocatello Formation record middle Cryogenian glaciation and alkaline to subalkaline within-plate magmatism during Rodinia rifting. New mapping along the Oxford Ridge segment of the southern Bannock Range in SE Idaho has resolved stratigraphic relationships between the Scout Mountain and underlying Bannock volcanic members of the Pocatello Formation. Bannock Volcanic Member metabasalt has an upper gradational contact with over 250 m of Scout Mountain Member that includes extrabasinal and volcaniclastic diamictite, in turn overlain by a volcaniclastic unit (the Oxford Mountain tuffite). Previous attempts to date the tuffite include three sets of analyses of the original sample (06PL00) and one resample (04JK09) that yielded sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon concordia ages of ca. 709, 702, and 686 Ma and one isotope dilution–thermal ionization mass spectrometry (ID-TIMS) age of 687.4 ± 1.3 Ma. Several new samples of plagioclase-phyric volcanic sandstone and the tuffite, dated via high-precision (∼0.1%) chemical abrasion (CA) ID-TIMS, have multimodal zircon populations with single-crystal ages ranging from as old as 709 Ma to as young as 685 Ma, confirming the epiclastic nature of the deposit. The majority of grains in one sample yielded a 206Pb/238U weighted mean age of 685.5 ± 0.4 Ma, which provides a robust maximum age of deposition.

From the type section of the lower Scout Mountain Member, Pocatello Formation at Portneuf Narrows, we report four new SHRIMP maximum depositional ages between 705 ± 5 Ma and 682 ± 6 Ma. A 691 ± 4 Ma (SHRIMP) volcanic clast from the cobble conglomerate member provides a maximum depositional age, and provides a geochronologic correlation with the Oxford Mountain tuffite. The data are interpreted to support a lithostratigraphic correlation between the diamictite on Oxford Mountain and the lower diamictite at Portneuf Narrows and to show that the upper glaciogenic diamictite in the Portneuf Narrows section is younger than 685 Ma. This 685 Ma age from rift-related rocks that underlie the Brigham Group passive-margin succession provides a maximum age for onset of rift subsidence.

Lu-Hf analyses of 685–730 Ma igneous zircons yield enriched initial εHf values in the range +2 to −17, indicating that they crystallized from magma that incorporated depleted Paleoproterozoic to Archean crustal components of the underlying Farmington Canyon Complex and Wyoming craton.

]]> Joshua A. Keeley et al. Late Moscovian Fusulinids from the "N" Formation (Donets Basin, Ukraine) http://scholarworks.boisestate.edu/geo_facpubs/148 http://scholarworks.boisestate.edu/geo_facpubs/148 Fri, 22 Feb 2013 14:10:16 PST A fusulinoidean taxonomic study of the Gurkovo and Kalinovo sections allows us to refine the biostratigraphy of the poorly studied Myachkovian (upper Moscovian) strata of the "N" Formation in the Donets Basin. Three fusulinid biozones, Hemifusulina graciosa–Fusiella spatiosa, Fusulina cylindrica–Fusulinella pseudobocki, and Fusulinella ? kumpani, are proposed in the interval from the top of Limestone M10 to the base of N3, and they are correlated with coeval strata in the historical type area of the Moscow Basin. A total of 33 fusulinid species and subspecies belonging to eight genera are described, including three new species: Hemifusulina gurkovensis n. sp., Beedeina innaeformis n. sp., and Fusulina sosninae n. sp. The main evolutionary trend in fusulinoidean morphology in the late Moscovian is the appearance of massive secondary deposits in the limestone of the "N" Formation.

Specific temporal and distributional patterns of the Middle Pennsylvanian fusulinoidean assemblages indicate variations in sea level stand. Variations are cyclic, with periods 600,000–1,000,000 years. A Hemifusulina-association indicates the beginning of transgression; the late transgression–high sea level stand is designated by the Beedeina–Neostaffella–Ozawainella–Taitzehoella assemblage which is successively replaced by the most diverse Fusulinella-dominant association, which occupied a progressively shallowing sea.

The similarity of fusulinoidean assemblages in the Moscow and Donets Basins and their cognate evolution trends reveal a connection between both regions at least during Podolskian–Myachkovian time.

]]> Rimma R. Khodjanyazova et al. Trace Element Diffusivities in Bone Rule Out Simple Diffusive Uptake During Fossilization but Explain in vivo Uptake and Release http://scholarworks.boisestate.edu/geo_facpubs/147 http://scholarworks.boisestate.edu/geo_facpubs/147 Fri, 22 Feb 2013 13:49:45 PST Diffusion rates of numerous trace elements in bone at 20 °C were determined using laser-ablation inductively coupled plasma mass spectrometry analysis of experimentally induced diffusion profiles. Diffusivities are about 1 order of magnitude slower than current semiquantitative geochemical views and about 1.5 orders of magnitude faster than indirect radiotracer estimates. Intrabone volume diffusion is too slow and too similar among many elements to explain trace element profiles in young fossils and archeological materials. Diffusivity differences among elements do, however, explain disparate biokinetic washout of Sr vs. Ba and of light vs. heavy rare earth elements (REEs). These results improve the understanding of the physical principles underlying biokinetic models and rates and mechanisms of trace element alteration of phosphatic tissues in paleontological, archeological, and crystal-chemical contexts. Recrystallization and transport limitations in soils explain trace element profiles in young fossils better than intrabone volume diffusion alone and imply that diffusion of REE and other trivalent cations is likely controlled by a common charge–compensating species rather than ionic radii or partition coefficients.

]]> Matthew J. Kohn et al. Trace Element Concentrations in Teeth – A Modern Idaho Baseline with Implications for Archeometry, Forensics, and Palaeontology http://scholarworks.boisestate.edu/geo_facpubs/146 http://scholarworks.boisestate.edu/geo_facpubs/146 Fri, 22 Feb 2013 13:01:18 PST Concentrations of 69 minor and trace elements were measured in situ using laser ablation inductively-coupled plasma mass spectrometry in multiple teeth of modern herbivores (Cervus elaphus, Odocoileus hemionus, Odocoileus virginianus; n = 52), omnivores (Ursus americanus; n = 56), and carnivores (Felis concolor; n = 33; Canis lupus; n = 4) from Idaho, USA. On each tooth, two to five analyses were collected on enamel, primary dentine, and secondary dentine with spot diameters of 30–100 μm. Continuous 30-μm-wide line traverses were collected across deer, elk, and wolf teeth. Results confirm trace element concentrations below 1 ppm for many elements, including Li, Be, transition metals (excepting Mn, Fe and Zn), heavy metals (excepting Hg and Pb), the rare earths, and actinides. Strontium and Ba generally biopurify with increasing trophic level, but Ba shows decreasing discrimination with tissue type in the order secondary dentine – primary dentine – enamel. Most elements show strong zoning within tissues and variable trophic level behavior, so concentrations in omnivores rarely fall between herbivores and carnivores. Trace element mass balance suggests that soil and dust, not food, commonly deliver the largest trace element load in terrestrial carnivores and omnivores, even for elements that biopurify, like Ba. Use of trace elements for inferring past diets are likely compromised by unknown rates of dust and soil ingestion rather than indicating the degree of herbivory and carnivory. The low concentrations of many elements provide multiple sensitive markers of post-burial overprinting that can be used to discriminate altered vs. original biogenic compositions. REE and actinide trends do not directly follow bedrock compositions.

]]> Matthew J. Kohn et al. A New Chronology for Middle Eocene-Early Miocene South American Land Mammal Ages http://scholarworks.boisestate.edu/geo_facpubs/145 http://scholarworks.boisestate.edu/geo_facpubs/145 Thu, 24 Jan 2013 09:33:15 PST

Cenozoic South American Land Mammal Ages (SALMAs) have historically been correlated to the geologic time scale using 40Ar/39Ar dating and magnetostratigraphy. At Gran Barranca (68.7°°W, 45.7°S)–one of South America’s key areas for constraining SALMAs–existing radioisotopic ages have uncertainties of up to 4 m.y. To better constrain the ages of mammalian assemblages, we employed high-precision (±<40 >k.y.) U-Pb dating using single zircon crystals. We dated nine tuffs from the Sarmiento Formation containing middle Eocene–early Miocene faunas (Barrancan, Mustersan, Tinguirirican, Deseadan, Colhuehuapian, and “Pinturan”). The new dates span from 39.861 ± 0.037 Ma to 19.041 ± 0.027 Ma. The La Cancha Tuff, occurring within the Tinguirirican faunal level yielded an age of 33.581 ± 0.015 Ma, confirming that the Vera Member contains the only fossiliferous geologic section encompassing the Eocene–Oligocene transition in the Southern Hemisphere. The pre-Deseadan fauna, La Cantera, is ≤30.77 Ma, the age of the Colhuehuapian is expanded to 21.1–20.1 Ma, and the Pinturan may be as old as ca. 19 Ma.

The new U-Pb dates confirm that atmospheric temperatures and vegetation remained constant across the Eocene–Oligocene transition in Patagonia and that hypsodonty occurred in South American ungulates much earlier than on any other continent. Additionally, refinement of the SALMA boundaries will eventually provide the context necessary to compare faunal transitions across continents, although currently too much data are missing to allow such comparisons. Finally, the new ages provide a high-resolution age model from which hypotheses about rates of environmental and evolutionary change at Gran Barranca can be tested.

]]> Regan E. Dunn et al. Variability of Pennsylvanian-Permian Carbonate Associations and Implications for NW Pangea Palaeogeography, East-Central British Columbia, Canada http://scholarworks.boisestate.edu/geo_facpubs/144 http://scholarworks.boisestate.edu/geo_facpubs/144 Tue, 22 Jan 2013 12:07:44 PST Different stages of Pennsylvanian-Permian carbonate sedimentation in east-central British Columbia record a complex history of changing environments influenced by evolving palaeogeography and climate. Newly recognized tectonically controlled features affected the distribution and variability of carbonate associations, providing new interpretations for this portion of the west coast of Pangea. Both a heterozoan (cool water) and photozoan (warm-water) association were identified on either side of a palaeogeographic high here informally termed “Tipinahokan Peninsula”. Cool water carbonates were located outboard, or to the west of this high, an area influenced by upwelling waters. Inboard of this high, a warm, protected sea developed, here termed “Kisosowin Sea”. This configuration and palaeolatitude is similar to that of Baja California, Mexico and the Sea of Cortéz, providing a good modern analog for these deposits where warm water carbonates grow at latitudes otherwise dominated by cool water deposits. The warm sea provided a place for a photozoan association to develop during the Permian when the low latitude NW coast of Pangea was dominated by cool water carbonates.

]]> K. D. Zubin-Stathopoulos et al. Late Paleoproterozoic Terrane Accretion in Northwestern Canada and the Case for Circum-Columbian Orogenesis http://scholarworks.boisestate.edu/geo_facpubs/143 http://scholarworks.boisestate.edu/geo_facpubs/143 Tue, 11 Dec 2012 12:22:56 PST The reconstruction of the paleocontinental configuration involving ancestral North America (Laurentia) at the Paleoproterozoic–Mesoproterozoic boundary has been developed in the last 30 years with different scenarios being proposed and different combinations of landmasses assembled together. However, the lack of information for the northwestern side of the North American craton has so far been an obstacle for the complete paleocontinental reconstruction and its tectonic history. Here we provide new age determinations on rocks of the Wernecke Supergroup and of the Wernecke Breccia of the Wernecke Mountains in Yukon to provide a more complete picture of the entire North American craton and its possible conterminous at 1600 Ma. The six youngest U–Pb ages of the detrital zircon from quartz sandstones of the Wernecke Supergroup suggest that the sedimentary succession is as old as 1640 Ma. Lu–Hf garnet ages on garnet bearing schists of the Fairchild Lake Group (lower Wernecke Supergroup) give a bimodal population of ages of approximately 1600 Ma and 1370 Ma: the first age is related to the Racklan Orogeny, and the younger event is likely attributable to a reheating episode (Hart River Sills emplacement). The younger age of the Wernecke Supergroup puts into question the previous model concerning the emplacement of the Bonnet Plume River Intrusions, and requires the development of a new tectonic model for the northwestern margin of Laurentia. This new model involves obduction of an exotic terrane on top of the Wernecke Supergroup during the latest phases of the Racklan Orogeny (ca. 1600 Ma). This exotic terrane, herein called Bonnetia, contains rocks of the Bonnet Plume River intrusions and of the Slab volcanics. During the hydrothermal event that led to the emplacement of the Wernecke Breccia, clasts and megaclasts of the overlying Bonnetia foundered down to the breccia pipes to the level of the Wernecke Supergroup, and this dynamic explains the existence of older rocks engulfed within a younger sedimentary succession. The Racklan Orogeny is now interpreted as a northwestern expression of the Mazatzal Orogeny of southwestern United States, and of the Labradorian Orogeny of eastern Canada which was in turn connected with the Gothian Orogeny of Scandinavia. The connection among these orogenic events makes plausible the hypothesis of a circum-Laurentian orogenic belt with possible extensions in other landmasses (Australia, Antarctica, Siberia, or China) where coeval deformation belts are present.

]]> Francesca Furlanetto et al. Probing Local Wind and Temperature Structure Using Infrasound from Volcan Villarrica (Chile) http://scholarworks.boisestate.edu/geo_facpubs/142 http://scholarworks.boisestate.edu/geo_facpubs/142 Wed, 24 Oct 2012 11:58:19 PDT We use the continuous and intense (∼107 W) infrasound produced by Volcan Villarrica (Chile) to invert for the local dynamic wind and temperature structure of the atmosphere. Infrasound arrays deployed in March 2011 at the summit (2826 m) and on the NNW flank (∼8 km distant at 825 m) were used to track infrasound propagation times and signal power. We model an atmosphere with vertically varying temperature and horizontal winds and use propagation times (ranging from 23 to 24 s) to invert for horizontal slowness (2.75–2.94 s/km) and average effective sound speeds (328–346 m/s) for NNW propagating infrasound. The corresponding ratio of recorded acoustic power at proximal versus distal arrays was also variable (ranging between 0.15 to 1.5 for the peak 0.33–1 Hz infrasound band). Through application of geometrical ray theory in a uniform gradient atmosphere, these 'amplification factors' are modeled by effective sound speed lapse rates ranging from −15 to +4 m/s per km. NNW-projected wind speeds ranging from −20 m/s to +20 m/s at 2826 m and wind gradients ranging from −11 to +10 m/s per km are inferred from the difference between effective sound speed profiles and adiabatic sound speeds derived from local temperature observations. The sense of these winds is in general agreement with regional meteorological observations recorded with radiosondes. We suggest that infrasound probing can provide useful spatially averaged estimates of atmospheric wind structure that has application for both meteorological observation and volcanological plume dispersal modeling.

]]> Jeffrey B. Johnson et al. Persistent Metal Contamination Limits Lotic Ecosystem Heterotrophic Metabolism after More Than 100 Years of Exposure: A Novel Application of the Resazurin Resorufin Smart Tracer http://scholarworks.boisestate.edu/geo_facpubs/141 http://scholarworks.boisestate.edu/geo_facpubs/141 Fri, 05 Oct 2012 12:19:51 PDT Persistent stress from anthropogenic metal deposition in lotic ecosystems is a global concern. This long-term selective pressure shapes hyporheic microbial assemblages and influences ecosystem functional integrity. We hypothesized that, even after 100 years of adaptation opportunity, ecosystem function remains inhibited by sediment-associated metal stress and that the Resazurin Resorufin Smart Tracer can be used to quantify this impact. The Resazurin Resorufin Smart Tracer system is applied here in a novel capacity as an indicator of ecosystem function by quantifying ecosystem respiration of microbial communities. Hyporheic microbial communities exposed to differing magnitudes of chronic metal stress were compared to pristine reference sites in controlled column experiments. A Markov chain Monte Carlo technique was developed to solve the inverse smart tracer transport equation to derive community respiration data. Results suggest metals inhibit respiration by 13–30% relative to reference sites and this inhibition is directly related to the level of in situ metal stress. We demonstrate the first application of a hydrologic smart tracer as a functional indicator of ecological integrity within anthropogenically influenced flowing water systems and provide data suggesting resilience is limited in hyporheic ecosystems even after more than a century of microbial adaption to chronic pollutants.

]]> Daniel Stanaway et al. Image Interpretation Using Appraisal Analysis http://scholarworks.boisestate.edu/geo_facpubs/140 http://scholarworks.boisestate.edu/geo_facpubs/140 Tue, 02 Oct 2012 14:47:46 PDT In geophysical inversion, a significant effort is invested to obtain images of the Earth from finite data. The first step is to obtain an image i.e. solve the inverse problem. This step alone provides significant challenges that are not addressed inthis paper. The next step is to interpret the image in terms of specific questions. For example, what can we say about the average value of a physical property within a certain region of the model? What scale information can we resolve from the data? These questions are problem dependent and may require that inversion be carried out several times to arrive at a satisfactory answer. Therefore the solution to an inverse problem is only a step towards answering these questions. Appraisal analysis of the solution takes the next step by providing a set of tools to judge and select from the possibly infinite suite of images that adequately fit our observations. We discuss the use of point spread functions and averaging kernels in the interpretation of images. We use a controlled source electromagnetic example to demonstrate the methodology.

]]> Partha S. Routh et al. A Data Assimilation Approach for the Prediction of Soil Moisture At Tactical Scales Fusing Multiple Scale Data Sources and Models http://scholarworks.boisestate.edu/geo_facpubs/139 http://scholarworks.boisestate.edu/geo_facpubs/139 Thu, 27 Sep 2012 13:56:40 PDT Soil moisture is a critical environmental variable that impacts military trafficability through its impact on soil load bearing capacity. Adequate knowledge of soil moisture at scales of individual hillslopes (10s to 100s of m) would substantially improve efforts to assess trafficability and assist in erosion mitigation strategies on military lands. Field-based observations of soil moisture at the necessary high resolution over large areas is impractical, particularly for many Army operations. On the other hand, hydrologic models can simulate spatial patterns in moisture at the required scales, but are subject to errors in the model inputs and formulation. Anticipated L-band microwave remote sensing platforms offer accurate global observation of geo-physically obervable quantities that are related to soil moisture at revisit intervals of 2-3 days, but are too coarse in spatial scale for trafficability assessment. Numerical data assimilation provides a mathematical framework to leverage the benefits of models and remotely sensed observations, while potentially compensating for their respective weaknesses. This work provides a proof-of-concept illustration of how data assimilation with the Ensemble Kalman Filter (EnKF) can be used to improve hillslope-scale estimates of soil moisture. In a synthetic experiment in the Walnut Gulch experimental watershed in Arizona, USA, we show that immediately after a rainfall event, ingesting L-band microwave radar data into a watershed ecohydrology model using the EnKF increases the accuracy in a watershed-scale mapping of trafficability. Moreover, we demonstrate how the estimate of uncertainty in soil moisture provided by the EnKF can be used to convey risk in trafficability assessment.

]]> Alejandro N. Flores et al. Palaeolake Shoreline Sequencing Using Ground Penetrating Radar: Lake Alvord, Oregon, and Nevada http://scholarworks.boisestate.edu/geo_facpubs/138 http://scholarworks.boisestate.edu/geo_facpubs/138 Wed, 26 Sep 2012 13:31:04 PDT Field, map, and aerial photoreconnaissance in the Lake Alvord basin has focused on identifying late Pleistocene depositional shoreline features (e.g., tombolos, spits, barriers). Features in different areas of the basin are well defined, and their spatial extents are easily mapped; however, absolute---or even relative-ages of shoreline features are not clear. Ground penetrating radar (GPR) was used to distinguish between intermediate and highstand stage shorelines during what is thought to have been the latest Pleistocene, threshold-controlled lake cycle. Radar transects of 280 and 600 m imaged a spit and a baymouth barrier at sites in the northeastern quadrant of the basin where transects were aligned normal to the strike of each depositional geomorphic feature. Signal penetration with 100 MHz antennas was shallow (-4 m), but resolution was sufficient to locate and identify gross morphostratigraphic features. Flooding surfaces are shown to correspond to intermediate stage lake surface elevations, and the absence of a flooding surface at the elevation of the highest shoreline indicates this to be the maximum lake illrface elevation during this cycle. Elevations of intermediate lake stage elevations and highstand stage elevations were consistent at the two sites, with the highstand elevations corresponding closely to the basin threshold at Big Sand Gap. These data provide a firstorder approximation of lake stage sequence and the degree of postdepositional neotectonic activity and illustrate the utility of GPR when used in context with field measurements in distinguishing transgressive and highstand features.

]]> David E. Wilkins et al. Geology and Wine 11. Terroir of the Western Snake River Plain, Idaho, USA http://scholarworks.boisestate.edu/geo_facpubs/137 http://scholarworks.boisestate.edu/geo_facpubs/137 Wed, 26 Sep 2012 13:01:18 PDT This article explores the unique combination of factors that shape the terroir of Idaho's principal wine grape-growing district. Most Idaho wine grape vineyards are located in the Western Snake River Plain (WSRP) rift basin (~43°N, ~117°W) on soils derived from lake, river, volcanic and wind-blown sediments. The underlying Tertiary and Quaternary rocks record the geologic history of ancient Lake Idaho, its interaction with basaltic volcanism, and subsequent Pleistocene fluvial processes and catastrophic floods. The arid to semi-arid, mid-latitude steppe climate of the WSRP provides fewer growing degree days than American Viticultural Areas (AVAs) in Walla Walla, Washington and Napa Valley, California, but still allows cultivation of Vitis vinifera grapes. Other differences include lower precipitation, higher solar radiation during the growing season, and greater threat of cold injury. Wine grapes grown in the WSRP require irrigation, and irrigation is used to manage canopy size and manipulate vine physiology. Wine grape acreage in Idaho has increased dramatically since 1993 and is estimated, in 2003, at about 500 ha with the white wine cultivars Riesling, Chardonnay, and Gewürztraminer comprising about 60% of production, and Cabernet Sauvignon, Merlot and Syrah as principal red wine cultivars.

]]> Virginia S. Gillerman et al.