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At least 991 records · Page 55Linked to original sources
USGS2010

Development of a global land cover characteristics database and IGBP DISCover from 1 km AVHRR data

Researchers from the U.S. Geological Survey, University of Nebraska-Lincoln and the European Commission's Joint Research Centre, Ispra, Italy produced a 1 km resolution global land cover characteristics database for use in a wide range of continental-to global-scale environmental studies. This database provides a unique view of the broad patterns of the biogeographical and ecoclimatic diversity of the global land surface, and presents a detailed interpretation of the extent of human development. The project was carried out as an International Geosphere-Biosphere Programme, Data and Information Systems (IGBP-DIS) initiative. The IGBP DISCover global land cover product is an integral component of the global land cover database. DISCover includes 17 general land cover classes defined to meet the needs of IGBP core science projects. A formal accuracy assessment of the DISCover data layer will be completed in 1998. The 1 km global land cover database was developed through a continent-by-continent unsupervised classification of 1 km monthly Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) composites covering 1992-1993. Extensive post-classification stratification was necessary to resolve spectral/temporal confusion between disparate land cover types. The complete global database consists of 961 seasonal land cover regions that capture patterns of land cover, seasonality and relative primary productivity. The seasonal land cover regions were aggregated to produce seven separate land cover data sets used for global environmental modelling and assessment. The data sets include IGBP DISCover, U.S. Geological Survey Anderson System, Simple Biosphere Model, Simple Biosphere Model 2, Biosphere-Atmosphere Transfer Scheme, Olson Ecosystems and Running Global Remote Sensing Land Cover. The database also includes all digital sources that were used in the classification. The complete database can be sourced from the website: http://edcwww.cr.usgs.gov/landdaac/glcc/glcc.html.

International Journal of Remote Sensing↗
USGS2015

Magma extrusion during the Ubinas 2013–2014 eruptive crisis based on satellite thermal imaging (MIROVA) and ground-based monitoring

After 3 years of mild gases emissions, the Ubinas volcano entered in a new eruptive phase on September 2nd, 2013. The MIROVA system (a space-based volcanic hot-spot detection system), allowed us to detect in near real time the thermal emissions associated with the eruption and provided early evidence of magma extrusion within the deep summit crater. By combining IR data with plume height, sulfur emissions, hot spring temperatures and seismic activity, we interpret the thermal output detected over Ubinas in terms of extrusion rates associated to the eruption. We suggest that the 2013–2014 eruptive crisis can be subdivided into three main phases: ( i ) shallow magma intrusion inside the edifice, (ii) extrusion and growing of a lava plug at the bottom of the summit crater coupled with increasing explosive activity and finally, (iii) disruption of the lava plug and gradual decline of the explosive activity. The occurrence of the 8.2 Mw Iquique (Chile) earthquake (365 km away from Ubinas) on April 1st, 2014, may have perturbed most of the analyzed parameters, suggesting a prompt interaction with the ongoing volcanic activity. In particular, the analysis of thermal and seismic datasets shows that the earthquake may have promoted the most intense thermal and explosive phase that culminated in a major explosion on April 19th, 2014. These results reveal the efficiency of space-based thermal observations in detecting the extrusion of hot magma within deep volcanic craters and in tracking its evolution. We emphasize that, in combination with other geophysical and geochemical datasets, MIROVA is an essential tool for monitoring remote volcanoes with rather difficult accessibility, like those of the Andes that reach remarkably high altitudes.

Journal of Volcanology and Geothermal Research↗
USGS2016

Reevaluating the age of the Walden Creek Group and the kinematic evolution of the western Blue Ridge, southern Appalachians

An integrated synthesis of existing datasets (detailed geologic mapping, geochronologic, paleontologic, geophysical) with new paleontologic and geochemical investigations of rocks previously interpreted as part of the Neoproterozoic Walden Creek Group in southeastern Tennessee suggest a necessary reevaluation of the kinematics and structural architecture of the Blue Ridge Foothills. The western Blue Ridge of Tennessee, North Carolina, and Georgia is composed of numerous northwest-directed early and late Paleozoic thrust sheets, which record pronounced variation in stratigraphic/structural architecture and timing of metamorphism. The detailed spatial, temporal, and kinematic relationships of these rocks have remained controversial. Two fault blocks that are structurally isolated between the Great Smoky and Miller Cove-Greenbrier thrust sheets, here designated the Maggies Mill and Citico thrust sheets, contain Late Ordovician-Devonian conodonts and stable isotope chemostratigraphic signatures consistent with a mid-Paleozoic age. Geochemical and paleontological analyses of Walden Creek Group rocks northwest and southeast of these two thrust sheets, however, are more consistent with a Late Neoproterozoic (550–545 Ma) depositional age. Consequently, the structural juxtaposition of mid-Paleozoic rocks within a demonstrably Neoproterozoic-Cambrian succession between the Great Smoky and Miller Cove-Greenbrier thrust sheets suggests that a simple foreland-propagating thrust sequence model is not applicable in the Blue Ridge Foothills. We propose that these younger rocks were deposited landward of the Ocoee Supergroup, and were subsequently plucked from the Great Smoky fault footwall as a horse, and breached through the Great Smoky thrust sheet during Alleghanian emplacement of that structure.

North Carolina, Tennessee↗
USGS2011

A trans-dimensional Bayesian Markov chain Monte Carlo algorithm for model assessment using frequency-domain electromagnetic data

A meaningful interpretation of geophysical measurements requires an assessment of the space of models that are consistent with the data, rather than just a single, ‘best’ model which does not convey information about parameter uncertainty. For this purpose, a trans-dimensional Bayesian Markov chain Monte Carlo (MCMC) algorithm is developed for assessing frequencydomain electromagnetic (FDEM) data acquired from airborne or ground-based systems. By sampling the distribution of models that are consistent with measured data and any prior knowledge, valuable inferences can be made about parameter values such as the likely depth to an interface, the distribution of possible resistivity values as a function of depth and non-unique relationships between parameters. The trans-dimensional aspect of the algorithm allows the number of layers to be a free parameter that is controlled by the data, where models with fewer layers are inherently favoured, which provides a natural measure of parsimony and a significant degree of flexibility in parametrization. The MCMC algorithm is used with synthetic examples to illustrate how the distribution of acceptable models is affected by the choice of prior information, the system geometry and configuration and the uncertainty in the measured system elevation. An airborne FDEM data set that was acquired for the purpose of hydrogeological characterization is also studied. The results compare favorably with traditional least-squares analysis, borehole resistivity and lithology logs from the site, and also provide new information about parameter uncertainty necessary for model assessment.

Geophysical Journal International↗
USGS1987

Lungfish burrows in the Upper Triassic Chinle and Dolores Formations, Colorado Plateau

Vertical-to-inclined, cylindrical trace fossils that occur in the Upper Triassic Chinle and Dolores Formations on the Colorado Plateau are interpreted to be the casts of lungfish burrows. The casts, which are as much as 11 cm in diameter and as much as 1.6 m long, were formed by passive silicilastic and carbonate sedimentation into apparently abandoned lungfish burrows. Locally, the burrow fillings are overwhelmingly abundant, and many intersect and have destroyed former burrow fillings. Superposition of bioturbation episodes has obliterated most primary sedimentary structures. This bioturbation has contributed to the mottled coloration and the knobby-weathering texture of the rocks. The burrow-fillings occur ubiquitously in three lithofacies, comprising 1) purple- and white-mottled, silicified sandstone and siltstone, 2) red and brown siltstone and mudstone, and 3) pink and green limestone. These strata were deposited in a continental environment that included fluvial channels and floodplains, sand sheets and playa mudflats, and lacustrine basins, marshes, and deltas. The identification of the trace fossils as the positive casts of lungfish burrows is based on their morphologic similarity to previously identified lungfish burrows and to available hand specimens. The widespread occurrence of the lungfish burrows in the Chinle and Dolores Formations attests to the extensive habitat that supported lungfish in the Late Triassic and to conditions favorable for burrow preservation. Analogy with the environments that support modern lungfish populations suggests that the Late Triassic climate in the study area provided sufficient moisture to support large populations of lungfish and that this climate was probably punctuated by seasonally dry periods.

Journal of Sedimentary Petrology↗
USGS2017

Benchmarking computational fluid dynamics models of lava flow simulation for hazard assessment, forecasting, and risk management

Numerical simulations of lava flow emplacement are valuable for assessing lava flow hazards, forecasting active flows, designing flow mitigation measures, interpreting past eruptions, and understanding the controls on lava flow behavior. Existing lava flow models vary in simplifying assumptions, physics, dimensionality, and the degree to which they have been validated against analytical solutions, experiments, and natural observations. In order to assess existing models and guide the development of new codes, we conduct a benchmarking study of computational fluid dynamics (CFD) models for lava flow emplacement, including VolcFlow, OpenFOAM, FLOW-3D, COMSOL, and MOLASSES. We model viscous, cooling, and solidifying flows over horizontal planes, sloping surfaces, and into topographic obstacles. We compare model results to physical observations made during well-controlled analogue and molten basalt experiments, and to analytical theory when available. Overall, the models accurately simulate viscous flow with some variability in flow thickness where flows intersect obstacles. OpenFOAM, COMSOL, and FLOW-3D can each reproduce experimental measurements of cooling viscous flows, and OpenFOAM and FLOW-3D simulations with temperature-dependent rheology match results from molten basalt experiments. We assess the goodness-of-fit of the simulation results and the computational cost. Our results guide the selection of numerical simulation codes for different applications, including inferring emplacement conditions of past lava flows, modeling the temporal evolution of ongoing flows during eruption, and probabilistic assessment of lava flow hazard prior to eruption. Finally, we outline potential experiments and desired key observational data from future flows that would extend existing benchmarking data sets.

Journal of Applied Volcanology↗
USGS2001

Nomad Rover field experiment, Atacama Desert, Chile 1. Science results overview

Nomad was deployed for a 45 day traverse in the Atacama Desert, Chile, during the summer of 1997. During this traverse, 1 week was devoted to science experiments. The goal of the science experiments was to test different planetary surface exploration strategies that included (1) a Mars mission simulation, (2) a science on the fly experiment, where the rover was kept moving 75% of the operation time. (The goal of this operation was to determine whether or not successful interpretation of the environment is related to the time spent on a target. The role of mobility in helping the interpretation was also assessed.) (3) a meteorite search using visual and instrumental methods to remotely identify meteorites in extreme environments, and (4) a time-delay experiment with and without using the panospheric camera. The results were as follow: the remote science team positively identified the main characteristics of the test site geological environment. The science on the fly experiment showed that the selection of appropriate targets might be even more critical than the time spent on a study area to reconstruct the history of a site. During the same operation the science team members identified and sampled a rock from a Jurassic outcrop that they proposed to be a fossil. The presence of paleolife indicators in this rock was confirmed later by laboratory analysis. Both visual and instrumental modes demonstrated the feasibility, in at least some conditions, of carrying out a field search for meteorites by using remote-controlled vehicles. Finally, metrics collected from the observation of the science team operations, and the use team members made of mission data, provided critical information on what operation sequences could be automated on board rovers in future planetary surface explorations.

Atacama Desert↗
USGS2012

Principal component analysis of geodetically measured deformation in Long Valley caldera, eastern California, 1983-1987

Typical geodetic measurements of deformation consist of repeated surveys of a particular geodetic network. Such deformation data can be interpreted as a consequence of one or more self-coherent sources by means of principal component analysis. A self-coherent source is defined as any source that produces deformation that is time and space separable. Principal component analysis then gives the time and space factors that characterize the deformation attributed to each self-coherent source. Geodetic measurements of deformation at Long Valley caldera provide two examples of the application of principal component analysis. A 40-line trilateration network surrounding the caldera was surveyed in midsummer 1983, 1984, 1985, 1986, and 1987. Principal component analysis indicates that the observed deformation can be represented by a single coherent source. The time dependence for that source displays a rapid rate of deformation in 1983–1984 followed by less rapid but uniform rate in the 1984–1987 interval. The spatial factor seems consistent with expansion of a magma chamber beneath the caldera plus some shallow right-lateral slip on a vertical fault in the south moat of the caldera. An independent principal component analysis of the 1982, 1983, 1984, 1985, 1986, and 1987 leveling across the caldera requires two self-coherent sources to explain the deformation. The deformation pattern produced by the larger of these two sources appears to be roughly consistent with that found from the trilateration data. The deformation due to the second source is a nearly uniform tilt in the uplift profile. Presumably, that tilt is simply an artifact of systematic error in the leveling.

Journal of Geophysical Research Solid Earth↗
USGS2013

Whole-coal versus ash basis in coal geochemistry: a mathematical approach to consistent interpretations

Several standard methods require coal to be ashed prior to geochemical analysis. Researchers, however, are commonly interested in the compositional nature of the whole-coal, not its ash. Coal geochemical data for any given sample can, therefore, be reported in the ash basis on which it is analyzed or the whole-coal basis to which the ash basis data are back calculated. Basic univariate (mean, variance, distribution, etc.) and bivariate (correlation coefficients, etc.) measures of the same suite of samples can be very different depending which reporting basis the researcher uses. These differences are not real, but an artifact resulting from the compositional nature of most geochemical data. The technical term for this artifact is subcompositional incoherence. Since compositional data are forced to a constant sum, such as 100% or 1,000,000 ppm, they possess curvilinear properties which make the Euclidean principles on which most statistical tests rely inappropriate, leading to erroneous results. Applying the isometric logratio (ilr) transformation to compositional data allows them to be represented in Euclidean space and evaluated using traditional tests without fear of producing mathematically inconsistent results. When applied to coal geochemical data, the issues related to differences between the two reporting bases are resolved as demonstrated in this paper using major oxide and trace metal data from the Pennsylvanian-age Pond Creek coal of eastern Kentucky, USA. Following ilr transformation, univariate statistics, such as mean and variance, still differ between the ash basis and whole-coal basis, but in predictable and calculated manners. Further, the stability between two different components, a bivariate measure, is identical, regardless of the reporting basis. The application of ilr transformations addresses both the erroneous results of Euclidean-based measurements on compositional data as well as the inconsistencies observed on coal geochemical data reported on different bases.

International Journal of Coal Geology↗
USGS2019

Size selectivity of sampling gears used to sample Kokanee

Kokanee Oncorhynchus nerka provide valued recreational fisheries and also serve as a prey resource for economically, socially, and ecologically important fishes. As such, management of kokanee is a major focus of natural resource agencies. Kokanee are typically monitored using midwater trawls, but the interpretation of data collected using midwater trawls is difficult due to the unknown size selectivity of the gear. We sought to assess the length selectivity of midwater trawls by comparing estimates obtained from midwater trawls with estimates obtained from gill nets adjusted for size selectivity. Experimental curtain gill nets and midwater trawls were used in conjunction to sample kokanee in seven lentic systems in Idaho. The size selectivity of gill nets was estimated by accounting for the probability of encounter and the probability of retention. Estimates of size selectivity were then used to adjust the length distribution of fish sampled in gill nets. The adjusted length distribution of fish sampled in gill nets was compared with estimates obtained from midwater trawls to identify potential size selectivity of midwater trawls. A pattern of size selectivity was apparent for both sampling techniques. The average length of kokanee sampled with midwater trawls was 111 mm; whereas, kokanee sampled with gill nets had a mean length of 235 mm. Our results suggest experimental gill nets are useful for common sampling of kokanee (e.g., trend monitoring) because the gear is less size selective than midwater trawls and is adjustable for size selectivity. However, midwater trawls are likely the best gear for addressing questions associated with early life history. Overall, our results provide a better understanding of gill-net and midwater trawl selectivity and ultimately improve the ability to sample and manage the species.

North American Journal of Fisheries Management↗
USGS2003

Biodiversity changes in Cretaceous palynofloras of eastern Asia and western North America

Palynology has great potential for providing comparative data and interpretations about changes in biodiversity during the Cretaceous Period. This is especially true for both eastern Asia and western North America because of strong floristic similarities that existed between these regions during Cretaceous time. Also, because palynomorphs of terrestrial origin can be deposited in offshore as well as terrestrial environments, significant potential exists for marine-to-continental palynostratigraphic correlations in both regions. Palynological biostratigraphy can improve the geologic dating of changes in biodiversity. During the Early Cretaceous, eastern Asia and western North America lay within the Cerebropollenites palynofloral province, a circumpolar phytogeographic zone characterized by distinctive palynological assemblages. During most of the Late Cretaceous, these regions lay within the palynofloristically unique Aquilapollenites Province, which was more restricted geographically than the Cerebropollenites Province. The most important development during Cretaceous time that is reflected in palynological assemblages was the rise of the angiosperms as the numerically and ecologically dominant forms of vegetation. The most striking short-term palynofloral event in the two regions was the sudden disappearance of species of Aquilapollenites and associated genera at the Cretaceous-Tertiary (K/T) boundary. Both of these occurrences produced major changes in biodiversity in the terrestrial realm. Geologic research in International Geological Correlation Program Project 434 can benefit from applications of palynostratigraphy. Palynologic research within Project 434 could include development of a comprehensive palynostratigraphic zonation for the Cretaceous, the definition of regional palynostratigraphic datums, and investigation of the record of floral change at the K/T boundary. ?? 2002 Elsevier Science Ltd. All rights reserved.

Journal of Asian Earth Sciences↗
USGS2013

Ambient seismic noise interferometry in Hawai'i reveals long-range observability of volcanic tremor

The use of seismic noise interferometry to retrieve Green's functions and the analysis of volcanic tremor are both useful in studying volcano dynamics. Whereas seismic noise interferometry allows long-range extraction of interpretable signals from a relatively weak noise wavefield, the characterization of volcanic tremor often requires a dense seismic array close to the source. We here show that standard processing of seismic noise interferometry yields volcanic tremor signals observable over large distances exceeding 50 km. Our study comprises 2.5 yr of data from the U.S. Geological Survey Hawaiian Volcano Observatory short period seismic network. Examining more than 700 station pairs, we find anomalous and temporally coherent signals that obscure the Green's functions. The time windows and frequency bands of these anomalous signals correspond well with the characteristics of previously studied volcanic tremor sources at Pu'u 'Ō'ō and Halema'uma'u craters. We use the derived noise cross-correlation functions to perform a grid-search for source location, confirming that these signals are surface waves originating from the known tremor sources. A grid-search with only distant stations verifies that useful tremor signals can indeed be recovered far from the source. Our results suggest that the specific data processing in seismic noise interferometry—typically used for Green's function retrieval—can aid in the study of both the wavefield and source location of volcanic tremor over large distances. In view of using the derived Green's functions to image heterogeneity and study temporal velocity changes at volcanic regions, however, our results illustrate how care should be taken when contamination by tremor may be present.

Hawai'i↗
USGS2006

Characterization and petrologic interpretation of olivine-rich basalts at Gusev Crater, Mars

Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesium and chromium-magnesium ratios. Gusev basalts and shergottites appear to have formed from primitive magmas produced by melting an undepleted mantle at depth and erupted without significant fractionation. However, apparent differences between Gusev rocks and shergottites in their ages, plagioclase abundances, and volatile contents preclude direct correlation. Orbital determinations of global olivine distribution and compositions by thermal emission spectroscopy suggest that olivine-rich rocks may be widespread. Because weathering under acidic conditions preferentially attacks olivine and disguises such rocks beneath alteration rinds, picritic basalts formed from primitive magmas may even be a common component of the Martian crust formed during ancient and recent times.

Journal of Geophysical Research E: Planets↗
USGS2002

Scaup migration patterns in North Dakota relative to temperatures and water conditions

Greater ( Aythya marila ) and lesser scaup ( A. affinis ) have protracted spring migrations. Migrants may still be present on southern breeding areas when the annual Waterfowl Breeding Population and Habitat Surveys (WBPHS) are being conducted. Understanding factors affecting the chronology and rate of spring migration is important for the interpretation of data from annual population surveys. We describe the general temporal pattern of scaup numbers in south-central North Dakota in spring, examine the relationships between scaup numbers and measures of local water conditions and spring temperatures, and assess timing of the WBPHS relative to numbers of scaup occurring in the study area in late May. Scaup were counted weekly on a 95-km, 400-m-wide transect from late March through May, 1957-1999. Average numbers of scaup per count were positively associated with numbers of seasonal, semipermanent, and total ponds. Average minimum daily ambient temperatures showed a trend of increasing temperatures over the 43 years, and dates of peak scaup counts became progressively earlier. Weeks of early migration usually had higher temperatures than weeks of delayed migration. The relationship between temperature and timing of migration was strongest during the second and third weeks of April, which is A# 1 week before numbers peak (median date = 19 Apr). Trends in sex and pair ratios were not consistent among years. Counts in late May-early June indicated considerable annual variability in the magnitude of late migrants. Scaup numbers during this period seemed to stabilize in only 5 of the 19 years when 2 or more surveys were conducted after the WBPHS. These findings corroborate concerns regarding the accuracy of the WBPHS for representing breeding populations of scaup and the possibility of double-counting scaup in some years.

North Dakota↗
USGS1992

Ground water chemistry and geochemical modeling of water-rock interactions at the Osamu Utsumi mine and the Morro do Ferro analogue study sites, Poços de Caldas, Minas Gerais, Brazil

Surface and ground waters, collected over a period of three years from the Osamu Utsumi uranium mine and the Morro do Ferro thorium/rare-earth element (Th/REE) deposits, were analyzed and interpreted to identify the major hydrogeochemical processes. These results provided information on the current geochemical evolution of ground waters for two study sites within the Poços de Caldas Natural Analogue Project. The ground waters are a K–Fe–SO 4 –F type, a highly unusual composition related to intense weathering of a hydrothermally altered and mineralized complex of phonolites. Tritium and stable isotope data indicate that ground waters are of meteoric origin and are not affected significantly by evaporation or water–rock interactions. Recharging ground waters at both study sites demonstrate water of less than about 35 years in age, whereas deeper, more evolved ground waters are below 1 TU but still contain in most cases detectable tritium. These deeper ground waters may be interpreted as being of 35 to 60 or more years in age, resulting mainly from an admixture of younger with older ground waters and/or indicating the influence of subsurface produced tritium. Geochemical processes involving water–rock–gas interactions have been modeled using ground water compositions, mineralogic data, ion plots and computations of speciation, non-thermodynamic mass balance and thermodynamic mass transfer. The geochemical reaction models can reproduce the water chemistry and mineral occurrences and they were validated by comparing the results of thermodynamic mass transfer calculations (using the PHREEQE program, Parkhurst et al., 1980). The results from the geochemical reaction models reveal that the dominant processes are production of CO 2 in the soil zone through aerobic decay of organic matter, dissolution of fluorite, calcite, K-feldspar, albite, chlorite and manganese oxides, oxidation of pyrite and sphalerite, and precipitation of ferric oxides, silica and kaolinite. Gibbsite precipitation can be modeled for the shallow (recharge) water chemistry at Morro do Ferro, consistent with known mineralogy. Recharge waters are undersaturated with respect to barite and discharging waters and deeper ground waters are saturated to supersaturated with respect to barite demonstrating a strong solubility control. Strontium isotope data demonstrate that sources other than calcium-bearing minerals are required to account for the dissolved strontium in the ground waters. These may include K-feldspar, smectite–chlorite mixed-layer clays and goyazite [SrAl 3 (PO 4 ) 2 (OH) 5 • H 2 O]. 1992.

Journal of Geochemical Exploration↗
USGS2007

Ovarian follicle dynamics of female Greater Scaup during egg production

Studies of female waterfowl nutrient reserve use during egg production require a precise understanding of ovarian follicle dynamics to correctly interpret breeding status, and, therefore, derive proper inference. Concerns over numerical declines of North American scaup have increased the need to better understand the role of female condition in reproductive performance. We quantified ovarian follicle dynamics of female Greater Scaup ( Aythya marila ) breeding on the Yukon–Kuskokwim Delta, Alaska, using a method that accounts for within day variation in follicle size. We considered several models for describing changes in follicle growth with the best supported model estimating the duration of rapid follicle growth (RFG) to be 5.20 ± 0.52 days (±95% confidence intervals) for each developing follicle. Average diameter and dry mass of preovulatory follicles were estimated to be 9.36 mm and 0.26 g, respectively, at the onset of RFG, and these follicle characteristics were 41.47 mm and 15.57 g, respectively, at ovulation. The average diameter of postovulatory follicles immediately following ovulation was estimated to be 17.35 mm, regressing quickly over several days. In addition, we derived predictive equations using diameter and dry mass to estimate the number of days before, and after, ovulation for pre- and postovulatory follicles, as well as an equation to estimate dry mass of damaged follicles. Our results allow precise definition of RFG and nest initiation dates, clutch size, and the daily energetic and nutritional demands of egg production at the individual level. This study provides the necessary foundation for additional work on Greater Scaup reproductive energetics and physiology, and offers an approach for quantifying ovarian follicle dynamics in other species.

Journal of Field Ornithology↗
USGS2019

National Gas Hydrate Program expedition 02: Identification of gas hydrate prospects in the Krishna-Godavari Basin, offshore India

After completing the first expedition of India's National Gas Hydrate Program (NGHP-01) in 2006, it was concluded that for the next expedition (National Gas Hydrate Program 02; NGHP-02), a new drill site review effort should focus on identifying potential deep-water offshore gas hydrate accumulations in sand dominated depositional environments. Therefore, geological and geophysical data analysis and 3D seismic data interpretation along with associated seismic modeling were carried out in three areas of the Krishna-Godavari Basin: Areas B, C, and E. Conventional petroleum exploration approaches of seismic amplitude evaluation were adapted to prospect for potential sand-rich depositional systems within the gas hydrate stability zone. Subsequently, these prospective areas were further assessed through the geological and geophysical evaluation of depositional setting, gas sources, and gas migration pathways. In Area B, prospecting focused on a large anticlinal structure with a prominent bottom-simulating reflector and several key horizons that indicated evidence for potential sand-hosted hydrate occurrences. In Area C, the prospects were distributed throughout various settings within a very large deep-water channel-levee-fan system with complex indications of potential gas hydrate occurrence in sand-prone seismic facies. In Area E, prospects were associated with high amplitude events within inferred channel-levee sequences. Based on the pre-expedition/onboard drill-site evaluation, the 22 most promising sites in the Krishna-Godavari Basin were identified and prioritized to investigate and delineate a total of 17 identified gas hydrate prospects. This paper describes the geo-scientific studies carried out prior to NGHP-02 for site identification, evaluation and prioritization. An important outcome of this study is the identification of two potentially producible gas hydrate systems inferred to host significant quantity of gas hydrate in stratigraphic-structural traps.

Journal of Marine and Petroleum Geology↗
USGS1994

Geochemistry of the 1989-1990 eruption of redoubt volcano: Part I. Whole-rock major- and trace-element chemistry

The 1989-1990 eruption of Redoubt Volcano produced medium-K calc-alkaline andesite and dacite of limited compositional range (58.2-63.4% SiO2) and entrained quenched andesitic inclusions (55% SiO2) which bear chemical similarities to the rest of the ejecta. The earliest (December 15) magmas are pumiceous, often compositionally banded, and the majority is relatively mafic (< 59% SiO2). The most silicic magmas of the eruption are the late December to early January domes (up to 63.4% SiO2). Subsequent magmas formed domes and rare pumices which converge on 60% SiO2. Chemical variations among ejecta comprise tight, linear, two-component arrays for all elements for which the analytical uncertainty is much less than the compositional range. The two-component arrays are interpreted as mixing arrays between unrelated magmas because several of the arrays are at steep angles to the normal liquid line of descent. Additionally, the felsic endmember cannot be easily related to the mafic endmember by normal high-temperature igneous processes (e.g., the silicic endmember has higher Zr yet lower Hf than the mafic endmember). Also relative enrichments of highly incompatible elements are dramatically different across the arrays. The mixing event must have preceded eruption by a significant, yet unspecified amount of time because groundmass glass compositions are homogeneous for all post-December samples (Swanson et al., 1994-this volume), in spite of the whole-rock chemical diversity. This implies time for additional crystallization after the mixing event. Swanson et al. (1994-this volume) discuss evidence for a potentially different mixing event recorded only in December 15 magmas. Cognate cumulate xenoliths composed of pl+cpx+opx+hb+mt+melt were recovered from January and April deposits. These blocks differ from local batholithic country rock in their low concentrations of incompatible elements (e.g., Rb < 5 ppm vs 20-90 ppm, Ba < 150 ppm vs 300-2000 ppm) and low SiO2 (< 50 wt.% vs > 60 wt.%). They have Mg, Cr, Ni, Sc, and V contents higher than the andesites, but lower than Redoubt basalts and basaltic andesites. Thus, they may be crystallization products of andesites, but do not represent the cumulate residue of basalt fractionation. The xenoliths were probably derived from a shallow or intermediate crustal chamber. ?? 1994.

Journal of Volcanology and Geothermal Research↗