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At least 361 records · Page 20Linked to original sources

USGS2008

Exponential decline of aftershocks of the M7.9 1868 great Kau earthquake, Hawaii, through the 20th century

The remarkable catalog of Hawaiian earthquakes going back to the 1820s is based on missionary diaries, newspaper accounts, and instrumental records and spans the great M 7.9 Kau earthquake of April 1868 and its aftershock sequence. The earthquake record since 1868 defines a smooth curve complete to M 5.2 of the declining rate into the 21st century, after five short volcanic swarms are removed. A single aftershock curve fits the earthquake record, even with numerous M 6 and 7 main shocks and eruptions. The timing of some moderate earthquakes may be controlled by magmatic stresses, but their overall long‐term rate reflects one of aftershocks of the Kau earthquake. The 1868 earthquake is, therefore, the largest and most controlling stress event in the 19th and 20th centuries. We fit both the modified Omori (power law) and stretched exponential (SE) functions to the earthquakes. We found that the modified Omori law is a good fit to the M ≥ 5.2 earthquake rate for the first 10 years or so and the more rapidly declining SE function fits better thereafter, as supported by three statistical tests. The switch to exponential decay suggests that a possible change in aftershock physics may occur from rate and state fault friction, with no change in the stress rate, to viscoelastic stress relaxation. The 61‐year exponential decay constant is at the upper end of the range of geodetic relaxation times seen after other global earthquakes. Modeling deformation in Hawaii is beyond the scope of this paper, but a simple interpretation of the decay suggests an effective viscosity of 10 19 to 10 20 Pa s pertains in the volcanic spreading of Hawaii's flanks. The rapid decline in earthquake rate poses questions for seismic hazard estimates in an area that is cited as one of the most hazardous in the United States.

Hawaii↗

USGS2021

Temporal seismic velocity variations: Recovery following from the 2019 Mw 7.1 Ridgecrest, California earthquake

We investigated seismic velocity changes ( dv / v ) associated with the 2019 Ridgecrest earthquake sequence with high‐frequency autocorrelations of ambient seismic noise data. Daily autocorrelation functions were computed for the entirety of 2019 and the first quarter of 2020 for broadband stations within the region, including the temporary broadband stations installed during the aftershock deployment. Travel time shifts in the daily autocorrelation functions, relative to the mean autocorrelation waveform, were computed to produce dv / v time series, which are sensitive to the evolving material properties of the shallow crust surrounding the Ridgecrest fault zone (RFZ). A short‐term velocity drop follows the M w 7.1 earthquake at stations in the vicinity of the rupture surface, while those greater than 50 km away showed no such drop. The maximum, absolute changes in seismic velocity are proportional to the logarithm of distance from the fault rupture and to the peak dynamic strain experienced during the earthquake. Near the areas of the highest coseismic slip within the RFZ, seismic velocities recovered over 3 months. However, in the vicinity of the nearby Garlock fault, where triggered slip manifested, and north of the RFZ, seismic velocities recovered within a month. We interpret the seismic velocity changes and their recovery to be largely due to changes in the physical properties of the shallow crust, such as fault zone damage recovery caused by the earthquake rupture process and in response to the large dynamic stresses of passing seismic waves from the mainshock.

California↗

USGS2025

Environmental DNA metabarcoding for monitoring fish biodiversity in remote lakes

Objective Environmental DNA (eDNA) metabarcoding provides an attractive option for monitoring biodiversity in remote freshwater ecosystems, where the deployment of conventional gears encounters major logistical constraints. We evaluated eDNA metabarcoding for monitoring fish communities and early detection of nonnative species in three remote lakes on Isle Royale, Michigan, USA. Methods At each of the three lakes, we collected surface, midwater, and lake bottom samples from 10 sites during spring and fall sampling events. We performed metabarcoding on all the water samples, targeting the 12S region of all fish species. Results Despite a relatively small sample size ( N = 60 samples per lake across two visits; 10 locations with three depths per location), we recovered 70% of all the species that were previously observed using conventional methods. We recovered several detections of putative Cisco Coregonus artedi , a vulnerable coldwater species, providing evidence that Cisco have persisted in these lakes. However, we found disentangling likely false positives from rare species challenging, which we overcame by employing multiple types of detection thresholds and a species-specific quantitative PCR assay. Conclusions Although we were able to successfully characterize the fish communities using eDNA metabarcoding, more attention needs to be given to the detection thresholds and communication protocols that provide guidance in interpretating new eDNA detections and using eDNA detections to inform management decisions. Although eDNA metabarcoding has limitations that should be accounted for at the outset of the project, the ease of sample collection makes eDNA metabarcoding an option for monitoring freshwater biodiversity in remote systems.

Michigan↗

USGS2016

Blood serum chemistry of wild Alaskan Black-capped Chickadees ( Poecile atricapillus ) with avian keratin disorder

We measured serum chemistries in wild Black-capped Chickadees ( Poecile atricapillus ) from Alaska to test for potential differences associated with beak deformities characteristic of avian keratin disorder. Lower uric acid in affected birds was the only difference detected between groups, although sample sizes were small. This difference could be associated with fasting or malnutrition in birds with beak deformities, but it is challenging to interpret its biologic significance without reference values. Black-capped Chickadees had high levels of aspartate aminotransferase, lactate dehydrogenase, and creatine kinase relative to reference values for companion birds. However, all serum chemistry parameters from our study were within the range of values reported from other apparently healthy wild-caught birds.

Journal of Wildlife Diseases↗

USGS2023

Grizzly bear responses to restrictions of recreation in Yellowstone National Park

Avoiding humans will be more difficult and energetically costly for animals as outdoor recreation increases and people venture farther into wildland areas that provide high-quality habitat for wildlife. Restricting human access can be an attractive management tool to mitigate effects of human recreation activities on wildlife; however, the efficacy of such measures is rarely assessed. In 1982, Yellowstone National Park identified areas important to grizzly bears ( Ursus arctos ) to help protect critical grizzly bear habitat and reduce the likelihood of human injuries by bears. Referred to as bear management areas (BMAs), human access is restricted in these areas for 2–8 months each year, with timing and type of restrictions varying by area. We examined 2 datasets to evaluate grizzly bear selection of BMAs and differences of bear density in BMAs and non-BMAs. First, we used 17 years of recent global positioning system telemetry data for grizzly bears to assess their selection of BMAs during periods when human access was allowed, and when access was restricted. We used step-selection functions to test the hypothesis that bears spend time in places that allow them to avoid people and select quality food sources. There was support that grizzly bears differentially select for BMAs regardless of whether human access was restricted at the time, compared with areas outside BMAs, and that selection changed with sex and season. Only males during the summer and hyperphagic seasons changed their selection of BMAs based on whether access restrictions were in place, and overall, male bears preferred unrestricted BMAs (BMAs without restrictions in place). Females preferentially selected BMAs regardless of whether the area had access restrictions in place only during the mating season. Individuals varied widely in their preference for BMAs and access restrictions. Bears likely choose to spend time in BMAs based on available food resources rather than restrictions to human access. Supporting this interpretation, our analyses indicated that a greater proportion of BMA in an area was associated with higher densities of grizzly bear. Thus, restrictions to human access likely help reduce the potential for human–bear interactions, accomplishing one of the original objectives for establishing the BMAs.

Idaho, Montana, Wyoming↗

USGS2009

Interbasin flow in the Great Basin with special reference to the southern Funeral Mountains and the source of Furnace Creek springs, Death Valley, California, U.S.

Interbasin flow in the Great Basin has been established by scientific studies during the past century. While not occurring uniformly between all basins, its occurrence is common and is a function of the hydraulic gradient between basins and hydraulic conductivity of the intervening rocks. The Furnace Creek springs in Death Valley, California are an example of large volume springs that are widely accepted as being the discharge points of regional interbasin flow. The flow path has been interpreted historically to be through consolidated Paleozoic carbonate rocks in the southern Funeral Mountains. This work reviews the preponderance of evidence supporting the concept of interbasin flow in the Death Valley region and the Great Basin and addresses the conceptual model of pluvial and recent recharge [Nelson, S.T., Anderson, K., Mayo, A.L., 2004. Testing the interbasin flow hypothesis at Death Valley, California. EOS 85, 349; Anderson, K., Nelson, S., Mayo, A., Tingey, D., 2006. Interbasin flow revisited: the contribution of local recharge to high-discharge springs, Death Valley, California. Journal of Hydrology 323, 276-302] as the source of the Furnace Creek springs. We find that there is insufficient modern recharge and insufficient storage potential and permeability within the basin-fill units in the Furnace Creek basin for these to serve as a local aquifer. Further, the lack of high sulfate content in the spring waters argues against significant flow through basin-fill sediments and instead suggests flow through underlying consolidated carbonate rocks. The maximum temperature of the spring discharge appears to require deep circulation through consolidated rocks; the Tertiary basin fill is of insufficient thickness to generate such temperatures as a result of local fluid circulation. Finally, the stable isotope data and chemical mass balance modeling actually support the interbasin flow conceptual model rather than the alternative presented in Nelson et al. [Nelson, S.T., Anderson, K., Mayo, A.L., 2004. Testing the interbasin flow hypothesis at Death Valley, California. EOS 85, 349] and Anderson et al. [Anderson, K., Nelson, S., Mayo, A., Tingey, D., 2006. Interbasin flow revisited: the contribution of local recharge to high-discharge springs, Death Valley, California. Journal of Hydrology 323, 276-302]. In light of these inconsistencies, interbasin flow is the only readily apparent explanation for the large spring discharges at Furnace Creek and, in our view, is the likely explanation for most large volume, low elevation springs in the Great Basin. An understanding of hydrogeologic processes that control the rate and direction of ground-water flow in eastern and central Nevada is necessary component of regional water-resource planning and management of alluvial and bedrock aquifers.

Journal of Hydrology↗

USGS2015

Riverbed clogging associated with a California riverbank filtration system: An assessment of mechanisms and monitoring approaches

An experimental field study was performed to investigate riverbed clogging processes and associated monitoring approaches near a dam-controlled riverbank filtration facility in Northern California. Motivated by previous studies at the site that indicated riverbed clogging plays an important role in the performance of the riverbank filtration system, we investigated the spatiotemporal variability and nature of the clogging. In particular, we investigated whether the clogging was due to abiotic or biotic mechanisms. A secondary aspect of the study was the testing of different methods to monitor riverbed clogging and related processes, such as seepage. Monitoring was conducted using both point-based approaches and spatially extensive geophysical approaches, including: grain-size analysis, temperature sensing, electrical resistivity tomography, seepage meters, microbial analysis, and cryocoring, along two transects. The point monitoring measurements suggested a substantial increase in riverbed biomass (2 orders of magnitude) after the dam was raised compared to the small increase (∼2%) in fine-grained sediment. These changes were concomitant with decreased seepage. The decreased seepage eventually led to the development of an unsaturated zone beneath the riverbed, which further decreased infiltration capacity. Comparison of our time-lapse grain-size and biomass datasets suggested that biotic processes played a greater role in clogging than did abiotic processes. Cryocoring and autonomous temperature loggers were most useful for locally monitoring clogging agents, while electrical resistivity data were useful for interpreting the spatial extent of a pumping-induced unsaturated zone that developed beneath the riverbed after riverbed clogging was initiated. The improved understanding of spatiotemporally variable riverbed clogging and monitoring approaches is expected to be useful for optimizing the riverbank filtration system operations.

Journal of Hydrology↗

USGS2003

Source mechanism of long-period events at Kusatsu-Shirane Volcano, Japan, inferred from waveform inversion of the effective excitation functions

We investigate the source mechanism of long-period (LP) events observed at Kusatsu-Shirane Volcano, Japan, based on waveform inversions of their effective excitation functions. The effective excitation function, which represents the apparent excitation observed at individual receivers, is estimated by applying an autoregressive filter to the LP waveform. Assuming a point source, we apply this method to seven LP events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1-3 Hz. The results of the waveform inversions show dominant volumetric change components accompanied by single force components, common to all the events analyzed, and suggesting a repeated activation of a sub-horizontal crack located 300 m beneath the summit crater lakes. Based on these results, we propose a model of the source process of LP seismicity, in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack. The rapid discharge of fluid causes the collapse of the fluid-filled crack and excites acoustic oscillations of the crack, which produce the characteristic waveforms observed in the LP events. The presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid-filled conduit linking the crack and the base of the crater lake. ?? 2003 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗

USGS2004

Strain accumulation across the Coast Ranges at the latitude of San Francisco, 1994-2000

A 66-monument geodetic array spanning the Coast Ranges near San Francisco has been surveyed more than eight times by GIPS between late 1993 and early 2001. The measured horizontal velocities of the monuments are well represented by uniform, right-lateral, simple shear parallel to N29°W. (The local strike of the San Andreas Fault is ∼N34°W.) The observed areal dilatation rate of 6.9 ± 10.0 nstrain yr −1 (quoted uncertainty is one standard deviation and extension is reckoned positive) is not significantly different from zero, which implies that the observed strain accumulation could be released by strike-slip faulting alone. Our results are consistent with the slip rates assigned by the Working Group on California Earthquake Probabilities [2003] to the principal faults (San Gregorio, San Andreas, Hayward-Rodgers Creek, Calaveras-Concord-Green Valley, and Greenville Faults) cutting across the GPS array. The vector sum of those slip rates is is 39.8 ± 2.6 mm yr −1 N29.8°W ± 2.8°, whereas the motion across the GPS array (breadth 120 km) inferred from the uniform strain rate approximation is 38.7 ± 1.2 mm yr −1 N29.0°W ± 0.9° right-lateral shear and 0.4 ± 0.9 mm yr −1 N61°E ± 0.9° extension. We interpret the near coincidence of these rates and the absence of significant accumulation of areal dilatation to imply that right-lateral slip on the principal faults can release the accumulating strain; major strain release on reverse faults subparallel to the San Andreas Fault within the Coast Ranges is not required.

California↗

USGS2000

Magma mixing, recharge and eruption histories recorded in plagioclase phenocrysts from El Chichón Volcano, Mexico

Consistent core-to-rim decreases of 87 Sr/ 86 Sr ratios and coincident increases in Sr concentrations in plagioclase phenocrysts of varying size (∼1 cm to 2 mm) are reported from samples of the 1982 and pre-1982 (∼200 ka) eruptions of El Chichón Volcano. Maximum 87 Sr/ 86 Sr ratios of ∼0·7054, significantly higher than the whole-rock isotopic ratios (∼0·7040–0·7045), are found in the cores of plagioclase phenocrysts, and minimum 87 Sr/ 86 Sr ratios of ∼0·7039 are found near some of the rims. Plagioclase phenocrysts commonly display abrupt fluctuations in An content (up to 25 mol %) that correspond to well-developed dissolution surfaces. The isotopic, textural and compositional characteristics suggest that these plagioclase phenocrysts grew in a system that was periodically recharged by higher-temperature magma with a lower 87 Sr/ 86 Sr ratio and a higher Sr concentration. Rim 87 Sr/ 86 Sr ratios in plagioclase phenocrysts of rocks from the 200 ka eruption indicate that, at that time, the magma had already attained the lowest recorded 87 Sr/ 86 Sr value of the system (∼0·7039). In contrast, cores from plagioclase phenocrysts of the 1982 eruption, inferred to have grown in the past few thousand years, have the highest recorded 87 Sr/ 86 Sr ratios of the system. Collectively, the Sr isotopic data (for plagioclase and whole rock), disequilibrium textural features of the phenocrysts, known eruption frequencies, and inferred crystal-residence times of the plagioclases are best interpreted in terms of an intermittent magma chamber model. Similar processes, including crustal contamination, magma mixing, periodic recharge by addition of more mafic magma to induce plagioclase disequilibrium (possibly triggering eruption) and subsequent re-equilibration, apparently were operative throughout the 200 ky history of the El Chichón magma system.

Chiapas↗

USGS1968

Aerial estimation of the size of gull breeding colonies

Counts on photographs and visual estimates of the numbers of territorial gulls are usually reliable indicators of the number of gull nests, but single visual estimates are not adequate to measure the number of nests in individual colonies. To properly interpret gull counts requires that several islands with known numbers of nests be photographed to establish the ratio of gulls to nests applicable for a given local census. Visual estimates are adequate to determine total breeding gull numbers by regions. Neither visual estimates nor photography will reliably detect annual changes of less than about 25 percent.

Journal of Wildlife Management↗

USGS1996

Cyclic stressing and seismicity at strongly coupled subduction zones

We use the finite element method to analyze stress variations in and near a strongly coupled subduction zone during an earthquake cycle. Deformation is assumed to be uniform along strike (plane strain on a cross section normal to the trench axis), and periodic earthquake slip is imposed consistent with the long-term rate of plate convergence and degree of coupling. Simulations of stress and displacement rate fields represent periodic fluctuations in time superimposed on an average field. The oceanic plate, descending slab, and continental lithosphere are assumed here to respond elastically to these fluctuations, and the remaining mantle under and between plates is assumed to respond as Maxwell viscoelastic. In the first part of the analysis we find that computed stress fluctuations in space and time are generally consistent with observed earthquake mechanism variations with time since a great thrust event. In particular, trench-normal extensional earthquakes tend to occur early in the earthquake cycle toward the outer rise but occur more abundantly late in the cycle in the subducting slab downdip of the main thrust zone. Compressional earthquakes, when they occur at all, have the opposite pattern. Our results suggest also that the actual timing of extensional outer rise events is controlled by the rheology of the shallow aseismic portion of the thrust interface. The second part of the analysis shows the effects of mantle relaxation on the rate of ground surface deformation during the earthquake cycle. Models without relaxation predict a strong overall compressional strain rate in the continental plate above the main thrust zone, with the strain rate constant between mainshocks. However with significant relaxation present, a localized region of unusually low compressional, or even slightly extensional, strain rate develops along the surface of the continental plate above and somewhat inland from the downdip edge of the locked main thrust zone. The low strain rate starts in the middle or late part of the cycle, depending on position. This result suggests that the negligible or small contraction measured on the Shumagin Islands, Alaska, during 1980 to 1991, may not invalidate an interpretation of that region as being a moderately coupled subduction zone. In contrast, mantle relaxation causes only modest temporal nonuniformity of uplift rates in the overriding plate and of extensional stress rates in the subducting plate, even when the Maxwell time is an order of magnitude less than the recurrence interval.

Journal of Geophysical Research B: Solid Earth↗

USGS2023

Converted-wave reverse time migration imaging in subduction zone settings

We use a newly developed 2-D elastic reverse time migration (RTM) imaging algorithm based on the Helmholtz decomposition to test approaches for imaging the descending slab in subduction zone regions using local earthquake sources. Our elastic RTM method is designed to reconstruct incident and scattered wavefields at depth, isolate constituent P- and S- wave components via Helmholtz decomposition, and evaluate normalized imaging functions that leverage dominant P and S signals. This method allows us to target particular converted-wave scattering geometries, for example incident S to scattered P , which may be expected to have dominant signals in any given data set. The method is intended to be applied to dense seismic array observations that adequately capture both incident and converted wavefields. We draw a direct connection between our imaging functions and the first-order contrasts in shear wave material properties across seismic discontinuities. Through tests on synthetic data using either S → P or P → S conversions, we find that our technique can successfully recover the structure of a subducting slab using data from a dense wide-angle array of surface stations. We also calculate images with a small-aperture array to test the impact of array geometry on image resolution and interpretability. Our results show that our imaging technique is capable of imaging multiple seismic discontinuities at depth, even with a small number of earthquakes, but that limitations arise when a small aperture array is considered. In this case, the presence of artefacts makes it more difficult to determine the location of seismic discontinuities.

Geophysical Journal International↗

USGS2021

Whole‐genome resequencing reveals persistence of forest‐associated mammals in Late Pleistocene refugia along North America’s North Pacific Coast

Aim Numerous glacial refugia have been hypothesized along North America's North Pacific Coast that may have increased divergence of refugial taxa, leading to elevated endemism and subsequently clustered hybrid zones following deglaciation. The locations and community composition of these ice‐free areas remains controversial, but whole‐genome sequences now enable detailed analysis of the demographic and evolutionary histories of refugial taxa. Here, we use genomic data to test spatial and temporal processes of diversification among martens with respect to the Coastal Refugium Hypothesis, to understand the role of climate cycling in shaping diversity across complex landscapes. Location North America and North Pacific Coast archipelagos. Taxon North American martens ( Martes ). Methods Short‐read whole‐genome resequencing data were generated for 11 martens: four M. americana , four M. caurina , two hybrids, and one outgroup ( Martes zibellina ). Sampling was representative of known genetic clades within New World martens, including sampling within insular and continental hybrid zones and along the North Pacific Coast (five island populations). ADMIXTURE , F‐statistics, and D ‐statistics (ABBA‐BABA) were used to identify introgression and infer directionality. Heterozygosity densities, estimated via PSMC, were used to characterize historical demography at and below the species level to infer refugial and colonization processes. Results Forest‐associated Pacific martens ( M. caurina ) are divided into distinct insular and continental clades consistent with the Coastal Refugium Hypothesis. There was no evidence of introgression on islands that received historical translocations of American pine martens ( M. americana ), but introgression was detected in two active zones of secondary contact: one insular and one continental. Only early‐generational hybrids were identified across multiple hybrid zones, a pattern consistent with potential genetic swamping of M. caurina by M. americana . Main conclusions Despite an incomplete fossil record, genomic evidence supports the persistence of forest‐associated martens, likely the insular Pacific marten lineage, along the western edges of the Alexander Archipelago during the Last Glacial Maximum. This discovery informs our understanding of refugial paleoenvironments, critical to interpreting refugial timing, duration, and community composition. Genomic reevaluations of other taxa along North America's North Pacific Coast may yield new and deeper perspectives on the history of refugial forest communities and the role of dynamic climate shifts in shaping high‐latitude diversity across complex insular landscapes.

Alaska, British Columbia, California, Oregon, Wash↗

USGS2016

Automatic delineation of seacliff limits using lidar-derived high-resolution DEMs in southern California

Seacliff erosion is a serious hazard with implications for coastal management and is often estimated using successive hand-digitized cliff tops or bases (toe) to assess cliff retreat. Even if efforts are made to standardize manual digitizing and eliminate subjectivity, the delineation of cliffs is time-consuming and depends on the analyst's interpretation. An automatic procedure is proposed to extract cliff edges from high-resolution lidar-derived bare-earth digital elevation models, generalized coastal shoreline vectors, and approximate measurements of distance between the shoreline and the cliff top. The method generates orthogonal transects and profiles with a minimum spacing equal to the digital elevation model resolution. The method also extracts the xyz coordinates for each profile for the cliff top and toe, as well as second major inflections along the profile. Over 75% of the automated cliff top points and 78% of the toe automated points are within 95% confidence interval of the hand-digitized top and toe lines, and over 79% of the digitized top points and 84% of the digitized toe points are within the 95% confidence interval of the automated top and toe lines along a stretch of coast in Del Mar, California. Outlier errors were caused by either the failure to remove all vegetation from the bare-earth digital elevation model or errors of interpretation. The automatic method was further applied between Point Conception and Los Angeles Harbor, California. This automatic method is repeatable, takes advantage of detailed topographic information within high-resolution digital elevation models, and is more efficient than hand-digitizing.

California↗

USGS1995

Age-class separation of blue-winged ducks

Accurate determination of age is of fundamental importance to population and life history studies of waterfowl and their management. Therefore, we developed quantitative methods that separate adult and immature blue-winged teal ( Anas discors ), cinnamon teal ( A. cyanoptera ), and northern shovelers ( A. clypeata ) during spring and summer. To assess suitability of discriminant models using 9 remigial measurements, we compared model performance (% agreement between predicted age and age assigned to birds on the basis of definitive cloacal or rectral feather characteristics) in different flyways (Mississippi and Pacific) and between years (1990-91 and 1991-92). We also applied age-classification models to wings obtained from U.S. Fish and Wildlife Service harvest surveys in the Mississippi and Central-Pacific flyways (wing-bees) for which age had been determined using qualitative characteristics (i.e., remigial markings, shape, or wear). Except for male northern shovelers, models correctly aged lt 90% (range 70-86%) of blue-winged ducks. Model performance varied among species and differed between sexes and years. Proportions of individuals that were correctly aged were greater for males (range 63-86%) than females (range 39-69%). Models for northern shovelers performed better in flyway comparisons within year (1991-92, La. model applied to Calif. birds, and Calif. model applied to La. birds: 90 and 94% for M, and 89 and 76% for F, respectively) than in annual comparisons within the Mississippi Flyway (1991-92 model applied to 1990-91 data: 79% for M, 50% for F). Exclusion of measurements that varied by flyway or year did not improve model performance. Quantitative methods appear to be of limited value for age separation of female blue-winged ducks. Close agreement between predicted age and age assigned to wings from the wing-bees suggests that qualitative and quantitative methods may be equally accurate for age separation of male blue-winged ducks. We interpret annual and flyway differences in remigial measurements and reduced performance of age classification models as evidence of high variability in size of blue-winged ducks' remiges. Variability in remigial size of these and other small-bodied waterfowl may be related to nutrition during molt.

Louisiana↗

USGS1977

A comparison of some analytical techniques for determining uranium, thorium, and potassium in granitic rocks

Geochemical exploration for uranium requires accurate and precise determinations of low-level concentrations. We have used seven different techniques and four different treatments of the fluorometric method to analyze for uranium in granitic rocks. In addition we have used four analytical techniques for thorium and three analytical techniques for potassium, two elements that are commonly present in anomalous amounts within uranium provinces. Our results show that commonly used techniques for thorium and potassium determinations are both adequately precise and accurate, but that many techniques used for uranium determinations lack the necessary precision or accuracy for complete geochemical prospecting. We suggest that a combination of delayed-neutron determinations for uranium and γ -ray spectrometric analyses for radium equivalent uranium, thorium, and potassium provides the best data base for geochemical exploration for uranium. If more detailed interpretations are desired, the combination of γ -ray spectrometry and α -spectrometry may be best. Carefully done fluorometric analyses should be adequate for water, ore, mineralized rock, and other applications where high precision and accuracy are not required.

Journal of Research of the U.S. Geological Survey↗

USGS1997

Organic geochemical study of sequences overlying coal seams; example from the Mansfield Formation (Lower Pennsylvanian), Indiana

Roof successions above two coal seams from the Mansfield Formation (Lower Pennsylvanian) in the Indiana portion of the Illinois Basin have been studied with regard to sedimentary structures, organic petrology and organic geochemistry. The succession above the Blue Creek Member of the Mansfield Formation is typical of the lithologies covering low-sulphur coals (< 1%) in the area studied, whereas the succession above the unnamed Mansfield coal is typical of high-sulphur coals (>2.%). The transgressive-regressive packages above both seams reflect the periodic inundation of coastal mires by tidal flats and creeks as inferred from bioturbation and sedimentary structures such as tidal rhythmites and clay-draped ripple bedforms. Geochemistry and petrology of organic facies above the Blue Creek coal suggest that tidal flats formed inland in fresh-water environments. These overlying fresh water sediments prevented saline waters from invading the peat, contributing to low-sulphur content in the coal. Above the unnamed coal, trace fossils and geochemical and petrological characteristics of organic facies suggest more unrestricted seaward depositional environment. The absence of saline or typically marine biomarkers above this coal is interpreted as evidence of very short periods of marine transgression, as there was not enough time for establishment of the precursor organisms for marine biomarkers. However, sufficient time passed to raise SO 4 2− concentration in pore waters, resulting in the formation of authigenic pyrite and sulphur incorparation into organic matter.

International Journal of Coal Geology↗