SEARCH · USGS Science

Results for “Journal of Basin Research”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources

USGS2014

Improving groundwater predictions utilizing seasonal precipitation forecasts from general circulation models forced with sea surface temperature forecasts

Recent studies have found a significant association between climatic variability and basin hydroclimatology, particularly groundwater levels, over the southeast United States. The research reported in this paper evaluates the potential in developing 6-month-ahead groundwater-level forecasts based on the precipitation forecasts from ECHAM 4.5 General Circulation Model Forced with Sea Surface Temperature forecasts. Ten groundwater wells and nine streamgauges from the USGS Groundwater Climate Response Network and Hydro-Climatic Data Network were selected to represent groundwater and surface water flows, respectively, having minimal anthropogenic influences within the Flint River Basin in Georgia, United States. The writers employ two low-dimensional models [principle component regression (PCR) and canonical correlation analysis (CCA)] for predicting groundwater and streamflow at both seasonal and monthly timescales. Three modeling schemes are considered at the beginning of January to predict winter (January, February, and March) and spring (April, May, and June) streamflow and groundwater for the selected sites within the Flint River Basin. The first scheme (model 1) is a null model and is developed using PCR for every streamflow and groundwater site using previous 3-month observations (October, November, and December) available at that particular site as predictors. Modeling schemes 2 and 3 are developed using PCR and CCA, respectively, to evaluate the role of precipitation forecasts in improving monthly and seasonal groundwater predictions. Modeling scheme 3, which employs a CCA approach, is developed for each site by considering observed groundwater levels from nearby sites as predictands. The performance of these three schemes is evaluated using two metrics (correlation coefficient and relative RMS error) by developing groundwater-level forecasts based on leave-five-out cross-validation. Results from the research reported in this paper show that using precipitation forecasts in climate models improves the ability to predict the interannual variability of winter and spring streamflow and groundwater levels over the basin. However, significant conditional bias exists in all the three modeling schemes, which indicates the need to consider improved modeling schemes as well as the availability of longer time-series of observed hydroclimatic information over the basin.

Georgia↗

USGS2016

The geologic history of Margaritifer basin, Mars

In this study, we investigate the fluvial, sedimentary, and volcanic history of Margaritifer basin and the Uzboi-Ladon-Morava (ULM) outflow channel system. This network of valleys and basins spans more than 8000 km in length, linking the fluvially dissected southern highlands and Argyre Basin with the northern lowlands via Ares Vallis. Compositionally, thermophysically, and morphologically distinct geologic units are identified and are used to place critical relative stratigraphic constraints on the timing of geologic processes in Margaritifer basin. Our analyses show that fluvial activity was separated in time by significant episodes of geologic activity, including the widespread volcanic resurfacing of Margaritifer basin and the formation of chaos terrain. The most recent fluvial activity within Margaritifer basin appears to terminate at a region of chaos terrain, suggesting possible communication between surface and subsurface water reservoirs. We conclude with a discussion of the implications of these observations on our current knowledge of Martian hydrologic evolution in this important region.

Journal of Geophysical Research E: Planets↗

USGS2022

Stream corridor and upland sources of fluvial sediment and phosphorus from a mixed urban-agricultural tributary to the Great Lakes

Like many impaired Great Lakes tributaries, Apple Creek, Wisconsin (119 km 2 ) has Total Maximum Daily Load (TMDL) targets for reducing suspended sediment and total phosphorus by 51.2 % and 64.2 %, respectively. From August 2017 - October 2018, a stream sediment budget and fingerprinting integrated study was conducted to quantify upland and stream corridor sources of suspended sediment and sediment-bound phosphorus. Phosphorus concentrations varied among source groups and fluvial sediments, with higher concentrations among suspended sediment and cropland soils. Eroding streambanks identified in the stream corridor sediment budget accounted for 100 % of the TMDL Soil and Water Assessment Tool (SWAT) suspended sediment load but only 20 % of the total phosphorus load. Fine-grained streambed sediment equated to approximately-three years of modeled suspended sediment load but only one third of total phosphorus load. The two primary sources of fine-grained streambed sediment were streambanks and cropland, with relative streambank contributions increasing with downstream direction and watershed area. The relative proportion of suspended sediment varied by season and streamflow; however, cropland and streambank erosion accounted for 54 % and 23 % of the suspended sediment when weighted by of the proportion for representative streamflow. Urban land was a source in the upper watershed, but the signature was sequestered by a mid-watershed detention basin. Contributions from construction sites were higher in the fall 2018, likely corresponding to increased activity following a wet spring. These integrated techniques helped describe sources, transport, and sinks of fluvial sediment and phosphorus throughout the watershed at a range of spatial and temporal scales.

Wisconsin↗

USGS2010

Source and fate of inorganic solutes in the Gibbon River, Yellowstone National Park, Wyoming, USA: I. Low-flow discharge and major solute chemistry

The Gibbon River in Yellowstone National Park (YNP) is an important natural resource and habitat for fisheries and wildlife. However, the Gibbon River differs from most other mountain rivers because its chemistry is affected by several geothermal sources including Norris Geyser Basin, Chocolate Pots, Gibbon Geyser Basin, Beryl Spring, and Terrace Spring. Norris Geyser Basin is one of the most dynamic geothermal areas in YNP, and the water discharging from Norris is much more acidic (pH 3) than other geothermal basins in the upper-Madison drainage (Gibbon and Firehole Rivers). Water samples and discharge data were obtained from the Gibbon River and its major tributaries near Norris Geyser Basin under the low-flow conditions of September 2006. Surface inflows from Norris Geyser Basin were sampled to identify point sources and to quantify solute loading to the Gibbon River. The source and fate of the major solutes (Ca, Mg, Na, K, SiO 2 , Cl, F, HCO 3 , SO 4 , NO 3 , and NH 4 ) in the Gibbon River were determined in this study and these results may provide an important link in understanding the health of the ecosystem and the behavior of many trace solutes. Norris Geyser Basin is the primary source of Na, K, Cl, SO 4 , and N loads (35–58%) in the Gibbon River. The largest source of HCO 3 and F is in the lower Gibbon River reach. Most of the Ca and Mg originate in the Gibbon River upstream from Norris Geyser Basin. All the major solutes behave conservatively except for NH 4 , which decreased substantially downstream from Gibbon Geyser Basin, and SiO 2 , small amounts of which precipitated on mixing of thermal drainage with the river. As much as 9–14% of the river discharge at the gage is from thermal flows during this period.

Wyoming↗

USGS1996

Geographical distributions of lake trout strains stocked in Lake Ontario

Geographical distributions of lake trout ( Salvelinus namaycush ) stocked at seven locations in U.S. waters and at four locations in Canadian waters of Lake Ontario were determined from fish caught with gill nets in September in 17 areas of U.S. waters and at 10 fixed locations in Canadian waters in 1986–95. For fish of a given strain stocked at a given location, geographical distributions were not different for immature males and immature females or for mature males and mature females. The proportion of total catch at the three locations nearest the stocking location was higher for mature fish than for immature fish in all 24 available comparisons (sexes combined) and was greater for fish stocked as yearlings than for those stocked as fingerlings in all eight comparisons. Mature fish were relatively widely dispersed from stocking locations indicating that their tendency to return to stocking locations for spawning was weak, and there was no appreciable difference in this tendency among strains. Mature lake trout were uniformly distributed among sampling locations, and the strain composition at stocking locations generally reflected the stocking history 5 to 6 years earlier. Few lake trout moved across Lake Ontario between the north and south shores or between the eastern outlet basin and the main lake basin. Limited dispersal from stocking sites supports the concept of stocking different genetic strains in various parts of the lake with the attributes of each strain selected to match environmental conditions in the portion of the lake where it is stocked.

Journal of Great Lakes Research↗

USGS2023

Aquatic carbon export and dynamics in mountain headwater streams of the western U.S.

Mountain headwater streams actively cycle carbon, receiving it from terrestrial landscapes and exporting it through downstream transport and gas exchange with the atmosphere. Although their importance is now widely recognized, aquatic carbon fluxes in headwater streams remain poorly characterized. In this study, aquatic carbon fluxes were measured in 15 mountain headwater streams and were used in a geostatistical analysis to determine how landscape characteristics influence aquatic carbon fluxes. In-stream sensors were used to measure fluorescent dissolved organic matter (fDOM) (a surrogate for dissolved organic carbon (DOC)) at a subset of sites to characterize dynamic responses to hydroclimatic events. Wetlands have a positive influence on aquatic carbon fluxes, whereas perennial snow/ice has the opposite effect, reflecting differences in soil organic matter content in these landscapes. Mean annual temperature (MAT) has a complex influence on DOC, with peak DOC exports in basins with MAT of 0–2°C. Precipitation has a strong positive influence on aquatic carbon fluxes, and declining snowpacks in the western United States may reduce future aquatic carbon exports. fDOM (and by implication DOC) and

Journal of Geophysical Research: Biogeosciences.↗

USGS2012

Superposed local and regional paleostresses: fault-slip analysis of Neogene extensional faulting near coeval caldera complexes, Yucca Flat, Nevada

Numerous reduced stress tensors are computed by multiple inversions of 906 temporally and spatially partitioned fault-slip data from the Yucca Flat region in the southwest Nevada volcanic field to constrain the Neogene paleostress and faulting history and to investigate how the regional tectonic stress field was affected by local caldera magmatism. Perturbed, shallow (<400 m), pre-11 Ma paleostress configurations, determined west and northwest of present (post-11 Ma) Yucca Flat basin, existed during mild extensional faulting and are attributed to superposition of transient caldera-magmatic stresses on the regional stress field. Northwest of Yucca Flat a progressive shift in least principal stress (σ 3 ) directions near known calderas located 5–15 km to the west occurred under a normal-slip stress state during caldera development between about 15 and 13 Ma. A brief (∼0.5 m.y.) change to a strike-slip stress state occurred at about 13 Ma and was accompanied by small-offset, quasi-conjugate strike-slip faulting. This stress state was most distinct, relative to a normal-slip state, near calderas where stress solutions and fault relations indicate closer affinities to a reverse-slip state. Inferred 11.6–11.45 Ma paleostress tensors indicate radial tension associated with either initial caldera collapse or local post-collapse topographic modification of the stress field. Post-11 Ma normal-slip stress tensors are associated with normal- and oblique-slip faults that accommodated subsidence and eastward extension of Yucca Flat basin away from the caldera complexes. These tensors do not indicate stress modifications due to residual caldera-related effects and thus were used to infer post-11 Ma regional stress changes. The stress field has rotated as much as 65° clockwise since 11 Ma during extensional development of Yucca Flat basin, with most of the rotation and extension occurring before about 8.5 Ma. Results suggest that shallow magmatism and caldera development can strongly alter extensional tectonic stress fields, fault patterns, and slip directions in the uppermost crust out to distances of roughly two magma chamber radii away from a magma body.

Journal of Geophysical Research↗

USGS2012

Tertiary basin development and tectonic implications, Whipple Detachment System, Colorado River Extensional Corridor, California and Arizona

Colorado River extensional corridor. In the Mohave Mountains and Aubrey Hills of Arizona and the eastern Whipple Mountains of California near Parker Dam, these deposits comprise four unconformity-bounded sequences composed of locally derived epiclastic and volcanic rocks and the Peach Springs Tuff. The three older sequences represent syntectonic units that were deposited coeval with detachment faulting, and the fourth is interpreted to be postextensional. The sequences are correlated between four fault-bounded regions, which are the remnants of four different depositional basins. Similar sequences can be correlated over broad areas of the extensional corridor despite the general lack of widespread units. The basins developed in about the same positions, relative to each other and to volcanic sources, as they occupy at present. This is shown by gradational changes of pre-Tertiary rock types between regions, systematic variations in the abundance of magmatic units, and correlative volcanic units that occur in two adjacent regions. The basins formed in the early Miocene from segmentation of the upper crust into blocks bounded by high-angle faults that trended both parallel and perpendicular to the direction of extension and which were terminated at middle crustal depths by a low-angle detachment fault. Extreme rotation of one large crustal block, which constitutes the central Mohave Mountains, is recorded by a major unconformity in the lower Miocene section of one basin. Because coeval sections that formed in adjoining basins do not record this rotation, the underlying crustal blocks must have been separated by transfer faults that allowed them to rotate independently. These proposed transfer faults are represented at present by major faults with trends that parallel the direction of extension on the Whipple detachment system.

Arizona, California↗

USGS2026

An integrated mudstone facies classification scheme and revised interpretation of the sedimentologic processes driving carbon burial in the Cenomanian–Turonian Greenhorn Formation, Colorado, U.S.A.

Standardizing facies descriptions has proven key to integrating interpretations of depositional processes and environments from sedimentologic observations with geochemistry data for mudstone lithologies. Because of their fine-grained nature, high degree of compaction, and heterogeneous composition, standardizing methods for mudstone descriptions has proven difficult, but it is critical to formulating meaningful interpretations of the processes that govern the accumulation of organic-rich lithologies and their role in both petroleum systems and the global carbon cycle. In this study, we have developed a modified facies classification scheme for mudstone lithologies that incorporates sedimentologic and compositional observation at the hand-sample and thin-section scales with geochemical measurements, including bulk organic and inorganic geochemistry, to characterize these rocks and their variability more completely for improved interpretations of depositional environments during a low-order sea-level transgression. The facies described in this study are of the Cenomanian–Turonian Greenhorn Formation in the USGS #1 Portland Core drilled in Fremont County, Colorado. Strata of the Greenhorn Formation span Oceanic Anoxic Event 2 (OAE-2) and the preceding interval. Lithologies range from organic-rich argillaceous mudstones with varied sedimentary structures to organic-lean, highly bioturbated limestones. Six facies were identified, each differentiated by varied sedimentary structures and geochemical composition. These facies occur in a predictable stratigraphic stacking pattern that represents a low-order sea-level transgression with interpreted depositional environments ranging from terrigenous-dominated pro-delta and muddy continental shelf at the base of the interval to pelagic offshore marine at the top of the Greenhorn Formation. Though the facies are consistent with previous interpretations of depositional environments at this locale in the Cretaceous Western Interior Seaway during the Greenhorn cyclothem, the sedimentary processes governing the accumulation of organic-rich strata that have defined this interval are significantly revised. Variability in the proximity and intensity of bottom currents driven by storms and geostrophic flows were key to the accumulation of each facies, with significant sediment transport occurring even through deposition in the most oxygen-depleted bottom waters. The methodology and interpretations provided here are now being employed to basin-scale predictions of organic enrichment utilizing calibrated petrophysical methods. The approach and results from this study improve understanding of how organic and inorganic carbon was sequestered during perturbations to the global carbon cycle associated with events such as OAE-2.

Colorado↗

USGS1975

Age of volcanism, intrusion, and mineralization in the Thomas Range, Keg Mountain, and Desert Mountain, western Utah

Twenty-six new age determinations by the fission-track method establish a chronology for volcanism, intrusion, and mineralization in the Thomas Range, Keg Mountain, and Desert Mountain, in western Utah. The fission-track ages confirm D. R. Shawe's three-fold classification of igneous rocks. The oldest group of rocks consists of flows, agglomerates, and some ash-flow tuffs that were deposited 38-39 m.y. ago. The middle group contains widespread rhyolitic ash-flow tuffs that originated from local volcanic centers 30-32 m.y. ago. A dike emplaced along the probable ring-fracture zone of the Keg caldera about 31 m.y. ago indicates that caldera collapse occurred soon after eruption of ash-flow tuffs. Rocks believed to belong-to the middle group also were intruded by the quartz monzonite of Desert Mountain 27-30 m.y. ago. Little or no igneous activity took place within the next 20 m.y., during which time the region was strongly broken by Basin-and-Range faulting. Rhyolites of the youngest group were extruded 8-10 m.y. ago in the Keg Mountain area and 6-7 m.y. ago in the Thomas Range. The beryllium-fluorite mineralization at Spor Mountain occurred after the rhyolitic volcanism in the Thomas Range.

Utah↗

USGS1978

Origin of two clay-mineral facies of the Potomac Group (Cretaceous) in the Middle Atlantic States

Sedimentary clay that crops out in the coastal plains of New Jersey, Delaware, the part of Maryland north and east of Washington, B.C., and the northeast half of Washington, D.C., in the nonmarine Cretaceous Potomac Group is predominantly kaolinite and illite. In contrast, in part of southeastern Maryland, the southwest half of Washington, D.C., and most of eastern Virginia, Potomac Group clay is predominantly montmorillonite. Kaolinite and illite were probably derived by intense acid weathering of metamorphic and granitic rocks to the west during the Cretaceous and were deposited in a well-drained basin. Montmorillonite was most likely produced by deep weathering of a mainly granitic source. Poor drainage and alkaline surface- and ground-water conditions probably accompanied the production, transportation, deposition, and burial of the montmorillonite. Kaolinization of the montmorillonite is taking place now at the surface in northern Virginia.

Delaware, Maryland, New Jersey, Pennsylvania, Virg↗

USGS2003

The crustal structure from the Altai Mountains to the Altyn Tagh fault, northwest China

[1] We present a new crustal section across northwest China based on a seismic refraction profile and geologic mapping. The 1100‐km‐long section crosses the southern margin of the Chinese Altai Mountains, Junggar Accretional Belt and eastern Junggar basin, easternmost Tianshan Mountains, and easternmost Tarim basin. The crustal velocity structure and Poisson's ratio (σ), which provide a constraint on crustal composition, were determined from P and S wave data. Despite the complex geology, the crustal thickness along the entire profile is nearly uniform at 50 km. The thickest crust (56 km) occurs at the northern end of the profile beneath the Altai Mountains and the thinnest (46 km) crust is beneath the Junggar basin. Beneath surficial sediments, the crust is found to have three layers with P wave velocities ( V p ) of 6.0–6.3, 6.3–6.6, and 6.9–7.0 km/s, respectively. The southern half of the profile, including the eastern Tianshan Mountains and eastern margin of the Tarim basin, shows low P wave velocities and σ = 0.25 to a depth of 30 km, which suggests a quartz‐rich, granitic upper crustal composition. The northern half of the profile below the Altai Mountains and Junggar Accretional Belt has a higher Poisson's ratio of σ = 0.26–0.27 to a depth of 30 km, indicative of an intermediate crustal composition. The entire 1100‐km‐long profile is underlain by a 15–30 km thick high velocity (6.9–7.0 km/s; σ = 0.26–0.28) lower‐crustal layer that we interpret to have a bulk composition of mafic granulite. At the southern end of the profile, a 5‐km‐thick midcrustal low‐velocity layer ( V p = 5.9 km/s, σ = 0.25) underlies the Tianshan and the region to the south, and may be indicative of a near‐horizontal detachment interface. P n velocities are ∼7.7–7.8 km/s between the Tianshan and the Junggar basin, and ∼7.9–8.0 km/s below the Altai Mountains and eastern margin of the Tarim basin. We interpret the consistent three‐layer stratification of the crust to indicate that the crust has undergone partial melting and differentiation after Paleozoic terrane accretion. The thickness (50 km) of the crust appears to be related to compression resulting from the Indo‐Asian collision.

Altai Mountains↗

USGS2011

The Sculptured Hills of the Taurus Highlands: Implications for the relative age of Serenitatis, basin chronologies and the cratering history of the Moon

New images from the Lunar Reconnaissance Orbiter Camera show the distribution and geological relations of the Sculptured Hills, a geological unit widespread in the highlands between the Serenitatis and Crisium basins. The Sculptured Hills shows knobby, undulating, radially textured, and plains-like morphologies and in many places is indistinguishable from the similarly knobby Alpes Formation, a facies of ejecta from the Imbrium basin. The new LROC image data show that the Sculptured Hills in the Taurus highlands is Imbrium ejecta and not directly related to the formation of the Serenitatis basin. This occurrence and the geological relations of this unit suggests that the Apollo 17 impact melts may not be not samples of the Serenitatis basin-forming impact, leaving their provenance undetermined and origin unexplained. If the Apollo 17 melt rocks are Serenitatis impact melt, up to half of the basin and large crater population of the Moon was created within a 30 Ma interval around 3.8 Ga in a global impact "cataclysm." Either interpretation significantly changes our view of the impact process and history of the Earth-Moon system. Copyright 2011 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2012

Discharge rates of fluid and heat by thermal springs of the Cascade Range, Washington, Oregon, and northern California

Fluid and heat discharge rates of thermal springs of the Cascade Range have been determined using the chloride inventory method. Discharge rates of thermal spring groups range from 1 to 120 L s −1 . Most of the fluid (50%) and heat (61%) are discharged from two hot spring groups in northern Oregon. Total discharge from thermal springs in the Cascade Range of California, Oregon, and Washington is about 340 Ls −1 , which corresponds to about 8.2×10 4 kJ s −1 of heat. This does not include hot springs developed on the flanks of Mount St. Helens after the 1980 eruption. The Cascade Range consists of geologically and technically distinct segments; rates of convective heat discharge by the thermal springs in these segments correlate with volcanic rock extrusion rates for the last 2 m. y. In Oregon and Washington, many streams without known thermal or mineral springs in their drainage basins also were sampled for chloride and sodium to detect chemical anomalies that might be associated with previously unknown thermal or mineral waters. Only three chloride anomalies not associated with known thermal or mineral springs were identified in the streams of the Cascade Range.

Journal of Geophysical Research↗

USGS2003

The effects of summer flow augmentation on the migratory behavior and survival of juvenile Snake River fall Chinook salmon. Annual report 2003

This report summarizes results of research activities conducted in 2002 and years previous to aid in the management and recovery of fall chinook salmon Oncorhynchus tshawytscha in the Columbia River basin. The report is divided into self-standing chapters. For detailed summaries, we refer the reader to the abstracts given on the second page of each chapter. The Annual Reporting section includes information provided to fishery managers in-season and post-season, and it contains a detailed summary of life history and survival statistics on wild Snake River fall chinook salmon juveniles for the years 1992-2002. Peer-review publication remains a high priority of this research project, and it insures that our work meets high scientific standards. The Bibliography of Published Journal Articles section provides citations for peer-reviewed papers coauthored by personnel of project 199102900 that were written or published from 1998 to 2003.

Report↗

USGS2006

Shrinking ponds in subarctic Alaska based on 1950-2002 remotely sensed images

Over the past 50 years, Alaska has experienced a warming climate with longer growing seasons, increased potential evapotranspiration, and permafrost warming. Research from the Seward Peninsula and Kenai Peninsula has demonstrated a substantial landscape-level trend in the reduction of surface water and number of closed-basin ponds. We investigated whether this drying trend occurred at nine other regions throughout Alaska. One study region was from the Arctic Coastal Plain where depp permafrost occurs continuously across the landscape. The other eight study regions were from the boreal forest regions where discontinuous permafrost occurs. Mean annual precipitation across the study regions ranged from 100 to over 700 min yr-1. We used remotely sensed imagery from the 1950s to 2002 to inventory over 10,000 closed-basin ponds from at least three periods from this time span. We found a reduction in the area and number of shallow, closed-basin ponds for all boreal regions. In contrast, the Arctic Coastal Plain region had negligible change in the area of closed-basin ponds. Since the 1950s, surface water area of closed-basin ponds included in this analysis decreased by 31 to 4 percent, and the total number of closed-basin ponds surveyed within each study region decreased from 54 to 5 percent. There was a significant increasing trend in annual mean temperature and potential evapotranspiration since the 1950s for all study regions. There was no significant trend in annual precipitation during the same period. The regional trend of shrinking ponds may be due to increased drainage as permafrost warms, or increased evapotranspiration during a warmer and extended growing season. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗

USGS2022

Contemporary spatial extent and environmental drivers of larval coregonine distributions across Lake Ontario

Coregonine fishes are important to Laurentian Great Lakes food webs and fisheries and are central to basin-wide conservation initiatives. In Lake Ontario, binational management objectives include conserving and restoring spawning stocks of cisco ( Coregonus artedi ) and lake whitefish ( C. clupeaformis ), but the spatial extent of contemporary coregonine spawning habitat and the environmental factors regulating early life success are not well characterized. In Spring 2018, we conducted a binational ichthyoplankton assessment to describe the spatial extent of coregonine spawning habitat across Lake Ontario. We then quantified the relative importance of a suite of biophysical variables hypothesized to influence coregonine early life success using generalized additive mixed models and multimodel inference. Between April 10 and May 14, we conducted 1,092 ichthyoplankton tows and captured 2,350+ coregonine larvae across 17 sampling areas, predominantly within embayments. Although 95% of catches were in the eastern basin, coregonine larvae were also found in historical south shore spawning areas. Most coregonine larvae were cisco; <6% were lake whitefish. Observed catches of both species across sampling areas were strongly and similarly associated with ice cover duration, but the importance of site-specific characteristics varied, such as distance to shore and site depth for cisco and lake whitefish, respectively. These results suggest that regional-scale climatic drivers and local environmental habitat characteristics interact to regulate early life stage success. Furthermore, strong regional and cross-species variation in larval distributions emphasize the importance of lake-wide assessments for monitoring both the current eastern basin populations and potential expansions into western Lake Ontario habitats.

Lake Ontario↗

USGS2018

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater – Clan Alpine caldera complex, western Nevada, USA

Geologic mapping, new U-Pb zircon ages, and new and published 40 Ar/ 39 Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4–28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3–24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1–2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of ~ 1500 km 2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500–5000 km 3 .

Nevada↗