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At least 505 records · Page 28Linked to original sources
USGS2022

The geochemical and textural transition between the Reef Package and its hanging wall, Stillwater Complex, Montana, USA

The highest grade Pd-Pt deposit on Earth, the J-M Reef, is hosted in coarse-grained to pegmatoidal cumulates called the Reef Package. Decades of mine development of the J-M Reef have revealed that a distinct discontinuity in rock fabric marks the top of the rock unit that hosts economic-grade sulfide mineralization. Mine geologists refer to this discontinuity as the hanging wall contact. This contact is the top of the Reef Package and is always locatable—either by the change in rock fabric or by distinctive hanging wall textures of silicate minerals—even when the reef sulfide mineralization is absent. This rather subtle textural feature is used reliably by mine geologists to follow the Reef during exploration and mine development. Although some high tenor sulfides (>1000 ppm Pd in 100% sulfide) are found sporadically in the hanging wall cumulates, these accumulations are too small to be economically viable. We present quantitative rock fabric data for four Reef Package and hanging wall intersections collected by electron back-scattered diffraction (EBSD). Plagioclase fabrics in the hanging wall are characterized by low variance in grain sizes and a strong point maximum concentration of (010) and a perpendicular girdle distribution of [100] consistent with an axial B-type fabric. These fabrics are indicative of either compaction of the crystal mush or crystal settling of nucleated crystals, the bulk magma in a chamber. Conversely, the fabrics of the Reef Package show higher variance grain in size distributions and weak to undeveloped preferred orientation of plagioclase crystals that did not undergo significant alignment or textural equilibration of plagioclase grains. The absence of foliation in the Reef Package stands in contrast both to hanging wall fabrics and to other reported EBSD datasets of plagioclase crystals orientations from the Bushveld Complex, the Skaergaard Intrusion, and the Rum Intrusion. Furthermore, plagioclase crystal size distributions for the Reef Package show flatter slopes and convex profiles with fewer crystals at small size fractions indicating the dissolution of small crystals during partial melting and textural coarsening (i.e . Ostwald ripening) and crystal growth. Crystal growth was favored over the nucleation of new crystals during prolonged interaction with a hot infiltrating melt into the resident mush resulting in the coarse-grained textures of the Reef Package cumulates. The hanging wall contact represents a boundary between partially remelted crystal mush of the Reef Package, where sulfide mineralization formed and accumulated, and an overlying essentially barren cumulate pile. The hanging wall cumulates formed following the cessation of footwall erosion and the resumption of crystal accumulation by normal magma chamber processes.

Montana↗
USGS2020

Spatial ecology of closely-related taxa: The case of the little shearwater complex in the North Atlantic Ocean

Seabirds inhabiting vast water masses provide numerous examples where opposing phenomena, such as natal and breeding philopatry vs. vagility have dug cryptic taxonomic boundaries among closely related taxa. The taxonomy of little shearwaters of the North Atlantic Ocean (Little–Audubon’s shearwater complex, Puffinus assimilis – lherminieri ) still remains unclear, and complementary information on non-breeding distributions and at-sea behaviour becomes essential to unravel divergent local adaptations to specific habitats. Using miniaturized light-level geolocators from seven study areas in the North Atlantic, we evaluate the spatial and habitat segregation, estimate the timing of their key life-cycle events and describe the at-sea behaviour of three taxa of these little shearwaters year-round to distinguish ecological patterns and specializations that could ultimately unravel potential lineage divergences. We also assess morphometric data from birds that were breeding at each study area to further discuss potential adaptations to specific habitats. Our results show that, while birds from different taxa segregated in space and habitats, they share ecological plasticity, similar annual phenology and diel foraging behaviour. These ecological inconsistencies, while defining the evolutionary stressors faced by these taxa, do not suggest the existence of three Evolutionary Significant Units. However, they confirm the recent evolutionary divergence among the three little shearwaters of the North Atlantic.

Zoological Journal of the Linnean Society↗
USGS2014

Ocean warming and acidification have complex interactive effects on the dynamics of a marine fungal disease

Diseases threaten the structure and function of marine ecosystems and are contributing to the global decline of coral reefs. We currently lack an understanding of how climate change stressors, such as ocean acidification (OA) and warming, may simultaneously affect coral reef disease dynamics, particularly diseases threatening key reef-building organisms, for example crustose coralline algae (CCA). Here, we use coralline fungal disease (CFD), a previously described CCA disease from the Pacific, to examine these simultaneous effects using both field observations and experimental manipulations. We identify the associated fungus as belonging to the subphylum Ustilaginomycetes and show linear lesion expansion rates on individual hosts can reach 6.5 mm per day. Further, we demonstrate for the first time, to our knowledge, that ocean-warming events could increase the frequency of CFD outbreaks on coral reefs, but that OA-induced lowering of pH may ameliorate outbreaks by slowing lesion expansion rates on individual hosts. Lowered pH may still reduce overall host survivorship, however, by reducing calcification and facilitating fungal bio-erosion. Such complex, interactive effects between simultaneous extrinsic environmental stressors on disease dynamics are important to consider if we are to accurately predict the response of coral reef communities to future climate change.

Proceedings of the Royal Society B↗
USGS2016

Discharge and nutrient transport between lakes in a hydrologically complex area of Voyageurs National Park, Minnesota, 2010-2012

An acoustic Doppler velocity meter (ADVM) was deployed in the narrows between Namakan and Kabetogama Lakes in Voyageurs National Park, Minnesota, from November 3, 2010, through October 3, 2012. The ADVM can account for wind, seiche, and changing flow direction in hydrologically complex areas. The objectives were to (1) estimate discharge and document the direction of water flow, (2) assess whether specific conductance can be used to determine flow direction, and (3) document nutrient and chlorophyll a concentrations at the narrows. The discharge direction through the narrows was seasonal. Water generally flowed out of Kabetogama Lake and into Namakan Lake throughout the ice-covered season. During spring, water flow was generally from Namakan Lake to Kabetogama Lake. During the summer and fall, the water flowed in both directions, affected in part by wind. Water flowed into Namakan Lake 70% of water year 2011 and 56% of water year 2012. Nutrient and chlorophyll a concentrations were highest during the summer months when water-flow direction was unpredictable. The use of an ADVM was effective for assessing flow direction and provided flow direction under ice. The results indicated the eutrophic Kabetogama Lake may have a negative effect on the more pristine Namakan Lake. The results also provide data on the effects of the current water-level management plan and may help determine if adjustments are necessary to help protect the aquatic ecosystem of Voyageurs National Park.

Minnesota↗
USGS2020

The historical context of contemporary climatic adaptation: A case study in the climatically dynamic and environmentally complex southwestern United States

The process of adaptation can be highly dependent upon historical and contemporary factors, especially in environmentally and topographically complex regions affected by Pleistocene glaciations. Here, we investigate Hilaria jamesii (Poaceae), a dryland C 4 graminoid, to test how patterns of adaptive genetic variation are linked to its glacial and post‐glacial history. We show that the species persisted in a single, southern refugium during the last glacial period and subsequently migrated throughout its current distribution concurrent with post‐glacial warming. The species’ putative adaptive genetic variation correlates with climatic gradients (e.g. monsoon precipitation and mean diurnal temperature range) that covary with the species’ probable route of demographic expansion. The short timescale and multiple climatic dimensions of adaptation imply that natural selection acted primarily upon standing genetic variation. These findings suggest that restoration and conservation practices should prioritize the maintenance of standing genetic variation to ensure that species have the capacity to respond to future environmental changes.

Arizona, California Colorado, Nevada, New Mexico, ↗
USGS2020

Forests do not limit bumble bee foraging movements in a montane meadow complex

1. Understanding the roles of habitat fragmentation and resource availability in shaping animal movement are integral for promoting species persistence and conservation. For insects like bumble bees, their movement patterns affect the survival and reproductive potential of their colonies as well as the pollen flow of plant species. However, our understanding of their mobility or the impact of putative barriers in natural environments is limited due to the technical difficulties of studying wild populations. 2. We used genetic mark-recapture to estimate the foraging distance, resource use, and site connectivity of two bumble bee species in a montane meadow complex composed of open meadows within a matrix of forest. 3. There was no evidence that forests or changes in landcover function as barriers to the fine‐scale movement for either species. Substantially greater colony‐specific foraging distances were found for Bombus vosnesenskii (maximum: 1867 m) compared to Bombus bifarius (maximum: 362 m). Despite this difference in absolute range, both species were detected across putative forest barriers at frequencies expected by uninhibited movement. Siblings separated by greater distances were more likely to be foraging on different floral species, potentially suggesting a resource‐based motivation for movement. 4. These results suggest that bumble bee foraging patterns are influenced by species-specific differences in movement capacity, with little influence of matrix composition between resource patches. They also support the perspective that habitat conservation for bumble bees should prioritize providing abundant and diverse patches of resources within species-specific movement radii with less emphasis on matrix composition.

Ecological Entomology↗
USGS2009

Complex influences of low-head dams and artificial wetlands on fishes in a Colorado River tributary system

Low-head dams in arid regions restrict fish movement and create novel habitats that have complex effects on fish assemblages. The influence of low-head dams and artificial wetlands on fishes in Muddy Creek, a tributary of the Colorado River system in the USA was examined. Upstream, fish assemblages were dominated by native species including two species of conservation concern, bluehead sucker, Catostomus discobolus Cope, and roundtail chub, Gila robusta Baird and Girard. The artificial wetlands contained almost exclusively non-native fathead minnow, Pimephales promelas Rafinesque, and white sucker, Catostomus commersonii (Lacep??de). Downstream, fish assemblages were dominated by non-native species. Upstream spawning migrations by non-native white suckers were blocked by dams associated with the wetlands. However, the wetlands do not provide habitat for native fishes and likely inhibit fish movement. The wetlands appear to be a source habitat for non-native fishes and a sink habitat for native fishes. Two non-native species, sand shiner, Notropis stramineus (Cope), and redside shiner, Richardsonius balteatus (Richardson), were present only downstream of the wetlands, suggesting a beneficial role of the wetlands in preventing upstream colonisation by non-native fishes. ?? 2009 Blackwell Publishing Ltd.

Fisheries Management and Ecology↗
USGS2007

Climatic variation and the distribution of an amphibian polyploid complex

1. The establishment of polyploid populations involves the persistence and growth of the polyploid in the presence of the progenitor species. Although there have been a number of animal polyploid species documented, relatively few inquiries have been made into the large-scale mechanisms of polyploid establishment in animal groups. Herein we investigate the influence of regional climatic conditions on the distributional patterns of a diploid-tetraploid species pair of gray treefrogs, Hyla chrysoscelis and H. versicolor (Anura: Hylidae) in the mid-Atlantic region of eastern North America. 2. Calling surveys at breeding sites were used to document the distribution of each species. Twelve climatic models and one elevation model were generated to predict climatic and elevation values for gray treefrog breeding sites. A canonical analysis of discriminants was used to describe relationships between climatic variables, elevation and the distribution of H. chrysoscelis and H. versicolor . 3. There was a strong correlation between several climatic variables, elevation and the distribution of the gray treefrog complex. Specifically, the tetraploid species almost exclusively occupied areas of higher elevation, where climatic conditions were relatively severe (colder, drier, greater annual variation). In contrast, the diploid species was restricted to lower elevations, where climatic conditions were warmer, wetter and exhibited less annual variation. 4. Clusters of syntopic sites were associated with areas of high variation in annual temperature and precipitation during the breeding season. 5. Our data suggest that large-scale climatic conditions have played a role in the establishment of the polyploid H. versicolor in at least some portions of its range. The occurrence of the polyploid and absence of the progenitor in colder, drier and more varied environments suggests the polyploid may posses a tolerance of severe environmental conditions that is not possessed by the diploid progenitor. 6. Our findings support the hypothesis that increased tolerance to severe environmental conditions is a plausible mechanism of polyploid establishment.

Maryland, Virginia↗
USGS2009

The timing of eclogite facies metamorphism and migmatization in the Orlica–Śnieżnik complex, Bohemian Massif: Constraints from a multimethod geochronological study

The Orlica–Śnieżnik complex (OSC) is a key geological element of the eastern Variscides and mainly consists of amphibolite facies orthogneisses and metasedimentary rocks. Sporadic occurrences of eclogites and granulites record high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic conditions. A multimethod geochronological approach ( 40 Ar– 39 Ar, Rb–Sr, Sm–Nd, U–Pb) has been used to gain further insights into the polymetamorphic evolution of eclogites and associated country rocks. Special attention was given to the unresolved significance of a 370- to 360 Ma age group that was repeatedly described in previous studies. Efforts to verify the accuracy of c. 370 Ma K–Ar phengite and biotite dates reported for an eclogite and associated country-rock gneiss from the location Nowa Wieś suggest that these dates are meaningless, due to contamination with extraneous Ar. Extraneous Ar is also considered to be responsible for a significantly older 40 Ar– 39 Ar phengite date of c. 455 Ma for an eclogite from the location Wojtowka. Attempts to further substantiate the importance of 370–360 Ma zircon dates as an indicator for a melt-forming high-temperature (HT) episode did not provide evidence in support of anatectic processes at this time. Instead, SHRIMP U–Pb zircon dating of leucosomes and leucocratic veins within both orthogneisses and (U)HP granulites revealed two age populations (490–450 and 345–330 Ma respectively) that correspond to protolith ages of the magmatic precursors and late Variscan anatexis. The results of this study further underline the importance of Late Carboniferous metamorphic processes for the evolution of the OSC that comprise the waning stages of HP metamorphism and lower pressure HT overprinting with partial melting. Eclogites and their country rocks provided no chronometric evidence for an UHP and ultrahigh-temperature episode at 387–360 Ma, as recently suggested for granulites from the OSC, based on Lu–Hf garnet ages ( Anczkiewicz et al. , 2007 ).

Orlica-Snieznik complex↗
USGS2019

Parallel signatures of selection at genomic islands of divergence and the major histocompatibility complex in ecotypes of sockeye salmon across Alaska

Understanding the genetic mechanisms that facilitate adaptive radiation is an important component of evolutionary biology. Here, we genotyped 82 neutral SNPs, seven SNPs in islands of divergence identified in a previous study (island SNPs), and a region of the major histocompatibility complex (MHC) in 32 populations of sockeye salmon to investigate whether conserved genes and genomic regions are involved in adaptive radiation. Populations representing three ecotypes were sampled from seven drainages with differing habitats and colonization histories spanning a range of 2,000 km. We found strong signatures of parallel selection across drainages at the island SNPs and MHC, suggesting that the same loci undergo divergent selection during adaptive radiation. However, patterns of differentiation at most island SNPs and the MHC were not associated with ecotypes, suggesting that these loci are responding differently to a mosaic of selective pressures. Our study provides some of the first evidence that conserved genomic islands may be involved in adaptive divergence of salmon populations. Additionally, our data provide further support for the hypothesis that sockeye salmon inhabiting rivers unconnected to lakes harbour similar genetic diversity across large distances, are likely the ancestral form of the species, and have repeatedly recolonized lake systems as they have become available after glacial recession. Finally, our results highlight the value and importance of validating outlier loci by screening additional populations and regions, a practice that will hopefully become more common in the future.

Alaska↗
USGS2022

Luminescence sediment tracing reveals the complex dynamics of colluvial wedge formation

Paleoearthquake studies that inform seismic hazard rely on assumptions of sediment transport that remain largely untested. Here, we test a widespread conceptual model and a new numerical model on the formation of colluvial wedges, a key deposit used to constrain the timing of paleoearthquakes. We perform this test by applying luminescence, a sunlight-sensitive sediment tracer, at a field site displaying classic colluvial wedge morphostratigraphy. The model and data comparison reveals complex sediment transport processes beyond the predictions of either conceptual or numerical models, including periods of simultaneous debris and wash facies forming processes, erosion, and reworking. These processes could lead to preservation bias, such as incomplete or overinterpretable paleoearthquake records, given the right environmental conditions. Attention to the site-specific mechanics of fault zone depositional systems, such as via sediment tracing, may buffer against the possible effects of preservation bias on paleoseismic study.

Science↗
USGS2023

Large increases in methane emissions expected from North America’s largest wetland complex

Natural methane (CH 4 ) emissions from aquatic ecosystems may rise because of human-induced climate warming, although the magnitude of increase is highly uncertain. Using an exceptionally large CH 4 flux dataset (~19,000 chamber measurements) and remotely sensed information, we modeled plot- and landscape-scale wetland CH 4 emissions from the Prairie Pothole Region (PPR), North America’s largest wetland complex. Plot-scale CH 4 emissions were driven by hydrology, temperature, vegetation, and wetland size. Historically, landscape-scale PPR wetland CH 4 emissions were largely dependent on total wetland extent. However, regardless of future wetland extent, PPR CH 4 emissions are predicted to increase by two- or threefold by 2100 under moderate or severe warming scenarios, respectively. Our findings suggest that international efforts to decrease atmospheric CH 4 concentrations should jointly account for anthropogenic and natural emissions to maintain climate mitigation targets to the end of the century.

North Dakota↗
USGS2001

Imaging of small-scale features on 433 Eros from NEAR: Evidence for a complex regolith

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

Science↗
USGS1989

Rhenium-osmium and samarium-neodymium isotopic systematics of the Stillwater Complex

Isotopic data for the Stillwater Complex, Montana, which formed about 2700 Ma (million years ago), were obtained to evaluate the role of magma mixing in the formation of strategic platinum-group element (PGE) ore deposits. Neodymium and osmium isotopic data indicate that the intrusion formed from at least two geochemically distinct magmas. Ultramafic affinity (U-type) magmas had initial ε Nd of -0.8 to -3.2 and a chondritic initial 187 Os/ 186 Os ratio of ∼0.88, whereas anorthositic affinity (A-type) magmas had ε Nd of -0.7 to +1.7 and an initial 187 Os/ 186 Os ratio of ∼1.13. These data suggest that U-type magmas were derived from a lithospheric mantle source containing recycled crustal materials whereas A-type magmas originated either by crustal contamination of basaltic magmas or by partial melting of basalt in the lower crust. The Nd and Os isotopic data also suggest that Os, and probably the other PGEs in ore horizons such as the J-M Reef, was derived from A-type magmas. The Nd and Os isotopic heterogeneity observed in rocks below the J-M Reef also suggests that A-type magmas were injected into the Stillwater U-type magma chamber at several stages during the development of the Ultramafic series.

Montana↗
USGS2011

In Vivo fitness associated with high virulence in a vertebrate virus is a complex trait regulated by host entry, replication, and shedding

The relationship between pathogen fitness and virulence is typically examined by quantifying only one or two pathogen fitness traits. More specifically, it is regularly assumed that within-host replication, as a precursor to transmission, is the driving force behind virulence. In reality, many traits contribute to pathogen fitness, and each trait could drive the evolution of virulence in different ways. Here, we independently quantified four viral infection cycle traits, namely, host entry, within-host replication, within-host coinfection fitness, and shedding, in vivo , in the vertebrate virus Infectious hematopoietic necrosis virus (IHNV). We examined how each of these stages of the viral infection cycle contributes to the fitness of IHNV genotypes that differ in virulence in rainbow trout. This enabled us to determine how infection cycle fitness traits are independently associated with virulence. We found that viral fitness was independently regulated by each of the traits examined, with the largest impact on fitness being provided by within-host replication. Furthermore, the more virulent of the two genotypes of IHNV we used had advantages in all of the traits quantified. Our results are thus congruent with the assumption that virulence and within-host replication are correlated but suggest that infection cycle fitness is complex and that replication is not the only trait associated with virulence.

Journal of Virology↗
USGS1997

Igneous evolution of a complex laccolith-caldera, the Solitario, Trans-Pecos Texas: Implications for calderas and subjacent plutons

The Solitario is a large, combination laccolith and caldera (herein termed “laccocaldera”), with a 16-km-diameter dome over which developed a 6×2 km caldera. This laccocaldera underwent a complex sequence of predoming sill, laccolith, and dike intrusion and concurrent volcanism; doming with emplacement of a main laccolith; ash-flow eruption and caldera collapse; intracaldera sedimentation and volcanism; and late intrusion. Detailed geologic mapping and 40 Ar/ 39 Ar dating reveal that the Solitario evolved over an interval of approximately 1 m.y. in three distinct pulses at 36.0, 35.4, and 35.0 Ma. The size, duration, and episodicity of Solitario magmatism are more typical of large ash-flow calderas than of most previously described laccoliths.

Texas↗
USGS1991

Oxygen-isotope exchange and mineral alteration in gabbros of the Lower Layered Series, Kap Edvard Holm Complex, East Greenland

Multiple intrusions of gabbros, mafic dikes, and syenites in the Kap Edvard Holm Complex gave rise to prolonged circulation of meteoric hydrothermal solutions and extreme isotope exchange and mineral alteration in the 3600-m-thick Lower Layered Series gabbros. In the Lower Layered Series, δ 18 O of plagioclase varies from +0.3‰ to -5.8‰, and it decreases with an increase in the volume of secondary talc, chlorite, and actinolite. In the same gabbros, pyroxenes have a more restricted range in δ 18 O, from 5.0‰ to 3.8‰ and values of δ 18 O pyroxene are independent of the abundance of secondary minerals, which ranges from 14% to 30%. These relations indicate that large amounts of water continued to flow through the rocks at temperatures of <500-600°C, altering the gabbros to assemblages of talc + chlorite + actinolite ± epidote ±albite and causing significant oxygen-isotope exchange in plagioclase, but not in pyroxene. The extensive low-temperature secondary mineralization and 18 O depletion of plagioclase in the Lower Layered Series are associated with the later emplacement of dikes and gabbros and syenites, which created new fracture systems and provided heat sources for hydrothermal fluid circulation. This produced subsolidus mineral alteration and isotope exchange in the Lower Layered Series that are distinct from those in the Skaergaard and Cuillin gabbros of the North Atlantic Tertiary province, but are similar to those observed in some oceanic gabbros.

Kap Edward Holm Complex↗
USGS2007

Assessing the state of our knowledge of continental arc volcanism: The Tatara-San Pedro Complex, 36°S, Andean Southern Volcanic Zone: Talca and Tatara-San Pedro, Chile 4-12 February 2007

Tatara-San Pedro Volcanic Complex in Chile is one of the best studied continental arc volcanic centers in the world. In connection to this, a field forum was conducted to discuss the processes involved in the construction of such volcanoes and the origins of its magmas. With 40 international participants from diverse scientific backgrounds, the forum opened in the Talca municipal library with two days of presentation, fieldworks and a hike to the trailhead. The key issues that were tackled include information on the compositions, ages, and distributions of preserved eruptive products.

Tatara-San Pedro Volcanic Complex↗