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At least 847 records · Page 47Linked to original sources
USGS2024

Paleogene mid-crustal intrusions in the Ruby Mountains–East Humboldt Range metamorphic core complex, northeastern Nevada, USA

Middle Eocene to early Oligocene intrusions, widespread in the Ruby Mountains–East Humboldt Range metamorphic core complex, Nevada, USA, provide insights into a major Paleogene magmatic episode and its relation to tectonism in the northeastern Great Basin. These intrusions, well-exposed in upper Lamoille Canyon, range in composition from gabbro to leucomonzogranite. They form small plutons, sheets, and dikes that intrude the metamorphic and granitic infrastructure of the core complex. Two types of Paleogene monzogranite were recognized. The first is exemplified by two of the larger intrusive bodies, the Snow Lake Peak and Castle Lake intrusions, which occur as sheet-like bodies near and at the structural base of metamorphosed Neoproterozoic and Cambrian Prospect Mountain Quartzite where it is inverted above Cambrian and Ordovician marble of Verdi Peak in the Lamoille Canyon nappe. Swarms of dikes are associated with these intrusions. U-Pb (zircon) ages range ca. 40–33 Ma and typically display relatively simple and minor inheritance. The rocks have the lowest ε Hf (zircon) and ε Nd (whole rock) of any of the middle Cenozoic granites. The second type of monzogranite, Overlook type, typically occurs as thin, isolated dikes and leucosome-like bodies in Late Cretaceous granites of the infrastructure, with no obvious relationship to the large monzogranite bodies. Overlook-type monzogranite displays complex zircon inheritance, yields igneous ages ca. 37–32 Ma, and has ε Hf (zircon) and ε Nd (whole rock) identical to those of Late Cretaceous granites in the core complex. These isotopic and field data indicate that Overlook-type monzogranite formed in situ through anatexis of host Cretaceous granites. A pervasive thermal event was required to stimulate this crustal melting.

Nevada↗
USGS2023

Precursors to a continental-arc ignimbrite flare-up: Early central volcanoes of the San Juan Mountains, Colorado, USA

Our newly acquired and recently published map, geochronologic, and compositional data for early intermediate-composition central volcanoes in the northeastern San Juan Mountains provide insights about the broad magmatic precursors to the large continental-arc ignimbrite flare-up in the mid-Cenozoic Southern Rocky Mountain volcanic field (SRMVF). Initial volcanism migrated from central Colorado to northern New Mexico ca. 40–29 Ma, as part of a more regional trend of southward-progressing mid-Cenozoic magmatism in the U.S. segment of the North American Cordillera. Within the San Juan locus, which represents the largest preserved erosional remnant of the SRMVF and site of most intense eruptive activity, new 40 Ar/ 39 Ar and U-Pb zircon ages show that eruptions at many individual edifices began nearly concurrently, at ca. 35 Ma, with peak activity at 34–32 Ma. Broadly similar precursor effusive volcanism characterizes other major loci of continental-arc ignimbrite magmatism along the western American cordilleras, but none of these sites records early volcanism as voluminous, spatially widespread, well exposed, or compositionally diverse as the San Juan locus in Colorado.

Colorado↗
USGS2024

Mantle melting in regions of thick continental lithosphere: Examples from Late Cretaceous and younger volcanic rocks, Southern Rocky Mountains, Colorado (USA)

Major- and trace-element data together with Nd and Sr isotopic compositions and 40 Ar/ 39 Ar age determinations were obtained for Late Cretaceous and younger volcanic rocks from north-central Colorado, USA, in the Southern Rocky Mountains to assess the sources of mantle-derived melts in a region underlain by thick (≥150 km) continental lithosphere. Trachybasalt to trachyandesite lava flows and volcanic cobbles of the Upper Cretaceous Windy Gap Volcanic Member of the Middle Park Formation have low εNd(t) values from −3.4 to −13, 87 Sr/ 86 Sr(t) from ~0.705 to ~0.707, high large ion lithophile element/high field strength element ratios, and low Ta/Th (≤0.2) values. These characteristics are consistent with the production of mafic melts during the Late Cretaceous to early Cenozoic Laramide orogeny through flux melting of asthenosphere above shallowly subducting and dehydrating oceanic lithosphere of the Farallon plate, followed by the interaction of these melts with preexisting, low εNd(t), continental lithospheric mantle during ascent. This scenario requires that asthenospheric melting occurred beneath continental lithosphere as thick as 200 km, in accordance with mantle xenoliths entrained in localized Devonian-age kimberlites. Such depths are consistent with the abundances of heavy rare earth elements (Yb, Sc) in the Laramide volcanic rocks, which require parental melts derived from garnet-bearing mantle source rocks. New 40 Ar/ 39 Ar ages from the Rabbit Ears and Elkhead Mountains volcanic fields confirm that mafic magmatism was reestablished in this region ca. 28 Ma after a hiatus of over 30 m.y. and that the locus of volcanism migrated to the west through time. These rocks have εNd(t) and 87 Sr/ 86 Sr(t) values equivalent to their older counterparts (−3.5 to −13 and 0.7038–0.7060, respectively), but they have higher average chondrite-normalized La/Yb values (~22 vs. ~10), and, for the Rabbit Ears volcanic field, higher and more variable Ta/Th values (0.29–0.43). The latter are general characteristics of all other post– 40 Ma volcanic rocks in north-central Colorado for which literature data are available. Transitions from low to intermediate Ta/Th mafic volcanism occurred diachronously across southwest North America and are interpreted to have been a consequence of melting of continental lithospheric mantle previously metasomatized by aqueous fluids derived from the underthrusted Farallon plate. Melting occurred as remnants of the Farallon plate were removed and the continental lithospheric mantle was conductively heated by upwelling asthenosphere. A similar model can be applied to post–40 Ma magmatism in north-central Colorado, with periodic, east to west, removal of stranded remnants of the Farallon plate from the base of the continental lithospheric mantle accounting for the production, and western migration, of volcanism. The estimated depth of the lithosphere-asthenosphere boundary in north-central Colorado (~150 km) indicates that the lithosphere remains too thick to allow widespread melting of upwelling asthenosphere even after lithospheric thinning in the Cenozoic. The preservation of thick continental lithospheric mantle may account for the absence of oceanic-island basalt–like basaltic volcanism (high Ta/Th values of ~1 and εNd[t] > 0), in contrast to areas of southwest North America that experienced larger-magnitude extension and lithosphere thinning, where oceanic-island basalt–like late Cenozoic basalts are common.

Geosphere↗
USGS1969

Structural geology of the Quad-Wyoming-Line Creeks area, Beartooth Mountains, Montana

The Quad-Wyoming-Line Creeks area is in the northeastern part of the Beartooth Mountains of Montana. The rocks of the area consist mainly of banded migmatite, granitic gneisses, amphibolite, quartzite, and agmatite; small amounts of biotite schist and biotite gneiss, iron-silicate rocks, ultramafic rocks, mafic dikes, and felsic porphyries are also present. Quartzite outcrops continuously around the major folds, and agmatite is especially widespread in the axial zone of a major anti-form. Two fold sets have been revealed by detailed mapping (scale 1:7200) and statistical analysis of the penetrative subfabric elements. The large later folds, F 2 , are the south-plunging Quad Creek synform and the south-southwest-plunging Wyoming Creek antiform; they are nearly upright and non-isoclinal. A metanorite intrusion is located in the axial zone of the Quad Creek synform. Small F 2 fold style varies from similar in relatively ductile rocks to open, concentric folds in non-ductile rocks. Only one large F 1 , located immediately north of the metanorite pluton, has been mapped. F 1 folds are characteristically similar in style. Refolding of small F 1 folds by small F 2 folds has been observed throughout the map area. Statistical analysis of the compositional layering, So, and the axial planes of small F 1 folds, S 1 , shows that the πS 0 - and πS 1 -axes constructed in the Wyoming Creek antiform are nearly coincident with each other and with south-southwest-plunging maxima of small F 2 fold axes, B 2 . Both B 2 and the axial planes of F 2 folds, S 2 , are dispersed, showing that the later folds are noncylindrical and nonplane. The axes of small F 1 folds, B 1 , are generally dispersed along well defined π-girdles. B 1 and B 2 maxima are generally coincident at some stations in the Wyoming Creek antiform-axial zone, suggesting that B 1 and B 2 are, at least locally, collinear. The long axes of hornblende crystals, L 1 , are also dispersed, but are not parallel to B 1 ; the L 1 -subfabric appears to indicate that L 1 developed during the F 1 folding but plunged somewhat more steeply to the south-southwest to south than Bi and that the F 2 folds are concentric rather than similar in the amphibolite. In the Quad Creek synform (F 2 ), all of the above-mentioned fabric elements diverge around the north side of the metanorite body. The Precambrian deformational history of the present map area, and probably the remainder of the eastern Beartooth Mountains, appears to be comprised of two phases of folding. During the first phase (F 1 ) south-southwest plunging, isoclinal or nearly isoclinal folds formed by passive flow during metamorphism to at least the upper amphibolite facies; these F, folds were not upright and may have been nearly recumbent. L 1 was formed during this phase. Metamorphic differentiation of a sedimentary sequence occurred at this time, but it is not clear whether any new material was added. The second phase of deformation is characterized by upright, non-isoclinal folds which also formed about south-southwest to south plunging axes. Flexural flow was the dominant mechanism in the development of the Quad Creek synform and the Wyoming Creek antiform, but passive flow was important in layers of ductile rocks. Granitization was generally synchronous with the F 2 phase; pegmatite dikes were emplaced later in a passive manner. Quartzite and amphibolite acted as resisters to granitization; their termination in granitic gneisses and migmatites is usually most adequately explained by refolding rather than granitization of the quartzite. It is possible that partial melting occurred in some areas such as the agmatized zones. Time of emplacement of the metanorite body is still questionable, but it clearly predates the F 2 folding; intrusion prior to F 1 is probable because B 1 , B 2 , and L 1 diverge in the vicinity of the body.

Montana↗
USGS1983

Fission-track ages of apatite in the Wasatch Mountains, Utah: An uplift study

Apatite fission-track ages from basement rocks in the Wasatch Mountains between Ogden and Bountiful, Utah, range from 5 m.y. near the Wasatch fault along the west margin of the mountains to 94 m.y. on the crest of the range and show a correlation with altitude within individual fault blocks. Analysis of these ages yields an uplift rate of 0.4 mm/yr for the last 10 m.y. for the fault blocks having the most sustained rapid uplift. A variety of intermediate ages of apatite from the crest of the range and at lower altitudes is interpreted as representing fault blocks with rocks having mixed ages due to various degrees of tilting and varying but lesser amounts of uplift.

Utah↗
USGS1988

Deformation along the northeast side of Blacktail Mountains salient, southwestern Montana

The Blacktail Mountains salient is a convex-eastward area of stacked Laramide-age thrust faults that trend north and dip west at moderate angles. The thrusts occur in Mississippian to Cretaceous strata above a basement of Archean metamorphic rocks. The northern margin of the salient is delimited by the Jake Canyon fault, a northwest-trending, northeast-dipping Laramide reverse fault. During the Laramide orogeny, the fault formed a common boundary of the present-day Blacktail Mountains and a structural high that existed in the area of the present-day valley of Blacktail Deer Creek. The fault juxtaposed Archean metamorphic rocks upon Phanerozoic strata in the northwest-era half of its extent, and against other Archean metamorphic rocks in the southeastern half. General structural relationships and study of small-scale structures in local areas show that movement along the Jake Canyon fault caused deformation of the north-trending thrust faults and associated folds. During Cenozoic extensional faulting, the Blacktail fault developed northeast of the Jake Canyon fault, and generally delimits the southwestern side of the basin of sedimentary rocks that lies beneath the valley of Blacktail Deer Creek.

Idaho, Montana↗
USGS1990

Chapter 19: Magmatic components of a tilted plutonic system, Klamath Mountains, California

The Slinkard pluton (SP) and Wooley Creek batholith (WCB) are the lower and upper parts, respectively, of a tilted Middle Jurassic magma system. The SP and lower WCB intruded structurally lower ophiolitic mélange of the Marble Mountain terrane; the upper WCB intruded successively structurally higher metavolcanic and metasedimentary rocks of the western and eastern Hayfork terranes. The predominant volume of the system comprised a two-layer chamber in which an upper dacitic magma crystallized to form tonalite to granite in the upper WCB and a lower andesitic magma crystallized to form gabbro to tonalite in the lower WCB and SP. The upper part of the system had Sr i , = 0.7043 and a range of δ 18 O from +8.7 to +11.2%o; the lower part had average Sr i = 0.7046 and δ 18 O from +8.1 to +8.8%o The two layers of the system are separated by a transition zone that is intermediate in isotopie composition. The compositional differences between upper and lower parts of the system can be explained as (1) the result of intrusion of two separate pods of noncogenetic magma, or (2) the product of in situ assimilation-fractional crystallization. The second explanation requires that a relatively 87 Sr-rich contaminant such as the structurally lower Marble Mountain terrane was assimilated in the lower part of the system, whereas an 18 O-rich, generally 87 Sr-poor contaminant such as the structurally intermediate western Hayfork terrane was assimilated by the upper part. Trace-element evidence suggests that gradational upward zoning (from gabbro to granite) resulted from an upward decrease in the efficiency of crystal-melt segregation and crystal accumulation. H 2 O-rich basaltic magma preceded development of the two-layer system, and basaltic pulses into the lower part of the system continued during most of its solidification history. Most basaltic rocks display evidence of some degree of fractional crystallization and interaction with crustal rocks; however, a few have low Sr i and high concentrations of Cr and Ni, characteristics of undifferentiated mantle melts. Two-mica granite of the western Slinkard pluton cannot be related to the remainder of the system by fractional crystallization. High δ 18 O, high Ba, and low Sr abundances suggest that the two-mica granite is probably a partial melt of crustal material.

California↗
USGS2013

Spatio-temporal variability in movement, age, and growth of mountain whitefish ( Prosopium williamsoni ) in a river network based upon PIT tagging and otolith chemistry

Connectivity of river networks and the movements among habitats can be critical for the life history of many fish species, and understanding of the patterns of movement is central to managing populations, communities, and the landscapes they use. We combined passive integrated transponder tagging over 4 years and strontium isotopes in otoliths to demonstrate that 25% of the mountain whitefish ( Prosopium williamsoni ) sampled moved between the Methow and Columbia rivers, Washington, USA. Seasonal migrations downstream from the Methow River to the Columbia River to overwinter occurred in autumn and upstream movements in the spring. We observed migration was common during the first year of life, with migrants being larger than nonmigrants. However, growth between migrants and nonmigrants was similar. Water temperature was positively related to the proportion of migrants and negatively related to the timing of migration, but neither was related to discharge. The broad spatio-temporal movements we observed suggest mountain whitefish, and likely other nonanadromous fish, require distant habitats and also suggests that management and conservation strategies to keep connectivity of large river networks are imperative.

Washington↗
USGS1999

Response of high-elevation forests in the Olympic Mountains to climatic change

The gap model ZELIG was used to examine the effects of increased temperature (2°C) and altered precipitation on high-elevation ecosystems of the Olympic Mountains, Washington, U.S.A. Changes in tree species distribution and abundance, as well as stand biomass, were examined on north and south aspects in the dry northeast (NE) and wet southwest (SW) regions of the Olympics for ( i ) warmer, ( ii ) warmer and 20% wetter, and ( iii ) warmer and 20% drier climatic-change scenarios. Dominant tree species shift upwards 300-600 m in elevation in the SW, with subalpine meadows and Tsuga mertensiana (Bong.) Carr. forests being replaced by Abies amabilis (Dougl.) Forbes forests at higher elevations and A. amabilis forests being replaced by Tsuga heterophylla (Raf.) Sarg. forests at lower elevations. In the NE, drought-tolerant species become dominant approximately 200 m lower than present, with A. lasiocarpa dominating the north aspect and Pinus contorta Dougl. ex Loud. the south aspect. Biomass increases in the SW and generally decreases in the NE, depending on aspect and precipitation regime. This study suggests that species and site-specific responses at mesoscale (e.g., wet vs. dry climatic regime) and microscale (e.g., north vs. south aspect) resolutions must be characterized to quantify the variation in potential effects of climatic change on forest vegetation in mountainous regions.

Canadian Journal of Forest Research↗
USGS2018

Major element and oxygen isotope geochemistry of vapour-phase garnet from the Topopah Spring Tuff at Yucca Mountain, Nevada, USA

Twenty vapour-phase garnets were studied in two samples of the Topopah Spring Tuff of the Paintbrush Group from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350 m thick, devitrified, moderately to densely welded ash-flow tuff that is zoned compositionally from high-silica rhyolite to latite. During cooling of the tuff, escaping vapour produced lithophysae (former gas cavities) lined with an assemblage of tridymite (commonly inverted to cristobalite or quartz), sanidine and locally, hematite and/or garnet. Vapour-phase topaz and economic deposits associated commonly with topaz-bearing rhyolites (characteristically enriched in F) were not found in the Topopah Spring Tuff at Yucca Mountain. Based on their occurrence only in lithophysae, the garnets are not primary igneous phenocrysts, but rather crystals that grew from a F-poor magma-derived vapour trapped during and after emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter and fractured. The garnets also contain inclusions of tridymite. Electron microprobe analyses of the garnets reveal that they are almandine-spessartine (48.0 and 47.9 mol.%, respectively), have an average composition of (Fe 1.46 Mn 1.45 Mg 0.03 Ca 0.10 )(Al 1.93 Ti 0.02 )Si 3.01 O 12 and are comparatively homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have δ18O values of 7.2 and 7.4‰. The associated quartz (after tridymite) has δ 18 O values of 17.4 and 17.6‰, values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a δ 18 O of 11.1‰ which, when coupled with the garnet δ 18 O values in a quartz-garnet fractionation equation, indicates isotopic equilibration (vapour-phase crystallization) at temperatures of ~600°C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50–70°C) of calcite, quartz and opal secondary mineralization, formed from downward-percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.

Nevada↗
USGS2013

Controls on the deposition and preservation of the Cretaceous Mowry Shale and Frontier Formation and equivalents, Rocky Mountain region, Colorado, Utah, and Wyoming

Regional variations in thickness and facies of clastic sediments are controlled by geographic location within a foreland basin. Preservation of facies is dependent on the original accommodation space available during deposition and ultimately by tectonic modification of the foreland in its postthrusting stages. The preservation of facies within the foreland basin and during the modification stage affects the kinds of hydrocarbon reservoirs that are present. This is the case for the Cretaceous Mowry Shale and Frontier Formation and equivalent strata in the Rocky Mountain region of Colorado, Utah, and Wyoming. Biostratigraphically constrained isopach maps of three intervals within these formations provide a control on eustatic variations in sea level, which allow depositional patterns across dip and along strike to be interpreted in terms of relationship to thrust progression and depositional topography. The most highly subsiding parts of the Rocky Mountain foreland basin, near the fold and thrust belt to the west, typically contain a low number of coarse-grained sandstone channels but limited sandstone reservoirs. However, where subsidence is greater than sediment supply, the foredeep contains stacked deltaic sandstones, coal, and preserved transgressive marine shales in mainly conformable successions. The main exploration play in this area is currently coalbed gas, but the enhanced coal thickness combined with a Mowry marine shale source rock indicates that a low-permeability, basin-centered play may exist somewhere along strike in a deep part of the basin. In the slower subsiding parts of the foreland basin, marginal marine and fluvial sandstones are amalgamated and compartmentalized by unconformities, providing conditions for the development of stratigraphic and combination traps, especially in areas of repeated reactivation. Areas of medium accommodation in the most distal parts of the foreland contain isolated marginal marine shoreface and deltaic sandstones that were deposited at or near sea level lowstand and were reworked landward by ravinement and longshore currents by storms creating stratigraphic or combination traps enclosed with marine shale seals. Paleogeographic reconstructions are used to show exploration fairways of the different play types present in the Laramide-modified, Cretaceous foreland basin. Existing oil and gas fields from these plays show a relatively consistent volume of hydrocarbons, which results from the partitioning of facies within the different parts of the foreland basin.

Colorado;Utah;Wyoming↗
USGS1989

Kinky vitrinite reflectance well profiles: Evidence of paleopore pressure in low-permeability, gas-bearing sequences in Rocky Mountain foreland basins

Vitrinite reflectance (R m ) profiles of wells drilled in abnormally pressured, low-permeability gas-bearing sequences in Rocky Mountain foreland basins are commonly nonlinear with two or more nonparallel segments. These kinky profiles are most likely due to perturbations of the thermal gradient caused by contrasting heat transfer processes associated with the development of abnormally high pressures. We interpret the intersection of the shallow and intermediate R m segments to mark the approximate original boundary between normal-pressured, water-bearing rocks and underlying overpressured gas- and water-bearing rocks. The intersection of the intermediate and deep R m segments marks the approximate original boundary between overpressured gas- nd water-bearing rocks and underlying overpressured gas-bearing rocks. However, because overpressuring is a transient condition that eventually evolves into normal pressuring or underpressuring, these intersections may not coincide with the present top of abnormal pressuring. These segmented R m profiles occur in several Rocky Mountain basins of the United States and Canada.

Alberta, Colorado, Wyoming↗
USGS1995

Geologic framework of a transect of the central Brooks Range: Regional relations and an alternative to the Endicott Mountains allochthon

This paper evaluates the geologic framework and tectonic development of the central Brooks Range based on a transect through the range and Arctic foothills. A geologic cross section constructed through the transect is confirmed by comparing the retrodeformed section with the regional distribution of lithofacies in the central Brooks Range. Stratigraphic relations in the retrodeformed section are further explained by comparing them to similar stratigraphic relations in the Ikpikpuk-Umiat basin under the Arctic coastal plain. The structural framework of the central Brooks Range and Arctic foothills consists of fold nappes, thrust faults, and detached folds that sole in decollements and late-stage high-angle faults. In the central Brooks Range, shortening is by north-directed thrust faulting and folding of mostly Paleozoic rocks, and transport of any individual thrust sheet relative to underlying rocks is less than 30 km. In the middle of the range, imbricate blocks of lower Paleozoic basement are exposed in the core of the Doonerak anticline, and thrust sheets of stratigraphically higher Paleozoic rocks that overlie basement are exposed in the limbs of the anticline. In the northeast part of the anticline, the Amawk thrust emplaces Silurian and Upper Devonian rocks on a succession of Lower Mississippian an stratigraphically higher rocks that have been detached from the underlying basement along the Blarney Creek thrust. The Slatepile fault system, a system of high-angle faults in the north limb of the Doonerak anticline, drops the core and part of the north limb of the anticline down, giving the impression that the succession of Lower Mississippian and stratigraphically higher rocks that lie on basement south of the system high-angle faults extends under the Upper Devonian rocks that extensively crop out north of the high-angle faults. In the Arctic foothills, the mostly Paleozoic rocks of the north-central Brooks Range extend under Lower Cretaceous rocks of the North Slope foreland basin, and blind thrusts that sole in the Paleozoic rocks ramp up into the Lower Cretaceous and stratigraph cally higher rocks. Also in the Arctic foothills, a thrust sheet that contains the Arctic foothills assemblage overlies rocks of the north-central Brooks Range and Lower Cretaceous rocks of the North Slope foreland basin. Thrust transport of the Arctic foothills assemblage more than 40 km from south of the Doonerak anticline took place during the Early Cretaceous, but thrusting that deformed rocks of the North Slope foreland basin took place during the early Tertiary, with the vertical uplift of the Doonerak anticline being a late-formed feature. Conclusions based on the retrodeformed cross section contrast significantly with previous work in which the Upper Devonian and stratigraphically higher rocks north of the Doonerak anticline are considered part of the Endicott Mountains allochthon, a regional allochthon that extends the breadth of the Brooks Range. In these models, Upper Devonian and younger rocks in the north-central Brooks Range have been thrust-transported 90 or 200 km from south of the Doonerak anticline, and emplacement of the allochthon could reflect as much as 885 km of tectonic shortening. The Lower Mississippian and stratigraphically higher rocks together with the underlying basement in the northeast part of the anticline are considered to be in a window in the Endicott Mountains allochthon and to extend northward beneath allochthonous Upper Devonian and stratigraphically higher rocks in the north-central Brooks Range. Lithofacies patterns in rocks in the central Brooks Range are consistent with the retrodeformed cross section and imply plausible Upper Devonian and Carboniferous depositional systems. Thick Upper Devonian and Lower Mississippian(?) clastic prisms were deposited in basins north of the Doonerak anticline. Mississippian carbonate rocks that overlie these clastic prisms were deposited in differentially subsiding shelf environments that included rocks in the Doonerak anticline. Restored across the Blarney Creek thrust, the Mississippian shelf carbonate rocks that presently lie north of the Doonerak anticline are those that were deposited on basement in the anticline. A carbonate ramp at the south edge of these shelf deposits extends east-southeast across the central Brooks Range and in th retrodeformed section lies south of the Doonerak anticline where Upper and Middle(?) Devonian shaly rocks thicken to the south. Unrestored, the ramp would extend across the Doonerak anticline. Restored Late Devonian and Carboniferous lithofacies patterns in the central Brooks Range also are plausible from a regional perspective and have implications for exploration of basins under the Arctic coastal plain. The Late Devonian to Early Mississippian(?) basins in the north-central Brooks Range are part of a system of Early(?) Devonian to Early Mississippian(?) clastic basins that extend the length of the Brooks Range and include basins under the Arctic coastal plain. These basins are a template for depositional patterns in overlying rocks. Marine shelves between these basins where Mississippian strata unconformably lie on basement, such as in the northeastern Brooks Range and the Doonerak anticline, have depositional histories that are in contrast to areas that overlie the basi s. The resulting stratigraphic framework, together with the structural framework in the basement rocks that controlled the basins, has had a profound effect on the structural style of the fold belt, the salient effect being folds and thrust faults that are not orthogonal to the direction of structural transport. Stratigraphic relations exposed in the fold belt, especially the distribution of potential source rocks, likely model little-explored basins that underlie the North Slope foreland basin.

Alaska↗
USGS1995

Ebb and flow of encroachment by nonnative rainbow trout in a small stream in the southern Appalachian Mountains

Brook trout Salvelinus fontinalis is the native salmonid species of streams in the southern Appalachian Mountains. The present distribution of this species, once widespread from headwaters to lower reaches of large streams, is restricted to mostly headwater areas. Changes in the distribution of native brook trout in the presence ofˈ nonnative rainbow trout Oncorhynchus mykiss have been documented in Great Smoky Mountains National Park. When rainbow trout were first found in a tributary (Rock Creek) in the park in 1979, a study was begun to assess changes through time in distribution and abundance of rainbow trout in Rock Creek and to compare the brook trout and rainbow trout associations in Rock Creek with associations found in other park streams. Abundance of brook trout was low in the downstream sections of Rock Creek in 1979–1993. Brook trout abundance was highest in the steep‐gradient, pool‐dominated headwater section which was only 2 km from the confluence of Rock Creek and Cosby Creek. Rainbow trout were present in low densities in Rock Creek during the same period. Although rainbow trout were most abundant in the lower stream sections and never found in the headwater section, adult and age‐0 rainbow trout were found in the middle section in 1988. Rainbow trout were absent in the middle section in 1991, but one large adult rainbow trout was present in the section in 1992 and 1993. Floods, freshets, and periods of low stream discharge appeared to play an important role in the distribution and population structure of rainbow trout in Rock Creek. The lower portion of Rock Creek was poor trout habitat because the sections were dominated by cobble–rubble substrate and shallow riffle areas. Stream habitat appeared to be better suited for brook trout than for rainbow trout in the steep‐gradient upstream sections which were dominated by boulder‐cobble substrate and deep pools. The results of this study suggest that encroachment by rainbow trout can exhibit considerable ebb and flow in steep‐gradient tributaries in the park, and they suggest substantial evolutionary adaptation by brook trout to the hydrological conditions in the Rock Creek drainage.

North Carolina, Tennessee↗
USGS2008

Response of fish populations to natural channel design restoration in streams of the Catskill Mountains, New York

Many streams and rivers throughout North America have been extensively straightened, widened, and hardened since the middle 1800s, but related effects on aquatic ecosystems have seldom been monitored, described, or published. Beginning in the early 1990s, reach-level restoration efforts began to base projects on natural channel design (NCD) techniques and Rosgen's (1994b, 1996) river classification system in an effort to duplicate or mimic stable reference reach geomorphology. Four reaches in three streams of the Catskill Mountains, New York, were restored from 2000 to 2002 using NCD techniques to decrease bed and bank erosion rates, decrease sediment loads, and improve water quality. The effects of restoration on the health of fish assemblages were assessed through a before-after, control-impact (BACI) study design to quantify the net changes in population and community indices at treatment reaches relative to index changes at unaltered reference reaches from 1999 to 2004. After restoration, community richness and biomass at treatment reaches increased by more than one-third. Changes in fish communities were caused mainly by shifts in dominant species populations; fish community biomass and total fish abundance were generally dominated by daces or daces and sculpins before restoration and by one or more salmonid species after restoration. Density and biomass of eastern blacknose dace Rhinichthys atratulus, longnose dace R. cataractae, and slimy sculpin Cottus cognatus did not change appreciably, whereas net salmonid density and biomass increased substantially after restoration. These changes were driven primarily by large increases in populations of brown trout Salmo trutta. The findings demonstrate that the structure, function, and ultimately the health of resident fish populations and communities can be improved, at least over the short term, through NCD restoration in perturbed streams of the Catskill Mountains. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗
USGS2011

Variable responses of fish assemblages, habitat, and stability to natural-channel-design restoration in Catskill Mountain streams

Natural-channel-design (NCD) restorations were recently implemented within large segments of five first- and second-order streams in the Catskill Mountains of New York in an attempt to increase channel stability, reduce bed and bank erosion, and sustain water quality. In conjunction with these efforts, 54 fish and habitat surveys were done from 1999 to 2007 at six restored reaches and five stable control reaches to evaluate the effects of NCD restoration on fish assemblages, habitat, and bank stability. A before–after–control–impact study design and two-factor analysis of variance were used to quantify the net changes in habitat and fish population and community indices at treatment reaches relative to those at unaltered control reaches. The density and biomass of fish communities were often dominated by one or two small prey species and no or few predator species before restoration and by one or more trout (Salmonidae) species after restoration. Significant increases in community richness (30%), diversity (40%), species or biomass equitability (32%), and total biomass (up to 52%) in at least four of the six restored reaches demonstrate that NCD restorations can improve the health and sustainability of fish communities in geomorphically unstable Catskill Mountain streams over the short to marginally long term. Bank stability, stream habitat, and trout habitat suitability indices (HSIs) generally improved significantly at the restored reaches, but key habitat features and trout HSIs did not change or decreased at two of them. Fish communities and trout populations at these two reaches were not positively affected by NCD restorations. Though NCD restorations often had a positive effect on habitat and fish communities, our results show that the initial habitat conditions limit the relative improvements than can be achieved, habitat quality and stability do not necessarily respond in unison, and biotic and abiotic responses cannot always be generalized.

New York↗
USGS2011

Effects of natural-channel-design restoration on habitat quality in Catskill Mountain streams, New York

Stream restoration has received much attention in recent years, yet there has been little effort to evaluate its impacts on physical habitat, stability, and biota. A popular but controversial stream restoration approach is natural channel design (NCD), which cannot be adequately evaluated without a long-term, independent assessment of its effects on stream habitat. Six reaches of five Catskill Mountain streams in southeastern New York were restored during 2000–2003 following NCD techniques to decrease bed and bank degradation, decrease sediment loads, and improve water quality. Habitat surveys were conducted during summer low flows from 2001 to 2007. The effects of the NCD projects on stream condition were assessed via a before–after–control–impact study design to quantify the net changes in stream and bank habitat variables relative to those in unaltered control reaches. Analysis of variance tests of three different measures of bank stability show that on average stream stability increased at treatment sites for 2–5 years after restoration. Mean channel depth, thalweg depth, and the pool–riffle ratio generally increased, whereas mean channel width, percent streambank coverage by trees, and shade decreased. Habitat suitability indices for local salmonid species increased at four of six reaches after restoration. The changes in channel dimensions rendered them generally more characteristic of stabler stream forms in the given valley settings. Although these studies were done relatively soon after project completion, our findings demonstrate that habitat conditions can be improved in degraded Catskill Mountain streams through NCD restoration.

New York↗
USGS2017

Distributional changes and range predictions of downy brome (Bromus tectorum) in Rocky Mountain National Park

Downy brome (Bromus tectorum L.), an invasive winter annual grass, may be increasing in extent and abundance at high elevations in the western United States. This would pose a great threat to high-elevation plant communities and resources. However, data to track this species in high-elevation environments are limited. To address changes in the distribution and abundance of downy brome and the factors most associated with its occurrence, we used field sampling and statistical methods, and niche modeling. In 2007, we resampled plots from two vegetation surveys in Rocky Mountain National Park for presence and cover of downy brome. One survey was established in 1993 and had been resampled in 1999. The other survey was established in 1996 and had not been resampled until our study. Although not all comparisons between years demonstrated significant changes in downy brome abundance, its mean cover increased nearly fivefold from 1993 (0.7%) to 2007 (3.6%) in one of the two vegetation surveys (P = 0.06). Although the average cover of downy brome within the second survey appeared to be increasing from 1996 to 2007, this slight change from 0.5% to 1.2% was not statistically significant (P = 0.24). Downy brome was present in 50% more plots in 1999 than in 1993 (P = 0.02) in the first survey. In the second survey, downy brome was present in 30% more plots in 2007 than in 1996 (P = 0.08). Maxent, a species-environmental matching model, was generally able to predict occurrences of downy brome, as new locations were in the ranges predicted by earlier generated models. The model found that distance to roads, elevation, and vegetation community influenced the predictions most. The strong response of downy brome to interannual environmental variability makes detecting change challenging, especially with small sample sizes. However, our results suggest that the area in which downy brome occurs is likely increasing in Rocky Mountain National Park through increased frequency and cover. Field surveys along with predictive modeling will be vital in directing efforts to manage this highly invasive species. ?? Weed Science Society of America 2011.

Invasive Plant Science and Management↗