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At least 1,099 records · Page 61Linked to original sources

USGS2023

Timing of reproduction underlies fitness tradeoffs for a salmonid fish

Life history diversity is generated and maintained in part by density-dependent fitness tradeoffs that inhibit a single trait value from reaching fixation. While central to our understanding of evolution, demonstrating density dependence in the strength of fitness tradeoffs is difficult in natural systems. The timing of reproduction is a key life history trait that determines access to breeding habitat and exposure of offspring to competitive interactions and environmental conditions. Understanding the processes underlying diversity in reproductive timing will aid efforts to increase adaptive capacity under global environmental change. Here, we used detailed field studies, genetic parentage assignment, and simulation modeling to evaluate the fitness tradeoffs associated with the timing of reproduction for Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri in groundwater-dominated tributaries to the upper Snake River, Wyoming, USA. We conducted our study across two years to understand how the strength of tradeoffs changes with population density. We found that early breeders experienced reduced reproductive success relative to later breeders due to the negative impact of nest superimposition (where later breeders construct nests overlapping those constructed previously) on embryo survival. However, as the risk of superimposition declined in the low-density year and early breeders experienced fewer losses, reproductive success became more similar among individuals breeding at different times. Further, in the spring following the critical period for growth and survival, offspring of early breeders had experienced longer growing seasons, attained larger body sizes, and were equally abundant relative to those of later breeders, suggesting that fitness losses due to superimposition may be offset by size-dependent competitive ability and overwinter survival. Our results illustrate a mechanism underlying diversity in the timing of reproduction for salmonids. This type of life history diversity will help to ensure the resilience and stability of salmonid populations attempting to adapt to changing local stressors associated with global climate change.

Oikos↗

USGS1975

Magma beneath Yellowstone National Park

The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain. Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators, the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a fundamental structure in the relatively shallow and brittle lithosphere overhead. The concept that a northeastward-propagating major crustal fracture controls the migration path of the major foc

Wyoming↗

USGS2004

Complete genome sequence of Fer-de-Lance Virus reveals a novel gene in reptilian Paramyxoviruses

The complete RNA genome sequence of the archetype reptilian paramyxovirus, Fer-de-Lance virus (FDLV), has been determined. The genome is 15,378 nucleotides in length and consists of seven nonoverlapping genes in the order 3??? N-U-P-M-F-HN-L 5???, coding for the nucleocapsid, unknown, phospho-, matrix, fusion, hemagglutinin-neuraminidase, and large polymerase proteins, respectively. The gene junctions contain highly conserved transcription start and stop signal sequences and tri-nucleotide intergenic regions similar to those of other Paramyxoviridae. The FDLV P gene expression strategy is like that of rubulaviruses, which express the accessory V protein from the primary transcript and edit a portion of the mRNA to encode P and I proteins. There is also an overlapping open reading frame potentially encoding a small basic protein in the P gene. The gene designated U (unknown), encodes a deduced protein of 19.4 kDa that has no counterpart in other paramyxoviruses and has no similarity with sequences in the National Center for Biotechnology Information database. Active transcription of the U gene in infected cells was demonstrated by Northern blot analysis, and bicistronic N-U mRNA was also evident. The genomes of two other snake paramyxovirus genotypes were also found to have U genes, with 11 to 16% nucleotide divergence from the FDLV U gene. Pairwise comparisons of amino acid identities and phylogenetic analyses of all deduced FDLV protein sequences with homologous sequences from other Paramyxoviridae indicate that FDLV represents a new genus within the subfamily Paramyxovirinae. We suggest the name Ferlavirus for the new genus, with FDLV as the type species.

Journal of Virology↗

USGS1962

Late cenozoic structure of west-central Idaho

The massive Salmon River Mountains of interior Idaho are bounded on the west by a belt 30 miles wide of post-Miocene, west-tilted normal-fault blocks and west-dipping monoclines. The belt is coincident with the western border zone of the middle Cretaceous Idaho batholith, as it extends from the west edge of the massive interior of the batholith to about the western limit of the border zone of gneisses and schists. West of this belt is the Columbia Plateau province of irregular domal and anticlinal uplifts and northwest-trending normal faults. These structures are superimposed upon east- to northeast-trending, low-grade metamorphic rocks intruded by semi-concordant stocks and small batholiths, products largely of Late Jurassic (?) orogeny. The Idaho batholith has been little deformed, and its border-zone rocks of intermediate competence are broken by concordant structures. Young structures cut directly across the relatively incompetent rocks of the older orogen to the west. The mountains flanking the Snake River and Salmon River canyons are higher than those farther away, suggesting that local isostatic uplift may be compensating for their erosion.

Idaho↗

USGS1965

Biota of a late glacial rocky mountain pond

The sediments of a late glacial sag pond in Huerfano Park, south-central Colorado, have yielded a varied biota consisting of vertebrates, terrestrial and fresh-water mollusks, sponges, and pollen. Wood from the sediments has a radiocarbon age of 9600 ± 200 years. The vertebrate fauna contains the tooth of a prairie dog and the remains of frog, salamander, snake, and fish—all characteristic of present-day montane lakes and ponds and their margins in Colorado. The mollusks are all living species, and the fauna is dominated by gastropods. With the exception of one form (Vitrina alaskana Dall), whose known range does not extend as far south as Huerfano Park, the fauna is not significantly different from the mollusks living in the area today. The sediments also contain an abundant and unusually diversified sponge fauna in which as many as six species may be represented. A pollen spectrum from the sediments is composed of arboreal pollen characteristic of the present-day Transition Zone flora which, in Colorado, grows on the upper edge of the Great Plains and all of the foothills belt. Vertical variation in the sediment types and the enclosed biota makes it possible to recreate the changing depositional environment and local climate throughout the life of the pond. The basal sediments, interbedded marl and clastic materials, are interpreted as indicating deposition during alternating wet and dry periods. A bed of nearly pure calcium carbonate marl, which reaches a thickness of 2 feet, forms the middle stratigraphic unit. It is highly fossiliferous and is thought to have been deposited during a warm dry period with relatively mild winters. The uppermost stratigraphic unit is a gray carbonaceous clay which filled the basin as vegetation encroached upon the lake and the lake itself was reduced to a marsh. Because of the radiocarbon age and the reconstruction of the climate based upon faunal and sedimentological changes, the lower two stratigraphic units are thought to correlate with the Lubbock Subpluvial, and the uppermost unit, the gray carbonaceous clay, with the early part of the Yellow House Interval as described in the Llano Estacado, New Mexico.

Colorado↗

USGS1970

Geochronology of Tertiary igneous rocks in central Nevada

Potassium-argon dating of Tertiary igneous rocks in Lander County, central Nevada, indicates that igneous activity was episodic and can be separated into three periods. Igneous activity started abruptly about 37 m.y. ago with local extrusion of andesitic to quartz-latitic lava flows and intrusion of hypabyssal rocks of similar composition. This activity ceased about 33 m.y. ago and was followed by extrusion of rhyolite ash-flow sheets that blanketed large parts of the region. These ash-flow sheets range from about 34 to 22 m.y. in age. The final phase, represented by basalt and basaltic-andesite flows and intrusive rhyolite flow-dome complexes, took place about 16 to 10 m.y. ago. Andesitic to dacitic lava and hypabyssal rocks about 35 m.y. old are widespread east of Lander County and rhyolitic ash-flow tuffs 34 to 20 m.y. old are found south and east of Lander County. The younger (16 to 10 m.y.) basalt and basaltic-andesite flows are related to volcanism of the Snake River plain province to the north. The precision of the ages was evaluated by means of: (1) repeat analyses of the same mineral separate, (2) age determination of mineral pairs from the same hand specimen, and (3) age determinations on widely spaced samples from the same geologic body or formation. The last method seems most meaningful from a geologic point of view.

Nevada↗

USGS1985

Genetic interpretation of lead-isotopic data from the Columbia River basalt group, Oregon, Washington, and Idaho

Lead-isotopic signatures of basalts from the Columbia River Basalt Group of central Oregon, Washington, and western Idaho, and of the high-alumina olivine basalts from southeastern Oregon plot mostly in the field of Pb-isotopic data from volcanic rocks of the Cascade Range. In contrast to the mid-ocean ridge basalts (MORB), the Pb-isotopic data for several of the formations form small, tight clusters, and the Nd- and Sr-isotopic data show discrete variation between these basalt groups. Pseudoisochrons are not observed. A single model will account for the observed isotopic and trace-element data from samples from most of the Columbia River Basalt Group. This model calls for partial melting of the convecting oceanic-type mantle and mixing with, or contamination by, fluids derived from continental-derived sediments. It requires that crustal components are not only subducted along the trench, but that they are also transported in the low-velocity zone of the mantle at least 400 km behind the active volcanic arc into the back-arc environment represented by the Columbia Plateaus province. Lead isotopes in the Saddle Mountains Basalt, the youngest formation, suggest that these magmas were formed by partial melting of a 2.6-b.y.-old subcontinental lithosphere that extends as far west as south-central Washington near Ice Harbor Dam. The source material for these flows is characterized by high Th/U, Th/Pb, Rb/Sr, and Nd/Sm ratios and light REE enrichment. An additional component, presumably granitic crust, is necessary to explain the Pb-isotopic data of the Umatilla and perhaps the Pomona Members of the Saddle Mountains Basalt. This contamination model is supported by published δ 18 O data and petrological interpretation. Published studies of basalts from the Deccan Traps, the Tasmanian dolerites, the Snake River Group, and the volcanics of the Yellowstone Plateau province also suggest that melting of old subcontinental lithosphere beneath the continental crust may be an important process in basalt genesis on a global scale.

Idaho, Oregon, Washington↗

USGS1993

Late Cenozoic structure and correlations to seismicity along the Olympic-Wallowa Lineament, northwest United States

Late Cenozoic fault geometry, structure, paleoseismicity, and patterns of recent seismicity at two seismic zones along the Olympic-Wallowa lineament (OWL) of western Idaho, northeast Oregon, and southeast Washington indicate limited right-oblique slip displacement along multiple northwest-striking faults that constitute the lineament. The southern end of the OWL originates in the Long Valley fault system and western Snake River Plain in western Idaho, where it accommodates basin-and-range extension. Several kilometers west of the Long Valley fault system, post-middle Miocene displacement along the OWL has resulted in adjacent areas of uplift and subsidence. The OWL in northeast Oregon consists of a wide zone of northwest-striking faults and is associated with several large, inferred, pull-apart basins. The OWL then emerges from the Blue Mountain uplift as a much narrower zone of faults in the Columbia Plateau known as the Wallula fault zone (WFZ). Structural relationships in the WFZ strongly suggest that it is a right-slip extensional duplex. An ash horizon that correlates with the Mount St. Helens "J" composition (10.7 Ka) is displaced vertically 5 m by a normal fault along a segment of the WFZ. The intensity center for a damaging M = 6.1 earthquake in 1936 is located in the WFZ only a few kilometers northeast of this Holocene fault. Other youthful-appearing, strike-slip and thrust faults are located farther northwest along the OWL and may pose a seismic hazard to adjacent population centers and critical facilities.

Geological Society of America Bulletin↗

USGS2002

Upper-mantle origin of the Yellowstone hotspot

Fundamental features of the geology and tectonic setting of the northeast-propagating Yellowstone hotspot are not explained by a simple deep-mantle plume hypothesis and, within that framework, must be attributed to coincidence or be explained by auxiliary hypotheses. These features include the persistence of basaltic magmatism along the hotspot track, the origin of the hotspot during a regional middle Miocene tectonic reorganization, a similar and coeval zone of northwestward magmatic propagation, the occurrence of both zones of magmatic propagation along a first-order tectonic boundary, and control of the hotspot track by preexisting structures. Seismic imaging provides no evidence for, and several contraindications of, a vertically extensive plume-like structure beneath Yellowstone or a broad trailing plume head beneath the eastern Snake River Plain. The high helium isotope ratios observed at Yellowstone and other hotspots are commonly assumed to arise from the lower mantle, but upper-mantle processes can explain the observations. The available evidence thus renders an upper-mantle origin for the Yellowstone system the preferred model; there is no evidence that the system extends deeper than ???200 km, and some evidence that it does not. A model whereby the Yellowstone system reflects feedback between upper-mantle convection and regional lithospheric tectonics is able to explain the observations better than a deep-mantle plume hypothesis.

Geological Society of America Bulletin↗

USGS1974

Tectonic significance of the Kodiak-Bowie seamount chain, northeastern Pacific

The hypothesis of a fixed melting spot reference frame (M) for relative plate motion is tested in the northeastern Pacific Ocean, where the Kodiak-Bowie seamount chain intersects the northern triple junction between the Pacific, American, and Juan de Fuca plates. Available age determinations on Kodiak and Giacomini Seamounts provide an estimated average rate of volcanic propagation along the chain of 6.5 cm per yr and allow estimates of plate movements relative to the melting spot. The inferred motion of the American plate relative to M is close to that observed along the Yellowstone-Snake River Plain volcanic trend and broadly supports the concept of a fixed melting spot reference frame. However, the convex northward curvature of the Kodiak-Bowie chain and of several chains to the south does not support the hypothesis. The lack of parallelism between these seamounts and the Hawaiian chain suggests slow relative movement between the Kodiak-Bowie and Hawaiian melting spots.

Geology↗

USGS2009

Introduction to paleoenvironments of Bear Lake, Utah and Idaho, and its catchment

In 1996 a group led by the late Kerry Kelts (University of Minnesota) and Robert Thompson (U.S. Geological Survey) acquired three piston cores (BL96-1, -2, and -3) from Bear Lake. The coring arose from their recognition of Bear Lake as a potential repository of long records of paleoenvironmental change. They recognized that the lake is located in an area that is sensitive to changes in regional climate patterns (Dean et al., this volume), that the lake basin is long lived (see Colman, 2006; Kaufman et al., this volume), and that, unlike many lakes in the Great Basin, Bear Lake was never dry during warm dry periods. Bear Lake lies in the northeastern Great Basin to the northeast of Great Salt Lake, just south of the Snake River drainage, and a short distance west of the Green River drainage that makes up part of the Upper Colorado River Basin (Fig. 1). Similarity among the historic Bear Lake and Great Salt Lake hydrographs and flows on the Green River indicates that the hydrology of Bear Lake reflects regional precipitation (Fig. 2). Therefore, paleorecords from Bear Lake are important to understanding past climate for a large region, including the Upper Colorado River Basin, the source of much of the water for the southwestern United States. Initially, paleoenvironmental studies of Bear Lake sediments focused on cores BL96-1, -2, and -3. Additional coring was conducted to elucidate the spatial distribution of sedimentary units and to extend the record back in time. The study was also expanded to include extensive study of the catchment, including the properties of catchment materials and the processes that could potentially affect the delivery of catchment materials to the lake. Cores BL96-1, -2, and -3 were taken with a Kullenburg piston corer along an east–west profile in roughly 50, 40, and 30 m of water, respectively (Table 1, Fig. 3). These three cores, each taken as a single 4- to 5-m-long segment, provide a nearly complete composite section from ca. 26 cal ka to the late Holocene. In 1998 a number of short gravity cores were taken from the uppermost water-rich sediments that were not sampled by the 1996 cores. During 2000, cores were taken with a percussion piston corer (manufactured by UWITEC) at three locations in and around Mud Lake and at two locations in the northern end of Bear Lake (Fig. 3). Cores acquired with the percussion corer comprise as many as three overlapping segments up to 2 m in length. In 2002, additional percussion piston cores and associated gravity cores of the uppermost sediments were acquired from five sites in the northern half of the lake. In conjunction with two of the cores collected in 2000, these cores form a north–south profile along a seismic line and span water depths from less than 10 m to ~40 m. Data from this profile provide much of the evidence for lake-level variations (Smoot and Rosenbaum, this volume). Finally, during 2000, two long cores, BL00-1D and -1E (collectively referred to here simply as BL00-1), were taken at a site near the depocenter during testing of the GLAD800 coring platform (Fig. 4; Dean et al., 2002). These cores provide a record back to ca. 220 ka.

Idaho;Utah;Wyoming↗

USGS2014

Hells Canyon to the Bitterroot front: A transect from the accretionary margin eastward across the Idaho batholith

This field guide covers geology across north-central Idaho from the Snake River in the west across the Bitterroot Mountains to the east to near Missoula, Montana. The regional geology includes a much-modified Mesozoic accretionary boundary along the western side of Idaho across which allochthonous Permian to Cretaceous arc complexes of the Blue Mountains province to the west are juxtaposed against autochthonous Mesoproterozoic and Neoproterozoic North American metasedimentary assemblages intruded by Cretaceous and Paleogene plutons to the east. The accretionary boundary turns sharply near Orofino, Idaho, from north-trending in the south to west-trending, forming the Syringa embayment, then disappears westward under Miocene cover rocks of the Columbia River Basalt Group. The Coolwater culmination east of the Syringa embayment exposes allochthonous rocks well east of an ideal steep suture. North and east of it is the Bitterroot lobe of the Idaho batholith, which intruded Precambrian continental crust in the Cretaceous and Paleocene to form one of the classical North American Cordilleran batholiths. Eocene Challis plutons, products of the Tertiary western U.S. ignimbrite flare-up, intrude those batholith rocks. This guide describes the geology in three separate road logs: (1) The Wallowa terrane of the Blue Mountains province from White Bird, Idaho, west into Hells Canyon and faults that complicate the story; (2) the Mesozoic accretionary boundary from White Bird to the South Fork Clearwater River east of Grangeville and then north to Kooskia, Idaho; and (3) the bend in the accretionary boundary, the Coolwater culmination, and the Bitterroot lobe of the Idaho batholith along Highway 12 east from near Lewiston, Idaho, to Lolo, Montana.

Idaho↗

USGS2017

Geology and vertebrate paleontology of Tule Springs Fossil Beds National Monument, Nevada, USA

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley, Nevada, USA. TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two and possibly three distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights some of the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Nevada↗

USGS2021

Late Cenozoic tephrochronology of the Mount Diablo area within the evolving plate-tectonic boundary zone of northern California

We present a tephrochronologic/chronostratigraphic database for the Mount Diablo area and greater San Francisco Bay region that provides a spatial and temporal framework for geologic studies in the region, including stratigraphy, paleogeography, tectonics, quantification of earth surface processes, recurrence of natural hazards, and climate change. We identified and correlated 34 tephra layers within this region using the chemical composition of their volcanic glasses, stratigraphic sequence, and isotopic and other dating techniques. Tephra layers range in age from ca. 65 ka to ca. 29 Ma, as determined by direct radiometric techniques or by correlation to sites where they have been dated. The tephra layers are of Quaternary or Neogene age except for two that are of Oligocene age. We correlated the tephra layers among numerous sites throughout northern California. Source areas of the tephra layers are the Snake River–Yellowstone hotspot trend of northern Nevada, southern Idaho, and western Wyoming; the Nevadaplano caldera complex of central Nevada; the Jemez Mountains–Valles Caldera in northwestern New Mexico; the Southern Nevada volcanic field and related source areas in eastern California and west-central Nevada; the Quien Sabe–Sonoma volcanic centers of the California Coast Ranges; and the young Cascade Range volcanic centers of northeastern California and Oregon.

GSA Memoirs↗

USGS2022

Tephrochronology of the Miocene Monterey and Modelo Formations, California

Tuff beds have been known in the Miocene Monterey and Modelo Formations since the initial descriptions; however, age control and correlation is predominantly biostratigraphy. Here we combine tephrochronology and biostratigraphy in order to provide numerical age control for eight sedimentary sequences of the Monterey and Modelo Formations from Monterey, California to Orange County, California. We correlate 38 tuffs and tephra beds in the Monterey and Modelo Formations to 26 different dated tuffs found mainly in non-marine sequences in Nevada, Idaho and New Mexico. We also include geochemical data for an additional 19 tuffs in the Monterey and Modelo Formations for which there are no known correlative tuffs and geochemical data for 11 additional tuffs in other units that will add to the Miocene tephrostratigraphy. The identified tuffs range in age from 16 to 7 Ma with 31 tuffs erupted from volcanic centers of the Snake River Plain of northern Nevada to eastern Idaho. Twelve other tuffs erupted from the Southern Nevada Volcanic Field, one from the Sonoma Volcanic Field, north of San Francisco, and the eruptive source of 12 other tuffs is uncertain. These tuffs provide useful correlations of marine sequences deposited at varying depths along offshore Miocene California and possible insight into the distribution of air-fall tephra from so-called super eruptions

GSA Special Papers↗

USGS2004

The 87Sr/86Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system

Lakes in the Bonneville basin have fluctuated dramatically in response to changes in rainfall, temperature, and drainage diversion during the Quaternary. We analyzed tufas and shells from shorelines of known ages in order to develop a relation between 87Sr/86Sr ratio of carbonates and lake level, which then can be used as a basis for constraining lake level from similar analyses on carbonates in cores. Carbonates from the late Quaternary shorelines yield the following average 87Sr/86Sr ratios: 0.71173 for the Stansbury shoreline (22-20 14C ka; 1350 m), 0.71153 for the Bonneville shoreline (15.5-14.5 14C ka; 1550 m), 0.71175 for the Provo shoreline (14.4-14.0 14C ka; 1450 m), 0.71244 for the Gilbert shoreline (???10.3-10.9 14C ka; 1300 m), and 0.71469 for the modern Great Salt Lake (1280 m). These analyses show that the 87Sr/86Sr ratio of lacustrine carbonates changes substantially at low- to mid-lake levels but is invariant at mid- to high-lake levels. Sr-isotope mixing models of Great Salt Lake and the Bonneville paleolake system were constructed to explain these variations in 87Sr/86Sr ratios with change in lake level. Our model of the Bonneville system produced a 87Sr/86Sr ratio of 0.71193, very close to the observed ratios from high-shoreline tufa and shell. The model verifies that the integration of the southern Sevier and Beaver rivers with the Bear and others rivers in the north is responsible for the lower 87Sr/86Sr ratios in Lake Bonneville compared to the modern Great Salt Lake. We also modeled the 87Sr/86Sr ratio of Lake Bonneville with the upper Bear River diverted into the Snake River basin and obtained an 87Sr/86Sr ratio of 0.71414. Coincidentally, this ratio is close to the observed ratio for Great Salt Lake of 0.71469. This means that 87Sr/86Sr ratios of >0.714 for carbonate can be produced by climatically induced low-lake conditions or by diversion of the upper Bear River out of the Bonneville basin. This model result also demonstrates that the upper Bear River had to be flowing into the Bonneville basin during highstands of other late Quaternary lake cycles: carbonates from the Little Valley (130-160 ka) and Cutler Dam (59 ?? 5 ka) lake cycles returned 87Sr/86Sr ratios of 0.71166 and 0.71207, respectively, and are too low to be produced by a lake without the upper Bear River input. ?? 2004 Geological Society of America.

Geological Society of America Bulletin↗

USGS2009

SHRIMP U-Pb dating of recurrent Cryogenian and Late Cambrian-Early Ordovician alkalic magmatism in central Idaho: Implications for Rodinian rift tectonics

Composite alkalic plutonic suites and tuffaceous diamictite, although discontinuously exposed across central Idaho in roof pendants and inliers within the Idaho batholith and Challis volcanic-plutonic complex, define the >200-km-long northwest-aligned Big Creek-Beaverhead belt. Sensitive highresolution ion microprobe (SHRIMP) U-Pb zircon dates on these igneous rocks provide direct evidence for the orientation and location of the Neoproterozoic-Paleozoic western Laurentian rift margin in the northern U.S. Cordillera. Dating delimits two discrete magmatic pulses at ca. 665-650 Ma and 500-485 Ma at the western and eastern ends, respectively, of this belt. Together with the nearby 685 Ma volcanic rocks of the Edwardsburg Formation, there is a 200 Ma history of recurrent extensional magmatic pulses along the belt. A similar history of recurrent uplift is reflected in the stratigraphic record of the associated miogeoclinal and cratonal platform basins, suggesting that the Big Creek-Beaverhead belt originated as a border fault during continental rift events. The magmatic belt is paired with the recurrently emergent Lemhi Arch and narrow miogeoclinal facies belts and it lies inboard of a northwest-striking narrow zone of thinned continental crust. These features define a northeast-extending upper-plate extensional system between southeast Washington and southeast Idaho that formed a segment of the Neoproterozoic-Paleozoic miogeocline. This segment was flanked on the north by the St. Mary-Moyie transform zone (south of a narrow southern Canadian upper-plate margin) and on the south by the Snake River transfer zone (north of a broad Great Basin lower-plate margin). These are the central segments of a zigzagshaped Cordilleran rift system of alternating northwest-striking extensional zones offset by northeast-striking transfers and transforms. The data substantiate polyphase rift and continental separation events that included (1) pre-and syn-Windermere rifting, (2) Windermere margin subsidence, (3) late Ediacaran-Cambrain rifting, and (4) welldeveloped late Ediacaran-Devonian passive margin subsidence and deposition. Timing and geometries support synchronous but opposing divergence along Cordilleran and Atlantic rifts with a junction in Southern California-Sonora. ?? 2010 Geological Society of America.

Geological Society of America Bulletin↗

USGS2017

Miocene−Pleistocene deformation of the Saddle Mountains: Implications for seismic hazard in central Washington, USA

The Yakima fold province, located in the backarc of the Cascadia subduction zone, is a region of active strain accumulation and deformation distributed across a series of fault-cored folds. The geodetic network in central Washington has been used to interpret large-scale N-S shortening and westward-increasing strain; however, geodetic data are unable to resolve shortening rates across individual structures in this low-strain-rate environment. Resolving fault geometries, slip rates, and timing of faulting in the Yakima fold province is critically important to seismic hazard assessment for nearby infrastructure and population centers. The Saddle Mountains anticline is one of the most prominent Yakima folds. It is unique within the Yakima fold province in that the syntectonic strata of the Ringold Formation are preserved and provide a record of deformation and drainage reorganization. Here, we present new stratigraphic columns, U-Pb zircon tephra ages, U-series caliche ages, and geophysical modeling that constrain two line-balanced and retrodeformed cross sections. These new constraints indicate that the Saddle Mountains anticline has accommodated 1.0−1.3 km of N-S shortening since 10 Ma, that shortening increases westward along the anticline, and that the average slip rate has increased 6-fold since 6.8 Ma. Provenance analysis suggests that the source terrane for the Ringold Formation was similar to that of the modern Snake River Plain. Using new slip rates and structural constraints, we calculate the strain accumulation time, interpretable as a recurrence interval, for earthquakes on the Saddle Mountains fault and find that large-magnitude earthquakes could rupture along the Saddle Mountains fault every 2−11 k.y.

Washington↗