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At least 181 records · Page 10Linked to original sources

USGS1982

Modern sedimentary environments on the Rhode Island inner shelf, off the eastern United States

Analyses of side-scan sonar records along with previously published bathymetric, textural and subbottom data reveal the sedimentary environments on the inner Continental Shelf south of Narragansett Bay, Rhode Island. The bottom topography in this area is characterized by a broad central depression bordered by shallow, irregular sea floor on the north and east and by a discontinuous, curvilinear ridge on the south and west. Four distinct environments were identified: (1) Pre-Mesozoic coastal rocks are exposed on the sea floor at isolated locations near the shore (waterdepths < 32 m). These exposures have pronounced, irregular topographic relief and produce blotchy patterns op side-scan sonographs. (2) Glacial moraine deposits form the discontinuous offshore ridge. These deposits have hummocky sea-floor relief, are covered by lag gravel and boulders, and appear as predominantly black (strongly reflective) patterns on the side-scan records. (3) Over most of the shallow, irregular bottom in the northeast, on the flanks of the morainal ridge, and atop bathymetric highs, the sea floor is characterized as a mosaic of light and dark patches and lineations. The dark (more reflective) zones are areas of coarse sands and megaripples (wavelengths = 0.8--1.2 m) that either have no detectable relief or are slightly depressed relative to surrounding (fight) areas of finer-grained sands. (4) Smooth beds that produce nearly featureless patterns on the sonographs occupy the broad central bathymetric depression as well as smaller depressions north and east of Block Island. Within the broad depression, sonographs having practically no shading indicate a central zone of modern sandy silt, whereas records having moderate tonality define a peripheral belt of silty sand. The sedimentary environments that are outlined range from erosional or nondepositional (bedrock, glacial moraine) to depositional (featureless beds), and include areas that may reflect a combination of erosional and depositional processes (textural patchiness). The distribution and characteristics of the environments reveal the general post-glacial sedimentary history of this area and provide a guide to future utilization of the shelf surface.

Rhode Island↗

USGS2010

Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay, California; 2009

Results reported herein include trace element concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica (Cohen and Carlton, 1995)), clam reproductive activity, and benthic macroinvertebrate community structure for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in South San Francisco Bay. This report includes data collected for the period January 2009 to December 2009 and extends a critical long-term biogeochemical record dating back to 1974. These data serve as the basis for the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. In 2009, metal concentrations in both sediments and clam tissue were among the lowest concentrations on record and consistent with results observed since 1991. Following significant reductions in the late 1980s, silver (Ag) and copper (Cu) concentrations appeared to have stabilized. Annual mean concentrations have fluctuated modestly (2–4 fold) in a nondirectional manner. Data for other metals, including chromium, mercury, nickel, selenium, vanadium, and zinc, have been collected since 1994. Over this period, concentrations of these elements, which more likely reflect regional inputs and systemwide processes, have remained relatively constant, aside from typical seasonal variation that is common to all elements. Within years, the winter months (January–March) generally exhibit maximum concentrations, with a decline to annual minima in spring through fall. Mercury (Hg) in sediments and M. petalum were comparable to concentrations observed in 2008 and were generally consistent with data from previous years. Selenium (Se) concentrations in sediment varied among years and showed no sustained temporal trend. In 2009, sedimentary Se concentrations declined from the record high concentrations observed in 2008 to concentrations that were among the lowest on record. Selenium in M. petalum was unchanged from 2008. Overall, Cu and Ag concentrations in sediments and soft tissues of the clam, M. petalum , remained representative of the concentrations observed since 1991 following significant reductions in the discharge of these elements from the PARWQCP. This suggests that, as with other elements of regulatory interest, regional-scale factors now largely influence sedimentary and bioavailable concentrations of Ag and Cu. Analyses of the benthic community structure of a mudflat in South San Francisco Bay over a 36-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum , from the same area. Analysis of the reproductive activity of M. petalum shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable, with almost all animals initiating reproduction in the fall and spawning the following spring of most years. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that suggests a more stable community that is subjected to fewer stressors. In addition, two of the opportunistic species ( Ampelisca abdita and Streblospio benedicti ) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals; both species had short-lived rebounds in abundance in 2008 and 2009. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance, with the last several years prior to 2008 showing a stable population. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for those deep-dwelling animals like Macoma petalum . Animals immediately returned to the mudflat in 2008, which was the first indication that the disturbance was not due to a persistent toxin or to anoxia. The use of functional ecology was highlighted in the 2009 benthic community data, which show that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today we see plenty of animals that consume the sediment, have pelagic larvae that must survive landing on the sediment, and in some cases have eggs that must survive being laid in the sediment. We continue to observe the community’s response to the defaunation event, because it allows us to examine the response of the community to a natural disturbance (possible causes include sediment accretion or freshwater inundation) and compare this recovery to the longer-term recovery we observed in the 1970s, when the decline in sediment pollutants was the dominating factor.

California↗

USGS2008

Age, distribution, and stratigraphic relationship of rock units in the San Joaquin Basin Province, California: Chapter 5 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

The San Joaquin Basin is a major petroleum province that forms the southern half of California’s Great Valley, a 700-km-long, asymmetrical basin that originated between a subduction zone to the west and the Sierra Nevada to the east. Sedimentary fill and tectonic structures of the San Joaquin Basin record the Mesozoic through Cenozoic geologic history of North America’s western margin. More than 25,000 feet (>7,500 meters) of sedimentary rocks overlie the basement surface and provide a nearly continuous record of sedimentation over the past ~100 m.y. Further, depositional geometries and fault structures document the tectonic evolution of the region from forearc setting to strike-slip basin to transpressional margin. Sedimentary architecture in the San Joaquin Basin is complicated because of these tectonic regimes and because of lateral changes in depositional environment and temporal changes in relative sea level. Few formations are widespread across the basin. Consequently, a careful analysis of sedimentary facies is required to unravel the basin’s depositional history on a regional scale. At least three high-quality organic source rocks formed in the San Joaquin Basin during periods of sea level transgression and anoxia. Generated on the basin’s west side, hydrocarbons migrated into nearly every facies type in the basin, from shelf and submarine fan sands to diatomite and shale to nonmarine coarse-grained rocks to schist. In 2003, the U.S. Geological Survey (USGS) completed a geologic assessment of undiscovered oil and gas resources and future additions to reserves in the San Joaquin Valley of California (USGS San Joaquin Basin Province Assessment Team, this volume, chapter 1). Several research aims supported this assessment: identifying and mapping the petroleum systems, modeling the generation, migration, and accumulation of hydrocarbons, and defining the volumes of rock to be analyzed for additional resources. To better understand the three dimensional relationships between hydrocarbon source and reservoir rocks, we compiled a database consisting of more than 13,000 well picks and of one-mile resolution seismic grids. Both the well picks and the seismic grids characterize the depths to the top of key stratigraphic units. This database formed the basis of subsequent numerical modeling efforts, including the construction of a three- dimensional geologic model (Hosford Scheirer, this volume, chapter 7) and simulation of the petroleum systems in space and time (Peters, Magoon, Lampe, and others, this volume, chapter 12). To accomplish this modeling, we synthesized the age, geographic distribution, lithology, and petroleum characteristics of hydrocarbon source and reservoir rocks in the basin. The results of that synthesis are presented in this paper in the form of new stratigraphic correlation columns for the northern, central, and southern San Joaquin Valley (fig. 5.1; note that all figures are at the back of this report, following the References Cited). The stratigraphic relationships and ages published here draw heavily on published and unpublished studies of the San Joaquin Basin. The stratigraphy presented in each of the columns necessarily idealizes the subsurface geology over a relatively large area, instead of representing the specific geology at an individual well, oil and gas field, or outcrop. In this paper we present the background rationale for defining the geographic divisions of the basin (inset map, fig. 5.1), the paleontological time scales used for assigning absolute ages to rock units (figs. 5.2 and 5.3), and the supporting maps illustrating the geographic distribution of each rock type included in the stratigraphic column (figs. 5.4 through 5.64).

California↗

USGS2013

Geologic map of MTM -15027, -20027, -25027, and -25032 quadrangles, Margaritifer Terra region of Mars

Mars Transverse Mercator (MTM) quadrangles −15027, −20027, −25027, and −25032 (lat 12.5°−28° S., long 330°−335° E. and lat 22.5°−28° S., long 324.5°−330° E.) in southwestern Margaritifer Terra include diverse erosional landforms, sedimentary deposits, and tectonic structures that record a long geologic and geomorphic history. The northeastern regional slope of the pre-Noachian crustal dichotomy (as expressed along the Chryse trough) and structures of the informally named Middle Noachian or older Holden and Ladon impact basins dominate the topography of the map area. A series of mesoscale outflow channels, Uzboi, Ladon, and Morava Valles, integrated these formerly enclosed basins by overflow and incision around the Noachian/Hesperian transition, although some flooding may have occurred earlier. The area includes excellent examples of Late Noachian to Hesperian valley networks, dissected crater rims, alluvial fans, deltas, and light-toned layered deposits, particularly in Holden and Eberswalde craters. Structural forms include Tharsis-radial grabens, Hesperian wrinkle ridges, floor-fractured impact craters, and severely disrupted chaotic terrains. These well-preserved landforms and sedimentary deposits represent multiple erosional epochs and discrete flooding events, which provide significant insight into the geomorphic processes and climate change on early Mars.

Scientific Investigations Map↗

USGS2004

Aquifers of the Denver Basin, Colorado

Development of the Denver Basin for water supply has been ongoing since the late 1800s. The Denver Basin aquifer system consists of the water-yielding strata of Tertiary and Cretaceous sedimentary rocks within four overlying formations. The four statutory aquifers contained in these formations are named the Dawson, Denver, Arapahoe, and Laramie-Fox Hills. For water rights administrative purposes, the outcrop/subcrop of the Laramie-Fox Hills aquifer defines the margins of the Basin. Initial estimates of the total recoverable groundwater reserves in storage, under this 6700-mi2 area, were 295 million acre-ft. Recent geologic evidence indicates that the aquifers are very heterogeneous and their composition varies significantly with distance from the source area of the sediments. As a result, available recoverable reserves may be one-third less than previously estimated. There is no legal protection for pressure levels in the aquifer, and water managers are becoming increasingly concerned about the rapid water level declines (30 ft/yr). Approximately 33,700 wells of record have been completed in the sedimentary rock aquifers of the Denver Basin for municipal, industrial, agricultural, and domestic uses.

Mountain Geologist↗

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↗

USGS2002

Using tsunami deposits to improve assessment of tsunami risk

In many places in the world the written record of tsunamis is too short to accurately assess the risk of tsunamis. Sedimentary deposits left by tsunamis can be used to extend the record of tsunamis to improve risk assessment. The two primary factors in tsunami risk, tsunami frequency and magnitude, can be addressed through field and modeling studies of tsunami deposits. Recent advances in identification of tsunami deposits and in tsunami sedimentation modeling increase the utility of using tsunami deposits to improve assessment of tsunami risk.

Conference Paper↗

USGS2016

Changing exhumation patterns during Cenozoic growth and glaciation of the Alaska Range: Insights from detrital thermochronology and geochronology

Cenozoic growth of the Alaska Range created the highest topography in North America, but the space-time pattern and drivers of exhumation are poorly constrained. We analyzed U/Pb and fission-track double dates of detrital zircon and apatite grains from 12 catchments that span a 450 km length of the Alaska Range to illuminate the timing and extent of exhumation during different periods. U/Pb ages indicate a dominant Late Cretaceous to Oligocene plutonic provenance for the detrital grains, with only a small percentage of grains recycled from the Mesozoic and Paleozoic sedimentary cover. Fission-track ages record exhumation during Alaska Range growth and incision and reveal three distinctive patterns. First, initial Oligocene exhumation was focused in the central Alaska Range at ~30 Ma and expanded outward along the entire length of the range until 18 Ma. Oligocene exhumation, coeval with initial Yakutat microplate collision >600 km to the southeast, suggests a far-field response to collision that was localized by the Denali Fault within a weak Mesozoic suture zone. Second, the variable timing of middle to late Miocene exhumation suggests independently evolving histories influenced by local structures. Time-transgressive cooling ages suggest successive rock uplift and erosion of Mounts Foraker (12 Ma) through Denali (6 Ma) as crust was advected through a restraining bend in the Denali Fault and indicate a long-term slip rate ~4 mm/yr. Third, Pliocene exhumation is synchronous (3.7–2.7 Ma) along the length of the Alaska Range but only occurs in high-relief, glacier-covered catchments. Pliocene exhumation may record an acceleration in glacial incision that was coincident with the onset of Northern Hemisphere glaciation.

Alaska↗

USGS1982

Uraniferous opal, Virgin Valley, Nevada: Conditions of formation and implications for uranium exploration

Uraniferous, fluorescent opal, which occurs in tuffaceous sedimentary rocks at Virgin Valley, Nevada, records the temperature and composition of uranium-rich solutions as well as the time of uranium-silica coprecipitation. Results are integrated with previous geologic and geochronologic data for the area to produce a model for uranium mobility that may be used to explore for uranium deposits in similar geologic settings. Uraniferous opal occurs as replacements of diatomite, or silicic air-fall ash layers in tuffaceous lakebeds of the Virgin Valley Formation (Miocene) of Merriam (1907). Fission-track radiography shows uranium to be homogeneously dispersed throughout the opal structure, suggesting coprecipitation of dissolved uranium and silica gel. Fluid inclusions preserved within opal replacements of diatomite have homogenization temperatures in the epithermal range and are of low salinity. Four samples of opal from one locality all have U-Pb apparent ages which suggest uraniferous opal precipitation in late Pliocene time. These ages correspond to a period of local, normal faulting, and highangle faults may have served as vertical conduits for transport of deep, thermalized ground water to shallower levels. Lateral migration of rising solutions occurred at intersections of faults with permeable strata. Silica and some uranium were dissolved from silica-rich host strata of 5–20 ppm original uranium content and reprecipitated as the solutions cooled. The model predicts that in similar geologic settings, ore-grade concentrations of uranium will occur in permeable strata that intersect high-angle faults and that contain uranium source rocks as well as efficient reductant traps for uranium. In the absence of sufficient quantities of reductant materials, uranium will be flushed from the system or will accumulate in low-grade disseminated hosts such as uraniferous opal.

Nevada↗

USGS2014

New ichnological, paleobotanical and detrital zircon data from an unnamed rock unit in Yukon-Charley Rivers National Preserve (Cretaceous: Alaska): Stratigraphic implications for the region

A paleontological reconnaissance survey on Cretaceous and Paleogene terrestrial units along the Yukon River drainage through much of east-central Alaska has provided new chronostratigraphic constraints, paleoclimatological data, and the first information on local biodiversity within an ancient, high-latitude ecosystem. The studied unnamed rock unit is most notable for its historic economic gold placer deposits, but our survey documents its relevance as a source rock for Mesozoic terrestrial vertebrates, invertebrates, and associated flora. Specifically, new U-Pb ages from detrital zircons combined with ichnological data are indicative of a Late Cretaceous age for at least the lower section of the studied rock unit, previously considered to be representative of nearly exclusively Paleogene deposition. Further, the results of our survey show that this sedimentary rock unit preserves the first record of dinosaurs in the vast east-central Alaska region. Lastly, paleobotanical data, when compared to correlative rock units, support previous interpretations that the Late Cretaceous continental ecosystem of Alaska was heterogeneous in nature and seasonal.

Palaios↗

USGS2003

Tectonic evolution of the Proterozoic Colorado Province, Southern Rocky Mountains: A summary and appraisal

The Colorado province is a major component of a >1000-km-wide belt of Paleoproterozoic ocean-arc rocks that occupies the southwestern United States. Known as the Transcontinental Proterozoic provinces, this belt of largely juvenile rocks was added to the southern margin of the North American craton during the interval 1.8-1.70 Ga by convergent tectonism along the Cheyenne belt. A growing body of data suggests that these rocks were deposited, at least locally, on older rocks of earliest Proterozoic and Archean ages, probably correlative with the Trans-Hudson and Penokean orogens. The volcano-plutonic and associated sedimentary rocks of the Colorado province record two major, regional orogenies: (1) an older, protracted thermotectonic episode (1.78-1.70 Ga), named the Colorado orogeny, which involved mainly amphibolite-facies metamorphism during piecemeal assembly of various ocean-arc terranes; and (2) a younger, Mesoproterozoic intra-continental orogeny, named the Berthoud orogeny, which involved associated regional heating and A-type plutonism chiefly during the interval 1.45-1.40 Ga. The term "Colorado orogeny" is proposed for the regional Paleoproterozoic dynamothermal deformation. To distinguish differences in the geodynamics and ages of deformation and facilitate comparisons from place to place, type localities are proposed for separate phases or events of the Colorado orogeny. The central Front Range is suggested as a type area for the Berthoud orogeny, because the character and orientation of structures there are readily distinguished from those of the older Colorado orogeny.

Colorado↗

USGS2004

Desert Landforms and Surface Processes in the Mojave National Preserve and Vicinity

Landscape features in the Mojave National Preserve are a product of ongoing processes involving tectonic forces, weathering, and erosion. Long-term climatic cycles (wet and dry periods) have left a decipherable record preserved as landform features and sedimentary deposits. This website provides and introduction to climate-driven desert processes influencing landscape features including stream channels, alluvial fans, playas (dry lakebeds), dunes, and mountain landscapes. Bedrock characteristics, and the geometry of past and ongoing faulting, fracturing, volcanism, and landscape uplift and subsidence influence the character of processes happening at the surface.

Open-File Report↗

USGS2011

Depositional setting and geochemistry of phosphorites and metalliferous black shales in the Carboniferous-Permian Lisburne Group, Northern Alaska

Phosphatic rocks are distributed widely in the Lisburne Group, a mainly Carboniferous carbonate succession that occurs throughout northern Alaska. New sedimentologic, paleontologic, and geochemical data presented here constrain the geographic and stratigraphic extent of these strata and their depositional and paleogeographic settings. Our findings support models that propose very high oxygen contents of the Permo-Carboniferous atmosphere and oceans, and those that suggest enhanced phosphogenesis in iron-limited sediments; our data also have implications for Carboniferous paleogeography of the Arctic. Lisburne Group phosphorites range from granular to nodular, are interbedded with black shale and lime mudstone rich in radiolarians and sponge spicules, and accumulated primarily in suboxic outer- to middle-ramp environments. Age constraints from conodonts, foraminifers, and goniatite cephalopods indicate that most are middle Late Mississippian (early Chesterian; early late Visean). Phosphorites form 2- to 40-cm-thick beds of sand- to pebble-sized phosphatic peloids, coated grains, and (or) bioclasts cemented by carbonate, silica, or phosphate that occur through an interval =12 m thick. High gamma-ray response through this interval suggests strongly condensed facies related to sediment starvation and development of phosphatic hardgrounds. Phosphorite textures, such as unconformity-bounded coated grains, record multiple episodes of phosphogenesis and sedimentary reworking. Sharp bed bases and local grading indicate considerable redeposition of phosphatic material into deeper water by storms and (or) gravity flows. Lisburne Group phosphorites contain up to 37 weight percent P2O5, 7.6 weight percent F, 1,030 ppm Y, 517 ppm La, and 166 ppm U. Shale-normalized rare earth element (REE) plots show uniformly large negative Ce anomalies Ce/Ce*=0.11 + or - 0.03) that are interpreted to reflect phosphate deposition in seawater that was greatly depleted in Ce due to increased oxygenation of the atmosphere and oceans during the Carboniferous evolution of large vascular land plants. Black shales within the phosphorite sections have up to 20.2 weight percent Corg and are potential petroleum source rocks. Locally, these strata also are metalliferous, with up to 1,690 ppm Cr, 2,831 ppm V, 551 ppm Ni, 4,670 ppm Zn, 312 ppm Cu, 43.5 ppm Ag, and 12.3 ppm Tl; concentrations of these metals covary broadly with Corg, suggesting coupled redox variations. Calculated marine fractions (MF) of Cr, V, and Mo, used to evaluate the paleoredox state of the bottom waters, show generally high CrMF/MoMF and VMF/MoMF ratios that indicate deposition of the black shales under suboxic denitrifying conditions; Re/Mo ratios also plot mainly within the suboxic field and support this interpretation. Predominantly seawater and biogenic sources are indicated for Cr, V, Mo, Zn, Cd, Ni, and Cu in the black shales, with an additional hydrothermal contribution inferred for Zn, Cd, Ag, and Tl in some samples. Lisburne Group phosphorites formed in the Ikpikpuk Basin and along both sides of the mud- and chert-rich Kuna Basin, which hosts giant massive sulfide and barite deposits of the Red Dog district. Lisburne Group phosphatic strata are coeval with these deposits and formed in response to a nutrient-rich upwelling regime. Phosphate deposition occurred mainly in suboxic bottom waters based on data for paleoredox proxies (Cr, V, Mo, Re) within contemporaneous black shales. Recent global reconstructions are consistent with Carboniferous upwelling in northern Alaska, but differ in the type of upwelling expected (zonal versus meridional). Paleoenvironmental data suggest that meridional upwelling may better explain phosphorite deposition in the Lisburne Group.

Alaska↗

USGS1959

Geology of Glacier National Park and the Flathead Region, Northwestern Montana

This report summarizes available data on two adjacent and partly overlapping regions in northwestern Montana. The first of these is Glacier National Park plus small areas east and west of the park. The second is here called, for convenience, the Flathead region; it embraces the mountains from the southern tip of Glacier Park to latitude 48 deg north and between the Great Plains on the east and Flathead Valley on the west. The fieldwork under the direction of the writer was done in 1948, 1949, 1950, and 1951, with some work in 1952 and 1953. The two regions together include parts of the Swan, Flathead, Livingstone, and Lewis Ranges. They are drained largely by branches of the Flathead River. On the east and north, however, they are penetrated by tributaries of the Missouri River and in addition by streams that flow into Canada. Roads and highways reach the borders of the regions; but there are few roads in the regions and only two highways cross them. The principal economic value of the assemblage of mountains described in the present report is as a collecting ground for snow to furnish the water used in the surrounding lowlands and as a scenic and wildlife recreation area. A few metallic deposits and lignitic coal beds are known, but these have not proved to be important and cannot, as far as can now be judged, be expected to become so. No oil except minor seeps has yet been found, and most parts of the two regions covered do not appear geologically favorable to the presence of oil in commercial quantities. The high, Hungry Horse Dam on which construction was in progress during the fieldwork now floods part of the Flathead region and will greatly influence the future of that region. The rocks range in age from Precambrian to Recent. The thickest units belong to the Belt series of Precambrian age, and special attention was paid to them. As a result, it is clear that at least the upper part of the series shows marked lateral changes within short distances. This fact introduces complexities into stratigraphic correlation and should be remembered wherever the series is studied. The stromatolites, or fossil algae, in the Belt series, although still imperfectly understood, give clues with respect to problems of ecology and stratigraphy. The subdivisions of the Belt series within the areas covered by the present report are, in ascending order, Altyn limestone, Appekunny argillite, Grinnell argillite, Siyeh limestone, and Missoula group. Local subdivisions of the Missoula group are possible in certain areas, and all the units just named are expected to be subdivided when detailed studies are undertaken. In the Glacier National Park and Flathead regions together, it is probable that between 25,000 and 30,000 feet of beds belonging to the Belt series, possibly more, are present. These consist largely of quartzitic argillite, quartzite, and carbonate rocks, mostly dolomitic. Small gabbroic and diabasic intrusive bodies and, at one horizon, basaltic lava are associated with the Belt series. Above the Belt series is a thick sequence of Cambrian, Devonian, and Carboniferous strata, in which limestone is dominant, followed by strata of Jurassic and Cretaceous age, largely limestone and shale and partly of terrestrial origin. Slightly consolidated gravel, sand, and silt of Tertiary age are preserved in some valleys and as erosional remnants on the plains close to the mountain border. Pleistocene and Recent glacial and fluviatile deposits are plentiful in mountain valleys and on the plains east of the mountains. Sufficient crustal movements took place during the latter part of Belt time to produce tension cracks that permitted some intrusion and related extrusion to occur. Broad crustal warping probably took place at intervals during the Paleozoic era, but these successive movements left little record other than the absence of sedimentary rock units that might otherwise have been deposited. The same can be said of much of the Me

Professional Paper↗

USGS2019

Linking direct measurements of turbidity currents to submarine canyon-floor deposits

Submarine canyons are conduits for episodic and powerful sediment density flows (commonly called turbidity currents) that move globally significant amounts of terrestrial sediment and organic carbon into the deep sea, forming some of the largest sedimentary deposits on Earth. The only record available for most turbidity currents is the deposit they leave behind. Therefore, to understand turbidity current processes, we need to determine the degree to which these flows are represented by their deposits. However, linking flows and deposits is a major long-standing scientific challenge. There are few detailed measurements from submarine turbidity currents in action, and even fewer direct measurements that can be compared to resulting seabed deposits. Recently, an extensive array of moorings along Monterey Canyon, offshore California, took measurements and samples during sediment density flow events, providing the most comprehensive dataset to date of turbidity current flows and their deposits. Here, we use sediment trap samples, velocity measurements, and seafloor cores to document how sand is transported through a submarine canyon, and how the transported sediment is represented in seafloor deposits. Sediment trap samples from events contain primarily fine to medium-grained sand with sharp bases, normal grading, and muddy tops. Sediment captured from the water column during the flow shows normal grading, which is broadly consistent with the initial peak and waning of flow velocities measured at a single height within the flow, and may be enhanced by collapsing flows. Flow events contain coarser sand concentrated toward the seafloor and larger grain sizes on the seafloor or in the dense near-bed layer, possibly representative of stratified flows. Although flow velocity varies, sand grain sizes in sediment traps are similar over distances of 50 km down-canyon, suggesting that grain size is an unfaithful record of down-canyon changes in maximum flow speeds. Sand transported within flow events and sampled in sediment traps is similar to sand sampled from the seafloor shortly after the events, but traps do not contain pebbles and gravel common in seabed deposits. Seabed deposits thus appear to faithfully record the sand component that is transported in the water column during sub-annual turbidity currents.

California↗

USGS2018

Fire, vegetation, and Holocene climate in a southeastern Tibetan lake: a multi-biomarker reconstruction from Paru Co

The fire history of the Tibetan Plateau over centennial to millennial timescales is not well known. Recent ice core studies reconstruct fire history over the past few decades but do not extend through the Holocene. Lacustrine sedimentary cores, however, can provide continuous records of local environmental change on millennial scales during the Holocene through the accumulation and preservation of specific organic molecular biomarkers. To reconstruct Holocene fire events and vegetation changes occurring on the southeastern Tibetan Plateau and the surrounding areas, we used a multi-proxy approach, investigating multiple biomarkers preserved in core sediment samples retrieved from Paru Co, a small lake located in the Nyainqentanglha Mountains (29°47′45.6′′ N, 92°21′07.2′′ E; 4845 m a.s.l.). Biomarkers include n -alkanes as indicators of vegetation, polycyclic aromatic hydrocarbons (PAHs) as combustion proxies, fecal sterols and stanols (FeSts) as indicators of the presence of humans or grazing animals, and finally monosaccharide anhydrides (MAs) as specific markers of vegetation burning processes. Insolation changes and the associated influence on the Indian summer monsoon (ISM) affect the vegetation distribution and fire types recorded in Paru Co throughout the Holocene. The early Holocene (10.7–7.5 cal kyr BP) n -alkane ratios demonstrate oscillations between grass and conifer communities, resulting in respective smouldering fires represented by levoglucosan peaks, and high-temperature fires represented by high-molecular-weight PAHs. Forest cover increases with a strengthened ISM, where coincident high levoglucosan to mannosan (L ∕ M) ratios are consistent with conifer burning. The decrease in the ISM at 4.2 cal kyr BP corresponds with the expansion of regional civilizations, although the lack of human FeSts above the method detection limits excludes local anthropogenic influence on fire and vegetation changes. The late Holocene is characterized by a relatively shallow lake surrounded by grassland, where all biomarkers other than PAHs display only minor variations. The sum of PAHs steadily increases throughout the late Holocene, suggesting a net increase in local to regional combustion that is separate from vegetation and climate change.

Climate of the Past↗

USGS2019

Reconstructing precipitation in the tropical South Pacific from dinosterol 2H/1H ratios in lake sediment

The South Pacific Convergence Zone (SPCZ) is the Southern Hemisphere’s largest precipitation feature supplying freshwater to 11 million people. Despite its significance, little is known about the location and intensity of SPCZ precipitation prior to instrumental records, hindering attempts to predict precipitation changes in a warming world. Here we use sedimentary molecular fossils to establish a tool for extending the historical record of precipitation. Freshwater lake sediments and water samples were collected from 30 lakes that span a 4.6 mm d −1 range in precipitation rates from the Global Precipitation Climatology Project (GPCP). δ 2 H lakewater values from 29 lakes ranged from −29 to +23‰ and were inversely correlated ( r = −0.51, p < 0.001) with precipitation rates, likely due to the combination of the amount of precipitation plus evaporation. δ 2 H values of the dinoflagellate sterol dinosterol in surficial sediments from 21 lakes ranged from −316‰ in the Solomon Islands to −245‰ in French Polynesia. These δ 2 H dinosterol values were significantly correlated ( r = 0.71, p < 0.001) with δ 2 H lakewater and inversely correlated ( r = −0.77, p < 0.001) with mean annual precipitation rates with a sensitivity of −12.1 ± 2.6‰ (mm d −1 ) −1 . Fractionation between dinosterol and lake water (ε dinosterol/lakewater ) decreased at the driest lake sites ( r = − 0.70, p < 0.001). The empirical relationship between δ 2 H dinosterol and GPCP rainfall, although indirect, provides a means of quantitatively reconstructing past precipitation in the SPCZ region with an uncertainty of less than 3.1 mm d −1 , which compares favorably to the 1.5 mm d −1 uncertainty for the satellite-gauge based GPCP precipitation data.

Geochimica et Cosmochimica Acta↗

USGS2024

Paleogene sedimentary basin development in southern Nevada, USA

The cause of the transition from Mesozoic and early Cenozoic crustal shortening to later extension in the western United States is debated. In many parts of the extant Sevier hinterland, now the Basin and Range Province, the sedimentary sections that provide the most direct record of that transition remain poorly studied and lack meaningful age control. In this paper, we present field characterization supported by U-Pb detrital zircon and 40 Ar/ 39 Ar feldspar ages for ten sections across southern Nevada. We describe a newly identified basin, here named the Fallout Hills basin, which preserves >1.0 km of sedimentary deposits as old as middle Eocene, ca. 48 Ma. Deposition occurred during the 20 m.y. (million years) before the 27.60 ± 0.03 Ma Monotony Tuff blanketed much of south-central Nevada, based on 47.6 Ma and younger detrital zircon maximum depositional ages (MDAs) from near the Pintwater and Spotted Ranges. Elsewhere in southern Nevada, prevolcanic Cenozoic strata commonly form thinner (~100 m), isolated exposures that yield detrital zircon MDAs ≤10 m.y. older than (and in some cases essentially the same age as) the ca. 27–28 Ma ignimbrites that cap the sections. A variable but overall upward-fining facies pattern is observed in both the Fallout Hills basin and the thinner sections. These localized patterns imply topographic changes that are unlikely to reflect plate-scale processes and are not consistent with large-magnitude extension. Instead, variable uplift due to magmatism combined with antecedent topographic relief from thrust faulting and subsequent erosion likely provided accommodation for these deposits.

Nevada↗