Filters: Tags: Loess (X)
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Temporal and spatial sources of silica for chert remain poorly constrained. Modern sources to the worlds oceans include silica in rivers > aeolian (dust) deposition > sea floor vents and submarine weathering. However, changes in aridity and dust flux during the Phanerozoic may explain variations in the ocean silica cycle and times and places of chert formation. The chemistry of fine quartz dust (FQD) provides a chemical mechanism for the transformation of FQD to polymorphs of silica in chert; FQD is readily dissolved, then reprecipitated as Opal-A by either biotic or abiotic processes. An unequivocal relation between increases in dust flux and biogenic opal-A in the western Pacific Ocean during the past 200 kyr...
During 2009, the Alaska Division of Geological & Geophysical Surveys continued a program, begun in 2006, of reconnaissance mapping of surficial geology in the proposed natural-gas pipeline corridor through the upper Tanana River valley. The study area is a 12-mi-wide (19.3-km-wide) area that straddles the Alaska Highway from the western boundaries of the Tanacross B-3 and A-3 quadrangles near Tetlin Junction eastward to the eastern boundaries of the Nabesna D-1 and C-1 quadrangles along the Canada border. Mapping during 2008-2009 in the Tanacross and Nabesna quadrangles linked with the mapping completed in the Tanacross, Big Delta and Mt. Hayes quadrangles in 2006-2008. Surficial geology was initially mapped in...
This map illustrates extents and types of unconsolidated deposits and bedrock in the Big Delta A-4 Quadrangle, Alaska. This map is based on field observations begun by P�w� in 1949 and by Reger in 1976. Unit characteristics and extents were determined during field visits and by interpreting 1:40,000-scale black-and-white aerial photographs taken in August 1949 and 1:63,360-scale, false-color infrared aerial photographs taken in July 1978, August 1980, and August 1981.
This dataset was created as part of the USGS Afghanistan Project investigating artisanal and small-scale mining activity. Clay mining for brick making purposes represents a small but important segment of the mineral extraction industry in Kabul, Afghanistan. Over the past several decades Kabul has grown from a relatively small city, with a 1970 population of less than 500,000 people, to a sprawling urban center with approximately 4.2 million people in 2020 (CIA 2020). Population growth has expanded the need for housing, commercial, and industrial buildings, and associated infrastructure. This has greatly increased demand for bricks, the primary construction material of the region. In this study, very high-resolution...
Categories: Data;
Types: Downloadable,
Map Service,
OGC WFS Layer,
OGC WMS Layer,
Shapefile;
Tags: Afghanistan,
Geography,
Loess,
Mineral Resources,
USGS Science Data Catalog (SDC),
This digital database is the product of collaboration between the U.S. Geological Survey, the Alfred Wegener Institute for Polar and Marine Research Potsdam, Foothill College GeoSpatial Technology Certificate Program, and the Geophysical Institute at the University of Alaska. The primary goal for creating this digital database is to enhance current estimates of organic carbon stored in deep permafrost, in particular Late Pleistocene syngenetic ice-rich loess permafrost deposits, called Yedoma. This deposit is vulnerable to thermokarst and erosion due to natural and anthropogenic disturbances. The original paper maps were issued by the Department of Natural Resources of the Russian Federation or its predecessor the...
Types: Citation,
Map Service,
OGC WFS Layer,
OGC WMS Layer,
OGC WMS Service;
Tags: Bykovsky,
Central Siberia,
Deputatsky,
East Siberia,
Khonuu,
This report provides detailed (1:63,360-scale) surficial-geologic mapping in the Dalton Highway area, from the Sagavanirktok to the Itkillik Rivers, in the west-central Philip Smith Mountains quadrangle. The map area extends from the northern flank of the Endicott Mountains into the Arctic Foothills province.
Thin loess deposits on the uplands of the southeastern Colorado Plateau have previously not been well studied. We sampled deposits and soils from trenches on Hatch Point mesa near Canyonlands National Park, Utah, and from two outcrops in Mesa Verde National Park, Colorado. At Hatch Point, the oldest buried unit yielded two OSL ages of 10,370 and 7,555 yr; the middle unit yielded 10 OSL ages from 6220 to 1385 yr; and the youngest unit has a single age of 1740 yr. At Mesa Verde, three loess units are preserved in the two outcrops we examined; six OSL ages range from 51 to 17 ka. At least one buried soil is present between two units with ages of about 50 and 40 ka. The ages of the loess units in both study areas correspond...
Categories: Data;
Tags: Canyonlands National Park,
Colorado,
Colorado Plateau,
Colorado River,
Geochemistry,
This report presents the findings of a geologic and geotechnical evaluation of a landslide at the Yukon River bridge (the E.L. Patton Bridge). The Yukon River bridge landslide occurred in fall 2012 between approximately 375 and 575 feet west of the bridge. Although there was no damage to the bridge foundation, the landslide's close proximity to the bridge and concerns over additional failures prompted multiple evaluations, including landslide documentation, drainage assessments, and geotechnical studies. This report was prepared to convey the general characteristics of the rock mass, characteristics of rock discontinuities, and the geomorphic expression of the 2012 landslide in the vicinity of the bridge. We determined...
The shrub-steppe area near Shaartuz, Tadzhik, S.S.R., is shown to be a net accumulator of dust despite being an occasional source of dust. For the accumulation of the dust to form the observed surface crust, a net deposition of about 290–490 g m−2 yr−1 of particles smaller than 20 μm is required, depending on the duration of the deposition period. The particles smaller than 20 μm are mixed with particles brought up from the sandy material below the surface crust by bioturbation and are incorporated into the surface crust. Measurements during the 16 and 20 September 1989 dust storms provided a total deposition of 41.1 g m−2 of particles smaller than 20 μm. Because 10–30 dust storms...
Categories: Publication;
Types: Citation,
Journal Citation;
Tags: Atmospheric Environment,
crust formation,
deposition,
dust,
loess
This digital data release contains geospatial geologic data compiled for the Lamar 250k quadrangle, a region in eastern Colorado and western Kansas, which is predominantly covered by Quaternary deposits that overlay Cretaceous bedrock. Geologic data, compiled from published sources, include the location and characteristics of geologic contacts and faults, mapped geologic polygons, and ammonite fossils. The geologic database includes spatial feature classes that collectively contain the geologic information that are presented in the previously published map plate. The spatial data are accompanied by non-spatial tables that describe the sources of geologic information, a description of geologic map units, a glossary...
Categories: Data;
Types: ArcGIS REST Map Service,
ArcGIS Service Definition,
Downloadable,
Map Service;
Tags: Colorado,
GeMS,
Geologic Map Schema,
Information Sciences,
Kansas,
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