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At least 91 records · Page 5Linked to original sources
USGS2009

Sustainability of Water Resources in the Fractured-Rock Area of Maryland

The fractured-rock area of Maryland encompasses the region of the State west of the Fall Line, which is approximated by the Interstate 95 corridor. It includes the Piedmont, Blue Ridge, Ridge and Valley, and Appalachian Plateau Physiographic Provinces (fig. 1). Surface water and ground water are important and interconnected water sources in this area. Streamflow characteristics vary in response to different land use, geology, topography, soil, and other factors. Ground-water flow is quite localized, tending to be controlled by local watersheds. Water in this region moves down through the soil and decomposed rock (saprolite) and along joints, faults, and fractures in the underlying rock (fig. 2). Water availability depends upon the size of fractures as well as the interconnections between fractures.

Fact Sheet↗
USGS2003

Preliminary geologic map of the Murrieta 7.5' quadrangle, Riverside County, California

The Murrieta quadrangle is located in the northern part of the Peninsular Ranges Province and includes parts of two structural blocks, or structural subdivisions of the province. The quadrangle is diagonally crossed by the active Elsinore fault zone, a major fault zone of the San Andreas fault system, and separates the Santa Ana Mountains block to the west from the Perris block to the east. Both blocks are relatively stable internally and within the quadrangle are characterized by the presence of widespread erosional surfaces of low relief. The Santa Ana Mountains block, in the Murrieta quadrangle, is underlain by undifferentiated, thick-layered, granular, impure quartzite and well-layered, fissile, phyllitic metamorphic rock of low metamorphic grade. Both quartzite and phyllitic rocks are Mesozoic. Unconformably overlying the metamorphic rocks are remnants of basalt flows having relatively unmodified flow surfaces. The age of the basalt is about 7-8Ma. Large shallow depressions on the surface of the larger basalt remnants form vernal ponds that contain an endemic flora. Beneath the basalt the upper part of the metamorphic rocks is deeply weathered. The weathering appears to be the same as the regional Paleocene saprolitic weathering in southern California. West of the quadrangle a variable thickness sedimentary rock, physically resembling Paleogene rocks, occurs between the basalt and metamorphic rock. Where not protected by the basalt, the weathered rock has been removed by erosion. The dominant feature on the Perris block in the Murrieta quadrangle is the south half of the Paloma Valley ring complex, part of the composite Peninsular Ranges batholith. The complex is elliptical in plan view and consists of an older ring-dike with two subsidiary short-arced dikes that were emplaced into gabbro by magmatic stoping. Small to large stoped blocks of gabbro are common within the ring-dikes. A younger ring-set of hundreds of thin pegmatite dikes occur largely within the central part of the complex. These pegmatite dikes were emplaced into a domal fracture system, apparently produced by cauldron subsidence, and include in the center of the complex, a number of flat-floored granophyre bodies. The granophyre is interpreted to be the result of pressure quenching of pegmatite magma. Along the eastern edge of the quadrangle is the western part of a large septum of medium metamorphic grade Mesozoic schist. A dissected basalt flow caps the Hogbacks northeast of Temecula, and represents remnants of a channel filling flow. Beneath the basalt is a thin deposit of stream gravel. Having an age of about 10Ma, this basalt is about 2-3Ma older than the basalt flows in the Santa Ana Mountains. The Elsinore fault zone forms a complex of pull-apart basins. The west edge of the fault zone, the Willard Fault, is marked by the high, steep eastern face of the Santa Ana Mountains. The east side of the zone, the Wildomar Fault, forms a less pronounced physiographic step. In the center of the quadrangle a major splay of the fault zone, the Murrieta Hot Springs Fault, strikes east. Branching of the fault zone causes the development of a broad alluvial valley between the Willard Fault and the Murrieta Hot Springs Fault. All but the axial part of the zone between the Willard and Wildomar Faults consist of dissected Pleistocene sedimentary units. The axial part of the zone is underlain by Holocene and latest Pleistocene sedimentary units.

California↗
USGS2006

Hydrogeology of the Lloyd aquifer on Long Island, New York— A brief summary of USGS investigations

The four counties of Long Island (fig. 1) are underlain by a wedge-shaped sequence of unconsolidated deposits of Late Cretaceous and Pleistocene age that lie unconformably on crystalline bedrock (fig. 2). A saprolitic (weathered bedrock) zone 20 to 100 ft thick overlies the bedrock in most areas. The sequence of unconsolidated deposits thickens to the south and southeast by about 65 to 100 feet per mile and contains Long Island's fresh ground water. Long Island's ground-water system consists of four main aquifers-the upper glacial, the Jameco, the Magothy, and the Lloyd. The Lloyd aquifer underlies nearly all of Long Island (fig. 3), but pumpage from the Lloyd has been limited to the northern and southern coastal areas of the island by the New York State Department of Environmental Conservation since about 1955 (Garber, 1986). Coastal areas are exempt where the Lloyd is the only source of potable water. The former Jamaica Water Supply Corporation (now owned by New York City) is a noted exception withdrawing as much as 6 million gallons per day (Mgal/d) since the mid-1930s from the Lloyd in central Queens County. This paper: (1) provides a brief history of U.S. Geological Survey (USGS) studies that provided significant data on the Lloyd, (2) summarizes the hydraulic characteristics of the Lloyd as reported in those studies, and (3) describes present-day monitoring of the Lloyd by the USGS.

New York↗
USGS1971

Selected fluvial monazite deposits in the southeastern United States

Farther southwest in Georgia, around Griffin and Zebullon, along streams tributary to the Flint River in the monazite belt the flood plains are generally small and discontinuous, and only about 1 percent of the sediment is gravel. The area between Griffin, Zebullon, and the Flint River is underlain by biotite schist and biotite gneiss into which biotite granite has been intruded. Only along one stream, Flat Creek, which drains monazite-bearing granite near Zetella, Ga., are the tenors in monazite even moderately high, but a combination of thick, clayey overburden and discontinuous flood plains make the stream unsuitable for placer mining. Elsewhere in the Flint River area the heavy-mineral concentrates contain less than 1 percent monazite. The southwesternmost area in which reconnaissance of the monazite belt was conducted includes a groups of southwest-flowing tributaries to the Chattahoochee River north of Pine Mountain and near La Grange, Ga. A combination of three characteristics of the alluvium make the area unfavorable for mining: (1) the upper half of the sedimentary sequence is clay and silt, (2) there is scant gravel, and (3) much of the sand is fine grained. Monazite is associated with the Snelson Granite, schists, and gneisses north of the Towaliga fault, but even in this area the tenor of most riffle sediments is only 0.1 to 0.5 pound of monazite per cubic yard, and the average tenor of the alluvium is about 0.2 pound per cubic Yard. Rocks south of the Towaliga fault contain scant monazite. The monazite-bearing area in the drainage basin of the Chattahoochee River has no monazite placers. Evidence from the areas on the Flint and Chattahoochee Rivers shows that streams in western Georgia are a much poorer source of monazite than streams farther to the northeast in Georgia, South Carolina, and North Carolina. Also, the northeastern part of the belt in the drainage basins of the Yadkin and Dan Rivers is a poorer source for monazite than the area between the Savannah and Catawba Rivers, S.C.-N.C. Monazite-bearing crystalline rocks in the western belt contain about 0.06 pound of monazite per cubic yard. Residual soil derived from the crystalline rocks contains about 0.3 to 0.4 pound of monazite per cubic yard, and colluvial sediments formed by sheet-wash from saprolite, residual soil, and, rarely, old stream deposits, have an average of 3.1 pounds of monazite to the cubic yard. The data on the tenors of residual and colluvial deposits are far less comprehensive than those an the quantity of monazite in the crystalline rocks, but the tenors are probably of the correct order of magnitude. Neither the crystalline rocks nor the residual soils are ores of monazite. Because the colluvial deposits are thin and have patch distribution they could not be mined independently, but some colluvium could be stripped from the adjoining hills in conjunction with the mining of alluvial deposits in the valleys. It is most unlikely that alluvial monazite placers have formed in the trunk streams leading southeastward out of the monazite belt. Churn drilling on the Broad and North Tyger Rivers, South Carolina, at the east edge of the belt has shown that the bulk of the alluvium is fine-grained sediment that contains 0.2 to 0.4 pound of monazite per cubic yard--tenors that represent no considerable enrichment over those in the crystalline rocks and residual soils. The probable persistence of predominantly fine-grained alluvium downstream to the Coastal Plain and the certain dilution of monazite-bearing concentrates by the inflow of monazite-free suites of heavy minerals between the belt and the fall line suggest that the trunk streams east of the belt are the least favorable sources for alluvial monazite in the Piedmont?

Open-File Report↗
USGS1973

Porphyry copper deposits in Puerto Rico and their relation to arc-trench tectonics

The study of porphyry copper deposits in islands arcs provides an opportunity to observe closely the direct relationship between tectonics and ore deposition, and to avoid such complications as multiple orogenies and contamination of magmas that are common to deposits on continental margins. Puerto Rico has proved to be an ideal laboratory to make these observations. In the west central part of the island 240 million tons of .7 to .8 percent copper ore has been proved up in three deposits (Lutjen, 1971). Although deep saprolite covers most of the mineralized area, two marginal deposits, Helecho and Sapo Alegre, are partly exposed by deep stream valleys. The U. S. Geological Survey, in cooperation with the Puerto Rico Department of Natural Resources is in the middle of a five year geologic and geochemical study of copper deposits in the island. Drill core was made available through the courtesy of Kennecott Copper Corporation, American Metals Climax Corporation and the Puerto Rico Mining Commission. I wish to acknowledge the help of the Puerto Rico Laboratory of Geology for the chemical work, and Richard Marvin and J. Thomas Nash of the USGS for geochronologic and fluid inclusion data, respectively. This report will briefly describe the porphyry copper deposits of Puerto Rico and their tectonic-chronologic position in the development of the Greater Antilles. By extrapolation from this data it will be suggested that these deposits and several others are related to a process of subduction zone deactivation.

Open-File Report↗
USGS1973

Geology and mineral resources of central Antioquia Department (Zone IIA), Colombia

This report summarizes the geology of an area of some 6000 square kilometers in the northern part of the Central Cordillera of the Colombian Andes. The area, in north-central Department of Antioquia, was mapped between 1964 and 1968 as part of the Inventario Minero Nacional (IMN) project. Mineral resources are summarized within a larger area, designated as subzone ILK of IMN Zone If, which comprises almost 22,000 sq. kin, including the area mapped geologically by IMN and additional areas mapped by other agencies. The oldest formation is a micaceous paragneiss of early Paleozoic or possibly late Precambrian age. A thick geosynclinal sedimentary series accumulated during the Paleozoic Era and became regionally metamorphosed to greenschist (locally amphibolite) facies during the Permian or early Triassic; these schists and gneisses are designated collectively as the Valdivia Group. The Permian(?) orogenic episode included intrusion of concordant syntectonic plutons, mostly of tonalitic composition. Rocks of unequivocal Triassic or Jurassic age are not recognized. The Cretaceous is well represented by both igneous and sedimentary assemblages. Eugeosynclinal alpine ophiolites comprising submarine basalt flows and numerous intrusions of gabbro and serpentinite are prominent in the Lower Cretaceous, together with flysch composed of marine shale and lesser sandstone and conglomerate. The Upper Cretaceous is represented along the west border of the mapped area by submarine basalt flows and pyroclastic rocks, locally Interbedded with fine-grained clastic sedimentary beds, and lenses of dark laminated chert, at least part of which is radiolarian. The Late Cretaceous was marked by an orogenic event that profoundly folded and faulted all rocks and in the Central Cordillera caused low-grade metamorphism, the overprint of which is hardly observable in pre-Cretaceous rocks elsewhere. The Late Cretaceous orogeny culminated with discordant intrusion of the epizonal tonalitic Antioquian batholith. Displacement along the great Romeral wrench fault may have begun in the Cretaceous. Plutonism continued into the Cenozoic, exemplified by the hornblende-diorite Sabanalarga pluton. Intermontane basins were filled with molasse derived from the erosion of adjacent highlands; Tertiary sedimentation in marshy areas included organic carboniferous matter subsequently converted to lignite or subbituminous coal. The Sabanalarga fault system originated in the Late Tertiary; intermittent displacement continued on the older wrench faults such as the Romeral. Epeirogenic uplift, which probably began in the Pliocene and continued through the Pleistocene and Holocene, brought on renewed erosion which has sculptured the mountains into their present form. Mineral resources in subzone IIA are varied but not of outstanding importance. Gold and silver mining, significant in past centuries, is minor today. Ferruginous laterite on serpentinite once considered as a potential source of iron ore is not economically exploitable. IMN has explored nickeliferous laterite at the extreme northwest corner of subzone IIA; this is a potential resource, exploitable only after exhaustion of the larger and richer nickel laterite deposit at Cerro Matoso, farther to the north and outside the boundaries of Zone If. Known deposits of mercury, chromium, manganese, and copper are small, with limited economic potential. Nonmetallic resources include raw materials for cement, including portland cement. Saprolite clay is widely used in making common red brick and tile, still a dominant construction material in all but the most modern multistory buildings. Aggregate materials are varied and abundant. Kaolin of good quality near La Union is important as a ceramic raw mineral filler. Tertiary subbituminous coal beds are an important energy resource in western subzone IIA, and have a good potential for greater development. Deposits of sodic feldspar, talc, decorative stone, and silica a

Open-File Report↗
USGS1976

Trace elements in some rocks and slag from the Yemen Arab Republic and their bearing on the iron ore near Sa'dah

Thirty-seven samples of rocks, saprolite, laterite, gossan, and slag were collected in the Yemen Arab Republic during June-July 1975 when field work was conducted to refine an interpretation of the regional geology made from LANDSAT-1 images by M. J. Grolier. These samples we reanalyzed in the laboratories of the U. S. Geological Survey, and the results were interpreted for use in programs of economic development as a guide for the evaluation of mineral resources in the Yemen Arab Republic. The work was undertaken as part of the program of the U. S. Agency for International Development with the cooperation of the Mineral and Petroleum Authority, Ministry of Economy, Yemen Arab Republic.

Open-File Report↗
USGS1977

Surficial and applied surficial geology of the Belchertown Quadrangle, Massachusetts

Till and stratified drift overlie maturely dissected topography in the Belchertown quadrangle, an area that straddles the New England Upland and Connecticut Valley Lowland in central Massachusetts. Lower Paleozoic, massive quartzo-feldspathic gneiss, quartzite and schist of the Pelham dome and Devonian granodiorite and quartz diorite of the Belchertown intrusive complex are in contact with Triassic arkosic fanglomerate and basalt along a lengthy normal fault separating the New England Upland from the Connecticut Valley Lowland. The orientation of striae, roches moutonnees, and streamline ridges indicate that the last Wisconsinian glacier advanced generally south 12? east. This glacier removed several meters of rock from the upland and an unknown larger quantity from the preglacial valley of the Connecticut River. Till is thin in the uplands, but several tens of feet of drift overlie bedrock in the lowland. Three lithic facies of sandy, clast-rich, non-compact, subarkosic till derived from the three major source rocks rest on bedrock or on highly weathered, compact, clast-poor, fissile probably older till. The mean for all upper till is 69.6% sand, 21.7% silt, and 8.8% clay; lower till consists of 48% sand, 23% silt and 29% clay. Mud-rich, compact, sparsely stony till in drumlins in and along the flank of the Connecticut Valley Lowland is composed of 51.5% sand, 28% silt, and 20.5% clay. Upper tills are facies equivalent deposits of the youngest Wisconsinian drift. Lower till is compact deeply weathered, jointed and stained suggesting it is correlative with other lower till in New England deposited by an earlier Wisconsinian glacier. Drumlin till may be a facies equivalent of a lower till or a mud-rich upper till derived from earlier glaciolacustrine deposits. Upper and lower till of the Belchertown quadrangle is texturally similar to other New England upper and lower tills to which they are equivalent. Both tills are interpreted as lodgment till derived from similar bedrock terrane by two different glaciers. The older glacier incorporated mud-rich saprolite producing a fine grained till, while the younger glacier eroded fresh bedrock or a thin regolith produced by mechanical weathering. During stagnation zone retreat of the last glacier, stratified drift was deposited by melt water in, on, alongside or down valley from stagnant ice. The absence of stratified drift along upland divides indicates that stagnation did not begin till large nunataks were emergent. Kame terraces, kame deltas, and ice channel fillings indicate that melt water flowed along stagnant ice and emptied into temporary proglacial lakes. As downwasting progressed, water was able to drain at lower elevation into expanding lakes, the last of which merged with northward-expanding proglacial Lake Hitchcock in the Connecticut Valley. Initial melt water drainage to the southeast was followed by drainage to the southwest to the ancestral Chicopee River. With the opening of the Narrows, Lake Hitchcock expanded northward and eastward to form the Amherst embayment into which melt water from the eastern uplands drained. Sand and gravel overlying varves in the Amherst embayment was deposited in late-glacial Lake Lawrence, which coalesced with equivalent Lake Hadley through cols between drumlins in the Connecticut Valley Lowland. Deglaciation of the Belchertown quadrangle probably occurred in a span of about 100 years in the interval 12,000 to 12,500 years B.P. Unconsolidated sediments of the Belchertown quadrangle are summarized as to their geologic and geotechnical properties for land use planning. Drift as it influences groundwater flow, yield, and quality and as a construction material is assessed. Some environmental degradation has occurred from the indiscriminant disposal of liquid and solid waste as well as injudicious use of road salt.

Open-File Report↗
USGS1997

Stratigraphy and geophysical logs from a corehole drilled to bedrock at Robins Point, J-Field, Edgewood area, Aberdeen Proving Ground, Maryland

A continuous core was recovered from a 961-foot- deep stratigraphic corehole at Robins Point, located at the southeastern tip of the Gunpowder Neck Peninsula, Harford County, Maryland. A 2-inch- diameter ground-water-quality observation well was installed with the screen set at a depth of 392 to 402 feet (ft). Geophysical logs obtained from thecorehole include: natural gamma, multipoint normal resistivity (16-inch and 64-inch), 4-ft-guard focused resistivity, acoustic (sonic) velocity, and caliper. Pollen analysis of 34 samples provided relativestratigraphic ages. Lithologies encountered in ascending order (surface elevation 4 ft above mean sea level), include: 72.4 ft of weatheredmetamorphic rock and saprolie, 711.4 ft of lower and upper Cretaceous fluvio-deltaic deposits, and 145.9 ft of Pleistocene and 31.3 ft of Holocene(?) fluvial and estuarine deposits. Aquifers and confining units identified include, in descending order: 41.8 ft of surficial aquifer, 90.9 ft of upper paleochannel confining unit, 28.8 ft of paleochannel confined aquifer, 15.7 ft of lower paleochannel confining unit, 123.7 ft of Upper Patapsco aquifer, 44.6 ft of Upper Patapsco confining unit, 92.8 ft of Middle Patapsco aquifer, 57.3 ft of Lower Patapsco confining unit, 151.7 ft of Lower Patapsco aquifer, 115.4 ft of Potomac confining unit, 126.4 ft of Patuxent aquifer, an aquifer of 23.4 ft of saprolite, and 48.7 ft of weathered-rock/saprolite confining unit.

Open-File Report↗
USGS1998

Evaluation of geophysical logs, phase I, for Crossley Farms Superfund Site, Berks County, Pennsylvania

Twenty-one wells were drilled at Crossley Farms Superfund Site between December 15, 1987, and May 1, 1988, to define and monitor the horizontal and vertical distribution of ground-water contamination emanating from a suspected contaminant source area (Blackhead Hill). Eight well clusters were drilled on or near the Crossley Site and three well clusters were drilled at locations hydrologically down gradient from the site. Depths of wells range from 21 to 299 feet below land surface. These wells were installed in saprolite in shallow, intermediate, and deep water-producing zones of the fractured bedrock aquifer. Borehole-geophysical and video logging were conducted between April 24, 1997, and May 8, 1997, to determine the water-producing zones, water-receiving zones, zones of vertical flow, borehole depth, and casing integrity in each well. This data and interpretation will be used to determine the location of the well intake for the existing open-hole wells, which will be retrofitted to isolate and monitor water-producing zones and prevent further cross-contamination within each open borehole, and identify wells that may need rehabilitation or replacement. Caliper and video logs were used to locate fractures, inflections on fluid-temperature and fluid-resistivity logs indicated possible fluid-bearing fractures, and flowmeter measurements verified these locations. Single-point-resistance and natural-gamma logs provided information on stratigraphy. After interpretation of geophysical logs, video logs, and driller's notes, all wells will be constructed so that water-level fluctuations can be monitored and discrete water samples collected from shallow, intermediate, and deep water-bearing zones in each well. Geophysical logs were run on seven bedrock and two deep bedrock wells. Gamma logs were run on 10 bedrock wells. Twenty-two wells were inspected visually with the borehole video camera for casing integrity.

Open-File Report↗
USGS1982

Physiographic divisions and differential uplift in the Piedmont and Blue Ridge

The Piedmont and Blue Ridge are dynamic landscapes that have undergone substantial change since the orogenies that ended in late Paleozoic or, as some believe, early Mesozoic time. The southern Blue Ridge region south of Roanoke, Va., lies on the crest of a topographic uplift that corresponds to the eastern continental drainage divide. To the north, this uplift and divide cross the Appalachian Valley and form the crest of the Appalachian Plateaus as far north as central Pennsylvania. The northern Blue Ridge Mountains as well as parts of the Piedmont are on the eastern part of the uplift area. The southeastern margin of the uplift corresponds to a line within the Piedmont physiographic province that extends northeastward from the Tallapoosa River at the Fall Zone and crosses the Rappahannock River at the Fall Zone. The differential elevation on either side of this line is sharp in some places, as, for example, northeast of Atlanta, Ga. In other places, the difference in elevation is difficult to detect, and, in effect, the line becomes a broad monoclinal slope. The region as a whole can be divided into at least six broad subregions that have somewhat different histories in late geologic time. The Piedmont Lowlands subprovince, southeast of the uplifted area, is dominated by a monotonous topography of low rounded ridges and ravines largely underlain by saprolite on crystalline rocks. Isolated ranges of hills of greater relief are scattered across the region; those investigated are directly related to the presence of erosionally resistant rocks. Stream patterns as well as broad topographic forms indicate that although the southern part of the Piedmont Lowlands was probably once covered by younger sediments, this area has been exposed to erosion for a long time. In North Carolina, the inner part of the Piedmont Lowlands has strongly trellised stream patterns, which suggest that subaerial erosion was active for an even longer time period, perhaps since the latest orogeny. North of the Cape Fear River, the outer part of the Piedmont Lowlands was covered by either fluvial or marine sediments or both, probably during Miocene time. Tectonic activity has affected the Piedmont Lowlands in late geologic time. The Fall Zone that forms the southeast border is, at least in places, controlled by faults active in Tertiary time. Late faults have also been found in the Pine Mountain area of Georgia. Minor differences in relief affecting large regions within the Piedmont Lowlands may be related to different rates of uplift in addition to rock resistance, either past or present. The Piedmont northeast of the Potomac River (Northeastern Highlands) rises to more than 300 m in altitude. The major streams have convex profiles that steepen as they near the Coastal Plain. Unusually narrow valleys and broad upland surfaces indicate an increased rate of erosion and show that the relief is now or recently has been increasing because of uplift or tilting. West of the southern end of the Piedmont Lowlands is an area herein called the Southwestern Highlands that in some respects is similar. The area is crossed by two large streams that have convex profiles. The highest mountain ranges in the area rise to altitudes greater than 600 m. Northwest of the Piedmont Lowlands, the topography and relief are higher, and in some places, the rise is gradual, forming a Foothill zone between the Piedmont Lowlands and the high Blue Ridge. This zone is morphologically more complex than the Piedmont Lowlands. North of the Roanoke River, the foothills are commonly chains of isolated hills and ridges generally underlain by resistant rocks. The hills increase in height near the Blue Ridge, an indication that they owe their height to tectonism of late geologic age. South of the Yadkin River, the hills are believed to be residual, the remnants of a larger highland that has been only partially reduced to the lower relief of the general Piedmont surface. The

Professional Paper↗
USGS2005

Petrography, structure, age, and thermal history of granitic coastal plain basement in the Chesapeake Bay impact structure, USGS-NASA Langley core, Hampton, Virginia

The USGS-NASA Langley corehole at Hampton , Va., was drilled in 2000 and was the first corehole to reach coastal plain basement in the late Eocene Chesapeake Bay impact structure . The Langley core provided samples of granite that had been concealed by 626.3 meters (2,054.7 feet) of preimpact, synimpact, and postimpact sediments. The granite, here named the Langley Granite, is pale red, medium grained, massive, and homogeneous in composition and fabric. It has a peraluminous composition (alumina saturation index 1.1) and a seriate-inequigranular, hypidiomorphic, isotropic fabric. A pervasive secondary mineral assemblage of chlorite + albite + clinozoisite is consistent with either deuteric alteration or lower greenschist-facies metamorphism. Chlorite, the principal mafic mineral, occurs as tabular masses that suggest pseudomorphous replacement of biotite. The top of the granite is weathered but not saprolitized and is nonconformably overlain by Lower Cretaceous clastic sediments. A SHRIMP 206 Pb/ 238 U weighted average zircon age of 612±10 Ma (2σ) indicates Neoproterozoic crystallization of the Langley Granite. The 40 Ar/ 39 Ar ages of microcline and plagioclase are consistent with regional cooling and uplift after the late Paleozoic Alleghanian orogeny. Zircon and apatite fission-track cooling ages of 375±44 Ma and 184±32 Ma (2σ), respectively, indicate no discernible impact -related thermal disturbance at the Langley corehole location in the annular trough of the structure about 19 kilometers (12 miles) outside the margin of the central crater. Modeling the apatite fission-track data places upper limits on the impact -related heating at this location. For an impact -related thermal disturbance equivalent to a modeled thermal spike having a duration of 1 to 0.1 million years, temperatures in this part of the impact structure could not have been higher than about 100°C-120°C. Most fractures, faults, and veins in the Langley Granite contain lower greenschist-facies minerals and are inferred to predate the impact . No shock-metamorphosed minerals or other features clearly attributable to the impact were found in the granite. Studies of the granite provide a glimpse into the nature of crystalline terranes beneath the Atlantic Coastal Plain and Chesapeake Bay and provide limits on the geographic extent of impact -generated shock and thermal effects.

Chesapeake Bay↗
USGS1963

Geology of Mount Rainier National Park, Washington

Mount Rainier National Park includes 378 square miles of rugged terrain on the west slope of the Cascade Mountains in central Washington. Its mast imposing topographic and geologic feature is glacier-clad Mount Rainier. This volcano, composed chiefly of flows of pyroxene andesite, was built upon alt earlier mountainous surface, carved from altered volcanic and sedimentary rocks invaded by plutonic and hypabyssal igneous rocks of great complexity. The oldest rocks in the park area are those that make up the Olmnapecosh Formation of late Eocene age. This formation is more than 10,000 feet thick, and consists almost entirely of volcanic debris. It includes some lensoid accumulations of lava and coarse mudflows, heaped around volcanic centers., but these are surrounded by vastly greater volumes of volcanic clastic rocks, in which beds of unstratified coarse tuff-breccia, about 30 feet in average thickness, alternate with thin-bedded breccias, sandstones, and siltstones composed entirely of volcanic debris. The coarser tuff-breccias were probably deposited from subaqueous volcanic mudflows generated when eruption clouds were discharged directly into water, or when subaerial ash flows and mudflows entered bodies of water. The less mobile mudflows and viscous lavas built islands surrounded by this sea of thinner bedded water-laid clastics. In compostion the lava flows and coarse lava fragments of the Ohanapecosh Formation are mostly andesite, but they include less abundant dacite, basalt, and rhyolite. The Ohanapecosh Formation was folded, regionally altered to minerals characteristic of the zeolite facies of metamorphism, uplifted, and deeply eroded before the overlying Stevens Ridge Formation of Oligocene or early Miocene age was deposited upon it. The Stevens Ridge rocks, which are about 3,000 feet in maximum total thickness, consist mainly of massive ash flows. These are now devitrified and altered, but they originally consisted of rhyodacite pumice lapilli and glass shards, which compacted and welded into thick massive units during emplacement and cooling. Subordinate water-laid clastic rocks occur t(ward the top of the formation, and thin-bedded pyroclastic layers occur between some of the ash flows. Exposures on Backbone Ridge and on Carbon River below the mouth of Cataract Creek show that in places the thick basal Stevens Ridge ash flows swept with great violence over an old erosion surface developed on rocks of the Ohanapecosh Formation. Masses of mud, tree trunks, and other surface debris were swirled upward into the base of the lowermost ash fiery, and lobes and tongues of hot ash were forced downward into. the saprolitic mud. The Stevens Ridge Formation is concordantly overlain by the Fifes Peak Formation of probable early Miocene age, which consists of lava flows, subordinate mudflows, and minor quantities of tuffaceous clastic rocks. The lavas are predominantly olivine basalt and basaltic andesite, but they include a little rhyolite. They are slightly to moderately altered: the ferromagnesian phenocrysts are generally replaced by saponite, chiprite, or carbonate ; the glass is devitrified ; and the rocks are locally permeated by veinlets of zeolite. Swarms of diabase sills and dikes are probably intrusive equivalents of the Fifes Peak lavas. The upper part of the Fifes Peak Formation has been mostly eroded from Mount Rainier National Park, but farther north, in the Cedar Lake quadrangle, it attains a thickness of more than 5,000 feet. The Fifes Peak and earlier formations were gently folded, faulted, uplifted, and eroded before the. late Miocene Tatoosh pluton worked its way upward to shallow depths and eventually broke through to the surface. The rise of the pluton was accompanied by .the injection of a complicated melange of satellitic stocks, sills, and dikes. A favored horizon for intrusion of sills was along or near the unconfo

Professional Paper↗
USGS1978

The Potential for Prophyry Copper-Molybdenum Deposits in the Eastern United States

Several significant porphyry-type deposits of Paleozoic age are known in New England and eastern Canada. Disseminated copper-molybdenum deposits of Paleozoic age are in the Southeastern United States, and copper is produced from porphyry-type deposits of both Precambrian and Paleozoic age in eastern Canada. Although these old deposits are surely less abundant than those in Cenozoic and Tertiary porphyry belts, the known Precrambrian and Paleozoic deposits in Eastern North America appear to be valid exploration targets. The difficult of 'prospecting in drift-covered and saprolite-mantled terrains suggests that all such deposits probably have not been discovered. Although such deposits are more costly to discover in this region than a massive sulfide deposit, the total amount of copper in even a medium-sized porphyry copper deposit is much greater than in most massive sulfide deposits. This report summarizes current knowledge of porphyry copper-molybdenum-type deposits in the Eastern United States and suggests more favorable areas for mineral exploration. Selected Canadian deposits are discussed because of their bearing on planning exploration in this country.

Professional Paper↗
USGS2006

Geologic Map of the Upper Wolf Island Creek Watershed, Reidsville Area, Rockingham County, North Carolina

This geologic map provides a foundation for hydrogeologic investigations in the Reidsville area of Rockingham County, north-central North Carolina. The 16-mi2 area within the Southeast Eden and Reidsville 7.5-min quadrangles includes the watershed of Wolf Island Creek and its tributary, Carroll Creek, upstream of their confluence. Layered metamorphic rocks in this area of the Milton terrane, here informally named the Chinqua-Penn metamorphic suite, include a heterogeneous mica gneiss and schist unit that contains interlayers and lenses of white-mica schist, felsic gneiss, amphibolite, and ultramafic rock; a felsic gneiss that contains interlayers of amphibolite, white-mica schist, and minor ultramafic lenses; and a migmatitic biotite gneiss. Crushed stone is produced from an active quarry in the felsic gneiss. Igneous intrusive rocks include a mafic-ultramafic assemblage that may have originated as mafic intrusive bodies containing ultramafic cumulates, a foliated two-mica granite informally named the granite of Reidsville, and unmetamorphosed Jurassic diabase dikes. The newly recognized Carroll Creek shear zone strikes roughly east-west and separates heterogeneous mica gneiss and schist to the north from structurally overlying felsic gneiss to the south. Regional amphibolite-facies metamorphism accompanied polyphase ductile deformation in the metamorphic rocks. Two phases of isoclinal to tight folding and related penetrative deformation, described as D1 and D2, were followed by phases of high-strain mylonitic deformation in shear zones and late gentle to open folding. Later brittle deformation produced minor faults, steep joints, foliation-parallel parting, and sheeting joints. The metamorphic and igneous rocks are mantled by saprolite and residual soil derived from weathering of the underlying bedrock, and unconsolidated Quaternary alluvium occupies the flood plains of Wolf Island Creek and its tributaries. The geologic map delineates lithologic and structural features that may act as barriers or conduits for ground-water flow. It provides a hydrogeologic framework for the upper Wolf Island Creek drainage basin, including coreholes and ground-water monitoring wells along two transects. Collaborative hydrogeologic investigations by the North Carolina Department of Environment and Natural Resources and the U.S. Geological Survey are in progress to increase understanding of the influence of geological features on ground-water quality, availability, and transport in an area representative of large areas in the west-central Piedmont.

Scientific Investigations Map↗
USGS2013

Investigations of groundwater system and simulation of regional groundwater flow for North Penn Area 7 Superfund site, Montgomery County, Pennsylvania

Groundwater in the vicinity of several industrial facilities in Upper Gwynedd Township and vicinity, Montgomery County, in southeast Pennsylvania has been shown to be contaminated with volatile organic compounds (VOCs), the most common of which is the solvent trichloroethylene (TCE). The 2-square-mile area was placed on the National Priorities List as the North Penn Area 7 Superfund site by the U.S. Environmental Protection Agency (USEPA) in 1989. The U.S. Geological Survey (USGS) conducted geophysical logging, aquifer testing, and water-level monitoring, and measured streamflows in and near North Penn Area 7 from fall 2000 through fall 2006 in a technical assistance study for the USEPA to develop an understanding of the hydrogeologic framework in the area as part of the USEPA Remedial Investigation. In addition, the USGS developed a groundwater-flow computer model based on the hydrogeologic framework to simulate regional groundwater flow and to estimate directions of groundwater flow and pathways of groundwater contaminants. The study area is underlain by Triassic- and Jurassic-age sandstones and shales of the Lockatong Formation and Brunswick Group in the Mesozoic Newark Basin. Regionally, these rocks strike northeast and dip to the northwest. The sequence of rocks form a fractured-sedimentary-rock aquifer that acts as a set of confined to partially confined layers of differing permeabilities. Depth to competent bedrock typically is less than 20 ft below land surface. The aquifer layers are recharged locally by precipitation and discharge locally to streams. The general configuration of the potentiometric surface in the aquifer is similar to topography, except in areas affected by pumping. The headwaters of Wissahickon Creek are nearby, and the stream flows southwest, parallel to strike, to bisect North Penn Area 7. Groundwater is pumped in the vicinity of North Penn Area 7 for industrial use, public supply, and residential supply. Results of field investigations by USGS at the site and results from other studies support, and are consistent with, a conceptual model of a layered leaky aquifer where the dip of the beds has a strong control on hydraulic connections in the groundwater system. Connections within and (or) parallel to bedding tend to be greater than across bedding. Transmissivities of aquifer intervals isolated by packers ranged over three orders of magnitude [from about 2.8 to 2,290 square feet per day (ft 2 /d) or 0.26 to 213 square meters per day (m 2 /d)], did not appear to differ much by mapped geologic unit, but showed some relation to depth being relatively smaller in the shallowest and deepest intervals (0 to 50 ft and more than 250 ft below land surface, respectively) compared to the intermediate depth intervals (50 to 250 ft below land surface) tested. Transmissivities estimated from multiple-observation well aquifer tests ranged from about 700 to 2,300 ft 2 /d (65 to 214 m 2 /d). Results of chemical analyses of water from isolated intervals or monitoring wells open to short sections of the aquifer show vertical differences in concentrations; chloride and silica concentrations generally were greater in shallow intervals than in deeper intervals. Chloride concentrations greater than 100 milligrams per liter (mg/L), combined with distinctive chloride/bromide ratios, indicate a different source of chloride in the western part of North Penn Area 7 than elsewhere in the site. Groundwater flow at a regional scale under steady-state conditions was simulated by use of a numerical model (MODFLOW-2000) for North Penn Area 7 with different layers representing saprolite/highly weathered rock near the surface and unweathered competent bedrock. The sedimentary formations that underlie the study area were modeled using dipping model layers for intermediate and deep zones of unweathered, fractured rock. Horizontal cell model size was 100 meters (m) by 100 meters (328 ft by 328 ft), and model layer thickness ranged from 6 m (19.7 ft) representing shallow weathered rock and saprolite up to 200 m (656 ft) representing deeper dipping bedrock. The model did not include detailed structure to account for local-scale differences in hydraulic properties, with the result that local-scale groundwater flow may not be well simulated. Additional detailed multi-well aquifer tests would be needed to establish the extent of interconnection between intervals at the local scale to address remediation of contamination at each source area. This regional groundwater-flow model was calibrated against measured groundwater levels (1996, 2000, and 2005) and base flow estimated from selected streamflow measurements by use of nonlinear-regression parameter-estimation algorithms to determine hydraulic conductivity and anisotropy of hydraulic conductivity, streambed hydraulic conductivity, and recharge during calibration periods. Results of the simulation using the calibrated regional model indicate that the aquifer appears to be anisotropic where hydraulic conductivity is greatest parallel to the orientation of bedding of the formations underlying the area and least in the cross-bed direction. The maximum hydraulic conductivity is aligned with the average regional strike of the formations, which is “subhorizontal” in the model because the altitudes of the beds and model cells vary in the strike, as well as dip, direction. Estimated subhorizontal hydraulic conductivities (in strike direction parallel to dipping beds) range from 0.001 to 1.67 meters per day (0.0032 to 5.5 feet per day). The ratio of minimum (dip direction) to maximum (strike direction) subhorizontal hydraulic conductivity ranges from 1/3.1 to 1/8.6, and the ratio of vertical to horizontal hydraulic conductivity ranges from 1/1 to 1/478. However, limited available field data precluded rigorous calibration of vertical anisotropy in the model. Estimated recharge rates corresponding to calibration periods in 1996, 2000, and 2005 are 150, 109, and 124 millimeters per year (5.9, 4.3, and 4.9 inches per year), respectively. The calibrated groundwater-flow model was used to simulate groundwater flow under steady-state conditions during periods of relatively high withdrawals (pumpage) (1990) and relatively low withdrawals (2000 and 2005). Groundwater-flow paths originating from recharge areas near known areas of soil contamination (sources) were simulated. Pumped industrial and production wells captured more groundwater from several of these sources during 1990 than after 1990 when pumping declined or ceased and greater amounts of contaminated groundwater moved away from North Penn Area 7 Superfund site to surrounding areas. Uncertainty in simulated groundwater-flow paths from contaminant sources and contributing areas, resulting from uncertainty in estimated hydraulic properties of the model, was illustrated through Monte Carlo simulations. The effect of uncertainty in the vertical anisotropy was not included in the Monte Carlo simulations. Contributing areas indicating the general configuration of groundwater flow towards production well MG-202 (L-22) in the study area also were simulated for the different time periods; as simulated, the flow paths do not pass through any identified contaminant source in North Penn Area 7. However, contributing areas to wells, such as MG-202, located near many pumped wells are particularly complex and, in some cases, include areas that contribute flow to streams that subsequently recharge the aquifer through stream loss. In these cases, water-quality constituents, including contaminants that are present in surface water may be drawn into the aquifer to nearby pumped wells. Results of a simulated shutdown of well MG-202 under steady-state 2005 conditions showed that the area contributing recharge for nearby production well MG-76 (L-17), when MG-202 is not pumping, shifts downstream and is similar to the area contributing recharge for MG-202 when both wells are pumping. Concentrations of constituents in groundwater samples collected in fall 2005 or spring 2006 were compared to simulated groundwater-flow paths for the year 2005 to provide a qualitative assessment of model results. The observed spatial distribution of selected constituents, including TCE, CFC-11, and CFC-113 in groundwater in 2005 and the chloride/bromide mass ratios in 2006, generally were consistent with the model results of the simulated 2005 groundwater-flow paths at North Penn Area 7, indicating the presence of several separate sources of contaminants within North Penn Area 7.

Pennsylvania↗
USGS2002

Preliminary hydrogeologic assessment and study plan for a regional ground-water resource investigation of the Blue Ridge and Piedmont provinces of North Carolina

Prolonged drought, allocation of surface-water flow, and increased demands on ground-water supplies resulting from population growth are focuses for the need to evaluate ground-water resources in the Blue Ridge and Piedmont Provinces of North Carolina. Urbanization and certain aspects of agricultural production also have caused increased concerns about protecting the quality of ground water in this region. More than 75 percent of the State's population resides in the Blue Ridge and Piedmont Provinces in an area that covers 30,544 square miles and 65 counties. Between 1940 and 2000, the population in the Piedmont and Blue Ridge Provinces increased from 2.66 to 6.11 million; most of this increase occurred in the Piedmont. Of the total population, an estimated 1.97 million people, or 32.3 percent (based on the 1990 census), relied on ground water for a variety of uses, including commercial, industrial, and most importantly, potable supplies. Ground water in the Blue Ridge and Piedmont traditionally has not been considered as a source for large supplies, primarily because of readily available and seemingly limitless surface-water supplies, and the perception that ground water in the Blue Ridge and Piedmont Provinces occurs in a complex, generally heterogeneous geologic environment. Some reluctance to use ground water for large supplies derives from the reputation of aquifers in these provinces for producing low yields to wells, and the few high-yield wells that are drilled seem to be scattered in areas distant from where they are needed. Because the aquifers in these provinces are shallow, they also are susceptible to contamination by activities on the land surface. In response to these issues, the North Carolina Legislature supported the creation of a Resource Evaluation Program to ensure the long-term availability, sustainability, and quality of ground water in the State. As part of the Resource Evaluation Program, the North Carolina Division of Water Quality, Groundwater Section, in cooperation with the U.S. Geological Survey, initiated a multiyear study of ground water in the Blue Ridge and Piedmont Provinces. The study began in 1999. Most of the study area is underlain by a complex, two-part, regolith-fractured crystalline rock aquifer system. Thickness of the regolith throughout the study area is highly variable and ranges from 0 to more than 150 feet. The regolith consists of an unconsolidated or semiconsolidated mixture of clay and fragmental material ranging in grain size from silt to boulders. Because porosities range from 35 to 55 percent, the regolith provides the bulk of the water storage within the Blue Ridge and Piedmont ground-water system. At the base of the regolith is the transition zone where saprolite grades into unweathered bedrock. The transition zone has been identified as a potential conduit for rapid ground-water flow. If this is the case, the transition zone also may serve as a conduit for rapid movement of contaminants to nearby wells or to streams with channels that cut into 1 U.S. Geological Survey, Raleigh, North Carolina. 2 North Carolina Department of Environment and Natural Resources, Division of Water Quality, Groundwater Section. or through the transition zone. How rapidly a contaminant moves through the system largely may be a function of the characteristics of the transition zone. The transition zone is one of several topics identified during the literature review and data synthesis, for which there is a deficiency in data and understanding of the processes involved in the movement of ground water to surface water. Because the Blue Ridge and Piedmont study area is so large, and the hydrogeology diverse, it is not feasible to study all of the area in detail. A more feasible approach is to select areas that are most representative of the land use, geology, and hydrology to obtain an understanding of the hydrologic processes in the selected areas, and transfer the knowledge from these local "type areas" to similar regional hydrogeologic areas. For the purpose of this study, the term "type area" applies to a 10- to 100-square mile area within a hydrogeologic terrane where information is sufficient to develop and test a concept of ground-water flow by using analytical or numerical methods that can be validated by field measurements. Ideally, these type areas are selected to be representative of the flow system that is present wherever a particular hydrogeologic terrane is present. This report consists of two basic parts. The first part describes the results of a comprehensive review and synthesis of information and literature that provides the basic background for the study. This includes current (2002) knowledge regarding general geology and the hydrogeologic framework of the fractured-rock aquifer system that underlies the Blue Ridge and Piedmont Provinces. In spite of the quantity of information identified during the literature review and the amount of past work that has been documented, there are still research needs to be met. The second part of the report describes State ground-water issues and problems, available data, and data deficiencies. It also describes the design and implementation of efforts to characterize ground-water quality and to quantify factors that influence the movement and availability of ground water in the hydrogeologic terranes characterized by (1) massive or foliated crystalline rocks overlain by thick regolith and (2) massive or foliated crystalline rocks overlain by thin regolith. As of September 2001, seven sites had been identified as potential study sites to be used to characterize the hydrogeology and water quality of ype areas considered representative of the larger terranes. Detailed geologic mapping, core drilling, well installation, and surface and borehole geophysical surveys are in progress at four of the sites.

North Carolina↗
USGS1996

Soil, water, and streambed quality at a demolished asphalt plant, Fort Bragg, North Carolina, 1992-94

A number of potentially hazardous chemicals were used at an asphalt plant on the Fort Bragg U.S. Army Reservation near Fayetteville, North Carolina. This plant was demolished in the late 1960's. Samples collected from soil, ground water, surface water, and streambed sediment were tested for the presence of contaminants. The sediment immediately underlying the demolished asphalt plant site consists mainly of sands, silts, and clayey sands with interbedded clay occurring at various depths. About 12 inches of rainfall per year infiltrate the unconfined surficial aquifer. The water table in this area is about 233 to 243 feet above sea level. Local ground water moves laterally, mainly towards the north- to-northwest at a rate of about 35 feet per year. where it discharges to Tank Creek, Little River, or one of their tributaries. A series of confining clays separate the surficial aquifer from the underlying upper Cape Fear aquifer. These clays help retard vertical migration of constituents dissolved in ground water. The saprolite-bedrock aquifer lies below the upper Cape Fear aquifer. In general ground water in the seven monitoring wells screened in the upper and lower part of the surficial aquifer did not contain detectable concentrations of chemicals related to past asphalt-plant activities. A small number of chemicals that were assumed to be unrelated to the asphalt plant were present in some of the study area monitoring wells. Ground water in four wells contained concentrations of organochlorine pesticides. Of these pesticides, concentrations of gamma-benzene hexachloride (lindane) (maximum of 0.76 micrograms per liter) exceeded the U.S. Environmental Protection Agency maximum contaminant level of 0.2 micrograms per liter in two wells. In addition, one well contained a trichloroethane concentration (7.7 micrograms per liter) that is assumed to be unrelated to demolished asphalt-plant operations, but exceeded the U.S. Environmental Protection Agency maximum contaminant level of 5.0 micrograms per liter. One well contained a fluoride concentration of 5.2 milligrams per liter that exceeded the U.S. Environmental Protection Agency maximum contaminant level of 4.0 milligrams per liter. Total and dissolved metals concentrations were generally typical of background levels. Some of the wells contained elevated levels of chloride (maximum of 749 milligrams per liter), specific conductance (maximum of 2,780 microsiemens per centimeter at 25 degrees Celsius), and dissolved solids (maximum of 1,520 milligrams per liter). Twelve of twenty-two soil samples that were collected at various depths at monitoring-well locations did not contain volatile organic compounds or polynuclear aromatic hydrocarbons. The remaining ten soil samples contained very low concentrations of polynuclear aromatic hydrocarbons and (or) analytical laboratory-related volatile organic compounds. The maximum concentrations were for fluoranthene and pyrene, at 780 and 750 micrograms per kilogram, respectively. In general, the polynuclear aromatic hydrocarbon concentrations were in sediment near the land surface. Streambed sediment from an unnamed, eastern tributary to Tank Creek in the eastern part of the site contained a small number of organochlorine pesticide compounds (a maximum of 1,400 milligrams per kilogram of 4,4'-DDD) and total petroleum hydrocarbons (113 milligrams per kilogram). Concentrations of metals and other inorganic constituents were generally typical of background concentrations. Surface water in this tributary did not contain elevated concentrations of anthropogenic chemicals.

North Carolina↗