Geology topics
Research about Virginia
Source-linked reports with geographic coverage including Virginia.
Hydrologic conditions and trends in Shenandoah National Park, Virginia, 1983-84
No abstract available.
Geologic map of the Annandale quadrangle, Fairfax and Arlington Counties, and Alexandria City, Virginia
No abstract available.
Maps showing mines, prospects, and mineral localities in and near the Dolly Ann Roadless Area, Alleghany County, Virginia
The Dolly Ann Roadless Area comprises 7,900 acres (3,200 ha) in the George Washington National Forest in west-central Virginia. The study area is in central Alleghany County, northeast of Covington, Va. (fig. 1). U.S. Forest Service Route 125 and U.S. Highway 220 furnish vehicular access to the edges of the area, and several foot trails provide access to the interior and peripheral regions.
Maps showing mines and prospects in the Southern Massanutten Roadless Area, Page and Rockingham counties, Virginia
The Southern Massanutten Roadless Area contains about 11,800 acres in the George Washington National Forest in the Valley and Ridge physiographic province of west-central Virginia. The area, which is 13 mi long and 1 to 2 mi wide, is in Page and Rockingham Counties on the eastern side of the Shenandoah Valley, between the North and South Forks of the Shenandoah River. The north end is 11 mi southwest of Luray and the south end is 7 mi east of Harrisonburg (fig. 1). The roadless area is characterized by a series of long sandstone ridges collectively called Massanutten Mountain. Ridge crests are 1,100 to 1,900 ft above the Shenandoah Valley floor, and are composed principally of resistant Massanutten Sandstone, which is overlain by thin shales and limestones bearing iron mineralization. The Martinsburg Shale and several limestones rock units underlie the Massanutten Sandstone (Brent, 1960, pl. 1.; Allen, 1967, pl. 1). The entire sequence has been folded into a synclinorium (Brent, 1960, p. 81). Although many of these strata have been mined in the Shenandoah Valley, production of mineral commodities from within the roadless area has been minimal (fig. 1).
Maps showing geology, geochemistry, and mineral resources assessment of the Rough Mountain Roadless Area, Alleghany and Bath counties, Virginia
The Rough Mountain Roadless Area comprises about 9,300 acres of George Washington National Forest land in the Valley and Ridge province in west-central Virginia. The area, which is about 6 mi long and 2 mi wide, is in Bath and Alleghany Counties, about 3 mi south of Millboro Springs, Va. (Index Map). State Route 42 forms part of the western boundary of the area, the Cowpasture River forms part of the southern boundary and the Chesapeake and Ohio Railroad and Pads Creek form the eastern boundary. The northern boundary follows the crests of two small ridges that lead east and west from the main ridgeline of Rough Mountain.
Geology of the Harrisonburg and Bridgewater quadrangles, Virginia
The Harrisonburg and Bridgewater quadrangles comprise an area of approximately 117 square miles in Rockingham County in northwestern Virginia.This area is in the western part of the Shenandoah Valley, a portion of the Valley and Ridge physiographic province, and contains parts of three major geologic structures-the Staunton and North Mountain thrust faults and the Massanutten synclinorium.The roeks within the two quadrangles are folded and faulted limestones, dolomites, shales, and sandstones of Paleozoic age. These rocks have been divided into groups, formations, and members that include the Elbrook and Conococheague formations (Cambrian), the Stonehenge Formation, the Beekmantown Group, the New Market Limestone, and the Lineolnshire, Edinburg, and Martinsburg formations (Ordovieian), the Massanutten Sandstone and the Bloomsburg Formation (Silurian), and probably Upper Silurian and Iower and Middle Devonian limestones and shales that are not exposed but are judged to be on Massanutten Mountain. Triassic diabase dikes and Eocene volcanic pipes intrude the Paleozoic sequence locally. Much of the sequenee is eovered by alluvium or talus of Quaternary age. Selected strata of the Cambrian and Ordovician carbonate roek sequence are sources for road aggregate, agricultural lime, concrete aggregate, dimension stone, tettazzo, portland cement, flux stone, and pellet lime. Some of the carbonate rocks may be potential sources of lead and zinc minerals. Ordovician shale formations have potential for structural clay products.
Experimental chemical weathering of various bedrock types at different pH-values. 1. Sandstone and granite
Experimental chemical weathering of the so-called Old Rag Granite and Massanutten Sandstone, Virginia, U.S.A., has produced a comparison with the natural environment, and prediction of the effect of acid precipitation. The experimental results of the release of elements, dissolution of minerals, total rock weathered and the degree of weathering as function of volume of leachate were plotted. These data were compared with the natural environment. The use of the plots to predict the effect of high levels of rain acidity on weathering of these rocks is demonstrated. A nonexpandable 14-Å clay was developed from the alteration of biotite during the experimental chemical weathering of the granite at pH 4. This interstratified Al(OH)—mica clay resembles those of the soil developed on the granite and sandstone. Hydroxy-Al may be precipitating between the mica interlayers and producing a 14-Å spacing. Development of this clay by chemical alteration of biotite may change the current hypotheses about its origin in the soils of northeastern U.S.A. While Al-hydroxide seems to regulate Al concentrations in stream waters at the present level of rain acidity, it was found that at lower pH and in the presence of high sulfate concentrations, Al solubility may be controlled by Al-sulfate phase(s).
The relation of water quality to geology and land use changes in Fairfax County and vicinity, Virginia
No abstract available.
Geochemical maps of the Southern Massanutten Roadless Area, Page and Rockingham counties, Virginia
The U.S. Geological Survey (USGS) made a reconnaissance geochemical survey of the Southern Massanutten Roadless Area to test for indistinct or unexposed mineral deposits that might be recognized by their geochemical halos. Sixty-two stream-sediment and 52 rock samples were collected from within and near the study area by Lesure, assisted by J. H. DeYoung, Jr. (USGS) and A. E. Grosz (USGS) in October 1979. All samples were analyzed for 31 elements by means of semiquantitative emission spectrographic methods by Forn in USGS laboratories, Denver, COlo. (table 1). The samples were also analyzed for zinc by means of an atomic absorption method by B. F. Arbogast, USGS laboratories, Denver, Colo.
Geochemical data for Triassic sedimentary and thermally metamorphosed rocks of the northern Culpeper basin, Virginia
No abstract available.
Tectonic implications of the Indian Run Formation— A newly recognized sedimentary mélange in the northern Virginia Piedmont
Sedimentary melange in the northeastern part of Fairfax County, Virginia, contains both mesoscopic and mappable fragments of Accotink Schist, Lake Barcroft Metasandstone, metagabbro, and ultramafic rocks as well as smaller fragments of other rock types. This melange was originally mapped as the Sykesville Formation, a major precursory sedimentary melange in northern Virginia and Maryland. The fragments of Accotink Schist and Lake Barcroft Metasandstone within the Sykesville were considered to be rip-ups of these units over which the Sykesville slid when finally emplaced. More recent study has shown that fragments of Accotink and Lake Barcroft are restricted to a certain area of sedimentary melange originally defined as Sykesville, and this part of the melange is now considered to be a separate mappable unit, here named the Indian Run Formation. The Indian Run underlies the sequence Accotink Schist and Lake Barcroft Metasandstone which is here formally named the Annandale Group. The Indian Run is intruded by the Occoquan Granite of Cambrian age, so it is of Cambrian or Late Proterozoic age. The Sykesville Formation (restricted) is a much more extensive unit than the Indian Run Formation and is characterized by its contained olistoliths of the Peters Creek Schist, the unit that tectonically overlies it. The Sykesville and Peters Creek constitute a precursory melange-allochthon pair which is here termed a 'tectonic motif.' The Indian Run-Annandale pair then forms a tectonically lower motif, and the overlying pair, the Yorkshire Formation-Piney Branch Complex, forms a tectonically higher motif. The Chopawamsic Formation and underlying sedimentary melange in the area south of Fairfax County may form a tectonic motif beneath the Indian Run-Annandale tectonic motif. Thus, three and perhaps four repetitions of precursory melange-allochthon pairs occur in northern Virginia. Other percursory melanges and motifs may occur in the Maryland Piedmont to the north. The tectonic setting of the motif formation and assemblage is uncertain at this time. A model involving the obduction of several separate sheets onto the ancestral North American continental margin is appealing in that it involves the closing and destruction of a marginal basin, a relatively simple concept. This model fails, however, to supply a source for the sediment necessary to form the precursory melanges. A trench-slope origin would supply the vast amount of needed sediment by accretion. The precursory melangeallochthon motifs would then be stacked near the base of the trench slope. This model is appealing and requires a rather complicated assemblage of continental, arc, and oceanic fragments, such as those that occur on many modern continental margins.
Stratigraphy and characteristic mollusks of the Pamunkey Group (Lower Tertiary) and the Old Church Formation of the Chesapeake Group— Virginia coastal plain
Along the Pamunkey River and its tributaries can be found a very complete, well-preserved, Tertiary stratigraphic record that reflects the sea-level changes as well as the local tectonic history of the central Virginia Coastal Plain. Using this record, I have described the lower Tertiary units and proposed a sequential model for their occurrence. Sediments examined in this study range in age from early Paleocene to latest Oligocene or earliest Miocene. Upper Tertiary units are described where they occur in the same sections with the lower Tertiary beds. The Brightseat Formation (lower Paleocene), Aquia Formation (upper Paleocene), Marlboro Clay (upper Paleocene), Nanjemoy Formation (lower Eocene), Piney Point Formation (middle Eocene) and Old Church Formation (new unit, upper Oligocene and lower Miocene) were studied. The definitions of the Piscataway and Paspotansa Members of the Aquia are amended, and a lectostratotype (principal reference section) is designated for those units as well as the Aquia on the Potomac River just below the mouth of Aquia Creek. A lectostratotype section is also designated for the Nanjemoy and its two members, the Potapaco and the Woodstock. That section is on the Potomac above Popes Creek. Beds assigned to the Piney Point and Old Church Formations, previously known only in the subsurface, crop out extensively on the Pamunkey River. A hypostratotype (reference section) is selected for the Piney Point Formation on the Pamunkey River at Horseshoe. The Old Church Formation (named herein) is included in the Chesapeake Group. Areal extent of the stratigraphic units was determined by correlation of outcropping beds on the Pamunkey, Patuxent, Potomac, Rappahannock, Mattaponi, Chickahominy, and James Rivers supplemented by well data. Comparisons of the onlap histories of the Salisbury, Albemarle, and Charleston Embayments indicate a number of simultaneous transgressive events implying global sea-level rises. More restricted transgressions appear to be the result of local downwarping.
Effects of fracturing on well yields in the coalfield areas of Wise and Dickenson counties, southwestern Virginia
Fracturing associated with lineaments are the primary influence on yields from wells in the coalfields of southwestern Virgnia. Graphical comparison of yield from wells shows that wells located in valleys with lineaments produce larger quantities of water than wells in valleys without lineaments. Pumping tests at wells located in valleys with lineaments indicate transmissivities as high as 598 ft2/d, caused principally by secondary permeability. Analysis of data collected from packer-injection tests in a test hole located on a ridge indicate relatively large hydraulic conductivities ranging from 2x10(sup -2) to 1x10(sup -1) feet per day in upper parts of the test hole, compared to values typical of unfractured rocks in the study area. Fracturing due to stress relief contribute to these large values. Yields from wells located on lineaments are consistently higher than well yields from wells in unfractured rock in the study area, but well yields from wells placed randomly in areas suspected of having stress relief fractures cannot be predicted.
Relation between ground-water quality and mineralogy in the coal-producing Norton Formation of Buchanan County, Virginia
The geochemical processes controlling ground-water chemistry in the coal-producing strata of southwestern Virginia include hydrolysis of silicates, dissolution of carbonates, oxidation of pyrite, cation exchange, and precipitation of secondary minerals, kaolinite and goethite. Core material from the Norton Formation of the Pennsylvania Period is composed of slightly more than one-half sandstone; siltstone and minor amounts of shale, clay, and coal account for the majority of the remainder. Petrographic analyses and x-ray diffraction studies indicate that the sandstone is about 75 percent quartz, 15 percent plagioclase feldspar, 2 percent potassium feldspar, 2 percent muscovite, 4 percent chlorite, and 1 percent siderite. Calcite is present in small amounts and in a few strata as clasts or cement. No limestone strata were identified. The siltstone is about 50 percent quartz, 10 percent plagioclase feldspar, 10 percent mica, 20 percent chlorite, and from 0 to 25 percent siderite. Pyrite is associated with some siltstone and, where present, generally accounts for less than 1 percent. Total sulfur generally constitutes less than 0.1 percent of core samples but about 4 percent in the more pyrite-rich layers. Three reaction models are used to account for the observed water chemistry. The models derive sulfate from pyrite, iron from pyrite and siderite, calcium from plagioclase and calcite, sodium from plagioclase and cation exchange, magnesium from chlorite, and carbon from carbon dioxide, calcite, and siderite. Kaolinite, chalcedony, and goethite are formed authigenically. Carbon-13 data define the relative contributions of carbon sources to models. Comparison of adjacent unmined and mined basins indicates that surface mining significantly increases the weathering reaction of pyrite in contrast to weathering reactions of other minerals. However, in the area studied, reactive pyrite does not appear to be present in sufficient quantities in strata associated with mined coal seams to cause acid mine drainage.