Search USGS⌕ Search

Geology topics

Research about Shenandoah Valley

Source-linked reports with geographic coverage including Shenandoah Valley.

11 recordsLinked to original sources
USGS2017

Hypogene caves of the central Appalachian Shenandoah Valley in Virginia

Several caves in the Shenandoah Valley in Virginia show evidence for early hypogenic conduit development with later-enhanced solution under partly confined phreatic conditions guided by geologic structures. Many (but not all) of these caves have been subsequently invaded by surface waters as a result of erosion and exhumation. Those not so affected are relict phreatic caves, bearing no relation to modern drainage patterns. Field and petrographic evidence shows that carbonate rocks hosting certain relict phreatic caves were dolomitized and/or silicified by early hydrothermal fluid migration in zones that served to locally enhance rock porosity, thus providing preferential pathways for later solution by groundwater flow, and making the surrounding bedrock more resistant to surficial weathering to result in caves that reside within isolated hills on the land surface. Features suggesting that deep phreatic processes dominated the development of these relict caves include (1) cave passage morphologies indicative of ascending fluids, (2) cave plans of irregular pattern, reflecting early maze or anastomosing development, (3) a general lack of cave breakdown and cave streams or cave stream deposits, and (4) calcite wall and pool coatings within isolated caves intersecting the local water table, and within unroofed caves at topographic locations elevated well above the lo cal base level. Episodes of deep karstification were likely separated by long periods of geologic time, encompassing multiple phases of sedimentary fill and excavation within caves, and reflect a complex history of deep fluid migration that set the stage for later shallow speleogenesis that continues today.

Virginia↗
USGS2014

Karst geomorphology and hydrology of the Shenandoah Valley near Harrisonburg, Virginia

The karst of the central Shenandoah Valley has characteristics of both shallow and deep phreatic formation. This field guide focuses on the region around Harrisonburg, Virginia, where a number of these karst features and their associated geologic context can be examined. Ancient, widespread alluvial deposits cover much of the carbonate bedrock on the western side of the valley, where shallow karstification has resulted in classical fluviokarst development. However, in upland exposures of carbonate rock, isolated caves exist atop hills not affected by surface processes other than exposure during denudation. The upland caves contain phreatic deposits of calcite and fine-grained sediments. They lack any evidence of having been invaded by surface streams. Recent geologic mapping and LIDAR (light detection and ranging) elevation data have enabled interpretive association between bedrock structure, igneous intrusions, silicification and brecciation of host carbonate bedrock, and the location of several caves and karst springs. Geochemistry, water quality, and water temperature data support the broad categorization of springs into those affected primarily by shallow near-surface recharge, and those sourced deeper in the karst aquifer. The deep-seated karst formation occurred in the distant past where subvertical fracture and fault zones intersect thrust faults and/or cross-strike faults, enabling upwelling of deep-circulating meteoric groundwater. Most caves formed in such settings have been overprinted by later circulation of shallow groundwater, thus removing evidence of the history of earliest inception; however, several caves do preserve evidence of an earlier formation.

Virginia↗
USGS2013

Comparison of age distributions estimated from environmental tracers by using binary-dilution and numerical models of fractured and folded karst: Shenandoah Valley of Virginia and West Virginia, USA

Measured concentrations of environmental tracers in spring discharge from a karst aquifer in the Shenandoah Valley, USA, were used to refine a numerical groundwater flow model. The karst aquifer is folded and faulted carbonate bedrock dominated by diffuse flow along fractures. The numerical model represented bedrock structure and discrete features (fault zones and springs). Concentrations of 3 H, 3 He, 4 He, and CFC-113 in spring discharge were interpreted as binary dilutions of young (0–8 years) water and old (tracer-free) water. Simulated mixtures of groundwater are derived from young water flowing along shallow paths, with the addition of old water flowing along deeper paths through the model domain that discharge to springs along fault zones. The simulated median age of young water discharged from springs (5.7 years) is slightly older than the median age estimated from 3 H/ 3 He data (4.4 years). The numerical model predicted a fraction of old water in spring discharge (0.07) that was half that determined by the binary-dilution model using the 3 H/ 3 He apparent age and 3 H and CFC-113 data (0.14). This difference suggests that faults and lineaments are more numerous or extensive than those mapped and included in the numerical model.

Virginia;West Virginia↗
USGS2012

Interlaboratory comparison of three microbial source tracking quantitative polymerase chain reaction (qPCR) assays from fecal-source and environmental samples

During summer and early fall 2010, 15 river samples and 6 fecal-source samples were collected in West Virginia. These samples were analyzed by three laboratories for three microbial source tracking (MST) markers: AllBac, a general fecal indicator; BacHum, a human-associated fecal indicator; and BoBac, a ruminant-associated fecal indicator. MST markers were analyzed by means of the quantitative polymerase chain reaction (qPCR) method. The aim was to assess interlaboratory precision when the three laboratories used the same MST marker and shared deoxyribonucleic acid (DNA) extracts of the samples, but different equipment, reagents, and analyst experience levels. The term assay refers to both the markers and the procedure differences listed above. Interlaboratory precision was best for all three MST assays when using the geometric mean absolute relative percent difference (ARPD) and Friedman's statistical test as a measure of interlaboratory precision. Adjustment factors (one for each MST assay) were calculated using results from fecal-source samples analyzed by all three laboratories and applied retrospectively to sample concentrations to account for differences in qPCR results among labs using different standards and procedures. Following the application of adjustment factors to qPCR results, ARPDs were lower; however, statistically significant differences between labs were still observed for the BacHum and BoBac assays. This was a small study and two of the MST assays had 52 percent of samples with concentrations at or below the limit of accurate quantification; hence, more testing could be done to determine if the adjustment factors would work better if the majority of sample concentrations were above the quantification limit.

West Virginia↗
USGS2000

Mobilization and transport of soil particles during infiltration experiments in an agricultural field, Shenandoah Valley, Virginia

Evidence that fine particles mobilized and transported in soils and aquifers can have a profound influence on contaminant migration has spawned much interest recently in understanding colloid transport in natural materials. Repeated infiltration experiments on an initially dry field soil were conducted to evaluate rates of mobilization of fine particles over time and to investigate the importance of transient-flow events on particle transport. Water flow was measured in zero-tension lysimeters at 25 cm depth. For repeated infiltration events and for all plots, water flow sharply increased shortly after initial ponding of water at the soil surface, maintained a relatively steady level during the period of ponding, and decreased gradually thereafter. Particle concentrations measured in the pan lysimeters ranged from 7 mg L - 1 to 265 mg L - 1 and were typically on the order of 10 to 100 mg L - 1 . Greatest particle mass flux was observed during the initial infiltration experiment on each plot. During four subsequent infiltration experiments, all conducted within 250 min of the first event, steady mass fluxes were observed that were approximately 70% of the average value seen in the first flush of water through a dry soil, indicating that the supply of mobile soil particles is only sparingly reduced over closely spaced infiltration events. All peak particle concentrations and mass fluxes occurred near either the rising limb or the falling limb of the water flux hydrograph, presumably reflecting the movement of air−water interfaces during imbibition and drainage.

Virginia↗
USGS1990

Pesticide and PCB residues for loggerhead shrikes in the Shenandoah Valley

The decline in loggerhead shrike ( Lanius ludovicianus ) populations is widespread and coincides with the use of organochlorines that began in the late 1940's and increased until the 1970's (Morrison 1981; Robbins et al. 1986; Tate 1986). An inhabitant of farmland areas, loggerhead shrikes prey on invertebrates and small vertebrates (Bent 1950), and thus risk exposure to pesticides and other agricultural chemicals. The role of contaminants in the decline of loggerhead shrikes has only been partially assessed (Busbee 1977; Anderson and Duzan 1978; Morrison 1979; Rudd et al. 1981). Studies of the nesting and winter ecology of loggerhead shrikes (Luukkonen 1987; Blumton 1989) during 1985-88 in the Shenandoah Valley, Virginia provided the opportunity to collect eggs and carcasses for contaminant residue analysis. In this paper we provide pesticide and polychlorinated biphenyl (PCB) residue data for eggs and carcasses collected.

Shenandoah Valley↗
USGS1946

Lower Middle Ordovician stratigraphy of the Shenandoah Valley, Virginia

In classifying the lower Middle Ordovician of the Shenandoah Valley, the formation names Stones River, Mosheim, Lenoir, Holston, Whitesburg, and Athens have been used without adequate evidence. Detailed study shows that the so-called Athens and Whitesburg, as developed near Harrisonburg, are laterally continuous with the greater part of the Chambersburg limestone, which is supposed to be younger than the Athens. The newly discovered relations of these formations affect the classification of the Middle Ordovician in much of the northern Appalachian region. The present study has been high-lighted by the discovery that Cryptophragmus antiquatus , widely regarded as a valid guide to the lower Black River, ranges through several hundred feet of beds, possibly as high as lower Trenton. In the Shenandoah Valley, this fossil is most abundant near the top of the Chambersburg, which is supposed to be late Black River or early Trenton. In the proposed reclassification, the lower Middle Ordovician is divided into six time-stratigraphic units, in ascending order: the New Market limestone, Whistle Creek limestone, Lincolnshire limestone, Edinburg formation, Oranda formation, and Collierstown limestone. The Edinburg embraces two equivalent facies: one of cobbly limestone (Lantz Mills facies) which is mainly developed in the northern and western parts of the Shenandoah Valley; and a relatively thicker body of black limestone and shale (Liberty Hall facies) which is typically developed in the Harrison-burg-Staunton area. In the western part of Shenandoah County, the topmost division of the Edinburg formation is composed of light-gray calcilutite and calcarenite, named the St. Luke limestone member. The rusty-brown granular limestones just below Butts' Athens in the Harrisonburg-Staunton-Lexington area are here named the Botetourt limestone member of the Edinburg formation. At least part of the New Market limestone is linked with a part of the New York Chazy and type Lenoir, but the Lincolnshire seems to be post-Chazy. All the succeeding beds, comprising the greater part of the lower Middle Ordovician succession, are Black River or Trenton.

Virginia↗
USGS1945

Industrial limestones and dolomites in Virginia: northern and central parts of the Shenandoah Valley

The area described in this report includes the northern and central parts of Shenandoah Valley in Virginia extending from the West Virginia line southwestward to the vicinity of Greenville, Augusta County. It contains extensive deposits of high-calcium limestone averaging more than 97 per cent calcium carbonate. The Mosheim limestone, composed largely of high-calcium limestone, is the important "quarry rock" of the area. Other formations containing high-calcium limestone include locally a part of the Lenoir, the upper part of the Chambersburg in the western belts of Shenandoah County, and relatively thin units in the Beekmantown along the eastern side of the Massanutten Mountain syncline north of Rockingham County. Some of the thickest deposits of high-calcium limestone near railroads are in Frederick, Shenandoah, Rockingham, and Augusta counties. Extensive exposures of the Tomstown (Shady) dolomite, containing more than 42 per cent magnesium carbonate, occur in the eastern part df Clarke County. Locally near the North Mountain fault in parts of Shenandoah and Rockingham counties, 80 feet or more of brecciated dolomite in the Elbrook formation contains about 43.5 per cent magnesium carbonate and generally less than 2 per cent silica. Most of the sampled dolomite units in the Elbrook, Conococheague, and Beekmantown formations contain less than 40 per cent magnesium carbonate. Special study was made of the carbonate rocks suitable for chemical use and favorably located near railroads. Limestones, containing less than 95 per cent calcium carbonate, were studied locally in some detail. Descriptions of the belts of industrial limestone and dolomite are supplemented by geologic maps and sections, and chemical analyses.

Virginia↗