Search USGS⌕ Search

Geology topics

Mark W. Carter

Publications and source records attributed to Mark W. Carter.

At least 19 recordsLinked to original sources
USGS2026

Preliminary geologic map of the Sparta East, Sparta West, and parts of the Glade Valley and Whitehead 7.5-minute quadrangles, North Carolina and Virginia, and the epicentral area of the August 9, 2020, Mw 5.1 earthquake near Sparta, North Carolina

Introduction New bedrock and surficial geologic mapping in the Sparta East, Sparta West, and parts of the Glade Valley and Whitehead 7.5-minute quadrangles, North Carolina and Virginia, investigates the geologic framework and causative mechanisms of the August 9, 2020, Mw 5.1 earthquake near Sparta, North Carolina. The mapping documents (1) the coseismic surface rupture from the 2020 earthquake and related brittle structures in the bedrock; (2) the fault contact between the western Blue Ridge and eastern Blue Ridge; (3) lithostratigraphy in the Lynchburg Group, Ashe Metamorphic Suite, and Alligator Back Metamorphic Suite; (4) the nature of the contact between the Lynchburg Group, Ashe Metamorphic Suite, and Alligator Back Metamorphic Suite; and (5) surficial deposits.

North Carolina, Virginia↗
USGS2025

Geologic map of the Buckner 7.5-Minute quadrangle, Louisa County, Virginia

The Buckner 7.5-minute quadrangle straddles three terrane boundaries in the Piedmont Physiographic Province in central Virginia: the Chopawamsic terrane, the Elk Hill Complex, and the Goochland terrane. In much of the map area, the Elk Hill Complex separates the Chopawamsic and Goochland terranes. Rocks of the Chopawamsic terrane include Ordovician metavolcanic and metasedimentary rocks of the Chopawamsic Formation, Ordovician to Silurian granodiorite sheet intrusions, and Paleozoic mafic intrusions. Silurian to Devonian rocks of the Quantico Formation, mostly garnet-mica schist, crop out in the northwesternmost part of the map area, and are in unconformable contact with rocks of the Chopawamsic Formation on the southeastern limb of the Quantico synclinorium. The main map unit in the Elk Hill Complex is Neoproterozoic mica gneiss, which is in pre-metamorphic fault contact with rocks of the Chopawamsic Formation to the west. The main map unit of the Goochland terrane is the Maidens Gneiss. Except for Jurassic diabase dikes, all rocks on the Buckner 7.5-minute quadrangle were metamorphosed to amphibolite facies during the Alleghanian orogeny and preserve multiple compositional and phyllosilicate penetrative foliations. Evidence of amphibolite-facies metamorphism during the Taconic orogeny is preserved in rocks of the Elk Hill Complex. The entire width of the Maidens Gneiss on the Buckner 7.5-minute quadrangle is within the Spotsylvania high-strain zone and amphibolite-facies mylonitic textures are pervasive. Quartz veins and Jurassic diabase dikes crosscut all older rocks of the quadrangle. Multiple levels of terrace deposits are present along and near the major streams of the quadrangle. The lower terrace deposits are likely remnants of former positions of the Little River on the landscape, whereas higher deposits may be remnants of former deposits of the Atlantic Coastal Plain that covered this portion of the Piedmont Province. A linear cluster of aftershocks from the magnitude 5.8 earthquake that occurred near Mineral, Virginia, in 2011 defines the Fredericks Hall fault, which is at depth on the Buckner quadrangle. Most of the aftershocks occurred in the core of the Elk Creek antiform and have no relation to faults mapped at the surface. Several abandoned crushed stone and building stone quarries, as well as a mica prospect, exist in the quadrangle.

Virginia↗
USGS2025

Pocoshock Creek Gneiss and redefinition of the Petersburg Granite, central-eastern piedmont of Virginia

The Petersburg Granite (sensu lato) was formerly interpreted to be a single late Paleozoic composite batholith in the central-eastern part of the Piedmont Physiographic Province of Virginia. Detailed mapping beginning in the mid 2000s resulted in the subdivision of these voluminous granitic rocks into five units—layered granitic gneiss, foliated granite, porphyritic granite, subidiomorphic (equigranular) granite, and pegmatitic granite. U-Pb zircon geochronology demonstrate that foliated granite and layered granitic gneiss currently assigned to the batholith are 100 million years (m.y.) older, and yield Silurian to Devonian ages (ca. 425 mega-annum (Ma) to ca. 403 Ma). We propose the name Pocoshock Creek Gneiss for these strongly foliated and layered gneisses. Geochronologic data also require redefinition of the Petersburg Granite (sensu stricto). Massive equigranular and porphyritic rock types of the Petersburg Granite (sensu stricto) are geochemically distinct from a subset of Pocoshock Creek Gneiss samples. Massive equigranular and porphyritic rock types are similar to another, more granitic subset of the Pocoshock Creek Gneiss, which indicates different magma sources for the Petersburg Granite (sensu stricto) and Pocoshock Creek Gneiss but also likely indicates assimilation of Pocoshock Creek Gneiss during late Paleozoic intrusion of these Petersburg Granite (sensu stricto) rock types. Equigranular granite southwest of Petersburg, Virginia is 15–20 m.y. older than porphyritic granite, massive granite, and monzodiorite (ca 300 Ma) near Richmond, Virginia. The Petersburg Granite (sensu stricto) consists of two regional plutons—the northern Richmond pluton and the southern DeWitt-Sutherland pluton. The DeWitt-Sutherland pluton of Early Pennsylvanian age is separated from Late Pennsylvanian to early Permian granite of the Richmond pluton by a map scale septum of Pocoshock Creek Gneiss. Geochemical analyses of 15 samples of Pocoshock Creek Gneiss are compared to other igneous suites throughout the Appalachian orogen. Whole rock geochemistry shows elevated average thorium and uranium values in porphyritic granite compared to massive equigranular granite and Pocoshock Creek Gneiss and suggest that homes and businesses built on that rock type of the Richmond pluton may be most at risk for uranium and (or) dissolved radon in groundwater or radon gas in confined spaces.

Professional Paper↗
USGS2024

Mesoproterozoic to Paleozoic tectonics, Pleistocene landforms, and Holocene seismicity in the Blue Ridge: Results from integrated studies of the 9 August 2020, Mw 5.1 earthquake area near Sparta, North Carolina, USA

This field trip examines the results of integrated geologic studies of the 9 August 2020, M w 5.1 earthquake near Sparta, North Carolina, USA. The earthquake generated ~4 km of coseismic surface rupture of the Little River fault and uplifted a surface area of ~11 km 2 . The Little River fault is a thrust fault oriented 110–130°/45–70°SW, and mapped fault segments are en echelon with scarp heights from <5–30 cm. The epicenter is in polydeformed rocks of the Ashe and Alligator Back Metamorphic Suites in the eastern Blue Ridge. Bedrock structure formed during multiple Paleozoic orogenies; the regional foliation strikes NE-SW and dips SE (mean orientation 063°/52°SE). Mapping identified late Paleozoic veins and shear zones, a regional joint set striking 330–340° and 250–240°, and brittle faults that cut the Paleozoic foliation. Brittle faults oriented similar to the Little River fault are mapped up to 4 km along strike from the coseismic rupture along Bledsoe Creek valley, and the combined length of the Little River fault system is ~8 km. Paleoseismic trenches across the Little River fault corroborate the reactivation of an older fault by the 2020 earthquake and reveal two events during late Pleistocene (<50 ka). Surficial mapping identified several terrace deposits, including a deposit along Bledsoe Creek that yielded a 26 Al/ 10 Be isochron burial age of 0.46 ± 0.13 Ma and overlies a brittle fault, thus constraining the timing of movement of the fault at that location. Paleoliquefaction studies document soft-sediment deformation features in alluvium that may represent paleoseismic events. Collectively, these results highlight long-lived paleoseismicity of the Blue Ridge and that the 9 August 2020 earthquake reactivated an older, suitably oriented brittle fault in the bedrock. The Little River fault is an example of a previously unknown but active fault lying outside of known seismic zones with demonstrated recurrence of paleo-ruptures, raising questions about the assumption that damaging earthquakes are limited to areas of ongoing background seismicity, which is counter to seismic hazard assessments in the eastern United States. Bedrock mapping separates eastern Blue Ridge lithostratigraphy of the Lynchburg Group and Ashe and Alligator Back Metamorphic Suites into separate fault-bound packages juxtaposed over various 1.3–1.0 Ga basement rocks of the northern French Broad massif by the Gossan Lead fault.

North Carolina↗
USGS2023

Preliminary map of the surface rupture from the August 9, 2020, Mw 5.1 earthquake near Sparta, North Carolina—The Little River fault and other possible coseismic features

This publication is a preliminary map and geodatabase of the coseismic surface rupture and other coseismic features generated from the August 9, 2020, Mw 5.1 earthquake near Sparta, North Carolina. Geologic mapping facilitated by analysis of post-earthquake quality level 0 to 1 lidar, document the coseismic surface rupture, named the Little River fault, and other coseismic features. The Little River fault is traced for approximately 4 kilometers and cuts the regional Paleozoic fabric (mean foliation, 063°/57°), and the dominant strike of joint sets are 0°–10°, 130°–150°, and 320°–340°. Individual fault strands occur in an en echelon pattern within an approximately 10-meter-wide zone. Trenches across the Little River fault document a thrust fault oriented 110°/45° with at least 10 centimeters (cm) of displacement. The Little River fault is marked by a flexure or scarp with a height of 5–30 cm and a local maximum height of 50 cm. Southwest-side-up displacement is consistent along the fault and indicates thrust kinematics. The strike of the Little River fault changes from 110° to 130° near Duncan Farm where it crosses Chestnut Grove Church Road (NC Rt. 1426). Although the surface expression of the fault terminates and (or) is imperceptible at both ends, deformation is still clear in residual surface maps showing the change between pre- and post-earthquake lidar elevations. Other coseismic features documented are rockfalls, ground cracks, fissures, lateral spreading on a sandbar, and mass-wasting scarps; several possible faults that were identified from lidar analyses strike E-W and oblique to the Little River fault.

North Carolina↗
USGS2023

Redefinition of the Petersburg batholith and implications for crustal inheritance in the Dinwiddie terrane, Virginia, USA

Field relations as well as geochemical and petrologic studies of metaigneous rocks assigned to the Pennsylvanian–Permian Petersburg batholith identify at least two distinct rock types: foliated metagranitoid gneiss and massive to porphyritic granite. Foliated metagranitoid gneiss of mostly granodioritic composition is geochemically distinct from associated massive and porphyritic granitic rocks. These gneissic rocks yield radiometric ages from ca. 425 Ma to ca. 403 Ma and document that many of the rocks assigned to the late Paleozoic Petersburg batholith are 100 m.y. older than the youngest portions of the composite batholith and are part of an earlier infrastructural terrane. Two samples of massive equigranular granite southwest of Petersburg, Virginia, yield ages of ca. 321 Ma and ca. 317 Ma, which are 15–20 m.y. older than ca. 300 Ma ages for porphyritic granite, massive granite, and monzodiorite near Richmond, Virginia. Geologic mapping shows that the Early Pennsylvanian granite southwest of Petersburg is separated from Late Pennsylvanian to early Permian granite near Richmond by a map-scale septum of Silurian–Devonian foliated metagranitoid gneiss, referred to herein as the informal Pocoshock Creek gneiss. Laser ablation–inductively coupled plasma–mass spectrometry data from one sample of a quartz-muscovite felsic schist xenolith show a peak age mode of ca. 529 Ma that we interpret to be the maximum depositional age. Inherited zircons from foliated metagranitoid gneiss and massive equigranular granite range from ca. 631 Ma to ca. 376 Ma, but many are Cambrian. Neoproterozoic–Cambrian quartz-muscovite felsic schist and amphibolite, Silurian–Devonian Pocoshock Creek gneiss, and Pennsylvanian–Permian granite comprise a fault-bounded terrane referred to herein as the Dinwiddie terrane. Ages of inherited cores in zircon from igneous rocks and limited detrital zircon geochronology suggest the terrane is of peri-Gondwanan affinity. U/Pb ages of healed fractures in zircon grains from foliated metagranitoid gneiss indicate low-grade deformation of the gneiss at ca. 378–376 Ma, while ca. 320–280 Ma rims on many grains record intrusion of late Paleozoic granite. The temperature-time-deformation history of the Dinwiddie terrane is distinct from the adjacent Goochland and Roanoke Rapids terranes. Orogen-scale dextral transpression likely translated the Dinwiddie terrane southward during the Alleghanian orogeny, at which time they were intruded by Pennsylvanian to Permian granite.

Virginia↗
USGS2022

Implementation plan of the National Cooperative Geologic Mapping Program strategy — Appalachian Piedmont and Blue Ridge Provinces

The National Cooperative Geologic Mapping Program is publishing a strategic plan titled “Renewing the National Cooperative Geologic Mapping Program as the Nation’s Authoritative Source for Modern Geologic Knowledge.” The plan provides a vision, mission, and goals for the program for the years 2020–30: Vision: create an integrated, three-dimensional, digital geologic map of the United States. Mission: characterize, interpret, and disseminate a national geologic framework model of the Earth through geologic mapping. Goal: focus on geological mapping as a core function of the U.S. Geological Survey within the long-term vision of adequately mapping the Nation’s geologic framework in three dimensions.

Alabama, Georgia, Illinois, Indiana, Kentucky, Mar↗
USGS2022

Preliminary geologic map of the Cherry Hill quadrangle, Dinwiddie, Sussex, and Greensville Counties, Virginia

The Cherry Hill 7.5-minute quadrangle straddles the Coastal Plain and Piedmont Provinces along the Tidewater Fall Line. Rocks of the eastern Piedmont Roanoke Rapids terrane crop out in the western part of the quadrangle and consist of greenschist- to amphibolite-facies Neoproterozoic felsic to intermediate metavolcanic rocks, some of which contain flattened quartz phenocrysts and are locally isoclinally folded; greenstone that locally preserves primary layering; and intrusive metadiorite and metagabbro, much of which has been altered to amphibolite. Most of these rocks are strongly foliated and jointed. Greenschist-facies metasiltstone that preserves primary bedding also occurs locally in the Roanoke Rapids terrane. Neoproterozoic mica schist, middle Paleozoic foliated metagranite, and late Paleozoic massive and porphyritic granite crop out in the eastern part of the quadrangle and are part of the Dinwiddie terrane and the late Paleozoic De Witt pluton. Upper greenschist- to lower amphibolite-facies mica schist consists of stringers and boudins of vein quartz and contains porphyroclasts of staurolite that preserve an earlier foliation as inclusion trails. Porphyroblasts of garnet, staurolite, and kyanite also occur locally. Foliation in granites of the De Witt pluton may be magmatic. Separating the Dinwiddie terrane from the Roanoke Rapids terrane are greenschist-facies, highly strained granitic mylonite and bodies of less deformed granite within the Nottoway River fault zone, which is a strand of the eastern Piedmont fault system. Paleozoic pegmatite dikes and quartz veins cross-cut rocks of the Dinwiddie terrane, and quartz veins and Jurassic diabase dikes cross-cut rocks of the Roanoke Rapids terrane. Sand and gravel deposits of the Atlantic Coastal Plain overlie Piedmont rocks. Two units assigned to the upper part of the Neogene Chesapeake Group occur at elevations up to 295 feet (90 meters) above sea level atop the Richmond plain in the central part of the quadrangle. Two units of the Quaternary Bacons Castle Formation occupy the Essex plain and Norge uplands at elevations up to 180 feet (55 meters) above sea level in the eastern part of the quadrangle. In the western part of the quadrangle, multiple levels of terrace deposits are the fluvial equivalent of estuarine to marine units of the Atlantic Coastal Plain to the east. Holocene alluvium occurs along creeks and the Nottoway River. Quaternary colluvial deposits occur locally. Numerous Carolina bays pock the landscape of the Richmond and Essex plains, and three abandoned channelways represent former locations of Sappony Creek, one of the major drainages of the quadrangle. Brittle faults juxtapose Piedmont basement rocks against Neogene sediments of the upper part of the Chesapeake Group. These Cenozoic faults were first uncovered in mine excavations in the late 1990s; new mapping indicates that many of these faults are reactivated silicified cataclasite zones that occur throughout the Piedmont basement rocks. Silicified cataclasites and associated quartz veins are typically mineralized with iron and iron sulfide minerals. The quadrangle was the focus of extensive mining for heavy minerals, including ilmenite and zircon, in upland Atlantic Coastal Plain deposits beginning in the mid-1990s. Other mineral resources, including precious metals, clay for structural brick, crushed stone, and building stone for millstones, have also been prospected or quarried in the quadrangle.

Virginia↗
USGS2022

The Mw 5.1 9 August 2020, Sparta earthquake, North Carolina: The first documented seismic surface rupture in the eastern United States

At 8:07 a.m. EDT on 9 Aug. 2020 a Mw 5.1 earthquake located ~3 km south of Sparta, North Carolina, USA, shook much of the eastern United States, producing the first documented surface rupture due to faulting east of the New Madrid seismic zone. The co-seismic surface rupture was identified along a 2-km-long traceable zone of predominantly reverse displacement, with folding and flexure generating a scarp averaging 8–10-cm-high with a maximum observed height of ~25 cm. Widespread deformation south of the main surface rupture includes cm-dm–long and mm-cm–wide fissures. Two trenches excavated across the surface rupture reveal that this earthquake propagated to the surface along a preexisting structure in the shallow bedrock, which had not been previously identified as an active fault. Surface ruptures by faulting are rarely reported for M <6 earthquakes, and hence the Sparta earthquake provides an opportunity to improve seismic hazard knowledge associated with these moderate events. Furthermore, this earthquake occurred in a very low strain rate intraplate setting, where earthquake surface deformation, regardless of magnitude, is sparse in time and rare to observe and characterize.

North Carolina↗
USGS2021

The liquefaction record of past earthquakes in the Central Virginia Seismic Zone, Eastern United States

Following the 2011 moment magnitude, M "> M M 5.7 Mineral, Virginia, earthquake, we conducted a search for paleoliquefaction features and found 41 sand dikes, sand sills, and soft‐sediment deformation features at 24 sites exposed in cutbanks along several rivers: (1) the South Anna River, where paleoliquefaction features were found in the epicentral area of the Mineral earthquake and farther downstream to the southeast; (2) the Mattaponi and Pamunkey Rivers east of the Fall Line, where liquefiable sediments are more common than in the epicentral area; and (3) the James River and Rivanna River–Stigger Creek, where a few sand dikes were found in the 1990s. Liquefaction features are grouped into two age categories based on dating of host sediment in which they occur and weathering characteristics of the features. A younger generation of features that formed during the past 350 yr are small, few in number, and appear to be limited to the James and Pamunkey Rivers. Though there are large uncertainties in their locations and magnitudes, one or more preinstrumental earthquakes, including the 1758, 1774, and 1875 events, likely caused these features. An older generation of liquefaction features that formed between 350 and 2800 yr ago are larger, more numerous, and more broadly distributed than the younger generation of features. Several earthquakes could account for the regional distribution of paleoliquefaction features, including one event of M "> M M 6.25–6.5 near Holly Grove, or two events of M "> M M 6.0 near Mineral and M "> M M 6.25 near Ashland. Amplification of ground motions in Coastal Plain sediment might have contributed to liquefaction along the Mattaponi and Pamunkey Rivers.

Seismological Research Letters↗
USGS2021

River terrace evidence of tectonic processes in the eastern North American plate interior, South Anna River, Virginia

We show that long-recognized seismicity in the central Virginia seismic zone of the eastern North American intraplate setting arises primarily from tectonic processes predicted by new, fully coupled plate tectonic geodynamic models. The study leverages much new geophysical and geologic data following the 2011 Mineral, Virginia, earthquake that ruptured a steeply dipping, northwest-verging reverse fault traversed by the South Anna River. The data are primarily assembled from a flight of six fluvial terrace geomorphic markers identified and correlated on texture, relative weathering, and numeric ages including one terrestrial cosmogenic nuclide (TCN) profile and 30 luminescence dates. Terrace thickness, stratigraphic age models, and incision rates downstream and upstream of the 2011 rupture are different. Long-term river incision rates of ∼25–30 m/My are superimposed on regional TCN-determined erosion rates of ∼8.5 m/My; however, there are at least 10 m of tectonically driven incision in the epicentral region at rates of ∼30–94 m/My. The inferred deformation resembles a hanging wall anticline above a blind reverse fault with a diffuse overlying carapace of minor brittle faults, an interpretation supported by seismology as well as bedrock and saprolite mapped across the epicentral region. These results are further supported by channel metrics that show nonuniform channel steepness ( k sn ) and a predicted steady-state channel elevation different from the actual channel elevation across the epicentral region. If all of the observed deformation is a consequence of the fault that ruptured in 2011, the recurrence interval of Mineral-sized events would be ∼5.5 ky.

Virginia↗
USGS2021

Stop 3 – The Petersburg “Granite” redefined: Recognition and implications of Silurian to Devonian rocks in central-eastern Virginia

Introduction Although the Petersburg Granite had long been in practical use as a building stone since the 1830s (Watson, 1906; 1907; 1910; Darton, 1911; Steidtmann, 1945), it was first formally defined as a geologic unit by Anna Jonas on the 1928 geologic map of Virginia. Anna Jonas defined this unit as a Precambrian coarse-grained porphyritic biotite granite that was intruded by finer grained granite and cut by pegmatite (Nelson, 1928). This belt of mostly granitic rocks extends from near Ashland, Virginia north of Richmond, to near Stony Creek, south of Petersburg, Virginia (e.g., Virginia Division of Mineral Resources, 1993) and is bounded by the Hylas fault zone to the northwest, the Mesozoic Richmond basin to the west, and the newly recognized Nottoway River fault zone to the southwest (e.g., Carter and others, 2020; 2021). The eastern boundary of this belt is covered by Coastal Plain sediments, but geophysical and deep borehole data suggest an orogen-scale suture separates it from the Neoproterozoic Chesapeake block to the east (Figure 1; Carter and others, 2021).

Virginia↗
USGS2021

Fundamental framework geology in the southern Appalachian crystalline core: The U.S. Geological Survey National Cooperative Geologic Mapping Program (FEDMAP Component) Piedmont-Blue Ridge pPoject

The USGS NCGMP Piedmont-Blue Ridge (PBR) Project aims to develop 4D geologic framework models across the southern Appalachian orogen. The primary objective of the Project is to construct geologic maps and accompanying GeMS geodatabases at scales of 1:24K and 1:100K across the VA-NC-TN state lines where existing geologic map coverage is not adequate (>1:250K) to solve societal and scientific challenges. Two tasks and regional field areas comprise the PBR Project: (1) Piedmont Geology Along the Southeastern Fall Zone, Virginia and North Carolina focuses on eastern Piedmont geology from Richmond, Virginia to Rocky Mount, North Carolina; and (2) Blue Ridge-Inner Piedmont geology covers from the junction of Virginia, North Carolina, and Tennessee eastward into the Piedmont. Both areas host potential critical mineral deposits, including rare earth elements (REE), lithium, tin, and others (e.g., Ti, U, Ta, Nb, Be, Mn, Ba, Zr). Radon in groundwater is a concern in northwestern North Carolina and southwestern Virginia where preliminary investigation suggests a correlation between REE concentration and radon/uranium in certain rock units and major shear zones. The Fall Zone in southeastern Virginia and northeastern North Carolina is the recharge area for the largest aquifer (Cretaceous Potomac Group) on the southeastern seaboard; this region also hosts marketable deposits of REE-bearing heavy minerals. Slope-stability and earthquake hazards are issues in both areas. Developing the 4-D geologic framework of these relatively unexplored regions and producing seamless geologic maps and geodatabases is necessary to address societal needs and resolve “state-line border faults”. Both Tasks work closely with USGS NCGMP STATEMAP and EDMAP components to further the overall goals of the Program.

North Carolina, Virginia↗
USGS2020

Geochronologic age constraints on tectonostratigraphic units of the central Virginia Piedmont, USA

New geologic mapping coupled with uranium-lead (U-Pb) zircon geochronology (sensitive high-resolution ion microprobe-reverse geometry [SHRIMP-RG] and laser ablation-inductively coupled plasma-mass spectrometry [LA-ICP-MS]) analyses of 10 samples, provides new constraints on the tectonostratigraphic framework of the central Virginia Piedmont. Detrital zircon analysis confirms that the Silurian-Devonian Quantico Formation is a postorogenic successor basin, with zircons derived primarily from Ordovician Chopawamsic Formation volcanic rocks. Detrital zircons from strata of the Long Island syncline, previously mapped as a separate successor basin, have a peri-Gondwanan component distinct from Laurentian-sourced rocks of the Potomac terrane to the west. Volcanism of the Chopawamsic Formation spanned at least 14 million years during the Ordovician. The Chopawamsic Formation contains sheet-like Late Ordovician-Silurian granodioritic and tonalitic intrusions that were once mapped as Carboniferous. Biotite-muscovite migmatitic paragneiss, which borders the Chopawamsic Formation on its southeast side and also occurs east of the Lakeside fault, preserves evidence of Silurian deformation and metamorphism, with a Carboniferous (Alleghanian) overprint. Limited SHRIMP-RG analysis of detrital zircons from this paragneiss yields a Laurentian (Mesoproterozoic) signature, which suggests that the structurally concordant contact between volcanic rocks of the Chopawamsic Formation and paragneiss is either a pre-Alleghanian fault or an unconformity.

Virginia↗
USGS2020

Foreward: Geology Field Trips in and around the U.S. Capital

The first annual meeting of the Geological Society of America (GSA) was held in 1888 in Ithaca, New York (Fairchild, 1932), but official Sections of GSA formed much later. During the spring of 1949, a symposium in Knoxville, Tennessee, on mineral resources of the southeastern United States became the catalyst for the creation of the Southeastern Section of the Geological Society of America (King, 1964), and the first annual meeting of the Southeastern Section was held in 1952 in Roanoke, Virginia (Wilson, 1954). The Northeastern Section formed much later, and its first annual meeting was held in 1966 in Philadelphia, Pennsylvania (Socolow, 1968). At all of these section meetings, field trips have been important venues for geologists and especially students to gather together, examine rocks in the field, and discuss ideas. These field trips have been especially important at combined section meetings because they provide settings for geologists who are experienced in one geographic region to examine and compare the geology of other regions. The first combined meeting of the Southeastern and Northeastern sections occurred in 1976 in Arlington, Virginia. Since then, the Southeastern and Northeastern sections have met together on numerous occasions, including 1982 in Washington, DC; 1991 in Baltimore, Maryland; 2004 in Tysons Corner, Virginia; and 2010 in Baltimore, Maryland. Since the first combined section meeting in 1976, there has been a gradual increase in the role of technology in geology field studies. In fact, during the past several decades there has been an increase in emphasis in our society on the instrumental component of science, the goal of which is operational techniques to do or control things, and a corresponding decrease in emphasis on the natural philosophy component of science, the goal of which is a greater understanding of the natural world (Dear, 2006). The modern education acronym STEM (Science, Technology, Engineering, and Mathematics), for example, is often used as a catch-all term that implies that science and technology are relatively synonymous, and implies that greater technology leads automatically to greater understanding of the natural world. This assumption, however, is not always valid (Dear, 2006), and technology should not be promoted as a substitute for field experiences. Technology can be a tool that leads to greater understanding of the natural world, but not all Science uses technology as a means of providing greater understanding. The benefits of new technologies include: (1) data of greater resolution; and (2) greater efficiency of capturing, storing, and visualizing data. The risks of new technologies include: (1) an overabundance of data, some of which may be of little value; (2) less time available for analysis of data, if geologists become occupied primarily with capturing and storing data; and (3) errors that arise from complacency and the perception that field-checking may not be necessary. In other words, there is a risk that a glut of data and vast amounts of time devoted to the capturing and storing of data may result in a reduced interest and (or) willingness to field-check data. In the spirit of the early GSA section meetings, we feel that there are still enormous advantages to conducting geology field trips in conjunction with traditional meeting presentations and posters. In 2020, with this current combined Southeastern and Northeastern section meeting in Reston, Virginia, we have assembled eight different field trips that cover a wide range of territory in and around the Nation’s capital. These field trip localities include the immediate vicinity of Washington, DC, as well as various locations in nearby areas of Virginia, Maryland, and West Virginia. The physiographic provinces include Mesozoic Rift Basins, the Piedmont, the Blue Ridge, the Valley and Ridge, and the Allegheny Plateau of the Appalachian Basin. The field trip sites exhibit a wide range of igneous, metamorphic, and sedimentary rocks, as well as rocks with a wide range of geologic ages from the Mesoproterozoic to the Holocene. We hope that this guidebook provides new motivation for geologists to examine rocks in the field, to discuss ideas with colleagues in the field, and to avoid becoming complacent. The editors of this volume would like to thank the authors of the different field trip guides, the field trip leaders, and all of the reviewers who made suggestions for improving the field trip manuscripts. The editors would also like to thank Elle Derwent of GSA for her logistical help and guidance regarding the field trips, and April Leo and the staff of the GSA Publications Department for seeing this book through to publication.

Maryland, Virginia, West Virginia↗
USGS2019

Paleoliquefaction field reconnaissance in eastern North Carolina—Is there evidence for large magnitude earthquakes between the central Virginia seismic zone and Charleston seismic zone?

In June 2016, approximately 64 kilometers (km) of riverbank were examined along the Tar and Neuse Rivers near Tarboro and Kinston, North Carolina, for evidence of liquefaction-forming earthquakes. The study area is in the vicinity of the Grainger’s fault zone in eastern North Carolina. The Grainger’s fault zone is a fault zone in the inner Coastal Plain Province that has well-documented Paleogene and younger deformation of Cretaceous to Eocene strata. Low-magnitude earthquakes near the fault zone (for example, magnitude [M] 2.1 in 2013, 13 km south-southwest of Kinston) suggest larger earthquakes may have struck this region in the past. The study area is about equidistant from newly documented Holocene paleoliquefaction sites in the Central Virginia Seismic Zone (CVSZ) and liquefaction sites formed during the 1886 M7.1 Charleston, South Carolina earthquake. The northernmost Holocene paleoliquefaction features associated with the Charleston Seismic Zone (CSZ) are in Southport, North Carolina. Conditions suitable for liquefaction were identified at 38 sites on both rivers, but only one site was classified as highly susceptible. Stratigraphy consists of Paleozoic gneiss; Cretaceous sandstone/shale; Paleocene mudstone/claystone to Eocene fossiliferous limestone; Quaternary unconsolidated, crossbedded sand and gravel; and Holocene alluvium. Three sets of stratigraphic conditions suitable for liquefaction—unconsolidated source sand beneath capping strata—were identified in detailed examinations at 105 sites: (1) Holocene alluvial sand beneath alluvial silt and clay beds; (2) Quaternary terrace sand beneath beds of silt and clay; and (3) Holocene alluvial sand or Quaternary terrace sand capped by clay-rich Bt soil horizons. Weathered and unconsolidated Cretaceous sand capped by a Bt soil horizon was identified at one site, but the weathered sand is likely too compacted to liquefy readily. One outcrop containing three small sand dikes, and four outcrops of soft-sediment deformation features—mostly load casts—were observed, but none of these features could be conclusively established as seismogenic. A few examples of pseudo-sand-dikes were also identified: sand-filled cypress root casts and pedogenic weathering fronts created the appearance of sand dikes and sills. A comparable survey in 2015 of 119 km of riverbank exposures in the CVSZ yielded 19 paleoliquefaction sites of probable earthquake origin; these features formed from at least one M~6 earthquake in the past 6,000 years (6 ka). This survey in eastern North Carolina revealed no definitive paleoliquefaction features; earthquakes of sufficient magnitude to produce liquefaction likely have not affected this region during the Holocene.

North Carolina↗
USGS2019

The Appalachian Geo-STEM Camp: Learning about geology through experiential adventure recreation

The inaugural Appalachian Geo-STEM Camp (AGC) was a partnership between West Virginia University (WVU), the U.S. Geological Survey (USGS) and the West Virginia Geological and Economic Survey (WVGES). Designed to engage high school students in geoscience-oriented Science, Technology, Engineering and Mathematics (STEM) activities through adventure-based outdoor recreation, the inaugural AGC took place in June 2018, with its base operations at the WVU Natural Resources Center (NRC), located northeast of Morgantown, West Virginia. The goals of the AGC are to increase the knowledge of the teenaged campers about the geological formations and biodiversity in the region, to acquaint them with geologic mapping technology used by USGS, WVGES, and WVU, and to foster interest in STEM-based careers. Nine students participated, with a cadre from the USGS, WVGES, and WVU teaching lessons in local geology and ecology. Inaugural-year efforts were focused on development and logistics of the camp and what activities best complimented the STEM research. Post-evaluations by the participants were generally favorable. Year-two goals are to fully develop a curriculum, and conduct a thorough pre-camp and post-camp participant survey to quantify learning objectives and guide the sustainability of the effort.

West Virginia↗