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At least 1,675 records · Page 93Linked to original sources
USGS1917

Relation of the Wissahickon mica gneiss to the Shenandoah limestone and Octoraro schist of the Doe Run and Avondale region, Chester County, Pennsylvania

The region discussed in this paper lies in Chester County, Pa., and is included in the eastern half of the Coatesville quadrangle. (See fig. 3.) It is within the belt of crystal-line schists and gneisses of the Piedmont Plateau. The northern half of the area, which will be called the Doe Run region, from the village of that name (see Fig. 4, p. 15), has been surveyed by Eleanora F. Bliss in connection with the problem of the relation of the Wissahickon mica gneiss to the Octoraro schist.

Pennsylvania↗
USGS1917

Revision of the Beckwith and Bear River formations of southeastern Idaho

In the detailed geologic mapping of the Wayan and Montpelier quadrangles, in south-eastern Idaho and adjacent territory, it has been found necessary to apply new names to strata hitherto referred to the Beckwith and Bear River formations or to portions of the Laramie as mapped by the Hayden Survey. The two quadrangles are contiguous, and the Montpelier quadrangle lies south of the Wayan. They occupy the corner of the State and include a very narrow strip in northeastern Utah and a somewhat broader strip in western Wyoming.

Idaho↗
USGS1916

The Pliocene Citronelle Formation of the Gulf Coastal Plain. The flora of the Citronelle Formation

In the spring of 1910 the writer, working under the direction of T. Wayland Vaughan, geologist in charge of Coastal Plain investigations, undertook a study of the later Tertiary formations of the Gulf Coastal Plain. According to the plans outlined before the work was begun, the beds that had formerly been grouped under the names Lafayette formation and Grand Gulf formation were to be studied with a view to their possible separation into more satisfactory stratigraphic units that might be correlated with other formations which, on the basis of their fossils, had been assigned to their proper positions in the geologic time scale. The original plan included a study of the post-Vicksburgian Tertiary deposits from western Florida to Mississippi River and correlations with formations previously recognized in Florida, southern Alabama, and Louisiana. This plan was subsequently modified to extend the investigation as far west as Sabine River. The field work was interrupted and the office work was delayed by calls for geologic work in other areas, so that the preparation of the reports could not be begun until the spring of 1914.

Alabama, Florida, Georgia, Louisiana, Mississippi↗
USGS1916

The Catahoula sandstone

The name Catahoula was first used in 1905 by Veatch as a synonym for "typical Grand Gulf," but the description of the formation, which is here quoted, was not published until the following year.

Mississippi↗
USGS2004

Precambrian basement geologic map of Montana– An interpretation of aeromagnetic anomalies

Newly compiled aeromagnetic anomaly data of Montana, in conjunction with the known geologic framework of basement rocks, have been combined to produce a new interpretive geologic basement map of Montana. Crystalline basement rocks compose the basement, but are exposed only in the cores of mountain ranges in southwestern Montana. Principal features deduced from the map are: (1) A prominent northeast-trending, 200-km-wide zone of spaced negative anomalies, which extends more than 700 km from southwestern Montana's Beaverhead Mountains to the Canadian border and reflects suturing of the Archean Mexican Hat Block against the Archean Wyoming Province along the Paleoproterozoic Trans-Montana Orogen (new name) at about 1.9-1.8 Ga; (2) North-northwest-trending magnetic lows in northeastern Montana, which reflect the 1.9-1.8 Ga Trans-Hudson Orogen and truncate the older Trans-Montana Zone; and (3) Subtle northwest- and west-trending negative anomalies in central and western Montana, which represent the northernmost segment of brittle-ductile transcurrent faults of the newly recognized Mesoproterozoic Trans-Rocky Mountain fault system. Structures developed in the Proterozoic provided zones of crustal weakness reactivated during younger Proterozoic and Phanerozoic igneous and tectonic activity. For example, the Trans-Montana Zone guided basement involved thrust faulting in southwestern Montana during the Sevier Orogeny. The Boulder Batholith and associated ore deposits and the linear belt of alkaline intrusions to the northeast were localized along a zone of weakness between the Missouri River suture and the Dillon shear zone of the Trans-Montana Orogen. The northwest-trending faults of Trans-Rocky Mountain system outline depocenters for sedimentary rocks in the Belt Basin. This fault system provided zones of weakness that guided Laramide uplifts during basement crustal shortening. Northwest-trending zones have been locally reactivated during Neogene basin-range extension.

Montana↗
USGS2008

Geology of the Southern Appalachian Mountains

The Southern Appalachian Mountains includes the Blue Ridge province and parts of four other physiographic provinces. The Blue Ridge physiographic province is a high, mountainous area bounded by several named mountain ranges (including the Unaka Mountains and the Great Smoky Mountains) to the northwest, and the Blue Ridge Mountains to the southeast. Metamorphic rocks of the mountains include (1) fragments of a billion-year-old supercontinent, (2) thick sequences of sedimentary rock that were deposited in subsiding (sinking) basins on the continent, (3) sedimentary and volcanic rocks that were deposited on the sea floor, and (4) fragments of oceanic crust. Most of the rocks formed as sediments or volcanic rocks on ocean floors, islands, and continental plates; igneous rocks formed when crustal plates collided, beginning about 450 million years ago. The collision between the ancestral North American and African continental plates ended about 270 million years ago. Then, the continents began to be stretched, which caused fractures to open in places throughout the crust; these fractures were later filled with sediment. This product (U.S. Geological Survey Scientific Investigations Map 2830) consists of a geologic map of the Southern Appalachian Mountains overlain on a shaded-relief background. The map area includes parts of southern Virginia, eastern West Virginia and Tennessee, western North and South Carolina, northern Georgia and northeastern Alabama. Photographs of localities where geologic features of interest can be seen accompany the map. Diagrams show how the movement of continental plates over many millions of years affected the landscapes seen today, show how folds and faults form, describe important mineral resources of the region, and illustrate geologic time. This two-sided map is folded into a convenient size (5x9.4 inches) for use in the field. The target audience is high school to college earth science and geology teachers and students; staffs of educational and interpretive programs within Federal, State, and private agencies; and tourists and residents of the Southern Appalachian region who want to know more about the area. The map is companion to the DVD, 'The Southern Appalachians, a Changing World' (http://pubs.usgs.gov/gip/so_app/) and the Teacher's Guide and brochure, 'Birth of the Mountains' (http://pubs.usgs.gov/gip/birth). The map shows the location of sites that are featured in these publications.

Scientific Investigations Map↗
USGS2004

Geologic map of the Peach Orchard Flat quadrangle, Carbon County, Wyoming, and descriptions of new stratigraphic units in the Upper Cretaceous Lance Formation and Paleocene Fort Union Formation, eastern Greater Green River Basin, Wyoming-Colorado

This report provides a geologic map of the Peach Orchard Flat 7.5-minute quadrangle, located along the eastern flank of the Washakie Basin, Wyo. Geologic formations and individual coal beds were mapped at a scale of 1:24,000; surface stratigraphic sections were measured and described; and well logs were examined to determine coal correlations and thicknesses in the subsurface. In addition, four lithostratigraphic units were named: the Red Rim Member of the Upper Cretaceous Lance Formation, and the China Butte, Blue Gap, and Overland Members of the Paleocene Fort Union Formation.

Wyoming↗
USGS2006

Geologic map of the Wrangell-Saint Elias National Park and Preserve, Alaska

Wrangell-Saint Elias National Park and Preserve, the largest national park within the U.S. National Park Service system, extends from the northern Pacific Ocean to beyond the eastern Alaska Range into interior Alaska. It features impressively spectacular scenery such as high and craggy mountains, active and ancient volcanoes, expansive ice fields, immense tidewater glaciers, and a myriad of alpine glaciers. The park also includes the famous Kennecott Mine, a world-class copper deposit that was mined from 1911 to 1938, and remnant ghost town, which is now a National Historic Landmark. Geologic investigations encompassing Wrangell-Saint Elias National Park and Preserve began in 1796, with Dmitriv Tarkhanov, a Russian mining engineer, who unsuccessfully ventured up the Copper River in search of rumored copper. Lieutenant H.T. Allen (1897) of the U.S. Army made a successful epic summer journey with a limited military crew up the Copper River in 1885, across the Alaska Range, and down the Tanana and Yukon Rivers. Allen?s crew was supported by a prospector named John Bremner and local Eyak and Ahtna native guides whose tribes controlled access into the Copper River basin. Allen witnessed the Ahtnas? many uses of the native copper. His stories about the copper prompted prospectors to return to this area in search of the rich copper ore in the years following his journey. The region boasts a rich mining and exploration history prior to becoming a park in 1980. Several U.S. Geological Survey geologists have conducted reconnaissance surveys in the area since Allen?s explorations. This map is the result of their work and is enhanced by more detailed investigations, which began in the late 1950s and are still continuing. For a better understanding of the processes that have shaped the geology of the park and a history of the geologic investigations in the area, we recommend U.S. Geological Survey Professional Paper 1616, ?A Geologic Guide to Wrangell-Saint Elias National Park and Preserve, Alaska,? an exceptionally well illustrated and informative book by Gary R. Winkler, 2000. Geologically, the park consists of a collage of seven tectonostratigraphic terranes that formed south in the equatorial Pacific Ocean and rafted northward on oceanic plates, eventually accreting to Alaska and the North American continent. Each terrane features a distinct stratigraphy and is separated from neighboring terranes by major strike-slip or thrust faults.

Alaska↗
USGS2007

Geologic Map of the Frederick 30' x 60' Quadrangle, Maryland, Virginia, and West Virginia

The Frederick 30? ? 60? quadrangle lies within the Potomac River watershed of the Chesapeake Bay drainage basin. The map area covers parts of Montgomery, Howard, Carroll, Frederick, and Washington Counties in Maryland; Loudoun, Clarke, and Fairfax Counties in Virginia; and Jefferson and Berkeley Counties in West Virginia. Many geologic features (such as faults and folds) are named for geographic features that may or may not be shown on the 1:100,000-scale base map. The geology of the Frederick 30? ? 60? quadrangle, Maryland, Virginia, and West Virginia, was first mapped on the 32 1:24,000-scale 7.5-minute quadrangle base maps between 1989 and 1994. The geologic data were compiled manually at 1:100,000 scale in 1997 and were digitized between 1998 and 1999. The geologic map and database may be used to support activities such as land-use planning, soil mapping, groundwater availability and quality studies, identifying aggregate resources, and conducting engineering and environmental studies. The map area covers distinct geologic provinces and sections of the central Appalachian region that are defined by unique bedrock and resulting landforms. From west to east, the provinces include the Great Valley section of the Valley and Ridge province, the Blue Ridge province, and the Piedmont province; in the extreme southeastern corner, a small part of the Coastal Plain province is present. The Piedmont province is divided into several sections; from west to east, hey are the Frederick Valley synclinorium, the Culpeper and Gettysburg basins, the Sugarloaf Mountain anticlinorium, the Westminster terrane, and the Potomac terrane. The geology of the Frederick quadrangle is discussed by geologic province and sections; the geologic units within each province are discussed from oldest to youngest. Where applicable, the discussion includes information on tectonic origins. For more information concerning the report, please contact the author.

Scientific Investigations Map↗
USGS2006

Geologic map of the Mead quadrangle (V-21), Venus

The Magellan spacecraft orbited Venus from August 10, 1990, until it plunged into the Venusian atmosphere on October 12, 1994. Magellan Mission objectives included (1) improving the knowledge of the geological processes, surface properties, and geologic history of Venus by analysis of surface radar characteristics, topography, and morphology and (2) improving the knowledge of the geophysics of Venus by analysis of Venusian gravity. The Mead quadrangle (V-21) of Venus is bounded by lat 0 deg and 25 deg N., long 30 deg and 60 deg E. This quadrangle is one of 62 covering Venus at 1:5,000,000 scale. Named for the largest crater on Venus, the quadrangle is dominated by effusive volcanic deposits associated with five major coronae in eastern Eistla Regio (Didilia, Pavlova, Calakomana, Isong, and Ninmah), corona-like tectonic features, and Disani Corona. The southern extremity of Bell Regio, marked by lava flows from Nyx Mons, north of the map area, forms the north-central part of the quadrangle. The shield volcanoes Kali, Dzalarhons, and Ptesanwi Montes lie south and southwest of the large corona-related flow field. Lava flows from sources east of Mead crater flood low-lying areas along the east edge of the quadrangle.

Scientific Investigations Map↗
USGS2006

Stratigraphic framework and depositional sequences in the Lower Silurian regional oil and gas accumulation, Appalachian Basin: From Licking County, Ohio, to Fayette County, West Virginia

The Lower Silurian regional oil and gas accumulation was named by Ryder and Zagorski (2003) for a 400-mile (mi)-long by 200-mi-wide hydrocarbon accumulation in the central Appalachian basin of the Eastern United States and Ontario, Canada. From the early 1880s to 2000, approximately 300 to 400 million barrels of oil and eight to nine trillion cubic feet of gas have been produced from the Lower Silurian regional oil and gas accumulation (Miller, 1975; McCormac and others, 1996; Harper and others, 1999). Dominant reservoirs in the regional accumulation are the Lower Silurian "Clinton" and Medina sandstones in Ohio and westernmost West Virginia and coeval rocks in the Lower Silurian Medina Group (Grimsby Sandstone (Formation) and Whirlpool Sandstone) in northwestern Pennsylvania and western New York. A secondary reservoir is the Upper Ordovician(?) and Lower Silurian Tuscarora Sandstone in central Pennsylvania and central West Virginia, a more proximal eastern facies of the "Clinton" sandstone and Medina Group (Yeakel, 1962; Cotter, 1982, 1983; Castle, 1998). The Lower Silurian regional oil and gas accumulation is subdivided by Ryder and Zagorski (2003) into the following three parts: (1) an easternmost part consisting of local gas-bearing sandstone units in the Tuscarora Sandstone that is included with the basin-center accumulation; (2) an eastern part consisting predominantly of gas-bearing "Clinton" sandstone-Medina Group sandstones that have many characteristics of a basin-center accumulation (Davis, 1984; Zagorski, 1988, 1991; Law and Spencer, 1993); and (3) a western part consisting of oil- and gas-bearing "Clinton" sandstone-Medina Group sandstones that is a conventional accumulation with hybrid features of a basin-center accumulation (Zagorski, 1999). With the notable exception of the offshore part of Lake Erie (de Witt, 1993), the supply of oil and (or) gas in the hybrid-conventional part of the regional accumulation continues to decline because of the many wells drilled there since the late 1880s. However, new gas and local oil continues to be discovered in the deeper basin-center part (Zagorski, 1991; Pees, 1994; Petroleum Information Corporation, 1994). In general, only small quantities of gas have been produced from the Tuscarora Sandstone fields because of their generally poor reservoir quality and because of the low energy (Btu) content of the gas (Avary, 1996). Although fracture porosity is the dominant porosity type in the Tuscarora Sandstone gas reservoirs (Avary, 1996), there are several fields, such as Indian Creek, where intergranular porosity seems to be important (Bruner, 1983; Castle and Byrnes, 2005). In order to better understand the character and origin of the Lower Silurian regional oil and gas accumulation and its component parts, six cross sections were drawn through the Lower Silurian strata in parts of New York, Ohio, Pennsylvania, and West Virginia. The locations of all six cross sections are shown on sheet 2 (figs. 1 and 2) of this report. Each cross section shows the stratigraphic framework, depositional setting, sequence stratigraphy, and hydrocarbon-producing intervals of the Lower Silurian sandstone reservoirs and adjoining strata. Cross section F–F′ presented here is about 215 mi long and trends northwestward, approximately normal to the depositional strike of the Lower Silurian sandstone system, and extends through large stretches of the basin-center and hybrid-conventional parts of the Lower Silurian regional oil and gas accumulation.

Ohio, West Virginia↗
USGS2008

Historic trail map of the La Junta 1 degree x 2 degree quadrangle, southeastern Colorado and western Kansas

This historic trail map of the La Junta quadrangle contains all or part of eight Colorado and Kansas counties. Many of the historic trails in the La Junta quadrangle were used by Indians long before the white man reached the area. The earliest recorded use of the trails by white men in the quadrangle was in the 1820s when traders brought goods from St. Louis for barter with the Indians and for commerce with the Mexican settlements in New Mexico. The map and accompanying pamphlet include an introduction and the method of preparation used by the authors. The pamphlet includes a description of the early explorers along the Arkansas River and on the Santa Fe Trail, as well as roads established or proposed under General Assembly session law, Colorado Territorial corporations and charters, 1859-1876, and freighting companies. Stage companies that probably operated in the La Junta quadrangle also are described. The authors include a section on railroads in the quadrangle and north of the quadrangle along the Arkansas River. Military and civilian camps, forts, and bases are reported. Moreover, fossils and plants in the quadrangle are described. Indian tribes - Early Man or paleo-Indians, Archaic Indians, prehistoric and historic Indians, and historic Indian tribes in the quadrangle - are reported. Authors include place names within and along freight routes leading to the La Junta quadrangle. A full description of the contents along with three figures can be found in the Introduction.

Colorado, Kansas↗
USGS2007

Hydrostratigraphic Framework and Selection and Correlation of Geophysical Log Markers in the Surficial Aquifer System, Palm Beach County, Florida

The surficial aquifer system is the major source of freshwater for public water supply in Palm Beach County, Florida, yet many previous studies of the hydrogeology of this aquifer system have focused only on the eastern one-half to one-third of the county in the more densely populated coastal area (Land and others, 1973; Swayze and others, 1980; Swayze and Miller, 1984; Shine and others, 1989). Population growth in the county has resulted in the westward expansion of urbanized areas into agricultural areas and has created new demands on the water resources of the county. Additionally, interest in surface-water resources of central and western areas of the county has increased. In these areas, plans for additional surface-water storage reservoirs are being made under the Comprehensive Everglades Restoration Plan originally proposed by the U.S. Army Corps of Engineers and the South Florida Water Management District (1999), and stormwater treatment areas have been constructed by the South Florida Water Management District. Surface-water and ground-water interactions in the Everglades are thought to be important to water budgets, water quality, and ecology (Harvey and others, 2002). Most of the previous hydrogeologic and ground-water flow simulation studies of the surficial aquifer system have not utilized a hydrostratigraphic framework, in which stratigraphic or sequence stratigraphic units, such as those proposed in Cunningham and others (2001), are delineated in this stratigraphically complex aquifer system. A thick zone of secondary permeability mapped by Swayze and Miller (1984) was not subdivided and was identified as only being within the Anastasia Formation of Pleistocene age. Miller (1987) published 11 geologic sections of the surficial aquifer system, but did not delineate any named stratigraphic units in these sections. This limited interpretation has resulted, in part, from the complex facies changes within rocks and sediments of the surficial aquifer system and the seemingly indistinct and repetitious nature of the most common lithologies, which include sand, shell, sandstone, and limestone. Model construction and layer definition in a simulation of ground-water flow within the surficial aquifer system of Palm Beach County utilized only the boundaries of one or two major hydrogeologic zones, such as the Biscayne aquifer and surficial aquifer system; otherwise layers were defined by average elevations rather than geologic structure or stratigraphy (Shine and others, 1989). Additionally, each major permeable zone layer in the model was assumed to have constant hydraulic conductivity with no allowance for the possibility of discrete (thin) flow zones within the zone. The key to understanding the spatial distribution and hydraulic connectivity of permeable zones in the surficial aquifer system beneath Palm Beach County is the development of a stratigraphic framework based on a consistent method of county-wide correlation. Variability in hydraulic properties in the system needs to be linked to the stratigraphic units delineated in this framework, and proper delineation of the hydrostratigraphic framework should provide a better understanding and simulation of the ground-water flow system. In 2004, the U.S. Geological Survey, in cooperation with the South Florida Water Management District, initiated an investigation to develop a hydrostratigraphic framework for the surficial aquifer system in Palm Beach County.

Scientific Investigations Map↗
USGS2008

Geologic Map of the Kings Mountain and Grover Quadrangles, Cleveland and Gaston Counties, North Carolina, and Cherokee and York Counties, South Carolina

This geologic map of the Kings Mountain and Grover 7.5-min quadrangles, N.C.-S.C., straddles a regional geological boundary between the Inner Piedmont and Carolina terranes. The Kings Mountain sequence (informal name) on the western flank of the Carolina terrane in this area includes the Neoproterozoic Battleground and Blacksburg Formations. The Battleground Formation has a lower part consisting of metavolcanic rocks and interlayered schist and an upper part consisting of quartz-sericite phyllite and schist interlayered with quartz-pebble metaconglomerate, aluminous quartzite, micaceous quartzite, manganiferous rock, and metavolcanic rocks. The Blacks-burg Formation consists of phyllitic metasiltstone interlayered with thinner units of marble, laminated micaceous quartzite, hornblende gneiss, and amphibolite. Layered metamorphic rocks of the Inner Piedmont terrane include muscovite-biotite gneiss, muscovite schist, and amphibolite. The Kings Mountain sequence has been intruded by metatonalite and metatrondhjemite (Neoproterozoic), metagabbro and metadiorite (Paleozoic?), and the High Shoals Granite (Pennsylvanian). Layered metamorphic rocks of the Inner Piedmont in this area have been intruded by the Toluca Granite (Ordovician?), the Cherryville Granite and associated pegmatite (Mississippian), and spodumene pegmatite (Mississippian). Diabase dikes (early Jurassic) are locally present throughout the area. Ductile fault zones of regional scale include the Kings Mountain and Kings Creek shear zones. In this area, the Kings Mountain shear zone forms the boundary between the Inner Piedmont and Carolina terranes, and the Kings Creek shear zone separates the Battleground Formation from the Blacksburg Formation. Structural styles change across the Kings Mountain shear zone from steeply dipping layers, foliations, and folds on the southeast to gently and moderately dipping layers, foliations, and recumbent folds on the northwest. Mineral assemblages in the Kings Mountain sequence show a westward decrease from upper amphibolite facies (sillimanite zone) near the High Shoals Granite in the eastern side of the map area to upper greenschist (epidote-amphibolite) facies in the south-central part of the area near the Kings Mountain shear zone. Amphibolite-facies mineral assemblages in the Inner Piedmont terrane increase in grade from the kyanite zone near the Kings Mountain shear zone to the sillimanite zone in the northwestern part of the map area. Surficial deposits include alluvium in the stream valleys and colluvium along ridges and steep slopes. These quadrangles are unusual in the richness and variety of the mineral deposits that they contain, which include spodumene (lithium), cassiterite (tin), mica, feldspar, silica, clay, marble, kyanite and sillimanite, barite, manganese, sand and gravel, gold, pyrite, and iron.

Scientific Investigations Map↗
USGS2008

Geologic map of the Prescott National Forest and the headwaters of the Verde River, Yavapai and Coconino Counties, Arizona

This 1:100,000-scale digital geologic map details the complex Early Proterozoic metavolcanic and plutonic basement of north-central Arizona; shows the mildly deformed cover of Paleozoic rocks; reveals where Laramide to mid-Tertiary plutonic rocks associated with base- and precious-metals deposits are exposed; subdivides the Tertiary volcanic rocks according to chemically named units; and maps the Pliocene to Miocene fill of major basins. Associated digital files include more than 1,300 geochemical analyses of all rock units; 1,750 logs of water wells deeper than 300 feet; and interpreted logs of 300 wells that define the depth to basement in major basins. Geophysically interpreted buried features include normal faults defining previous unknown basins, mid-Tertiary intrusive rocks, and half-grabens within shallow bains.

Arizona↗
USGS2010

Geologic Map of the Greenaway Quadrangle (V-24), Venus

The Greenaway quadrangle (V-24; lat 0 degrees -25 degrees N., long 120 degrees -150 degrees E.), Venus, derives its name from the impact crater Greenaway, centered at lat 22.9 degrees N., long 145.1 degrees E., in the northeastern part of the quadrangle. Greenaway was a well-noted writer and illustrator of children`s books in Britain during the nineteenth century. In Greenaway`s honor, the Library Association of Great Britain presents the annual Kate Greenaway Medal to an illustrator living and publishing in Britain who has produced the most distinguished children`s book illustrations for that year. The Greenaway quadrangle occupies an 8,400,000 km2 equatorial swath of lowlands and highlands. The map area is bounded by the crustal plateau, Thetis Regio, to the south and Gegute Tessera to the west. The rest of the quadrangle consists of part of Llorona Planitia, which is part of the vast lowlands that cover about 80 percent of Venus` surface. The southern map area marks the north edge of Aphrodite Terra, including Thetis Regio, that includes the highest topography in the quadrangle with elevations reaching >1 km above the Mean Planetary Radius (MPR; 6,051.84 km). Northern Aphrodite Terra abruptly slopes north to Llorona Planitia. A broad northeast-trending topographic arch pocked with coronae separates two northeast-trending elongate basins, Llorona Planitia on the east, that form depositional centers for shield and coronae-sourced materials; both basins drop to elevations of <-1 km. In addition to these major features, the map area hosts thousands of small volcanic constructs (shields); seven coronae; ribbon-tessera terrain; suites of faults, fractures, and wrinkle ridges; 23 impact craters; and one craterless splotch. Our goal for mapping the geology of the Greenaway quadrangle was to determine the geologic history for this region, which in turn provides insights into volcanic and tectonic processes that shaped the Venusian surface. Map relations illustrate that aerially expansive shield terrain (unit st) played a primary role and coronae played a secondary role in volcanic resurfacing across the map area.

Scientific Investigations Map↗
USGS2010

Geologic map of the Artemis Chasma quadrangle (V-48), Venus

Artemis, named for the Greek goddess of the hunt, represents an approximately 2,600 km diameter circular feature on Venus, and it may represent the largest circular structure in our solar system. Artemis, which lies between the rugged highlands of Aphrodite Terra to the north and relatively smooth lowlands to the south, includes an interior topographic high surrounded by the 2,100-km-diameter, 25- to 200-km-wide, 1- to 2-km-deep circular trough, called Artemis Chasma, and an outer rise that grades outward into the surrounding lowland. Although several other chasmata exist in the area and globally, other chasmata have generally linear trends that lack the distinctive circular pattern of Artemis Chasma. The enigmatic nature of Artemis has perplexed researchers since Artemis Chasma was first identified in Pioneer Venus data. Although Venus' surface abounds with circular to quasi-circular features at a variety of scales, including from smallest to largest diameter features: small shield edifices (>1 km), large volcanic edifices (100-1,000 km), impact craters (1-270 km), coronae (60-1,010 km), volcanic rises and crustal plateaus (~1,500-2,500 km), Artemis defies classification into any of these groups. Artemis dwarfs Venus' largest impact crater, Mead (~280 km diameter); Artemis also lacks the basin topography, multiple ring structures, and central peak expected for large impact basins. Topographically, Artemis resembles some Venusian coronae; however Artemis is an order of magnitude larger than the average corona (200 km) and about twice the size of Heng-O Corona (which is 1,010 km in diameter), the largest of Venusian coronae. In map view Artemis' size and shape resemble volcanic rises and crustal plateaus; however, both of these classes of features differ topographically from Artemis. Volcanic rises and crustal plateaus form broad domical regions, and steep-sided regions with flat tops, respectively; furthermore, neither rises nor plateaus include circular troughs. So although it seems clear what Artemis is not, there is little consensus about what Artemis is, much less how Artemis formed. Debate during the past decade has resulted in the proposal of at least four hypotheses for Artemis' formation. The first (herein referred to as H1) is that Artemis Chasma represents a zone of northwest-directed convergence and subduction. The second hypothesis (herein referred to as H2) is that Artemis consists of a composite structure with a part of its interior region marking the exposure of deformed ductile deep-crustal rocks analogous to a terrestrial metamorphic core complex. The third (herein referred to as H3) is that Artemis reflects the surface expression of an ancient (>3.5 Ga) huge bolide impact event on cold strong lithosphere. The fourth hypothesis (herein referred to as H4) is that Artemis marks the surface expression of a deep mantle plume. Each of these hypotheses holds different implications for Venus geodynamics and evolution processes, and for terrestrial planet processes in general. Viability of H1 would provide support that terrestrial-like plate-tectonic processes once occurred on Earth's sister planet. The feasibility of H2 would require high values of crustal extension and therefore imply that significant horizontal displacements occurred on Venus-displacement that may or may not be related to terrestrial-like plate-tectonic processes. The possibility of H3 would suggest that Venus' surface is extremely old, and that Venus has experienced very little dynamic activity for the last 3.5 billion years or more; this would further imply that Venus is essentially tectonically dead, and has been for most of its history. This view contrasts strongly with studies that highlight a rich history of Venus including activity at least as young as 750 million years ago, and quite likely up to the present. If H4 has credibility, then Artemis could provide clues to cooling mechanisms of Earth's sister planet. Each of these hypotheses

Scientific Investigations Map↗
USGS2010

Bedrock geologic map of the Montpelier and Barre West quadrangles, Washington and Orange Counties, Vermont

The bedrock geology of the Montpelier and Barre West quadrangles consists of Silurian and Devonian metasedimentary rocks of the Connecticut Valley-Gaspe synclinorium (CVGS) and metasedimentary, metavolcanic, and metaintrusive rocks of the Cambrian and Ordovician Moretown and Cram Hill Formations. Devonian granite dikes occur throughout the two quadrangles but are more abundant in the Silurian and Devonian rocks. The pre-Silurian rocks are separated from the rocks of the CVGS by the informally named 'Richardson Memorial Contact,' historically interpreted as either an unconformity or a fault. The results of this report represent mapping by G.J. Walsh, Jonathan Kim, and M.H. Gale from 2002 to 2005. S.M. King assisted Kim and Gale from 2002 to 2003. A.M. Satkoski (Indiana University) assisted Walsh, and L.R. Pascale (University of Vermont) and C.M. Orsi (Middlebury College) assisted Kim and Gale as summer interns in 2003. This study was designed to map the bedrock geology in the area. This map supersedes a preliminary map of the Montpelier quadrangle (Kim, Gale, and others, 2003). A companion study in the Barre West quadrangle (Walsh and Satkoski, 2005) determined the levels of naturally occurring radioactivity in the bedrock from surface measurements at outcrops during the course of 1:24,000-scale geologic mapping to identify which rock types were potential sources of radionuclides. Results of that study indicate that the carbonaceous phyllites in the CVGS have the highest levels of natural radioactivity.

Vermont↗