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USGS1943

Structural determinations from diamond drilling

Several problems may arise in the geometrical determinations of strike and dip from core drilling. If the stratigraphic or structural surfaces are plane, as the bedding planes of a homocline, two problems may exist, depending upon whether the drill cores do or do not penetrate to some recognizable horizon. The first of these is solved by a simple graphic interpolation, and is not discussed in this paper. The second, however, is solved for the most general case of three non-parallel drill holes, no one of which is necessarily vertical. Errors are necessarily present in this solution, due to: 1. Inaccuracies in the measurement of the initial directions and dips of the drill holes. 2. Deviations of the drill holes from their initial directions. 3. Inaccuracies in the measurement of the angles between the axes of the drill cores, and the stratigraphic or structural planes. The second and third of these causes result in initial errors in the measurement of the core angles. Hence, for this simplest case, error formulm are developed for finding the final errors in the angles of strike and dip, under certain specified assumptions. To illustrate the solution, a problem is stated and solved. This problem is of a general nature, selected to show the necessary operations when the three drill holes occur in different octants. The error formulae are subsequently applied. For curved surfaces, as where folded beds are present, the same two problems arise, depending upon whether the drill holes do or do not penetrate to some recognizable horizon. Only the first of these problems is considered. It is shown, in this case, that 9 drill holes are required to obtain a satisfactory solution. The method consists essentially in fitting nine known points to a ternary quadric surface; and in determining the equations of the planes tangent to this surface at any of the nine points, or at any other points on the surface. The strikes and dips are then derived from these equations. © 1943 Society of Economic Geologists, Inc.

Economic Geology↗

USGS1980

Textural and structural evidence for a predeformation hydrothermal origin of the Tungsten Queen Deposit, Hamme District, North Carolina

The Hamme tungsten district is composed of a series of steeply dipping quartz-wolframite veins in the Piedmont of North Carolina. Veins are concentrated near the border of the lower Paleozoic Vance County pluton, along its western contact with green-schist-facies metapelites and metavolcanic rocks of the Carolina slate belt. One of these quartz veins, the Snead-Walker, hosts the Tungsten Queen deposit. The vein is 0 to 10 m thick and trends N 35 degrees E for approximately 3,500 m through slate belt rocks and the granitic pluton. The deposit has been worked to a depth of nearly 520 m and contains eight en echelon ore lodes that plunge 42 degrees to 65 degrees between S 10 degrees E and S 10 degrees W. Ore lodes commonly are encased in thin lenses of quartz-sericite greisen. The principal ore mineral is huebnerite and is accompanied by scattered occurrences of pyrite, sphalerite, galena, chalcopyrite, and tetrahedrite. The gangue is predominantly quartz with minor amounts of fluorite, sericite, and carbonate.Studies of minor structures and mineral textures indicate that both the wall rock and the ore and gangue minerals within the vein have been deformed by at least two events. The first event produced relatively gentle, open, and shallow-plunging folds; later, an intense episode of right-lateral shearing developed steeply plunging, tight folds and numerous northeast-trending shears. This latter deformation also developed a prominent alignment of ore and gangue minerals oblique to the vein walls and may have formed the en echelon distribution of ore lodes.In relatively undeformed parts of the vein, clusters of euhedral huebnerite crystals are oriented perpendicular to vein layering. Some prismatic crystals have terminations with cappings of sulfides and in polished thin section show concentric growth zones. These features are similar to textures found in unmetamorphosed tungsten-bearing hydrothermal vein deposits such as those at Pasto Bueno, Peru; Carrock Fell, England; and Panasqueria, Portugal. The relationships of mineral textures and minor structures indicate that the Tungsten Queen deposit formed by open-space fillings of linear faults or fractures and was subsequently deformed by at least two episodes of folding and shearing.

North Carolina↗

USGS1994

Structure and bulk composition of the Tin Mountain pegmatite, Black Hills, South Dakota

Construction of structure contour and isopach maps has yielded a rather simple and orderly interpretation of the structure and has led to calculations of the tonnage of each of the internal units and of the bulk composition of the pegmatite. The outcropping part of the pegmatite trends S 75° E for 90 m and then connects with an arm of the pegmatite that plunges gently N-NW for approximately another 90 m. An albite-quartz-muscovite wall zone completely surrounds four inner units. Though these four inner units are termed zones, in accordance with standard practice, differentiation is more in a vertical direction than in a concentric arrangement. The upper two of these units are perthite rich.

North Dakota↗

USGS2007

Microbial reduction of structural Fe3+ in nontronite by a thermophilic bacterium and its role in promoting the smectite to illite reaction

The illitization process of Fe-rich smectite (nontronite NAu-2) promoted by microbial reduction of structural Fe3+ was investigated by using a thermophilic metal-reducing bacterium, Thermoanaerobacter ethanolicus, isolated from the deep subsurface. T. ethanolicus was incubated with lactate as the sole electron donor and structural Fe3+ in nontronite as the sole electron acceptor, and anthraquinone-2, 6-disulfonate (AQDS) as an electron shuttle in a growth medium (pH 6.2 and 9.2, 65 ??C) with or without an external supply of Al and K sources. With an external supply of Al and K, the extent of reduction of Fe3+ in NAu-2 was 43.7 and 40.4% at pH 6.2 and 9.2, respectively. X-ray diffraction and scanning and transmission electron microscopy revealed formation of discrete illite at pH 9.2 with external Al and K sources, while mixed layers of illite/smectite or highly charged smectite were detected under other conditions. The morphology of biogenic illite evolved from lath and flake to pseudo-hexagonal shape. An external supply of Al and K under alkaline conditions enhances the smectite-illite reaction during microbial Fe3+ reduction of smectite. Biogenic SiO2 was observed as a result of bioreduction under all conditions. The microbially promoted smectite-illite reaction proceeds via dissolution of smectite and precipitation of illite. Thermophilic iron reducing bacteria have a significant role in promoting the smectite to illite reaction under conditions common in sedimentary basins.

American Mineralogist↗

USGS1988

Guild structure of a riparian avifauna relative to seasonal cattle grazing

The avifauna within the willow ( Salix spp.) community on the Arapaho National Wildlife Refuge (NWR) was dominated (96% of all observations each year) by 11 species of passerine birds during the summers of 1980-81. Using 28 vegetation variables measured or calculated for randomly selected points and points where birds were sighted, we assigned the species to 3 distinct response guilds relative to historical patterns of seasonal grazing. A eurytopic response guild (habitat generalists) included yellow warblers ( Dendroica petechia ) (YEWA), savannah sparrows ( Passerculus sandwichensis ) (SASP), and song sparrows ( Melospiza melodia ) (SOSP). A stenotopic response guild (habitat specialists) included willow flycatchers ( Empidonax traillii ) (WIFL). Lincoln's sparrows ( Melospiza lincolnii ) (LISP), and white-crowned sparrows ( Zonotrichia leucophrys ) (WCSP). The intermediate, mesotopic response guild included American robins ( Turdus migratorius ) (AMRO), red-winged blackbirds ( Agelaius phoeniceus ) (RWBL), and brown-headed cowbirds ( Molothrus ater ) (BHCO). Population densities of the eurytopic response guild differed little between healthy (historically winter-grazed) and decadent (historically summer-grazed) willow communities within a year. Densities of species in the mesotopic response guild differed more dramatically, and stenotopic response-guild species were absent or accidental in decadent willows. Information on habitat use patterns of the individual species between years supported the definition of response guilds; vegetation structure was most variable in habitats of eurytopic species and least variable in habitats of stenotopic species. Comparisons between used and available vegetation features indicated that species in the stenotopic response guild used locations that differed from random on the basis of bush spacing. We hypothesize that the response-guild structure primarily reflects the impact of cattle upon the horizontal patterning of the vegetative community.

Colorado↗

USGS2025

Assessment of coastal and fluvial morphodynamic changes using Structure-for-Motion: A case study of the Sfȃntu Gheorghe Mouth (Danube Delta, Romania)

The ability to accurately map erosion, flooding, and habitat loss in coastal environments is crucial for formulating national strategies aimed at preventing and mitigating the impacts of natural disasters. A fundamental component of this process is the implementation of coastal morphodynamics monitoring through Structure-from-Motion (SfM) techniques, utilizing high-resolution 2D/3D data obtained from aerial photogrammetry. To assess morphodynamic changes over a three-year period (2022 – 2024), several SfM-based photogrammetric studies were conducted, each year, in the Romanian sector of the Danube-Black Sea coastal zone, specifically at the mouth of one of the Danube River distributaries (Sf Gheorghe branch) into the Black Sea, and along the left bank, near Sf Gheorghe locality, located within the Danube Delta Biosphere Reserve (DDBR). The essential equipment for aerial photogrammetry comprises Unmanned Aerial Vehicles (UAVs) and Global Navigation Satellite Systems (GNSS). In this study, the UAV used was a DJI Mavic 3T (Enterprise/Thermal) drone, complemented by two Trimble R12i and R4 GNSS systems, as well as approximately 10 Ground Control Points (GCPs). Data acquisition and processing were carried out using specialized photogrammetric software (Agisoft Metashape) along with various GIS tools (e.g., Blue Marble Geographics Global Mapper and ESRI ArcMap). The photogrammetric products generated for the study, as detailed in this paper, include Digital Elevation Models (DEMs), Digital Terrain Models (DTMs), orthomosaics (orthophotos), and others. At Sfântu Gheorghe beach, a comparison between 2023 and 2024 photogrammetric surveys revealed that the left bank of the Sf. Gheorghe Arm, at the river mouth into the Black Sea, suffered from a twist (erosion) of up to 64 metres. Additionally, on the selected perimetre (total area of 31,910 square meters ) from the beach and dune zone of Sf. Gheorghe, an area of up to 16,202 square meters was eroded between 2023 and 2024. This contrasts with the period between 2022 and 2023, during which deposition predominated. Erosion at the Danube mouths and the adjacent Black Sea coastline is driven by a complex interaction of natural and anthropogenic factors. Natural processes, including subsidence, sea-level rise, and episodic extreme storm events, contribute significantly to coastal dynamics. Meanwhile, human-induced factors, such as upstream hydrotechnical works that limits sediment transport, cutting of navigation canals, as well as the exacerbating effects of climate change, further accelerate erosion. The recent Structure-from-Motion (SfM) surveys provide essential quantitative data, enabling a detailed analysis of both short-term and long-term morphodynamic changes influenced by seasonal variations and extreme hydrometeorological events in this highly dynamic coastal system.

Sfȃntu Gheorghe Mouth (Danube Delta)↗

USGS1963

Preliminary report on seismic-reflection studies of crustal structure in the western, central, and southern United States

During 1963 the U.S. Geological Survey, with the assistance of United ElectroDynamics, Inc., recorded five separate reversed seismic profiles. In addition to these profiles, the U.S. Geological Survey participated in a seismic-calibration program for the DRIBBLE experiment at Tatum Dome, Mississippi, a 20,000-pound shot near Dexter, Missouri, and in a cooperative seismic experiment in the Lake Superior region. This work is a continuation of the program started in 1961; however, the emphasis has shifted from a detailed study of the earth's crust in the western United States to a study of crustal structure in various geologic environments including the Wyoming thrust belt, Colorado Plateau, Central Lowlands, the Gulf Coastal Plain, and the southern part of the Canadian Shield. The U.S. Geological Survey has now completed reversed seismic-refraction profiles in nine different geologic provinces. These data present a promising indication that it may be possible to predict the crustal structure in unexplored areas by considering the regional geologic and physiographic environment. The following P n velocities have been determined: 8.2 km/sec in the Wyoming thrust belt, 7.9 km/sec in the Colorado Plateau, 8.1 km/sec in the Central Lowlands, and about 8.2 km/sec in the Gulf Coastal Plain. The data from the Lake Superior region have not yet been interpreted.

Arizona;Idaho;Mississippi;Missouri;Utah↗

USGS1998

Structure contours of base of Laramie-Fox Hills and Arapahoe aquifers

This digital geospatial data set consists of structure contours of the base of the Laramie-Fox Hills aquifer and the base of the Arapahoe aquifer along the Front Range of Colorado. The U.S. Geological Survey developed this data set as part of a project described in the report, "Structure, Outcrop, and Subcrop of the Bedrock Aquifers Along the Western Margin of the Denver Basin, Colorado" (Robson and others, 1998).

Colorado↗

USGS1946

Stratigraphy and structure of the area of the Killik, Chandler, Anaktuvuk, and Colville Rivers, Alaska

This report deals with results of field and laboratory studies carried out to May 1946 by the Geological Survey, largely as part of the Navy Department's program of petroleum investigations in northern Alaska. The immediate purpose of the work has been to collect and interpret stratigraphic and structural data pertinent to drilling in the Umiat area. Field studies were made during the summers of 1944 and 1945 in the drainage areas of the Colville, Killik, Chandler, and. Anaktuvuk Rivers (fig. 1). Paleontologic and microlithologic studies, together with stratigrahica1 and structural analysis of the areas, were carried out in the petroleum laboratory in Fairbanks. This work led. to preparation of a preliminary report submitted. in December, 1945. Additional detailed studies, in the Survey laboratories and offices in Washington, D. C., have resulted in some modification of earlier conclusions and changes in illustrations. The changes are minor and have no significant bearing on drilling in the Umiat area. The present report is accompanied. by revised conies of figures 1, 2, 3 (sheet 1) and. 5. These illustrations should be substituted for the comparable figures of the preliminary report. Figures 3 (sheet 2), 4, and. 6 of the earlier report stand unchanged and should, be added to the illustrations accompanying the present report. It is believed that work to date has revealed the general geologic picture of the area and. that the sequence of Upper Cretaceous rocks is established. The section of rocks in Umiat Test No. 1 has been approximately located within the sequence. This report, and the work on which it is based was done under the supervision of George O. Gates, who has contributed. much to the study.

Alaska↗

USGS1947

Stratigraphy and structure of the area of Maybe Creek

During the summer of 1946 the United States Geological Survey continued its program of stratigraphic and structural investigations in Naval Petroleum Reserve No. 4, northern Alaska. This report summarizes the results of work in the area of Maybe Creek (see inset, fig. 1). The area studied is southwest of Umiat and includes about 500 square miles lying generally between the headwaters and mouth of Maybe Creek. Structural data covering approximately 250 square miles of this area has been compiled from aerial photographic studies. The area is bordered generally on the north by the lake country and on the west by the Ikpikpuk River. Most of the area is north of Maybe Creek except for that part extending for 6 miles south of Maybe Creek between longitudes 153° 30' W. and 154° 20' W. The latitude of Maybe Creek is about 69° 15' N. The stream flows generally westward and at longitude 154° 40' W. unites with the eastward-flowing Kigalik River to form the Ikpikpuk River, which has a northerly course across the Arctic Slope to the ocean.

Alaska↗

USGS1951

Preliminary report on the stratigraphy and structure of the Shaviovik and upper Sagavanirktok Rivers area, Alaska

During the 1951 field season, U. S. Geological Survey Navy Oil Unit party 1 conducted stratigraphic and structural studies of the rocks in the area between the westernmost fork of the Shaviovik River and the East Kuparuk River. This area is drained by the Sagavanirktok River and its major tributaries; the Echooka River, the Ivishak River, and Lupine River. Owing to the nature of the investigation, the studies were confined to a relatively narrow geographic strip, rarely exceeding a distance of 20 miles north of the northernmost occurrence of the Lisburne limestone of the Brooks Range province. The work was thus conducted in an area of approximately 2,000 square miles, which lies wholly within the Brooks and Arctic Foothill provinces; within this area approximately 1,000 square miles was mapped geologically. The party consisted of six men: A. S. Keller and R. L. Detterman, geologists; I. W. Marine and D. E. Reed, field assistants; L. G. Barbin, cook-field assistant; and T. F. Derrington, weasel mechanic. The party utilized 3 weasels for transportation of equipment and personnel during the season, during which time 15 camps ware established. Work was initiated on the Shaviovik River on May 24, 1951, and the party concluded its investigations on the Kuparuk River drainage on August 24, 1951. In 1947, G. Gryc and E. H. Lathram conducted reconnaissance studies of the rocks in the vicinity of camps 12-15 (pl. 1); and during the same year, G. Gryn visited outcrops on the Ivishak River in the vicinity of camps 6-7 (pl. 1). These studies were made by the Navy Oil Unit of the U. S. Geological Survey in conjunction with the investigations of NPR-4. No other work of a geologic nature had been done in the area in the past. The primary objective of the 1951 party was the correlation of the Mesozoic and upper Paleozoic strata of the foothills province west of the Itkillik River, with that of the Shaviovik and Canning Rivers region. A secondary objective was to determine the cause of the pronounced northeasterly swing in the trend of the Brooks Range front in the Sagavanirktok drainage and to determine the structural implications of this swing. The area was mapped at a scale of 1:20,000 on vertical photographs and transferred to trimetrogon drainage maps at a scale of 1:48,000 and 1:96, 00. An altimeter traverse was carried concurrently with the geologic mapping.

Alaska↗

USGS1953

Stratigraphy and structure of outcropping pre-Selma Coastal Plain beds of Fayette and Lamar Counties, Alabama

The Coastal Plain sediments of Fayette and Lamar Counties, Ala., are pre-Selma Late Cretaceous in age and are divided into three mappable units, from oldest to youngest: (i) the Coker formation, (2) the Gordo formation, and (3) a unit composed of the McShan and Eutaw formations undifferentiated. The Coker formation as here defined includes the Cottondale, Eoline, and Coker formations of earlier workers; the name Gordo is used as previously defined. The Coker and Gordo formations constitute the Tuscaloosa group. Structure contours on formational contacts locally show marked irregularities that are partly the result of structural disturbances. Some of these disturbances were probably of post-Morreville (post-Austin) age.

Circular↗

USGS2004

Isotopic views of food web structure in the Florida Everglades

Introduction Nearly one million acres of the Everglades are under a health advisory that discourages the human consumption of largemouth bass and several other fish because of high mercury contents. Food web structure (base of food web, number of trophic steps) plays a potentially critical role in determining the patterns of mercury contamination of the Everglades ecosystem. Methylmercury (MeHg) is present in low concentrations in water, yet after entering the base of the food web it biomagnifies to toxic concentrations in organisms that occupy higher trophic positions (like bass). One of the main research questions under investigation by a multi-agency task force in the Everglades is how MeHg bioaccumulates up the food chain in this complex aquatic ecosystem. Understanding variations in food web structure may help explain mercury patterns in the Everglades and ultimately lead to more effective restoration of Everglades ecosystems.

Florida↗

USGS2009

Evaluation of Structural Best Management Practices for Highway Runoff in Beaufort and Colleton Counties, South Carolina, 2005-2006

As part of the National Pollutant Discharge Elimination System (NPDES) permit program mandated in the Clean Water Act, the South Carolina Department of Transportation (SCDOT) is required to address the quality of stormwater runoff from state-maintained roadways. From 2005 to 2006, the SCDOT and the U.S. Geological Survey (USGS) worked cooperatively in Beaufort and Colleton Counties, South Carolina (SC), to evaluate the performance of four different structural devices that served as best management practices (BMPs). These structural devices were installed to lessen the potential effects of stormwater runoff on water quality in waterways near state roads. The purpose of this Fact Sheet is to summarize results published in the USGS Scientific Investigations Report 2008-5150. The report documents the ability of these four BMP devices to remove suspended sediment, metals, nutrients, and organics compounds in stormwater runoff. The quantity of rainfall and stormflow and quality of stormwater entering and leaving the BMPs were monitored during 12-13 storms over a 21-month period. The results provide the SCDOT with quantitative information to evaluate whether or not the BMPs effectively enhanced stormwater quality. This information can be used by the SCDOT and other State, local, and Federal agencies in the selection of appropriate BMPs for future installation.

Fact Sheet↗

USGS2015

The Chesapeake Bay impact structure

About 35 million years ago, during late Eocene time, a 2-mile-wide asteroid or comet smashed into Earth in what is now the lower Chesapeake Bay in Virginia. The oceanic impact vaporized, melted, fractured, and (or) displaced the target rocks and sediments and sent billions of tons of water, sediments, and rocks into the air. Glassy particles of solidified melt rock rained down as far away as Texas and the Caribbean. Models suggest that even up to 50 miles away the velocity of the intensely hot air blast was greater than 1,500 miles per hour, and ground shaking was equivalent to an earthquake greater than magnitude 8.0 on the Richter scale. Large tsunamis affected most of the North Atlantic basin. The Chesapeake Bay impact structure is among the 20 largest known impact structures on Earth.

Virginia↗

USGS1983

Map showing distribution of small-scale deformation structures in a part of the upper coastal plain of South Carolina and adjacent Georgia

As a contribution to the assessment of neotectonics in the area of the Upper Coastal Plain of South Carolina, field traverses were made between Columbia, S.C., and Augusta, Ga., in 1975 and early 1976 in order to locate and describe small-scale deformation structures within exposed Coastal Plain rocks. The study covered most of the area between the Fall Line (northwest margin of the Coastal Plain) and the Orangeburg (Citronelle) escarpment (fig. 1). Fieldwork was done principally by vehicle along roads, but also included railroad cuts and excavation sites, such as quarries and landfills. Natural exposures are rare and provided no examples of deformation structures for this study. The geologic units exposed in the area are chiefly clastic sediments deposited in nearshore marine to continental environments. They include semi-consolidated sand, silt, clay, and rare thin impure limestone beds of Late Cretaceous to Eocene age (fig. 2). These sedimentary beds generally have a gentle regional dip to the southeast (Faye and Prowell, 1982, p. 6).

Georgia, South Carolina↗

USGS1986

Structure contour map of the tops of the Kreyenhagen Formation and Cretaceous strata in the Coalinga area, Fresno and Kings counties, California

This structure contour map, originally compiled during a study of the 1983 Coalinga earthquakes, shows the general structural configuration of the upper several kilometers of section in the Coalinga area. It was compiled by using electric well-log data available through April 1982 (Ammann Map Services, 1978; Petroleum Information Corporation, 1982; California Division of Oil and Gas, 1982) and surface geology (Dibblee, 1971; Mansfield, 1971).

California↗

USGS1992

Geophysically inferred structural and lithologic map of the precambrian basement in the Joplin 1° x 2° quadrangle, Kansas and Missouri

This report is an analysis of regional gravity and aeromagnetic data that was carried out as part of a Conterminuous United States Mineral Assessment Program (CUSMAP) study of the Joplin 1° X 2° quadrangle, Kansas and Missouri. It is one in a series of reports representing a cooperative effort between the U.S. Geological Survey, Kansas Geological Survey, and Missouri Department of Natural Resources, Division of Geology and Land Survey. The work presented here is part of a larger project whose goal is to assess the mineral resource potential of the Paleozoic sedimentary section and crystalline basement within the quadrangle. Reports discussing geochemical, geological, and various other aspects of the study area are included in this Miscellaneous Field Studies Map series as MF-2125-A through MF-2125-E. Geophysical interpretation of Precambrian crystalline basement lithology and structure is the focus of this report. The study of the crystalline basement is complicated by the lack of exposures due to the presence of a thick sequence of Phanerozoic sedimentary cover. In areas where there are no outcrops, the geologist must turn to other indirect methods to assist in an understanding of the basement. Previous investigations of the buried basement in this region used available drill hole data, isotope age information, and regional geophysical data (Sims, 1990; Denison and others, 1984; Bickford and others, 1986). These studies were regional in scope and were presented at state and multistate scales. The work documented here used recently collected detailed gravity and aeromagnetic data to enhance the regional geologic knowledge of the area. Terrace-density and terrace-magnetization maps were calculated from the gravity and aeromagnetic data, leading directly to inferred physical-property (density and magnetization) maps. Once these maps were produced, the known geology and drill-hole data were reconciled with the physical-property maps to form a refined structural and lithologic map of the crystalline basement.

Kansas, Missouri↗