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At least 1,207 records · Page 67Linked to original sources
USGS1967

Areal geology of the western Mojave Desert, California

This report and map represent part of a geologic investigation by the U.S. Geological Survey of the known and potential deposits of borate minerals in the southern California desert regions. The primary purpose of this report and the geologic map (pl. 1) is to provide a geologic background for the exploration for possible concealed borate deposits in the western Mojave Desert, based upon (1) the geology of the known deposits of these minerals within the region, (2) the areal geology of the region, and (3) the subsurface geology as determined insofar as possible from logs of exploratory test holes, mine workings, and geophysical data. Available logs of test holes so used, including those drilled for petroleum and some for water, and of borate mine shafts are summarized in tabulated form (tables 2-4); the gravity geophysical data are published separately (Mabey, 1960). The resulting geologic data are of use for many secondary purposes, such as exploration for other commodities, including petroleum and gas, and in evaluation of ground-water conditions. The base for the geologic map was prepared by joining parts of the Bakersfield, Trona, Los Angeles, and San Bernardino quadrangles, as published by the U.S. Geological Survey at a scale of 1:250,000, and then enlarging the mosaicked map to a scale of 1:125,000. Although lacking in detail and accuracy, the base is the best that is available. Numerous maps at a scale of an inch to a mile or larger show the geology of most of the complex areas in greater detail.

California↗
USGS2004

Hydrogeologic characterization of the Modesto Area, San Joaquin Valley, California

Hydrogeologic characterization was done to develop an understanding of the hydrogeologic setting near Modesto by maximizing the use of existing data and building on previous work in the region. A substantial amount of new lithologic and hydrologic data are available that allow a more complete and updated characterization of the aquifer system. In this report, geologic units are described, a database of well characteristics and lithology is developed and used to update the regional stratigraphy, a water budget is estimated for water year 2000, a three-dimensional spatial correlation map of aquifer texture is created, and recommendations for future data collection are summarized. The general physiography of the study area is reflected in the soils. The oldest soils, which have low permeability, exist in terrace deposits, in the interfan areas between the Stanislaus, Tuolumne, and Merced Rivers, at the distal end of the fans, and along the San Joaquin River floodplain. The youngest soils have high permeability and generally have been forming on the recently deposited alluvium along the major stream channels. Geologic materials exposed or penetrated by wells in the Modesto area range from pre-Cretaceous rocks to recent alluvium; however, water-bearing materials are mostly Late Tertiary and Quaternary in age. A database containing information from more than 3,500 drillers'logs was constructed to organize information on well characteristics and subsurface lithology in the study area. The database was used in conjunction with a limited number of geophysical logs and county soil maps to define the stratigraphic framework of the study area. Sequences of red paleosols were identified in the database and used as stratigraphic boundaries. Associated with these paleosols are very coarse grained incised valley-fill deposits. Some geophysical well logs and other sparse well information suggest the presence of one of these incised valley-fill deposits along and adjacent to the Tuolumne River east of Modesto, a feature that may have important implications for ground-water flow and transport in the region. Although extensive work has been done by earlier investigators to define the structure of the Modesto area aquifer system, this report has resulted in some modification to the lateral extent of the Corcoran Clay and the regional dip of the Mehrten Formation. Well logs in the database indicating the presence of the Corcoran Clay were used to revise the eastern extent of the Corcoran Clay, which lies approximately parallel to the axis of valley. The Mehrten Formation is distinguished in the well-log database by its characteristic black sands consisting of predominantly andesitic fragments. Black sands in wells listed in the database indicate that the formation may lie as shallow as 120 meters (400 feet) below land surface under Modesto, approximately 90 meters (300 feet) shallower than previously thought. The alluvial aquifer system in the Modesto area comprises an unconfined to semiconfined aquifer above and east of the Corcoran Clay confining unit and a confined aquifer beneath the Corcoran Clay. The unconfined aquifer is composed of alluvial sediments of the Modesto, Riverbank, and upper Turlock Lake formations. The unconfined aquifer east of the Corcoran Clay becomes semiconfined with depth due to the numerous discontinuous clay lenses and extensive paleosols throughout the aquifer thickness. The confined aquifer is composed primarily of alluvial sediments of the Turlock Lake and upper Mehrten Formations, extending from beneath the Corcoran Clay to the base of fresh water. Ground water in the unconfined to semiconfined aquifer flows to the west and southwest. The primary source of present-day recharge is percolating excess irrigation water. The primary ground-water discharge is extensive ground-water pumping in the unconfined to semiconfined aquifer, imposing a significant component of vertical flow in the system. A water budget was calculated for water year 2000 using a land-use approach. During water year 2000, the total water supply in the Modesto area was more than 2.5 billion m3 (cubic meter) (2 million acre-ft [acre-foot]). Surface-water deliveries accounted for 60 percent of the total water supply, whereas ground-water pumpage accounted for 40 percent. Ninety-four percent of the water supply was used to meet irrigation demand and approximately 6 percent was used to meet urban demand. The total recharge in the model area was estimated at 1.4 billion m3 (1,100,000 acre-ft). The largest component of recharge is from excess irrigation water (58 percent); precipitation in excess of crop requirements accounted for 41 percent of the recharge. Geostatistical methods were used to develop a spatial correlation model of the percentage of coarse-grained texture in the Modesto area. The mean percentage coarse-grained texture calculated for each depth increment indicates a regional trend of decreasing coarse-grained texture with increasing depth, which is consistent with increasingly consolidated sediments with depth in the study area. The three-dimensional kriged estimates of percentage coarse-grained texture show significant heterogeneity in the texture of the sedimentary deposits. Assuming the hydraulic conductivity is correlated to the texture, the kriged result implies significant heterogeneity in the hydrogeologic framework.

California↗
USGS1992

Geohydrologic systems in Kansas: Physical framework of the upper aquifer unit in the western interior plains aquifer system

The purpose of this Hydrologic Investigations Atlas is to provide a description of the principal geohydrologic systems in Upper Cambrian through Lower Cretaceous rocks in Kansas. This investigation was made as part of the Central Midwest Regional Aquifer-System Analysis (CMRASA). The CMRASA is one of several major investigations by the U.S. Geological Survey of regional aquifer systems in the United States. These regional investigations are designed to increase knowledge of the flow regime and hydrologic properties of major aquifer systems and to provide quantitative information for the assessment, development, and management water supplies. The CMRASA study area includes all or parts of 10 Central Midwestern States (Jorgensen and Signor, 1981), as shown on the envelope cover. This Hydrologic Investigations Atlas, which consists of a series of nine chapters, presents a description of the physical framework and the geohydrology of principal aquifers and confining systems in Kansas. Chapter D presents maps that show the areal extent, altitude and configuration of the top, and thickness of Mississippian rocks that compose the upper aquifer unit of the Western Interior Plains aquifer system in Kansas, The chapter is limited to the presentation of the physical framework of the upper aquifer unit. The interpretation of the physical framework of the upper aquifer unit is based on selected geophysical and lithologic logs and published maps of stratigraphically equivalent units. Maps indicating the thickness and the altitude and configuration of the top of the upper aquifer unit in the Western Interior Plains aquifer system have been prepared as part of a series of interrelated maps that describe the stratigraphic interval from the Precambrian basement through Lower Cretaceous rocks. A concerted effort was made to ensure that maps of each geohydrologic unit are consistent with the maps of underlying and overlying units. Chapter A of this atlas series (Wolf and others, 1990) describes the relation of principal geohydrologic systems in Kansas and presents a more detailed discussion of the methods and data used to prepare and ensure consistency among the sets of maps.

Kansas↗
USGS2005

Geologic map of the Ikpikpuk River quadrangle, Alaska

This map is a product of the USGS Digital Geologic Maps of Northern Alaska project, which captures in digital format quadrangles across the entire width of northern Alaska. Sources include geologic maps previously published in hardcopy format and recent updates and revisions based on field mapping by the Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys and Division of Oil and Gas, and the U.S. Geological Survey. Individual quadrangles are digitized at either 1:125,000 or 1:250,000 depending on the resolution of source maps. The project objective is to produce a set of digital geologic maps with uniform stratigraphic nomenclature and structural annotation, and publish those maps electronically. The paper version of this map is available for purchase from the USGS Store.

Alaska↗
USGS2006

Geologic map of the Lookout Ridge quadrangle, Alaska

This map is a product of the USGS Digital Geologic Maps of Northern Alaska project, which captures in digital format quadrangles across the entire width of northern Alaska. Sources include geologic maps previously published in hardcopy format and recent updates and revisions based on field mapping by the Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys and Division of Oil and Gas, and the U.S. Geological Survey. Individual quadrangles are digitized at either 1:125,000 or 1:250,000 depending on the resolution of source maps. The project objective is to produce a set of digital geologic maps with uniform stratigraphic nomenclature and structural annotation, and publish those maps electronically. The paper version of this map is available for purchase from the USGS Store.

Alaska↗
USGS2008

Geologic map of the Point Lay quadrangle, Alaska

This map is a product of the USGS Digital Geologic Maps of Northern Alaska project, which captures in digital format quadrangles across the entire width of northern Alaska. Sources include geologic maps previously published in hardcopy format and recent updates and revisions based on field mapping by the Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys and Division of Oil and Gas, and the U.S. Geological Survey. Individual quadrangles are digitized at either 1:125,000 or 1:250,000 depending on the resolution of source maps. The project objective is to produce a set of digital geologic maps with uniform stratigraphic nomenclature and structural annotation, and publish those maps electronically. The paper version of this map is available for purchase from the USGS Store.

Alaska↗
USGS2019

Three-dimensional geologic map of the southern Carson Sink, Nevada, including the Fallon FORGE area

The three-dimensional (3–D) geologic map characterizes the subsurface in the southern Carson Sink region. We created the 3–D map by integrating the results from seismic-reflection, potential-field-geophysical, and lithologic well-logging inves­tigations completed in and around the Fallon FORGE site as part of the U.S. Department of Energy Frontier Observatory for Research in Geothermal Energy (FORGE) initiative from 2015–2018. The FORGE initiative was part of an effort to develop the technologies, techniques, and knowledge needed to make enhanced geothermal systems a commercially viable electricity-generation option for the United States. Geo­logic units and structures mapped during the Fallon FORGE study, which particularly focused on the Mesozoic basement, were extrapolated to create the 3–D map of the southern Carson Sink area. The 3–D map area is 10 km wide along the east-west and north-south axes and extends 2.5 km below sea level, ~3.7 km below the land surface. Views of the map include horizontal and vertical sections and oblique perspective views from several angles. We describe the geologic units and structures and dis­cuss the methods used to integrate the geologic and geophysical information in a 3–D geologic interpretation. We provide digital data for elements of the map, such as individual 3–D fault and stratigraphic surfaces and surface-fault traces. Input data are available from various data repositories through cited web links. A brief movie displaying the 3–D map is available at https://doi.org/10.3133/sim3437 .

Nevada↗
USGS2023

Three-dimensional geologic map the southeastern Gabbs Valley geothermal area, Nevada

This three-dimensional (3D) geologic map displays the subsurface geology in the upper ~4 kilometers of the Earth’s crust in the southeastern Gabbs Valley geothermal area of west-central Nevada. The 3D map was constructed by integrating the results from detailed geologic mapping, 3D gravity inversion modeling, and potential-field-geophysical studies. This effort was undertaken as part of the Nevada Play Fairway Project, a regional effort to characterize new geothermal resources in the United States. Local data collection and analysis in southeastern Gabbs Valley, Nevada, including the construction of this 3D map, led to the drilling of six temperature gradient wells and identification of previously unknown hydrothermal fluids at 150 meters depth. The measured temperatures, which are as high as 124.9 degrees Celsius, indicate that the southeastern Gabbs Valley hydrothermal system has temperatures that are comparable to geothermal fields that have been developed for electricity generation in the region. We describe the geologic units and structures displayed by the map and discuss the methods used to integrate the geologic and geophysical information into the 3D geologic interpretation. The accompanying map provides horizontal and vertical section views and oblique perspective views from several angles. The digital data for elements of the map, the individual 3D fault surfaces, and stratigraphic surfaces are available from Siler (2022). The accompanying map sheet and video displaying the 3D map are available at https://doi.org/10.3133/sim3498 .

Nevada↗
USGS2010

Archive of digital Chirp sub-bottom profile data collected during USGS Cruise 07SCC01 offshore of the Chandeleur Islands, Louisiana, June 2007

In June of 2007, the U.S. Geological Survey (USGS) conducted a geophysical survey offshore of the Chandeleur Islands, Louisiana, in cooperation with the Louisiana Department of Natural Resources (LDNR) as part of the USGS Barrier Island Comprehensive Monitoring (BICM) project. This project is part of a broader study focused on Subsidence and Coastal Change (SCC). The purpose of the study was to investigate the shallow geologic framework and monitor the enviromental impacts of Hurricane Katrina (Louisiana landfall was on August 29, 2005) on the Gulf Coast's barrier island chains. This report serves as an archive of unprocessed digital 512i and 424 Chirp sub-bottom profile data, trackline maps, navigation files, Geographic Information System (GIS) files, Field Activity Collection System (FACS) logs, observer's logbook, and formal Federal Geographic Data Committee (FGDC) metadata. Gained (a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report. The USGS St. Petersburg Coastal and Marine Science Center (SPCMSC) assigns a unique identifier to each cruise or field activity. For example, 07SCC01 tells us the data were collected in 2007 for the Subsidence and Coastal Change (SCC) study and the data were collected during the first field activity for that study in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity identification (ID). All Chirp systems use a signal of continuously varying frequency; the Chirp systems used during this survey produce high resolution, shallow penetration profile images beneath the seafloor. The towfish is a sound source and receiver, which is typically towed 1 - 2 m below the sea surface. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by a receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.125 s) and recorded for specific intervals of time (for example, 50 ms). In this way, a two-dimensional vertical image of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters. See the digital FACS equipment log (11-KB PDF) for details about the acquisition equipment used. Table 2 lists trackline statistics. Scanned images of the handwritten FACS logs and handwritten science logbook (449-KB PDF) are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y rev 1 format (Norris and Faichney, 2002); ASCII character encoding is used for the first 3,200 bytes of the card image header instead of the SEG-Y rev 0 (Barry and others, 1975) EBCDIC format. The SEG-Y files may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2010). See the How To Download SEG-Y Data page for download instructions. The web version of this archive does not contain the SEG-Y trace files. These files are very large and would require extremely long download times. To obtain the complete DVD archive, contact USGS Information at 1-888-ASK-USGS or infoservices@usgs.gov. The printable profiles provided here are GIF images that were processed and gained using SU software; refer to the Software page for links to example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992). The processed SEG-Y data were also exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce an interactive version of the profile that allows the user to obtain a geographic location and depth from the profile for a given cursor position. This information is displayed in the status bar of the browser.

Louisiana↗
USGS1993

Geohydrologic systems in Kansas, geohydrology of the Great Plains aquifer system

Sedimentary rocks of Late Cambrian through Early Cretaceous age in Kansas are part of a regional flow system of hydraulically connected aquifers and confining units. Future demands for water require that these deeply buried rocks be studied to describe hydrologic properties and ground-water-flow conditions and to provide information that will serve as the basis for decisions concerning the protection and the management of the water resources contained therein, Toward this end, the U.S. Geological Survey, as a part of its Central Midwest Regional Aquifer-System Analysis (CMRASA), began a 5-year hydrologic investigation of this regional flow system in Arkansas, Colorado, Kansas, Missouri, Nebraska, New Mexico, Oklahoma, South Dakota, and Texas (Jorgensen and Signor, 1981). This chapter is one of nine contained in Hydrologic Investigations Atlas HA-722, which present a description of the physical framework (Chapters B-F) and the geohydrology (Chapters G-I} of principal aquifers and confining systems in Upper Cambrian through Lower Cretaceous rocks in Kansas; the stratigraphic relations of these geohydrologic systems are discussed in detail in Chapter A (Wolf and others, 1990). This chapter (G) describes the geohydrology of the Great Plains aquifer system; the physical framework of the Great Plains aquifer system is presented in Chapter B (Spinazola and others, 1992). The maps in this chapter are based on existing data from selected geophysical and lithologic logs, drill-stem tests, water-level measurements, water-quality analyses, and published maps of stratigraphically equivalent units. An index to the geohydrologic data compiled for the CMRASA in Kansas is presented in Spinazola and others (1987). For the most part, data used to construct the maps were collected over many years and do not reflect aquifer conditions for any specific time period.

Kansas↗
USGS2024

Hydrogeologic framework and extent of saltwater intrusion in Kings, Queens, and Nassau Counties, Long Island, New York

In 2016, the U.S. Geological Survey began a multiyear cooperative study with the New York State Department of Environmental Conservation to evaluate the sustainability of Long Island’s sole-source aquifer system through hydrogeologic mapping, compilation of groundwater chloride concentrations, and groundwater flow modeling. In the initial phase of the islandwide study, the hydrogeologic framework and extent of saltwater intrusion in aquifers in Kings, Queens, and Nassau Counties on western Long Island, N.Y., were investigated. The aquifer system underlying western Long Island has been under stress from pumping of public, irrigation (golf course), and industrial supply wells. Saltwater intrusion has occurred from surrounding embayments (East River, Long Island Sound, Jamaica Bay, and the Atlantic Ocean) due to pumping. Eighteen boreholes were drilled and cores taken during 2019–21 to collect hydrogeologic, geochemical, and geophysical data to delineate the complex subsurface hydrogeology and extent of saltwater intrusion within the study area. Evaluation of the new cores, reexamination of legacy core descriptions, and analysis of borehole geophysical logs was used to refine the previously published hydrogeologic framework of Pleistocene and Cretaceous unconsolidated sediments in the area, including delineation of a previously undefined hydrogeologic unit between the Magothy aquifer and the Raritan confining unit, herein named the “upper Raritan aquifer.” The upper Raritan aquifer was first recognized in southeastern Nassau County from an analysis of about 50 closely spaced boreholes with high-resolution core descriptions and gamma-ray (gamma) logs. Further analysis of borehole logs across the study area indicated that the upper Raritan aquifer was also present in Kings and Queens Counties. Nuclear magnetic resonance (NMR) logging was used for the first time on Long Island to provide estimates of the hydraulic properties of the major aquifer and confining units. Unlike other geophysical logs that record responses to the rock matrix and fluid properties and are strongly dependent on mineralogy, NMR logs record responses to the presence of hydrogen protons in the formation fluid to determine water fraction and pore-size distribution. NMR log analysis provided estimates of the clay-bound, capillary-bound, and mobile water fractions and hydraulic conductivity of aquifers and confining units penetrated by five wells in Nassau County. Pumpage for public-supply and industrial wells on Long Island began in the 1870s with small, localized suppliers of populated areas in Kings and Queens Counties. By 1904–16, pumpage for public water supply in Kings County averaged 21 million gallons per day, and averaged 37 million gallons per day in Queens County, mostly from the upper glacial aquifer. Saltwater intrusion was reported as early as the beginning of the 20th century and included the upper glacial-Jameco-Magothy and Lloyd-North Shore aquifer systems. By 1936, pumping in central Kings County created a major cone of depression in the water table extending to the south shore of much of Kings County and into southwestern Queens County. Saltwater intrusion has caused the shutdown of public-supply wells in Kings, Queens, and Nassau Counties. A large saltwater intrusion wedge in the Lloyd aquifer was indicated in southern Queens County in the early part of the 20th century, and the saltwater interface may have been onshore predevelopment. Most of Kings and Queens Counties are intruded with saltwater in both the upper glacial-Jameco-Magothy and Lloyd-North Shore aquifers systems. Saltwater increased during the 20th century and continues to increase to the present (2023) in the Lloyd-North Shore aquifer system in Great Neck and Manhasset Neck in northern Nassau County. A major wedge of saltwater intrusion in the upper glacial-Jameco-Magothy aquifer in southwestern Nassau County appears to be increasing.

New York↗
USGS2006

Aeromagnetic Map with Geology of the Los Angeles 30 x 60 Minute Quadrangle, Southern California

Introduction: An important objective of geologic mapping is to project surficial structures and stratigraphy into the subsurface. Geophysical data and analysis are useful tools for achieving this objective. This aeromagnetic anomaly map provides a three-dimensional perspective to the geologic mapping of the Los Angeles 30 by 60 minute quadrangle. Aeromagnetic maps show the distribution of magnetic rocks, primarily those containing magnetite (Blakely, 1995). In the Los Angeles quadrangle, the magnetic sources are Tertiary and Mesozoic igneous rocks and Precambrian crystalline rocks. Aeromagnetic anomalies mark abrupt spatial contrasts in magnetization that can be attributed to lithologic boundaries, perhaps caused by faulting of these rocks or by intrusive contacts. This aeromagnetic map overlain on geology, with information from wells and other geophysical data, provides constraints on the subsurface geology by allowing us to trace faults beneath surficial cover and estimate fault dip and offset. This map supersedes Langenheim and Jachens (1997) because of its digital form and the added value of overlaying the magnetic data on a geologic base. The geologic base for this map is from Yerkes and Campbell (2005); some of their subunits have been merged into one on this map.

Scientific Investigations Map↗
USGS2014

Digital surfaces and thicknesses of selected hydrogeologic units within the Ozark Plateaus aquifer system, northwestern Arkansas

Digital surfaces and thicknesses of nine hydrogeologic units of the Ozark Plateaus aquifer system from land surface to the top of the Gunter Sandstone in northwestern Arkansas were created using geophysical logs, drillers’ logs, geologist-interpreted formation tops, and previously published maps. The 6,040 square mile study area in the Ozark Plateaus Province includes Benton, Washington, Carroll, Madison, Boone, Newton, Marion, and Searcy Counties. The top of each hydrogeologic unit delineated on geophysical logs was based partly on previously published reports and maps and also from drillers’ logs. These logs were then used as a basis to contour digital surfaces showing the top and thickness of the Fayetteville Shale, the Boone Formation, the Chattanooga Shale, the Everton Formation, the Powell Dolomite, the Cotter Dolomite, the Roubidoux Formation, the Gasconade Dolomite, and the Gunter Sandstone.

Arkansas↗
USGS2010

Revised hydrogeologic framework of the Floridan aquifer system in the northern coastal area of Georgia and adjacent parts of South Carolina

The hydrogeologic framework for the Floridan aquifer system has been revised for eight northern coastal counties in Georgia and five coastal counties in South Carolina by incorporating new borehole geophysical and flowmeter log data collected during previous investigations. Selected well logs were compiled and analyzed to determine the vertical and horizontal continuity of permeable zones that make up the Upper and Lower Floridan aquifers and to define more precisely the thickness of confining beds that separate these aquifers. The updated framework generally conforms to the original framework established by the U.S. Geological Survey in the 1980s except for adjustments made to the internal boundaries of the Upper and Lower Floridan aquifers and the individual permeable zones that compose these aquifers. The revised boundaries of the Floridan aquifer system were mapped by taking into account results from local studies and regional correlations of geologic and hydrogeologic units. Because the revised framework does not match the previous regional framework along all edges, additional work will be needed to expand the framework into adjacent areas. The Floridan aquifer system in the northern coastal region of Georgia and parts of South Carolina can be divided into the Upper and Lower Floridan aquifers, which are separated by a middle confining unit of relatively lower permeability. The Upper Floridan aquifer includes permeable and hydraulically connected carbonate rocks of Oligocene and upper Eocene age that represent the most transmissive part of the aquifer system. The middle confining unit consists of low permeability carbonate rocks that lie within the lower part of the upper Eocene in Beaufort and Jasper Counties, South Carolina, and within the upper to middle parts of the middle Eocene elsewhere. Locally, the middle confining unit contains thin zones that have moderate to high permeability and can produce water to wells that tap them. The Lower Floridan aquifer includes all permeable strata that lie below the middle confining unit and above the base of the aquifer system. Beneath Hilton Head Island, South Carolina, the middle Floridan aquifer is now included as part of the Lower Floridan aquifer. The base of the Floridan aquifer system generally is located at the top of lower Eocene rocks in Georgia and the top of Paleocene rocks in South Carolina. The Upper and Lower Floridan aquifers are interconnected to varying degrees depending on the thickness and permeability of the middle confining unit that separates these aquifers. In most places, hydraulic head differences between the two aquifers range from a few inches to a few feet or more. Monitoring at several vertically clustered well-point sites where wells were set at different depths in the aquifer revealed variations in the degree of hydraulic separation with depth. In general, the head separation between the Upper and Lower Floridan aquifers increases with depth, which indicates that the deeper zones are more hydraulically separated than the shallower parts of the Lower Floridan aquifer.

Georgia, South Carolina↗
USGS2014

Geology and hydrostratigraphy of Guadalupe River State Park and Honey Creek State Natural Area, Kendall and Comal Counties, Texas

Hydrogeologic mapping and descriptions of the lithostratigraphy and hydrostratigraphy of Guadalupe River State Park and Honey Creek State Natural Area, Kendall and Comal Counties, Texas, are presented in this first detailed 1:24,000 geologic map, along with proposed names and descriptions of the hydrostratigraphic units in the study area. Variations in the amount and type of porosity of the lithostratigraphic unit, which vary depending on the depositional environment, lithology, structural history and diagenesis support the resulting hydrostratigraphy proposed herein. Rocks exposed in the study area consist of Early Cretaceous sedimentary rocks that are assigned to the Trinity Group. The lithostratigraphy includes the Hammett Shale, Cow Creek Limestone, Hensell Sand Members of the Pearsall Formation, and the lower member of the Glen Rose Limestone. These lithologic units contain shale, grainstone, sandstone, and fossiliferous limestone, alternating and interfingering with mudstone, wackestone, packstone, and grainstone. The Trinity aquifer hydrostratigraphic units shown on the map and described herein are characterized by their porosity types. Porosity types were first determined from an analysis of two boreholes conducted in comparison with 143 geophysical logs from northern Bexar County, Texas. The cores and geophysical log comparison resulted in division of the lower member of the Glen Rose Limestone into six hydrostratigraphic units, designated A through F. Of those six units, only three remain in the study area because of erosion. The proposed naming of these three hydrostratigraphic units is based on topographic or historical features that occur in the outcrop area of those units. Hydrostratigraphic units that correlate with the boundaries of the formation have been given formational names excluding the lithologic modifier. The Doeppenschmidt hydrostratigraphic unit is stratigraphically the highest interval in the study area, characterized by interparticle, moldic, burrowed, bedding plane, fracture, and cave porosity. The underlying Rust hydrostratigraphic unit appears to be a confining unit with springs/seeps issuing near the contact with the overlying Doeppenschmidt unit. The Rust unit has interparticle, fracture, and cave porosity with cave porosity primarily associated with faulting. The Honey Creek hydrostratigraphic unit is an aquifer in the subsurface and exhibits extremely, well developed porosity and permeability including— interparticle, moldic, burrowed, bedding plane, fracture, channel, and cave porosity. This unit is named for Honey Creek Cave, which discharges water into Honey Creek. The Hensell hydrostratigraphic unit contains primarily interparticle porosity, but also exhibits some moldic and cave porosity in its upper parts. The Cow Creek hydrostratigraphic unit contains interparticle, moldic, vug, burrowed, fracture, bedding plane, channel, and cave porosity. The Cow Creek hydrostratigraphic unit is an aquifer in the subsurface and is the primary target for water-well drillers in the area. The Hammett hydrostratigraphic unit is not exposed in the study area but is thought to underlie parts of the Guadalupe River, based on mapping of the overlying units and comparisons with subsurface thicknesses obtained from the geophysical log. The Hammett unit restricts the downward migration of groundwater, resulting in springs that discharge at the base of the Cow Creek unit. These springs also create some base flow to the Guadalupe River during periods of extreme drought. The faulting and fracturing in the study area are part of the Miocene Balcones Fault Zone, which is an extensional system of faults that generally trend southwest to northeast in south-central Texas. An igneous dike, containing aphanitic texture, cuts through the center of the study area near the confluence of Honey Creek and the Guadalupe River. The dike penetrates the Cow Creek Limestone and the lower part of the Hensell Sand, which outcrops at three locations.

Texas↗
USGS1989

Map showing the depth to the base of the deepest ice-bearing permafrost as determined from well logs, North Slope, Alaska

Because gas hydrates from within a limited temperature range, subsurface equilibrium temperature data are necessary to calculate the depth and thickness of the gas-hydrate stability field. Acquiring these data is difficult because drilling activity often disrupts equilibrium temperatures in the subsurface, and a well mush lie undisturbed until thermal equilibrium is reestablished (Lachenbruch and Brewer, 1959). On the North Slope if Akaska, a series of 46 oil and gas exploratory wells, which were considered to be near thermal equilibrium (Lachenbruch and others, 1982; 1987), were surveyed with high-resolution temperature devices (see table 1). However, several thousand other exploratory and production wells have been drilled on the North Slope, and although they do not include temperature profiles, their geophysical logs often allow descrimination between ice-bearing and non-ice-bearing strata. At the outset of this study, the coincidence of the base of ice-bearing strata being near the same depth as the 0 °C isotherm at Prudhoe Bay (Lachenbruch and others, 1982) appeared to offer an opportunity to quickly and inexpensively expand the size of our subsurface temperature data base merely by using well logs to identify the base of the ice-bearing strata.

Alaska↗
USGS2017

Electrical resistivity investigation of fluvial geomorphology to evaluate potential seepage conduits to agricultural lands along the San Joaquin River, Merced County, California, 2012–13

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage losses could result from these higher restoration flows, which could exacerbate existing drainage problems in neighboring agricultural lands and potentially damage crops. Channel deposits of abandoned river meanders that are hydraulically connected to the river could act as seepage conduits, allowing rapid and widespread water-table rise during restoration flows. There is a need to identify the geometry and properties of these channel deposits to assess their role in potential increased seepage effects and to evaluate management alternatives for reducing seepage. Electrical and electromagnetic surface geophysical methods have provided a reliable proxy for lithology in studies of fluvial and hyporheic systems where a sufficient electrical contrast exists between deposits of differing grain size. In this study, direct-current (DC) resistivity was used to measure subsurface resistivity to identify channel deposits and to map their subsurface geometry. The efficacy of this method was assessed by using DC resistivity surveys collected along a reach of the San Joaquin River in Merced County, California, during the summers of 2012 and 2013, in conjunction with borings and associated measurements from a hydraulic profiling tool. Modeled DC resistivity data corresponded with data from cores, hand-auger samples, a hydraulic profiling tool, and aerial photographs, confirming that DC resistivity is effective for differentiating between silt and sand deposits in this setting. Modeled DC resistivity data provided detailed two-dimensional cross-sectional resistivity profiles to a depth of about 20 meters. The distribution of high-resistivity units in these profiles was used as a proxy for identifying areas of high hydraulic conductivity. These data were used subsequently to guide the location and depth of wells installed onsite for monitoring flow in the channel deposits. Estimates of the cross-sectional area of channel deposits from DC resistivity pseudosections can provide critical input for groundwater-flow models designed to simulate river seepage and evaluate seepage-management alternatives.

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USGS2023

Summary of the history and research of the U.S. Geological Survey gas hydrate properties laboratory in Menlo Park, California, active from 1993 to 2022

The U.S. Geological Survey (USGS) Clathrate Hydrate Properties Project, active from 1993 to 2022 in Menlo Park, California, stemmed from an earlier project on the properties of planetary ices supported by the National Aeronautics and Space Administration’s (NASA’s) Planetary Geology and Geophysics Program. We took a material science approach in both projects, emphasizing chemical purity of samples, having controlled grain size and grain texture, and having verified crystal structures and phase relations. A foundational contribution from our USGS Gas Hydrate Properties Laboratory (GHPL) was in demonstrating the ability to reproducibly create such pure clathrate hydrate samples for study. Clathrate sample synthesis was achieved by heating sieved and weighed pure granular water ice in the presence of cold clathrate-forming gas or liquid. During heating, the ice melts at the grain scale and reacts with the gas to form clathrate. The resulting material has the desired uniformity and purity, with known intergranular porosity; our subsequent measurements showed that these clathrates exhibited the established clathrate structures and phase relations. This novel synthesis method was successful in creating clathrates of pure methane, ethane, propane, carbon dioxide, and multi-component gases. By mixing sand or silt with granular ice, we were also able to make clathrate-sediment aggregates with controlled grain textures. This simple method, adopted by many others in the community, permitted us to measure the physical and chemical properties of well-characterized and well-crystallized clathrates and clathrate/sediment aggregates. At about the same time, we adapted conventional scanning electron microscopy to cryogenic conditions for analysis of grain-scale characteristics of clathrates made in the GHPL as well as those collected from nature by drill core. The uniformity and reproducibility of our samples also allowed us to investigate how clathrates respond to environmental changes in chemistry, temperature, and pressure: we measured chemical exchange rates with dissolved gas species—such as noble gases and chlorofluorocarbons—as well as rates of clathrate dissolution and decomposition. These advances include the first accurate mapping of the conditions that promote the remarkable process of “anomalous preservation” at room pressure, a metastability that offers potential application for low-cost and safe transportation of natural gas from gas fields far from pipelines. Another advancement stemming from the GHPL was the compaction of as-synthesized porous clathrates to nearly full density by applying external pressure using three different techniques. Compaction allows for high-accuracy measurements of many fundamental physical and chemical properties of these materials, such as elastic wavespeeds and moduli, complete thermal properties, decomposition rates, thermal expansion, and clathrate equations of state. These properties and others, in turn, have helped USGS scientists to interpret geophysical well logs and active geophysical surveys, as well as model the rates of gas production from hydrate deposits in nature. Studying this class of icy minerals that occur in abundance on Earth and in the outer solar system has been a fascinating laboratory journey. Here, we summarize the history and major findings of the USGS GHPL in Menlo Park, including both in-house research as well as findings from the synergistic collaborations with other agencies and institutes that were key to the success of our laboratory. The Menlo Park GHPL was more formally incorporated within the USGS Gas Hydrates Project, a collaboration among multiple USGS Science Centers, in the early 2000s under the leadership of Deborah Hutchinson, and now under the leadership of Carolyn Ruppel and Timothy Collett.

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