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At least 73 records · Page 4Linked to original sources
USGS1999

Monitoring the Water Quality of the Nation's Large Rivers: Mississippi River Basin NASQAN Program

The U.S. Geological Survey (USGS) has monitored water quality in the Mississippi River Basin as part of the National Stream Quality Accounting Network (NASQAN) since 1995, applying a basinwide perspective to understanding water quality on a regional scale (Hooper and others, 1997). The objectives of the Mississippi River Basin NASQAN Program are to provide an ongoing characterization of the concentrations and mass fluxes of sediment and chemicals at key locations in the basin, to determine regional source areas for these materials, and to assess the effect of human influences on observed concentrations and fluxes. NASQAN complements the ongoing USGS National Water-Quality Assessment (NAWQA) Program, which is performing a detailed assessment in 23 subbasins within the Mississippi River Basin (Hirsch and others, 1988). NASQAN monitors the large rivers in the Mississippi River Basin, downstream of NAWQA study units. NASQAN, in conjunction with NAWQA, can provide the data and information needed by other USGS programs, Federal and State agencies, other segments of the scientific community, and by the public to address the present and future status of water quality in the Mississippi River Basin.

Fact Sheet↗
USGS2019

Revisions to suspended-sediment concentration, percent smaller than 0.063 millimeter, and instantaneous suspended-sediment discharge reported for a cooperative program between the U.S. Geological Survey and the U.S. Army Corps of Engineers in the lower Mississippi-Atchafalaya River Basin, October 1989 to February 2015

This report presents revised results for four parameters reported for suspended-sediment samples that were collected in the lower Mississippi-Atchafalaya River Basin as part of a cooperative program between the U.S. Army Corps of Engineers, Mississippi Valley Division, New Orleans District and the U.S. Geological Survey (USGS). The cooperative program has been active since 1973 at seven sites: two sites on the main stem of the Mississippi River, three sites on the Atchafalaya River, one site on the Old River Outflow Channel, and one site on the lower Red River above the confluence with the Old River Outflow Channel. The four parameters—suspended-sediment concentration, percent by mass of the sediment that passes through a 0.063-millimeter (US 230) sieve, instantaneous stream discharge, and instantaneous suspended-sediment discharge—reported for 2,895 samples have been modified to reflect the findings of a full review of the cooperative program, which was initiated by both agencies in January 2015. The revised results are for samples collected from October 1989 through February 2015. Ninety-four percent of the revised values for suspended-sediment concentration are lower than their corresponding original reported values, indicating that less suspended sediment moves through the lower Mississippi River system than was previously reported. For example, the median revised instantaneous suspended-sediment discharge at the Mississippi River at Tarbert Landing, Miss. (USGS station 07295100), was 315,000 short tons per day, compared to 378,000 short tons per day as originally reported. At the Atchafalaya River at Simmesport, La. (USGS station 07381490), the median revised suspended-sediment discharge was 105,000 short tons per day, compared to 143,000 short tons per day as originally reported. The systematic downward revision in instantaneous suspended-sediment discharge values was due to a systematic downward revision in the suspended fine (less than 0.063 millimeter) sediment concentration. The effect of the revision on the suspended-sand concentration and instantaneous suspended-sand discharge was weaker. Any model of sediment load or transport processes in the basin that uses data from the affected samples should be reevaluated on the basis of the revised results.

Lower Mississippi basin↗
USGS2008

Potentiometric Surface in the Sparta-Memphis Aquifer of the Mississippi Embayment, Spring 2007

The most widely used aquifer for industry and public supply in the Mississippi embayment in Arkansas, Louisiana, Mississippi, and Tennessee is the Sparta-Memphis aquifer. Decades of pumping from the Sparta-Memphis aquifer have affected ground-water levels throughout the Mississippi embayment. Regional assessments of water-level data from the aquifer are important to document regional water-level conditions and to develop a broad view of the effects of ground-water development and management on the sustainability and availability of the region's water supply. This information is useful to identify areas of water-level declines, identify cumulative areal declines that may cross State boundaries, evaluate the effectiveness of ground-water management strategies practiced in different States, and identify areas with substantial data gaps that may preclude effective management of ground-water resources. A ground-water flow model of the northern Mississippi embayment is being developed by the Mississippi Embayment Regional Aquifer Study (MERAS) to aid in answering questions about ground-water availability and sustainability. The MERAS study area covers parts of eight states including Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee and covers approximately 70,000 square miles. The U.S. Geological Survey (USGS) and the Mississippi Department of Environmental Quality Office of Land and Water Resources measured water levels in wells completed in the Sparta-Memphis aquifer in the spring of 2007 to assist in the MERAS model calibration and to document regional water-level conditions. Measurements by the USGS and the Mississippi Department of Environmental Quality Office of Land and Water Resources were done in cooperation with the Arkansas Natural Resources Commission; the Arkansas Geological Survey; Memphis Light, Gas and Water; Shelby County, Tennessee; and the city of Germantown, Tennessee. In 2005, total water use from the Sparta-Memphis aquifer in the Mississippi embayment was about 540 million gallons per day (Mgal/d). Water use from the Sparta-Memphis aquifer was about 170 Mgal/d in Arkansas, about 68 Mgal/d in Louisiana, about 97 Mgal/d in Mississippi, and about 205 Mgal/d in Tennessee. The author acknowledges, with great appreciation, the efforts of the personnel in the U.S. Geological Survey Water Science Centers of Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee, and the Mississippi Department of Environmental Quality Office of Land and Water Resources that participated in the planning, water-level measurement, data evaluation, and review of the potentiometric-surface map. Without the contribution of data and the technical assistance of their staffs, this report would not have been completed.

Scientific Investigations Map↗
USGS2011

Archive of Side Scan Sonar and Swath Bathymetry Data collected during USGS Cruise 10CCT02 Offshore of Petit Bois Island Including Petit Bois Pass, Gulf Islands National Seashore, Mississippi, March 2010

In March of 2010, the U.S. Geological Survey (USGS) conducted geophysical surveys offshore of Petit Bois Island, Mississippi, and Dauphin Island, Alabama (fig. 1). These efforts were part of the USGS Gulf of Mexico Science Coordination partnership with the U.S. Army Corps of Engineers (USACE) to assist the Mississippi Coastal Improvements Program (MsCIP) and the Northern Gulf of Mexico (NGOM) Ecosystem Change and Hazards Susceptibility Project by mapping the shallow geologic stratigraphic framework of the Mississippi Barrier Island Complex. These geophysical surveys will provide the data necessary for scientists to define, interpret, and provide baseline bathymetry and seafloor habitat for this area and to aid scientists in predicting future geomorphological changes of the islands with respect to climate change, storm impact, and sea-level rise. Furthermore, these data will provide information for barrier island restoration, particularly in Camille Cut, and protection for the historical Fort Massachusetts on Ship Island, Mississippi. For more information please refer to http://ngom.usgs.gov/gomsc/mscip/index.html. This report serves as an archive of the processed swath bathymetry and side scan sonar data (SSS). Data products herein include gridded and interpolated surfaces, seabed backscatter images, and ASCII x,y,z data products for both swath bathymetry and side scan sonar imagery. Additional files include trackline maps, navigation files, GIS files, Field Activity Collection System (FACS) logs, and formal FGDC metadata. Scanned images of the handwritten and digital FACS logs are also provided as PDF files. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report.

Data Series↗
USGS2005

Preliminary integrated geologic map databases for the United States: Alabama, Florida, Georgia, Mississippi, North Carolina, and South Carolina

The growth in the use of Geographic Information Systems (GIS) has highlighted the need for regional and national digital geologic maps attributed with age and lithology information. Such maps can be conveniently used to generate derivative maps for purposes including mineral-resource assessment, metallogenic studies, tectonic studies, and environmental research. This Open-File Report is a preliminary version of part of a series of integrated state geologic map databases that cover the entire United States. The only national-scale digital geologic maps that portray most or all of the United States for the conterminous U.S. are the digital version of the King and Beikman (1974a, b) map at a scale of 1:2,500,000, as digitized by Schruben and others (1994) and the digital version of the Geologic Map of North America (Reed and others, 2005a, b) compiled at a scale of 1:5,000,000 which is currently being prepared by the U.S. Geological Survey. The present series of maps is intended to provide the next step in increased detail. State geologic maps that range in scale from 1:100,000 to 1:1,000,000 are available for most of the country, and digital versions of these state maps are the basis of this product. In a few cases, new digital compilations were prepared (e.g. OH, SC, SD) or existing paper maps were digitized (e.g. KY, TX). For Alaska and Hawaii, new regional maps are being compiled and ultimately new state maps will be produced. The digital geologic maps are presented in standardized formats as ARC/INFO (.e00) export files and as ArcView shape (.shp) files. Accompanying these spatial databases are a set of five supplemental data tables that relate the map units to detailed lithologic and age information. The maps for the CONUS have been fitted to a common set of state boundaries based on the 1:100,000 topographic map series of the United States Geological Survey (USGS). When the individual state maps are merged, the combined attribute tables can be used directly with the merged maps to make derivative maps. No attempt has been made to reconcile differences in mapped geology across state lines.

Alabama, Florida, Georgia, Mississippi, North Caro↗
USGS2009

Mississippi River delta plain, Louisiana coast, and inner shelf Holocene geologic framework, processes, and resources

Extending nearly 400 km from Sabine Pass on the Texas-Louisiana border east to the Chandeleur Islands, the Louisiana coastal zone (Fig. 11.1) along the north-central Gulf of Mexico is the southern terminus of the largest drainage basin in North America (>3.3 million km2), which includes the Mississippi River delta plain where approximately 6.2 million kilograms per year of sediment is delivered to the Gulf of Mexico (Coleman 1988). The Mississippi River, active since at least Late Jurassic time (Mann and Thomas 1968), is the main distributary channel of this drainage system and during the Holocene has constructed one of the largest delta plains in the world, larger than 30,000 km2 (Coleman and Prior 1980; Coleman 1981; Coleman et al. 1998). The subsurface geology and geomorphology of the Louisiana coastal zone reffects a complex history of regional tectonic events and fluvial, deltaic, and marine sedimentary processes affected by large sea-level fluctuations. Despite the complex geology of the north-central Gulf basin, a long history of engineering studies and Scientific research investigations (see table 11.1) has led to substantial knowledge of the geologic framework and evolution of the delta plain region (see also Bird et al., chapter 1 in this volume). Mississippi River delta plain, Louisiana coast, and inner shelf Holocene geologic framework, processes, and resources . Available from: https://www.researchgate.net/publication/262802561_Mississippi_River_delta_plain_Louisiana_coast_and_inner_shelf_Holocene_geologic_framework_processes_and_resources [accessed Sep 13, 2017].

Louisiana, Mississippi↗
USGS2020

Oil-source rock correlation studies in the unconventional Upper Cretaceous Tuscaloosa marine shale (TMS) petroleum system, Mississippi and Louisiana, USA

The U.S. Geological Survey assessed undiscovered unconventional hydrocarbon resources reservoired in the Upper Cretaceous Tuscaloosa marine shale (TMS) of southern Mississippi and adjacent Louisiana in 2018. As part of the assessment, oil-source rock correlations were examined in the TMS play area where operators produce light (38–45° API), sweet oil from horizontal, hydraulically-fractured wells in an overpressured ‘high-resistivity’ (>5 Ω-m) zone at the base of the TMS. Geochemical data from 39 oil samples and 17 source rock solvent extracts collected from the TMS play area indicate close correspondence for Tuscaloosa Group oils [from lower Tuscaloosa, middle Tuscaloosa (the TMS) and upper Tuscaloosa reservoirs] in thermal maturity (computed from MPI), SARA proportions, n- alkane distributions, isoprenoid and DBT/P ratios, monoaromatic steroids, and δ 13 C isotopic compositions (from whole oils, saturate and aromatic fractions). Other parameters (normal steranes, extended homohopanes, C 31 R/C 30 hopane, norhopane/hopane and tricyclic terpane ratios, gammacerane/hopane) show most oil samples have similar values, suggesting all Tuscaloosa Group oils are from a common mixed marine-terrigenous source rock. Tighter distributions for triaromatic steroid (TAS) and δ 13 C isotopic composition for conventional oils in lower and upper Tuscaloosa reservoirs may indicate charge occurred in a single or shorter pulse relative to TMS oils which show broader TAS and δ 13 C properties, possibly from their generation over an extended period of burial maturation. Dissimilarity in geochemical properties between lower Tuscaloosa source rock solvent extracts and Tuscaloosa Group oils indicates lower Tuscaloosa source rocks did not contribute significantly to conventional and unconventional Tuscaloosa Group hydrocarbon accumulations. Whereas, TMS solvent extracts are similar to Tuscaloosa Group oils, suggesting an oil-source rock correlation. Excluding the possibility for long-distance lateral migration from a similar source downdip (which is unnecessary given thermal maturity considerations), the observations indicate 1. the TMS is a self-sourced reservoir, 2. the TMS is the source of oils accumulated in nearby conventional Tuscaloosa Group reservoirs, and 3. thin organic-rich shales in the lower Tuscaloosa did not contribute substantially to any oil accumulations in the Tuscaloosa Group.

Louisiana, Mississippi↗
USGS2014

Assessing inundation hazards to nuclear powerplant sites using geologically extended histories of riverine floods, tsunamis, and storm surges

Most nuclear powerplants in the United States are near rivers, large lakes, or oceans. As evident from the Fukushima Daiichi, Japan, disaster of 2011, these water bodies pose inundation threats. Geologic records can extend knowledge of rare hazards from flooding, storm surges, and tsunamis. This knowledge can aid in assessing the safety of critical structures such as dams and energy plants, for which even remotely possible hazards are pertinent. Quantitative analysis of inundation from geologic records perhaps is most developed for and applied to riverine flood hazards, but because of recent natural disasters, geologic investigations also are now used widely for understanding tsunami hazards and coastal storm surges. Layered sedimentary deposits commonly give the most complete geologic record of large floods, storm surges, and tsunamis. Sedimentary layers may be preserved for hundreds or thousands of years in suitable depositional environments, thereby providing an archive of rare, high-magnitude events. All inundation hazards discussed in this report—riverine floods, tsunamis, and storm surges—have had long records extracted from sedimentary sequences, many specifically for hazard assessment. Geologic records commonly are imprecise, so most hazard assessments benefit from evaluation of many sites and rigorous uncertainty assessment. Despite uncertainties, geologic records commonly can improve knowledge of the types and magnitudes of hazards threatening specific sites or regions. New statistical tools and approaches can efficiently incorporate geologic information into frequency assessments. These tools are most developed for riverine flood hazards, but are to some degree transferable to other episodic natural phenomena such as tsunamis and storm surges. Even with these efficient statistical approaches for examining geologic records, systematic landscape changes may reduce the applicability of retrospective assessments. These non-stationarity issues (such as climate change, sea‑level rise, land-use, dams and flow regulation) may all affect the validity of using past experience—no matter how complete the record—to assess future likelihoods. These issues require site-specific consideration for nearly all hazard assessments drawn from geologic evidence. A screening of the 104 nuclear powerplants in the United States licensed by the Nuclear Regulatory Commission (at 64 sites) indicates several sites for which paleoflood studies likely would provide additional flood-frequency information. Two sites—Duane Arnold, Iowa, on the Cedar River; and David-Besse, Ohio, on the Toussaint River—have geologic conditions suitable for creating and preserving stratigraphic records of flooding and few upstream dams that may complicate flood-frequency analysis. One site—Crystal River, Florida1, on the Withlacoochee River and only 4 kilometers from the coast—has high potential as a candidate for assessing riverine and marine inundation hazards. Several sites on the Mississippi River have high geologic potential, but upstream dams almost certainly now regulate peak flows. Nevertheless, studies on the Mississippi River to evaluate long-term flood frequency may provide results applicable to a wide spectrum of regional hazard issues. Several sites in the southeastern United States have high geologic potential, and studies at these sites also may be helpful in evaluating hazards from outburst floods from landslide dams (river blockages formed by mass movements), which may be a regional hazard. For all these sites, closer investigation and field reconnaissance would be needed to confirm suitable deposits and settings for a complete paleoflood analysis. Similar screenings may help identify high-potential sites for geologic investigations of tsunami and storm-surge hazards.

Scientific Investigations Report↗
USGS2000

Importance of the Mississippi River Basin for investigating agricultural–chemical contamination of the hydrologic cycle

This special issue is devoted to recent and ongoing research relating to the fate and transport of agricultural chemicals in the Mississippi River Basin by the US Geological Survey Toxic Substances Hydrology (Toxics) Program. The Mississippi River Basin drains approximately 3 200 000 km 2 representing 41% of the United States. This is the largest river in the United States and the third largest in the world. The Mississippi River discharges an average of 19 920 m 3 /s of water into the Gulf of Mexico. The river is an extensively used resource, supplying drinking water to 70 cities in the United States. The Mississippi River Basin has undergone dramatic land use and cultural changes over the last 150 years. Approximately 70 million people now live within the basin, representing approximately 27% of the nation's population. This basin has also become one of the most productive agricultural regions in the world in terms of both crops and livestock grown. Approximately 65% of the nation's harvested cropland is grown in this basin, with more than 100 000 metric tons (t) of pesticides and approximately 6 500 000 t of commercial nitrogen fertilizers applied to cropland within the basin annually. The drainage of more than 20 000 000 ha within the basin has been enhanced by means of tile lines and ditches to lower the water table to make the cropland more productive. While removing the water from the soil as intended, this practice also leads to more rapid transport of contaminants to the river, and ultimately the Gulf of Mexico. Furthermore, the extensive chemical use in the Mississippi River Basin has led to the transport of pesticides and nitrate into the region’s streams, aquifers, and atmosphere. An estimated 1 000 000 t of nitrate-N is transported from the Mississippi River Basin into the Gulf of Mexico annually. The peak annual load of herbicides to the Gulf of Mexico has been documented at 1920 t. The fundamental goal of the papers presented in this volume is to provide a scientific basis for decisions necessary to promote sound and efficient agricultural practices and protect the quality of the nation's water resources.

Science of the Total Environment↗
USGS2009

Recent subsidence and erosion at diverse wetland sites in the southeastern Mississippi Delta Plain

A prior study (U.S. Geological Survey Open-File Report 2005-1216) examined historical land- and water-area changes and estimated magnitudes of land subsidence and erosion at five wetland sites in the Terrebonne hydrologic basin of the Mississippi delta plain. The present study extends that work by analyzing interior wetland loss and relative magnitudes of subsidence and erosion at five additional wetland sites in the adjacent Barataria hydrologic basin. The Barataria basin sites were selected for their diverse physical settings and their recent (post-1978) conversion from marsh to open water. Historical aerial photography, datum-corrected marsh elevations and water depths, sediment cores, and radiocarbon dates were integrated to evaluate land-water changes in the Mississippi delta plain on both historical and geological time scales. The thickness of the organic-rich sediments (peat) and the elevation of the stratigraphic contact between peat and underlying mud were compared at marsh and open-water sites across areas of formerly continuous marsh to estimate magnitudes of recent delta-plain elevation loss caused by vertical erosion and subsidence of the wetlands. Results of these analyses indicate that erosion exceeded subsidence at most of the study areas, although both processes have contributed to historical wetland loss. Comparison of these results with prior studies indicates that subsidence largely caused rapid interior wetland loss in the Terrebonne basin before 1978, whereas erosional processes primarily caused more gradual interior wetland loss in the Barataria basin after 1978. Decadal variations in rates of relative sea-level rise at a National Ocean Service tide gage, elevation changes between repeat benchmark-leveling surveys, and GPS height monitoring at three National Geodetic Survey Continuously Operating Reference Stations indicate that subsidence rates since the early 1990s are substantially lower than those previously reported and are similar in magnitude to time-averaged subsidence rates at geological time scales. The historical decrease in land-loss rates across the Mississippi delta plain generally is consistent with the recent decrease in subsidence rates within the same region.

Louisiana↗
USGS1983

Crustal structure of the northern mississippi embayment and a comparison with other continental rift zones

Previous geological and geophysical investigations have suggested that the Mississippi Embayment is the site of a Late Precambrian continental rift that was reactivated in the Mesozoic. New information on the deep structure of the northern Mississippi Embayment, gained through an extensive seismic refraction survey, supports a rifting hypothesis. The data indicate that the crust of the Mississippi Embayment may be characterized by six primary layers that correspond geologically to unconsolidated Mesozoic and Tertiary sediments (1.8 km/s), Paleozoic carbonate and clastic sedimentary rocks (5.9 km/s), a low-velocity layer of Early Paleozoic sediments (4.9 km/s), crystalline upper crust (6.2 km/s), lower crust (6.6 km/s), modified lower crust (7.3 km/s), and mantle. Average crustal thickness is approximately 41 km. The presence and configuration of the low-velocity layer provide new evidence for rifting in the Mississippi Embayment. The layer lies within the northeast-trending upper-crustal graben reported by Kane et al. (1981), and probably represents marine shales deposited in the graben after rifting. The confirmation and delineation of a 7.3 km/s layer, identified in previous studies, implies that the lower crust has been altered by injection of mantle material. Our results indicate that this layer reaches a maximum thickness in the north-central Embayment and thins gradually to the southeast and northwest, and more rapidly to the southwest along the axis of the graben. The apparent doming of the 7.3 km/s layer in the north-central Embayment suggests that rifting may be the result of a triple junction located in the Reelfoot Basin area. The crustal structure of the Mississippi Embayment is compared to other continental rifts: the Rhinegraben, Limagnegraben, Rio Grande Rift, Gregory Rift, and the Salton Trough. This comparison suggests that alteration of the lower crust is a ubiquitous feature of continental rifts.

Mississippi embayment↗
USGS2016

Accuracy assessment/validation methodology and results of 2010–11 land-cover/land-use data for Pools 13, 26, La Grange, and Open River South, Upper Mississippi River System

Introduction/Background The U.S. Geological Survey (USGS)-Upper Midwest Environmental Sciences Center (UMESC) was responsible for development of several land cover/land use (LCU) systemic datasets of the Upper Mississippi River System (UMRS). These efforts (1989 and 2000) were funded by the U.S. Army Corps of Engineers’ Upper Mississippi River Restoration Program (UMRR) Long Term Resource Monitoring (LTRM) element. Development of systemic datasets includes the acquisition, processing, and serving of high-resolution aerial photography and land cover/land use spatial datasets ( http://www.umesc.usgs.gov/data_library/land_cover_use/land_cover_use_data.html ). In 2008, the UMRR reached a collaborative agreement with the U.S. Fish and Wildlife Service-Region 3 to collect high-resolution digital imagery of the entire UMRS floodplain during 2010–11 for LTRM. The UMESC helped acquire, process, and serve this imagery, as well as produce and serve the 2010–11 LCU systemic dataset of the UMRS floodplain. Digital imagery for Pools 13, 26, La Grange, and Open River South was collected using an Applanix DSS 439 digital sensor system with a 40 millimeter lens and Color Infrared (CIR) filter. The imagery was collected at a resolution of 20 centimeters/pixel (8 inches/pixel) for Pool 13 and 40 centimeters/pixel (16 inches/pixel) for Pools 26, Open River South, and La Grange. All imagery was projected to Universal Transverse Mercator (UTM) Zone 15, North American Datum of 1983 (NAD 83). The General Wetland Vegetation Classification (GWVC) system used for mapping is hierarchical, and its 31 classes can be collapsed into broader categories using either a 15- or 7-class level. While the 1989 and 2000 LCU systemic datasets have not gone through a traditional thematic accuracy assessment (AA) in the past, nor have they undergone a validation analysis, the end products are of high quality. For each systemic dataset produced (1989, 2000, 2010–11), extensive field reconnaissance is performed before photointerpretation. The intent of this field reconnaissance is to learn, test, and verify image signatures as they relate to vegetation types. Questionable areas on the imagery are visited, and the plants or land features observed in the area are recorded for reference. This procedure verifies vegetation signatures on the imagery with those on the ground. In addition, once the photointerpretation is complete, the final LCU dataset undergoes extensive quality assurance/quality control to ensure the imagery is mapped correctly. Since the 2000 LCU systemic dataset was developed, there has been a growing interest in completing thematic AAs for the LTRM LCU spatial datasets. The objective of an AA is to measure the probability that a particular location has been assigned its correct vegetation class. An AA estimates thematic (map class) errors in the data, giving users information needed to determine data suitability for a particular application. At the same time, data producers are able to learn more about the nature of errors in the data. Thus, the two attributes of an AA are “producers’ accuracy,” which is the probability that an AA point has been mapped correctly (also referred to as an error of omission); and “users’ accuracy,” which is the probability that the map actually represents what was found on the ground (also referred to as error of commission). Producers’ and users’ accuracies can be obtained from the same set of data by using different analyses. Accuracy assessment is an extensive effort that requires seasonal field personnel and equipment, data entry, analyses, and post processing—tasks that are costly and time consuming. The geospatial team at the UMESC has suggested a validation process for understanding the accuracy of the spatial datasets, which will be tested on at least some areas of the UMRS. Validation is not a true verification of map-class type in the field; however, it can provide the user of the map with useful information that is similar to a field AA. Similar to an AA, validation involves generating random points based on the total area for each map class. However, instead of collecting field data, two or three individuals not involved with the photo-interpretative mapping separately review each of the points onscreen and record a best-fit vegetation type(s) for each site. Once the individual analyses are complete, results are joined together and a comparative analysis is performed. The objective of this initial analysis is to identify areas where the validation results were in agreement (matches) and areas where validation results were in disagreement (mismatches). The two or three individuals then perform an analysis, looking at each mismatched site, and agree upon a final validation class. (If two vegetation types at a specific site appear to be equally prevalent, the validation team is permitted to assign the site two best-fit vegetation types.) Following the validation team’s comparative analysis of vegetation assignments, the data are entered into a database and compared to the mappers’ vegetation assignments. Agreements and disagreements between the map and validation classes are identified, and a contingency table is produced. This document presents the AA processes/results for Pools 13 and La Grange, as well as the validation process/results for Pools 13 and 26 and Open River South.

Iowa, Illinois, Minnesota, Missouri, Wisconsin↗
USGS1983

Deep structure of northern Mississippi embayment

In September 1980, the U. S. Geological Survey conducted a seismic refraction investigation of the northern Mississippi Embayment. During the investigation, 34 shots from nine shotpoints were recorded along a series of profiles. The profiles were parallel to and across an inferred Precambrian rift zone which is outlined by a series of magnetic anomalies and covers an area at least 200 km (125 mi) long and 70 km (45 mi) wide. The paper presents an interpretation of the survey results. The tectonic model proposed to explain the origin of the embayment velocity structure includes a late Precambrian mantle plume that intruded the lower crust of the northern embayment, causing uplift (and/or crustal stretching) and subsequent rifting of the axial area. This was followed by erosion, subsidence, and subsequent deposition of sediments in the resulting trough.

Northern Mississippi embayment↗
USGS2021

Influence of antecedent geology on the Holocene formation and evolution of Horn Island, Mississippi, USA

Horn Island, one of the two most stable barriers along the Mississippi-Alabama chain (Cat, East and West Ship, Horn, West Petit Bois, Petit Bois, and Dauphin), provides critical habitat, helps regulate estuarine conditions in the Mississippi Sound, and reduces wave energy and storm surge before they reach the mainland shore. However, important details of the formation and evolution of the island in response to sea-level rise, storms, and antecedent geology remain unclear. This study integrates 2200 km of high-resolution geophysical data, 35 sediment cores, and 18 radiocarbon ages to better understand the geologic history of the island. Incised valleys of the Biloxi and Pascagoula Rivers underlie Horn Island and played a profound role in the evolution of the system. Within the incised valleys, sandy paleochannel deposits represent potential sediment sources during island development. Scour associated with wave and tidal ravinement processes liberated sand from the paleochannels and along with numerous other sizable sand sources on the shelf contributed to the formation and continued maintenance of Horn Island. Based on radiocarbon ages, transgressive ephemeral islands/shoals with no preserved shoreface existed at least 8000 cal yr BP and were frequently overwashed when sea-level rise rates were ~ 4–5 mm/yr. Approximately 5000 cal yr BP, coinciding with a deceleration in sea-level rise to about 1.4 mm/yr and attendant increased sand supply, radiocarbon ages associated with Horn Island's barrier complex and lower shoreface indicate a period of island stabilization. Seismic and sediment core data show a long history of westward lateral migration by longshore currents through tidal ravinement and inlet fill. Subsurface sand packages associated with tidal inlet fill and paleochannels are available for ravinement and may be important sand sources for Horn Island to maintain subaerial exposure with the expected accelerated future sea-level rise.

Mississippi↗