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Geochemical Characteristics of the Conterminous United States: % MgO

Metadata Updated: October 29, 2023

This raster depicts the percentage of lithological magnesium oxide (MgO) content in surface or near surface geology. We derived these rasters by calculating the average percent MgO content for each map unit in combined surficial-bedrock geologic maps. We used state geologic maps (Preliminary Integrated Geologic Map Databases for the United States, Open File Reports 2004-1355, 2005-1305, 2005-1323, 2005-1324, 2005-1325, 2005-1351, and 2006-1272), which depict surficial geology instead of bedrock when the surficial layers are sufficiently deep. For the state maps that do not incorporate surficial geology (i.e., midwestern states), we overlaid surficial geologic map units with thicknesses greater than 100 feet (from Soller and Reheis [2004]) to produce combined surficial-bedrock geologic maps that were similar to other states. We characterized geology based on the 201 different lithologies that the Geologic Map Database lists as occurring in the conterminous United States. Because some of these lithologies are known to have chemical attributes that vary widely, we created an additional 78 lithologic classes based on the common modifiers used in the geologic unit descriptions to better parse chemical variability within the lithologies (e.g., calcareous and noncalcareous sandstone). Modifiers were assigned base on descriptions of geologic formations obtained through either the Lexicon of Geologic Names of the United States or literature searches. Fifteen lithologic classes were not characterized because the class was not a specific rock type (e.g., mélange, water, and landslide). These classes were characterized as no data. We translated each state’s combined surficial-bedrock geologic maps into characteristics following the methods in Olson and Hawkins (2012) by assigning an estimate of each map unit’s percent MgO content to every occurrence of that map unit in the combined surficial-bedrock geologic map. This estimate was calculated as the average of literature or database values of the respective property for each lithological class contained within the map unit weighted by the prevalence of each lithological class within the map unit. The accompanying Excel workbook (Lith-MajorOxides.xls) contains a summary of all of the average geochemical characteristics for each lithology (“Lith Summary” tab) and tabs for each individual lithology that include the source of each record (e.g., originating from the Earth Chem Database or the specific literature reference), as well as the calculations used to determine the measure of central tendency (mean or median depending on the data). The final national raster was created by merging each of the individual state rasters. Users should be cognizant that some differences will exist in chemical and physical characterizations across state lines that are caused by unreconciled differences in lithologic descriptions or mapping scales used among the underlying state source maps.

Access & Use Information

Public: This dataset is intended for public access and use. License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Metadata Created Date June 1, 2023
Metadata Updated Date October 29, 2023

Metadata Source

Harvested from DOI EDI

Additional Metadata

Resource Type Dataset
Metadata Created Date June 1, 2023
Metadata Updated Date October 29, 2023
Publisher U.S. Geological Survey
Identifier USGS:552b001ae4b026915857df09
Data Last Modified 20220805
Category geospatial
Public Access Level public
Bureau Code 010:12
Metadata Context
Metadata Catalog ID
Schema Version
Catalog Describedby
Harvest Object Id 4914c7db-1c21-4369-a6ae-a620dc52b88d
Harvest Source Id 52bfcc16-6e15-478f-809a-b1bc76f1aeda
Harvest Source Title DOI EDI
Metadata Type geospatial
Old Spatial -129.567807626,22.397057588,-64.981807426,50.7850356
Publisher Hierarchy White House > U.S. Department of the Interior > U.S. Geological Survey
Source Datajson Identifier True
Source Hash be38aa77307d0f52b9be8619a9fb089e6c78c63bc24b20b2a12dce7e0b68e5cf
Source Schema Version 1.1
Spatial {"type": "Polygon", "coordinates": -129.567807626, 22.397057588, -129.567807626, 50.7850356, -64.981807426, 50.7850356, -64.981807426, 22.397057588, -129.567807626, 22.397057588}

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