OVERVIEW

The U.S. Geological Survey (USGS) ArcMap Sediment Classification tool is a custom toolbar that extends the Environmental Systems Research Institute, Inc. (ESRI) ArcGIS 9.2 Desktop application to aid in the analysis of seabed sediment classification.  The tool uses as input either a point data layer with field attributes containing percentage of gravel, sand, silt, and clay or four raster data layers representing a percentage of sediment (0-100%) for the various sediment grain size analysis: sand, gravel, silt and clay. This tool is designed to analyze the percent of sediment at a given location and classify the sediments according to either the Folk (1954, 1974) or Shepard (1954) as modified by Schlee(1973) classification schemes.  The sediment analysis tool is based upon the USGS SEDCLASS program (Poppe, et al. 2004).

Usage

System Requirements

• ArcGIS V9.2 software installed on a computer with Windows XP Operating System
• Four raster data sets representing percent sand, gravel, silt and clay for the area to be classified
  OR
• An ArcGIS feature or table data set containing percent sediment having values between 0 to 100%

Background

Image showing sediment classification for the Chesapeake Bay region.

A major component of the research conducted by the U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole, Science Center (WHSC) is seafloor mapping to map and characterize the sea floor.  This work provides insight into the geologic makeup of the seafloor and aids in research areas as diverse as habitat mapping, location of geohazards and identifying areas of erosion and deposition.  The geophysical tools including, seismic-reflection, sidescan-sonar and bathymetric systems used to remotely map the seafloor provide information regarding the sea floor and subsurface to define the surficial geology and geologic framework of a given region.

Ground-truth techniques, such as sediment grab and core sampling, are an integral part of seafloor mapping activities, and provide specific information from directly-sampled material that aid in interpretating the geophysics.  Sediment samples are analyzed within the WHSC sediment laboratory for mean grain size, percent content of gravel, sand, silt, clay, and mud, and additional analysis as required by a given research project.  After completing the various analytic processes, the sample data, with percent content of clay, silt, sand and gravel are processed using the program SEDCLASS (Poppe, et al, 2003).

The SEDCLASS program developed at the WHSC is used to classify sediment grain-size distributions based on relationships between size fractions.  The user may chose from either the Shepard (1954), as modified by Schlee (1973), or Folk (1954, 1974) classification schemes.  The program analyzes a comma delimited text file and must contain seven fields: sample-identifier, latitude, longitude, and the percentages of gravel, sand, silt, and clay in that specific order.  The output of the program is also a comma delimited text file similar to the input with the additional of an eight field containing the calculated sediment classification based upon the system selected by the user.

The sample data, with sediment classification information, output from program SEDCLASS is then converted to a Geographic Information System (GIS) point data layer.  This allows the sample points to be combined with other project data in a GIS mapview allowing the samples to be co-located over the geophysical data (such as a sidescan sonar mosaic).  This data integration aids the researchers in the interpretation of the surficial geology.

Point Data Classification

This option allows a user to add the modified from Folk or Shepard as modified by Schlee(1973) classification scheme to previously unclassified sample data.  It is intended to provide a way to classify sediment sample information that may have been analyzed outside of the Woods Hole Science Center and does not contain the desired classification information.  The input data must contain four fields representing the percent gravel, sand, silt and clay.  Those individual values together must total between 99 and 101% allowing for minor round-up and round-down of the total sum.  A total percentage of sediment outside of the range between 99 and 101 will not be assigned a sediment classification and will be given a value of zero and no text description.  A value of 0 is also assigned if any individual value of gravel, sand, silt or clay in a record is less than zero.

For more detailed information regarding this option, please see the section entitled Feature/Table Tutorial in the PDF Installation and Users Guide.

Raster Classification

Having the classified sediment sample point information is helpful when interpreting the surficial geology of an area.  Processing those points to produce a surface of the survey area may provide more insight into trends.  The Raster Classification option allows the user to produce a surface raster modified from Folk(1954, 1974) or Shepard, as modified by Schlee (1973), classified sediment distribution.  Implementing this option of the sediment classification toolbar is more involved and requires more prep work by the user.

To begin, the user must locate sediment data that contains, or that can be derived from, the four values of percent gravel, sand, silt and clay.  Each of those individual values must be gridded to produce a raster data layer representing the surface distribution.  One way to produce a grid is through the use of the ArcMap surface interpolation functions by interpolating point sample data. Interpolation is the estimation of surface values at un-sampled points based on known surface values of surrounding points. For further discussion on interpolation and different interpolation techniques please refer to the ArcGIS Desktop help system online at http://webhelp.esri.com/arcgisdesktop/9.2.

The four raster layers of gravel, sand, silt and clay must have the same spatial properties, i.e. cell size, extent, projection or an error message will be generated and you will not be able to continue. The calculation of the raster sediment type is accomplished using the four raster layers of gravel, sand, silt, and clay and applying the formula in the appropriate table of the "Installation and Users Guide" Appendix B to each raster on a cell-by-cell basis. When the four raster data layers are complete, they may be combined to create the output sediment classification raster.  The results of the raster classification for any given area will vary and depend on the accuracy of the sample points, number of sample points, distribution of the data points, gridded cell size and gridding method employed by the user.

For more details on the installation and usage of the USGS ArcMap Sediment Classification tool, the user should refer to the PDF Installation and Users Guide.

ArcMap symbolization layers may be downloaded for the Folk and Shepard classification.

References

Folk, R.L., 1954, The distinction between grain size and mineral composition in sedimentary rock nomenclature: Journal of Geology, v. 62, no. 4, p. 344-359.

Folk, R.L., 1974, The petrology of sedimentary rocks: Austin, Tex., Hemphill Publishing Co., 182 p.

Poppe, L.J., Eliason, A.H., and Hastings, M.E., 2003, A Visual Basic program to classify sediments based on gravel-sand-silt-clay ratios: Computers and Geosciences, v. 29, no. 6, p. 805-809.

Poppe, L.J., Williams, S.J., and Paskevich, V.F., 2005, U.S. Geological Survey east-coast sediment snalysis; procedures, database, and GIS data: U.S. Geological Survey Open-File Report 2005-1001.  Online at http://pubs.usgs.gov/of/2005/1001/

Reid, J.M., Reid, J.A., Jenkins, C.J., Hastings, M.E., Williams, S.J., and Poppe, L.J, 2005, usSEABED: Atlantic coast offshore surficial sediment data release: U.S. Geological Survey Data Series 118, version 1.0. Online at http://pubs.usgs.gov/ds/2005/118/

Schlee, J., 1973, Atlantic continental shelf and slope of the United States -- sediment texture of the northeastern part: U.S. Geological Survey Professional Paper 529-L, 64 p.

Shepard, F.P., 1954, Nomenclature based on sand-silt-clay ratios: Journal Sedimentary Petrology, v. 24, p. 151-158.