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| Value | Definition |
|---|---|
| Rg | The dominant texture (> 50%) Rock (R) is given the upper case letter and the subordinate texture (< 50%) gravel (g) is given a lower case letter. |
| Gr | The dominant texture (> 50%) Gravel (G) is given the upper case letter and the subordinate texture (< 50%) rock (r) is given a lower case letter. |
| Gs | The dominant texture (> 50%) Gravel (G) is given the upper case letter and the subordinate texture (< 50%) sand (s) is given a lower case letter. |
| M | The end-member texture (~ 100%) Mud (M) is the primary texture. |
| Ms | The dominant texture (> 50%) Mud (M) is given the upper case letter and the subordinate texture (< 50%) sand (s) is given a lower case letter. |
| S | The end-member texture (~ 100%) Sand (S) is the primary texture. |
| Sg | The dominant texture (> 50%) Sand (S) is given the upper case letter and the subordinate texture (< 50%) gravel (g) is given a lower case letter. |
| Sm | The dominant texture (> 50%) Sand (S) is given the upper case letter and the subordinate texture (< 50%) mud (m) is given a lower case letter. |
| Rs | The dominant texture (> 50%) Rock (R) is given the upper case letter and the subordinate texture (< 50%) sand (s) is given a lower case letter. |
| Sr | The dominant texture (> 50%) Sand (S) is given the upper case letter and the subordinate texture (< 50%) rock (r) is given a lower case letter. |
| Mg | The dominant texture (> 50%) Mud (M) is given the upper case letter and the subordinate texture (< 50%) gravel (g) is given a lower case letter. |
| G | The end-member texture (~ 100%) Gravel (G) is the primary texture. |
| N/A | There was not enough source input data to define sediment texture within this area. |
| Value | Definition |
|---|---|
| sand | Sediment whose main phase is <2 mm, but >0.062 mm |
| gravel | Sediment whose main phase (usually >50%) is >2 mm |
| sandy silt | Sediment whose main phase is silt, but with significant sand |
| solid | Sediment whose main phase is rock, cobble, or boulder |
| silty sand | Sediment whose main phase is sand, but with significant silt |
| silt | Sediment whose main phase (usually >50%) is < 0.062 mm |
| N/A | There was not enough source input data to define sediment texture within this area. |
| gravelly sediment | ediment whose main phase is >2 mm, but with significant other sediment. |
| clayey silt | Sediment whose main phase is silt, but with significant clay. |
| Value | Definition |
|---|---|
| sand | Sediment whose primary component (> 50%) is sand |
| hardbottom | Sediment whose primary component is rock, boulder, cobble, or coarse gravel |
| mud | Sediment whose primary component (> 50%) is silt and clay |
| N/A | There was not enough source input data to define simple sediment texture within this area. |
| Value | Definition |
|---|---|
| yes | bedforms are present within some part of the traced polygon in the source acoustic data |
| N/A | bedforms are not present within any part of the traced polygon in the source acoustic data |
| Value | Definition |
|---|---|
| coarse pebbles | sediment class whose phi size is between -4 and -5 |
| coarse silt | sediment class whose phi size is between 4 and 5 |
| coarse sand | sediment class whose phi size is between 0 and 1 |
| cobble | sediment class whose phi size is between -6 and -8 |
| fine pebbles | sediment class whose phi size is between -2 and -3 |
| fine sand | sediment class whose phi size is between 2 and 3 |
| fine silt | sediment class whose phi size is between 6 and 7 |
| granules | sediment class whose phi size is between -1 and -2 |
| medium pebbles | sediment class whose phi size is between -3 and -4 |
| medium sand | sediment class whose phi size is between 2 and 1 |
| medium silt | sediment class whose phi size is between 5 and 6 |
| solid | sediment class whose phi size could not be determined from grain size data, but was determined to be rock based on acoustic data |
| very coarse pebbles | sediment class whose phi size is between -5 and -6 |
| very coarse sand | sediment class whose phi size is between 0 and -1 |
| very fine sand | sediment class whose phi size is between 3 and 4 |
| very fine silt | sediment class whose phi size is between 7 and 8 |
| N/A | sediment class whose phi size could not be determined from grain size data or there were no samples with laboratory analyzed grain size statistics within the polygon |
| Value | Definition |
|---|---|
| 1 | Sediment texture regions that were defined based on the highest resolution bathymetry (5m) and backscatter (1m), bottom photos, sediment samples, and seismic interpretations were given the highest data interpretation confidence value of 1. |
| 2 | Areas where sediment texture was defined based on bathymetry of 30m resolution, backscatter of 1m resolution, bottom photos, and sediment samples were given an interpretation confidence value of 2. |
| 3 | A confidence value of 3 was given to areas with multibeam bathymetric and backscatter resolution of 10m and sediment samples, but no bottom photos or high density seismic interpretations were available. |
| 4 | The lowest confidence values (4) were given to areas where only lidar data at 2.5m resolution (and near full coverage) and sediment samples were available. |
| 0 | no cofidence in interpretation because there was not enough source data to make an interpretation |
| Range of values | |
|---|---|
| Minimum: | 0 |
| Maximum: | 85 |
| Units: | count |
| Resolution: | 1 |
| Range of values | |
|---|---|
| Minimum: | 0 |
| Maximum: | 89.9 |
| Units: | percent |
| Resolution: | 0.1 |
| Range of values | |
|---|---|
| Minimum: | 1.79 |
| Maximum: | 100 |
| Units: | percent |
| Resolution: | 0.01 |
| Range of values | |
|---|---|
| Minimum: | 0 |
| Maximum: | 68.37 |
| Units: | percent |
| Resolution: | 0.1 |
| Range of values | |
|---|---|
| Minimum: | 0 |
| Maximum: | 44.98 |
| Units: | percent |
| Resolution: | 0.1 |
| Range of values | |
|---|---|
| Minimum: | -4.07 |
| Maximum: | 7.83 |
| Units: | phi |
| Resolution: | 0.01 |
| Range of values | |
|---|---|
| Minimum: | -61.15 |
| Maximum: | -0.07 |
| Units: | meters |
| Resolution: | 0.01 |
| Range of values | |
|---|---|
| Minimum: | 125.941 |
| Maximum: | 144652.135 |
| Units: | meters |
| Resolution: | 0.001 |
| Range of values | |
|---|---|
| Minimum: | 899.009 |
| Maximum: | 208403761.365 |
| Units: | meters squared |
| Resolution: | 0.001 |
These sea floor sediment cover data were created from geophysical and sample data collected from Nahant to Northern Cape Cod Bay, and are used to characterize the sea floor in the area. Sediment type and distribution maps are important data layers for marine resource managers charged with protecting fish habitat, delineating marine boundaries, and assessing environmental change due to natural or human impacts.
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Are there legal restrictions on access or use of the data?Access_Constraints: None
Use_Constraints:Not to be used for navigation. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information. Additionally, there are limitations associated with qualitative sediment mapping interpretations. Because of the scale of the source geophysical data and the spacing of samples, not all changes in sea floor texture are captured. The data were mapped between 1:8,000 and 1:25,000, but the recommended scale for application of these data is 1:25,000. Features below 5,000 m2 or less than 50 m wide were not digitized due to positional uncertainty, lack of sample information, and the often ephemeral nature of small-scale sea floor features. Not all digitized sea floor features contained sample information, so often the sea floor texture is characterized by the nearest similar feature that contains a sample. Conversely, sometimes a digitized feature contained multiple samples and not all of the samples within the feature were in agreement (of the same texture). In these cases the dominant sediment texture was chosen to represent the primary texture for the polygon. Samples from rocky areas often only consist of bottom photographs, because large particle size often prevents the recovery of a sediment sample. Bottom photo classification can be subjective, such that determining the sediment type that is greater than 50% of the view frame is estimated by the interpreter and may differ among interpreters. Bottom photo transects often reveal changes in the sea floor over distances of less than 100 m and these changes are often not observable in acoustic data. Heterogeneous sea floor texture can change very quickly, and many small-scale changes will not be detectable or mappable at a scale of 1:25,000. The boundaries of polygons are often inferred based on sediment samples, and even boundaries that are traced based on amplitude changes in geophysical data are subject to migration. Polygon boundaries should be considered an approximation of the location of a change in texture.
Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
| Data format: | WinZip (v. 14.5) file contains qualitatively derived polygons that define sea floor texture and distribution from Nahant to Northern Cape Cod Bay, MA and the associated metadata in format Shapefile (version ArcGIS 9.3.1) Esri Polygon Shapefile Size: 1.87 |
|---|---|
| Network links: |
http://pubs.usgs.gov/of/2012/1157/GIS_catalog/SedimentTexture/SedCover.zip http://pubs.usgs.gov/of/2012/1157/html/GIS_catalog.html http://pubs.usgs.gov/of/2012/1157/ |
These data are available in Environmental Systems Research Institute (Esri) shapefile format. The user must have software capable of importing and processing this data type.
