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| Formal codeset | |
|---|---|
| Codeset Name: | Polygon |
| Codeset Source: | Esri |
| Formal codeset | |
|---|---|
| Codeset Name: | Qdt - Pleistocene glacial till and ice contact deposits (Qdt) are drift composed of poorly sorted mud, sand, gravel and boulders (typically 10 to 30 m thick, exceeds 60 m along the Buzzards Bay moraine). Seismic penetration is limited in chirp profiles. Boomer profiles locally penetrate Qdt. Internal reflections are irregular or parabolic. Underlies the transgressive (Ut) and regressive (Ur) unconformities and overlies the top of bedrock, the U1 unconformity. Qdt crops out at the sea-floor forming ridges and ledges, which are composed of sand, gravel, and in places, boulders. |
| Codeset Source: | U.S. Geological Survey |
| Formal codeset | |
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| Codeset Name: | Qdm - Pleistocene Buzzards Bay end moraine (Qdm) composed of poorly sorted mud, sand, gravel and boulders (typically 10 to 30 m thick, exceeds 60 m along the Buzzards Bay moraine). Seismic penetration is limited in chirp profiles. Similar to Qdt, boomer profiles locally penetrate Qdm. Internal reflections are irregular or parabolic. Underlies the transgressive (Ut) and regressive (Ur) unconformities and overlies the top of bedrock, the U1 unconformity. Qdm crops out at the sea-floor forming ridges and ledges, which are composed of sand, gravel, and in places, boulders. |
| Codeset Source: | U.S. Geological Survey |
| Formal codeset | |
|---|---|
| Codeset Name: | Qdl - Pleistocene glaciolacustrine (glaciodeltaic and lake floor) is stratified drift composed of mud and sand (locally up to 30 m thick). Produces strong to weak vertically laminated and horizontal to dipping reflections. Underlies the transgressive (Ut) and regressive (Ur) unconformities and typically drapes Qdt/Qdm. |
| Codeset Source: | U.S. Geological Survey |
| Formal codeset | |
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| Codeset Name: | Qdf - Pleistocene glaciofluvial (outwash and glaciodeltaic) is stratified drift composed of sand and gravel (typically 5 to 10 m thick). Contains vertically laminated, roughly horizontal to broadly undulating reflectors, cut and fill structures and zones of acoustic transparency. Underlies Ut and Ur. Typically overlies Qdl or Qdt and may locally incise Qdl. |
| Codeset Source: | U.S. Geological Survey |
| Formal codeset | |
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| Codeset Name: | Qfe/Qmn- Holocene nearshore marine unit (Qmn is mostly muddy deposits in the deeper basins and becoming sandy along the shallower margins of the survey area. Dredge spoil deposits are excluded. Generally acoustically transparent with faint, flat-lying reflections locally. Overlies transgressive unconformity (Ut).Holocene fluvial and estuarine unit is fluvial sands and gravels, and estuarine sands and muds (Qfe) that, together with Qmn, fill incised fluvial valleys (up to >20 m thick). Produces vertically laminated, horizontal to concave-up reflections and zones of acoustic transparency; local indications of cut-and-fill. Bounded above and below by transgressive (Ut) and regressive (Ur) unconformities, respectively. Qfe is often associated with acoustic attenuation from gas, which obscures this unit and the Ur unconformity and underlying units. Qfe/Qmn are thickest where they fill fluvial incised valleys. |
| Codeset Source: | U.S. Geological Survey |
| Range of values | |
|---|---|
| Minimum: | 0.000513 |
| Maximum: | 199.203575 |
| Units: | Square Kilometers |
| Resolution: | 0.000001 |
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| Access_Constraints | None |
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| 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 1:5,000 and 1:20,000, but the recommended scale for application of these data is 1:25,000. 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. |
| Data format: | WinZip version 14.5 file contains qualitatively derived polygons that define sea-floor geology from Buzzards Bay, MA and the associated metadata in format WinZip (version version 14.5) Esri Polygon Shapefile Size: 0.799 |
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| Network links: |
http://pubs.usgs.gov/of/2014/1220/GIS_catalog/SurficialGeology/BuzzardsBay_surfgeol.zip http://pubs.usgs.gov/of/2014/1220/ofr2014-1220-data_catalog.html http://dx.doi.org/10.3133/ofr20141220 |
