A two week cruise aboard the R/V GYRE focused on mapping surficial sedimentary processes and their connection to the subsurface geology. The study area was on the upper continental slope in the northwestern Gulf of Mexico; an area of active hydrocarbon exploration. Active salt movement, hydrocarbon movement up faults, the presence of gas hydrates associated with biogenic and thermogenic methane, and overpressured sand deposits all present hazards to oil exploration in this area. This study used sidescan sonar and high-resolution chirp subbottom profiling techniques to map the surficial and shallow subsurface expression of these processes in two areas roughly 15 by 25 km in size. High-resolution multi-channel seismic-reflection data were collected simultaneously with the sidescan imagery to provide a link to the deeper subsurface. Additional multi-channel and Huntec seismic data were collected along regional lines between the detailed study areas to tie these studies to other areas of known hydrates and to wells where shallow overpressured sands have been drilled.
The detailed studies attempted to map entire geological systems in this upper slope environment to provide a broader perspective than can be seen from studying a single lease block. One study area focused on two adjacent salt withdrawal basins to assess the processes that are shaping the flanks of the basins, the processes affecting sedimentation in the basin floors, and to compare the deeper structures and surficial processes between the basins. The second study area focused on three salt domes, the processes associated with them, and how they affect the shallow subsurface stratigraphy. Initial observations suggest that most of the surface and shallow subsurface geohazards are associated with the flanks of salt structures. Here active salt movement generates faults along which hydrocarbons can escape to the seafloor, and tectonic oversteepenning generates slope failures.
Foster, David, 2005, L15_27SP.SHP - Shot points (60 shot interval) for CHIRP seismic profiles 15-27 collected on GYRE cruise 99002: Open-File Report 2005-1071, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.This is part of the following larger work.Online Links:
Twichell, D.C., Cross, V.A., Paskevich, V.F., Hutchinson, D.R., Winters, W.J., and Hart, P.E., 2005, GIS of selected geophysical and core data in the northern Gulf of Mexico continental slope collected by the U.S. Geological Survey: Open-File Report 2005-1071, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.Online Links:
This is a Vector data set. It contains the following vector data types (SDTS terminology):
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000000. Longitudes are given to the nearest 0.000000. Latitude and longitude values are specified in Decimal degrees.
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257222.
Sequential unique whole numbers that are automatically generated.
Coordinates defining the features.
Character string containing the name of the survey line
| Range of values | |
|---|---|
| Minimum: | 6 |
| Maximum: | 11112 |
| Units: | integer count |
| Resolution: | 1 |
| Range of values | |
|---|---|
| Minimum: | 1020941 |
| Maximum: | 1041544 |
| Units: | integer |
| Resolution: | 1 |
| Range of values | |
|---|---|
| Minimum: | -91.876524 |
| Maximum: | -91.572242 |
| Units: | decimal degrees |
| Resolution: | .000001 |
| Range of values | |
|---|---|
| Minimum: | 27.702160 |
| Maximum: | 27.821626 |
| Units: | decimal degrees |
| Resolution: | .000001 |
| Range of values | |
|---|---|
| Minimum: | 218.2 |
| Maximum: | 918.9 |
| Units: | meters |
| Resolution: | 0.1 |
| Range of values | |
|---|---|
| Minimum: | 200 |
| Maximum: | 2000 |
| Units: | meters |
| Resolution: | 1 |
| Range of values | |
|---|---|
| Minimum: | -120.3214286 |
| Maximum: | 141.35 |
| Units: | degrees |
| Resolution: | .0000001 |
| Range of values | |
|---|---|
| Minimum: | -179.1 |
| Maximum: | 178.3 |
| Units: | degrees |
| Resolution: | .1 |
| Range of values | |
|---|---|
| Minimum: | -91.865667 |
| Maximum: | -91.571800 |
| Units: | decimal degrees |
| Resolution: | .000001 |
| Range of values | |
|---|---|
| Minimum: | 27.708310 |
| Maximum: | 27.822100 |
| Units: | decimal degrees |
| Resolution: | .000001 |
| Range of values | |
|---|---|
| Minimum: | 1 |
| Maximum: | 26 |
| Units: | integer count |
| Resolution: | 1 |
(508) 548-8700 x2271 (voice)
(508) 457-2310 (FAX)
dfoster@usgs.gov
This GIS data layer shows the shot points along which SIS-1000 chirp subbottom profile data and sidescan sonar data were collected. The shot point interval varies from 59 to 61. The navigation has been corrected to show the SIS-1000 vehicle location rather than the ship location (Foster and others, 2000).
Foster, D.S., Twichell, D.C., Danforth, W.W., Irwin, B.J., Nichols, D.R., and O'Brien, T.F., 1999, Archive of SIS-1000 CHIRP subbottom data, collected during USGS cruise GYRE 99002 Gulf of Mexico, 9-22 April, 1999: Open-File Report 99-586, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.
Person who carried out this activity:
508-548-8700 x 2271 (voice)
508-457-2310 (FAX)
dfoster@usgs.gov
Data sources produced in this process:
Lines 15 and 16 of Mosaic Area Two do not have acoustic ranging data available. The SEG-Y file headers contain ship position (UTM zone 15). The ASCII shotpoint navigation files contain geographic coordinates for sonar fish position obtained by comparing fish depth and layback distance from lines 17 and 18 where acoustic slant ranges were good. Because lines 15 and 16 are in relatively shallow water and fish depths did not exceed 300 meters, this method of estimating layback is reasonable. Based on the layback verses fish depth analysis of lines 15 and 16, the horizontal errors may be as much as 50 meters. Layback depends on other variables other than fish depth. Ship speed was not considered in the analysis.
Lines 17 and 18 of Mosaic Area Two were determined to have good acoustic slant range, thus the calculated layback was used to obtain sonar fish position. The ASCII shotpoint contain geographic coordinates for sonar fish position as well as ship position. The SEG-Y file headers contain ship position (UTM zone 15).
Lines 19-27 of Mosaic Area Two had unreliable slant range information due to the length of fish layback and deeper water. Laybacks were estimated for lines 19 and 20 based on the analysis of fish depth and layback in lines 17 and 18, but when fish depths exceeded 300 meters the error in this method increases. Instead another method of comparing water depth from the sonar fish (fish depth and altitude combined) to NOAA gridded Seabeam bathymetry. Offsets between the bathymetry and the water depth from the fish showed the apparent layback for each line. Using this method, the layback was estimated and the corrected navigation compared to the gridded bathymetry. This showed good correlation between water depths and sea floor features. Furthermore, the estimated layback was used to navigate the sidescan sonar data in the mosaicking process, and features on adjacent sidescan sonar lines matched well. The ASCII navigation files contain ship position as well as layback positions. The SEG-Y file headers contain ship position (UTM zone 15).
The processing was done by David Foster, and is summarized in Foster and others (2000)
Person who carried out this activity:
(508) 548-8700 x2271 (voice)
(508) 457-2310 (FAX)
dfoster@usgs.gov
Person who carried out this activity:
(508) 548-8700 x2271 (voice)
(508) 457-2310 (FAX)
dfoster@usgs.gov
Person who carried out this activity:
(508) 548-8700 x2271 (voice)
(508) 457-2310 (FAX)
dfoster@usgs.gov
Foster, D.F., Twichell, D.C., Danforth, W.W., Irwin, B.J., Nichols, D.R., and O'Brien, T.F., 2000, Archive of SIS-1000 CHIRP subbottom data collected during USGS cruise GYRE 99002 Gulf of Mexico, 9-22 April, 1999: Open-File Report 99-586, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.
The ship was navigated with differential GPS, and location of the deep-towed sidescan vehicle was calculated in a variety of ways. In shallow water an acoustic ranging system was used in concert with vehicle depth and ship heading to compute vehicle location. In deeper water depths where the acoustic ranging system did not work, vehicle location was calculated in one of two ways. In some places the amount of wire out was used in place of the acoustic range. In other places, vehicle location was calculated by measuring the offset between features observed on the NOAA multibeam bathymetry and the tow vehicle echo sounder. This offset was measured at several points along each track and was used to compute vehicle navigation. Vehicle location was interpolated between the measured points. Comparison of features on the surface-towed seismic data with the same features on the deep-towed seismic data indicates that the offset mostly is less than 100 m.
No additional checks for topological consistency were performed on the data. No duplicate features are present.
Are there legal restrictions on access or use of the data?
- Access_Constraints: None
- Use_Constraints:
- 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.
(508) 548-8700 x2266 (voice)
(508) 457-2310 (FAX)
dtwichell@usgs.gov
Downloadable Data
Although this data set has been used by the U.S. Geological Survey (USGS), no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS 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: | The SHP file contains the geospatial data. The SHX file contains the index of the geospatial data. The DBF file contains the attribute data in dBase format. The PRJ file contains the coordinate system information (optional). The AVL file contains the legend information (optional). The SBN and SBX files contain the spatial index of the geospatial data (optional). The XML file contains the metadata describing the data set <data set name>.shp.xml. An ASCII version of the metadata file. A browse graphic showing the data layer coverage and extent (optional). in format SHP (version 3.3) ESRI point shapefile Size: 0.079 |
|---|---|
| Network links: |
<http://pubs.usgs.gov/of/2005/1071/data/seismic/1999/chirp/nav/l15_27sp.zip> |
| Media you can order: |
DVD-ROM
(Density 4.75
Gbytes)
(format UDF)
|
The data are available in Environmental Systems Research Institute (ESRI) shapefile format. The user must have ArcGIS® or ArcView® 3.0 or greater software to read and process the data file. In lieu of ArcView or ArcGIS, the user may utilize another GIS application package capable of importing data. A free data viewer, arcexplorer, capable of displaying the data is available from ESRI at www.esri.com.
(508) 548-8700 x2266 (voice)
(508) 457-2310 (FAX)
dtwichell@usgs.gov
