USGS Open-File Report 03-474, G1-03-GM, Gas Hydrates Cruise Report, R/V Gyre, 1-14 May 2003, Northern Gulf of Mexico
Title Page
ABSTRACT
Introduction
Acknowledgments
Geologic Settings
Cruise Objectives
Cruise Strategy
Instrumentation
Data Processing
Data Handling
Marine Mammal Mitigation
Operational Summary
Success in Meeting Objectives
Summary
References
Appendices
1. Multichannel
Line Statistics
2. Summary of
Digital Data
3. Marine
Mammal
Documents
4. Science
Roster
5. Ship Roster &
Specifications
6. Photo Gallery
Cruise Strategy
The two study areas posed different imaging challenges. Keathley Canyon 195 had evidence for a low-amplitude BSR in proprietary industry data, and therefore offered the opportunity to identify a mappable horizon and relate it to the surrounding geology. Atwater Valley 14, again from proprietary industry data, contained three possible mound/vent sites that were targets for potential hydrate formation, but no obvious BSR. Therefore, the strategy for mapping each survey area was different: for Keathley Canyon, the objective was to acquire a grid of data and define the regional extent of a possible BSR. Additional detailed (100 m spacing) lines were added to look at specifics of the BSR and at a possible mound/vent within the study area. For the Atwater Valley study area, the objective was multiple crossings over the three mound/vent sites from different azimuths and with close (100 m) line spacings.
The chronology of the cruise, showing the time spent in each survey area and doing the ties to other well and seismic information are given in Table 1.
Table 1. Cruise Chronology| Julian Day1 | Work Area | Seismic System | Strategy |
|---|---|---|---|
| 121-122 | Transit | None | Depart Galveston and transit to Keathley Canyon 195 Area |
| 123 | Keathley Canyon | All | Test single channel seismics, multichannel seismics and optimize acquisition parameters |
| 123-128 | Keathley Canyon | 13/13 in3 GI Gun; Knudsen | grid lines, detailed surveys, and well tie |
| 128-129 | Keathley Canyon /Garden Banks | 24/24 in3 GI Gun; Knudsen | Profile along LSU-B and tie to 1999 USGS data |
| 129-130 | Transit | None | Transit to Atwater Valley 14 area |
| 130-133 | Atwater Valley | 13/13 in3 GI Gun; Knudsen | Detailed grids in Atwater Valley and tie to Mississippi Canyon 802 Marion Dufresne (2002) core site |
| 133-134 | Transit | None | Return to Galveston |
1 G1-03-GM lasted for 14 days from 1-14 May, 2003. Julian Day 121 corresponds to 1 May.
Because of the large number of short lines anticipated on the cruise, a naming convention was used in which the line number always incremented by one, but the alpha-numeric leader would change depending on the region being surveyed (KC = Keathley Canyon, GB = Garden Banks, AV = Atwater Valley, MC = Mississippi Canyon). Hence line KC60 (for Keathley Canyon 60) was followed sequentially by line GB61 (for Garden Banks 61). The test lines at the start of the cruise were an exception. For the test multichannel water gun line, the multichannel data were labeled Test2. The test GI gun line was initially called test4, but renamed to KC1 when it was decided to use the GI gun as the primary source for the survey. The Knudsen bathymetry files for KC1 were labeled L1.