Other ID: 85 Leg 1; FRNL 85-1
Organization(s): USGS, Woods Hole Coastal and Marine Science Center
Principal Investigator(s): Bonnie McGregor
Affiliate Investigator(s): Guy Rothwell - IOS
Data Type(s): Electro-Magnetic: Magnetics, Location-Elevation: Navigation, Seismics: Air Gun / Water Gun, Seismics: Sub Bottom Profiler, Sonar: Sidescan, Sonar: Single Beam
Scientific Purpose/Goals: The purpose of this cruise was to map the sea floor between approximately the shelf edge and the seaward limit of the EEZ using the GLORIA system owned and operated by IOS. Leg 1 focused on the western half of the Gulf of Mexico seaward of Texas and Louisiana abutting GLORIA coverage from a 1982 survey. This portion of the Gulf is dominated by salt tectonics. The area mapped with GLORIA during this leg was 45,000 sq nautical miles.
Start Date: 1985-08-07
Start Port/Location: Miami, FL
End Date: 1985-09-03
End Port/Location: New Orleans, LA
Equipment Used: 3.5 kHz, Air gun, 10 kHz Bathymetry, GLORIA sidescan, Marine magnetometer, ABC navigation system, Loran-C, Single channel hydrophone
Information to be Derived:
Summary of Activity and Data Gathered: Hurricane Denny resulted in a loss of 13 hours of operation on August 14, 1985, and Hurricane Elena delayed arrival in New Orleans one day, from September 2 to September 3, 1985. The impact that the warm surface water and strong thermocline present in the Gulf of Mexico in the summer would have on the range of the GLORIA system was not realized. Although GLORIA was run at a 30 sec. repetition rate, 45 km swath width, the maximum swath width actually obtained was 8 km in approximately 1000 m of water. This required reducing the trackline spacing and adding additional tracklines and limited the effort in water depths shallower than 1000 m. Initially much time was spent getting all equipment operational. The GLORIA system suffered from logging problems resulting in a loss of approximately 24 hours of data during the cruise. The longest continuous down time period was 12 hours. Dirt particles in the air being pulled across the recording heads by the air conditioning system appears to have been the major problem. The air gun system was down a total of approximately 24 hours due to compressor, streamer and gun problems. The longest continuous period of down time was 7 hours. The magnetometer required 3 days to get operational initially but this was partly a result of its lower priority. A new computer system was installed for this cruise. Most of the leg was required to get the system operating properly. Navigation has to be plotted by hand for the duration of the cruise. Summary data plots for the cruise, however, were completed with the computer system at the end of the cruise. The data in the western Gulf are very interesting geologically. The Sigsbee Escarpment can be identified on the sonographs with piles of debris in places at its base. A continuous channel can be traced from the shelf edge through the diapir province of the slope, forming a reentrant in the Sigsbee Escarpment, and then meandering seaward across the rise into the deep water of the Gulf. The fan of the Rio Grande has a braided channel system and features which are interpreted to be bedforms on it. Similar bedforms are present seaward of the Sigsbee Escarpment suggesting that strong bottom currents are present in the region.
Staff: Dann Blackwood
Notes: Original Center People field contained: Dann Blackwood - photographer, Woods Hole.
western Gulf of Mexico, Texas, Louisiana, United States, North America, North Atlantic;
Lubinski, D.J., and Twichell, David C., 1989, Magnetic and bathymetric data from R/V FARNELLA Cruises FRNL85-1, 85-2, and 85-3 in the U.S. Gulf of Mexico EEZ: 6 URL: http://pubs.er.usgs.gov/publication/ofr89156, download PDF.
Twichell, D., Paskevich, V.F,, 1996, GLORIA sidescan-sonar field data and navigation data collected in the Gulf of Mexico during R/V FARNELLA cruises in 1982 and 1985: URL: http://woodshole.er.usgs.gov/publications/of96-707/OPR96_707/INTRO.HTM.
Twichell, D.C., Cross, VeeAnn A., Paskevich, Valerie F., Hutchinson, Deborah R., Winters, William J., and Hart, Patrick E., 2007, GIS of selected geophysical and core data in the northern Gulf of Mexico continental slope collected by the U.S. Geological Survey: URL: http://pubs.usgs.gov/of/2005/1071/.
Twichell, D.C., McGregor, Bonnie A., and Lubinski, David J., 1989, Seismic-reflection data from R/V FARNELLA Cruises FRNL82-7, FRNL85-1, FRNL85-2, and FRNL85-3A in the U.S. Gulf of Mexico EEZ: U.S. Geological Survey Open-File Report 89-549, 7 p., URL: http://pubs.er.usgs.gov/usgspubs/ofr/ofr89549, download PDF.