28 



FIGURE 27.— USGS 1971 Vnitedgeo I surveys: Leg 

 1, Bay of Campeche, and Leg 2, Margin of the 

 Yucatan Peninsula. 



ships, were completed by the U.S. Geological Survey (USGS) and 

 NOAA. These studies were made as part of both continental mar- 

 gin and sea floor dynamics projects. Underway bathymetry, gravity, 

 magnetics, and seismic reflection data were collected, and cores, 

 dredges, and sonobuoy records were obtained on several cruises. 

 Satellite navigation was used for position control on each cruise. 

 Table 1 summarizes the trackline miles of geophysical data and 

 related samples obtained during each study. 



In addition to the NOAA and USGS geophysical surveys, sev- 

 eral other institutions started work on Seabed Assessment studies 

 in 1972; projects were initiated that included compiling, evaluat- 

 ing, and reformatting geological and geophysical data collected 

 during previous years by various institutions. 



TTie following description of each completed study is based on 

 data reports, abstracts, and other information received from prin- 

 cipal investigators. 



USGS Unitedgeo I Surveys 



TTie work performed by the USGS consisted of six projects, 

 each designed to study a different problem and each limited to 

 separate legs of an ocean survey completed by the chartered ship 

 Unitedf>eo I. The six legs of the cruise were completed between 

 June and December 1971. USGS has published data reports con- 

 taining copies of the acoustic reflection records for the six legs 

 (see Seabed Assessment Bibliography). 



Leg 1, Bay of Campeche. TTiis survey was made in the .southern 

 part of the Bay of Campeche; an east-west trackline spacing of 

 about 9 km. was used (fig. 27). The region covered includes the 



north-trending sedimentary folds in the western part of the survey 

 area and a province of salt domes in the eastern part. 



Results to date include: (1) Correlation of prominent fold axes 

 and faults from track to track in the western part of the survey, 

 (2) evidence that the late Cenozoic Mexican volcanic belt appar- 

 ently ends abruptly on the continental shelf of the Bay, and (3) 

 evidence of salt intrusions (salt domes and anticlines) both inside 

 and outside the main tectonic belts. 



Leg 2, East Margin Yucatan Peninsula. This study (fig. 27) was 

 made along the coasts of Mexico and Briti.sh Honduras. The ob- 

 jectives were to study the structural evolution of the continental 

 margin east of the Yucatan Peninsula and to determine the history 

 and relationships of tectonic features, including the Yucatan Basin 

 and the Cayman Ridge and Trough. TTie possibility of stratigraphic 

 links between Cuba and the Yucatan Peninsula was also explored. 

 Results to date include: the obtaining of critical information (as 

 a result of dredging) about the types of rocks and sediments that 

 form major sea floor features, and the identification of an elongate 

 set of ridges parallel to the continental border. (These ridges ap- 

 pear to be belts of relatively resistant metamorphosed sedimentary 

 rocks bordering an elongated basin partially filled with sediments.) 



Leg 3, Eastern Greater Antilles. This survey (fig. 28) was made 

 in a region of the Atlantic Ocean and Caribbean Sea that includes 

 the Muertos Trough (south of Puerto Rico), the Anegada Trough 

 (where several linear tectonic elements seem to meet), and an area 

 where the faulting associated with the Puerto Rico Trench appears 

 to change from underthrusting to strike slip faulting. 



16 



