USGS CMG T-1-69-BS Metadata

To provide the field collections
necessary to interpret the stratigraphic history of the sediments
deposited during a major marine transgression across a continental
shelf-coastal plain complex. The area represents an excellent model
for the study of transgressive sedimentary sequences because of its
simplicity in sediment thickness, age, and marker horizons. The
sediment, predicted to average no greater than 10 to 15 m, can be
collected fully with presently available coring equipment where the
sediment is soft, and yet it is thick enough to provide detail of
sedimentologic events over the 20,000-year Holocene transgression.
Because of the importance of the area covered by this cruise to the
studies of the Bering Land Bridge and the migration of man to the
New World, it is hoped that it will be of use in interpreting the
paleotopography of the land bridge surface and the times of
inundation.

stratigraphic

Shallow-penetrating continuous seismic profiling (using a 3.5-khz
system, 150-joule sparker, and 1000- and 2000-joule air guns) and precision echo
sounding were planned to permit continuous monitoring of the changing thickness
of unconsolidated sediment. The 3.5-khz system was never successfully operated
because of malfunctioning of the equipment as supplied by the manufacturer. The
air gun was operated over about half of the total track, and the 150-joule
sparker was operated almost continuously. The precision echo-sounding system was
operated continuously. Continuous reduction of the data permitted tentative
location of buried Pleistocene drainage channels. A great deal of reduction and
interpretation remains, however, because the upper 15 m of the sediments
contained as many as six reflectors in some areas. Wherever the subbottom
reflectors indicated a thickened section of unconsolidated sediment, the bottom
was cored at least to the first major reflector and, where possible, through a
number of reflectors. As was the case during past cruises, the suspected
interfluves were covered by thinner sediment layers that were significantly more
difficult to core. The area east of 172 degrees W was apparently covered by more
recent coarser grained sands and silts, which make coring difficult and which
reduce the amount of subbottom penetration of acoustic energy. The buried
channels detected in the western part of the survey area were cored; the length
of the piston core barrel was varied at each station until maximum penetration
was attained. Additionally Van Veen or Shipek grab samples and gravity cores
were obtained at no greater than 56-km intervals along the cruise track.
Transmissometer measurements of suspended sediments were made along the leg
between Nunivak and Northeast Cape, St. Lawrence Island. One 20-foot piston core
assembly and one transmissometer were lost. Approximately 7200 km of track were
run, with the precision echo sounder continously in use. Approximately 4700 km
of sparker profiles and 2200 km of air-gun profiles were made.158 stations were
occupied, with grab samples collected at all stations and gravity cores
collected at 92 stations. Piston cores were collected at 44 stations.

Cruise conducted by the University of Washington
   Department of Oceanography, Seattle, Washington. Information is
   from the "Preliminary Report RV Thomas G. Thompson Cruise 42" by
   J.S. Creager and D.A. McManus, M69-80, September 1969