USGS CMG T-51-70-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. The Chukchi Sea portion of the cruise was made to
delineate further the details of a marine "delta" discovered north of
Bering Strait in 1957. The southern Bering Sea portion was made to
complete the reconnaissance survey of the Alaskan side of the
Bering Sea. Deep seismic reflection measurements were made to
study the deep structure and two anchor stations were occupied for
investigation of bottom currents and sediment transport.

stratigraphic, depth to basement

Shallow-penetrating continuous seismic profiling (using a 4.0-khz
system, 150-joule sparker, and 1000- and 2000-joule air guns) was planned to
permit continuous monitoring of the changing thickness of unconsolidated
sediment. The air gun and sparker were used alternatively depending upon the
depth to basement. 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 of the southern Bering Sea approximately delineated
by the piston core locations is apparently covered by more recent coarser
grained sands and silts, which make coring difficult to impossible and which
reduce the amount of subbottom penetration of acoustic energy. The buried
channels detected in the western and southern portions ofthe survey area were
cored; the length of the piston core barrel was varied at each station until
maximum penetration was attained. Additionally Van Veen grab samples were
obtained and gravity cores were attempted at no greater than 56 km intervals
along the cruise track in water less than 200 m deep in the southern Bering Sea.
In order to delineate further the extent and nature of the marine "delta"
evidently extending northward from Bering Straits and to add further information
bearing on the problem of sediment transport from the Bering to Chukchi seas
additional subbottom reflection profiles and piston cores were collected in the
delta area and two anchored current measuring stations were occupied. In a
cooperative study with Dr. David Scholl of the USGS, four subbottom profiling
tracks were run across the continental slope south of the Pribilof Islands and
samples were collected at three dredge stations. Approximately 9450 km of track
were run, with 4.0 khz continuous seismic profiling system in operation from
Station 1 to Dutch Harbor (8861 km).  Approximately 4780 km of sparker profiles
and 3627 km of air gun profiles were made.  Seismic refraction measurements were
made a seven locations, using sonobuoys and the sparker and air gun as sources.
A total of 154 stations were occupied, with grab samples collected at all but
three dredge stations.  Dredge samples were collected at three stations, box
cores at eight stations, and piston cores at 24 stations.

Cruise conducted by the University of Washington Department of
Oceanography, Seattle, Washington. Information is from the "Preliminary Report
RV Thomas G. Thompson Cruise 51" by J.S. Creager and D.A. McManus, M70-82,
September 1970.