Area of Operations: southern Chesapeake Bay, United States, North America, North Atlantic
Dates: October 15, 1984 to October 26, 1984
Chief scientist: Steve Colman
C.H. Hobbs, III - VIMS
Objectives: Collection of high-resolution seismic reflection and sidescan sonar data in order to define the geology and shallow structure of the Chesapeake Bay.
Type of Activity: Seismic profiling;
Information to be derived: Seismic reflection and sidescan sonar data
Summary: All equipment performed smoothly and satisfactorily with the following exceptions: (1) the ORE power supply failed (blown capacitor) during the second week of the cruise and was replaced by the EG&G unit; and (2) intermittent minor problems with the key signal from the EPC recorders occurred and were very difficult to trace; the cause seemed to be build-up of carbon and moisture inside the recorder and an incorrect ground connection in a switching box. The cruise was very successful, due in part to excellent weather and to little equipment-related down-time. More than 700 km (380 nm) of seismic profile lines were obtained in 11 days at sea. Local problems with penetration were encountered, apparently due to gas in the sediments or to hard substrates (packed sand or oyster reefs). However, penetration depths were typically about 75 m (0.1 seconds two-way travel time), allowing excellent resolution for the entire Quaternary section and for the upper part of the Tertiary section. On-board observation of the records suggests that cyclic incision and deposition related to sea level changes is recorded in the Quaternary sediments, and that filled paleochannels are commonly unrelated to present bathymetry. The sidescan sonar records showed most of the bay bottom to be smooth and featureless, but local areas of distinct bedforms were encountered, especially near the present channels.
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