Summary for Field Activity Number 2010-019-FA

Area of Operations: Mobile Bay, Alabama, Gulf of Mexico, United States, North America, North Atlantic

Dates: July 17, 2010 to July 21, 2010

Objectives: Conduct a reconnaissance mapping of the Holocene stratigraphy of Mobile Bay, AL to provide the framework for a coring program directed at reconstructing the recent history of the bay.

Type of Activity: Seismic profiling

Information to be derived: High-resolution seismic profiling

Summary: Five day-trips were completed aboard the R/V GILBERT in the southern half of Mobile Bay, AL to collect high-resolution seismic data to map the distribution and thickness of Holocene sediment that has accumulated in the bay. The EdgeTech 512i chirp subbottom system was used to acquire the data along tracklines spaced 1.5-7 km apart. The St. Pete group had just built a pontoon system for deploying their 512i (identical to the one the Woods Hole group uses), and this cruise was the first time it was used. The weather was excellent, and the BP oil spill had only a limited impact on our survey in the bay. Some of our lines near the mouth of the bay had to be shortened or shifted to avoid vessels associated with the oil spill cleanup. The data are of good quality - at least once we figured out how to keep the 512i out of the wash from the jet drive. The other problem we faced is that there are large patches where gas is pervasive in the bay sediments. Where gas was absent we could easily image the late Pleistocene lowstand surface, but where gas was present we could only image the upper 3-7 m of sediment before the recod was wiped out due to the gas.

USGS Project Number: 2921-E3S02 - Project Description

Contact: Dave Twichell (dtwichell@usgs.gov)