| Summary |
From July 24-31, 2009 the USGS Woods Hole Science Center's Sea Floor Mapping Group, aboard the R/V RAFAEL, collected 66 lines (totaling 192 km) of seismic reflection profile data in the Belfast Bay, ME pockmark field. Personnel included Emile Bergeron, William Danforth, Barry Irwin, and USGS volunteer and Principal Investigator Laura Brothers. Lines were collected with an east-west orientation every 200 m over 29 km2. Tie lines were collected perpendicular to the survey lines. In the northwest quadrant of the survey area, tie lines were collected at 200 m spacing to further resolve the geometry of seismic reflectors of interest (i.e. a proposed methane sourcebed, and paleo pockmarks). Seismic reflection profile data were collected using an EdgeTech FSSB 424 seismic profiling system operating at frequencies of 4-24 kHz. The data were acquired in EdgeTech Discover program, and saved in EdgeTech's JSF format. The data were then converted to SEG-Y format using custom USGS software. Data were processed in SioSeis, SeismicUnix, and will later be interpreted in Landmark Graphics software. Our objective was to gather seismic data where we had already acquired swath bathymetry data, but did not have corresponding subsurface data. In this latest initiative we identified seismic reflectors observed in other previously surveyed portions of the field. We found that recently mapped surficial flute-like features located in the southern portion of the field are structurally controlled by irregular bedrock. We observed the southern terminus of a proposed organic layer, potentially representing a sea-level lowstand, and identified potential coring sites. Also, subsurface data suggest that paleo pockmarks or failure features may exist at the Holocene/Pleistocene unconformity in the periphery of the main channel. This is the first time any such features have been observed and the geometry of the reflectors must be further examined to confirm the validity of this interpretation. With survey 09037 we completed a multiyear project that characterizes the spatial, morphological, and subsurface variability of the field. |
