| Structural
Control of the Spatial Distribution of
Hydrocarbon Seeps in the Northern Santa Barbara Channel, California
E C Bartsch (Inst. for Crustal Studies, and Dept. of Geological Sciences, Univ. of Calif., Santa Barbara, CA 93106-1100); L D Gurrola (Inst. for Crustal Studies, and Dept. of Geological Sciences, Univ. of Calif., Santa Barbara, CA 93106-1100); R D Francis (Dept. of Geology, Calif. State Univ., Long Beach 90840) D C Quigley, (Inst. for Crustal Studies, and Dept. of Geological Sciences, Univ. of Calif., Santa Barbara, CA 93106-1100) J S Hornafius (Inst. for Crustal Studies, Univ. of Calif., Santa Barbara, CA 93106-1100) B P Luyendyk, (Inst. for Crustal Studies, and Dept. of Geological Sciences, Univ. of Calif., Santa Barbara, CA 93106-1100) Natural hydrocarbon seeps in the northern Santa Barbara Channel of southern California have been mapped in detail using a 3.5 kHz sonar source and differential GPS. Geologic structures in the study area were identified using dart core data, seafloor beddin attitudes, 3.5 kHz and 1 kJ sparker seismic reflection data. Two east-west trending seep fields in the study area correlate to fold axes; the South Ellwood anticline and the Coal Oil Point fold complex. The South Ellwood anticline is mapped for nearly 30 km, 3 km offshore and controls the most intense seepage in the study area. Oil platform Holly lie above the anticline and produces oil from the Monterey Formation reservoir at 900-1350 meters subsea. Oil and gas in the Monterey Formation are trapped by the overlying Sisquoc formation cap rock, which is exposed on the seafloor. Oil and gas migrate through the cap rock along fractures on the anticlinal axis. Bore hole data suggest that maximum seep intensity following the trend of the axial surface correlates to locations where the Sisquoc/Monterey formation contact is more shallow. To the north of the South Ellwood anticline, a similar yet shorter linear trend of seeps is controlled by what is interpreted to be the Coal Oil Point fold complex. This fold complex consists of two east-west trending anticline- syncline pairs and can be traced for approximately 8 km, a few hundred meters offshore. Seepage appears to occur where anticline axes an synclinal limbs intersect the seafloor. More intense seepage occurs where axial surfaces are cut by north east-trending cross faults. Therefore, we conclude that seepage in the northern Channel is controlled by mostly folding but also faulting of the reservoir cap rock. AGU listing: |