Anatomy of Quaternary Conception Submarine Fan, Santa Barbara Basin, California

Peter J. Fischer, Denvir R. Thor, Victor B. Cherven

The Conception submarine fan is a small late Quaternary radial fan that lies in the northwestern corner of the Santa Barbara basin. Our interpretation is based upon an extensive data set consisting of high resolution to digitally processed profiles, side-scan sonar records, borings, cores, and surface samples.

Four major seismic sequences averaging 40 m thick near the middle-lower fan are defined by the borings and the processed seismic profiles. The major bounding surfaces of these elements are the sea floor and four unconformable (sand or mud) contacts. Using Miall's 1985 element classification scheme, the paleo-sequence boundaries are seventh-order surfaces and represent depositional pulses of coarser clastics during low sea level stands. During these low stands, the fan prograded southeasterly by the offset stacking of elongate (1-3 km wide × 17 + km long) fan lobes as shown by sequence isopach maps. Near the top of these four major sequences or elements are sixth-order surfaces that are mud/sand contacts and represent high sea level stand deposition when the influx of coarse clast cs was cut off. Within these major elements, fifth-order surfaces mark fan channel margins, individual depositional lobes, and interchannel areas, which were mapped using high and intermediate resolution seismic profiles, and on the fan surface, side-scan sonar. Fourth-order surfaces, including lateral accretionary fill complexes and mud channel plugs, are most readily defined within channel-fill complexes of the uppermost sequence. Within both, the channel-fill and depositional lobes internal reflectors define third-order surfaces that subparallel the boundaries of lateral accretion complexes. Third-, second-, and first-order surfaces are recognized in cores, especially x-radiographs of core slabs.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.