FILDANI, ANDREA, Stanford University, Stanford, CA, and USGS, Menlo Park, CA; and WILLIAM R. NORMARK, and JANE A. REID, U. S. Geological Survey, Menlo Park, CA

Abstract: Which Came First: Monterey Canyon or Fan? Elemental Architecture of Central California Turbidite Systems

The Monterey Canyon and submarine fan, although comprising one of the largest turbidite systems off North America, is unusual in not having a major river system to supply sediment. To understand better the depositional history of turbidite systems offshore of the Monterey Bay area, we focus on the key architectural elements and acoustic facies of the turbidite systems, including the channel, overbank, and lobe elements. This analysis is based on integration of all available seismic-reflection and 3.5 kHz profiles, GLORIA side-looking-sonar images, multibeam bathymetric data (limited to the eastern part) and stratigraphic control provided by deep outcrop samples obtained by submersible.

The morphology of the modern Monterey fan is dominated by the overbank element of the Upper Turbidite Sequence (UTS). The UTS forms half of the fan thickness (-500m) near the base of the continental slope, but is limited in areal extent to the area east of 124<deg>W. Submersible samples of outcrops from the middle of the UTS suggest the entire sequence is less than 500 ky. The UTS includes at least four channel-levee systems that show a complex history of channel switching resulting from autocyclic and tectonic influences. Not all the channel-levee systems in the UTS were fed by the Monterey Canyon, and extensive downcutting in the channel presently contiguous with the canyon partially obscures the expression of the older channels. The UTS is underlain by the much more extensive Lower Turbidite Sequence (LTS) that comprises a series of channel, overbank, and lobe elements. Over much of the Monterey fan area, the LTS is about the same thickness as the thickest part of the UTS. The LTS has no clear feeder source but the main pattern of the channel systems suggests sources unrelated to modern Monterey Canyon. Thus, the modern Monterey fan is only one component of a complex turbid itesystem offshore central California.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California