H. GARY GREENE, Moss Landing Marine Laboratories, Monterey Bay Aquarium Research Institute (MBARI), Moss Landing, CA; and NORMAN H. MAHER, MBARI, Moss Landing, CA

Abstract: Fluid Induced Mass Wasting in the Monterey Bay Region: Evidence from Recently collected EM300 Bathymetry Data

Recently collected Simrad EM300 (30 kHz) swath bathymetry in the Monterey Bay region reveals a continental slope, including submarine canyon walls, that are extensively deformed by mass wasting. Along the Ascension slope, north of Ascension Canyon, the continental shelf and slope exhibits youthful groundwater geomorphology, including rills, pipes, pits (pipe roof collapses or sinks), slumps, thin sheet flows and outwash plains. Locally, submarine gullies head at scallop-like (or cusp-like) features that we interpret to be fluid-induced slumps and appear to result from fluid sapping. Chemosynthetic communities are associated with some of these features.

Anomalous mounds found along the distal edge of the Ascension and Carmel-Point Sur shelves may result from carbonate buildup. These features are similar to fresh water produced carbonate mounds and blisters found on the southern Monterey Bay shelf. We speculate that many of these shelf depth (90-100 m) carbonate deposits were constructed by the flow of meteoric water from land to the seafloor along faults and aquifers.

Fluid-induced mass wasting were identified on slopes south and west of the allochthonous granitic Salinian block margin in areas of transpression where compressional squeezing of fluids take place. Two ridges, Smooth Ridge and Sur Ridge, are being tectonically elevated resulting in mass wasting along their bases. In addition, several areas of incipient fluidinduced seafloor failure exist along the crest of Smooth Ridge. South of Sur Ridge over 1500 pockmarks (100-200 m in diameter and 10-20 m deep) indicate extensive past gas and fluid venting.

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