Showing papers by "Daniel L. Orange published in 1999"

Widespread fluid expulsion on a translational continental margin: Mud volcanoes, fault zones, headless canyons, and organic-rich substrate in Monterey Bay, California

Abstract: Remotely operated vehicle (ROV)-based mapping of tectonic features, zones of anomalous reflectivity, and geomorphic targets in Monterey Bay, California, demonstrates the regional abundance of fluid expulsion along the active transform margin between the Pacific and North American plates. Cold seeps—extant communities characterized by chemosynthetic bivalves, bacterial mats, and rare tubeworms—are the surface manifestations of present-day fluid expulsion of sulfide- and methane-rich fluids, whereas slabs, veins, and chimneys of authigenic carbonate represent regions of either dormant methane-rich fluid expulsion, or areas where the present rate of flow is too low to support chemosynthetic fauna. We have found both active and dormant fluid seepage along fault zones, at the surface expression of mud volcanoes, on organic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The fluid egress at these sites may be driven by a combination of (1) pore-space reduction caused by rapid sedimentation and/or tectonic compaction related to residual Pacific–North America compression, and (2) increased buoyancy due to a decrease in pore-fluid density related to diagenesis and/or catagenesis at depth. Although provocative, the relationship between topographically driven aquifer discharge and sea-floor fluid expulsion remains speculative for Monterey Bay. The widespread distribution of fluid expulsion features controlled by a variety of conduits in Monterey Bay implies that cold seeps may be common features on translational margins.

Fluid Flow in the Offshore Monterey Bay Region

Abstract: Fluid flow out of the seafloor offshore Monterey Bay region is extensive. To date 16 major active and ancient, or dormant, seep sites have been identified and many of these sites are composed of smaller sites too numerous to map at a regional scale. These seeps have been identified by the presence of chemosynthetic communities that are primarily composed of chemoautotrophic organisms or by carbonate deposition and buildups. Of the 17 identified sites, 9 active cold seep sites support living chemosynthethic communities. Seven major dormant seep sites have been identified based upon the presence of carbonate deposits or buildups. Identified seep sites are primarily concentrated along fault trends associated with the boundary of the Salinian block or Palo Colorado-San Gregorio fault zone, and along the lower flanks and crests of tectonically uplifting slopes. A combination of transpressional squeezing and overburden pressures, vertical advection through hydrocarbon and organic-rich sediment, and seaward flow of meteoric waters supply fluids to the seep sites.