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

Remotely operated vehicle (ROV)-based mapping of tectonic features, zones o f anomalous reflectivity, and geomorphic targets in Monterey Bay, Californi a, 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 ex pulsion of sulfide- and methane-rich fluids, whereas slabs, veins, and chim neys of authigenic carbonate represent regions of either dormant methane-ri ch fluid expulsion, or areas where the present rate of flow is too low to s upport chemosynthetic fauna. We have found both active and dormant fluid se epage along fault zones, at the surface expression of mud volcanoes, on org anic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The fluid egress at these sites may b e driven by a combination of (1) pore-space reduction caused by rapid sedim entation and/or tectonic compaction related to residual Pacific-North Ameri ca compression, and (2) increased buoyancy due to a decrease in pore-fluid density related to diagenesis and/or catagenesis at depth. Although provoca tive, the relationship between topographically driven aquifer discharge and sea-floor fluid expulsion remains speculative for Monterey Bay. The widesp read distribution of fluid expulsion features controlled by a variety of co nduits in Monterey Bay implies that cold seeps may be common features on tr anslational margins.