Abstract

An area of active fluid discharge characterized by authigenic barite formation and populated by vestimentiferan tubeworms has been discovered by remotely operated vehicle exploration in Monterey Canyon. Slumping and mass wasting, presumably triggered by seismic activity, have exposed barium-rich pore fluids to sulfate-rich bottom water, leading to barite precipitation on the sea floor. Age estimates based on 210Pb/226Ra dating of the barite samples and growth rates of vestimentiferan tubeworms indicate that the seep site might be as young as 100 yr. Systematic variations in sulfur and strontium isotope ratios, the lack of visible fluid flow, and the abundance of dead tubeworms indicate decreasing flow rates. This newly discovered site shows many similarities to a previously described barite deposit in the California Borderland, possibly misinterpreted as a hydrothermal vent site. The discovery of a cold seep associated with barite deposits on the seismically active, transpressional California margin raises the possibility that numerous unexplored areas along the continental margins might have similar low-temperature deposits.

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