Early Jurassic hydrothermal vent community from the Franciscan Complex, San Rafael Mountains, California

The Figueroa massive sulfide deposit, located in Franciscan Complex rocks i n the San Rafael Mountains of California, preserves the only known Jurassic hydrothermal vent fossils. The Figueroa fossil assemblage is specimen rich but of low diversity and comprises, in order of decreasing abundance, vest imentiferan worm tubes, the rhynchonellid brachiopod Anarhynchia cf. gabbi and a species of ?nododelphinulid gastropod, The Figueroa fossil organisms lived at a deep-water, high-temperature vent site located on a mid-ocean ri dge or seamount at an equatorial latitude. The fossil vent site was then tr anslated northwestward by the motion of the Farallon plate and was subseque ntly accreted to its present location. An iron-silica exhalite bed, the pro bable lateral equivalent of the Figueroa deposit, contains abundant filamen tous microfossils with two distinct morphologies and probably represents a lower-temperature, diffuse flow environment. The Figueroa fossil community was subject to the same environmental conditions as modern vent communities , but it is unique among modern and other fossil vent communities in having rhynchonellid brachiopods.