The Figueroa Sulfide (also known as Figueroa Hydrothermal vent or Figueroa Massive Sulfide) is a geological formation in California, USA, dating to roughly between 185 and 181 million years ago and covering the Pliensbachian-Toarcian stages of the Jurassic Period in the Mesozoic Era. This deposits represent deep sea hydrothermal vents, with the oldest confirmed record of Siboglinidae and adjacent biotas, being one of the oldest records of such ecosystem, with similar occurrences found elsewhere in the Americas, for example from Los Molles Formation of Argentina.
Paleoenvironment
The Figueroa Sulfide is located in the San Rafael Mountains and is part of the Franciscan Complex, which formed during subduction of the Farallon Plate. This geological formation includes altered basalts, serpentinites, cherts, and tectonically sheared mudstones. The Figueroa Sulfide consists of a 1.5-meter-thick sulfide lens with a silicified core, flanked by more friable sulfides, and is structurally overlain by altered volcanics and cherts. The deposit shows evidence of tectonic brecciation and oxidation before silica deposition. Though small and not viable for large-scale mining, its mineralization and vent structures suggest similarities to modern hydrothermal vent systems.
Biostratigraphic analysis of the Figueroa Sulfide, based on radiolarian fossils extracted from chert samples, indicates a late Pliensbachian to early Toarcian age. The presence of key radiolarian taxa, such as Parahsuum ovale and Bagotum sp., supports this dating. Taphonomically, fossils found in the deposit, including brachiopods, gastropods, and vestimentiferan tubes, are preserved as pyrite molds, replicating fine details of the original shells and tubes. These fossils suggest an ancient hydrothermal vent community, where organisms like tube worms and brachiopods likely relied on chemosynthetic bacteria for nutrition, mirroring modern vent ecosystems.
The Figueroa sulfide fossil assemblage differs from modern vent communities in species diversity, composition, and trophic structure. Unlike modern vents, the Figueroa Sulfide has only three species, lacks common taxa such as Vesicomyidae and Bathymodiolus bivalves, arthropods, and gastropods, and has no predators. Possible explanations for these differences include taphonomic bias, where only high-temperature vent species were fossilized, and a genuinely low-diversity Jurassic vent ecosystem. Some "missing" taxa, such as Vesicomyidae, likely evolved later, supported by their fossil record starting in the early Cretaceous and molecular divergence estimates.
Biota
Radiolarians GenusSpeciesStratigraphic positionMaterialNotesImagesBagotum B. modestum North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family BagotidaeCanoptum C. poissoni North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family ParvicingulidaeCanutus C. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family BagotidaeCrucella C. ssp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family HagiastridaeDictyomitrella D.? sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family ParvicingulidaeEucyrtidiellum E. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family EucyrtidiellidaeKatroma K. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family SyringocapsidaeNapora N. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family UltranaporidaePantanellium P. cf. buntonense P. ssp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family PantanelliidaeParahsuum P. mostleri P. simplum P. ovale P. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family HsuidaeParonaella P. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family AngulobracchiidaePraeconocaryomma P. cf. immodica P. cf. magnimamma P. aff. magnimamma P cf. whiteavesi P.? fasciata P. cf. decora P. cf. media P. cf. parvimamma North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family PraeconocaryommidaePseudoristola P. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family ParvicingulidaeStaurolonche S.? sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family StylosphaeridaeStichocapsa S. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family EucyrtidiidaeTranshsuum T. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family HsuidaeTriactoma T. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family XiphostylidaeTrillus T. cf. elkhornensis North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family PantanelliidaeZartus Z. sp. North of Santa BarbaraCalcareous SkeletonsA Radiolarian of the family Pantanelliidae
Brachiopoda GenusSpeciesStratigraphic positionMaterialNotesImagesAnarhynchia A. cf. gabbi North of Santa BarbaraShellsA Brachiopod of the family Peregrinellidae
Gastropoda GenusSpeciesStratigraphic positionMaterialNotesImagesFrancisciconcha F. maslennikovi North of Santa BarbaraShellsA Top Snail of the family Trochidae
Polychaeta GenusSpeciesStratigraphic positionMaterialNotesImagesSiboglinidae "Figueroa tubes" North of Santa BarbaraCylindrical tubesA Vestimentiferan, considered to be similar to the modern genus Ridgeia, latter resolved among modern vestimentiferans.
Bibliography