Figueroa Sulfide Explained

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.^{[1] [2] [3]} This deposits represent deep sea hydrothermal vents, with the oldest confirmed record of Siboglinidae and adjecent 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.^{[4] [5]}

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.^[6] 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

Genus	Species	Stratigraphic position	Material	Notes	Images
Bagotum	B. modestum	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Bagotidae
Canoptum	C. poissoni	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Parvicingulidae
Canutus	C. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Bagotidae
Crucella	C. ssp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Hagiastridae
Dictyomitrella	D.? sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Parvicingulidae
Eucyrtidiellum	E. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Eucyrtidiellidae
Katroma	K. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Syringocapsidae
Napora	N. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Ultranaporidae
Pantanellium	P. cf. buntonense P. ssp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Pantanelliidae
Parahsuum	P. mostleri P. simplum P. ovale P. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Hsuidae
Paronaella	P. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Angulobracchiidae
Praeconocaryomma	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 Barbara	Calcareous Skeletons	A Radiolarian of the family Praeconocaryommidae
Pseudoristola	P. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Parvicingulidae
Staurolonche	S.? sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Stylosphaeridae
Stichocapsa	S. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Eucyrtidiidae
Transhsuum	T. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Hsuidae
Triactoma	T. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Xiphostylidae
Trillus	T. cf. elkhornensis	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Pantanelliidae
Zartus	Z. sp.	North of Santa Barbara	Calcareous Skeletons	A Radiolarian of the family Pantanelliidae

Polychaeta

Notes and References

1. Little . Crispin T. S. . Herrington . Richard J. . Haymon . Rachel M. . Danelian . Taniel . 1999 . Early Jurassic hydrothermal vent community from the Franciscan Complex, San Rafael Mountains, California . Geology . 27 . 2 . 167 . 10.1130/0091-7613(1999)027<0167:ejhvcf>2.3.co;2 . 1999Geo....27..167L . 0091-7613.
2. Little . C. T. . Danelian . T. . Herrington . R. J. . Haymon . R. M. . 2004 . Early Jurassic hydrothermal vent community from the Franciscan Complex . Journal of Paleontology . 78 . 3 . 542–559 . 10.1666/0022-3360(2004)078<0542:ejhvcf>2.0.co;2 . 0022-3360.
3. Hagstrum . Jonathan T. . Murchey . Benita L. . Bogar . Robert S. . 1996-01-10 . Equatorial origin for Lower Jurassic radiolarian chert in the Franciscan Complex, San Rafael Mountains, southern California . Journal of Geophysical Research: Solid Earth . 101 . B1 . 613–626 . 10.1029/95jb02854 . 1996JGR...101..613H . 0148-0227.
4. Georgieva . Magdalena N. . Little . Crispin T.S. . Maslennikov . Valeriy V. . Glover . Adrian G. . Ayupova . Nuriya R. . Herrington . Richard J. . 2021 . The history of life at hydrothermal vents . Earth-Science Reviews . 217 . 103602 . 10.1016/j.earscirev.2021.103602 . 2021ESRv..21703602G . 0012-8252.
5. Gómez-Pérez . Irene . 2003 . An Early Jurassic deep-water stromatolitic bioherm related to possible methane seepage (Los Molles Formation, Neuquén, Argentina) . Palaeogeography, Palaeoclimatology, Palaeoecology . 201 . 1–2 . 21–49 . 10.1016/s0031-0182(03)00508-x . 2003PPP...201...21G . 0031-0182.
6. Wahl . A.D. . 1995 . The geology of the Franciscan Complex, San Rafael Mountains me´lange, California . Master's Thesis, University of California, Santa Barbara . 1–121.
7. Georgieva . Magdalena N. . Little . Crispin T. S. . Watson . Jonathan S. . Sephton . Mark A. . Ball . Alexander D. . Glover . Adrian G. . 2017-12-28 . Identification of fossil worm tubes from Phanerozoic hydrothermal vents and cold seeps . Journal of Systematic Palaeontology . 17 . 4 . 287–329 . 10.1080/14772019.2017.1412362 . 1477-2019. 10141/622324 . free .