# Figueroa Sulfide

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

| Genus | Species | Stratigraphic position | Material | Notes |
| 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 |

### Brachiopoda

| Genus | Species | Stratigraphic position | Material | Notes | Images |
| Anarhynchia | A. cf. gabbi | North of Santa Barbara | Shells | A Brachiopod of the family Peregrinellidae | |

### Gastropoda

| Genus | Species | Stratigraphic position | Material | Notes | Images |
| Francisciconcha | F. maslennikovi | North of Santa Barbara | Shells | A Top Snail of the family Trochidae | |

### Polychaeta

| Genus | Species | Stratigraphic position | Material | Notes | Images |
| Siboglinidae | "Figueroa tubes" | North of Santa Barbara | Cylindrical tubes | A Vestimentiferan, considered to be similar to the modern genus Ridgeia, latter resolved among modern vestimentiferans. | Example of modern Ridgeia specimens |