Formation · Devonian
Silica Formation
Middle Devonian unit, Ohio · Michigan
The Silica Formation of northwestern Ohio and southeastern Michigan is a Middle Devonian shale that produced enrolled and prone Eldredgeops (formerly Phacops) rana with superb schizochroal eyes, Greenops, the winged brachiopods Mucrospirifer and Paraspirifer, horn corals and Hexagonaria. It is the source of most 'Phacops rana' in American collections. Olander Park's Fossil Park in Sylvania lets the public dig quarry spoil for free.
| Country | United States |
|---|---|
| Region | Ohio, Michigan |
| Age | Givetian, Middle Devonian |
| Age range | ~390–385 Ma |
| Macrostrat rank | Fm· Macrostrat |
| Macrostrat age | 393–382 Ma· Macrostrat |
| PBDB collections | 47 collections, 2015 occurrences· Paleobiology Database |
Collecting and legality
The Sylvania quarries (Medusa/Holcim) are private; access is limited to organised events such as Fossil Park in Sylvania, a free public park stocked with quarry spoil where collecting is encouraged for personal collections.
Lithology and setting
Grey calcareous shale and limestone of the Traverse Group equivalent, deposited in a Middle Devonian epicontinental sea.
Commonly recorded taxa (PBDB)
Genera most often recorded from this unit in the Paleobiology Database (first 200 occurrences): Hexagonaria (24), Devonochonetes (12), Emmonsia (10), Modiomorpha (10), Favosites (9), Aulocystis (6), Cylindrophyllum (6), Cystiphylloides (6), Mucrospirifer (6), Acleistoceras (5), Atrypa (5), Centroceras (5), Cladopora (5), Heracloceras (5), Leioclema (5).
Source: Paleobiology Database
Elsewhere
- Macrostrat: 78105
- macrostratConcept: 14483
- PBDB: strata:Silica
- Wikidata: Q18358688
- Macrostrat stratigraphic name
- PBDB occurrences for this unit
- Wikipedia: Silica Formation
- Mindat: Silica Formation
Cite this article
Stratum Study. "Silica Formation" (Formation). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/formations/silica-formation. Accessed 2026-09-20.
@misc{stratum-silica-formation,
title = {Silica Formation},
author = {{Stratum Study}},
howpublished = {\url{https://stratum.black/study/formations/silica-formation}},
year = {2026},
note = {Formation article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, macrostrat, pbdb, wikidata, commons. Accessed 2026-09-20.}
} Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.