Winneshiek Shale
Iowa geological formation
The Winneshiek Shale (originally the Winneshiek Lagerstätte) is a Middle Ordovician (Darriwilian-age) geological formation in Iowa. The formation is restricted to the Decorah crater, an impact crater near Decorah, Iowa. Despite only being discovered in 2005, the Winneshiek Shale is already renowned for the exceptional preservation of its fossils. The shale preserves a unique ecosystem, the Winneshiek biota, which is among the most remarkable Ordovician lagerstätten in the United States. Fossils include the oldest known eurypterid, Pentecopterus, as well as giant conodonts such as Iowagnathus and Archeognathus.
Geology
The Winneshiek Shale is a thin and geologically homogeneous package of dark grey to greenish-brown sandy shale. Drill core data has estimated a maximum thickness of 38 meters, though in most areas its thickness is only about 18–27 meters. The shale is replete with pyrite and organic carbon. It lies solely within the Decorah Structure, a 5.6 km (3.5 mile)-wide probable impact crater near Decorah, Iowa. Within the crater, the shale overlies a much thicker unnamed unit mostly composed of impact breccia.
Begin with the source’s own compact description: “Winneshiek Shale” is iowa geological formation. The dossier treats that line as a proposition to test through Winneshiek, Shale and Iowa, not as a finished interpretation.
Why this record matters
The phrase “iowa geological formation” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Apr 29, 2026. The linked authority identifier is Q104836057. None of the 0 selected statements returned an explicit reference. The first chronological checks are 2005.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Winneshiek Shale”, its source revision and the description used here.
- Expand the search: follow Winneshiek Shale primary sources, Winneshiek Shale archive and Winneshiek research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Winneshiek Shale”?
- Which cited source is closest to the event, object or claim?
- What terminology or title could unlock a more precise catalogue search?
Search terms from this dossier
This entry incorporates text from “Winneshiek Shale” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.