Tropic Shale
Primary: Shale Named for: Exposures near Tropic, Garfield County, Utah Named by: Gregory and Moore, 1931 Overlies: Dakota Formation Underlies: Straight Cliffs Formation Unit of: Kaiparowits Plateau
The Tropic Shale is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation, including Nothronychus graffami.
The Tropic Shale is a stratigraphic unit of the Kaiparowits Plateau of south central Utah. It was first named in 1931, after the town of Tropic, Utah, where the type section is located. The Tropic Shale outcrops in Kane and Garfield counties, with large sections of exposure found in the Grand Staircase–Escalante National Monument.
Geology
The Tropic Shale is predominantly marine mudstone and claystone, with several radioisotopically-dated bentonite marker beds and occasional sandstone layers, deposited during the late Cretaceous Period, during the Upper Cenomanian through the Middle Turonian (95-92 Ma). It has an average thickness range from 183–274 m.
The Tropic Shale conformity overlies the Dakota Formation and underlies the Straight Cliffs Formation. The top of the Dakota Formation is known for its sandier coarsening up sequences and estuarine shell beds. The distinction between the Tropic Shale and underlying Dakota is marked by the appearance of marine mudstones.
“Tropic Shale” enters the record as primary: Shale Named for: Exposures near Tropic, Garfield County, Utah Named by: Gregory and Moore, 1931 Overlies: Dakota Formation Underlies: Straight Cliffs Formation Unit of: Kaiparowits Plateau. Crown Archives preserves that source wording while asking what Tropic, Shale and Primary can confirm, complicate or overturn.
Why this record matters
“Tropic Shale” is worth following because a concise public description often conceals a longer documentary argument. Here, Tropic, Shale and Primary provides the most credible route into that argument.
Maps, plans, fabric surveys and administrative records can establish how the site’s name, extent and function changed over time. The source revision retrieved here is dated Mar 1, 2026. The linked authority identifier is Q7845732. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1931.
Modern boundaries and familiar names can conceal earlier jurisdictions or structures that do not align with the present site. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Treat names, boundaries and functions as historically changeable. Maps, plans, inventories and administrative records can clarify what the place meant at different dates.
- Historic place names
- Jurisdictional context
- Routes into maps and plans
Contemporary maps, plans, listed-building records, estate papers and the responsible local or national archive.
Three-step research path
- Establish the record: confirm the title “Tropic Shale”, its source revision and the description used here.
- Expand the search: follow Tropic Shale primary sources, Tropic Shale archive and Tropic 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 “Tropic Shale”?
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- Which earlier names or jurisdictions may reveal additional records?
Search terms from this dossier
This entry incorporates text from “Tropic 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.