Thaynes Limestone

{{Short description|Geologic formation in Montana and Idaho, USA}}

{{Use mdy dates|date=May 2023}}

{{Infobox rockunit

| name = Thaynes Formation

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| type = Formation

| age = Triassic

| prilithology = Limestone

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| region = Montana, Idaho, Wyoming

| country = United States

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| underlies = Ankareh Formation

| overlies = Woodside Formation

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File:Gren River Basin Stratigraphic Column.png

The Thaynes Formation is a geologic formation in Montana and Idaho, United States. It was recently elevated to group status, as the Thaynes Group.{{cite journal |last1=Lucas |first1=Spencer G. |author-link1=Spencer G. Lucas |last2=Krainer |first2=Karl |last3=Milner |first3=Andrew R. C. |year=2007 |title=The type section and age of the Timpoweap Member and stratigraphic nomenclature of the Triassic Moenkopi Group in Southwestern Utah |journal=New Mexico Museum of Natural History and Science Bulletin |volume=40 |pages=109–117 |url=https://www.researchgate.net/publication/237500803}}

It preserves fossils dating back to the Triassic period, such as Ammonoidea, Actinopterygii, Actinistia, Conodonta, Gastropoda, Nautiloidea, Ichthyosauria, and others. A diverse fauna known as the Paris biotaBrayard et al. (2017): Unexpected Early Triassic marine ecosystem and the rise of the Modern evolutionary fauna. Science Advances 3 (2):e1602159; doi:10.1126/sciadv.1602159 https://www.science.org/doi/10.1126/sciadv.1602159 has been described from the Thaynes Formation.