Poison Canyon Formation

The Poison Canyon Formation consists of thick sandstone beds separated by beds of mudstone and siltstone. It is found throughout most of the Raton Basin. The sandstone is arkosic and coarse-grained to conglomeratic. The mudstone and siltstone beds weather to yellow, are rich in mica, and are not resistant to erosion. The total thickness of the formation is up to {{convert|650|ft||sp=us}}.{{cite journal |last1=Flores |first1=Romeo M. |title=Sedimentology of Upper Cretaceous and Tertiary siliciclastics and coals in the Raton Basin, New Mexico and Colorado |journal=New Mexico Geological Society Field Conference Series |date=1987 |volume=38 |page=258 |url=https://nmgs.nmt.edu/publications/guidebooks/downloads/38/38_p0255_p0264.pdf |access-date=15 July 2021}}

The formation grades below into the Raton Formation, with the transition often very gradual, up to {{convert|150|ft||sp=us}}. In the western part of the Raton Basin, the formation intertongues with and partially replaces the Raton Formation. The two are distinguished by color (the Raton Formation is gray and the Poison Canyon Formation is yellow to orange), by the absence of arkosic sandstone in the Raton Formation, and by the absence of coal from the Poison Canyon Formation.{{cite journal |last1=Pillmore |first1=Charles L. |last2=Flores |first2=Romeo M. |title=Cretaceous and Paleocene rocks of the Raton Basin, New Mexico and Colorado--Stratigraphic-environmental framework |journal=New Mexico Geological Society Field Conference Series |date=1990 |volume=41 |pages=333–336 |url=https://nmgs.nmt.edu/publications/guidebooks/downloads/41/41_p0333_p0336.pdf |access-date=14 July 2021}} In addition, river channel deposits in the Raton Formation are up to six times wider and five times deeper than river channels in the Poison Canyon Formation, and the channels in the Poison River Formation tend to be isolated and lack any sheet-like amalgamation.{{cite journal |last1=Zhang |first1=J. |last2=Steel |first2=R. |last3=Ambrose |first3=W. |last4=Fisher |first4=W. |year=2015 |title=Decreased Channel Dimensions and Sediment Flux Through the Paleocene Raton-Wilcox Rivers: Implications for Wilcox Shelf Margin |journal=AAPG Annual Convention and Exhibition |url=https://www.searchanddiscovery.com/abstracts/html/2015/90216ace/abstracts/2104915.html |access-date=15 July 2021}}

The Poison Canyon Formation underlies the Cuchara Formation in the northern part of the Raton Basin.{{cite journal |last1=Flores |first1=R.M. |last2=Bader |first2=L.R. |title=A summary of Tertiary coal resources of the Raton basin, Colorado and New Mexico |journal=U.S. Geological Survey Professional Paper |date=1999 |volume=1625-A |doi=10.3133/pp1625A |location=Chapter SR}}

The formation derived its sediments from the San Luis uplift to the southwest and the Wet Mountains uplift to the north and northwest.{{cite journal |last1=Cullers |first1=Robert L. |title=The controls on the major- and trace-element evolution of shales, siltstones and sandstones of Ordovician to tertiary age in the Wet Mountains region, Colorado, U.S.A. |journal=Chemical Geology |date=June 1995 |volume=123 |issue=1–4 |page=110 |doi=10.1016/0009-2541(95)00050-V|bibcode=1995ChGeo.123..107C }} Its age ranges from late Cretaceous (where the formation partially replaces the Raton Formation) to Paleocene.{{cite journal|last1=Pillmore |first1=C.L. |year=1969 |title=Geology and coal deposits of the Raton coal field, Colfax County, New Mexico |journal=The Mountain Geologist |volume=6 |number=3 |pages=125–142 |url=https://archives.datapages.com/data/rmag/mg/1969/pillmore.htm |access-date=15 July 2021}}

The Poison Canyon Formation contains sparse fossilized plant remains characteristic of the Paleocene.{{cite journal |last1=Brown |first1=R.W. |title=Paleocene flora of the Rocky Mountains and great Plains |journal=U.S. Geological Survey Professional Paper |series=Professional Paper |date=1962 |volume=375 |doi=10.3133/pp375|hdl=2027/coo.31924002995300 |hdl-access=free }}

The formation is a significant freshwater aquifer in the Canon City, Colorado area.{{cite journal|last1=Alther |first1=G.R. |year=1977 |title=Geohydrologic setting of the environment near Cotter Mill, Canon City, Colorado |journal=The Mountain Geologist |volume=14 |number=2 |pages=69–73 |url=https://archives.datapages.com/data/rmag/mg/1977/alther.htm |access-date=15 July 2021}}{{cite journal |last1=Wolfe |first1=Amy L. |last2=Wilkin |first2=Richard T. |title=Evidence of Sulfate-Dependent Anaerobic Methane Oxidation within an Area Impacted by Coalbed Methane-Related Gas Migration |journal=Environmental Science & Technology |date=7 February 2017 |volume=51 |issue=3 |pages=1901–1909 |doi=10.1021/acs.est.6b03709|pmid=28029760 |pmc=7392614 |bibcode=2017EnST...51.1901W }}

The unit was first named as the "Poison Canyon conglomerates" by R.C. Hills in 1888. Hills later clarified the definition, separating the uppermost beds of his measured section to the Huerfano Formation.{{cite journal|last1=Hills |first1=R.C. |year=1890 |title=Orographic and structural features of Rocky Mountain geology |journal=Colorado Scientific Society Proceedings |volume=3 |number=3 |pages= 362–458}}

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Category:Paleogene Colorado

Category:Paleogene formations of New Mexico

Category:Sandstone formations of the United States

Category:Mudstone formations of the United States

Category:Siltstone formations of the United States