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Upper Triassic stratigraphy and biostratigraphy, Chama basin, northcentral New Mexico

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Andrew B. Heckert Ph.D., Assistant Professor of Geology (Creator)
Institution
Appalachian State University (ASU )
Web Site: http://www.library.appstate.edu/

Abstract: Triassic strata in the Chama basin of Rio Arriba County, New Mexico, pertain to the Upper Triassic Chinle Group (in ascending order, the Zuni Mountains, Shinarump, Salitral, Poleo, Petrified Forest and Rock oint formations). The local base of the Chinle Group is the Zuni Mountains Formation (formerly “mottled trata”), a pedogenic weathering profile as much as 7 m thick, developed in the top of the Pennsylvanian-Permian Cutler Group. Where the Zuni Mountains Formation is absent, the base of the Chinle Group is the Shinarump ormation, which also locally overlies the Zuni Mountains Formation. In the Chama basin, the Shinarump Formation = Agua Zarca Formation of previous usage) is as much as 13 m thick and consists mostly of troughcrossbedded, quartzose sandstone and siliceous conglomerate. The overlying Salitral Formation is as much as 31 m of mostly greenish and reddish brown, smectitic mudstone. We divide the Salitral Formation into two members amed here: a lower, Piedra Lumbre Member of greenish mudstone with a peristent sandstone bed (the El Cerrito ed, also named here) at its top, and an upper, Youngsville Member, mostly reddish-brown mudstone. The Poleo Formation is up to 41 m thick and is mostly grayish yellow, trough-crossbedded litharenitic and subarkosic andstone with minor amounts of both intrabasinal and siliceous conglomerate. Above the Poleo Formation, as uch as 200 m of strata, dominated by reddish brown, smectitic mudstone, constitute the Petrified Forest Formation. n the Chama basin, the Petrified Forest Formation consists of two members, the lower Mesa Montosa ember (named here), up to 24 m of thin-bedded sandstone, siltstone and mudstone, which is overlain by up to 76 m of the mudstone-dominated Painted Desert Member. The Rock Point Formation in the Chama basin is as uch as 70 m thick and mostly laterally persistent, repetitive beds of reddish brown and grayish red siltstone and ipple-laminar sandstone that disconformably overlie the Petrified Forest Formation. In the Chama basin, unionid bivalves from the Petrified Forest Formation suggest a Revueltian age, and alynomorphs from the Rock Point Formation are of Norian age. Three formations of the Chinle Group in the hama basin contain biochronologically important vertebrate fossils, notably the aetosaur Desmatosuchus aplocerus (Adamanian) in the Salitral Formation, the aetosaurs Typothorax coccinarum and Desmatosuchus hamaensis and the phytosaur Pseudopalatus (Revueltian) in the Petrified Forest Formation, and the phytosaur edondasaurus (Apachean) in the Rock Point Formation. These fossils and lithostratigraphy allow precise correlation f the Chinle Group strata exposed in north-central New Mexico with other Upper Triassic strata in New exico.

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Publication
Lucas, S.G., Zeigler, K.E., and Heckert, A.B., (2003) Upper Triassic stratigraphy and biostratigraphy, Chama basin, northcentral New Mexico. New Mexico Museum of Natural History and Science Bulletin 24 (Paleontology and Geology of the Upper Triassic (Revueltian) Snyder Quarry, New Mexico) p. 15-39. (ISSN 1524-4156) Archived in NC DOCKS with permission of the editor. The version of record is available at: http://econtent.unm.edu/
Language: English
Date: 2003