Geology of early Permian tracksites, Robledo Mountains, south-central New Mexico.

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Andrew B. Heckert Ph.D., Professor (Creator)
Appalachian State University (ASU )
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Abstract: Early Permian fossil localities, including numerous tracksites, in the southern Robledo Mountains of Dofia Ana County, New Mexico cover an area of approximately 20 km [superscript]2 Detailed mapping and measurement of seven stratigraphic sections shows that Lower Permian strata exposed here belong to three members of the Hueco Formation. In ascending order they are the middle, Robledo Mountains and upper members. We introduce the term Robledo Mountains Member of Hueco Formation to refer to strata previously termed Abo Tongue, Abo Formation, or Abo-Hueco Member. The Robledo Mountains Member is as much as 125 m of marine carbonates and shale, intercalated with siliciclastic red-beds that comprise about one-third ofthe unit's thickness. The red beds in the study area contain extensive invertebrate and vertebrate (tetrapod-footprint) trace fossils and a large, megafossil plant assemblage composed mainly of Walchia from more than 30 localities. Marine facies of the upper part of the Robledo Mountains Member contain an extensive late Wolfcampian assemblage of megafossil invertebrates, dominated by brachiopods and bryozoans, with considerable numbers of molluscs-bivalves, gastropods and a few specimens of ammonites. Non-fusulinid foraminiferans and ostracods dominate the microfossil assemblages. Conodonts from the middle part of the Robledo Mountains Member, found in strata that bracket most of the tracksites, indicate a late Wolfcampian (= late Artinskian) age. Quaternary alluvia overlie and Tertiary intrusive igneous rocks cut Hueco Formation strata in the southern Robledo Mountains. Most of the 34 red-bed tracksites in the Robledo Mountains Member occur at one stratigraphic level and thus represent a megatracksite that encompassed at least 20 km2• Carbonates of the Robledo Mountains Member were deposited in relatively quiet shallow-water shelf environments below active wavebase. They show a trend from restricted circulation (brackish?) waters in the lower part of the member to more open normal marine waters in the middle and upper parts of the member. Tracksites were formed on siliciclastic tidal flats during early stages of rising base level(transgression). Our data suggest deposition of the red beds of the Robledo Mountains Member that encompass the megatracksite during a transgressive episode, rather than a cycle of regression-transgression as previously suggested.

Additional Information

Lucas, S.G., Anderson, O.J., Heckert, A.B., and Hunt, A.P., (1995) Geology of early Permian tracksites, Robledo Mountains, south-central New Mexico. New Mexico Museum of Natural History and Science Bulletin 6 (Early Permian footprints and facies), p. 13-32. (ISSN 1524-4156) Archived in NC DOCKS with permission of the editor. The version of record is available at:
Language: English
Date: 1995

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