Pennsylvanian-Permian boundary at Carrizo Arroyo, central New Mexico
— Lucas, Spencer G., Barrick, James E., Krainer, Karl , Schneider, Jorg W.


At Carrizo Arroyo southwest of Albuquerque, New Mexico, an approximately 105-m-thick section of upper Paleozoic clastic and carbonate rocks yields extensive marine and nonmarine fossil assemblages. Most of the section at Carrizo Arroyo belongs to the Red Tanks Member of the Bursum Formation, ~100-m-thick, mostly variegated shale, mudstone and siltstone of nonmarine origin, intercalated with some beds of limestone and shale of marine origin forming six transgressive depositional sequences. Red Tanks Member fossils include palynomorphs, calcareous algae, charophytes, plant megafossils, non-fusulinid foraminifers, fusulinids, bryozoans, brachiopods, gastropods, bivalves, nautiloids, eurypterids, ostracods, syncarid crustaceans, conchostracans, insects and some other arthropods, echinoids, crinoids, conodonts, fish ichthyoliths, and bones of amphibians and reptiles. At stratigraphic levels 43 m and 68 m above the base of the section are Lagerstätten of plants, insects, crustaceans, eurypterids and other fossils that are unique late Paleozoic lacustrine assemblages. Most of the fossil groups from the Red Tanks Member have been used to support diverse placements of the Pennsylvanian-Permian boundary at Carrizo Arroyo. The insects indicate that the two Lagerstätten in the Red Tanks Member are of early Asselian age. Conodont data include the presence of Streptognathodus virgilicus in the uppermost part of the underlying Atrasado Formation, which constrains its age to the middle to upper part of the Virgilian. The only biostratigraphically-significant conodont assemblage in the Red Tanks Member comes from a marine horizon near the middle of the member, and the assemblage is probably equivalent in age to the Midcontinent Streptognathodus nevaensis Zone of early to middle Asselian age. A significant amount of latest Pennsylvanian to earliest Permian time apparently is not represented by rock record at the Carrizo Arroyo section, most likely because of a major disconformity at the top of the Atrasado Formation and because of smaller ones at the bases of depositional sequences in the lower part of the Red Tanks Member. The fact that the Bursum Formation section at Carrizo Arroyo has too few cycles to be matched to the succession of Midcontinent cyclothems is prima facie evidence that regional tectonic events of the Ancestral Rocky Mountains exerted a greater control over the creation and preservation of Bursum depositional sequences than did glacio-eustatic events.

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Recommended Citation:

  1. Lucas, Spencer G., Barrick, James E., Krainer, Karl , Schneider, Jorg W., 2016, Pennsylvanian-Permian boundary at Carrizo Arroyo, central New Mexico, in: The Geology of the Belen Area, Frey, Bonnie A.; Karlstrom, Karl E.; Lucas, Spencer G.; Williams, Shannon; Zeigler, Kate; McLemore, Virginia; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 67th Field Conference, pp. 303-311.

[see guidebook]