SCOYENIA ICHNOFACIES AT THE BASE OF THE LOWER PERMIAN ABO FORMATION, CARRIZO ARROYO, CENTRAL NEW MEXICO

The Carrizo Arroyo section of central New Mexico exposes an approximately 100-m-thick section of intercalated clastic rocks and limestones of the Virgilian Red Tanks Member of the Bursum Formation, immediately overlain by siliciclastic red beds of the Wolfcampian Abo Formation. New Mexico Museum of Natural History locality 5123 at the base of the Abo Formation contains an abundant ichnofauna of the Scoyenia ichnofacies that consists of two ichnogenera, Palaeophycus Hall 1852 and Protovirgularia M’Coy 1850. The fossiliferous interval is a 1.6-m-thick, multistoried, ripple-laminated sandstone. Two burrowed horizons are present in this sandstone: (1) at its base, immediately above estuarine shale, where the bedding plane bioturbation index (Miller and Smail, 1984) is 40%; and (2) a surface 33 cm above its base, where burrow size is smaller, and the bioturbation index is 10% to 25%. The burrowed surfaces are extensive and can be traced over at least several square km. Deposition is interpreted as having occurred in a paralic, estuarine setting. The low diversity, horizontal burrows and transitional nonmarine aquatic conditions are characteristic of the Scoyenia ichnofacies (sensu Frey et al., 1984), which is not known prior to the Permian. Locality 5123 includes the first records from New Mexico of Palaeophycus alternatus Pemberton & Frey 1982, Palaeophycus striatus Hall, 1852 and Protovirgularia dichotoma M’Coy 1850.