A REVISED STRATIGRAPHIC AND VERTEBRATE BIOCHRONOLOGIC MODEL OF THE UPPER TRIASSIC DOCKUM GROUP OF EASTERN NEW MEXICO AND WESTERN TEXAS

Recently published geochronologic and biostratigraphic data to suggest a new sequence stratigraphic and biochronologic model for the Dockum Group of eastern New Mexico and western Texas. The Tr-3 unconformity and siliceous "Palo Duro geosol" may have formed due to high precipitation during the Carnian Humid Interval rather than being eustatic or tectonic in origin, with the lower Cane Springs Formation of Nevada representing marine deposition of eroded material. Deposition of the Santa Rosa Sandstone may have occurred after that of the Garta Grit despite shared derivation from the Amarillo-Wichita Uplift. The Colorado City, Trujillo, and Bull Canyon formations are demoted to members of the Cooper Canyon Formation, which is characterized by micaceous lithic sandstones derived from the Ouachita-Marathon orogenic belt. The Los Esteros and Tres Lagunas members and the Garita Creek Formation are reassigned as members of the Tecovas Formation. Colorado City Member deposition in the Midland Basin was syndepositional with the more quartz- and chert-rich sediments of the Tecovas Formation further north, while the Trujillo Member represents later northerly progradation of the Cooper Canyon lithic sandstones, possibly as a large distributive fan. Trujillo progradation was driven by the filling of accommodation space rather the beginning of a new phase of accommodation gain, which is represented instead by the Bull Canyon Member. The lower conglomerate of the Popo Agie Formation may contain an early Carnian Otischalkian or even Berdyankian vertebrate fauna, while the rest of the Popo Agie Formation, Santa Rosa Sandstone, lower Colorado City Member, and lower Tecovas Formation contain late Carnian-earliest Norian Otischalkian faunas which could potentially be subdivided based on metoposaurids. The early-middle Norian upper Tecovas Formation, upper Colorado City Member, and lower Trujillo Member contain Adamanian faunas which can be subdivided based on aetosaurs. The middle Norian to early Rhaetian Bull Canyon Member and the Redonda Formation contain Revueltian and Apachean vertebrate faunas which can be potentially subdivided based on declining aetosaur diversity, although biostratigraphic data is more ambiguous. The testability of these correlations is currently hampered by large biostratigraphic sampling gaps and a lack of radiometric dates for the Dockum Group.