Abstract

Detailed Permian conodont studies in Idaho, Nevada, Utah, Arizona and west Texas are providing an increasingly valuable biostratigraphic framework for stage designations. Late Pennsylvanian (Virgilian) conodont faunas (Idiognathodus ellisoni assemblage zone) range into the Early Permian (Wolfcampian or Sakmarian): thereby, making Virgilian-Wolfcampian boundary determinations difficult if based upon conodonts. The post-crisis middle and upper Wolfcampian conodont fauna (Neogondolella bisselli-Sweetognathus whitei assemblage zone) is readily recognized and differentiated from early Leonardian (Artinskian) strata bearing Neostreptognathodus pequopensis Behnken. “Medial” Leonardian (pre-Roadian) faunas are diagnosed by the presence of Neogondolella idahoensis (Youngquist, Hawley and Miller), Neostreptognathodus sulcoplicatus (emend., Youngquist, Hawley and Miller), N. prayi Behnken and Xaniognathus abstractus (Clark and Ethington). Upper Leonardian (Roadian) strata are characterized by a conodont assemblage containing diagnostic species of Neogondolella (Bender and Stoppel) [N. gracilis (Clark and Ethington) and N. serrata serrata (Clark and Ethington)], Neostreptognathodus Clark (N. prayi Behnken and N. clinei Behnken), Anchignathodus typicalis Sweet and Xaniognathus abstractus (Clark and Ethington).

The Roadian-Wordian Stage boundary can be drawn tentatively on the last appearance of species of Neostreptognathodus (Roadian) in the absence of the first occurence of more diagnostic Wordian genera such as Xaniognathus tortilis (Tatge), Neogondolella serrata postserrata Behnken and-or the Neogondolella rosenkrantz-Neospathodus arcucristatus assemblage. The Capitanian interval in west Texas is characterized by the N. serrata postserrata assemblage. The base of the Capitanian Stage in the northern Delaware basin can be defined by the appearance of the species Caenodontus serrulatus Behnken and abundant Anchignathodus typicalis Sweet in the Manzanita Member of the Cherry Canyon Formation. Caenodontus is a unique coneshaped conodont restricted to the lower Capitanian Stage (first appearing in the Manzanita Member, Cherry Canyon Formation through the Hegler Member and into the basal few feet of the Pinery Member of the Bell Canyon Formation). The Wordian and Capitanian are differentiated in Nevada based upon a faunal change of an association of Neogondolella “rosenkrantzi” (Bender and Stoppel) with Neospathodus arcucristatus Clark and Behnken in the Wordian to N. “rosenkrantzi” and Neospathodus divergens in the Capitanian. The Amarassian (uppermost Guadalupian) Lamar Member of the Bell Canyon Formation in west Texas bears a conodont fauna similar to that of the Capitanian. The key to future differentiation of the west Texas Amarassian may be in detailed morphologic studies of Neogondolella and Ellisonia (Muller).

Studies of Permian conodont faunas have been concentrated in the central Cordilleran region rather than in the Permian reference sections in the west Texas area. Excellent conodont faunas have now been recovered from the west Texas Permian and future investigations should be concentrated in this region to provide conodont biostratigraphic indices complementary to established fusulinid and ammonite zonations. Once these relationships are firmly established in the reference sections, conodonts can be confidently used for correlative work when fusulinids and ammonites are lacking or impractical for study.