LATE PENNSYLVANIAN TO EARLY PERMIAN CONODONT SUCCESSION IN THE NEW WELL PEAK SECTION, HORQUILLA FORMATION, BIG HATCHET MOUNTAINS, SOUTHWESTERN NEW MEXICO

The New Well Peak section of the Horquilla Formation at the southeastern end of the Big Hatchet Mountains comprises over 1000 meters of cyclically-bedded, dominantly shallow-water subtidal, shelf carbonates that accumulated from the Early Pennsylvanian into the Early Permian. The excellent exposures and apparent stratigraphic continuity of the Horquillia Formation at this section, although complicated by minor faulting, should be an excellent location to obtain a succession of conodont faunas in well-constrained superpositional order. However, despite repeated sampling, recovery of diverse and age-diagnostic conodonts has been uneven, especially through the 500+ meter upper part of the section assigned a Late Pennsylvanian to Early Permian age based on fusulinids (Wilde, 2006).

The highest diverse Desmoinesian conodont fauna at the New Well Peak section includes Swadelina neoshoensis and Neognathodus morphotypes in association with Beedeina species. Sporadic specimens of Neognathodus occur at least 20 meters higher, but the latest Desmoinesian Sw. nodocarinatus Zone cannot be recognized. Abundant and diverse early Missourian conodonts appear just a few meters above a significant lithological break, at the same level from which early Triticites species were reported by Wilde. A diverse range of Idiognathodus morphotypes occur with Idioprionodus and Gondolella species, indicating a major early Missourian flooding event. Middle to late Missourian faunas are sparse and are characterized by examples of the Streptognathodus gracilis group followed higher in the section by S. pawhuskaensis forms. The base of the Virgilian cannot be identified using conodonts.

Conodont abundance and diversity increases in higher Virgilian strata and the Streptognathodus virgilicus Zone can be recognized. The radiation of new Streptognathodus species from S. bellus into the S. wabaunsensis species group during the latest Virgilian (Wilde fusulind zone PW-1; ”Bursumian” or “Newwellian”) is well represented. The appearance of S. isolatus with fusulinids of Wilde zone PW-2, allows precise placement of the base of the Permian in the New Well Peak section. Lower Permian strata, however, show a decrease in conodont abundance and diversity above the boundary level.