Triassic Brachiopod Faunas of Alaska

By

M.R. Sandy (University of Dayton) and R.B. Blodgett (Oregon State University)

Triassic brachiopods are known from both Middle and Upper Triassic strata of Alaska (see descriptions in Smith, 1927; Hoover, 1991), but still remain poorly recorded. However, recent field collections and a systematic survey of collections in a number of repositories indicates that they are more abundant than commonly believed and have great potential for biostratigraphic analysis of Triassic strata of the State. Brachiopods are known from nearly all of the major accreted terranes within the State, as well as in craton-bound strata of east-central Alaska. Warm-water, tropical faunas are known from the Alexander, Wrangellia, Chulitna, Peninsular and Farewell terranes of southern Alaska. These faunas are dominated by spondylospirid brachiopods (Spondylospira, Pseudospondylospira, and Dagyspirifer) as well as Zugmayerella, Laballa, Lobothyris, Zeilleria, and Pexidella. Coolwater, high-latitude brachiopods are found in craton-bound rocks of the lower part of the Glenn Shale of east-central Alaska. Genera found here include Piarorhynchia. Cold-water, high-latitude brachiopod faunas are present in the Arctic Alaska terrane, and are common in Ladinian-Norian strata of the Shublik and Otuk formations, as well as in probable late Norian-Rhaetian strata of the Sag River Sandstone. Genera found in the Shublik and Otuk formations include Piarorhynchia, Spiriferina, Ochotathyris, and allied to Aulacothyroides. The brachiopod faunas of the Shublik and Otuk formations show strong affinities with those of northeastern Russia, showing a high degree of similarity to forms described by Dagys (1965). The limited, probably late Norian-Rhaetian age brachiopod fauna from the Sag River Sandstone includes a poorly preserved rhynchonellid identified as cf. Tetrarhynchia.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.