PALEOBIOGEOGRAPHIC SIGNATURES FOR UPPER TRIASSIC BRACHIOPODS AND GASTROPODS FROM KUIU ISLAND AND ADJACENT KEKU STRAIT, SE ALASKA (ALEXANDER TERRANE)

Upper Triassic (Carnian-Norian) brachiopods and gastropods occur in the Keku Volcanics and Hyd Group on the northeastern side of Kuiu Island and adjacent Keku Strait, southeast Alaska. Brachiopods include a locally abundant small- to medium-sized smooth, uniplicate athyrid referred to Pexidella strohmayeri (Suess). The Alaskan material also has some similarities to Spirigera stoliczkai Bittner, a morphologically similar species that likely belongs to Pexidella. They represent the first athyrid brachiopods to be identified in the Triassic of North America. Small biplicate and large non-plicate terebratulids are also present, the latter may represent a variety of Lobothyris.

Spiriferids are well represented, but are less abundant than the athyrids. Peter Hoover (1991) recorded a number of spiriferid taxa from the Triassic of Kuiu Island: Spondylospira lewesensis (Lees), an Eastern Pacific form; Pseudospondylospira perplexa Hoover recorded from other localities in Alaska, Oregon, and Nevada; and Dagyspirifer fascicostata Hoover, known only from Kuiu Island.

Fragments of a large spiriferid (5 cm in width) are known from the Hound Island Volcanics (uppermost formation of the Hyd Group). These could simply be very large specimens of Spondylospira, but they are very wide. The pedicle valve is sulcate with an ornament of long, non-bifurcating costae. The wide outline of the valves is suggestive of Sinucosta. If this material represents Sinucosta it would be an additional Tethyan faunal signature with Pexidella.

Gastropods are known from both the Keku Volcanics and Hound Island Volcanics. Chulitnacula alaskana (Smith) occurs in late Norian strata of the Hound Island Volcanics and is also reported from the Chulitna and Farewell terranes of Alaska. Nearly all of the remaining gastropods represent new, undescribed species, quite unlike coeval gastropod taxa found in the outboard Wrangellia terrane.

The total dissimilarity between the Upper Triassic faunas and stratigraphies of the Alexander and Wrangellia terranes indicate that they were widely separated from one another at this time, and that they probably coalesced much later in the Mesozoic.