A REVIEW OF MESOZOIC BRACHIOPODS AS PALEOGEOGRAPHIC, PALEOECOLOGICAL, AND TECTONIC TOOLS IN TERRANE ANALYSIS IN THE WESTERN CORDILLERA OF NORTH AMERICA (IN PARTICULAR ALASKA AND BRITISH COLUMBIA)

Brachiopods have been used extensively in the Paleozoic for paleobiogeographic, paleogeographic and tectonic reconstructions. Mesozoic brachiopods are locally abundant in the Western Cordillera and we here summarize some recent work on these faunas to underscore their utility and potential in paleogeographic, paleoecological, and tectonic studies.

Triassic: A diverse Late Triassic (Norian) brachiopod fauna from the Chulitna Terrane (Stefanoff et al., 1999) shows Tethyan affinities and are considered to indicate a low latitude paleogeographic setting during the Late Triassic. Another Tethyan indicator is the athyrid Pexidella from the Late Triassic Hyd Group of Kuiu Island and adjacent Keku Strait, SE Alaska (Alexander Terrane). The spiriferid Spondylospira lewesensis (Lees) is well-known in the Norian of the Western Cordillera and is restricted to the Eastern Pacific, while other spiriferids are endemic (Hoover, 1991). The Norian terebratulid Pseudorhaetina may also prove to be restricted to the Eastern Pacific. In the Middle Triassic (Ladinian) of the Peace River, British Columbia, autochthonous brachiopod faunas are represented by the abundant terebratellid Aulacothyroides, a good Boreal indicator.

Jurassic: Brachiopods have been recorded from the Early Jurassic of the Farewell and Peninsular terranes (Sandy and Blodgett, 2000) and the Early and Middle Jurassic of the Queen Charlotte Islands (Wrangellia; Sandy et al., 1996). These all have links to low- to mid-latitude faunas from Europe. Jurassic brachiopods that have been reported to have associations with chemosynthetic communities include Anarhynchia (California, Oregon), Sulcirhynchia (Oregon), and Cooperrhynchia (California).

Cretaceous: The Early Cretaceous brachiopod Peregrinella was reported from the eastern Alaska Range, Wrangellia by Sandy and Blodgett (1996). Other occurrences of this brachiopod genus (e.g., California, France, Ukraine) have been considered to be associated with chemosynthetic environments. Given this association, the overriding control on Peregrinella's occurrence would be paleoecological. Therefore it would not be a good paleobiogeographic signal (and the Jurassic taxa mentioned above). Whether all of the Dimerellide taxa have a chemosynthetic association is subject to debate.