Jeannette M Yarnell
Paleontology of two North American Triassic reef faunas: implications for terrane paleogeography

Director: George Stanley

Massive Upper Triassic (Norian) reef limestone at Lime Peak Yukon and smaller deposits of reef associated carbonates at Long Creek, Alaska contain a variety of shallow-water marine fossils that are significant for paleobiogeographic reconstruction of terranes. Eleven scleractinian coral species and the alatoform bivalve, Wallowaconcha cf. W. raylenea are described critically for the first time from the Stikine terrane at Lime Peak, Yukon. In addition, the new discovery of five scleractinian coral species, the alatoform bivalve Wallowaconcha sp and one spongiomorph is also reported from the Chulitna terrane at Long Creek Alaska.

The newly described coral species from the Stikine and Chulitna terranes were added to a database comprised of 57 Triassic scleractinian coral species from seven North American displaced terranes, and one Siberian terrane The database was subjected to probabilistic similarity, cluster, and parsimony analysis in order to reconstruct terrane paleogeography based on faunal similarity. Results from the statistical analyses were compared with known paleomagnetic, stratigraphic, and tectonic data, as well as other paleogeographic interpretations to create a paleobiogeographic terrane reconstruction for the Triassic. Observations of the occurrence of wallowaconchid bivalves in both the Stikine and Chulitna terranes also were incorporated into the terrane reconstruction.

Results from the probabilistic similarity, cluster, and parsimony analyses are generally conformable and show temporal and spatial relationships within two main groups: 1) the Stikine, Chulitna, Quesnel, Eastern Klamath Luning Allochthon, and Antimonio terranes, and 2) the Wrangellia, Alexander Wallowa and Koryak terranes. These groups are interpreted to represent at least two ancient island arc chains that developed along the western margin of North America during Triassic time.