UPPER TRIASSIC SHALLOW-WATER MARINE FAUNA FROM THE WRANGELLIA AND ALEXANDER TERRANES (SOUTHERN ALASKA) AND THEIR PALEOBIOGEOGRAPHIC IMPLICATIONS

This study focuses on the identification, relative diversity, paleoecologic,and paleobiogeographic relationships of benthic sessile organisms such as scleractinian corals, sphinctozoid sponges, gastropods, bivalves, and brachiopods from Upper Triassic strata of the Alexander and Wrangellia terranes, Alaska. Shallow-water marine fossil organisms used in this study were collected from Upper Triassic limestones of the Hyd Group on Kuiu and Kupreanof islands, two correlative Upper Triassic units to the south on Gravina Island, and lower Norian strata of the uppermost Chitistone Limestone in the Wrangell Mountains.

Our analysis reveals species level relationships of scleractinian corals between the Wallowa and Wrangellia terranes, as well as similarities with the Alexander terrane. Forty-three species of Upper Triassic coral were identified (5 new species) from localities within the Alexander and Wrangellia terranes. Thirty-Six species were recognized from 9 principal Alexander terrane localities and 27 species from 1 locality within Wrangellia. Of the 36 species from the Alexander terrane, 27 were not previously known. Likewise, of the 27 species from Wrangellia, 21 were not mentioned from previous work.

Diverse gastropod faunas are present in Norian strata of both the Alexander and Wrangellia terranes. For the most part, gastropods from these terranes are quite distinct at the species level and represent new undescribed taxa. Taxa having lecithotrophic larval development, notably the more primitive groups such as the pleurotomarioideans tend to be endemic and are restricted only to one terrane. In contrast, some taxa characterized by planktotrophic larvae, such as certain elements of the neritomorphs and caenogastropods, tend to be broadly distributed and found in both terranes. These widely distributed elements, i.e., the early Norian Spinidelphunopsis whaleni, permit correlation between these differing gastropod faunas.

These results help to resolve discrepancies in the paleogeographic position for the Alexander, Wallowa, and Wrangellia terranes, as well as add a wealth of knowledge about Triassic coral, gastropod, and bivalve taxonomy within these terranes.