GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 271-7
Presentation Time: 9:00 AM-6:30 PM


HODGES, Montana S.1, STANLEY Jr., George D.2, BLODGETT, Robert B.3 and HODGES, Christopher L.1, (1)University of Montana, Paleontology Center, 32 Campus Drive # 1296, Missoula, MT 59812, (2)Geosciences, University of Montana Paleontology Center, 32 Campus Drive # 1296, Missoula, MT 59812, (3)Blodgett & Associates LLC, 2821 Kingfisher Drive, Anchorage, AK 99502,

During the Triassic corals and reefs reached maximum diversity with the development of extensive carbonate platforms. The end-Triassic breakup of Pangea resulted in rift volcanism leading to global perturbations that caused reefs to collapse with the extinction of most corals and marine biotas. After the end-Triassic mass extinction it took almost 25 million years for corals and reefs to recover to their former diversity and biotic structure. Early Jurassic corals are uncommon and corals from the earliest stages of the Jurassic are extremely rare in North America. Corals of the Hettangian to Sinemurian contain Triassic holdover species. Here we present details of Hettangian corals from Alaska which represent the earliest Jurassic appearances in North America. The corals occur as new species and range from the middle Hettangian to the early Sinemurian as simple, solitary forms from the marine sedimentary and volcanic rocks in the Peninsular terrane on the southwestern part of the Kenai Peninsula, Alaska. Other co-occurring fauna include bivalves and gastropods. Mid-Hettangian taxa include the oldest known species of the gastropod genus Pleurotomaria in North America, as well as a new species of the bivalve Weyla, again representing the oldest representative known in North America. To confirm the age of the fossils, detrital zircons were extracted from fossiliferous sandstones and analyzed for U-Pb ages. These were compared to ages derived from ammonites namely the occurrence of Psiloceras (Franziceras) cf. P. (F.) ruidum (Buckman). The combination of these geochronologic and biochronologic ages reinforces a middle Hettangian date. The fossils provide new data on Triassic holdover taxa surviving the extinction in island-arc refugia or an earlier Hispanic corridor migration from the Tethys to the Panthalassa. The Early Jurassic corals allow an opportunity to assess paleoecology, paleobiogeography and biotic recovery during the critical interval following the mass extinction and may offer insight for the recovery phase of the modern reef crisis.