EARLY JURASSIC CORAL FAUNA FROM THE SUNRISE FORMATION, NEW YORK CANYON, NEVADA: NEW EVIDENCE ON NORTH AMERICAN CORAL RECOVERY AFTER THE TRIASSIC-JURASSIC MASS EXTINCTION

The Triassic-Jurassic (T/J) mass extinction boundary is well represented stratigraphically with a continuous depositional section spanning the Gabbs and Sunrise formations at New York Canyon, Nevada. These marine deposits display a sedimentological and paleontological record of intense environmental changes and biotic turnover, particularly for corals. During this period of global climate change approximately 200 million years ago, sea level was dropping and the Central Atlantic Magmatic Province was releasing prodigious amounts of greenhouse gases and volatiles with increasing ocean acidity. Corals reefs collapsed abruptly at the end of the Triassic. While the Jurassic recovery was underway during the first few million years following the extinction, reefs and coral diversity did not fully recover until 25 million years later. Compared to the Tethys, precious little is known about western North America where reefs and diverse corals of the Late Triassic lived around volcanic islands of eastern Panthalassa. Here we report rare early Jurassic corals from New York Canyon. These are mostly solitary and represent a phase of the recovery for the earliest North American Jurassic corals. The corals, located approximately 20 meters above the T/J boundary in the Ferguson Hill Member of the lower Sunrise Formation, are in-situ and occur as a meter-thick limestone pavement. They are mostly solitary coral taxa and may be compared with counterparts in the Tethys and elsewhere in North America. Other noteworthy fossils are found at the coral interval including the bivalve Weyla. Ongoing research focuses on these earliest Jurassic corals and others including an exceptional Early Jurassic reef in the Santa Rosa Formation, Sonora, Mexico. In Sonora, the shallow-water patch reefs reach 20-30 meters in thickness and extend laterally for more than a kilometer. The coral faunas of both Nevada and Sonora provide useful data on the paleoecology, paleobiogeography and recovery of corals and reef-faunas following the end-Triassic mass extinction.