Collaborative Research: Filling the Triassic geochronologic gap: A continuous cored record of continental environmental change in western North America

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Collaborative Research: Filling the Triassic Geochronologic Gap: A Continuous Cored Record of Continental Environmental Change in Western North America.Paul Olsen, Lamont-Dougherty, EAR-0958976George Gehrels, University of Arizona, EAR-0959107Randall Irmis, University of Utah, Ear-0958915Dennis Kent, Rutgers University, EAR-0958859Roland Mundil, Berkeley Geochronology Laboratory, EAR-0958723ABSTRACTThe Triassic Period was punctuated by two of the largest mass-extinctions of all time and witnessed the evolution of most elements of the modern biota, as well as the advent of the age of the dinosaurs. One of the richest archives of the biotic and environmental changes on land for this period is on the Colorado Plateau, which despite over 100 years of study still remains poorly calibrated in time and poorly registered to the rest of the global record. To provide this desiderata, we will drill a continuous a ~500 m core through nearly the entire Triassic age section (Chinle and Moenkopi formations) at Petrified Forest National Park (PFNP), Arizona, USA, one of the most famous and best studied successions of the continental Triassic on Earth. A continuous sampling (core) is needed to place this spectacular record in a reliable quantitative and exportable time scale, which has proved impractical in outcrop. The Petrified Forest core will provide a quantitatively sound reference section in which magnetostratigraphic, geochronologic, environmental, and paleontologic data are registered to a common thickness scale with unambiguous superposition and will provide pristine unweathered samples. With such a reference section in hand the entire voluminous assemblage of outcrop data from the PFNP and the surrounding region can be integrated into the global framework. The hole will be deviated 30° from vertical to provide core-bedding orientation intersections for an azimuthal guide; additionally, the orientation of the core will be registered to the hole wall using whole-core-scans and compass-oriented acoustic and optical televiewer images and dipmeter surveys. Core orientation will facilitate the recovery of a high-resolution magnetic polarity stratigraphy for correlation to the fossil-rich outcrop sections. The polarity sequence will be calibrated by a series of high-precision U-Pb zircon dates obtained from discrete levels in the core, and will provide critical data to fill the geochronologic gap in global terrestrial and marine time scales for the Late Triassic. The age-calibrated chronostratigraphy of the PFNP core will be used to address major issues of early Mesozoic biotic and environmental change. These include whether marine and continental biotic turnover events in the Late Triassic were coupled; was the largest magnitude faunal turnover event on land during the Late Triassic synchronous with the giant Manicouagan impact; Is the NSF-funded Newark basin astronomically-calibrated time scale consistent with high precision U-Pb zircon age data from the Chinle Formation; and was the cyclical climate change recorded in the Newark basin lacustrine record paced by Milankovitch climate change? In addition to the science generated by the core and its integration into the local and global environmental and biotic framework, the project will have a major education and outreach component. The Petrified Forest National Park is a major tourist destination, averaging 600,000 visitors a year. We plan to leverage this huge resource by developing a permanent exhibit on the coring project and its important scientific results for the park. We will involve numerous student groups during the actual coring activities, including Native American geoscience concentrators at The University of New Mexico/Gallup and K-12 students from throughout the Gallup area. In addition, we will sponsor several workshops at the Park and will reach out to the general public for their participation. The project involves six co-PIs from different institutions and will last 24 months and is intended to provide an initial synopsis of basic stratigraphic, logging, magnetic polarity, and geochronologic data for utilization by the international scientific community for further research and integration with other studies, as well as a major platform for outreach, and a better understanding of how the modern world came to be.