Building on an earlier study that confirmed the stability of the 405-kyr eccentricity climate cycle and the timing of the Newark-Hartford astrochronostratigraphic polarity time scale back to 215 Ma, we extend the magnetochronology of the Late Triassic Chinle Formation to its basal unconformity in scientific drill core PFNP-1A from Petrified Forest National Park (Arizona, USA). The 335-m-thick Chinle section is imprinted with paleomagnetic polarity zones PF1r to PF10n, which we correlate to chrons E17r to E9n (~209 to 224 Ma) of the Newark-Hartford astrochronostratigraphic polarity time scale. A sediment accumulation rate of ~34 m/Myr can be extended down to ~270 m, close to the base of the Sonsela Member and the base of magnetozone PF5n, which we correlate to chron E14n that onsets at 216.16 Ma. Magnetozones PF5r to PF10n in the underlying 65-m-thick section of the mudstone-dominated Blue Mesa and Mesa Redondo members plausibly correlate to chrons E13r to E9n, indicating a sediment accumulation rate of only ~10 m/Myr. Published high-precision U-Pb detrital zircon dates from the lower Chinle tend to be several million years older than the magnetochronological age model. The source of this discrepancy is unclear but may be due to sporadic introduction of juvenile zircons that get recycled. The new magnetochronological constraint on the base of the Sonsela Member brings the apparent timing of the included Adamanian-Revueltian land vertebrate faunal zone boundary and the Zone II to Zone III palynofloral transition closer to the temporal range of the ~215 Ma Manicouagan impact structure in Canada.
Bibliographical noteFunding Information:
We again thank the National Park Service, particularly former superintendent Brad Traver, for permission to core in the park and for logistical support during site selection and drilling. On‐site and laboratory core processing, scanning and archiving was carried out by LacCore, particularly Anders Noren, Kristina Brady, and Ryan O'Grady; on‐site core‐handling volunteers Justin Clifton, Bob Graves, Ed Lamb, Max Schnurrenberger, and Riley Black are thanked for their round‐the‐clock efforts, and drilling manager Doug Schnurrenberger for overseeing a superb coring project. Thoughtful critical comments by the journal reviewers (Wout Krijgsman and anonymous) prompted us to improve the paper. This project was funded by NSF collaborative grants EAR 0958976 (PEO and J. W. G.), 0958723 (R. M.), 0958915 (R. B. I.), 0959107 (G. E. G.), and 0958859 (D. V. K.) and by the Deutsche Forschungsgemeinschaft for ICDP support. Additional support was provided by NSF grant EAR‐1338583 (G. E. G.) to the Arizona LaserChron Center; P. E. O. acknowledges support from the Lamont‐Climate Center, R. M. acknowledges support of the Ann and Gordon Getty Foundation, and D. V. K. is grateful to the Lamont‐Doherty Incentive Account for support of the Paleomagnetics Lab. Curation facilities for the working halves of the CPCP cores are provided by the Rutgers Core Repository, which will archive on its website any data not presented in Supplementary Information. Data will also be deposited at “CPCP/Google Drive/Core Metadata/CPCP_section metadata,” https://osf.io/5vd8u/ (CPCP; Identifier: DOI 10.17605/OSF.IO/5VD8U). Any opinions, findings, or conclusions of this study represent the views of the authors and not those of the U.S. Federal Government. This is Petrified Forest Paleontological Contribution 64 and LDEO Contribution 8360.
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- Colorado Plateau
- detrital zircons
- Late Triassic
- U-Pb geochronology
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