Magnetochronology of the Entire Chinle Formation (Norian Age) in a Scientific Drill Core From Petrified Forest National Park (Arizona, USA) and Implications for Regional and Global Correlations in the Late Triassic

Abstract

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.

LA-ICPMS U-Pb geochronology of detrital zircon grains from the Coconino, Moenkopi, and Chinle Formations in the Petrified Forest National Park (Arizona)

“…This assumption is supported by the relatively continuous distribution of U-Pb ages within the Cordilleran magmatic arc and back-arc (upper curves of Figure 13). This view is in contrast to the hypothesis of Kent et al (2019) that variations in the proportions of depositional-age versus older zircon grains result mainly from temporal changes in magmatic flux.…”

“…The depositional age of Triassic strata on the Colorado Plateau is of considerable interest because of the rich faunal and paleoclimatic records preserved within the Moenkopi Formation and Chinle Formation, and as the zircon-based geochronological framework for the early Mesozoic when coupled with paleomagnetic polarity stratigraphy and astrochronology (Olsen et al, 2018(Olsen et al, , 2019Kent et al, 2018Kent et al, , 2019Rasmussen et al, 2019). There accordingly have been many prior attempts to determine the depositional age of these strata by dating igneous zircon grains in ash beds or volcanic cobbles and detrital zircon grains in clastic strata (e.g., Riggs et al, 1996Riggs et al, , 2003Riggs et al, , 2012Riggs et al, , 2013Riggs et al, , 2016Heckert et al, 2009;Dickinson and Gehrels, 2009;Irmis et al, 2011;Ramezani et al, 2011Ramezani et al, , 2014Atchley et al, 2013;Nordt et al, 2015) Figure 13.…”

“…(1) Chinle Formation strata encountered in the CPCP core record nearly continuous deposition as described in the age model of Kent et al (2019), perhaps with a period of erosion or very slow deposition in the middle part of the Sonsela Member (Rasmussen et al, 2019).…”

“…Triassic strata of the Colorado Plateau and environs provide rich and geographically extensive records of environmental and biotic change during a critical period of Earth history, as well as the transition from passive-to convergent-margin tectonism along the North American Cordillera (e.g., Parker and Martz, 2011;Olsen et al, 2011). As demonstrated by Riggs et al (1996Riggs et al ( , 2003Riggs et al ( , 2012Riggs et al ( , 2013Riggs et al ( , 2016, Dickinson and Gehrels (2008), Irmis et al (2011), Ramezani et al (2011Ramezani et al ( , 2014, Atchley et al (2013), Nordt et al (2015), Kent et al (2018Kent et al ( , 2019, Olsen et al (2018Olsen et al ( , 2019, Marsh et al (2019), and Rasmussen et al (2019), Chinle Formation strata have the potential to record the timing of these changes in great detail given their several-hundredmeter thickness, abundance of near-depositional-age zircon grains, and recoverable paleomagnetic reversal stratigraphy.…”

“…1). The objectives and primary findings of this project have been described by Olsen et al (2018Olsen et al ( , 2019, Kent et al (2018Kent et al ( , 2019, and Rasmussen et al (2019), and numerous related studies are currently in progress.…”