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

Abstract

<p><strong>Abstract.</strong> U-Pb geochronology was conducted by Laser Ablation-Inductively Couple Plasma Mass Spectrometry (LA-ICPMS) on detrital zircon grains from twenty-nine samples from the Coconino Sandstone, Moenkopi Formation, and Chinle Formation. These samples were recovered from ∼520 m of drill core that was acquired during the Colorado Plateau Coring Project (CPCP), located in Petrified Forest National Park (Arizona). </p> <p> A sample from the lower Permian Coconino Sandstone yields a broad distribution of Proterozoic and Paleozoic ages that are consistent with derivation from the Appalachian and Ouachita orogens, with little input from local basement or Ancestral Rocky Mountain sources. Four samples from the Holbrook Member of the Moenkopi Formation yield a different set of Precambrian and Paleozoic age groups, indicating derivation from the Ouachita orogen, the East Mexico Arc, and the Permo-Triassic arc built along the Cordilleran margin. </p> <p> Twenty-three samples from the Chinle Formation contain variable proportions of Proterozoic and Paleozoic zircon grains, but are dominated by Late Triassic grains. LA-ICPMS ages of these grains belong to five main groups that correspond to the Mesa Redondo Member, Blue Mesa Member and lower part of the Sonsela Member, upper part of the Sonsela Member, middle part of the Petrified Forest Member, and upper part of the Petrified Forest Member. The ages of pre-Triassic grains also correspond to these chronostratigraphic units, and are interpreted to reflect varying contributions from the Appalachian orogen to the east, Ouachita orogen to the southeast, Precambrian basement exposed in the Ancestral Mogollon Highlands to the south, East Mexico arc, and Permian-Triassic arc built along the southern Cordilleran margin. Triassic grains in each chronostratigraphic unit also have distinct U and Th concentrations, which are interpreted to reflect temporal changes in the chemistry of arc magmatism. </p> <p> Comparison of our LA-ICPMS ages with available CA-TIMS ages and new magnetostratigraphic data provides new insights into the depositional history of the Chinle Formation, as well as methods utilized to determine depositional ages of fluvial strata. For parts of the Chinle Formation that are dominated by fine-grained clastic strata (e.g. mudstone and siltstone), such as the Blue Mesa Member and Petrified Forest Member, all three chronometers agree (to within ∼1 m.y.), and robust depositional chronologies have been determined. In contrast, for stratigraphic intervals dominated by coarse-grained clastic strata (e.g., sandstone), such as most of the Sonsela Member, the three chronologic records disagree due to recycling of older zircon grains and variable dilution of syn-depositional-age grains. This results in LA-ICPMS ages that significantly pre-date deposition, and CA-TIMS ages that range between the other two chronometers. These complications challenge attempts to establish a well-defined chronostratigraphic age model for the Chinle Formation, and to evaluate possible connections among fundamental Late Triassic biotic and climatic changes, a red siliceous horizon encountered in the CPCP core, and the ∼215.5 Ma Manicouagan impact.</p>

U-Pb zircon geochronology and depositional age models for the Upper Triassic Chinle Formation (Petrified Forest National Park, Arizona, USA): Implications for Late Triassic paleoecological and paleoenvironmental change

“…The model 2 correlation implies that the maximum depositional ages from the lower Chinle Formation, as we derive them above, independent if obtained from core or outcrop, tend to be anomalously old and therefore are not close to the true depositional age, but rather reflect older, recycled zircon material (see also Gehrels et al, 2020). For example, if chron PF5n, which extends almost down to the base of the Sonsela Member, is correlated to E14n (N-H APTS) the base of the member should not be older than ca.…”

“…Thirteen volcaniclastic-bearing siltstone and sandstone samples (data on four of the samples were previously published by Kent et al, 2018) from every ∼20 m throughout the Chinle Formation part of CPCP core 1A were analyzed in this study (see also Gehrels et al, 2020). The zircon mineral separation was conducted at the Arizona LaserChron Center using standard techniques adjusted for the relatively small (quarter core width, 20 cm in length), often clay rich, core samples (see also Gehrels, 2000;Gehrels et al, 2008;Gehrels and Pecha, 2014).…”

“…For each sample, ∼80-300 zircon crystals were analyzed. (Further details of the analytical set-up are reported by Gehrels et al, 2020).…”

“…A few U-Pb CA-TIMS ages are also available for the Chinle Formation outside of the PFNP area. Irmis et al 2011 A large number of U-Pb LA-ICP-MS detrital zircon ages from sandstones have been published by Dickinson and Gehrels (2008a, 2008b, Riggs et al (2012Riggs et al ( , 2013Riggs et al ( , 2016, and more recently by Gehrels et al (2020) from CPCP core 1A of the Chinle Formation. U-Pb ages ranged from Late Archean to Late Triassic.…”

Magnetostratigraphy of the Triassic Moenkopi Formation From the Continuous Cores Recovered in Colorado Plateau Coring Project Phase 1 (CPCP‐1), Petrified Forest National Park, Arizona, USA: Correlation of the Early to Middle Triassic Strata and Biota in Colorado Plateau and Its Environs

“…Correlation of the magnetic polarity stratigraphy from core CPCP-2B to the astronomically tuned (405 Kyr cycle) Early-Middle Triassic magnetostratigraphic timescale from Li et al (2018, their Figure9), which incorporates magnetic polarity patterns and nomenclature for the Early Triassic from theSzurlies (2007), andHounslow and Muttoni (2010) proposed geomagnetic polarity time scales; and for the Anisian (Middle Triassic) from theLehrmann et al (2015), andHounslow and Muttoni (2010) proposed polarity time scales. Blue represents the relative probability distribution curves of the CA-TIMS (chemical abrasion-isotope dilution-thermal ionization mass spectrometry)(Gehrels et al, 2020) and LA-ICPMS (laser ablation-inductively coupled plasma mass spectrometry)(Rasmussen et al, 2020) U-Pb dates from zircon populations of samples from equivalent stratigraphic positions in core CPCP-1A (see FigureS4for full age distribution curves). Lithostratigraphic column shows the color profile from the spectrophotometer for that part of the core CPCP-2B.…”