The Newark-Hartford astrochronostratigraphic polarity timescale (APTS) was developed using a theoretically constant 405-kiloyear eccentricity cycle linked to gravitational interactions with Jupiter-Venus as a tuning target and provides a major timing calibration for about 30 million years of Late Triassic and earliest Jurassic time. While the 405-ky cycle is both unimodal and the most metronomic of the major orbital cycles thought to pace Earth's climate in numerical solutions, there has been little empirical confirmation of that behavior, especially back before the limits of orbital solutions at about 50 million years before present. Moreover, the APTS is anchored only at its younger end by U-Pb zircon dates at 201.6 million years before present and could even be missing a number of 405-ky cycles. To test the validity of the dangling APTS and orbital periodicities, we recovered a diagnostic magnetic polarity sequence in the volcaniclastic-bearing Chinle Formation in a scientific drill core from Petrified Forest National Park (Arizona) that provides an unambiguous correlation to the APTS. New high precision U-Pb detrital zircon dates from the core are indistinguishable from ages predicted by the APTS back to 215 million years before present. The agreement shows that the APTS is continuous and supports a stable 405-kiloyear cycle well beyond theoretical solutions. The validated Newark-Hartford APTS can be used as a robust framework to help differentiate provinciality from global temporal patterns in the ecological rise of early dinosaurs in the Late Triassic, amongst other problems.

The Gravina belt consists of Upper Jurassic through Lower Cretaceous marine clastic strata and mafic-intermediate volcanic rocks that occur along the western flank of the Coast Mountains in southeast Alaska and coastal British Columbia. This report presents U-Pb ages and Hf isotope determinations of detrital zircons that have been recovered from samples collected from various stratigraphic levels and from along the length of the belt. The results support previous interpretations that strata in the western portion of the Gravina belt accumulated along the inboard margin of the Alexander-Wrangellia terrane and in a back-arc position with respect to the western Coast Mountains batholith. Our results are also consistent with previous suggestions that eastern strata accumulated along the western margin of the inboard Stikine, Yukon-Tanana, and Taku terranes and in a fore-arc position with respect to the eastern Coast Mountains batholith. The history of juxtaposition of western and eastern assemblages is obscured by subsequent plutonism, deformation, and metamorphism within the Coast Mountains orogen, but may have occurred along an Early Cretaceous sinistral transform system. Our results are inconsistent with models in which an east-facing subduction zone existed along the inboard margin of the Alexander-Wrangellia terrane during Late Jurassic-Early Cretaceous time.

The onset of modern central Asian atmospheric circulation is traditionally linked to the interplay of surface uplift of the Mongolian and Tibetan-Himalayan orogens, retreat of the Paratethys sea from central Asia and Cenozoic global cooling. Although the role of these players has not yet been unravelled, the vast dust deposits of central China support the presence of arid conditions and modern atmospheric pathways for the last 25 million years (Myr). Here, we present provenance data from older (42–33 Myr) dust deposits, at a time when the Tibetan Plateau was less developed, the Paratethys sea still present in central Asia and atmospheric pCO2 much higher. Our results show that dust sources and near-surface atmospheric circulation have changed little since at least 42 Myr. Our findings indicate that the locus of central Asian high pressures and concurrent aridity is a resilient feature only modulated by mountain building, global cooling and sea retreat.

Many applications specific to detrital mineral U‐Th‐Pb geochronology in the Earth sciences necessitate large numbers of age observations to be made from samples and require accurate and precise isotope measurements across wide dynamic ranges in elemental concentrations and signal intensities. This implies that the laser system and mass spectrometer cannot be tuned between individual analyses as to optimize measurements based on the isotope composition and concentrations of samples and that intensity matching between the unknowns to be dated and the reference material(s) used for fractionation correction is impossible to ensure. We describe methodologies for optimization of laser ablation‐single collector‐inductively coupled plasma‐mass spectrometer for the accurate determination of initial‐Pb‐corrected (using measured 204Pb) U‐Th‐Pb zircon ages, taking full advantage of the high sensitivity provided by the Thermo Element 2 ICP‐MS instruments fitted with a high‐performance low ultimate vacuum Jet interface. “We describe an approach that corrects for nonlinearity of the detector—the primary obstacle avoided with sample‐specific tuning—as well as element‐ and mass‐dependent fractionation and instrumental drift by using a suite of three zircon reference materials with known isotopic ratios from isotope dilution‐thermal ionization mass spectrometry measurements but with differing U and Pb concentrations.” This approach allows for (experimentally) determining an instrumental fractionation versus ion beam intensity curve used for standard‐sample bracketing, thus taking into consideration an important instrumental variable that is commonly ignored in most applications of U‐Pb dating using laser ablation‐single collector‐inductively coupled plasma‐mass spectrometer. We show that these methodologies yield uncertainties and age offsets typically better than ±2.0% for individual measurements of small (e.g., 10‐μm depth × 20‐μm diameter) volumes of material.

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.