Astrochronology and radio-isotopic dating of the Alano di Piave section (NE Italy), candidate GSSP for the Priabonian Stage (late Eocene)

Abstract

We have carried out an integrated chronostratigraphic analysis of the Alano di Piave section, proposed GSSP for the Bartonian/Priabonian boundary (Late Eocene). Age constraints were derived independently from a floating cyclochronology based on carbon isotope and wt.% CaCO 3 records, and 206 Pb/ 238 U dating of zircons from four volcanic tuffs. Orbital and radio-isotopic estimates of the duration of intervals bracketed by consecutive crystal-rich volcanic tuff layers are in good overall agreement, but discrepancies of 40-160 kyr are present between nominal volcanic tuff dates derived from astrochronology and 206 Pb/ 238 U. The degree to which these discrepancies are statistically significant at the 2σ level depends on the interpretation of the U-Pb zircon data, and the uncertainties assigned to the astronomical age model. The possible source and significance of these discrepancies are explored in detail. The resulting age model, combined with published bio-, and magnetostratigraphic data, is used to establish the duration of individual magnetochrons in the interval spanning the Bartonian/Priabonian transition, and the timing of late Bartonian-early Priabonian biostratigraphic and magnetostratigraphic events relative to the proposed GSSP, the regionally traceable crystal-rich tuff layer "Tiziano Bed". The chronostratigraphic framework developed at Alano di Piave will facilitate the global correlation of the Priabonian GSSP based on both bio-and magnetostratigraphic criteria. The obtained astrochronology allows a precise correlation of the Alano di Piave 13 C record with oceanic successions confirming a strong dependency of the marine carbon cycle on astronomical forcing although with inter-site differences, which could be related to water mass organization.

An evaluation of Deccan Traps eruption rates using geochronologic data

“…To be clear, this paper is not meant to suggest that the pulsed eruption model based on the U−Pb geochronology is correct. This model should be treated as a working hypothesis that needs to be tested with additional high-precision geochronology on samples that can test the stratigraphic correlations used in Schoene et al (2019); in addition, continued work to produce more robust estimates for eruption ages from complex zircon datasets is needed (Galeotti et al, 2019;Keller et al, 2018;Schoene et al, 2010). Additional geochronology is also needed to provide a broader perspective on Deccan volcanism regionally (Knight et al, 2003;Eddy et al, 2020;Parisio et al, 2016;Schöbel et al, 2014;Sheth et al, 2019).…”

“…Advances in geochronological techniques and applications over the last 2 decades have evolved to show that LIPs erupt > 10 5 km 3 , usually in less than a million years, as opposed to tens of millions as previously thought (Burgess and Bowring, 2015;Kasbohm et al, 2020;Davies et al, 2017;Svensen et al, 2012). However, large uncertainties remain regarding the rates of extrusive versus intrusive magmatism, as well as the flux of volcanic versus non-eruptive volatiles, such as CO 2 and SO 2 , that are thought to drive climate change (Black and Manga, 2017;Burgess et al, 2017;Ganino and Arndt, 2009;Self et al, 2014;Svensen et al, 2004).…”

The Österplana Fossil Meteorites and… What Else? Terrestrial Cr-Spinels and Zircons in the Ordovician Limestones of the Thorsberg Quarry (Sweden)

“…They are elongated to acicular morphologies, with aspect ratios greater than 3, and have well-defined crystal faces and sharp edges, with no signs of transport abrasion. According to [32,33], these zircons are probably from volcanic ash or tuff, as they show no signs of transport abrasion, and share common features with the elongated acicular morphologies typical of rapid crystallization. zircons are probably from volcanic ash or tuff, as they show no signs of transport abrasion, and share common features with the elongated acicular morphologies typical of rapid crystallization.…”

Supplemental Material: Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information

“…Secondly, it must be acknowledged that the accuracy of an age depends on the robustness of the interpretations of how a date corresponds to a geologic process or event. For example, an eruption age for an ash bed based on U-Pb zircon dates may require interpretation of a potentially complex data set that includes zircon dates that predate eruption (Galeotti et al, 2019;Griffis et al, 2019;Keller et al, 2018;Ovtcharova et al, 2015;Sahy et al, 2017). Indeed, increased precision of ID-TIMS U-Pb data has led to a situation in which different approaches to inferring a geologic process (such as eruption) from a complicated data set can result in different highprecision age interpretations from the same data set.…”