New Chronostratigraphic Constraints on the Lower Jurassic Pliensbachian–Toarcian Boundary at Chacay Melehue (Neuquén Basin, Argentina)

Abstract

The Pliensbachian–Toarcian boundary interval is characterized by a ~3‰ negative carbon-isotope excursion (CIE) in organic and inorganic marine and terrestrial archives from sections in Europe, such as Peniche (Portugal) and Hawsker Bottoms, Yorkshire (UK). A new high-resolution organic-carbon isotope record, illustrating the same chemostratigraphic feature, is presented from the Southern Hemisphere Arroyo Chacay Melehue section, Chos Malal, Argentina, corroborating the global significance of this disturbance to the carbon cycle. The negative carbon-isotope excursion, mercury and organic-matter enrichment is accompanied by high-resolution ammonite and nannofossil biostratigraphy together with U-Pb CA-ID-TIMS geochronology derived from intercalated volcanic ash beds. A new age of ~183.71 ± 0.40/-0.51 Ma for the Pliensbachian–Toarcian boundary, and 182.77 +0.11/-0.21 for the tenuicostatum–serpentinum zonal boundary, is assigned based on high-precision U-Pb zircon geochronology and a Bayesian Markov chain Monte Carlo (MCMC) stratigraphic age model.

Initial results of coring at Prees, Cheshire Basin, UK (ICDP JET project): towards an integrated stratigraphy, timescale, and Earth system understanding for the Early Jurassic

“…However, the diverse Early Jurassic biostratigraphic, astrochronologic, magnetostratigraphic, and chemostratigraphic schemes have, for the most part, remained poorly integrated with each other and have lacked accurate numerical calibration, leaving many uncertainties with regard to the rates and relative timing of key Earth system processes (e.g. Hesselbo et al, 2020a;Al-Suwaidi et al, 2022). Although astrochronologic studies, which make use of stable orbital cycles, have been used to great advantage recently, incompatible interpretations for the Early Jurassic are not uncommon (see e.g.…”

“…Carbon-isotope stratigraphy based on analysis of bulk organic matter has proven to be particularly useful for local to regional and, potentially, even global correlations to help refine those based on ammonite chronostratigraphy (e.g. Al-Suwaidi et al, 2022). Although it is broadly acknowledged that the finer details of carbon-isotope curves may be due to factors under local controls, such as mixing of different organic matter components with their individual carbonisotopic compositions (e.g.…”