New age constraints on the Lower Jurassic Pliensbachian-Toarcian Boundary at Chacay Melehue (Neuquen Basin, Argentina)

The Pliensbachian-Toarcian boundary interval is characterized by a similar to 3 parts per thousand 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 are 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 similar to 183.73 + 0.35/- 0.50 Ma for the Pliensbachian-Toarcian boundary, and 182.77 + 0.11/- 0.15 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.

Automated summary

The Pliensbachian-Toarcian boundary interval is characterized by a significant negative carbon-isotope excursion (CIE) in various marine and terrestrial archives, indicating a global disturbance to the carbon cycle. A new high-resolution organic-carbon isotope record from the Arroyo Chacay Melehue section in Argentina confirms the global significance of this anomaly. It also provides precise age assignments for the boundary and zonal boundaries using U-Pb zircon geochronology and a Bayesian Markov chain Monte Carlo (MCMC) stratigraphic age model.