A high-precision U–Pb zircon age constraints the timing of the faunistic and palynofloristic events of the Carnian Ischigualasto Formation, San Juan, Argentina

• Published in: Journal of South American earth sciences 2021-11, Vol.111, p.103433, Article 103433
• Main Authors: Colombi, Carina, Martínez, Ricardo N., Césari, Silvia N., Alcober, Oscar, Limarino, Carlos O., Montañez, Isabel
• Format: Article
• Language: English
• Subjects: Absolute age; Dinosaurs; Extinction; Onslow microflora; Paleovertebrate; Palynomorphs; Upper Triassic
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2021.103433

The Late Triassic represents records many of the most critical biotic crises in life-history (from Carnian to the end-Triassic extinction, ETE). Some hypotheses propose that these life changes were linked with shifts in the environmental setting during the initial stages of the Pangea breakup. These crises were likely not sudden events but a series of step-changes that reached their peak at the end of the Triassic. The Carnian-Norian Ischigualasto Formation is a world-renown terrestrial sequence that records both the Triassic Dinosaur Diversification Event (DDE) and at least one crucial terrestrial environmental and biotic turnover. A notable increase in humidity and volcanism was the setting of critical faunal replacement represented by the passage of the Hyperodapedon-Exaeretodon-Herrerasaurus to Exaeretodon tetrapod biozones. That environmental modification, together with the paleofaunistic turnover, has been accurately constrained by a new high-precision CA-TIMS U/Pb zircon age of 228.91 ± 0.14 Ma obtained from a tuff layer located in the exact stratigraphic position of the major biotic-paleoenvironmental disturbance in the middle part of the Valle de la Luna Member, at ~310 m from the base of the Ischigualasto Formation. Palynological assemblages containing the first records in westernmost Gondwana of European Tethyan and Onslow palynological species are also recognized close to the dated tuff level. Thus, this age is the first isotopic record for the Onslow Microflora diagnostic species in Gondwana. Moreover, the CA-TIMS date promotes a discussion about the accurate chronostratigraphic position for the beginning (after the Carnian Pluvial Event) of a series of environmental-biological disturbances that culminated at the end of the Triassic. [Display omitted] •Drastic paleoenvironment-biotic perturbation occurred at 310 m of Ischigualasto Fm.•This event dated at 228.91 Ma.•This is the first date for Carnian Tethyan palynomorphs in western Gondwana.