Geochemical insights into Triassic plant fossils from western Gondwana (Argentina): interpreting diagenetic and δ13Corg variability

Abstract

Fossil plant assemblages from the Triassic of western Argentina provide a valuable archive for understanding paleoenvironmental and climatic dynamics in southwestern Gondwana. In this study, we integrate geochemical and isotopic analyses to assess the preservation conditions and paleoenvironmental significance of plant remains from two lacustrine successions from Argentina: the Los Rastros Formation (Ischigualasto–Villa Uni´ on Basin) and the Potrerillos–Cacheuta formations (Cuyana Basin). We employed Energy Dispersive X-ray Spectroscopy to examine the elemental composition of the fossil remains and evaluate diagenetic pathways. Stable carbon isotope analysis (δ 13 δ 13 C org C org ) was carried out to investigate its environmental significance. We also reviewed published data from coeval and geographically diverse Triassic units to contextualize our results within broader temporal and spatial trends. Our findings indicate three preservation types, with original organic material partially retained due to rapid burial, volcanic ash input, and early diagenetic anoxia. The δ reflects changes in water availability, temperature, atmospheric CO 2 13 C org variability levels, and ecosystem productivity. The lower section of the Los Rastros Formation records negative δ 13 C org excursion consistent with warmer and more humid conditions during the Carnian Pluvial Episode, whereas the Cacheuta Formation displays δ 13 C shifts likely influenced by local dynamics. This isotopic signal, interpreted alongside the paleobotanical assemblage, supports a regional climatic response at low southern paleolatitudes and contributes to growing evidence for global carbon cycle perturbations during the Late Triassic. Our results reinforce the picture of the Late Triassic world as a time of dynamic climate, with major environmental differences across latitudinally-arrayed climate zones.