TAPHONOMIC AND PALEOENVIRONMENTAL INFLUENCE ON ATMOSPHERIC PALEO-CO₂ SIMULATIONS USING BRYOCARB IN DEVONIAN FOSSILS FROM SOUTHERN GONDWANA

This study applies the BRYOCARB model to fossil cuticles of Spongiophyton Kräusel, 1954 derived from two Devonian deposits of the Paraná Basin: Unit 3 of the Chapada Group (393.3 Ma) and the São Domingos Formation (387.7 Ma). The aim is to estimate physiological parameters of the plant and reconstruct atmospheric CO₂ concentrations in high southern paleolatitude environments during the Middle Devonian. Carbon and nitrogen stable isotope compositions (δ¹³C and δ¹⁵N) were determined using EA-IRMS (UC Davis), with analytical precision of ±0.2‰ and ±0.3‰, respectively, and normalized to the VPDB (δ¹³C) and atmospheric N₂ (δ¹⁵N) standards. Samples from Unit 3 yielded average atmospheric CO₂ concentrations of approximately 374.5 ppm, with Δ¹³C ranging from ~14.7‰ to 18.5‰ and photosynthetic assimilation rates (A) between ~9.7 and 10.2 μmol m⁻² s⁻¹. For the São Domingos Formation, mean CO₂ values increased slightly to 384.7 ppm, with Δ¹³C values between ~15.8‰ and 16.7‰. The ~10 ppm increase over ~6 million years may reflect changes in continental biogeochemical cycles, volcanic CO₂ outgassing, or shifts in large-scale primary productivity. The statistical consistency of the dataset, expressed by low standard deviations and narrow confidence intervals, indicates both excellent cuticle preservation and relatively stable environmental conditions at the study sites. Spongiophyton appears to have inhabited microclimatically stable, low-competition environments, such as seasonally moist floodplains or protected coastal lagoons. The samples from Unit 3, interpreted as a deltaic setting, displays finely laminated facies and an absence of intense bioturbation, favoring both plant growth and tissue preservation. In contrast, samples of the São Domingos Formation, deposited in a shallow marine platform setting, exhibit signs of greater environmental regulation, including lower variability in A and slightly higher Ca concentrations, suggesting more buffered thermal and hydric regimes. These taphonomic and physiological patterns indicate that Spongiophyton possessed high ecological plasticity, tolerating poorly developed soils and fluctuating moisture availability. The absence of extreme Δ¹³C values and the uniformity in A suggest persistent plant communities composed of taxa adapted to mild climatic variability. This resilience may have been a key factor in the widespread distribution of Spongiophyton along the continental margins of Gondwana during the Devonian. [CAPES  88882.329724/2014-01, FAPESP 2023/16631-1, 2019/01747-5 e FULBRIGHT]