Influence of the local controling factors over the Early Triassic paired carbon isotopoes fluctuations

International audienceImportant and recurrent perturbations of the carbon isotope signals are recorded during the Early Triassic, in the aftermath of the end-Permian mass extinction (~252 Ma). These perturbations, among the largest observed throughout the Phanerozoic, are most notably represented by a globally recognized couplet of a negative and a positive excursions, before and across the Smithian/Spathian boundary (SSB, ~1.5 Myr after the Permian/Triassic boundary), imprinted in both the carbonate and organic matter reservoirs. These fluctuations are generally assumed to be linked to environmental perturbations related to a late degassing of the Siberian Traps. Recent works on the Early Triassic Sonoma Foreland Basin (western USA) have shown that local secondary processes can have a strong influenceon the carbon isotope record, preventing its usual use for long-distance correlations and global climatic interpretations. Here, new measurements of paired carbon isotopes (carbonate and organic matter fractions) from the Griesbachian-Dienerian up to the lower Spathian have been performed on a section of the Sonoma Foreland Basin, at Hot Springs (SE Idaho). We show that both carbonate and organic matter δ13C signals mirror the signal recognized at the global-scale, particularly for the SSB event, and that this signal is not due to secondary diagenetic processes. However, if SSB excursions are observed in both signals, dampened variations in the organic reservoir are observed. These variations in the net isotopic effect (i.e., δ13C) reflect a complex set of locally controlled forcing parameters (including, but not restricted to, e.g. mixing of terrestrial and marine organic matters in relation to variation in sedimentary depositional setting), rather than suggested CO2-driven temperature variations. We argue that even if the globally recognized variations of the carbon isotope record are observed, the Hot Springs isotope signal most probably reflects primarily the local geological context rather than diagenetic or exogenic carbon cycle processes. We therefore question the validity of high-resolution carbon signals for long-distance correlations during the Early Triassic. Rather, we suggest to use the carbon signal to characterize fluctuating local conditions during deposition