Patterns of organic carbon enrichment in a lacustrine system across the K-T boundary : Insight from a multi-proxy analysis of the Yacoraite Formation, Salta rift basin, Argentina

In this study, an integrated approach was applied using available sedimentary, geochronology, geochemical and isotopic datasets to better understand the complex interactions between production, destruction, and dilution processes that characterize the organic-rich sediments dynamic across the K-T boundary in a lacustrine system. This approach was tested here on the Late Cretaceous to Early Cenozoic Yacoraite Formation, a typical lacustrine source rock from the Salta rift Basin (NW Argentina). The Yacoraite Formation corresponds to a mixed carbonate-siliciclastic lacustrine sedimentary system, deposited during the sag phase (post-rift). We demonstrated here that new ashes U-Pb dating tie the K-T boundary during the deposition of the Yacoraite Formation. The Yacoraite Formation recorded major climate changes that can be documented in terms of catchment dynamic, erosion processes, carbonate accumulation trends, lacustrine dynamic and source rock quality. The pattern of organic carbon enrichment in the Yacoraite Formation illustrates how a biological pump came across a major climatic change. The background organic matter correspond to Type I dominated by algal growth (mean HI 600–800 mgHC/gTOC, TOC0 1–2 wt%). The K-T boundary was the climax of a climate change initiated ca. 0.3 Myr before and induced a major change in the catchment weathering processes, which temporally corresponds to the accumulation of poor quality source rock intervals (TOC0 ≤ 0.2 wt% and HI < 50 mgHC/gTOC) in these series. The K-T boundary is highlighted by the main negative anomaly in δ13C of the carbonate deposits of the Yacoraite Formation. It was followed by a major pulse in paleoproductivity, itself followed by a major pulse in TOC0 (10–15 wt%) under anoxia conditions. In ca. 0.2 Myr the lacustrine dynamic and its related organic‑carbon enrichment resumed to their initial setting, just prior to the preluding K-T boundary climate change. Results suggest that the Yacoraite Formation can be considered as a world-class example to illustrate how the K-T boundary is recorded in lacustrine sediments.