Negative ?13Ccarb values at the Jurassic-Cretaceous boundary – Vaca Muerta Formation, Neuquén Basin, Argentina

The stable carbon isotopic compositions of carbonate sediments (?13Ccarb) have been widely used to reconstruct the global cycle and as a stratigraphic correlation tool. This work investigates ?13Ccarb record marine organic-rich, mixed siliciclastic?carbonate mudstones accumulated from Tithonian (late Jurassic) early Valanginian (early Cretaceous) in retro-arc basin connected Proto-Pacific Ocean (Neuquén Basin, Argentina). high-resolution values these strata outcrops at various locations differ those coeval pelagic Tethys. profile Puerta Curaco area shows an overall increasing trend average ?7‰ Tithonian) approximately 0‰ Valanginian). negative occur ~ 400 m thick TOC-rich succession (TOC > 2%) are arranged 3 large-scale increasing-decreasing cycles. Although absolute offset, main trends similar other subsurface wells. co-occurrence highest U/Th (>1.4) most suggests that major might be modulated by oscillations oxygen content within probably driven sea-level changes. Clastic-dominated transgressive hemicycles higher TOC more while opposite occurs carbonate-rich regressive hemicycles. A “normal” surface-water (avg. +2‰) southern shelf increasingly towards center indicates mixing between platform-derived material unaffected diagenesis precipitated or altered dysoxic/anoxic basin. Tethyan realm does not this episode high burial organic occurred Neuquén during Berriasian but display slightly decreasing +2.5 +1.5‰.