Paleo-environmental evolution of the southern Neuquen basin (Argentina) during the Tithonian-Berriasian (Vaca Muerta and Picun Leufu Formations): a multi-proxy approach

The Tithonian-Berriasian interval in the southern part of the Neuquen Basin is represented by the Vaca Muerta and the Picun Leufu Formations. Facies analysis and correlation of the Vaca Muerta Formation and the lower part of the Picun Leufu Formation in the Picun Leufu Anticline allow us to characterize the evolution of successive facies belts representing silici-clastic shelf and mixed ramp environments. Shore-face and offshore facies are developed on the silici-clastic shelf in the western and southern parts of the Picun Leufu Anticline. The offshore transition domain is characterized by storm beds and slump features, whereas the offshore domain corresponds to black to grey shales and turbidites. The mixed silici-clastic-carbonate ramp is characterized by the development of a lagoon and high-energy shoal in the proximal part of the inner ramp, whereas the distal part comprises a tidal complex. The mid-ramp zone is characterized by storm influence and the outer ramp by fine-grained deposits. Two major transgressive-regressive sequences and five high-frequency transgressive-regressive sequences are recognized. The high-frequency transgressive-regressive sequences make up three pro-gradational sequences, an aggradational-pro-gradational sequence and an aggradational sequence. The geochemical characteristics and clay mineralogy of the Tithonian-Berriasian interval in the southern Neuquen Basin indicate that (1) climate played a key role in the evolution of the sedimentary environment, (2) a 'normal marine' depositional environment with oxic sea water and sediment pore waters, rapidly changing to sub-oxic conditions at shallow depth below the seabed and (3) the occurrence of episodically restricted water-mass circulation at the onset of deposition of the Vaca Muerta Formation. (authors)