The Vaca Muerta-Quintuco system (Tithonian - Valanginian) in the Neuquén Basin, Argentina: a view from the outcrops in the Chos Malal fold and thrust belt

KIETZMANN, D.A.; AMBROSIO, A; SURIANO, J.; ALONSO, S.; GONZALEZ TOMASSINI, F.; DEPINE, G.; REPOL, D.

AAPG BULLETIN

AMER ASSOC PETROLEUM GEOLOGIST

Lugar: Tulsa; Año: 2016 vol. 100 p. 743 - 771

0149-1423

The Vaca Muerta-Quintuco system (uppermost lower Tithonian ? lower Valanginian) is a thick shallowing-upward sedimentary cycle consisting of dark bituminous shales, marlstones, limestones, and sandstones, cropping out in the Neuquén Basin, west-central Argentina. This paper analyzes three outcrop sections in Chos Malal area, northem Neuquén province. Detailed facies analysis allows to differentiate six facies associations, representing basinal to proximal outer ramp facies of a homoclinal carbonate ramp system (Vaca Muerta Formation), and basinal to shoreface facies of a mixed carbonate-siliciclastic shelf system (Quintuco Formation), prograding westward from the eastern margin of the basin. Two sequence hierarchies were recognized: five composite depositional sequences (3rd order), and fifteen high-frequency sequences (4th order). Fluctuations in organic matter content within the Vaca Muerta Formation suggests relationship with depositional sequences, finding the highest values associated with transgressive systems tract, while the transition to the Quintuco Formation shows a strong decrease in total organic carbon. X-ray diffraction studies show an increase of clay minerals and quartz in the transgressive systems tract of the Vaca Muerta Formation, and an increase in the content of calcite in high-stand systems tracts. This pattern is reversed in the Quintuco Formation. Our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter, clay minerals, facies, stacking pattern and relative sea-level changes in this exceptional shale-oil and shale-gas unconventional reservoir. This study may be helpful for a better postulate of petrophysical and geomechanical models for unconventional exploration.