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The Vaca Muerta-Quintuco Mixed System: A Regional Outcrop to Subsurface Overview

Massaferro, Jose L.; Zeller, Michael; Giunta, David L.; Sagasti, Guillermina; Eberli, Gregor

Vaca Muerta (VMF) and Quintuco (QF) Formations consist of a Late Jurassic-Early Cretaceous mixed system succession deposited in the Neuquén Basin, southwest Argentina. Deposition was dominated by marine deposits where VMF represents the basinal, northwest-ward prograding shale/carbonate units and QF corresponds to shallow marine, more aggrading carbonate-dominated mixed deposits. Lithostratigraphic boundaries are diachronous where VMF is the time equivalent basinal succession to the shelfal, higher energy QF younger units.

Seismically, VMF and QF can be subdivided into a number of sequences defined by reflection terminations. The lower part of the VMF corresponds to continuous, aggrading seismic reflections, which represents the basinal, high TOC organic shales. The top of this unit becomes a downlap surface of a northwestward gently-dipping prograding clinoforms, which is interpreted as a maximum flooding surface. Geometries of these sequences are sigmoids with poor-developed shelf breaks and limited vertical accommodation space. Slope angles increase in younger sequences changing geometries to complex-oblique clinoforms depicting more pronounced shelf breaks. Geometrical pattern indicates also a change to more vertical aggradation within the overall dominant lateral progradation. Configuration of younger prograding sequences show well-developed shelf breaks showing prograding, downstepping and prograding/aggrading geometries. Accommodation space was progressively filled up basinward where seismic reflections progressively converged. Increase in subsidence towards the northwest is represented by onlap units, which separates the lower prograding seismic configuration into mainly aggrading, younger mixed carbonate siliciclastic units. Seismic geometries include: retrogradation at the base and agraddation in younger units represented by skeletal-oolitic shoal complexes intercalated with more open marine siliciclastic deposits.

Two large-scale outcrop exposures in the western part of the basin display a very similar character in architecture. Based on geometrical analyses and synthetic seismic models, they follow the same transitions from gently dipping prograding clinoforms in older sequences to steeper clinoforms with clearly developed break in younger sequences. This strong similarity underlines the control of eustatic sea level on the entire system and supports the applicability of the outcrop sections as analogs for subsurface exploration.

 

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013