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Andean Overthrusting, Northern Neuquen Basin, Argentina

Richardson B. Allen, Jeffrey G. Feehan

The Neuquen basin of Argentina is a remnant of the Mesozoic back-arc basin system of western South America. Triassic through Upper Cretaceous rocks of the central and northern Neuquen basin show predominantly northwesterly depositional trends. The more north-trending foreland fold and thrust belt of the eastern Andean foothills is superimposed across these earlier depositional trends; thus, the location of the thrust belt changes from south to north from the basin center to the eastern basin platform.

The Jurassic-Upper Cretaceous sequence of the undeformed eastern flank of the central Neuquen basin is characterized by a gradual northeast to southwest change from a thin, inner platform section to transitional outer platform and thick basinal sections. Toward the north, the thrust belt of the northern Neuquen basin juxtaposes a thick basinal section to the west against a thin inner platform section to the east. The absence of a transitional outer platform section in the northern basin suggests large shortening across the thrust belt, with possible eastward thrusting of the basinal section over the transitional outer platform section.

Balanced cross sections for the northern Neuquen basin based on these observations show large-scale duplexing and repetition of section above a major detachment horizon within the pre-Jurassic economic basement. The cross sections demonstrate that such a structural model for the northern Neuquen basin is geometrically possible and consistent with the known surface and subsurface geology. Further information, particularly deep seismic data from the area, is needed to confirm this model.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.