--> Abstract: Transgressions, Condensed Sections, and Bituminous Shales in Neuquen Basin, by C. M. Urien and O. L. Gamundi; #91012 (1992).

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ABSTRACT: Transgressions, Condensed Sections, and Bituminous Shales in Neuquen Basin

URIEN, CARLOS MARIA, Urien & Associates, Buenos Aires, Argentina, and OSCAR LOPEZ GAMUNDI, Texaco, Houston, TX

The Lower Cretaceous Avile sandstone constitutes a fluvial-eolian sedimentary complex present in the central west of the Neuquen basin. This sedimentary complex is restricted to central areas of the basin where it rests on shelf mudstones and has been interpreted as deltas deposited during a sea level lowstand.

An important relative sea level rise took place after the deposition of the Avile sandstone with the consequence shoreline retreat and encroachment of marine environments. An extensive basin-margin transgression can be inferred by the presence of outer shelf to basin shales, marls, and limestone beds. These deposits onlap the Avile sandstone throughout the central and western portions of the basin. This sea level rise was coupled with an expansion of the oxygen-defficient bottom layer. Bituminous shales were preserved under these anoxic conditions and characterize the basal reach of the marine flooding event.

These sharp vertical facies changes have been identified along the outcrop belt on the western thrust belt and in subsurface in the platform as well. Well logs and seismic lines show an abrupt vertical change between the lowstand wedge deposits (Avile Complex) and the underlying shelf mudstones. In turn, the transgressive bituminous shales resting on top of the Avile sandstone exhibit a characteristic well log response: depressed SP curves and strong resistivity peaks. These marine condensed sections represent distinctive log markers of basinwide scale. This sedimentary complex has opened a new exploratory trend in North Central Neuquen with already proved commerical production in the Eastern platform and hinge line.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)