Seismic Stratigraphy and Structural Setting of Early Jurassic to Mid-Cretaceous Sedimentary Rocks in Southern Neuquen Basin, Argentina

Marc W. Harder, Richardson B. Allen

The structural evolution of the Neuquen, or Huincul, "dorsal" and its effect on sedimentation and stratigraphy is interpreted from seismic and well data in the southern Neuquen basin, a Mesozoic back-arc basin located in west-central Argentina, Seismic cross sections reveal that dominantly marine Jurassic sediments began filling the basin as a series of thick, discontinuous, progradational packages. Transpressional forces during the Late Jurassic Araucanian phase resulted in the formation of an extensive east-northeast-trending anticlinal structure in the southern Neuquen basin, known as the Huincul dorsal, which is important as a structural trap for hydrocarbons. Regional regression and erosion during this phase resulted in a pronounced angular unconformity, readily iden ifiable throughout the southern basin. The subsequent deposition of Late Jurassic to mid-Cretaceous sediments is seen on seismic cross sections as a series of low-angle, laterally continuous reflectors. Reactivation of the Huincul dorsal occurred during the mid-Cretaceous Mirano phase. Due to uplift and regression during this phase, a low-angle erosional unconformity, although often subtle, can be observed on several seismic cross sections. Uplift and deformation of the Huincul dorsal originated in basement along dominantly northward-dipping, high-angle thrust faults with up to 2,000 m of vertical offset. The initial uplift and compressional deformation of the Andean Cordillera began in the mid-Cretaceous to the west of the Neuquen basin. This resulted in a final stage of primarily conti ental sedimentation, lasting through the Tertiary.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.