Deformation Style in a Forearc Basin with Shale Gas Potential, Northern Chile

Peter Nester and Teresa E. Jordan
Earth and Atmospheric Sciences, Cornell University, Ithaca, NY

Renewed interest in a Mesozoic shale gas play beneath the Pampa del Tamarugal (PdT) basin in the forearc of northern Chile leads to new focus on the structural geology of the area. Superimposed on strongly folded Mesozoic shallow marine sedimentary units is a nonmarine Oligocene to modern sedimentary basin, at the foot of the western slope of the Central Andes. North of the play (~20°30’S), between 18-20°30’S, studies have reported Andean uplift commencing in the latest Oligocene, largely controlled by the Western Thrust System (WTS), a series of thick-skinned, high-angle, west-vergent reverse faults striking roughly parallel to the mountain front. Movement along these faults may have accommodated as much as 2500 m of Andean uplift during the Miocene. The WTS largely ceased activity by the latest Miocene. New information between 20°30’ and 21°30’S, provided by a grid of reflection seismic data, indicates a continuation of this WTS within the PdT subsurface to 21°S. South of 21°S, in addition to the continuation of west-vergent faulting, the PdT structural style is dominated by high-angle east-vergent reverse faults in the basin center, and normal faults near the western boundary of the basin. The majority of this southern faulting also ended by the latest Miocene, similar to the fault chronology farther north. After the local-scale faulting ceased, uplift continued, as indicated by long-wavelength westward surface rotation that accommodated about 1300 m of western Andean uplift at 21°S. If the current drilling program confirms the gas potential of this region, knowledge of the superposition of these young faults and associated fractures on the Mesozoic folds and faults will contribute to definition of a drilling and production strategy.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas