--> Abstract: Structural, Topographic and Climatic Control on Sedimentation and Facies Distribution in a Hyper-Arid, Nonmarine Forearc Basin, Atacama Desert, Northern Chile, by Peter L. Nester and Teresa E. Jordan; #90039 (2005)

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Structural, Topographic and Climatic Control on Sedimentation and Facies Distribution in a Hyper-Arid, Nonmarine Forearc Basin, Atacama Desert, Northern Chile

Peter L. Nester and Teresa E. Jordan
Cornell University, Ithaca, NY

Sedimentary sequences in nonmarine environments are known to be controlled by a combination of pre-existing topography, tectonics and climate, but the relative importance of these three inputs is often difficult to distinguish. The Pampa del Tamarugal is an elongate north-south trending nonmarine forearc basin located in the hyper-arid Atacama Desert of northern Chile, bounded by the Coastal Cordillera to the west and the Andean Cordillera to the east. At least four Oligocene-Recent seismically identifiable sequences onlap a high amplitude sequence boundary above deformed Mesozoic rocks. Channelized Lower and Middle Miocene strata observed in both outcrop and seismic data indicate focusing of drainage networks along relict topography. Reactivation of Mesozoic, west-vergent thrust faults from the Early Miocene until ~10 Ma created NNW-trending sub-basins, resulting in sometimes isolated but genetically related depositional sequences. The facies and landform progression at the eastern basin margin attest to intensified aridity from the middle Miocene until present, ultimately creating an environment in which surface water was insufficient to transport appreciable clastic material to the central and western parts of the basin. Therefore, the relative importance of groundwater increased in the distal part of the system, resulting in deposition of lacustrine carbonates and evaporites. The working hypothesis for this basin is that sequence formation during the Early and Middle Miocene was controlled by tectonics, but the cessation of tectonics and intensification of aridity favored climatically controlled sequences since the Late Miocene.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005