Mesozoic-Cenozoic Sedimentation, Provenance, and Basin Evolution Along the Eastern Margin of the Central Andes (19-22°S)
New insights on Mesozoic-Cenozoic sedimentation and fold-thrust deformation are critical to improved assessment of established petroleum systems and potential new plays in the central Andes. We provide a progress report on the regional distribution and long-term evolution of Andean and pre-Andean basins in southern Bolivia (19-22°S). The spatial-temporal responses to tectonic, climatic, and drainage-network modifications are evaluated for a protracted record involving pre-Andean (Mesozoic) extension and post-rift thermal subsidence followed by Andean (Cenozoic) shortening and cratonward advance of a retroarc foreland basin system. Sediment dispersal trends are derived from new and published facies analyses, paleocurrents, detrital zircon U-Pb age distributions, sandstone petrography, and conglomerate clast compositions. Detailed surface and subsurface stratigraphic analyses combined with sediment provenance data along the Eastern Cordillera and Subandean belt reveal clastic deposition of distal to proximal facies (fluviolacustrine, fluvial megafan, alluvial fan) in different depozones characteristic of a progressively compartmentalized foreland basin. Depositional age constraints and sediment accumulation rates for Cenozoic basin fill are refined through newly dated tuffs and maximum depositional age constraints defined by the youngest detrital zircon populations. A >4 km-thick clastic succession exposed in the Eastern Cordillera records the transition from a Cretaceous post-rift sag basin to a Paleocene–Miocene eastward-advancing foreland basin. Similarly, deposition of up to 6 km-thick upward-coarsening and thickening succession in both the Subandes and modern Chaco basin records the cratonward propagation of the fold-thrust belt and resulting deposition in different foreland depozones. Analyses of new growth stratal relationships preserved in the Eastern Cordillera (Incapampa syncline) and western Subandean zone (El Rosal syncline) provide clear evidence for syndeformational deposition and elucidate the exhumation history of the older components of the advancing basin. Regional-scale analyses of stratigraphic signatures (depositional facies, sediment composition, dispersal pathways) shed light on the propagation of the Andean thrust belt and associated basin compartmentalization, which progressed eastward from the Eastern Cordillera (middle Eocene) to Interandean zone (early Miocene), and finally into the Subandean zone (middle Miocene).
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014