HR: 09:15h
AN: T51D-06    [Abstracts]
TI: Controls on Cenozoic Chaco Foreland Basin Development, Bolivia
AU: * Uba, C E
EM: ejikeuba@zedat.fu-berlin.de
AF: Institut fuer Geologische Wissenschaften, Freie Universitaet Berlin, Malteserstr. 74-100, Berlin, 12249 Germany
AU: Heubeck, C
EM: cheubeck@zedat.fu-berlin.de
AF: Institut fuer Geologische Wissenschaften, Freie Universitaet Berlin, Malteserstr. 74-100, Berlin, 12249 Germany
AU: Ege, H
EM: ege@zedat.fu-berlin.de
AF: Institut fuer Geologische Wissenschaften, Freie Universitaet Berlin, Malteserstr. 74-100, Berlin, 12249 Germany
AU: Hulka, C
EM: chulka@zedat.fu-berlin.de
AF: Institut fuer Geologische Wissenschaften, Freie Universitaet Berlin, Malteserstr. 74-100, Berlin, 12249 Germany
AB: The up to 200 km wide, Oligocene to Recent Chaco basin is a type example of a retroarc foreland basin system. It is bordered by the Brazilian Shield to the west and by the Subandean Zone to the east. This study combines outcrop stratigraphic, sedimentologic, paleoelevation, seismic, and well data to demonstrate the tectonic, climatic, and eustatic influence on sequence development in the Chaco basin. The Cenozoic fill of the Chaco foreland basin contains an overall coarsening- and thickening-upward stratigraphic succession up to 7.5 km thick and consists of five stratigraphic units: (1) The basal, Oligocene-Miocene-age Petaca Formation consists of dominantly calcretes and fluvial facies in arid setting; (2) The overlying, Late Miocene Yecua Formation records numerous small-scale transgressive-regressive-cycles of marginal marine facies; (3) The Late Late Miocene Tariquia Formation consists of poorly channelized, low-sinuosity anastomosed deposits in semi-arid setting (4) The overlying, Lower Pliocene Guandacay Formation composes of fluvial and distal alluvial fan facies with thin-bedded coal indicating humid paleoclimate; (5) The Late Pliocene, Emborozu Formation consists predominantly of proximal alluvial-fan-facies. Our study shows a marked upsection change in fluvial styles, fluctuations in accommodation space and sediment supply, regulated by basin subsidence. This is supported by a sourceward shift of the depositional system and shown by asymmetrical lateral and vertical variations in grain size and consistent thickness variation and facies changes. Based on our results, the Cenozoic basin development in the Subandean Zone primarily was driven by compressional tectonics and secondarily by climatic and eustatic changes. Tectonically, it formed as response to Andean lithospheric loading, erosion, and shortening by the Subandean thin-skinned fold- and thrust belt. Late Late Miocene arid-to-humid climatic shift contributed to the sedimentation style and rate, whereas global eustacy influenced the sequence only during a Late Miocene marginal-marine incursion.
DE: 8100 TECTONOPHYSICS
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting