Facies analysis and basin architecture of the Neogene Subandean synorogenic wedge, southern Bolivia

摘要: Foreland sedimentation in the Subandean Zone of south-central Bolivia spans from Upper Oligocene to present. It records sediment dispersal patterns an initially distal and later proximal retroarc foreland basin, thereby contains stratigraphic information on tectonic evolution adjacent Andean fold-thrust belt. Within Neogene orogenic wedge individual siliciclastic-dominated depositional systems formed ahead eastward-propagating deformation regime. We defined, described, interpreted eight architectural elements 24 lithofacies 15 outcrop locations representing basin Chaco Plain. These are combined interpret settings. The up 7.5 km-thick is subdivided five units basis facies associations overall architecture: (1) basal, Oligocene–Miocene, 250 m-thick Petaca Formation consists dominantly calcrete, reworked conglomeratic pedogenic clasts, fluvial sandstone mudstone. This unit represent extensive pedogenesis under arid semiarid climate with subordinate braided processes. (2) overlying, Miocene, 350 m thick Yecua numerous small-scale transgressive–regressive cycles marginal marine, tidal, shoreline sandstone, ooid limestones, varicoloured (3) 4500 Tariquia principally interbedded sandstone–mudstone couplets frequent crevassing anastomosing streams upsection-increasing degree connectedness. (4) 1500 Lower Pliocene Guandacay represents granule cobble conglomerate sandy (5) Pliocene, 2000 Emborozu predominantly alluvial-fandeposited boulder coarsening- thickening-upward pattern eastward progradation, coupled variable proportions overbank facies, channel size, abandonment, Tariquia, Guandacay, Formations reflect a through megafan environment. long-lived grew by high rates northeast-through-southeast radial paleoflow large, coarse-grained lobes. marked