Depositional setting of the middle to Late Miocene Yecua formation of the Chaco Foreland Basin, Southern Bolivia

Middle-Late Miocene marine incursions are known from several foreland basin systems adjacent to the Andes, likely a result of combined foreland basin loading and sea-level rising. The equivalent formation in the southern Bolivian Chaco foreland Basin is the Middle-Late Miocene (14-7 Ma) Yecua Formation. New lithological and paleontological data permit a reconstruction of the facies and depositional environment. These data suggest a coastal setting with humid to semiarid floodplains, shorelines, and tidal and restricted shallow marine environments. The marine facies diminishes to the south and west, suggesting a connection to the Amazon Basin. However, a connection to the Paranense Sea via the Paraguayan Chaco Basin is also possible. (c) 2005 Elsevier Ltd. All rights reserved.