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.