title: Late Miocene sedimentary environments in south-western Amazonia (Solimões Formation; Brazil).
abstract: In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ18O and δ13C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake ("Lake Pebas") or any influx of marine waters can be excluded for that region during the Late Miocene.
authors.affiliation: Department for Geology and Palaeontology, Universalmuseum Joanneum, Weinzöttlstrasse 16, 8045 Graz, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Gross
authors.affiliation: Institute for Earth Sciences, Karl-Franzens-University, Heinrichstrasse 26, 8010 Graz, Austria.
authors.forename: Werner E
authors.initials: WE
authors.lastname: Piller
authors.affiliation: Coordenação de Ciências da Terra e Ecologia, Museu Paraense Emílio Goeldi, Avenida Perimetral, s/n Terra Firme, Belém-PA 66077-530, Brazil.
authors.forename: Maria Ines
authors.initials: MI
authors.lastname: Ramos
authors.affiliation: Instituto de Ciências Exatas e da Terra, Departamento de Recursos Minerais, Universidade Federal de Mato Grosso, Avenida Fernando Corrêa, s/n Coxipó, Cuiabá-MT 78060-900, Brazil.
authors.forename: Jackson
authors.initials: J
authors.lastname: Douglas da Silva Paz
keywords: Fluvial sediments; Late Miocene; Western Amazonia; “Lake Pebas”