Research Article| August 01, 2003 Paleogeography of Miocene Western Amazonia: Isotopic composition of molluscan shells constrains the influence of marine incursions H.B. Vonhof; H.B. Vonhof 1Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar F.P. Wesselingh; F.P. Wesselingh 2Naturalis—Nationaal Natuurhistorisch Museum, P.O. Box 9517, 2300 RA Leiden, Netherlands and Department of Biology, University of Turku, 20014 Turku, Finland Search for other works by this author on: GSW Google Scholar R.J.G. Kaandorp; R.J.G. Kaandorp 3Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar G.R. Davies; G.R. Davies 3Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar J.E. van Hinte; J.E. van Hinte 3Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar J. Guerrero; J. Guerrero 4Departamento de Geociencias, Universidad Nacional, AA 14490, Bogota, Colombia Search for other works by this author on: GSW Google Scholar M. Räsänen; M. Räsänen 5Department of Geology, University of Turku, 20014 Turku, Finland Search for other works by this author on: GSW Google Scholar L. Romero-Pittman; L. Romero-Pittman 6Instituto Geológico Minero y Metalúrgico, Avenida Canada 1470, Lima 41, Peru Search for other works by this author on: GSW Google Scholar A. Ranzi A. Ranzi 7Departamento de Biologia, Laboratorio de Paleontologia, Universidade Federal do Acre 69.915-900, Rio Branco, Acre, Brazil Search for other works by this author on: GSW Google Scholar Author and Article Information H.B. Vonhof 1Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands F.P. Wesselingh 2Naturalis—Nationaal Natuurhistorisch Museum, P.O. Box 9517, 2300 RA Leiden, Netherlands and Department of Biology, University of Turku, 20014 Turku, Finland R.J.G. Kaandorp 3Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands G.R. Davies 3Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands J.E. van Hinte 3Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands J. Guerrero 4Departamento de Geociencias, Universidad Nacional, AA 14490, Bogota, Colombia M. Räsänen 5Department of Geology, University of Turku, 20014 Turku, Finland L. Romero-Pittman 6Instituto Geológico Minero y Metalúrgico, Avenida Canada 1470, Lima 41, Peru A. Ranzi 7Departamento de Biologia, Laboratorio de Paleontologia, Universidade Federal do Acre 69.915-900, Rio Branco, Acre, Brazil Publisher: Geological Society of America Received: 03 Jan 2002 Revision Received: 13 Nov 2002 Accepted: 26 Dec 2002 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (8): 983–993. https://doi.org/10.1130/B25058.1 Article history Received: 03 Jan 2002 Revision Received: 13 Nov 2002 Accepted: 26 Dec 2002 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation H.B. Vonhof, F.P. Wesselingh, R.J.G. Kaandorp, G.R. Davies, J.E. van Hinte, J. Guerrero, M. Räsänen, L. Romero-Pittman, A. Ranzi; Paleogeography of Miocene Western Amazonia: Isotopic composition of molluscan shells constrains the influence of marine incursions. GSA Bulletin 2003;; 115 (8): 983–993. doi: https://doi.org/10.1130/B25058.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Strontium, oxygen, and carbon isotope compositions of well-preserved mollusks (bivalves) indicate a dominantly freshwater depositional setting for the lower Miocene–upper Miocene Pebas Formation in Western Amazonia. Molluscan 87Sr/86Sr ratios identify different freshwater sources. Andean runoff was the dominant water source in Miocene Western Amazonia, though there was occasional influx of waters from cratonic catchments.At only one stratigraphic level, isotope signals indicate increased (mesohaline) aquatic salinities, in concert with a clearly more saline molluscan faunal assemblage.Strontium isotope–based salinity estimates are surprisingly low when compared to other paleosalinity estimates based on the interpretation of (ichno)faunal assemblages and sedimentological structures. We propose that these seemingly contrasting observations can be unified if Miocene Western Amazonia was occupied by a long-lived (lacustrine) wetland system with a restricted connection, via the Los Llanos Basin, to the Caribbean Sea. Abundant runoff supplied fresh water to this system, which effectively blocked the influx of saline waters through the restricted marine connection to the north. Much like modern Lake Maracaibo, such a system could have been the site of microtidal currents and thus could have hosted brackish-water fauna in a dominantly freshwater depositional system. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.