Isotopic, paleontologic, and ichnologic evidence for late Miocene pulses of marine incursions in the central Andes
- 1Institut für Geowissenschaften, Universität Potsdam, 14476 Potsdam, Germany
- 2Department of Geology and Paleontology, University of Geneva, Boulevard du Pont-d'Arve 40, CH-1211 Geneva, Switzerland
- 3Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
- 4Department of Earth and Space Sciences, University of California–Los Angeles, Los Angeles, California 90095-1567, USA
- 5Deutsches Geo Forschungs-Zentrum, Potsdam 14473, Germany
Abstract
Recognition of an inferred Miocene marine incursion affecting areas from Colombia through Peru and Bolivia and into Argentina is essential to delineate the South American Seaway. In Bolivia, corresponding strata of inferred marine origin have been assigned to the late Miocene Yecua Formation. We carried out high-resolution δ13C and δ18O isotopic studies on 135 in situ carbonates from 3 outcrops, combined with detailed sedimentologic, paleontologic, and ichnologic analysis. Four less negative δ13C excursion levels were recorded that coincide well with beds containing marine body (barnacle) and trace (Ophiomorpha) fossils. These strata are interbedded with red-green beds containing mudcracks, plant roots, gypsum, and trace fossils of the continental Scoyenia ichnofacies. Our data are significant in that they show for the first time four possible short-lived marine incursions in the Bolivian central Andes during the late Miocene. The result is constrained by a new U-Pb date of 7.17 ± 0.34 Ma at the top of Yecua strata.
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- Received 8 January 2009.
- Revision received 20 April 2009.
- Accepted 28 April 2009.
