20 The Caribbean Plate and its Geologic Connections with North and South America

Friday, 30 March 2012
8:30 AM - 1:00 PM
Siglo XVIII

SR-ISOTOPE STRATIGRAPHY AS AN ALTERNATIVE PROVENANCE TOOL OF OLIGOCENE AND MIOCENE SEDIMENTS ALONG NW COLOMBIA: PALEOGEOGRAPHIC IMPLICATIONS FOR THE CARIBBEAN PLATE- SOUTH AMERICA INTERACTION

Paper number: 20-12
Program: Theme Sessions
Time: 12:10 PM – 12:30 PM

Authors

Abstract

The Sr-isotope composition of marine carbonates has been extensively used as a tool to infer their depositional age. The use of the Sr-isotope stratigraphy as a chronostratigraphic tool is based on the fact that the Sr-composition of marine carbonates reflect that of the seawater from which they deposited. Colloraries of the Sr-isotope stratigraphic approach are: 1) that the Sr-isotope composition of the seawater is controlled by the mass balance between the unradiogenic (mantle derived) and the radiogenic (crustal derived) input to the seawater and 2) that the residence time of Sr isotopes in the seawater is 2.4 My.

Here we report the Sr-isotope compositions of Early Oligocene (Tolu Viejo Fm) and Early Miocene (Cienaga de Oro Fm) carbonate successions to 1) investigate the preservation of marine Sr-isotope composition of carbonates and to access the use of such composition as a provenance tool.

Sr-isotope compositions between 0,708092 and 0,708231 suggest a depositional age between 24 and 22 My for the Cienaga de Oro formation carbonates. This age is in agreement with the first reported Cenozoic U-Pb age on carbonates of 22.4±1.1 Ma. Sr-isotope composition between 0,707347 and 0,707597 has been in turn obtained for the Tolu Viejo Formation. Those values do not fall within the range of global values for Cenozoic carbonates, suggesting thus anomalous Sr-isotope compositions. The trace element compositions of such carbonates disregard any diagenetic origin for these anomalous Sr-isotope compositions. We use the 27.7±2.5 Ma U-Pb age obtained for the Tolu Viejo Formation to suggest that the anomalous Sr-isotope compositions of the Tolu Viejo Formation reflect the runoff of continental waters from oceanic volcanic cropping out along the Western Cordillera of Colombia. This contention is supported by integrated provenance analysis on sandstones and mudstones cropping out in the same area. These data also support an early interaction of the Caribbean Plate and the South American block.