Brian K. Horton¹, Mauricio Parra², Joel E. Saylor², Junsheng Nie², Andrés Mora³, Vladimir Torres³, Daniel F. Stockli⁴, Manfred R. Strecker⁵

¹ Dept. of Geological Sciences and Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78712-0254, USA
² Dept. of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78712-0254, USA
³ Instituto Colombiano del Petróleo, Ecopetrol, Bucaramanga, Colombia
⁴ Dept. of Geology, University of Kansas, Lawrence, Kansas 66045, USA
⁵ Institut für Geowissenschaften, Universität Potsdam, 14476 Potsdam, Germany

Abstract

Uplift of the Eastern Cordillera in the northern Andes has been linked to orographic climate change and genesis of South America’s largest river systems. The timing of initial uplift remains poorly constrained, with most estimates ranging from ca. 60 to ca. 5 Ma. New detrital zircon U-Pb ages from proximal fill of the Llanos foreland basin in Colombia reveal a pronounced mid-Cenozoic shift in provenance from an Amazonian craton source to an Andean fold-thrust belt source. This shift corresponds with changes in detrital zircon (U-Th)/He ages, a conglomeratic unroofing sequence, and a sharp increase in foredeep accumulation rates. These nearly simultaneous changes in zircon age spectra, clast compositions, and sediment accumulation are attributable to latest Oligocene uplift of the eastern flank of the Eastern Cordillera. The timing relationships suggest an early activation of the frontal thrust system, implying a long-term (up to 25 m.y.) cessation of orogenic wedge advance, potentially driven by structural inheritance and/or climate change.

Manuscript received 12 Aug. 2009; accepted 6 Jan. 2010

DOI: 10.1130/GSATG76A.1