Abstract
At ~3500 m above sea level in the Eastern Andean Cordillera, Quebrada Honda Basin exposes more than 300 m of middle Miocene sedimentary strata, developed on distal alluvial fan sediments interstratified with volcanoclastic deposits, overlying Paleozoic basement. These deposits are rich in exotic vertebrate fauna adapted to a wetter and warmer climate at lower paleoelevation, as contrasted with the present high-elevation cold and dry Andean conditions. This study provides new magnetostratigraphic and 40Ar/39Ar age control of the Quebrada Honda, Río Rosario and Huayllajara fossiliferous areas, demonstrating that they are 13.1–12.4 Ma. Part of the succession evidences cyclical deposition of calcretes and reddish mudstones which may be a response to precessional orbital-forcing climatic processes. Paleomagnetic measurements show a significant clockwise tectonic rotation related to postdepositional tectonism, associated with evidence of an important uplift after the deposition of Quebrada Honda sediments. This uplift of the Andean Eastern Cordillera was associated with the formation of the Subandean fold-thrust belt and the development of the Amazon and La Plata drainage basins. Proposed uplift rates of >200 m/Ma are compatible with well-established rates of uplift recorded in contemporaneous alpine sections.
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