Uplift and exhumation of the Eastern Cordillera of Colombia and its interactions with climate




Anderson, Veronica Jacqueline

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Recent breakthroughs in assessing past elevation using stable isotopes of sedimentary materials have provided important constraints on the timing and geodynamics of surface uplift in various orogenic systems. These advances in paleoaltimetry have enabled discrimination between competing models of topographic development in the Tibetan plateau, have provided constraints on the longevity of the Sierra Nevada as a major topographic feature in western North America, and have highlighted the possible role of lower lithospheric delamination in the central Andes of South America. However, there remains considerable debate over the geodynamic mechanisms involved in Andean uplift, as most available estimates on the timing and pace of past elevation gain show an irregular spatial and temporal distribution.

In particular, uncertainty persists over the timing of surface uplift of the Eastern Cordillera in the tropical northern Andes of Colombia. Although changes in sediment accumulation, provenance, and thermochronometric estimates of bedrock exhumation suggest Andean shortening in the Eastern Cordillera since late Eocene-Oligocene time, the rise of the ~2600-m-high Bogotá plateau (Sabana de Bogotá), a intermontane hinterland basin appears to have significantly lagged the onset of shortening in the fold-thrust belt. In addition, there is dramatic variation in structural style along strike within the Eastern Cordillera, making it unclear whether a major basement-involved topographic high (the Garzón Massif) at the southern end of the range was contemporaneous with the rest of the Eastern Cordillera. Studies of pollen assemblages in clastic sedimentary fill of the Bogotá plateau suggest that it may have risen rapidly from ~6-3 Ma and has maintained the same elevation thereafter. However, this scenario of rapid latest Miocene-Pliocene uplift followed by post-3 Ma stasis appears inconsistent with the structural geologic record, as more than half of the total shortening along the eastern Andean flank has occurred since ~3 Ma.

We investigate the elevation history of the Bogotá plateau using novel lipid biomarker proxies for past surface temperature and isotopic composition of precipitation, and update the geochronologic framework of this basin using a refined magnetic polarity stratigraphy. We also utilize a multidisciplinary approach to determine the timing of uplift-induced exhumation of the Garzón Massif, employing U-Pb detrital zircon geochronological and sandstone petrographic results as tracers of sedimentary provenance, apatite fission track (AFT) thermochronometry to constrain exhumation, and the isotopic composition and elemental composition of paleosols and carbonate nodules to track climatic shifts associated with the uplift of the Garzón Massif. These approaches indicate that (1) the Bogotá Plateau had likely been partialy elevated prior to the late Miocene (~7.5 Ma) and has been uplifting continuously since then, (2) and that while the timing onset of exhumation of the Garzón Massif is similar to other parts of the Eastern Cordillera, it did not begin to build substantial topography until ~ 6 Ma. These results imply that the Eastern Cordillera did not become a contiguous topographic barrier, until late Miocene-Pliocene time, providing new constraints on the establishment of the Magdalena River, a northward-draining system that contributes an enormous sediment load to the Caribbean Sea, as a discrete system fully separated from the Amazon basin.


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