Paleoelevation records from lipid biomarkers: Application to the tropical Andes

New results from two novel lipid bio-marker-based proxies help to constrain the late Cenozoic surface elevation history of the Eastern Cordillera in the tropical northern Andes of Colombia. Previous well-known studies have suggested rapid latest Miocene-Pliocene (6-3 Ma) uplift on the basis of an abrupt shift in pollen species assemblages within sedimentary basin fill of the elevated Bogotá Plateau. From resampling of these original study localities, we provide a re-vised chronology based on magnetic polarity stratigraphy, and we evaluate paleotempera-tures using the MBT'/CBT indices (meth-ylation of branched tetraethers/cyclization of branched tetraethers) and hydrogen iso-topic composition (dD) of leaf waxes as two independent proxies of past surface eleva-tion. Reconstructed paleotemperatures from the MBT'/CBT proxy show a more gradual cooling trend from ca. 7.6 Ma to present, consistent with less than 1000 m of elevation gain since latest Miocene-Pliocene time and in agreement with geologic evidence for ac-celerated shortening and exhumation at this time. The leaf wax isotopic data, on the other hand, lack a systematic trend, potentially due to fractionation changes associated with uplift-induced turnover in floral populations. Such changes could obscure isotopic varia-tions in meteoric water, suggesting that leaf-wax isotopic compositions may not provide a direct proxy for elevation in this particular situation involving uplift in a heterogeneous tropical environment. More promising in this case is the MBT'/CBT proxy, which may offer a suitable alternative to carbonate-based paleo elevation proxies in tropical re-gions where year-round high precipitation rates prevent formation of soil carbonates.