Paleosol carbon isotope stratigraphy, major oxides, and rock magnetic record of climate change across the Paleocene-Eocene boundary in the Bogota Basin, Colombia.

Abstract

Paleosols spanning the Paleocene-Eocene (P-E) in the Bogota Basin record an increase of chemical weathering around the P-E boundary due to climatic forcing. Rock magnetic properties and major element geochemistry allowed the identification of this increase in weathering while previously published palynological zones and a U/Pb date in volcanic zircons (56.13±0.87 Ma) established the P-E boundary in the section. I identified a significant anomaly in magnetic susceptibility in coalescence with an order of magnitude increase in all magnetic minerals (magnetite/maghemite, goethite, and hematite) in the interval within the margin of error of the radiometric age. Pedogenic features in the paleosols, lack of iron oxides as cement and friability of the sandstones, and the shallow burial of the section (<500 m) exclude the possibility that magnetic minerals were formed during burial. Thus, the signal provided by magnetic proxies is purely climatic. Fe2O3, Al2O3, loss on ignition, and rubification of paleosols also increase in this interval suggesting an enhancement in chemical weathering and moisture. The lack of carbonate nodules in this interval and a decrease in SiO2 also indicate an increase of precipitation. Thus I hypothesize that the intensification of chemical weathering may be related to perturbation of the hydrological cycle of the Paleocene-Eocene Thermal Maximum (PETM). However, poor reproducibility of the carbon record prevented confident identification of the negative carbon isotopic excursion (CIE) associated with the PETM. Therefore, the carbon isotopic record of the section needs to be improved to verify i) the correlation between the intensified chemical weathering and the CIE, and ii) to decipher whether the negative feedback of silicate weathering was the mechanism yielding the long-term temperature stabilization of the globe’s surface, as proposed in previous studies.