Paper No. 4
Presentation Time: 8:50 AM
PALEOSOL CARBON ISOTOPE STRATIGRAPHY AND A ROCK MAGNETIC RECORD OF CLIMATE CHANGE ACROSS THE PALEOCENE-EOCENE BOUNDARY IN THE BOGOTA BASIN, COLOMBIA
MORÓN, Sara, Department of Earth Sciences, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0231, FOX, David L., Department of Earth Sciences, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0219, FEINBERG, Joshua M., Institute for Rock Magnetism, University of Minnesota, Department of Earth Sciences, 100 Union Street SE, Minneapolis, MN 55455, BAYONA, Germán, Corporación Geológica ARES, Calle 44 A # 53-96, Bogotá, Colombia and VALLEJO, Maria Camila, Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002, Balboa, Ancon, 0843-03092, Panama, moro0041@umn.edu
The Paleocene/Eocene Thermal Maximum (PETM) was an event of rapid global climatic change that occurred at 56.3 Ma and is associated with a major negative carbon isotope excursion (CIE) ascribed to massive release of isotopically light carbon into the linked ocean-atmosphere-terrestrial biosphere reservoirs of the global carbon cycle. Terrestrial proxy records from mid to high northern latitudes suggest brief but intense warming across the Northern Hemisphere, but changes in the hydrologic cycle are controversial as paleoprecipitation estimates spanning the PETM vary widely. The Bogota Basin of Colombia preserves a 2 km conformable sequence of paleosols that offers an ideal setting to examine terrestrial climate change across the PETM in the paleotropics (paleolatitude <5˚N). However, existing paleoprecipitation proxies based on paleosols elemental ratios are calibrated only for temperate soils under mean annual precipitation <1500 mm.
We examined the PETM in the Bogota Basin using the carbon isotope composition of bulk paleosol organic matter (n=80) to identify the CIE and the magnetic susceptibility and mineralogy of the paleosols to examine changes in weathering intensity associated with the PETM. Increased precipitation should intensify silicate weathering via hydrolysis reactions involving carbonic acid. For Fe-bearing silicate minerals, these reactions liberate Fe ions, which are often sequestered in Fe-oxides such as goethite and hematite. Increased precipitation could also enhance soil biological activity, increasing production of biogenic magnetite and maghemite. These Fe-oxides all have distinct magnetic properties that are easily measured and potentially can be used as proxies for changes in weathering and precipitation. Carbon isotopes reveal a CIE (~-2‰) in stratigraphic proximity to a tuff dated at 56.13±0.87 Ma. The same interval has a 100% increase in both susceptibility and concentrations of Fe-bearing magnetic minerals. We suggest that a sharp decrease in magnetic mineral concentration immediately after the CIE indicates decreased weathering and precipitation rates after the PETM. Our results suggest that chemical weathering in the tropics, as a proxy for the terrestrial hydrologic cycle, intensified in response to the onset of the PETM and decreased after its termination
