GP42A-01
Do Magnetic Minerals Record Paleoprecipitation? Insights from Paleocene-Eocene Paleosols in the Bighorn Basin, WY
Thursday, 17 December 2015: 10:20
300 (Moscone South)
Daniel Maxbauer, Department of Earth Sciences, University of Minnesota, Minneapolis, MN, United States; Institute for Rock Magnetism, University of Minnesota, Minneapolis, MN, United States, Joshua M Feinberg, University of Minnesota, Minneapolis, MN, United States, David L. Fox, University of Minnesota Twin Cities, Minneapolis, MN, United States and William Clyde, University of New Hampshire Main Campus, Durham, NH, United States
Abstract:
The magnetic mineralogy of soils and paleosols is a rich archive of paleoclimatic information. However, efforts to quantify parameters such as mean annual precipitation (MAP) or temperature using environmental magnetism are still in their infancy. Inherent in any magnetic paleoclimate proxy is a fundamental understanding of how the concentration, grain size distribution, and composition of iron oxides and oxyhydroxides formed during pedogenesis reflect the climatic conditions that prevailed during soil formation. The influence of diagenetic processes on magnetic minerals, particularly for paleosols in pre-Quaternary systems, may compromise our ability to recover a climatic signal due to mineral alterations or incomplete preservation. Here, we evaluate the rock magnetic properties of non-loessic paleosols across the Paleocene-Eocene Thermal Maximum (PETM, ~55.5 Ma) in the Bighorn Basin, WY. Our study compares data from nine paleosol layers sampled from outcrop, exposed to surficial weathering, as well as the equivalent paleosol layers sampled from drill core, all of which are preserved below a pervasive oxidative weathering front and presumably unweathered. Despite variation in magnetic properties within paleosol layers, there is no clear change in magnetic mineralogy that we can attribute to surficial weathering. Further, common measures of magnetic enhancement in susceptibility and remanence show similar trends across the PETM, in both core and outcrop, when compared to estimates of MAP from geochemical weathering indices. Taken together, our record suggests that the magnetic minerals preserved in ancient paleosols retain at least qualitative information about paleoprecipitation and could be an important source of information for paleoclimatic studies. Further work to improve our understanding of the relative preservation of various pedogenic components in paleosols will ultimately determine their viability as quantitative indicators of paleoclimate.
