1 / 15

Paleoprecipitation Reconstructions for the Brady Soil Based on Rock-Magnetic Analyses

Paleoprecipitation Reconstructions for the Brady Soil Based on Rock-Magnetic Analyses . Christoph E. Geiss Pooja Shakya Emily Quinton William C. Johnson Joseph Mason. Pedogenic Magnetic Component . fine grained (d < 0.1 μ m) ferrimagnetic minerals (magnetite, maghemite)

wyanet
Download Presentation

Paleoprecipitation Reconstructions for the Brady Soil Based on Rock-Magnetic Analyses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Paleoprecipitation Reconstructions for the Brady Soil Based on Rock-Magnetic Analyses Christoph E. Geiss Pooja Shakya Emily Quinton William C. Johnson Joseph Mason

  2. Pedogenic Magnetic Component • fine grained (d < 0.1 μm) ferrimagnetic minerals (magnetite, maghemite) • remarkably consistent in it’s magnetic properties throughout the Midwestern U.S. • under certain conditions we can calculate its abundance in a sample

  3. estimates of pedogenic magnetic minerals • ARM ratios (presented today) • ARM is highly sensitive for fine magnetic particles • easily measured • magnetic coercivity distributions • more time consuming, but yields more information about the samples for moderns soils from the Midwestern U.S. both methods yield equivalent results

  4. some magnetism basics saturation magnetization (Ms) magnetization of a sample when exposed to a (pretty strong) magnetic field remanent magnetization (Mr) magnetization of a sample in zero field various flavors (ARM, IRM etc.) simple linearized model: Mr = α× Ms For many natural samples Mr is additive Mtot = M1 + M2

  5. pedogenic contribution to magnetic remanence background contribution to magnetic remanence 2-component mixing model • pedogenic component (fine-grained maghemite) • background component (here coarse-grained rest) fped = relative volume (or mass) fraction of pedogenic component

  6. ARM Ratios (ARM / IRM) • Sensitive for fine-grained (SD) ferrimagnets • Can write simple model to predict ARM / IRM ratios Note: Js cancels out and if the a’s are known fped is the only variable left therefore, can calculate fped from ARM ratios

  7. observed range

  8. ARM-ratios of modern enhanced horizons

  9. precipitation reconstructions

  10. comparison with modern precipitation

  11. Caveats ! • technique might underestimate ppt • no loss of pedogenic material • magnetic enhancement reaches equilibrium state rapidly • magnetic properties of parent material can be distinguished from pedogenic material • inherited pedogenic Fe-oxides / redeposited soils

More Related