CALL FOR PROPOSALS:

ORGANIZERS

  • Harvey Thorleifson, Chair
    Minnesota Geological Survey
  • Carrie Jennings, Vice Chair
    Minnesota Geological Survey
  • David Bush, Technical Program Chair
    University of West Georgia
  • Jim Miller, Field Trip Chair
    University of Minnesota Duluth
  • Curtis M. Hudak, Sponsorship Chair
    Foth Infrastructure & Environment, LLC

 

Paper No. 16
Presentation Time: 12:45 PM

ACTUALISTIC CALIBRATION OF THE PEDOGENIC SIDERITE PALEOCLIMATE PROXY


VILLARREAL, Mark A., Department of Geology, University of Kansas, Lawrence, KS 66045-7594, LUDVIGSON, G.a., Kansas Geological Survey, University of Kansas, Lawrence, KS 66047, FOWLE, D.A., Geology, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr, Lawrence, KS 66047, GONZALEZ, Luis A., Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Rm. 120, Lindley Hall, Lawrence, KS 66045, ROBERTS, Jennifer A., Geology, University of Kansas, 1475 Jayhawk Blvd, Lindley Hall, Room 120, Lawrence, KS 66047, SMITH, Jon J., Kansas Geological Survey, 1930 Constant Ave, Lawrence, KS 66047-3726, DRIESE, Steven G., Terrestrial Paleoclimatology Research Group, Dept. of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798-7354 and MCKAY, Larry D., Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, mvillarreal@ku.edu

Pedogenic (soil formed) siderite (FeCO3) is applied as a paleoclimate proxy for analysis of warm periods in Earth’s history, specifically to humid continental environments of the Cretaceous and Paleogene (145 to 65 Ma). Initial calibrations of this proxy were based on experimental laboratory studies. Actualistic studies of modern siderites are needed to substantiate the laboratory findings. Recently discovered modern (last 100 years) pedogenic siderite precipitation in Chattanooga Tennessee (Driese et al., 2010, JSR 80:943-954) provides such an opportunity. Siderite is forming in a wetland site contaminated with coal tar deposits, associated with coal coking operations from 1918-1987. This study examined the principal environmental parameters controlling modern pedogenic siderite precipitation; microbial ecology and groundwater chemistry. Carbon and oxygen isotopes were analyzed from the siderites. The δ18O values for siderite range from -5.1 to -4.1 (VPDB; Driese et al., 2010, JSR 80:943-954). Seasonal groundwater isotopes values range from -8.80 to -3.36 (VSMOW) and seasonal soil temperature measurements range from 9°C to 23°C. The outcomes of this study will have a significant impact on the use of the widely applied Carothers et al. (1988, GCA 52:2445-2450) siderite-water fractionation equation. Our data indicates that at low sedimentary temperatures, the Carothers et al (1988) fractionation equation estimates water δ18O values that are lower than is actually the case. The 18O fractionation equation from microbial laboratory synthesis experiments of Zhang et al. (2001, GCA 65:2257-2271) provides a much better fit to our field data. This critical, actualistic evaluation is important for interpretations of past climates because siderite is widely applied as a paleoclimate indicator, and unraveling these fractionation parameters will markedly improve the accuracy of future paleoclimate studies.
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