300 Reconstructing Earth Surface Processes in Orogenic Systems (Posters)

Advances and applications of detrital and stratigraphic records for reconstructing lithospheric, climatic, and earth surface interactions over geologic time scales.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Quantifying Relative Zircon Fertility of Sediment and Sedimentary Rocks: Implications for Detrital Zircon Mixture Modeling

Paper number: 300-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

  • Jack St.Peter Presenting Author
    University of Texas at Austin - Jackson School of Geosciences, Austin, TX
  • Matt Malkowski
    University of Texas at Austin - Jackson School of Geosciences, Austin, TX
  • Jacqueline Epperson
    University of Texas at Austin - Jackson School of Geosciences, Austin, TX
  • Richard Ketcham
    University of Texas at Austin - Jackson School of Geosciences, Austin, TX
  • Olivia Wachob
    University of Texas at Austin - Jackson School of Geosciences, Austin, TX

Abstract

Detrital zircon (DZ) mixture modeling is used to determine the relative contributions of multiple sediment sources to a given sink/basin. This approach relies on making inferences about relative sediment flux based on measured contributions of detrital zircon sources. While some studies assume relative DZ flux is a proxy for relative sediment flux, this may not be the case. The relative zircon concentrations of each source can impact this relationship, but they are not always considered due to the limited availability of zircon abundance data and methods to utilize them.

Different lithologies have different concentrations of zircon, or zircon fertility. Consequently, different bedrock sources of similar exposed surface areas and experiencing similar erosion rates can introduce different amounts of zircon into a sedimentary system. In order to use detrital zircon age populations to accurately estimate the relative contribution of all sources and changes in those relative contributions over time, the zircon fertility of each source must be considered. This project tests the efficacy of using whole-rock wavelength dispersive x-ray fluorescence (WD-XRF) spectrometry for estimating the zircon fertility of sediment and sedimentary rocks and to provide easily obtainable and widely accessible zircon abundance data.

We compared multiple sandstone and sediment samples, each with different lithology and composition. Sandstone samples were collected from the Cretaceous Great Valley Group, and sediment samples were collected from modern rivers in California and elsewhere. Each modern sediment sample represents different source rock lithologies, with variable zircon fertility. Aliquots of each sand sample were split for use in two analyses. (1) Zircons were isolated from each sample, and micro-Computed Tomography (CT) scans of these isolates provide the true number and volume of zircon grains in each separate. This provided what we assume is the most accurate measurement of the amount of zircon in a sample. (2) Bulk sediment was powdered and pressed into a disc for WD-XRF whole-rock geochemistry to determine the Zirconium mass concentration in each sample. A comparison of CT versus whole-rock XRF estimates of zircon yield shows that XRF estimates correlate with CT values in terms of tracking the relative abundance between samples. However, in all cases, the XRF values far overestimated the zircon separate yield relative to that measured by CT analysis.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413080

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