24-11 Assessing the natural bias imparted by riverine dynamics in the detrital record in the Bermejo River (Argentina)

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records, Part I

Presenting Author:

Martin Senger

Authors:

Senger, Martin Hugo¹, Lopes, Vicente², Kroeger, Emma³, Anderson, Brady N⁴, Ketcham, Richard A.⁵, Ghoshal, Gourab⁶, Pullen, Alexander⁷, Ibanez-Mejia, Mauricio⁸

(1) Department of Geosciences, University of Arizona, Tucson, Arizona, USA, (2) Department of Geosciences, University of Arizona, Tucson, Arizona, USA, (3) Clemson University, Anderson, South Carolina, USA, (4) Clemson University, Anderson, SC, USA, (5) University of Texas, Austin, TX, USA, (6) Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA, (7) Clemson University, Anderson, SC, USA, (8) Department of Geosciences, University of Arizona, Tucson, AZ, USA,

Abstract:

Detrital zircon (DZ) geochronology is a popular approach for reconstructing the geological record using sedimentary strata. It is widely used to assess maximum depositional ages and to determine contemporary sediment provenance. While this method has proven remarkably useful, it remains sensitive to naturally induced biases introduced by the complex mechanisms through which minerals are sorted, transported, and destroyed in natural systems, ultimately leading to inaccurate reconstructions of geologic processes. Amongst many factors inducing bias, zircon grain morphology and the integrity of the crystal lattice are arguably the dominant factors controlling the sorting and resilience of individual crystals–or populations–during transport.

To deconvolve the effects of such factors, we analyzed modern day sediments from the Bermejo River in northern Argentina. This riverine system provides an excellent natural system to isolate the factors playing a significant role in controlling DZ population at a large scale, as it gently drains the Chaco alluvial mega-fan and does not have any tributaries that would introduce additional sediments for over 800 km. Zircon crystals were characterized using a new approach that combines 3D X-ray micro-CT imaging, LA-ICP-MS U-Pb geochronology, and Raman spectroscopy to quantify the structural damage to the crystal lattice.

 Our results confirm that grain morphology plays a key role in controlling the U-Pb detrital spectra of samples from contrasting depositional facies. Further, the river preferentially removed zircon crystals with higher accumulated radiation damage. Despite the Bermejo headwaters overlap with a volcanically active segment of the Central Andes, calculated MDAs are consistently too old and predate the sedimentation of the sample by at least 3 Myr. We find that there are noticeable statistical differences across samples found in close geographic proximity, even in the same locality, when different riverine geomorphological elements are sampled. Our data set highlights the need for caution when interpreting the detrital record using existing statistical tools, especially when relying exclusively on U-Pb data. Our ongoing efforts are now focused on leveraging this large multidimensional dataset combining age, morphology, and radiation damage, to develop improved statistical metrics that can improve the accuracy of inter-sample quantitative comparisons applied to sediment provenance. Our results underscore the importance of acquiring different datasets in combination with U-Pb analyses to further enrich the interpretation of detrital zircon analyses in future studies.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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