Provenance bias between detrital zircons from sandstones and river sands: A quantification approach using 3-D grain shape, composition and age
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Abstract
Preservation bias may significantly impact the application of detrital zircon geochronology in reconstructing
Earth surface processes. Here we compare detrital zircons from the actively eroding Murchison River channel in
Western Australia with Ordovician fluvial sediments that have drained similar source rocks along the western
margin of the West Australian Craton. In addition to standard analysis of detrital zircon age spectra we apply
multivariate statistics to test the relation between 3-D grain shape, U-content and U–Pb ages, with the objective to
quantify differences between both sample groups and track preservation along the transport pathway of the
Murchison River. Our results show that zircon grains in modern river sands display an upstream trend toward
larger surface areas, volume equivalent diameters and grain widths, as well as toward higher U-contents and
lower apparent grain densities. 3-D grain shape, size and age spectra of Murchison River zircons evolve consistently
downstream, but even at the river outlet remain distinct from the Ordovician samples, as a less mature
representation of source. We interpret Ordovician river zircons to represent a significantly depleted subset from
which up to 22% of the zircon population may have been lost compared to the actively transported detrital load.
This discrepancy between the characteristics of detrital zircons in modern active rivers and ancient fluvial
Ordovician sandstones demonstrates a bias that could be relevant for other source-sink detrital transport systems
throughout Earth history.
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