Detrital zircon dating dating russian ireland

12-May-2020 18:33

They conclude that geologists need to be aware of their assumptions and not just assume that lots of data and statistical analysis will prevent bias. How long have they been unaware of the natural bias introduced by sediment transport?

These six geologists ran a test with a “simple experiment” and found a source of bias that “most studies” have ignored.

Although larger values of are evidently fundamental for improving representativity and statistical accuracy (Pullen et al., 2014; Zhang et al., 2016; Nie et al., 2018), Thus, in order to improve the quantitative use and application of geochronologic-based detrital mineral provenance approaches, we must better our understanding of how zircon crystals pass through, and fractionate from, sedimentary systems (Hietpas et al., 2011), and use that understanding to inform our statistical treatments accordingly.

This is particularly critical as the number of publications including a component of detrital zircon provenance continues to grow, because this is inevitably driving the community toward a “big data” approach that will (by necessity) continue to increase its reliance on robust statistical treatments. How long have geologists been publishing papers about formations dated with detrital zircons?

Their title hints of troubles ahead: “Use and abuse of detrital zircon U-Pb geochronology—A case from the Río Orinoco delta, eastern Venezuela.” The Abstract warns: Advancements in mass spectrometry methods over the past two decades have allowed for rapid measurement of (U-Th)/Pb isotopes for geochronologic applications, a tool that has deeply influenced the way sediment provenance and paleo-tectonic reconstructions are approached.

Geochronology-based studies of sediment provenance typically rely on dating ≈ 100–150 single detrital zircon crystals from individual samples, where the sample age distributions are used to make inferences about the parent age distributions, make qualitative geologic interpretations, and/or perform quantitative intersample comparisons.

Chamberlin ≈ 1000) results from unconsolidated fluvial sediments of the Río Orinoco delta, eastern Venezuela, to highlight the concealed pitfalls of making geological interpretations based on quantitative comparisons of U-Pb age distributions alone.

Three samples analyzed at large selected from contrastingly different mean sediment grain sizes along the active channel of the Río Orinoco, yield large dissimilarities amongst their age spectra, resulting in the misleading conclusion that these were likely not sourced from the same parent distribution.

How confident are geologists in the ages of formations they study?

We demonstrate that statistically significant differences amongst detrital zircon samples derived from the same (integrated) source region can be introduced by the dynamics of sediment transport, which may in turn lead to erroneous geologic interpretations arising from the inaccurate assumptions that, at present, condition the quantitative treatment of detrital zircon data.“The fascinating impressiveness of rigorous mathematical analysis, with its atmosphere of precision and elegance, should not blind us to the defects of the premises that condition the whole process.”—Thomas C. Most sediment provenance studies that apply quantitative detrital zircon U-Pb geochronology rely on the assumption that direct intersample comparisons using dissimilarity metrics allows for determination of similar and/or distinct sediment sources (e.g., Saylor and Sundell, 2016; Vermeesch, 2018, and references therein).

There are, however, two inconvenient and commonly ignored issues in geochronology-based sediment provenance: (1) detrital zircon U-Pb ages can cluster by grain size ; and (2) grain-size sorting is strongly influenced by the dynamics of sediment transport.

Does statistical convergence necessarily translate into geological convergence? In a new paper in , six geologists tested a widely-used technique of gathering detrital zircons: crystals of zirconium that often contain uranium (U) and its daughter product lead (Pb), found in debris piles below a slope.

They tested the assumptions in their samples collected in Venezuela.Most efforts to quantitatively compare detrital zircon age spectra make use of non-parametric dissimilarity statistics.