Hülscher, J., Sobel, E., Kallnik, N., Hoffmann, E., Millar, I., Hartmann, K. & Bernhardt, A. (2022). Apatites Record Sedimentary Provenance Change 4–5 Myrs Before Clay in the Oligocene/Miocene Alpine Molasse. Frontiers in Earth Science, 10:914409. doi: 10.3389/feart.2022.914409

Hülscher et al. (2022) investigate the sedimentary provenance of a Oligocene/Miocene basin in the Eastern European Alps and its response to a change in tectonic signal at around 28 Ma (tectonically induced exhumation of the Tauern Window metamorphic dome). The sedimentary record of apatite single-grain distributions and bulk-rock clay-sized fraction is investigated. Focus lies on a possible delay in the recording of the provenance change depending on the grain-size fraction and the implications for processes in the sediment-routing system.

This section will focus on the Nd isotope analyses in the clay-sized fraction and the conducted Monte Carlo simulation for estimating the sample mean and testing an observed shift in \(\varepsilon\)Nd values. For further details on the sand-sized apatite single-grain analysis and the interpretations please look into the original paper. The analyzed data is available in the Supplementary Material.

Method

The clay-sized fraction was separated from thirty drill-cutting samples and analyzed for the Nd isotopic composition. Normalized 143Nd/144Nd ratios are reported in \(\varepsilon\)Nd notation (DePaolo and Wasserburg, 1976) with \(2\sigma\) uncertainties.

As depicted by the following Figure, the five youngest samples (above 1420 m) show higher \(\varepsilon\)Nd values (mean: −9.12 ± 0.54) than the remaining older 25 samples (mean: −9.67 ± 0.52):