Challenges in constraining ages of fluvial terraces in the Vienna Basin (Austria) using combined isochron burial and pIRIR225 luminescence dating

5 years ago

Challenges in constraining ages of fluvial terraces in the Vienna Basin (Austria) using combined isochron burial and pIRIR225 luminescence dating

Burial dating with terrestrial cosmogenic nuclides and luminescence dating techniques have become two powerful tools to temporally constrain Quaternary deposits. A combination of both methods at the same geological setting has rarely been realized to date, although their viable time frames overlap by several tens of thousands of years. When Middle Pleistocene sediments with depositional ages ranging around ca. 120 ka to ca. 300 ka are targeted, both methods are employed, but come towards their lower and upper limits, respectively. A combined dating approach can be worthwhile at this age range and allows not only exploring the edges of both methods, but holds the opportunity to do a cross-check of results at an age spectrum, where both dating techniques are at risk to become fuzzy. Here we present a case study where numerical ages of two Middle Pleistocene terraces located in the Vienna Basin were generated by combining burial and luminescence dating. A variety of processes, such as changing sediment input rates, erosion, and tectonics controlled the formation of fluvial terraces in the basin and shaped its complex modern surface. Age correlation of the evolved mosaic of blocks and dislocated sediment bodies is challenging and requires quantitative geochronological information in order to establish a coherent terrace stratigraphy. Luminescence and burial samples originating from two fluvial terraces, the lower Gaenserndorf terrace (GDT) and the higher Schlosshof terrace (SHT), were analyzed and evaluated. Luminescence and burial ages at the GDT site are in good agreement and suggest a depositional age of 140 ± 170 ka bracketed by pIRIR225 luminescence ages ranging from 120 ± 10 ka to 260 ± 30 ka. Luminescence samples at the SHT site are in saturation, but provide minimum ages, which are coherent with the burial dating result of 340 ± 170 ka. The new numerical ages indicate that the vertical offset between the GDT site and the SHT site was not purely caused by fault activity, but suggest two independent episodes of sediment accumulation.

Besides providing new insights into the stratigraphic and morphological configuration of the central Vienna Basin area, the cosmogenic nuclide data set is compelling from a methodological point of view. At the GDT site, several samples exhibited ²⁶Al/¹⁰Be nuclide ratios exceeding the surface production ratio of 6.75. Even though affected samples were excluded from burial age calculations, a detailed investigation on possible scenarios, which could have caused an upwards shift of ²⁶Al/¹⁰Be ratios, was carried out.

Publisher URL: www.sciencedirect.com/science

DOI: S1040618217308017