GIS-based morphostratigraphic analysis of glaciofluvial terrace hypsometry in the North Alpine Foreland using R

The morphology of glaciofluvial terrace staircases is controlled by the interactions of fluvio- and geodynamic factors. Prerequisites for their formation are periodically aggradating rivers (e.g. associated with Quaternary cold periods), in combination with tectonic uplift (e.g. Bridgland & Westaway, 2008). Glaciation can thereby remarkably pronounce this effect where the end of a glacial cycle is typically associated with immediate incision. Abandoned plains represent then a morphologic snapshot, covering a very short period of time. Consequently, they can be highly suitable to act as a morphostratigraphic marker for climatic and geodynamic processes. Especially in this context, regional scale systematic analyses appear very promising and have so far not been subject to intense research.

We present a GIS-based morphostratigraphic method and toolset, using the R programming environment. The toolset can be used to project the full elevation information of a high-resolution digital elevation model (DEM) of a river channel (incl. full valley flanks and/or unconfined outwash plains), to 2D (paleo-) river long-profiles, together with other geodata, if available (e.g. existing terrace maps and outcrop information). DEM data is displayed semitransparently in the profile view, making terrace-tops stand out as more or less dark and flat lines. This allows plausibility/quality analysis of existing maps, as well as mapping procedures. Furthermore, on the basis of the projected data, DEM pixels of corelated terraces can be statistically evaluated and models (regression functions) fitted, which allows the reconstruction and measurement of parameters of paleo-riverbeds (e.g. relative height above local base-level, local slope, concavity).

We applied this method in the North Alpine Foreland to an extensive terraced landscape, representing a large age span until up to Early Pleistocene age, as well as abundant data on terrace stratigraphy (i.e. from geological mapping, drilling campaigns and relative and absolute age constrains), including high resolution digital elevation models. Despite the long history of Quaternary research in the region, a consistent stratigraphic model of the Quaternary period is currently missing. In fact, the last mountain range scale model was proposed more than 110 years ago by Penck and Brückner (1909). Local findings by geologic surveys (Switzerland, Germany and Austria) unveil strong inconsistencies and an updated model is highly needed.

Based on a new code in the R programming environment we evaluate existing stratigraphic models and show how glacio- and geodynamic implications can be statistically derived from terrace hypsometry.

References:

Bridgland, D., Westaway, R. (2008): Climatically controlled river terrace staircases: A worldwide Quaternary phenomenon. Geomorphology 98, S.285-315. Elsevier. doi:10.1016/j.geomorph.2006.12.032

Penck, A., & Brückner, E. (1909): Die Alpen im Eiszeitalter. Leipzig: Tauchnitz.