Cosmogenic burial dating of in cave-deposited alluvium: unravelling long-term incision rates and complex speleogenesis in multi-level cave systems
- 1Ecole Nationale du Génie de l’Eau et de l’Environnement de Strasbourg (ENGEES) & LIVE UMR 7362 - CNRS, Strasbourg, France (email@example.com)
- 2CEREGE, Aix-en-Provence, France
- 3Dept of Physical Geography and Quaternary, University of Liège, Belgium
- 4FSR-FNRS, Brussels, Belgium
Multi-level cave systems record the history of regional river incision in abandoned alluvium-filled phreatic passages which, mimicking fluvial terrace sequences, represent former phases of fluvial base-level stability. In this respect, cosmogenic burial dating of in cave-deposited alluvium (usually via the nuclide pair 26Al/10Be) represents a suitable method to quantify the pace of long-term river incision. Here, we present a dataset of fifteen 26Al/10Be burial ages measured in fluvial pebbles washed into a multi-level cave system developed in Devonian limestone of the uplifted Ardenne massif (eastern Belgium). The large and well-documented Chawresse system is located along the lower Ourthe valley (i.e. the main Ardennian tributary of the Meuse river) and spans altogether an elevation difference exceeding 120 m.
The depleted 26Al/10Be ratios measured in four individual caves show two main outcomes. Firstly, computed burial ages ranging from ~0.2 to 3.3 Ma allows highlighting an acceleration by almost one order of magnitude of the incision rates during the first half of the Middle Pleistocene (from ~25 to ~160 m/Ma). Secondly, according to the relative elevation above the present-day floodplain of the sampled material in the Manants cave (<35 m), the four internally-consistent Early Pleistocene burial ages highlight an “anomalous” old speleogenesis in the framework of a gradual base-level lowering. They instead point to intra-karsting reworking of the sampled material in the topographically complex Manants cave. This in turn suggests an independent, long-lasting speleogenetic evolution of this specific cave, which differs from the per descensum model of speleogenesis generally acknowledged for the regional multi-level cave systems and their abandoned phreatic galleries. In addition to its classical use for inferring long-term incision rates, cosmogenic burial dating can thus contribute to better understand specific and complex speleogenetic evolution.
How to cite: Rixhon, G., Bourlès, D. L., Braucher, R., Peeters, A., and Demoulin, A.: Cosmogenic burial dating of in cave-deposited alluvium: unravelling long-term incision rates and complex speleogenesis in multi-level cave systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19598, https://doi.org/10.5194/egusphere-egu2020-19598, 2020