Going deeper underground: multi-level cave systems dated by 26Al/10Be cosmogenic burial as valuable geomorphological markers of long-term landscape evolution

Underground karst systems have an unique geomorphological relevance for the reconstruction of long-term landscape evolution as it is widely acknowledged that “(…) cave features tend to be preserved far longer than correlative surface features [(e.g., alluvium-mantled terraces in fluvial environments)], which are more susceptible to weathering and erosion” (Audra and Palmer, 2013, p. 187). In this contribution, we thus consider (i) endokarstic fluvial sediments deposited in multi-levels cave systems or networks, which have formed in response to regional base-level changes over long periods of time (typically 10⁵-10⁶ years), and (ii) how to date them. More specifically, we aim at fostering the use of cosmogenic burial dating of cave-deposited clastic sediments to unravel the long-term evolution of fluvial landscapes. The formation of epigenic cave systems and their geomorphological relevance as a marker of long-term river incision is firstly discussed. After a brief presentation of cosmogenic burial dating works and how it can be applied to cave-deposited alluvium, this contribution focuses on how/where to sample within multi-level cave systems and on selecting the sampling material. It afterwards highlights the main drawbacks (analytical and geomorphological uncertainties) associated to this method and presents some strategies to avoid them (if possible). The combination of cosmogenic burial dating with other geochronological tools in the underground realm is also tackled in that respect. Whilst the multi-purpose use of this approach to unravel evolution of fluvial landscapes is briefly reviewed, we focus on the reconstruction of long-term incision rates, including their variation through time, and the drivers of incision. We conclude by a number of useful recommendations to fully benefit from this approach.

 

Reference

Audra, P., Palmer, A.N., 2013. The vertical dimension of karst: controls of vertical cave pattern. In: Shroder, J. (Editor in chief), Frumkin, A. (Ed.), Treatise on Geomorphology. Academic Press, San Diego, CA, vol. 6, Karst Geomorphology, pp. 186–206.