Variability of long-term denudation rates measured by 36Cl analyses on a karst levelled surface

Studies of karst denudation rates are great approach to provide an insight to karst landscape development. Traditionally, dissolution of carbonate rocks is considered to be the main process governing carbonate weathering, other processes should not be overlooked. Here we present research done in the North Dalmatian Plain, a carbonate erosive surface located in the Dinaric karst region. Although study site is composed of two different carbonate lithologies having different weathering style, there is no evident lithological impact on the topography of erosive surface. Analyses of ³⁶Cl were performed in ten proximal samples from both lithologies resulted in denudation rates from 14.7 to 22.7 m/Ma. Since no statistical significance was found between samples from different lithologies (all samples belong to a single normal population) having same geomorphological context and climate features, variable denudation rates are attributed to local differences in denudation.  

In the study site there are no large outstanding rock residuals, or deep soil patches, thus in order to maintain the levelled erosive surface local differential denudation rates have to vary with time. We hypothesize that lichens and pedogenic carbonates have a significant role in modulating local differences in denudation rates. Our study shows that even at outcrop scale, differences in local denudation rate can be significant and study of large set of samples is preferred to properly characterize the overall denudation rates of carbonate surfaces. Thus, the long-term denudation rate of the North Dalmatian Plain, including local variability, is 18.55 ±0.79 m/Ma. Despite classical studies on karst terrains assume that dissolution is the main process responsible for denudation of these landscapes, our research highlights the importance of physical weathering in combination with dissolution of carbonates as main controls on the denudation of karst landscapes.

 

Acknowledgements: This research is a part of the research project “Inter-comparison of karst denudation measurement methods” (KADEME) (IP-2018-01-7080) financed by Croatian Science Foundation.