First 36Cl cosmogenic moraine geochronology of the Dinaric mountain karst: Velež and Crvanj Mountains of Bosnia and Herzegovina

Abstract

This article presents the first attempt to date moraines in the Dinaric mountain karst using cosmogenic 36Cl surface exposure dating technique. Twenty samples were collected from moraine boulders from two sets of the lowest and largest lateral moraines on the Velež (1965 m asl) and Crvanj mountains (1920 m asl) in Bosnia and Herzegovina. The dated lateral-terminal moraine complexes, spanning elevations from ∼980 to 1350 m asl, are up to 2.7 km long and rise more than 100 m above the valley floor. The moraine boulders yielded 36Cl ages spanning from Oldest Dryas for Velež (14.9 ± 1.1 ka) to Younger Dryas for Crvanj (11.9 ± 0.9 ka), considering the average age of the two oldest samples from each lateral moraine as the most representative time of moraine emplacement. The dated moraines mark the largest extent of glaciers in both study areas, which have been reconstructed to ∼28 km2 for Velež and ∼24 km2 for Crvanj, having a mean equilibrium line altitude at 1388 m and 1541 m, respectively. Under modern precipitation values, which account for ∼2000 mm, the temperature depression between 8 and 10 °C is required to sustain the palaeoglaciers with reconstructed equilibrium line altitudes. Glaciers of similar size with such low equilibrium line altitudes during the Lateglacial have not been reported until now for the Balkan Peninsula. It is very likely that the boulder ages reflect complex exhumation and denudation histories, which at this point do not allow obtaining more precise moraine chronologies for the study areas. Nevertheless, this article delivers new data on the extent and timing of Quaternary glaciations in the Mediterranean mountains, where records of glacier fluctuations seem to be asynchronous amongst different areas. It is clear that dating moraines with cosmogenic 36Cl surface exposure dating in carbonate lithologies in areas of high precipitation like the Dinaric karst, remains challenging.