Publication Date:
2016-11-01
Description:
ABSTRACT Correct and precise age determination of prehistorical catastrophic rock-slope failures prerequisites any hypotheses relating this type of mass wasting to past climatic regimes or palaeo-seismic records. Despite good exposure, easy accessibility and a long tradition of absolute dating, the age of the 230 million-m 3 carbonate-lithic Tschirgant rock avalanche event of the Eastern Alps (Austria) still is relatively poorly constrained. We herein review the age of mass-wasting based on a total of seventeen absolute ages produced with three different methods ( 14 C, 36 Cl, 234 U/ 230 Th). 36 Cl cosmogenic surface exposure dating of five boulders of the rock avalanche deposit indicates a mean event age of 3.06 ± 0.6 ka. 234 U/ 230 Th dating of soda-straw stalactites formed in microcaves beneath boulders indicate mean precipitation ages of three individual soda straws at 3.20 ± 0.26 ka, 3.04 ± 0.10 ka and 2.81 ± 0.15 ka; notwithstanding potential internal errors, these ages provide an 'older-than' ( ante quam ) proxy for mass-wasting. This article is protected by copyright. All rights reserved. Based on radiocarbon ages (nine sites) only, it was previously suggested that the present rock avalanche deposit represents two successive failures (3.75 ± 0.19 ka BP, 3.15 ± 0.19 ka BP). There is, however, no evidence for two events neither in surface outcrops nor in LiDAR derived imagery and drill logs. The temporal distribution of all absolute ages ( 14 C, 36 Cl, 234 U/ 230 Th) also does not necessarily indicate two successive events but suggest that a single catastrophic mass-wasting took place between 3.4 and 2.4 ka BP. Taking into account the maximum age boundary given by reinterpreted radiocarbon datings and the minimum U/Th-ages of calcite precipitations within the rock avalanche deposits, a most probable event age of 3.01 ± 0.1 ka BP can be proposed. Our results underscore the difficulty to accurately date catastrophic rock slope failures, but also the potential to increase the accuracy of age determination by combining methods. This article is protected by copyright. All rights reserved.
Print ISSN:
0197-9337
Electronic ISSN:
1096-9837
Topics:
Geography
,
Geosciences
Permalink