Revision of river terrace geochronology in the Orawa-Nowy Targ Depression, south Poland: insights from OSL dating

摘要

Geochronologies of intramontane depression (basin) fluvial sedimentation enable to identify through time periods of alluviation and river erosion, and date fault movement. For these purposes the optically stimulated luminescence (OSL) dating has been applied to evaluate and to develop a geochronological framework of river terraces. We study the age of river terrace deposits of the Czarny Dunajec River and its tributaries, in the Orawa-Nowy Targ Depression situated at the contact of the Central and the Outer Carpathians; where alluvial sediment ages were derived mainly from morphostratigraphic dating. Thorough careful analysis our approach demonstrates that the OSL dates differ markedly from the previous age assignments. Alluvium of the terrace elevated 5.5-6.0 m above the present-day valley floor, in terms of cementation and lithology resembling sediments described as pre-Pleistocene, was found to have been deposited similar to 34 ka ago (MIS 3). Sediments of the lower terraces, 3 m and 3.5.m high, similar in elevation and internal structure to those of the Holocene terraces, are most likely of MIS 3 and MIS 2 ages, respectively. The architecture of the terraces introduces climate as a dominant driver for terrace formation at the southern border of the depression. We conclude that the morphostratigraphic approach appears insufficient for reliable dating of river terraces, especially in areas where they might be affected by young tectonic movements. Comprehensive and credible chronostratigraphy of fluvial deposits is required, particularly in the studies of the history of the fluvial systems and seismic hazard in the Carpathians. (C) 2016 The Geologists' Association. Published by Elsevier Ltd. All rights reserved.