OSL ages and origin of Late Quaternary sediments in the North Transdanubian Hills (Hungary): timing of neotectonic activity

The Transdanubian Hills, south of Lake Balaton, is a gently elevated area with well developed dissected morphology. A new highway constructed through the area provided an excellent opportunity to make field observations and date the neotectonic movements. Deformed and undeformed fluvial and eolian sequences were dated using optically stimulated luminescence on quartz, complemented by radiocarbon age data. The distribution of the equivalent doses measured on small aliquots indicates that the sediments were poorly bleached before deposition, and therefore the OSL ages, calculated by the mean equivalent doses, represent the maximum depositional ages of the sediments. To determine the source area of the sediments, microscopic study was applied.The oldest dated samples are 49–39 ka fluvial sands (at maximum). On the top of the sand, a forest-steppe type paleosol formed, which interfingers with the coeval fluvial channel sand body. These sediments are younger than about 30 ka. Loess-like sediments were deposited later than 25 and 10–8 ka, and fluvial sand was deposited a maximum of 22 and 9 ka. The fluvial sediments, except the youngest, were transported from NNW of the Transdanubian Central Range, indicating that Lake Balaton did not exist during the Late Pleistocene and the drainage network was quite different from the recent situation.Field structural observations and OSL dating showed that a deformation period started later than 49 ka in the study area, while folding started after 22 ka. Gentle late stage uplift at maximum 9 ka ago was identified, which might have been active sub-recently.