On the position and age of the highest-lying Lake Pannon deposits in the Mecsek Mts (SW Hungary)

Abstract

Sediments of the Late Miocene Lake Pannon occur at elevations up to nearly 400m a.s.l. on the slopes of the Mecsek Mts. However, up until now the age of the highest-lying outcrops has only been inferred from indirect data. Here we describe a section of a wave-eroded shoreline from a new exposure, where the age is proved by a bivalve fossil, and discuss the tectonic implications. Based on the occurrence of Dreissenomya cf. intermedia FUCHS and on the history of the regression process of Lake Pannon, the described shoreline sediments can be dated to the first part of the Prosodacnomya vutskitsi chron — i.e. to approximately 7–6 Ma. Nearby boreholes support the assumption that Lake Pannon sediments were deposited at elevations even higher than the present outcrop and covered most of the Mecsek Mountains. The presently high elevation of the sediments could have been equally caused by lake level oscillations and by post-sedimentary vertical tectonic movements; the contribution of each factor, however, is difficult to untangle. Wave-cut platforms of Lake Pannon are not suitable to trace syn-sedimentary vertical tectonic movements due to the low resolution of biostratigraphic methods used to date the raised beaches and to the high speed of lake level changes.