Comments on the geological map of the Breitenberg area (Northern Calcareous Alps, Austria)

Abstract

During two fieldtrips in June–July 2008 and June 2009 the geological structure of an 8 km2 large area between the Breitenberg and the St Wolfgangsee (Austria, Northern Calcareous Alps) was surveyed. The area—belonging to the Osterhorn Clod, a part of the Austroalpine—comprises mainly calcareous lithologies of Upper Triassic to Lower Cretaceous ages. The lithologies clearly show a general deepening of the basin throughout the Mesozoic. The lagoonal back reef sediments of the Triassic are overlain by basin-and-swell limestones of a moderate water depth of the Lower Jurassic and distal sediments of a deep basin of the Upper Jurassic/Lower Cretacoeus. The mapping area is characterised by a division into two parts, seperated by a major fault in between: (a) A northeastern part, in which folded Upper Jurassic and Lower Cretaceous sediments predominate, and (b) a southwestern part, comprising a large syncline of Triassic and Lower Jurassic deposits in the majority. The small scale tectonism mainly comprises brittle, rather than ductile deformation. Clefts and slickensides were used for a basical palaeostress analysis. Two deformation events could be reconstructed: (a) a N–S to NNE–SSW shortening that is responsible for most of the folding and faulting and (b) an E–W to ESE–WNW shortening that occured later at least in the northern mapping area and folded the fold axis of the first event. The fielddata were compiled into a geological map and cross sections of the Breitenberg and the northerly adjacent area