A geological snapshot from the front of the Northern Calcareous Alps: Well Obermoos TH-1, Salzburg, Austria

The deep thermal well Obermoos TH-1 (total depth 2468 m, year 1990) was drilled within the Upper Cretaceous Salzburg-Reichenhall basin of the Northern Calcareous Alps at the southwestern edge of Salzburg city, Austria. The lithologic log shows c. 200 m thick Quaternary sediments of the glacially overdeepened Salzach Valley above bedrock. The Quaternary infill is underlain by c. 250 m thick, almost horizontally lying coarse clastics and marls, which belong to the Upper Cretaceous Salzburg-Reichenhall Gosau basin. From 456 m to 2468 m, a steeply dipping, more or less continuous succession from Cenomanian strata to Upper Triassic Hauptdolomit was encountered. This succession is considered being part of the Bajuvaric nappe of the central Northern Calcareous Alps, which is entirely overridden by units of the Tyrolic arc in the study area. The new data from the deep drilling provides (i) new information on depth and filling of the deeper parts of the Pleistocene valley and (ii) new insights into the complex structure of the Bajuvaric nappe. We also discuss a potential fault crossing the Salzburg-Reichenhall basin being part of the Cenozoic Innsbruck-Salzburg-Amstetten fault system. On a larger scale, the Tyrolic unit exposed in the southern margin of the Salzburg-Reichenhall basin and potentially overlying the borehole section must be the same as in the flat-laying Tyrolic nappe found in two deep drill holes, 15 km southeast and 18 km east of the City of Salzburg (Vigaun 1 and Vordersee 1).