Eocene Stratigraphy of the Reichenhall Basin (Eastern Alps, Austria, Germany)
Egger, Hans; Briguglio, Antonino; Rögl, Fred
Newsletters on Stratigraphy Volume 50 Number 3 (2017), p. 341 - 362
published: May 1, 2017
ArtNo. ESP026005003006, Price: 29.00 €
One of the thickest Eocene sedimentary records in the Eastern Alps occurs in the Reichenhall Basin of the Northern Calcareous Alps, a detached part of the Adriatic Plate. Although the Ypresian and Lutetian deep-water deposits in the Reichenhall Basin have already been combined into the Nierental Formation of the Gosau Group, the overlying Bartonian to Priabonian deposits have not been lithostratigraphically formalized until now. This younger part of the succession shows a two-fold subdivision, with a deep-water and a shallow-water facies indicating syn-sedimentary differential vertical displacements of tectonic blocks. This caused subaerial exposure and erosion of local topographic highs, while basinal areas underwent continuous subsidence and sediment accumulation. Biostratigraphic constraints suggest that block-faulting began in the late Lutetian at c. 42 million years ago (Ma) and this event is interpreted to reflect the onset of the collision between the Adriatic and European Plates. After denudation, a transgression occurred on some of the up-lifted blocks in the early Bartonian. The base of this transgressive sequence is within Shallow Benthic Zone SBZ17 and at the transition of orthophragminids Zones OZ12 and OZ13 (c. 40.5 Ma – 40 Ma). The lower part of the sequence consists of shallow-water limestone (Kirchholz Formation, nom. nov.) and the upper part of siliciclastic deposits (Hallthurm Formation, nom. nov.). Coeval deposition in the basinal areas was dominated by mass-flow sedimentation of reworked intrabasinal Triassic to Lutetian components derived from the flanks of the topographic highs. These deposits (Marzoll Formation, nom. nov.) are interpreted to be submarine slope aprons, that flanked fault-controlled block margins. The Bartonian to Priabonian deposits of the Reichenhall Basin are considered to be the oldest part of the "Inneralpine Molasse", for which the lithostratigraphically correct term Inntal Group (nom. nov.) is proposed and defined. This group comprises Bartonian to Chattian marine and terrestrial deposits of the Northern Calcareous Alps.