Rohrbach formation

The Rohrbach Formation (traditionally also Rohrbacher Konglomerat or Ternitzer Konglomerat ) is a lithostratigraphic rock unit of the Upper Miocene and Lower Pliocene (highest Pannonian to Dazian ) of the southern Vienna Basin in the rank of a formation .

Geographical and stratigraphic distribution

The Rohrbach formation is limited to the southwestern tip of the Vienna Basin ( Steinfeld ). Type locality and name-giving is the Rohrbach quarry ( 47 ° 43 ′ 45 ″ N, 16 ° 03 ′ 10 ″ E ) or the Ternitz district of Rohrbach am Steinfelde, where the formation is almost 13 m thick (in some boreholes, however, at least 65 m).

The formation is the youngest Pre- Pleistocene rock unit in the Vienna Basin. They superimposed discordant the fine-grained sediments of the Lower Neufeld layers (deeper Pannonium) and is of plio Pleistocene fluvial gravel and gravel superimposed on the Mitterndorfer sink or without Hangendkontakt with Pliocene to recent soil formations in the most recent pending . Laterally, it meshes with the Upper Neufelder strata in its lower section and with the Würflacher torrent gravel in its upper section.

Lithologies and deposit environment

The type locality of the Rohrbach Formation comprises predominantly reddish-yellow conglomerates with rounded to well-rounded pebbles , which consist of rocks from the neighboring Alpine regions (predominantly limestone , dolomite and sandstone , subordinate to gneiss , quartzite , phyllite and other crystalline). So- called gravel corpses are typical, i.e. cavities in the sandy-silty matrix that are left behind by gravel and filled with calcite . Stored conglomerates are yellowish to brownish carbonate - and quartz- rich, sometimes obliquely layered (partly partly designed as calcarenites when carbonate-Litharenite or carbonate-lithic Wacken) sandstones and light brown in small parts of silt and gray and dark brown mudstones .

The Rohrbach Formation represents a fluvial bed ( alluvial cone ), which was built from the edge of the Alps into the southern Vienna Basin starting in the late Miocene. The conglomerates were deposited by the rapidly flowing water of a river with intertwined arms ("braided river") and / or periodically by large amounts of flowing water in a very short time (alluvial fan sedimentation). The finer-grained layers go back to a river with intertwined arms in times of low water flow or lower gradients. Silt and clay stones presumably represent flood deposits ("Overbank Deposits"), which were deposited in standing water in relatively poor relief terrain.

literature

• Veronika Koukal, Michael Wagreich: Sedimentology and definition of the Rohrbach Formation ("Rohrbacher Konglomerat", Upper Miocene - Pliocene) in the Rohrbach / Ternitz quarry (Lower Austria). Yearbook of the Federal Geological Institute. Vol. 149, No. 4, 2009, pp. 453–462, online (PDF; 1.7 MB)