Ruhpolding Formation
[1] This is the reason why Gawlik (2000) suggested a new type profile with a complete development of the radiolarite at Mörtlbach northeast of Hallein.
The type locality of the Ruhpolding Formation belongs to the Lechtal Nappe of the Bajuvaric Unit, one of the major tectonic subdivisions of the Northern Calcareous Alps.
The lower contact of the Ruhpolding Formation is very distinct and outlined by a several centimeter thick bedding joint.
The red coloration due to hematite is caused by the complete oxidation of iron compounds in oxygen-rich bottom waters.
In thin section it can be observed that the siliceous groundmass is derived from the innumerable skeletons of radiolarians (maximal size 0.1 mm in diameter) altered during diagenesis.
[6] Amongst the abundant radiolarians the following taxa are present: The fully marine Ruhpolding Formation was deposited in the pelagic domain at the northern edge of the Neotethys ocean, as indicated by rare ammonite finds like Hibolites semisulcatus.
In the Upper Jurassic the CCD was probably much higher and ranged somewhere between 2,000 and 3,000 metres (6,600 and 9,800 ft) depth due to a greatly diminished calcareous nanoplankton at that time.
It was a decisive and not a transient, repetitive change, because the deep-water radiolarites and later Aptychen Beds clearly differ in character from the lower and mid-Jurassic sediments.
This is exemplified by the increasing number of omission surfaces in the upper Klaus-Formation combined with a general slowed-down and more patchy sedimentation.
The tuff layers right at the onset of the Ruhpolding formation are without doubt the precursors of the Upper Jurassic magmatic pulse in the Alps.
[8] Also noticeable is a pronounced increase in autokinetic sediments such as turbidites, debris flows, slides at or near the turning point.
[10] For the Ruhpolding Radiolarite Group, Suzuki and Gawlick recommend the time span Bajocian before the Lower Tithonian,[11] or in absolute terms 171 through 147 Million Years BP.
