Loser Plateau: Geology and Speleogenesis

As it's quite hard to find information about the geological history of the Schwarzmooskogel in English, I started investigating. Not that I'd know much about geology, but as a German native speaker I had a large selection of literature available. Particularly helpful was the article "Joachim Kuhlemann et al. . "Eine Zeitreise in den zentralen Nördlichen Kalkalpen: von Tropischen Küstenebenen zu Eishöhlen. In Karst und Höhle 2002/2003, Der Schwarzmooskogel, p. 137-153. VdHK e.V. München. ISSN 0342-2062", but all the other articles in that journal issue are highly recommended as well. At the time of writing, there are furthermore two short articles on the appearance and sedimentation of the limestone here and here.

Formation of the Limestone

There appears to have been a shallow sea in the area during the Permian (299-251 Mya), which occasionally dried out. This is where the salt of the nearby salt mines formed, interspersed with some sandstone sediments. Most of the limestone then formed in the middle to late Triassic (250-200 Mya), when the shallow sea got a bit deeper, but was still well within reach of sunlight. This provided perfect conditions for algae and corals, which eventually turned into limestone. The base rock was sinking at the time, but the enormous production of sediments counterbalanced this downwards movement. These layers of sediments are nowadays called Dachstein-limestone ("Dachsteinkalk").

At the end of the Triassic and during the Jurassic (199-145 Mya), the sink rate increased and the production of sediments could not keep up any more. At the resulting deeper levels of the sea, dolomites and other limestones started to form. In our area, the Loser-group and Bräuningzinken are examples of these Jurassic limestones and dolomites. Due to various other minerals mixed into the rock, it is not as well suited for cave formation as the Dachsteinkalk, although major caves are still found (e.g. at Almberg).

Towards the end of the middle Jurassic, a new oceanic ridge started to form between the Eurasian plate in the north and the Apulian and Adriatic plates in the south. Due to the force this new Penninian ocean ridge exerted onto the continental plates, the various layers of limestone and dolomite were pushed on top of each other in so called thrust faults from the southeast to the northwest. Some parts of the newly formed oceanic crust were uplifted as well, and at the same time rocks were eroded and started back-filling the ocean. This ocean lasted up to the middle Cretaceous (145-65 Mya), when the ocean started to close again due to a change in tectonics. The subduction of the short lived oceanic crust continued a few more million years and the ocean has completely disappeared nowadays. In the process rocks were also eroded from the bottom of the continental crust by friction of the subducted oceanic crust. Generally the area around the Totes Gebirge also sunk a bit during the late Cretaceous and early Paleogene (65.5-23 Mya).

First Caves and Mountains

During the Eocene (55.8-33.9 Mya) the alpidian collision started to cause the uplift of the Alps. However, in the beginning this mostly caused an uplift in the western part of the Alps, and the eastern part including the Totes Gebirge was still relatively low, even partially flooded by seawater. As a result, a first karstification started in the area, which created what is called the cave ruin level ("Ruinenhöhlenniveau"). This level is nowadays about 1800m and higher above sea level and the stone bridge (Traungoldhöhle) is probably a prime example of this cave level.

However, the new mountain ridge to the southwest of the Totes Gebirge was exposed to erosion and lots of sediments started to back-fill and cover the cave ruin level in the Oligocene (33.9-23 Mya). The new sediments are called Augenstein-Formation, and the rubble consisted of all kinds of odd materials like quartz, gneiss, slate, some ore, sandstones and others. The sediments are getting finer in the north and fine sands at the northern edge of Totes Gebirge indicate that a coastline was present at the time, whereas coarser pebbles and stones are found further south. The exact mineral composition of the Augenstein-sediments found at various places even allows to reconstruct the river network of the time, which was mostly oriented south to north. Furthermore the absence of gneiss and slate in the Augenstein-sediments of the Totes Gebirge indicate that these rocks, which nowadays form the Tauern mountains south of our area, were mostly covered by limestone and other sediments at the time. These sedimentary rocks are nowadays only present around some peaks of the Tauern mountain range. Some rock metamorphosis has taken place in the Augenstein-sediments and indicate a thickness of at least 1300m up to maybe beyond 2000m, with a maximum of thickness around the Dachstein area.

In the early Miocene (23-5.3 Mya) the eastern Alps were laterally stretched in the east-west direction by more than 50%. This event also caused a collapse of the mountains further south-west, a new layout of the river network along the newly formed fault lines, and in the cause of both a complete stop of the sedimentation of Augenstein-layers. Most of these sediments had been eroded again by about 10 Mya. Karstification of the cave ruin level and below could start again.

More Caves

During the last 10 Mya, the Totes Gebirge was raised by about 2000m, which is equivalent to about 2mm per year. This uplift is generally considered to have happened in distinct phases instead of a continuous process, as there appear to be distinct levels of caves all around. The "level of big caves" ("Riesenhöhlenniveau") with extensive horizontal passages is nowadays at around 1550m-1640m above sea level. It was formed in the late Miocene, about 10 Mya.

Due to the absence of plants and due to glaciation and hence absence of flowing water, there was hardly any new cave formation in the Pleistocene (2.5 Mya - 10 Kya). However, most recently the level of spring caves ("Quellhöhlenniveau") has formed and is still actively forming at altitudes equivalent to the present valley bottoms. As the distance of this spring cave level to the older levels varies between 700m and 1000m in various parts of the Alps (Tennengebirge, Steinernes Meer, Totes Gebirge), it is believed that these different places have also been lifted by different rates in the Pliocene era (5.3-2.5 Mya).

It is obvious that the above geological history of the Totes Gebirge is mostly an interpretation of the sparse evidence that is nowadays found at Dachstein, Schönberg, Schwarzmooskogel, Woising, Tauplitz and the other areas. New finds and new caves might necessitate a complete or at least a partial rewrite.

Olaf Kähler, September 2012