Living with volcanoes: the ‘fossil lake Börtewitz’    

Supervolcanoes in Saxony 

Around 290 million years ago, in the Permian period, there was intense volcanism in the region between Rochlitz, Grimma and Mügeln, which left behind a collapse depression (Rochlitz caldera) with a diameter of more than 30 kilometres. This is filled with various types of porphyry – all products of volcanic activity. However, the rock layers found near Börtewitz have preserved the remains of plants and animals, the living world between the volcanoes. Over the course of millions of years, the porphyry weathered to kaolin on the surface. This porcelain clay is still mined for the ceramics industry between Kemmlitz and Mügeln. From around 350,000 years ago, during the Ice Age (Pleistocene), the inland glaciers of the northern European glaciation moved across the region several times, exposing the porphyry and lake deposits.


The ‘fossil lake’ of Börtewitz: a discovery of international importance

The fossilized remains of life in a lake that existed 290 million years ago has come to light in an open pit. Since 1989, several geoscientific excavations by the Freiberg University of Mining and Technology and the Schleusingen Natural History Museum have yielded rich fossil material. The almost ten metre thick fossil-bearing layer consists of yellowish to light brown mudstones: hard, finely layered slabs of silicified lake deposits and volcanic ash. They contain, for example, remains of conifers and fern seeds, but also amphibians, fish, arthropods and insects. Ash eruptions have extinguished Lake Börtewitz several times. During the dormant periods between volcanic eruptions, the lake re-formed repeatedly over the course of more than 4,000 years attracting new populations of amphibians and fish.


Ecosystem research on the Permian: opening a window into the past

The fossils recovered by palaeontologists in Börtewitz have provided information on the ecosystems of the Permian period under different environmental conditions. These and other fossil finds, for example in Thuringia or in the Chemnitz area, are of international importance for the reconstruction of life during that time and as comparative material for the global development of Permian fauna. They are evidence of a highly specialised habitat with low species diversity but often high numbers of individuals. Lake Börtewitz is an outstanding example of such a biotope – as is the forest of the same age excavated in Chemnitz.

Captions

  • The exhibition ‘Supervolcanoes in Saxony’ in the Röcknitz Geoportal shows volcanism and the living world over 290 million years ago.
  • The Rochlitz eruptions produced kilometre-high ejections of ash and gas, such as here from the Bromo volcano on Java (Indonesia), which repeatedly buried Lake Börtewitz.
  • „Supervolcanoes’ (above) and ‘Biosphere’ (below) theme rooms in Röcknitz.
  • Bedding conditions and age of the rock layers at the ‘Börtewitz fossil lake’ geotope.
  • The first excavation in 1989 was carried out with muscle power, later with technical support from Kemmlitzer Kaolinwerke GmbH; wearing a pale orange T-shirt: Dr Harald Walter, the discoverer of the ‘fossil lake’.
  • The rock profile of the ‘fossil lake Börtewitz’ with the excavated plants and animals (see also back panel).
  • During a volcanic eruption, a freshwater shark hunts its prey: bony fish and newt-like amphibians; a cockroach buzzes curiously above this scene.
  • Buried by the volcano 291 million years ago, excavated today in Chemnitz: A cordaite, pasronite and calamite forest with snails, scorpions, amphibians, insects and giant centipedes.


Imprint

Concept and texts: In cooperation with Museum für Naturkunde Chemnitz and TU Bergakademie Freiberg;
photos: M. Bertuch, R. Roscoe, L. Richter, TU Bergakademie Freiberg; geological profiles: GEOmontan GmbH Freiberg according to GK50 1992, P. Tschernay 2004 and Schneider & Puschmann 2024; design: Lebensbilder: Museum für Naturkunde Chemnitz based on designs by J. Schneider / F. Spindler and S. Schießl / I. Kogan;
Design: Lars Hoschkara, DESIGN & MULTIMEDIA (Wermsdorf).