Tertiary Period - volcanoes erupt, meteorites strike

After 50 million years it finally happens − the Jurassic Sea recedes and the Alb becomes a land mass. However, there are now only a few remaining traces from this era of the Cretaceous and early Tertiary periods. The reason for this is the strong erosion which has almost completely removed every trace of this period. The most exciting remnant of the Tertiary is the result of two natural catastrophes which both had a massive impact on the landscape.

The Swabian volcano
In the Tertiary, between 18 and 10 million years ago, many volcanoes erupted on the Swabian Alb and some of these can still be seen in the present landscape. The basaltic magma rose up through the fissured earth crust and tore away pieces of rock from the bedrock and the overlying Triassic and Jurassic layers. When it came into contact with the groundwater in the White Jurassic, there were immense steam explosions which blasted away the overlying rock layers. In this way, big calderas were formed which later filled with water and became freshwater lakes on the plateau of the Swabian Alb. The most famous of these former freshwater lakes is the Randecker Maar, a volcanic crater now located directly along the Alb escarpment. It left behind finely laminated limestones with beautifully preserved fossils: flowers and leaves of subtropical plants, insects, frogs and salamanders, and even the remains of mammals.

In the Alb foreland, the volcanic diatremes appear as cone-shaped mountains. For example the Limburg, the Turmberg, the Sulzburg near Oberlenningen, the Spitzberg and Engelberg near Beuren, the Georgenberg near Reutlingen, the Metzinger Weinberg and the Grafenberg and several others, they all have a core of volcanic origin. The volcanic rock filling of these hills is more resistant to weathering than the surrounding layers of the Brown Jurassic and so they stand out as flat cones on the foreland of the Swabian Alb. When humans settled on the Swabian Alb, the volcanic diatremes were particularly important for them as this is the place where they found water. The groundwater accumulated on the water-impermeable volcanic tuffs and did not drain away as quickly as it is usually the case on the karstified Alb plateau. The thermal springs and mineral springs containing carbonic acid in Bad Imnau, Bad Überkingen, Bad Ditzenbach, Bad Boll, Bad Urach, Beuren and Aalen are probably the latest consequences of the volcanic activity during the Tertiary.

A greeting from outer space leaves its mark
It only lasted a few minutes and happened 15 million years ago − a natural catastrophe of immense proportions that destroyed all life within a wide radius. Two meteorites struck the ground at a speed of about 25 km per second, only about 40 km away from the plateau of the Swabian Alb. The impact of the larger meteorite led to the formation of the famous Nördlinger Ries. The smaller meteorite had a diameter of about 80 m and left behind a circular crater of 3.5 km diameter in the area of today‘s municipality of Steinheim am Albuch. On impact, pressures of over 100,000 atm. and a temperature of some 10,000°C were generated. Consequently the meteorite and the surrounding rock evaporated on impact giving rise to a crater of around 250 metres in depth.

The impact caused shock waves to be released, the crater was blasted out and a huge amount of debris was expelled. Similar to a drop of water landing on the water surface, a peripheral rim was created and as a consequence of the rebound, the clearly visible cone of the central hill emerged which can be seen today. The rock was crushed and melted within seconds – from the hard White Jurassic layer on the surface deep down to the bedrock in the interior of the Earth. Rock ejecta, for example of White Jurassic limestones, were hurled for kilometres through the air and then inclined, compressed and folded on impact. Finally, a freshwater lake formed in the explosion crater, where then new life quickly evolved. The outcrops of sand in the Steinheim Basin with their freshwater snails are particularly famous, but fossil fish, turtles and mammals were also found there.

continue with Quarternary Period