Stop 4 at Ries

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Aumühle quarry is one of the best places to study the ejecta deposits of the Ries structure. It's one of the few remaining active quarries mining suevite, which is being used to make cement. The first thing to notice is that there are actually two layers of ejecta at Ries: Bunte Breccia and Suevite, and they are very different. Bunte Breccia was deposited first and underlies the suevite. It contains fragments of sedimentary rocks and some crystalline material (granites and gneisses), but no impact glass. Suevite, on the other hand, contains fragments of mainly crystalline rocks and substantial impact glass .

It is widely accepted that Bunte Breccia represents the ballistic ejecta blanket at the Ries structure. It consists of two main components: (1) primary ejecta excavated from the initial crater, which comprises sedimentary and crystalline rocks, and (2) local material or ‘ secondary ejecta’ , incorporated into the primary ejecta as it landed and then flowed outwards for some considerable distance — this is predominantly surficial sediments, such as sands and clays, that were present on the surface at the time of impact.

The origin of the Suevite is less well understood compared to Bunte Breccia despite several decades of study. The sharp contact between the suevite and the Bunte Breccia indicates that there was a time gap between the deposition of the two ejecta deposits. Some scientists believe that the suevite represents material that was thrown upwards into a vast ejecta plume and then settled down gently over the top of the Bunte Breccia. Others think that the suevites flowed outwards from the center of the crater during the final stages of crater formation.

In this photo we can see dark black fragments of impact glass and white fragments of shocked granite and gneiss.

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