Meteorites in Southern Germany
A visit to the Ries crater
January 29th, 2016
Our visit to the Ries crater started with a visit to the Rieskrater Museum which is housed in a 16th century barn in Nördlingen. We were welcomed by Gisela Pöges who with Michael Scheiber set up the museum which opened in 1990 and who cowrote the guide to the Museum.
The museum focuses on meteors and their collisions with Earth. 14.5 million years ago a meteorite with a satellite impacted the Bavarian area of Southern Germany forming the 25 km diameter Ries Crater along with a smaller crater at Steinheim (40 km SW of the Ries Crater). It is thought that these craters formed in a similar way to the Shoemaker-Levy 9 impact on Jupiter in 1994: the incoming bolide is thought to have broken up into smaller fragments; hence the two craters.
The old walled town of Nördlingen sits within the impact crater and many of its old buildings are constructed by rocks formed from the impact. Potassium/ Argon dating indicates an accepted age of 15±0.1 Ma: This is backed up with the help of index fossils from the sediments before and after the impact.
The bolide, a stony meteorite 1 km in diameter, caused the damage. The impact energy was sufficient to melt rocks down to the crystalline basement (Pre-Cambrian granites, gneisses and metabasites overprinted in the Variscan Orogeny). The energy of the impact was enough to shift a 150 km3 of overlying rocks and melted impact products; some of the blocks moved are very big and show striae radiating from the impact centre, indicating that some blocks slid over one another as a result of the impact. The form of the crater is complex, with an inner crystalline rim and an outer ejecta wall which forms the circular crater rim.
This site was not recognized as an impact crater, but was thought to be either volcanic or glacial in origin. However, with the visit of Eugene Shoemaker who recognized the minerals coesite and stishovite within the impact rocks (which are only formed as the result of progressive shockwave metamorphism) its fate as impact crater was sealed.
Two breccias resulted from the impact. Firstly, the Bunte Breccia formed from the pre-existing Jurassic Limestones (of clasts up to 25 cm diameter) and allochthonous blocks of Jurassic Limestone up to 50 m in diameter. Secondly, suevite which is a polymict crystalline breccia that includes melt fragments and clasts of granite, gneiss and glass in a fine-grained matrix of pulverized basement rock.
This also contains microdiamonds. This high pressure mineral was able to form because carbon was abundant in the lithologies of the Ries Crater. Other melt products are moldavites (in the group of tektites), bottle green glassy teardrops which have been found as far away as Bohemia and Upper Austria.
A hearty lunch was taken by some at the Red Ox, others went to explore the town and spot suevite in the buildings or walk round the town walls.
Gisela rejoined us for the afternoon, when we went to look at the effects of the impact at a couple of sites in the Geopark. We first went to Holheim, a quarry which was closed in the 1990’s and which now has a geo-trail displaying the Upper Jurassic sediments, bedded and bioherms (reef limestones). The quarry is well described via information boards and the impact effect on the Limestones is clear to see. The bedded imestones show little effect of breakage or shock, but in places the beds are seen to have slipped on the bedding planes to take up the impact. However, the reefal limestones are shattered and form a monomict breccia (Bunte Breccia).
When quarries are disused, the undergrowth tends to take over. To keep this under control there is a herd of black-necked goats. These are rotated to the different quarries within the Geopark. Such disused quarries are good places to encourage wildlife. In this case we did not see but were reliably informed that Bombina variegata (the yellow-bellied toad) is found because the vegetation upon which it feeds depends upon the alkaline soil derived from the limestones.
Another point of interest was a large box on a tree, alas we did not see the inhabitant, and such boxes are for the Bubo Bubo (the European Eagle Owl). On walking through the circular trail with viewing platforms so that you can appreciate the impact structures in the rocks from a distance, we did hear Woodpeckers drumming.
Eugene Shoemaker visited this quarry three times; the private quarry next door which we observed from a viewing platform was used as a training ground for the NASA Apollo programme. The Astronaut training quarry is the type locality for impact metamorphism as defined by Stöffler (1971).
Our final quarry was Altenbürg where we were able to get our hands on some suevite. This is the quarry where the building material for Nördlingen St George’s church was excavated. This quarry was where they finally disproved the idea that the Ries was not volcanic in origin, because drilling through the suevite went into underlying bedded and basement rocks. In the quarry you can see bedded and reefal limestones with suevite inbetween.
We have to remember that such interesting and colourful polymict breccias are a clear indicator of the intensely high pressure and temperature which can only be induced by impact events, such as when a bolide impacts at 20 km/s and produces a crater of this magnitude in less than 10 minutes.
Text: Diana Smith, Sue Vernon
Pictures: Neil Lawley
The place where all the known Archaeopteryx(s) where discovered
January 30th, 2016
After an hour driving on the mini-bus we arrived at the Buergermeister-Mueller-Museum in Solnhofen. We were welcomed by the head of the museum, Dr. Martin Roeper.
Unfortunately he had to go to Wuerzburg, where a meeting was held about a new law that intend to protect 'Objects of Cultural Value' from leaving the country. But so far that announcement had the opposite effect on private objects exhibited in museums; three excellent fossilised specimens from the Solnhofen museum have thus recently been retrieved by their owners, just in case they might be declared public property. We all wished Martin Roeper good luck.
A colleague, Anna Krippner (to the left in the picture), took over from Dr Roeper and gave us a guided tour in English, inviting us to a journey through archipelagos and basins bordering the Tethys Ocean during the Jurassic between 151 Ma and 149.4 Ma.
She explained that the museum was recently renovated and the new concept uses a colour code to guide the visitor through the exhibition. Each environment is represented by a colour and the walls of each room are painted according to that environment and hosts fossils from species that were living together: green for land, light blue for lagoon, turquoise for reef barrier, dark blue for the Tethys and yellow for air.
But of course the star of the museum is one of the 11 archteoreptyx hosted in the yellow room. According to our guide, it is the world best specimen, because : (i) 97% bones complete, (ii) it has extensive feather preservation on wings, tail,body and legs, (iii) it is a one year old baby dino (the head is larger yhan the body and will grow up to 6 to 7m when adult) and (iv) this specimen is at the bottom of the dino evolution tree.
This specimen made the cover of Nature (511, July 2014). The article explained that this "Urvogel" had different type of feathers, as shown with a dynamic 3D model in the museum.
This specimen is unique, as are the other ones, making Dr Tischlinger say that no one knows the number of taxon's of archaeopterys, each find has been different.
Fossils in all colours of the rainbow
UV light reveals hidden details
The visit of the museum was followed by an excellent presentation by Dr Helmut Tischlinger, about the use of UV light to photograph fossils, a technique that he has developed to reveal hidden details in fossils.
In a dark room he illuminates the specimen with ultra violet light, the reemitted fluorescent light is then filtered in front of digital or analogue cameras, the latter ones recording finer details than the digital ones. The skills of Dr Tischlinger are in the art of using filters he has himself developed. Years of practise are needed to reveal the hidden details. And nowadays this technique is used before (and during) the preparation of fossils, so that no details of the specimen in question are destroyed during the process.
It is quite fascinating to see how the recently prepared fossils show so many more details than the older ones, due to this new procedure; it is really possible to tell the difference by just looking at them.
What this technique reveals are, for example, fine muscles, wing membrane as a multi-layered mantle and not just a skin, feathers with colour pattern, fullsized head crest, fur (pycnofibers) around neck and body of pterosaurs (hairy monster!) .
What Dr. Tischlinger has never been able to see are the arm crowns of ammonites, although the museum has a good collection of ammonites. Thus the question remains open: did ammonites have little soft arms wiggling out of the shell and an eerie look in their eyes or not?
Helmut Tischlinger has kindly supplied some of the pictures he showed during the talk, so that we can publish them here in our newsletter.
"Solnhofen / Ein Fenster in die Jurazeit"; Arratia, G., Schultze, H-P., Tischlinger, H., Viohl, G.; ISBN 978-3-89937-075-1; Publishing house: Dr. Friedrich Pfeil, Munich, Germany