Fossils from Geisingen
- Kategorie: English articles
- Veröffentlicht am Sonntag, 09. Februar 2014 21:44
- Geschrieben von Roger Furze
- Zugriffe: 11512
Dieser Artikel ist schon 2009 in deutscher Sprache auf Steinkern.de erschienen. Er wurde erst kürzlich vom Autor ins Englische übersetzt. Jetzt zur deutschsprachigen Version wechseln.
I've been visiting the sporadically operated clay pit in Geisingen a.d. Donau since 2001. For those who don't know the way: Take the Geisingen exit from the A81. Drive through the town and take a left at the street after the last roundabout and then immediately right onto the road which runs parallel to the autobahn. After roughly 1 kilometer the clay pit can be seen on the left.
Stratigraphy and Fossils
The southern part of the pit is of main interest, since the fossiliferous layers of the Geisingen-Oolith of the upper Aalenian are regularly exposed there, or at least until recently. The border between the murchisonae and the concavum zones is to be found in this 40-70cm-thick block layer made up of iron oolith bearing limestone. Argillaceous shale full of concretions covers this layer and above that is the Conglomerate Bank which builds the transition to the Bajocian stage. Here one finds mostly bivalves and belemnites along with the occasional badly preserved ammonites. On top of that is the fossil-free Wedelsandstein, which builds the top of the exposure in the clay pit.
Over the years a lot of collectors, including myself, were able to collect a good amount of well-preserved fossils, sometimes with their shells still intact. I heard great tales from other collectors about the golden days and managed to learn more and more about the geological situation as time went on. Some highlights for me were a Brasilia decipiens with a circumference of 45 cm, a number of well-preserved Hammatoceratidae, some ichthyosaur vertebrae and a partial jaw from the crocodile Steneosaurus sp. The regular finds of Brasilia, Graphoceras, bivalves, belemnites and the occasional sea urchin rounded things off.
The present situation (2009)
The clay pit was still in full operation in 2001. At that time it belonged to the Breisgauer Portland Cement Co., which delivered the clay to its nearby cement plant to be mixed under the limestone which was won at the quarry on the other side of the autobahn. New portions of the Geisingen Oolith were regularly exposed and regular visits for collectors were always worthwhile. A few years later, however, the entire complex was taken over by Holcim, whose policy at the time was to shut down the competition, which is exactly what it did in Geisingen. It wasn't long before the cement plant lay in ruins, the work in the quarry was cut back radically and material was only moved occasionally in the clay pit. It was still possible to find fossils, but you had to do a lot of work beforehand.
Since then there's been a lot of talk about recultivating and creating a biotope, but those were just rumors. I decided to get to the bottom of things and have found out the following information. The clay pit and quarry are now run by the Geisinger Kalkstein Schotterwerk GmbH & Co. KG. The works manager has told me that yes, partial recultivation shall be taking place in the future, but that clay shall still be sporadically removed from the pit, which means that as long as collecting is still tolerated, it may still be worthwhile to try your luck here.
I'll close off now by showing some of my finds.
Graphoceras sp. (Buckman 1898), 6 cm. Cut and polished.
More than 4 years have passed since I wrote this article and since then pretty well nothing has changed at the pit. No more clay has been removed, and the plants are beginning to take over again. Now it really looks like an inoperative pit. As far as I know, collecting is still tolerated, but it's an incredible grind freeing up the Oolith in the hopes that something worth saving is to be found in the few blocks that you've managed to lever out after a whole day's work. The waste tip has been so worked through over the years that it's hardly worth a look any more.
Well anyway, I did manage to find some more nice stuff in the years in between which I'll show below along with a few older finds, but I don't think I'll be going back there that often any more.
Gründel, Ebert & Furze (2011): Die Gastropoden aus dem oberen Aalenium von Geisingen (Süddeutschland), in: Zitteliana 51, S. 99-114.