Looking for Ammonites in the German Braunjura
by Nando Musmarra and Diana Fattori
The German region north of the Bavarian Alps is characterized by beautiful landscapes: so many tourists are attracted by the natural features of the local Altmühltal Natural Park, but fossil lovers are more interested in ammonites than in the romantic Danube river. While today the region between the city of Nürnberg and the Altmühltal Natural Park is a charming place where a nature-lover can find himself in the peace of the green forests, during the Jurassic southern Germany, together with most of southern-central Europe, was covered by a shallow warm sea. In the beginning, the Jurassic was characterized by the global rising of the water and, as would be expected, these warm waters were teeming with both vertebrate and invertebrate life including ammonites, belemnites, and other molluscs, that reaching notable dimensions, did become an abundant source of food for ichthyosaurs, sharks, and the other marine predators that lived at that time.
Schwarzjura fossils from Mein-Donau Kanal - Eichstätt Jura Museum
These sea-bottom dwellers' ideal life conditions ended with the regression of the waters that led to a crisis with partial extinction of the organisms that lived at the bottom of the sea. The deposition of the oil shale, with its characteristic dark colour, composed for the most part of grey and black bituminous shale, is the evidence of that partial extinction. This extinction happened at the end of the Lower Jurassic (Lias), a geologic period that the German scientists call Schwarzjura (Schwarz is the German word for black). The most representative Schwarzjura member is the Posidonia shale (Toarcian). This formation is exposed at the surface near the city of Stuttgart. In the cities of Dotternhausen, Holzmaden, and Stuttgart there are the most notable museums that exhibit the black Posidonia shale with its incredible variety of ammonites, belemnites, fishes, ichthyosaurs, Hybodus sharks, crocodiles, and other marine reptiles' remains.
An exquisite specimen of Schwarzjura Hybodus shark showing its last meal: a lot of Belemnite sp. - Staatlichen Museum für Naturkunde Stuttgart
About 200 kilometers north-east of Stuttgart, there is another location where in the past years both scientists and fossil hunters found a bonanza of Posidonia shale. This happened in the ‘90s, during the excavation of the Mein-Donau-Kanal, a big artificial channel whose water flows in the Altmühltal river and later in the Danube river. Dr. Martin Görlich was one of the men who helped to recover the Posidonia shale fossils from the channel excavation. He is a dentist by profession and amateur paleontologist by avocation. Thanks to Martin and other professional and amateur paleontologists, an enormous collection of black Toarcian fossils is now preserved in the Eichstätt Jura Museum, the place that the exceptional Archeopteryx n.5 calls home.
The German Jurassic is characterized by three main colours: black, brown, and white that respectively indicate the Lower, the Middle, and the Upper Jurassic stages.
At the end of the excavation of the Mein-Donau channel, Dr. Martin Görlich planned to reopen to collectors the old Sengenthal Mine, where the whole Middle Jurassic succession is exposed. In Germany the Middle Jurassic (Dogger) is named Braunjura (Braun = brown) because of the presence of iron minerals. When those minerals oxidize, they assume the characteristic brown colour.
The complete stratigraphic succession of the Braunjura of Sengenthal Mine has crossed the national boundary, attracting fossil collectors from all over the world in search of fossils, especially beautiful ammonites. The Sengenthal mine also exposes the most part of Late Jurassic succession, the German Weißjura (Weiß = white, because of white calcareous limestone).
Sengenthal was a very popular collectors' spot from the beginning of the ‘60s until 1986, when the mine was closed. Rumours say that in the old times the collectors who lived near the mine used to assign a special duty to their wives: "Honey, if you hear an explosion, look toward the mine. If you see white dust, do not mind, but if the dust is reddish-brown, please, call me as soon as possible, so I will be the first to look for ammonites in the freshly-exposed Braunjura!!!"
This photo shows three different stages of the German Jurassic: Bajocian, Callovian, and Oxfordian. Are you able to identify them?
Martin was able to rent a big part of the mine (the remaining part is set aside as a nature preserve and the big wall with the whole Braunjura succession is left to professional paleontologists) to give to the collectors the chance to collect Middle Jurassic fossils. Martin organizes the dig with a total respect for nature. For this purpose, the mine observes a voluntary spring closure to assist the reproduction of amphibians and birds of prey.
Last September, Diana and I had the chance to look for ammonites in the Sengenthal mine. We met Martin Görlich at the big cement plant near the Mein-Donau channel, between the cities of Ingolstadt and Neumarkt. Under our feet there were the dark sediments of the last stage of the Schwarzjura. Martin drove us up the hill, through the Lower Aalenian sediments. We reached the little town of Winnberg, then we turned left through a dark green forest until we arrived at the gate of the mine. The landscape was incredible; we saw the endless brown-reddish hole, and at the end, the vertical white Weißjura high wall. In the mine there were Hannes and Wolfgang, two experienced fossil collectors, who joined us for the day.
In Germany the various Braunjura's stages (from Aalenian to Callovian) are identified with the first six letters of the Greek alphabet ( α β γ δ ε ζ ).
The elusive gastropod Pleurotomaria sp. is not found very often. Specimen courtesy of Martin Görlich collection
The following description of the Braunjura units begins with the Braunjura α (Lower Aalenian). Sadly, this first unit, that elsewhere contains very beautiful Leioceras opalinum opalescent ammonites, is not exposed in the Sengenthal mine.
To reach the fossil spot we walked down the old truck ramp, and after half mile, we reached the lower part of the mine, and from there, we started the trip trough the Middle Jurassic:
Braunjura β1 and β2 (Upper Aalenian). The Braunjura ß is well exposed on the bottom of the mine. These levels are 6 meters high, and they are composed for the most part of unfossiliferous coarse iron sandstone. This is the oldest stage exposed at the Sengenthal mine.
Braunjura γ1 (Lower Bajocian): The basal formation of the Bajocian is composed of limestone and sandstone layers with burrows and trails of organisms that lived on the bottom of the sea.
Braunjura γ2 (Lower Bajocian): This formation is composed of 2.10 meters of gravel and sandy grey marl with occasional ooids.
Braunjura γ3 (Lower Bajocian): This 50 cm. layer, a mix of reddish marl and sandstone, constitutes the last part of Lower Bajocian. Here it is possible to find Otoites sauzei, the older ammonite of the mine.
Braunjura δ1 and δ2 (Middle Bajocian): Approximately 40 cm. of light grey limestone and marl with ooids; these strata are not very fossiliferous.
If you look carefully you can spot a freshly exposed Parkinsonia parkinsoni ammonite
Braunjura δ3 (Upper Bajocian): Composed of two strata, this is the most popular area for fossil collecting, because these two formations (both 80 cm. thick) contain the highly-sought ammonites Garantiana garantiana and Parkinsonia parkinsoni. The two formations are a mix of brown/reddish oolitic ironstone, composed of countless minute rock spheres named "ooids" which consist of limestone and, in some cases like in the Braunjura, they are partially composed of iron minerals.
Some prepared fossils from the Sengenthal mine. Specimens courtesy of Martin Görlich
These schists are extraordinarily rich in big fossilized molluscs and point to hospitable living conditions at the time when the Braunjura δ was deposited. In a very short time we found some lenticular ammonites Oxycerites aspidoides and Oxycerites subinflexus, two Garentiana suevica, one Parkinsonia parkinsoni, and one Cadomites (Polyplectites) linguiferus. We also found the gastropods Obornella granulata and Bathrotomaria scrobinula; the bivalves Grammatodon subdecussatus, Pseudolimea duplicata, Coelastarte subtrigona, Trigonopis similis and one beautiful Trigonias interlaevigata. Sadly, we didn't find any gastropods Pleurotomaria teramachi and Pleurotomaria armata.
Differences between Parkinsonia parkinsoni ( left) and Garantiana (Hlawiceras) suevica (right)
Braunjura ε (Lower Bathonian): The contact zone between the Upper Bajocian and the Lower Bathonian is a very productive fossil level. In the hard limonitic matrix I found one absolutely perfect large Parkinsonia parkinsoni ammonite.
Braunjura ζ (Callovian): About 5 million years are condensed in 480 cm. of grey-green-bluish clay. On the slippery slopes there are, together with a lot of small mimetic living frogs, many beautiful belemnites (Hibolithes semihastatus rotundus) and small shark teeth. This is the last stage of Dogger (Middle Jurassic).
Going up the hill we reached the Weißjura α (Oxfordian): This is first unit of Malm (Upper Jurassic). It is a mixture of glauconitic marl and white calcareous sediments. In that formation we searched very carefully in order to find the smallest existing belemnites, the Suebibelus pressulus.
For more than one hour we searched with our noses to the ground for the smaller fossils, but we were able to find just small shark teeth, tiny pieces of the small sea star (Sphaeraster punctatus) and crinoid stems (Eugeniacrinites cariophyllites). Finally Diana was rewarded: a small squeezed belemnite, the Suebibelus pressulus appeared to her. This elusive belemnite is dark brown and very small (about 5 millimeters; it is very hard to spot with bare eyes). After a couple of hours, we found ten small Suebibelus sp.
Six Suebibelus pressulus. How big are they? Considering they are on a real size one cent, you do the math!!!
Back at the bottom of the mine, another fossil collector came to join us. His name is Helmut; he is a famous "Megateuthis specialist." Diana and I speak just a little German, and Helmut speaks only a very few English words, but the different languages never stopped us from communicating. Helmut told me that in the Sengenthal mine there are huge belemnites, Megateuthis gigantea, that could reach one full yard in length. Helmut also explained to us that the Megateuthis is called gigantea because of its huge size. He told us that usually the Megateuthis gigantea fossilizes in a horizontal position, parallel to the horizon of sedimentation.
Helmut Lehmann smiling with two big Megatheutis sp. specimens. Photo courtesy of Andreas E. Richter
For this reason it is practically impossible to extract the whole fossil without breaking it in several parts. Then, Helmut showed me where to dig, helping me with an enormous hammer in order to break one three-meter-long calcareous slab. Helmut suggested that I smash the slab in several smaller pieces because the Megateuthis gigantea are usually found in that way. So I began to break the brown calcareous slab, and just after a few minutes, I found a big section of a huge Megateuthis.
The long belemnite actually was parallel to the horizon of sedimentation, as Helmut taught me, and it was very easy to extract the remaining part of the long fossil. My Megatheutis is more than 50 centimeters long, and now it is the central piece of my belemnite collection. In the Segenthal mine, in the same day and in a single place, we were able to see belemnites from just a few millimeters to more than 70 centimeters!
Bratwurstgriller on duty. Photo by Martin Görlich
All of us were really happy with our finds, so we went back to the mine's shelter where Helmut was barbequing Würste (tasty German gigantic hot dogs) and other delicious dishes. Helmut isn't just a Megateuthis expert-he is also a famous Bratwurstgriller (in German means bbq's expert). The food and the beer were delicious and the company was very nice.
Martin speaks and writes in excellent English. The price includes the full insurance and the use of tools (including the heavy hammer and all the equipment you need to break the big rocks). The quarry is closed during spring. You can check for information at: http://www.ammos.org
Helmut also does classes to learn the techniques of cleaning and restoring Braunjura fossils: www.frankenfossil.de
Also in the local coffee shop everything remember the Braunjura....
Jäger Manfred, Das Fossilienmuseum im Werkforum, Ein Führer durch die ausstellung von Jura-Fossilien, 2001
Richter Andreas E., Geofürer Frankenjura, Geologische Sehenswürdigkeiten und Fossilfundstellen, Ammon Rey Verlag, 2000
Schmidt-Kaler, Tischlinger & Werner, Wanderungen in die Erdgeschichte. Sulzkirchen und Sengenthal zwei berühmte Fossilfundstellen am Spankers der Frankenalb, Pfeil Verlag, 1992
Ziegler Bernhard, Der Weiße Jura der Schwäbischen Alb, Stuttgarter Beiträge zur Naturkunde - serie C - n.23.
Nando Musmarra - Diana Fattori © 1999-2009