Seventh tone
The septarian (in some areas synonym for Rupelton ) is a particularly in the North German Plain common clayey sediment in which the eponymous marl - concretions ( Septaria ) are incorporated.
Genesis and Training
The Septarian Clay was deposited during the last Paleogenic marine transgression in the Lower Oligocene . After a sedimentation interruption at the Eocene / Oligocene boundary, the sedimentation of the Septarian Clay begins with a more or less thick base sand, which in southwest Mecklenburg is represented by a green clayey silt containing glaconite . These "green sands" can also be observed in the Hamburg area ("Neuengammer Sande") and Magdeburg ("Magdeburger Grünsands").
The greenish-gray to dark-gray, marine lime-poor clays and clay marls develop over the sandy-silty base layers , which often alternate with strongly calcareous layers. A characteristic feature of the sequence of layers are deposits of oval to head-sized septaries whose shrinkage cracks have healed with aragonite . A rich fauna of foraminifera , sponges , echinoderms , corals , mollusks as well as remains of fish and reptiles has been described in the clays .
The proportion of silt and sand in the sequence of layers increases again towards the hanging wall. In certain areas, concretions ("Stettiner spheres") are embedded in the hanging parts.
The thickness of the seventh tone varies greatly from region to region. Developed on average 90 m thick, in the interior of the basin, in southwest Mecklenburg, a development of up to 200 m can be observed, while the thickness of the sequence of layers in the Wismar area decreases to up to 20 m. Based on the position of the isobaths at the base of the Septarian tone, conclusions can be drawn about the extent of halokinetic movements in the subsurface.
literature
- Otto von Linstow : About the spread and transgression of the Septarientones (Rupeltons) in the area of the middle Elbe . In: Yearbook of the Royal Prussian State Geological Institute. 25, Berlin 1904, pp. 295-322.
- Wilhelm Deecke : Geology of Pomerania . Borntraeger Brothers, Berlin 1907, pp. 145ff.
- Gerhard Katzung : Geology of Mecklenburg-Western Pomerania . E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 2004, ISBN 3-510-65210-X , pp. 205-2.
- Anke Brückner, Dorte Janussen, Steffen Schneider: A new porifer fauna from the Septarienton (Oligocene, Rupelian) of Bad Freienwalde (NE-Germany) and the first fossil-preserved representative of the non-rigid Hexactinellid genus Asconema . In: Paleontological Journal. Vol. 77, No. 2, 2003, pp. 263-280.