Arnstadt formation
The Arnstadt-Formation (also stone marlkeuper) is a lithostratigraphic formation of the Keuper in the Germanic Triassic . The lithostratigraphic unit Arnstadt Formation is underlain by the Weser Formation and overlaid by the Exter Formation of the Upper Keuper .
definition
The lower limit of the Arnstadt formation is the upper limit of the so-called Heldburg marl in northern Germany. The upper limit is the lower edge of the "Rhätsandsteine". The thickness is on average around 100 to 150 m, in trench zones more than 400 m are reached. In threshold regions the thickness varies from 40 m to 60 m. Towards the eastern edge of the basin, it interlocks with the Löwenstein Formation and the Trossingen Formation . The Arnstadt Formation is mainly made of colored clay stones, in which individual dolomitic marl stones and limestones as well as sulphate tubers are inserted. In these series, soil horizons with lime and pebble crusts are repeatedly embedded. The Arnstadt Formation is biostratigraphically dated to the Middle to Higher Norium . The upper part is presumably separated from the lower part by a gap in the layers and should already be dated to the Lower Rhaetian . This part of the formation is z. Partly already replaced by the external formation . In southern Germany it meshes with the Trossingen formation. In the STD2002, the Lower Arnstadt Formation is assigned a period of 2.5 million years (period 214 to 211.5 mya). A period of 7 million years between the Arnstadt and the lying Weser Formation is therefore not documented by sediments. Another layer gap from 211.5 to 207 million years ago has formed between the Lower and Upper Arnstadt Formations. The Upper Arnstadt Formation spans about 1 million years. The type locality of the Arnstadt formation is near Arnstadt in Thuringia . Type region is the three equals area near Arnstadt.
structure
The Arnstadt formation is divided into four sub-formations (from top to bottom):
- Kielsberg subformation
- Schwalenberg subformation
- Valdorf subformation
- Harrow subformation
Seven small cycles have been developed in the Arnstadt formation.
Storage room
The Arnstadt Formation was deposited in a wide basin that was repeatedly flooded. Sulphates and limescale were deposited in the remaining lakes. Numerous soil horizons with limestone and pebble crusts locally indicate longer phases in which the area was dry.
Fossils
The Arnstadt Formation only delivered fossils in a few sections; Mussels (Bivalvia), snails (Gastropoda), mussel crabs (Ostracoda) and mussel shells (Conchostraca).
literature
- Gerhard Beutler: Lithostratigraphy. In: German Stratigraphic Commission (Ed.): Stratigraphie von Deutschland IV - Keuper. Courier Forschungsinstitut Senckenberg, 253: 65-84, Stuttgart 2005 ISSN 0341-4116
- Gerhard Beutler, Norbert Hauschke and Edgar Nitsch: Facies development of the Keuper in the Germanic Basin. In: Norbert Hauschke & Volker Wilde (Hrsg.): Trias - A whole different world of Central Europe in the early Middle Ages. Pp. 129–174, Verlag Dr. Friedrich Pfeil, Munich 1999 ISBN 3-931516-55-5
- Edgar Nitsch: The Keuper in the Stratigraphic Table of Germany 2002: Formations and consequences. Newsletters on Stratigraphy, 41 (1-3): 159-171, Stuttgart 2005 ISSN 0078-0421
Web links
- German Stratigraphic Commission (Ed.): Stratigraphische Tisch von Deutschland 2002 . Potsdam 2002, ISBN 3-00-010197-7 - PDF; 6.57 MB (large) (abbreviated STD2002)