Zur Petrographie des Schilfsandsteins

Abstract

A series of samples of a sandstone from the Middle Keuper Formation of Northern and Southern Germany have been investigated on their grain size distribution and mineral contents by microscopic and X-ray methods. Most of the minerals were subject to considerable changes during the diagnetic history of the sediment: Secondary growth of orthoclase around different feldspars including plagioclase, authigenic formation of glauconite and chlorite from biotite as well as formation of anatase and brookite from ilmenite. Various minerals cementing the porespace were observed: Magnesite, calcite and dolomite, quartz, rocksalt and ironoxides. The precipitation of anhydrite and gypsum in a particular region of the Rhine Rift Valley depends on the tectonic contact of the investigated sandstone with anhydrite bearing layers. The chemical reactions, which lead to the formation of the diagenetic minerals, and their temporal sequence are discussed.

Zusammenfassung

An Hand mineralogischer Messungen and struktureller Beobachtungen an Dünnschliffen kann zwischen dem primären and dem diagenetisch entstandenen Mineralbestand unterschieden werden. Von besonderem Nutzen ist dabei der Vergleich zwischen der sandigen Flutfazies and der tonigen Normalfazies. In der Normalfazies hat sich der angelieferte Mineralbestand wegen der geringeren Durchlässigkeit erhalten. Der Mineralbestand der Flutfazies war starker den diagenetischen Umwandlungen ausgesetzt.