Original paper

Erscheinungsform und Genese des Kluftgefüges glazidynamisch überprägter Tone

[Patterns and Origin of Joints in Glacidynamically Affected Pleistocene Clays]

Feeser, Volker

Kurzfassung

Glazidynamisch beanspruchte Tone weisen ein Kluftgefüge auf, das als unsystematisch beschrieben und meist auf die Schub- und Druckwirkung der Eismassen zurückgeführt wird. Am Beispiel einer Fazieseinheit des Lauenburger Tons wird dargestellt, daß im Gegensatz zu dieser bisher vertretenen Auffassung - das Kluftinventar aus zwei chronologisch entwickelten Teilgefügen besteht, die glazialen bzw. postglazialen Bildungscharakter tragen; zwischen primärem Kluftgefüge und glazitektonischem Deformationsplan statistisch nachweisbare Beziehungen bestehen, und - als Motor der Kluftgenese im wesentlichen Spannungsumlagerungen in der Folge von Entlastungsvorgängen anzusehen sind.

Abstract

In glacidynamically stressed clays there are joint patterns which are usually described as irregular and explained as due to compressional and shear forces induced by moving ice masses. The paper deals with a combined field and laboratory investigation on joints in the Lauenburg Clay of northern Germany. Orientation data from 800 readings are plotted and analysed in stereographic projection. The size, geometry and roughness of joint surfaces are observed in situ and compared with clay microfabric in scanning electron micrographs and thin section analyses. Joint orientation, distribution of surface features and microfabric are correlated to possible modes of origin. In contrast to conventional interpretations the study shows - that there arc two different joint patterns. Within the major joint pattern a geometric relation exists, both orientation and surface features of joints are related to the glacitectonic framework; - that origin of most joints is a result of stress variation due to destressing during glacier regression, i.e. most of jointing is extensional. Slickensides observed on joint surfaces are secondary features. This is compatible with recent results on folded competent sedimentary rocks, thus glacitectonic joint patterns correlate to tectonic joint patterns. In the field of structural and engineering geology new informations are to be expected from further comparsions between glacidynamically affected soft rocks and tectonically folded hard rocks.

Keywords

Clay (Lauenburger Ton)fabricsjointglaciotectonicsgeometrygraphic presentationElster glaciation North-West German Lowlands (Edewecht)Lower Saxony TK 25: Nr. 2813