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Glacitectonite was defined by Banham (1977) for glacially deformed pre-existing sedimentary rocks. Pedersen (1988) suggested a further classification of glacitectonites, and basically the term describes a sedimentary rock in which the primary structures are so disturbed that they can not be continuously traced and the lithology is superimposed by a glacitectonic fabric developed as joint fractures or shear surfaces.
In areas affected by glacitectonic complexes, which include thrust sheets of pre-glacial sedimentary rocks, these are subjected to shearing and dragged along the sole of the ice during its advances over the glacitectonic complex. Due to truncation and shear-drag the glacitectonite forms at the base of the deformational layer in a lodgement till. The detailed stratigraphy of a succession includes a glacitectonic unconformity at the base of the glacitectonite, the brecciated sediments identified as a glacitectonite, and an overlying lodgement till. From the source area, which typically is a detachment anticline, the glacitectonite thins out in the direction of transport from a meter to a thin shear zone only a few centimetres thick over a distance of one to a few kilometres (Pedersen 1996).
In a glacitectonic complex the idealised stratigraphy can be listed, from the base to top:
1) a tectonite at the base of the thrust sheets and duplexes related to brecciation and fracturing in the décollement zone, eventually including a hydrodynamic brecciation and mobilised mud diapirisme,
2) an allochtonuos unit of pre-Quaternary and/or pre-glacial sedimentary rocks,
3) a glacitectonic unconformity,
4) a glacitectonite, and finally 5) a lodgement till (Pedersen, 2005).
The principles of the glaciodynamic stratigraphy is exemplified by the Pleistocene drift deposits on Mors in Denmark, where the pre-Quaternary sedimentary rock units constitutes the Fur Formation, a Palaeogene succession of clayey diatomite with volcanic ash layers. Three main stratigraphic groups are here recognised: a Saalian unit, and two Weichselian units. Each unit has got a fabric impacted by the prevailing glacial advance related to each of the glacial event, and the glacitectonites facilitates the differentiation of the dynamic stratigraphy.
Banham, P.H. 1977: Glacitectonites in till stratigraphy. Boreas 6, 101-105. Pedersen, S.A.S. 1988: Glacitectonite: Brecciated sediments and cataclastic sedimentary rocks formed subglacially. In Goldthwait, R.P. & Matsch, C.L.(eds): Genetic classification of glacigenic deposits. A.A. Balkema, Rotterdam, 89-91. Pedersen, S.A.S. 1996: Progressive glaciotectonic deformation in Weichselian and Palaeogene deposits at Feggeklit, northern Denmark. Bulletin of the Geological Society of Denmark 42, 153?174.
Pedersen, S.A.S. 2005: Structural analysis of the Rubjerg Knude Glaciotectonic Complex, Vendsyssel, northern Denmark. Geological Survey of Denmark and Greenland Bulletin 8, 192 pp., +2 plates.
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