Superimposed deformation in glaciotectonics

Abstract

The identification of glaciotectonic structures is an exclusive field for the structural geologist. The structures comprise a series of different types and regimes. The sequential development of the glaciotectonic structures reflects superimposed subglacial and proglacial deformation processes. The glaciotectonic structures may involve earlier formed structures thus superimposed by the glaciotectonics, or the glaciotectonic structures may eventually be overprinted by neotectonic deformations. Four different superimposed settings may be distinguished: 1) glaciotectonic deformation superimposed on pre-Quaternary tectonics, 2) glaciotectonic deformation superimposed on earlier formed glaciotectonic structures (superimposed deformation involving two or more glaciodynamic events), 3) glaciotectonic deformations superimposed sequentially in the same glaciotectonic unit (two or more glaciotectonic phases in the same glaciodynamic event), and finally 4) neotectonic deformation superimposed on glaciotectonic structures. Examples of type 1 are taken from the deformed Palaeogene diatomites with ash layers at Hanklit, Mors, and Hestegården, Fur. Dokumentation of glaciotectonic deformation superimposed on halokinetic structures is demonstrated from Erslev, Mors, and further examplified by structures occurring at Junget on the north side of the Batum salt diapir in Salling. Type 2 is examplified by glaciotectonic structures in the Skarrehage mo-clay pit on Mors. An example of Elsterian glaciotectonics superimposed by Saalian glaciotectonics is recorded from the hilly island Møborg, central part of western Jylland. The classic glaciotectonic site Møns Klint is described as a combination of an imbricate fan and an antiformal stack formed by the Young Baltic ice advance in the Late Weichselian superimposed by a regressional re-advance from the east. Type 3 is exemplified by the glaciotectonic complex at Feggeklit. Type 4 is described from the island of Fur where glaciotectonic structures are cut by neotectonic faults roughly parallel to the main E-W trend of Limfjorden.