Progressive glaciotectonic deformation in Weichselian and Palaeogene deposits at Feggeklit, northern Denmark

Structural analysis of the glaciotectonic deformations at Feggeklit, Mors, Denmark, provide a unique record of succesive deformation phases in a progressive glaciotectonic deformation. The Feggeklit profile displays glaciotectonically folded, thrust-faulted and shearedPalaeogene diatomite with thin volcanic ash layers, the Fur Formation, overlain by a glacigenesuccession. The combination of stratigraphical and structural analysis shows that the Feggeklitwas affected by three glaciodynamic events. The first event is of Saalian age and is represented by the deposition of a till and the formation of a para-authochthonous glacitectonitein the top of the Fur Formation deposits.The second event is only represented by the deposition of a till, probably of Saalian age.The third event is of Late Weichselian age. It includes: 1) deposition of proglacial glaciolacustrine and -fluvial sediments, 2) the formation of a glaciotectonic unit (the Feggeklitdeformation complex) and 3) deposition of a till resting on a tectonic uncon-formity formedsubglacially.A detailed structural analysis of the glaciotectonic unit provides a subdivision into fivesuccesive deformation phases. The first four phases are related to the proglacial deformation and comprise 1) anastamosing jointing, 2) conjugate faulting, 3) buckle folding andlistric thrust faulting, and 4) large scale ramp thrusting. The final phase (5) is related tosubglacial shear deformation and loading which produced an allochthonous diatomiteglacitectonite at the sole of the overlying lodgement till.The formation of the structural complex at Feggeklit was caused by two glaciotectonicmechanisms: 1) a proglacial gravity spreading deformation, and 2) a subglacial cataclasticshearing. The balanced cross-section of the fold structures related to the first deformationmechanism indicates that the detachment of the dislocation is situated below the base of thediatomite formation in the plastic clay at a depth of 80-100 m below the surface. Based onthe glaciodynamic analysis and considerations on the dating of regional glacigenic settingthe velocity of the advancing ice is estimated at 10 m per year. This advance created thegravity spreading deformation reflected in the glaciotectonic structures preserved in theFeggeklit.