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 sheared
Palaeogene diatomite with thin volcanic ash layers, the Fur Formation, overlain by a glacigene
succession. The combination of stratigraphical and structural analysis shows that the Feggeklit
was 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 glacitectonite
in 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 Feggeklit
deformation complex) and 3) deposition of a till resting on a tectonic uncon-formity formed
subglacially.
A detailed structural analysis of the glaciotectonic unit provides a subdivision into five
succesive deformation phases. The first four phases are related to the proglacial deformation and comprise 1) anastamosing jointing, 2) conjugate faulting, 3) buckle folding and
listric thrust faulting, and 4) large scale ramp thrusting. The final phase (5) is related to
subglacial 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 glaciotectonic
mechanisms: 1) a proglacial gravity spreading deformation, and 2) a subglacial cataclastic
shearing. The balanced cross-section of the fold structures related to the first deformation
mechanism indicates that the detachment of the dislocation is situated below the base of the
diatomite formation in the plastic clay at a depth of 80-100 m below the surface. Based on
the glaciodynamic analysis and considerations on the dating of regional glacigenic setting
the velocity of the advancing ice is estimated at 10 m per year. This advance created the
gravity spreading deformation reflected in the glaciotectonic structures preserved in the
Feggeklit.
Progressive glaciotectonic deformation in Weichselian and
Palaeogene deposits at Feggeklit, northern Denmark
