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Abstract

The Långmarkberg Formation (Fm). rests on either the Neoproterozoic rift-related Risbäck Group or Palaeoproterozoic basement in central Scandinavia. It is always succeeded in stratigraphy by the marine Gärdsjön Fm. The Långmarkberg Fm. is a thin, generally less than 50-m-thick, discontinuous, but persistent unit, primarily in the Lower Allochthon; subordinately also in the Autochthon, and Middle Allochthon of the central Scandinavian Caledonides. The formation is composed of a lower diamictite and an upper laminated, lonestone-bearing mudstone.

Criteria supporting the glaciogenic origin of the formation are (i) a large regional extension of the formation (>5000 km2) and (ii) its fixed position in the regional stratigraphy, (iii) the ‘tillite-like’ appearance of the lower part of the formation, (iv) the lonestone-bearing mudstone in the upper part, (v) the presence of striated clasts and (vi) striated pavement. It is interpreted as having formed during one single glacial–deglacial cycle.

Information on chemostratigraphy and realistic geochronology from this region is missing. The Långmarkberg Fm. has commonly been correlated with the Moelv Fm. in southern Norway and the Mortensnes Fm. in northernmost Norway. The Lower Allochthon in this region also contains an older, potentially glacially influenced diamictite unit at the base of the Risbäck Group, which is also briefly discussed.

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