Evidence for late Neoproterozoic glaciation in the central Scandinavian Caledonides
Published:January 01, 2011
Risto A. Kumpulainen, Reinhard O. Greiling, 2011. "Evidence for late Neoproterozoic glaciation in the central Scandinavian Caledonides", The Geological Record of Neoproterozoic Glaciations, Emmanuelle Arnaud, Galen P. Halverson, Graham Shields-Zhou
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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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The Geological Record of Neoproterozoic Glaciations
In recent years, interest in Neoproterozoic glaciations has grown as their pivotal role in Earth system evolution has become increasingly clear. One of the main goals of the IGCP Project No. 512 was to produce a synthesis of newly available information on Neoproterozoic successions worldwide similar in format to Hambrey & Harland’s (1981) Earth’s pre-Pleistocene Glacial Record. This Memoir therefore consists of a series of overview chapters followed by site-specific chapters. The overview chapters cover key topics including the history of research on Neoproterozoic glaciations, identification of glacial deposits, chemostratigraphic techniques and datasets, palaeomagnetism, biostratigraphy, geochronology and climate modelling. The site specific chapters for 60 successions worldwide include reviews of the history of research on these rocks and up-to-date syntheses of the structural framework, tectonic setting, palaeomagnetic and geochronological constraints, physical, biological, and chemical stratigraphy, and descriptions of the glaciogenic and associated strata, including economic deposits.