Glaciogenic rocks of the Neoproterozoic Smalfjord and Mortensnes formations, Vestertana Group, E. Finnmark, Norway
Published:January 01, 2011
A. Hugh N. Rice, Marc B. Edwards, Tor A. Hansen, Emmanuelle Arnaud, Galen P. Halverson, 2011. "Glaciogenic rocks of the Neoproterozoic Smalfjord and Mortensnes formations, Vestertana Group, E. Finnmark, Norway", The Geological Record of Neoproterozoic Glaciations, Emmanuelle Arnaud, Galen P. Halverson, Graham Shields-Zhou
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The Vestertana Group in East Finnmark, North Norway, contains two Neoproterozoic glaciogenic sequences, the Smalfjord and Mortensnes formations, preserved on the northern edge of Baltica. The former comprises up to 420 m of aeolian, fluvioglacial and glaciomarine sediments and terrestrial diamictite. The latter consists of up to 50 m of predominantly diamictite. The Smalfjord Formation (Fm.) is underlain by dolostones (Grasdalen Fm., Tanafjorden Group), only locally preserved due to the sub-Smalfjord Fm. unconformity, which cuts down-section through a c. 2.5 km dominantly clastic sequence to rest on Baltic Shield gneisses. The two glaciogenic successions are separated by c. 350 m of mostly clastic sediments (Nyborg Fm.), with thin dolostones at the base and towards the top. The latter are generally absent due to the sub-Mortensnes Fm. unconformity, which also cuts down southwards through the Nyborg and Smalfjord formations to the Baltic Shield. No robust isotopic age constraints are available for the succession. δ13C data, together with cap dolostone characteristics, offer paradigmic correlations with other areas (Smalfjord ≡ Marinoan; Mortensnes ≡ Gaskiers). A limited Ediacaran fauna, including Aspidella, give only broad age constraints. Palaeomagnetic data are ambiguous; some suggest Baltica lay at equatorial (15°S) to mid-latitudes (50°S) for the period 750–550 Ma, respectively, while other interpretations place it at either 30°N or S at c. 550 Ma.
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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.