Glacigenic rocks of the Smalfjord and Mortensnes Formations, Vestertana Group, E. Finnmark, Norway.
The Vestertana Group in E Finnmark, N Norway, contains two Neoproterozoic glacigenic 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 is underlain by dolostones (Grasdalen Formation, Tanafjorden Group), only locally preserved due to the sub-Smalfjord Formation unconformity, which cuts down-section through a ca. 2.5 km dominantly clastic sequence to rest on Baltic Shield gneisses. The two glacigenic successions are separated by ca. 350 m of mostly clastic sediments (Nyborg Formation), with thin dolostones at the base and towards the top. The latter are generally absent due to the sub-Mortensnes Formation 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 (SmalfjordMarinoan; MortensnesGaskiers). 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, whilst other interpretations place it at either 30° N or S at ca. 550 Ma.