Chapter 57 Glaciogenic rocks of the Neoproterozoic Smalfjord and Mortensnes formations, Vestertana Group, E. Finnmark, Norway

Abstract

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. d 13 C 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 (158S) to mid-latitudes (508S) for the period 750-550 Ma, respectively, while other interpretations place it at either 308N or S at c. 550 Ma.

The origin of upper Precambrian diamictites, northern Norway: a case study applicable to diamictites in general

“…In Finnmark Fylke at Varangerfjord, Tanafjord and Laksefjord (northern Norway), there are numerous outcrops of upper Precambrian diamictites (Rice et al, 2011). Most of these form part of the Smalfjord Formation, which occurs over an area of approximately 20,000 km².…”

“…The palaeogeographical setting of the area is believed to have been either high polar or low to equatorial palaeolatitude, but in view of the fact that the palaeomagnetic data for the upper Proterozoic display a large scatter, it is difficult to draw any final conclusions (Schermerhorn, 1983;Chumakov, 1988;Elston et al, 1988;Perrin et al, 1988;Young, 1991;Jensen & Wulff-Pedersen, 1996, 1997Evans & Raub, 2011;Rice at al., 2011Rice at al., , 2012.…”

“…Dolostone beds are present both below and between diamictites in the area (Siedlecka & Roberts, 1992;Rice et al, 2011Rice et al, , 2012, and these commonly indicate a warm climate (Schermerhorn, 1974;Johnson et al, 1978;Zenger et al, 1980;Schermerhorn, 1983;McKenzie, 1991;Young, 1991). These dolostone beds have either not been discussed in a palaeoclimatological context, are believed to have formed in a cold environment, or are thought to result from climatological and chemical catastrophic turnovers on a worldwide scale (Shields, 2005).…”

Neoproterozoic Glacial and Associated Facies in the Tanafjord-Varangerfjord Area, Finnmark, North Norway

“…4). Halverson et al (2005) and Rice et al (2011) informally divided the uppermost unit, the Grasdal Formation into two formations, the Grasdal and overlying Fadnuvaggi formations. The contact of the Tanafjord Group with the underlying Ekkerøya Group is a very low-angled unconformity with little erosional relief (Johnson, 1978;Rice, 1994).…”

“…The line RØE refers to the correlation of the Veinesbotn Formation with the Gamasfjell Formation proposed by Røe (2003). Figure is modifi ed after Rice et al (2011) and Stodt et al (2011). Tremadocian Berlogaissa Formation, the youngest stratigraphic unit preserved within the Gaissa Basin.…”