Glacial or non-glacial origin for the Bigganjargga tillite, Finnmark, northern Norway

Abstract

Bigganjargga is the classic locality for the Varangian ice age in northern Scandinavia. The presence of two sets of striations on the underlying quartzite basement has been taken as evidence for a glacial origin of the Bigganjargga diamictite. However, soft-sediment surface structures on the underlying sandstone indicate that it was not consolidated when the diamictite was emplaced. Together with structures in the diamictite this shows that the deposit formed as a debris flow moving northwestwards over an unconsolidated substrate. There is no evidence for glacial origin or contribution for the diamictite material.

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

“…They were not observed in the area by Jensen & Wulff-Pedersen (1996), Arnaud & Eyles (2002) or by myself. None are found on gneisses and sandstones, but quartzite pebbles are reported to display striations (Bjørlykke, 1967), and other striated clasts have been recorded from Viernjárga (Edwards, 1975) and the Mortensnes Formation (Edwards, 1984).…”

“…However, others have suggested that there possibly was no glacial influence at all (except maybe from sea ice) for deposits which are considered to display the best proof of glaciation (e.g., Jensen & Wulff-Pedersen, 1996, 1997Arnaud & Eyles, 2002). Mainly the pavements and diamictites are taken as evidence of glacial action, and most other geological data are interpreted in that context.…”

“…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.…”

“…Rocks and soft mud-flakes were pressed down into the pavement, showing up as depressions, and there are small push-up rims around these depressions ( Fig. 6; see also Jensen & Wulff-Pedersen, 1996;Rice & Hofmann, 2000). One small clast, recorded in situ, was recorded as pushed down into the underlying soft substrate of a poorly striated surface at Viernjárga, and other workers have made similar observations at Geađgefális Jensen & Wulff-Pedersen, 1996;Rice & Hofmann, 2000), thus favouring the notion that substrate was soft and the striations formed below a debris flow.…”

“…This inference may be based on palaeoclimatic interpretations (see documentation in e.g., Jensen & Wulff-Pedersen, 1997;Arnaud & Eyles, 2004), and/or that the outcrops have "chaotic" appearances, with matrix-supported clasts, striated pavements and supposed dropstones nearby. If the research area is considered influenced by glaciers, geomorphological, depositional and tectonic data from nearby outcrops are often interpreted within that context.…”