Glacial retreat sedimentation in the Smalfjord Formation, Late Precambrian, North Norway

Abstract

Tillites, conglomerates and sandstones occurring in the basal part of the Smalfjord Formation along the Varangerfjord, East Finnmark, North Norway are believed to have formed during the retreat of a glacier. At Kvalnes, on the south side of the fjord, the following sequence, up to 20 m thick, is found: (1) massive monomict tillite interpreted as a subglacial till, (2) massive polymict tillite with lenticular intercalations of stratified sandstone and tillite, interpreted as supraglacial/proglacial drift, (3) polymict conglomerate interstratified with laminated sandstones, interpreted as braided stream deposits. The last named interfingers laterally and is overlain by marine sandstones. At Bigganjargga, near the head of the fjord, a lens of tillite about 3 m thick rests on a striated pavement and is overlain by sandstones and shales. Part of the tillite, containing irregular patches of slightly winnowed tillite, is interpreted as a melt‐out till, while a marginal part consisting of inclined tillite beds is interpreted as a series of flow till deposits. The lens is believed to be an oblique section through what was originally an ice‐cored moraine ridge. During a subsequent transgression, the moraine was partially eroded, a lag conglomerate was formed, and overlying marine sediments were deposited. Bedded flow tills formed in a supraglacial/proglacial environment may be preserved where the extent of current reworking is very low (such as an isolated end moraine). Stratified conglomerate and sandstone, intimately intercalated with tillite, is to be expected at a glacier margin where glacial meltwater is locally and occasionally abundant, and glacier ablation permits downslope flowage of mobilized supraglacial fluid till.

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

“…These geological structures are typical of debris flow deposits (Shanmugam, 2016) and do not closely resemble till. These observations corroborate descriptions by Edwards (1975Edwards ( , 1984, even though he interpreted the formations to be glaciogenic. In addition, these observations conform well to data on e.g., Eocene submarine debris flow deposits (Dakin et al, 2013).…”

“…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, striations on clasts are not uncommon in gravity flows, and even quartzites can be striated (e.g., Schermerhorn, 1974).…”

“…1). The outcrops on Viernjárga are smaller in size, not continuous but spread over a larger area, and display affinities that are less similar to tills than the Geađgefális (compare descriptions in Edwards, 1975Edwards, , 1984.…”

“…This interpretation is so widely accepted by some researchers that non-glaciogenic interpretations of the Varangerfjord area diamictites have been noted as having "caused some confusion" (Laajoki, 2002, p. 410). The diamictites include numerous deposits in Finnmark Fylke (Edwards, 1975(Edwards, , 1984, inclusive of the Mortensnes Formation in the northern part of Varangerfjord (Beynon et al, 1967) and the Smalfjord Formation (Fig. 1).…”

New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

“…2). Sand wedges are widespread in Cryogenian (720-635 million years ago) sedimentary successions in West Africa (Deynoux, 1982), Norway (Edwards, 1975), Scotland (Spencer, 1971), and South Australia (Figs. 2, 4a-f, 5a-h) (Williams and Tonkin, 1985).…”