The Bigganjárgga Tillite re-visited: a stratigraphic and sedimentological study

• Main Author: Edvardsen, Egil
• Format: Master Thesis
• Language: English
• Published: UiT Norges arktiske universitet 2019
• Subjects: VDP::Mathematics and natural science: 400::Geosciences: 450::Sedimentology: 456; VDP::Matematikk og Naturvitenskap: 400::Geofag: 450::Sedimentologi: 456; GEO-3900; Norway; Rip; Smalfjord; Varangerfjorden; Finnmark; Northern Norway; Varanger; Varangerbotn; Varangerfjord*
• Online Access: https://hdl.handle.net/10037/15459

The Neoproterozoic “tillite”-bearing sequences of the Smalfjord Formation in Varanger, northern Norway have retrieved considerable attention in geological literature since first described and discovered over a century ago. Much of the attention relates to the so-called Reusch’s Moraine also known as the Bigganjárgga Tillite, which rests directly on top of a striated sandstone surface pointing to glacial scouring and a glacial origin (i.e. a tillite). Correlations of similar deposits from the same era elsewhere in the world have resulted in theories of a world-spanning glaciation, the “snowball Earth”-theory, where great amounts of the Earth was covered by snow and ice. However, the theory is criticized by many, and better understanding of diamictite deposits in general have caused several re-evaluations (globally) of these presumed tillites, which apparently can be easily confused with various coarse-grained gravity flow deposits (i.e. debrites and slump deposits). In this thesis, the classical type locality for the Varanger Ice Age at Bigganjárgga in Varangerbotn, eastern Finnmark, has been scrutinized with one question in mind, is the Bigganjárgga Tillite really a tillite or may it represent something else? In order to answer this question, a detailed facies analysis is combined with a digital outcrop model and thin section analysis. From the facies analysis, four facies associations are recognized: FA 1 – thin-bedded sandstone (representing fluvial deposits), FA 2 – thick-bedded diamictite (representing tillite or debrite deposits), FA 3 – thin-bedded sandstone (representing turbidites) and FA 4 – thin-bedded diamictite (representing fine-grained debrite or slump deposit). The appearance of rip-up mud clasts and several associated negative imprints within FA 1 suggest that the unit most likely was consolidated before erosion of the Bigganjárgga Unconformity (a part of the regional Varangerfjorden Unconformity) and deposition of the Bigganjárgga Diamictite (FA 2) took place. A confirmation to this was given by ...