A Precambrian upper basin-slope and prodelta in Northeast Finnmark, North Northway; a possible ancient upper continental slope

Abstract

ABSTRACT The 60-m- to 540-m-thick lower Naeringselva Member of the Basnaering Formation crops out on Varanger Peninsula, North Norway, and is part of the 9-km-thick late Precambrian Barents Sea Group. It is underlain by at least 3.2 km of submarine fan deposits and is the oldest part of a 2.5-km- to 3.5-km-thick fluvio-deltaic succession (Basnaering Formation). The upper part of the member is delta front deposits. The lower Naeringselva Member mainly comprises fine-grained, thin-bedded deposits, divided into four facies: 1) Facies I, parallel-laminated mudstone; 2) Facies II, current-rippled siltstone, interpreted with Facies I as low density, low velocity turbidity current deposits; 3) Facies III, structureless mudstone, interpreted as possible hemipelagic deposits; and 4) Facies IV, wave-rippled fine/very fine-grained sandstone, interpreted as due to wave action. Soft-sediment deformation is abundant as various styles of slide, slump, and in situ disturbed layers up to tens of meters thick. Erosional-depositional discordances are evident between packets of beds. The stratigraphic position and sedimentology of the lower Naeringselva Member suggest that it is part of an ancient upper basin-slope and prodelta, with submarine fan deposits on the lower basin-slope. Paleocurrent data, with a limited number of slide fold readings, imply that deposits from downs-lope flowing sediment-laden currents prograded the slope towards the east-north-east. Apart from sporadic storm events, the slope was below wave base. Modern analogues for the lower Naeringselva Member appear to be the upper part of continental slopes separating submarine fan from delta deposits as in the Mississippi Delta-Slope-Fan system.