Provenance characteristics and regional implications of Neoproterozoic, Timanian-margin successions and a basal Caledonian nappe in northern Norway

Abstract

The autochthonous/parautochthonous lithostratigraphic successions of Varanger Peninsula, NE Norway, range in age from Tonian to Cambrian and constituted a passive (Baltican) margin depositional system throughout most of the Neoproterozoic. Sediment sources were mainly from the south on the Fennoscandian Shield. U–Pb zircon age spectra from sandstones of eight formations show significant input of Late Palaeoproterozoic and Mesoproterozoic age, as well as a prominent Neoarchaean peak. These mostly reflect derivation from rock complexes and terranes that are exposed on the present-day Baltic Shield, although the abundance of Mesoproterozoic zircon grains is less easy to explain. Possible sources may represent (i) possible basement of this age now concealed beneath the Caledonian nappes, (ii) a northward continuation of the Sveconorwegian orogen, (iii) recycling of a sandstone-dominated thrust sheet derived from the Rodinian margin and emplaced in the Tonian or (iv) recycled material from pre-existing extensive river systems farther south on the Fennoscandian Shield. One major exception to the above age-spectral pattern is provided by the Late Ediacaran to earliest Cambrian Stáhpogieddi Formation in the immediately overlying Gaissa Nappe Complex. Sandstones in this unit are derived from a northeasterly source, and show a major zircon age peak at c. 550Ma. The formation is considered to represent deposition in a foreland basin ahead of the rising Timanian orogen.