A sedimentary provenance study of modern river sands from northern Fennoscandia and its insight into the source of Mesozoic successions deposited on the southwest Barents Shelf

Northern Fennoscandia was periodically a major source of sediment to the Barents Shelf. As the modern exposures may broadly represent lithologies eroded in the past, the analysis of modern river sands can be used to evaluate the extent to which sand deposited on the Barents Shelf was sourced from this area.

Sedimentary provenance techniques were applied to twenty modern sand samples collected from twelve major river catchments in northern Fennoscandia. A highly distinctive provenance signature is recorded in samples from the Tana River, which crosses the Lapland Granulite Belt (LGB). Downstream of exposures of the LGB, modern sands are dominated by rutile with c. 1.9 Ga U-Pb ages and a chemistry indicating crystallization at c. 850 °C from a pelitic protolith.

A detrital rutile signature similar to that in the Tana River is replicated in the Late Triassic – Early Jurassic Realgrunnen Subgroup deposited in the vicinity of the southern Nordkapp Basin, and indicates a common origin from the LGB. The Realgrunnen Subgroup deposited in the southern Hammerfest Basin has a strikingly different provenance pattern. Here, rutiles have mostly 430-515 Ma ages and crystallised at c. 650 °C from a pelitic protolith. The similarity of this pattern to rutile data from the modern Målselva River indicates a source from Caledonian allochthons affected by Palaeozoic amphibolite-facies metamorphism.

Models depicting rejuvenation of a Fennoscandian sedimentary source region in the Late Triassic and early Jurassic are supported by these data. The rutile technique provides one of the clearest mechanisms for tracing the dispersal sediment across the Barents Shelf derived from different parts of northern Fennoscandia.

Despite these contrasting rutile signatures, the Nordkapp Basin and Hammerfest Basin samples yielded similar zircon U-Pb age patterns, dominated by 1.0-1.7 Ga grains. This age range does not correspond with widespread igneous or metamorphic events in northern Fennoscandia and so these zircons were probably recycled from (meta)sedimentary units.

A statistical assessment of the multi-proxy modern sand dataset helps to identify the Barents Sea Group as a source of recycled detrital zircon and hence can account for the mismatch of zircon and rutile patterns in some of the Mesozoic offshore samples. It also shows how readily sedimentary reworking, uneven erosion and fertility can affect and bias the various sedimentary provenance signals.