2020
Petrography, bulk-rock geochemistry, detrital zircon U–Pb geochronology and Hf isotope analysis for constraining provenance: An example from Middle Triassic deposits (Bravaisberget Formation), Sørkappøya, Svalbard
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Acceped manuscripct

The Bravaisberget Formation is an important succession to better understand time and facies equivalent offshore deposits of the Barents Shelf. However, few of its provenance studies were primarily based on a single-grain method. This study therefore presents new results about these Middle Triassic sandstones based on multi-method approach provenance interpretations. Bulk-rock approaches (petrography and geochemistry) and single-grain methods (detrital zircon ages and Hf isotope analysis) were combined in order to characterise potential upland sources for sediments. The analysed sandstones are quartz arenites, sublitharenites, subfeldsarenites to sublithwackes, attesting to a generally high mineralogical maturity. Trace and rare earth elements link the deposits to source rocks of a felsic composition, related to the late-melt fractionating crust. The zircon age pattern is well known from other deposits of the Arctic region and links the sandstones to a protosource of Laurentian and/or Baltican affinity. The multi-method related input data in our study highlights the importance of sedimentary reworking from older quartz-rich units. Due to the high degree of sedimentary reworking required, the information the zircon age pattern holds has no bearing on the source to sink system in the Middle Triassic in southern Spitsbergen. The Eu and Gd systematics coupled with the Hf isotope data reflect subtle changes in provenance evolution. We assume that the Somovbreen and Karentoppen members of the Bravaisberget Formation shared the same source located in NE Greenland that was a molasse basin filled with a detrital material of eroded low-grade Proterozoic successions of the Caledonides. The Karentoppen Member was additionally supplied by a sedimentary unit coming from the eroded part of an Archaean/Palaeoproterozoic basement. This study has shown that the provenance of compositionally mature sandstones is difficult to disentangle even despite the multi-method approach applied, and that in such cases any interpretations are best grounded by field constraints.

u.czarniecka[at]gmail.com
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