Compositional variations and provenance of Triassic sandstones from the Barents Shelf

Abstract

ABSTRACT Triassic sandstones from a large area ranging from the Pechora Sea and Novaya Zemlya in the southeast to the western Barents Sea and Svalbard have been analyzed by petrographic, mineralogical, mineral-chemical, and Sm-Nd bulk-rock isotopic methods. The largest compositional variation is seen in the Lower Triassic deposits. Epidote-bearing, lithic-rich sandstones are characteristic of the eastern Barents Sea, Novaya Zemlya, and the Timan-Pechora Basin, and indicate a provenance from the Polar Urals. Quartzo-feldspathic sandstones in the Hammerfest Basin may have been derived from deeper crustal plutonic and metamorphic rocks of the Caledonides and Baltic margin, whereas the source of quartz-dominated sandstones on Spitsbergen was a paleoland in the northwest, in the vicinity of paleo-Greenland. Calculated Sm-Nd provenance ages for Lower Triassic deposits are in the range of 1500-1880 Ma for sandstones from Spitsbergen, the Hammerfest Basin, and the Finnmark Platform. Sandstone provenance ages for samples analyzed from the eastern Barents Sea are significantly younger, with a range of 600-1280 Ma and an average of 780 Ma. Sandstones in central shelf areas, i.e., the Nordkapp Basin-Bjarmeland Platform, are rich in both lithics and feldspar and have intermediate provenance ages (960-1630 Ma). The largest influence of older components occurs in samples from the Nordkapp Basin. This may be related to sediment supply both from the Caledonized Baltic margin and Uralides, and from local uplifted areas composed of Paleozoic sedimentary rocks. Middle and Upper Triassic sandstones display compositional variations at different times in different areas due to local changes in provenance. However, in the Upper Triassic there appears to be a convergence in sandstone compositions reflecting both more extensive mixing of components from the eastern and western provenance areas as well as changes to more evolved compositions of the erosional products derived from the paleo-Urals. There is also a question of increasing influence from possible paleolands in the northeast. The most important compositional change was the distinct increase in sandstone maturity that took place on a regional scale in the Arctic in the latest Triassic-Early Jurassic. This may in part have been caused by extensive reworking connected with a regional transgression and sea-level raise.