Detrital zircons of the vast Triassic Snadd and De Geerdalen formations, Barents Shelf, reveal temporal changes in sediment source

Abstract

Studies of detrital-zircon age distributions from Triassic sedimentary rock successions on the Arctic Barents Shelf have resulted in different provenance interpretations. Here, we provide new U–Pb/Hf detrital-zircon data from eleven samples of the Snadd and De Geerdalen formations, covering the Barents Shelf in a north–south transect, that help refine the provenance of these sedimentary rocks and show how stratigraphic variations reflect changing source regions. The sample locations cover different stratigraphic levels and geographic locations within the formations. The detrital-zircon age spectra in the lower part (lowest Ladinian and lower Carnian) are dominated by two age peaks at 300 and 540 Ma, whereas the zircon distributions in the stratigraphically younger deposits (latest Carnian and early Norian) are dominated by a 235 Ma age peak and two minor peaks at 300 and 425 Ma. The apparent relative contribution of detritus of different ages changes gradually from lower to higher stratigraphic levels, marked by an increase in both the 235 and 425 Ma age peaks, a decrease in the 300 Ma component and a progressive loss of the 540 Ma age peak. The zircon Hf-isotopic compositions display predominantly juvenile zircon populations, except for a mixed juvenile and evolved signature in the youngest Permo-Triassic grains. A regional comparison of detrital-zircon age spectra in latest Carnian/early Norian deposits extends the depositional system into the Sverdrup Basin, supporting a much larger depositional system than hitherto known. The gradual change in detrital-zircon age spectra likely represents a gradual shift in zircon provenance. We interpret these variations to reflect an early source region in the north Urals, gradually changing to a dominant source region in the Taimyr Peninsula region.