An analysis of facies in the De Geerdalen Formation and provenance across the Middle to Late Triassic boundary on Spitsbergen, Svalbard
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At the end of the Paleozoic era, Svalbard and the Barents Sea were part of a large shallow embayment on the northern margin of Pangea. During the Triassic period, the embayment was filled with sediments from a large deltaic system that progressed across the Barents Shelf. The De Geerdalen Formation on Spitsbergen was deposited during the Carnian stage of the Late Triassic, and is composed of sediments that were deposited in a distal part of the deltaic system. This study documents and discusses the depositional environment of the De Geerdalen Formation through facies analysis of outcrops in the Fulmardalen area on Central Spitsbergen. The study builds on previous work, and aims to extend the present understanding of the environmental evolution on Svalbard during the Late Triassic.A total of 6 measured section from Fulmardalen are presented. The facies analyses display a general upwards shallowing environment, dominated by prodelta and open marine deposits in the lower part, shallow marine and delta front deposits in the middle part, and delta plain deposits in the upper part. The data indicate deposition in a highly dynamic environment, with significant facies variations both laterally and vertically. Laterally extensive sandstone bodies dominate the lower part of the De Geerdalen Formation in Fulmardalen, and are interpreted as barrier bars deposited in a shallow marine and delta front setting. Compared to more fluvial influenced sandstone bodies from the De Geerdalen Formation on the eastern islands of Svalbard, sandstone bodies in Fulmardalen are generally thin, with sedimentary structures that indicate a domination of basinal processes such as wave- and tidal energy. This may indicate that the deposition happened in a low accommodation space setting, where basinal processes could control the sediment distribution.In addition to facies data from Fulmardalen, detrital zircon U-Pb age data from Middle and Upper Triassic sandstones from the Festningen section are presented. In combination with existing detrital zircon age data, sedimentological, stratigraphic, and seismic data, the zircon ages are used to investigate provenance for the Triassic succession at Festningen. The data indicate a western source in northern Greenland for the Early and Middle Triassic deposits. At the transition between the Middle and Late Triassic, the data indicate a distinct shift in provenance. The deposits of the Upper Triassic De Geerdalen Formation show zircon ages that suggest domains within the Uralides and the Taimyr region as main sediment sources, with additional input from the Timanides and Caledonides. The presence of near-syn-depositional zircon ages in samples from the De Geerdalen Formation may reflect rapid transportation rates, deposition as airborne volcanic ash, or the presence of a proximal active margin.