Triassic paleogeography of the greater eastern Norwegian-Danish Basin: Constraints from provenance analysis of the Skagerrak Formation

•Provenance: the Sveconorwegian basement and its Paleozoic cover.•Erosion of the Skagerrak-Kattegat Platform and the Skagerrak Graben.•Deposition by alluvial fans, braided rivers and aeolian dunes.•Gradual overstepping of the basin margins during the Triassic.

Zircon U–Pb geochronometry and heavy mineral CCSEM analysis are used to determine the provenance of the Skagerrak Formation which was deposited during most of the Triassic period as an up to 3 km thick succession. The sampled sandstones are collected in well cores from the Norwegian-Danish Basin, the Sorgenfrei-Tornquist Zone and the Skagerrak-Kattegat Platform with the goal of obtaining a geographically and stratigraphically representative dataset usable for investigating provenance and the implications for Triassic paleogeography. The basement in the source terranes has pronounced differences in zircon ages, so it is possible to distinguish which terranes the zircon grains were derived from. The zircon ages found in the Skagerrak Formation are comparable to source terranes in southern Norway and southwestern Sweden including the Telemarkia Terrane, the Idefjorden Terrane and the Eastern Segment of the Sveconorwegian Orogen. The basement and Paleozoic sediments of the Skagerrak Graben and the Skagerrak-Kattegat Platform were presumably exposed to erosion during the early to middle Triassic as indicated by the abundant rock fragments present in the Skagerrak Formation south of this elevated area. This local input was mixed with vast amounts of material transported from other basement areas in the northeast and their cover. The material was transported by rivers that downstream developed into braid plains with braided rivers and aeolian activity. The decreasing grain size up through the Skagerrak Formation is reflecting the gradual overstepping of the basin margins. Thus, sediment supplied by local erosion is absent in the upper part of the formation. The heavy mineral assemblages are mineralogically immature due to the arid depositional conditions and the limited temporary storage during transport. The assemblages are very uniform in the Norwegian-Danish Basin, whereas they are characterized by local inputs on the Skagerrak-Kattegat Platform. A locally deposited basement conglomerate indicates that the basement beneath northern Denmark has ages corresponding to the Telemarkia Terrane in southern Norway similarly to the ages of the basement beneath southern Denmark.

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