Provenance Variability in Coeval Slope Channel Systems: Hermod S2 Member Sandstone (Eocene), South Viking Graben (North Sea)

Abstract

Conventional and varietal heavy mineral studies of the earliest Eocene Hermod S2 Member (Mbr) sandstones in the Greater Alvheim area of the northern North Sea have revealed marked lateral variations and more subtle vertical evolution in provenance signature. Major variations are of geographic rather than stratigraphic nature as biostratigraphy reveals that all investigated sandstones are coeval. The provenance variations show an organized pattern, with sandstones in the north showing a different signature than those in the south. The position of the sandstones relative to the East Shetland Platform (ESP) is inferred to be the main control on provenance, with sediment input from at least two different point sources. Sediment supplied from both catchments is predominantly recycled in nature, given the mineralogical maturity of the heavy mineral assemblages, consistent with the evidence for widespread Permo-Triassic and Devonian sediments on the ESP. However, some direct supply from metasedimentary (Moine and Dalradian) basement is implied by the sporadic occurrence of unstable minerals. The southern catchment incorporated a greater exposure of Permo-Triassic sandstones than the northern catchment. The Permo-Triassic part of the catchment can be reconstructed as comprising equivalents of the Foula and Otter Bank sandstones present to the west of Shetland, with the majority of the Foula section having been stripped off prior to Hermod S2 deposition, exposing Otter Bank equivalents for erosion and redeposition. However, remnant Foula-like sandstones remained exposed further south on the ESP until at least the earliest Eocene since Foula-type garnet signatures are found in the Forties Sandstone Mbr of the central North Sea. In addition to lateral differences, stratigraphic evolution of provenance can also be detected in the Hermod S2 Mbr, with variations in key provenance-sensitive parameters related to a sea-level rise that reduced the extent of alluvial storage and altered the geological framework of the hinterland.