Development of the Middle Triassic Kobbe Formation shelf-margin prism and transgressive-regressive cycles on the shelf (Hammerfest Basin, SW Barents Sea)

Abstract

Abstract The development and evolution of the middle Triassic shelf-margin prism of the southwestern Barents Sea has been so far under-researched. In particular, no attention has been paid to the thick transgressive packages developed at the top of the clastic prism. This study focuses on the Anisian-Early Ladinian Kobbe Formation, and it is based on a seismic and well log dataset from the Hammerfest Basin and adjacent Loppa High, as well as on a process-based investigation of available cores. 2D seismic lines show the development of shelf margin clinoforms up to 300 m thick, and shelf-edge trajectory analysis shows intervals with flat trajectories and intervals with ascending trajectories. The Kobbe Formation shelf-margin prism grew through repeated cross-shelf (regressive-transgressive) transits of deltaic systems. Mapping of the shelf-edge locations shows that the shelf-margin prism prograded ca. 30–50 Km in a north-westward direction, and localized protrusions of the shelf edges at different times can indicate cross-shelf sediment supply fairways. The farthest basinward extent of the sedimentary prism appears to have been controlled, at least in part, by the topographic relief of the paleo-Loppa High, as the bottomsets pinch out against this synsedimentary structural high. On the shelf, during regressive phases, the shoreline prograded from the south and from the east-southeast. This work recognizes, for the first time, the presence of thick transgressive packages within the Kobbe Formation. The transgressive sequence at the top of the Kobbe Formation is up to 50 m thick, and it is interpreted as stacked estuarine valley fills close to the Troms-Finnmark fault complex. In the Goliat area, the presence of an expanded sedimentary sequence, compared to adjacent areas, suggests a tectonic control in this area. Tectonic activity may have also influenced the development of stacked estuarine valleys in the same location, therefore controlling sand storage on the shelf.