The Sassendalen Group
Lower and Middle Triassic (Induan to Anisian)
The Sassendalen Group on the Barents Sea shelf consists of four formations: Havert, Klappmyss, Steinkobbe and Kobbe. The lower boundary is defined towards the Upper Paleozoic by mixed siliciclastic and carbonate sequences, while the upper boundary is marked by a shale interval at the base of the Fruholmen Formation (Realgrunnen Subgroup). This represents an important transgressive event which formed a traceable sequence boundary throughout most of the Arctic from the Barents Sea to the Sverdrup Basin. The type and reference area for the Ingøydjupet Subgroup is represented in blocks 7120/12 and 7120/9 in the western part of the Hammerfest Basin. In the type area the thickness is approximately 1700m, thickening northwards towards the reference area to 2400m (well 7120/9-2). The subgroup is thick throughout the Hammerfest Basin, where the lower part is onlapping the Loppa High to the north. Thick sequences are also found to the east on the Bjarmeland Platform, Norsel High and along the southeastern margin of the Nordkapp Basin. The dominant lithology of the Ingøydjupet Subgroup is black shale and claystone with thin grey silt- and sandstones, occurring particularly in the upper parts. Minor carbonate and coal interbeds are also present. Marine environments encountered by wells in the lower parts of the subgroup, together with seismic data, show evidence for coastlines to the south and southeast of the Hammerfest Basin, and progressive onlap of the submerged Loppa High to the north. The upper parts of the subgroup reflect northwestward outbuilding of deltaic sequences over an extensive, low relief depositional basin.
Fig-6-014
Fig-6-015
Palaeogeographic map showing the progradation of sediments into the Middle Triassic marine embayment, and the development of a paralic platform in the Late Triassic. In the map, the detailed boundaries between depositional areas are simpliļ¬ed, and the positions of the rivers are conceptual. The Kobbe aquifer in the Goliat area is indicated. (Riis et al. 2008)
The Havert Formation (Induan)
In the type well (7120/12-2) in the Hammerfest Basin, the formation consists of medium to dark grey shale with minor grey siltstone and thin sandstone layers, comprising two generally coarsening upwards sequences. The thickness in the type well is 105m. Further to the north, the reference well (7120/9-2) has a thickness of 150m with a more monotonous silt and shale sequence. Further to the east, on the Bjarmeland Platform and Norsel High, thicknesses in the order of 1000m have been reported, dominated by silt and claystone with subordinate sandstone lithologies. On the Finnmark Platform a thickness of more than 600m has been drilled. In well logs the lower boundary is defined at the top of the underlying Upper Paleozoic mixed siliciclastic and carbonate rocks. The formation was deposited in a shallow to open marine setting with coastal environments to the south and southeast.
Fig-6-016
Fig-6-017
The Klappmyss Formation (Olenekian)
In the type well (7120/12-2) in the Hammerfest Basin, the formation consists of medium to dark grey shale passing upwards into siltstones and sandstones. The reference well (7120/9- 2) shows a similar trend, but with higher content of shale. The thickness is 457m in the type well and 561m in the reference well. Thicknesses as high as 600m have been reported from the Bjarmeland Platform (well 7226/2-1) and the Norsel High (well 7226/11-1). On the central Finnmark Platform (well 7128/4-1 and 6-1), thicknesses around 260m have been drilled. Generally the formation thickens and becomes finer northwards from the southern margins of the Hammerfest Basin. In well logs the lower boundary is defined at the top of the underlying Havert Formation, interpreted to represent a sequence boundary. This boundary can be correlated across the southwestern Barents Sea shelf indicating a lower Triassic transgression. The Klappmyss Formation was deposited in a shallow to open marine environment, with renewed north- to northwestward coastal progradation.
Fig-6-018
