Impacts of small-scale faults on continental to coastal plain deposition: Evidence from the Realgrunnen Subgroup in the Goliat field, southwest Barents Sea, Norway

Abstract

In this study we synthesise sedimentological, fault, and Amplitude Versus Angle (AVA) analysis and propose that the Fruholmen and Tubåen formations (Realgrunnen Subgroup) are syn-kinematic deposits that record a previously undocumented early phase of Mesozoic rifting on the Troms-Finnmark fault Complex and within the Hammerfest Basin. The Realgrunnen Subgroup hosts one of two Triassic reservoirs currently being produced in the Goliat field. Here, the subgroup sits unconformably on top of the Storfjorden Subgroup (Carnian Snadd Formation). Away from the Goliat field, which is characterised by a periclinal anticline, the Realgrunnen Subgroup also comprises the Lower–Middle Jurassic Nordmela and Stø formations. Sedimentological analysis of six exploration wells reveals that the Fruholmen Formation was deposited in a prodelta to delta plain environment where tide-influenced and fluvial-dominated distributary channels are represented by clay/siltstones and very fine grained sandstones. The overlying Tubåen Formation is characterised by medium to very coarse-grained deposits (locally conglomeratic) and represents a widespread braid plain with localised alluvial fans. Displacement profiles of faults and along-fault thickness variations demonstrate that an immature fault system was active during deposition of the Realgrunnen Subgroup. A series of unconnected fault segments hosted isolated sub-basins and erosional catchment areas in their hanging and footwalls, respectively. An AVA attribute map generated from a 10 ms interval of the uppermost part of the subgroup reveals gross sand-prone depositional bodies, i.e., individual and amalgamated channels, (some of which show meandering geometries), ox-bow lakes and alluvial fans. Sand bodies frequently show elongate geometries parallel to faults indicative of syn-depositional fault-related subsidence. Driving mechanisms responsible for the Norian to Rhaetian event may relate to contemporaneous rejuvenation of the Fennoscandian hinterland, development of the Novaya Zemlya fold-and-thrust belt and/or the early Cimmerian tectonic phase in northern Europe.