Sedimentology and Sequence Stratigraphy of Shallow Marine Sediments in a Syn-Rift Setting: Hugin Formation, South Viking Graben

Abstract

Fault growth and linkage within rift basins generates localised uplift and subsidence, which may exert significant control over syn-rift sedimentation. The shallow-marine Hugin Formation within the South Viking Graben, a salt-influenced rift basin, is studied as an example of such sedimentation. The principal aims of this thesis are to: (1) characterise the sedimentology and sequence stratigraphy of the succession, (2) investigate structural development within the graben by analysis of the hangingwall dipslope, and (3) establish the impact of syn-depositional structural development on shallow marine sedimentation. Sedimentological analysis of the Hugin Formation has recognised fifteen facies that are grouped into six facies associations: bay-fill, shoreface, fluvio-tidal channel fill, mouth bar, coastal plain and offshore open marine. Combining the results of this analysis with biostratigraphy, the studied succession is subdivided into a series of units delineated by regionally correlatable maximum flooding surfaces. Within the stratigraphic framework delineated by these surfaces each of the main facies associations are developed coevally in distinct and different geographical locations. Higher order flooding surfaces, transgressive surfaces and candidate sequence boundaries can also be interpreted within this framework which are geographically localised. Structural analysis of the hangingwall dipslope identified a series of distinct structural features that were evolving contemporaneous with Hugin Formation deposition. To the north, the gravity-driven Gudrun-Brynhild fault array initiated as a series of distinct segments which subsequently propagated and linked. Further south, the salt-cored highs at Dagny and Alpha Central were also developing. Palaeogeographical localisation of facies associations is interpreted to reflect deposition within these different structural locations along with proximity to the axial fluvial feeder system to the south of the basin. Sediment supply via wave-driven longshore drift from the north of the basin and local re-working of structurally controlled palaeohighs was also important.