Controls from Transgressive Shallow-Marine Sedimentation in a Salt-Influenced Rift: Hugin Formation, South Viking Graben, Offshore Norway

Rachel L. Kieft¹, Chris A. Jackson¹, Gary J. Hampson¹, and Eirik Larsen^2
1Department of Earth Science and Engineering, Imperial College London, London, United Kingdom
²Statoil ASA, Bergen, Norway

The sedimentologic character and facies distribution of shallow-marine deposits is governed by the complex spatial and temporal interaction of physical processes (e.g. waves and tides). In syn-rift settings, prediction of facies distribution is further complicated by the effects of localised uplift and subsidence associated with faulting. This study focuses on the net-transgressive Hugin Formation (Middle Jurassic), deposited during southerly retreat of the Brent Delta system in the South Viking Graben, North Sea rift. The unit hosts economically important reservoirs.

Sedimentologic analysis of the Hugin Formation highlights the variability of the deposits on the hangingwall dipslope of the South Viking Graben. By integrating the results of sedimentologic analysis with seismic interpretation and high-resolution biostratigraphy it has been possible to develop detailed depositional models for the area. To the north, stacked coarsening-upward units reflect periodic infilling of a restricted marine embayment. Early syn-rift faulting controlled facies thickness in this area, but appears to have had little impact on facies distribution, indicating that sediment supply kept pace with developing fault-controlled topography. At the same time, a thick, aggradational, wave-dominated shoreface was deposited to the south. Subtle fluvial signatures within the shoreface unit are interpreted to reflect development of a large delta system even further south. The shoreface unit fringed actively growing salt-cored highs, whilst time-equivalent deep marine sediments were deposited in adjacent salt-withdrawal mini-basins. These models will aid future exploration within the region as well as providing important insights into the relationship between sedimentology, sequence stratigraphy and structural development that can be applied to other rift basins and areas of halokinesis.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas