The sequence stratigraphic development of the Late Jurassic / Early Cretaceous succession in the Egersund Basin, southern North Sea
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In this study, key factors controlling the sequence stratigraphic development of the Egersund Basin during the Late Jurassic / Early Cretaceous (late Kimmeridgian – Cenomanian) period were investigated. This was carried out by analyzing and interpreting 3D seismic data which were complimented by 2D seismic lines and well logs. The interval of interest was interpreted to comprise three complete and one incomplete sequence, which consist of seven systems tracts. The seismic facies and stacking pattern analysis suggest that the strata were deposited in a shelfal environment, in marine to open marine conditions. The late Kimmeridgian – early Aptian succession is dominated by fine-grained sediments, such as shale and claystone, while the Aptian – Cenomanian deposits are dominated by carbonates. During the initial phases, the basin was characterized by remnant paleo-topography formed during previous extensional events. The topography controlled the large-scale infill pattern during the early stages, limiting the lateral extent of the deposits. However, the main controlling factor for the late Kimmeridgian - mid Valanginian succession is the base level changes, which are well developed and preserved in the clinoforms. A secondary contributor to the stratigraphic development during this period is the sediment supply. The high sedimentation rates decreased the paleo-relief and, at least partly, filled the topographic depressions. This filling resulted in a laterally extensive shelfal area, with limited accommodation space. As a result, the mid Valanginian - late Hauterivian is dominated by small scaled clinoforms prograding on the shelf. In the late Hauterivian – early Aptian period, the base level returns as the controlling factor for the stratigraphic development, due to a relative sea level rise. During this period, the depocenter is at its most laterally extensive, indicating that the paleo-topography was filled by this time. The change in controlling factor is short lived, in the early Aptian to Cenomanian period a shift in sediment source terrain causes a major depocenter retreat and a drastic change in the lithological composition, from shale to carbonate dominated. The carbonates were uplifted and karstified during the following Turonian inversion.
Master's thesis in Petroleum Geosciences Engineering