Structural Interpretation and Investigation of the Displacement Gradients of the Normal Fault System beneath the Horda Platform, the northern North Sea

Abstract

The North Sea basin is one of the best-studied areas in the world with respect to thestructural and sedimentary architecture of rift zones. The Base Cretaceous Unconformity,which defines a mappable horizon at the transition from synrift to postrift sequencesassociated with the Jurassic Cretaceous rift, is well known as a reference marker for bothseismic and well log interpretations and covers most of the basin. This unconformity isinterpreted at the locations of the Øygarden Fault Zone, the Troll Fault Block, the NorthViking Graben, the Tampen Spur, the Snorre Fault Block, the Sogn Graben and the HordaPlatform. The complexities of the unconformity have been established and vary with thestructural and geographical position within the basin. However, as the Base CretaceousUnconformity covers most of the northern North Sea, its structural time map, is used to derivethe picture of post-structural framework of a rift basin and to locate essential structures in thedeeper sections.Three main reflectors (Pre-Jurassic 1, Pre-Jurassic 2 and Top seismic basement)located beneath the Base Cretaceous Unconformity on the Horda Platform, and have beeninterpreted using 2D seismic reflection data. These three reflectors have been studied in orderto investigate in detail the displacement gradients and possible linkage of the early faultsystem under the Horda Platform, and to evaluate their effect on the large-scale sedimentarchitecture. A main reason to work on the structures under the Horda Platform is due to thefact that these structures are believed to have existed already in the early stages of thenorthern North Sea basin development.The extensional normal fault systems of both the Permo-Triassic and the Late Jurassicrifts are considered a key control on the geological structures and sedimentary architecture ofthe region as presently seen. The basin evolution related Permo-Triassic rifting is mostpronounced on the eastern part of the Horda platform where its synrift geometry is obviouslyseen with the huge segment length and largest uplift explainable by a flexural stretchingmodel. The rift axis is transferred to position at base of the Viking graben during the Late-Jurassic rifting with the smaller magnitude of extension than the Permo-Triassic as clearlyseen by the less thickness of the synrift geometry. However, the structural evolution of normalfaults and the basin architecture under the Horda Platform is particularly affected by thecomplex interaction of fault linkage, fault propagation, fault growth, and death of faultthrough times from the early stage to the final stage of the basin development. Apart from theeffects of major tectonic controls, additionally, non-tectonic parameters, such as climate, seaor lake level changes, and differences in amount and type of sediment supply, should be takeninto account to influence the stratigraphic and sedimentation patterns in the basin.