This study is based on a regional grid of seismic data acquired by Merlin Geophysical. The main emphasis of this thesis was on the detailed structural mapping of the Danish Central Graben, since this area has the highest density of well and seismic data. The principal objective of the study was to explain why the North Sea Rift changes strike in the Danish Sector, from the N-S trending Dutch Central Graben, to the NW-SE trending U.K/Norwegian Central Graben. The Danish Central Graben opened initially in the Late Carboniferous, as part of a regional dextral transtensile deformation that affected much of Europe. The initial extensional structures developed by reactivation of a pre-existing basement fabric. The NNW trending Coffee Soil Fault bounding the rift, is interpreted as a planar structure transecting the entire crust, and is thought to have developed by extensional reactivation of an east-verging Caledonian thrust. Basement shear zones identified on the rift shoulders on the Ringkobing-Fyn High are interpreted as the along-strike continuation of the Caledonides of Southern Norway, offset to the east by syn-orogenic transform motion along fracture zone elements of the Tornquist Zone. The WNW trending fault zones that dominate the structural grain in the Danish Central Graben are shown to be closely related to WNW trending fracture zones on the Ringkobing-Fyn High, which are regarded as splay shears of the Tornquist Zone. The WNW trending transverse fault zones segment the Danish Central Graben. The segmentation exerted a fundamental influence on the structural and stratigraphic development of the rift, in that individual segments were free to subside at different rates, in different styles, at different times. Two main phases of rifting are recognised, Permo-Triassic, and Middle and Upper Jurassic. These two phases have contrasting patterns of subsidence, and contrasting structural expression, particularly as regards the extent of the involvement of the transverse fault zones. The Permo-Triassic phase is characterised by parallelism of stratal configurations, and horizontal subsidence of the graben floor, whereas the Jurassic phase is characterised by strongly divergent configurations and asymmetric, rotational subsidence directed towards and controlled by the Coffee Soil Fault. Active rifting ceased at the end of the Jurassic, and Lower Cretaceous sediments are found to onlap extant fault scarps in a passive infill of the rift basin. The major bounding structures of the rift change strike abruptly in several incremental steps across the points of intersection with the transverse segment boundaries. The re-orientation of the rift is therefore explained as a consequence of the underlying presence of the earlier transform dominated basement fabric. A model for the formation of the North Sea Rift is proposed, which draws heavily on observations of the fracture patterns in continental rifts such as the Oslo Rift and the Rio Grande Rift, and is a development of the Megashear-Rhombochasm concept of S.W.Carey.

This study focuses on the main depocenter of the Andrew Formation in the Moray Firth Basin, located at the junction of the Central and Viking Grabens, in the central North Sea. The objectives of this report are to (1) define the sequence stratigraphic framework of the Andrew Formation, (2) describe and characterize the depositional systems associated to the Andrew slope to basin system, and (3) interpret the depositional processes that have dominated sediment emplacement. Specific facies association of the Andrew Formation are determined by the nature (point source or linear source) and caliber (volume, grain size, sand:mud) of sediment supply to the slope environment. Genetic interpretation of the Andrew Formation focuses on understanding depositional processes which dominated sediment emplacement. Seven depositional facies have been identified for the Andrew slope and basinal system; turbidite channel-fills, turbidite lobes, mounded turbidite lobes, sheet turbidites, debris flows and slumps, low density turbidites and hemipelagic drapes. Seven depositional processes collectively create the above mentioned Andrew depositional facies; turbidity currents, cohesive mud flows, sandy debris flows, muddy debris flows, slumping, low density turbidity currents and suspension settling. The Andrew Formation consists of upper and lower depositional units identified on seismic by bounding downlap terminations and on well logs by high-gamma marker beds. The lower Andrew displays three distinct sand-rich lobes, delineated by isopach and sand percent maps and log motif characteristics. Proximal, mounded, sand-rich units disperse into unchannelized sheet turbidites in the basin plain areas. The upper Andrew downlaps the lower unit, and a single, linear sediment source was centered in the Witch Ground Graben. The sediment dispersal pattern and internal facies character suggest the upper unit is a proximal slope-apron downlapping and filling inter-lobe bathymetric lows of the underlying unit. The lower Andrew is interpreted to be a structurally focused, sand-rich lobe complex, without associated incised canyons. The Andrew system evolved as the delta platform expanded onto the proximal fan, resulting in a linear sediment source spilling over the slope as a fringing slope-apron. The Andrew depositional system in the slope and basin environment is characterized by a high degree of facies disorganization composed of a wide array of gravity-flow deposits. / text

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1982. / Microfiche copy available in Archives and Science / Bibliography: leaves 33-38. / by Marie Diane Schneider. / M.S.