Geophysical investigation of sedimentary basin development : Viking Graben, North Sea.
The purpose of this study is to investigate the structure of the Viking Graben and adjacent areas using geophysical and geological techniques. The results thus obtained are used to construct a model for the development of the sedimentary basins of the northern North Sea since the beginning of the Mesozoic era. The regional consideration of the gravity field of the northern North Sea basin revealed the presence of a mass excess beneath the low density sediments. This high amplitude, long wave length anomaly is explained by thinning of the crust. Predictions obtained from the gravity data confirm the crustal structure derived so far from seismic experiments. "Normal" porosity-depth curves were constructed for three different sedimentary rock types in order to backstrip and decompact the sediments. Montmorillonite to illite transformation is proposed to be the main cause of the few undercompacted sedimentary sequences observed. Using well data the subsidence of the basement was calculated by backstripping and decompacting the sediments. By comparing the observed subsidence paths with those predicted by a simple stretching mechanism, a model is proposed to account for the geophysical development of the northern North Sea since Top-Permian times. Finally very close agreement is shown between the present crustal thickness values estimated from the modelling of wells and the values derived from the investigation of the gravity field. CONTENTS CHAPTER 1 GEOLOGICAL HISTORY, SUBSIDENCE MECHANISMS, OBJECTIVES AND DATA Page Introduction 1 1.1 The Structural Framework and the Geological History of the North Sea Area. 2 1.1.1 Pre-Permian 2 1.1.2 Permian 4 1.1.3 Triassic 4 1.1.4 Jurassic 5 1.1.5 Cretaceous 5 1.1.6 Tertiary to Recent 5