Abstract for poster presentation
The Role of Pre-Existing Structural Fabrics on Normal Fault Growth, Offshore Mid-Norway
Antje Lenhart1, Christopher A-L. Jackson1, Rebecca E. Bell1, Oliver B. Duffy1, Haakon Fossen2, Robert L. Gawthorpe2, Paul S. Whipp3
1Basins Research Group, Department of Earth Science & Engineering, Imperial College, Prince Consort Road, London, United Kingdom, SW7 2BP
2Department of Earth Science, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway
3Statoil ASA, Sandslivegen 90, 5254 Sandsli, Norway
*Corresponding Author:
How pre-existing structural fabrics influence the nucleation, growth, interaction, and linkage of subsequent normal fault segments remains an important research theme given the potential wealth of hydrocarbons in rift basins which have evolved under the influence of such fabrics. Recent studies have highlighted how pre-existing structures- either fabrics or faults inherited from earlier rift phases, impart local stress perturbations and anisotropy upon subsequent phases of rifting.However, the degree to which pre-existing structures affect fault reactivation and the general rift geometry has not been fully explored yet. An understanding of these interactions is critical as the importance of fault reactivation in controlling the overall rift geometry is still controversial. This is mainly due to the lack of detailed knowledge of the deep sub-surface configuration due to limitations in seismic imaging, and complex overprinting of multiple tectonic events. Many previous studies have only addressed individual fault systems and have not considered the entire rift zone, and only a few studies have attempted to quantify fault activity during subsequent phases of extension. In addition, the time scales involved in the development of reactivated fault arrays are poorly constrained.
This study integrates 2D and 3D seismic, borehole and potential field data to examine the influence of pre-existing structures on normal fault growth and the rift structural style offshore Mid-Norway. In particular, we focus on the region ranging from the MåløySlope to the Slørebotn Sub-basin and the eastern Møre Basin, covering an area of approximately 3600 km2.Within this area, we investigate how pre-existing basement heterogeneities and faults associated with the Caledonian orogeny, Devonian transtension, and Permo-Triassic rifting have influenced normal fault evolution during the Late Jurassic and Early Cretaceous.
Due to relatively shallow burial of the basement and a rather thin sedimentary cover in the area, deep and intra-basement structuresare likely to be well-imaged on seismic and potential field data. Furthermore, the proximity of the study area to the land allows for a direct comparison of the observations with the onshore geology.
Previous interpretations show that the study area exhibits a distinct change in structural style, gradually changing from N-S striking structures in the MåløySlope area to predominantly NE-SW trends towards the north, which appears to be related to pre-existing structures and major lineaments (e.g. the Møre-Trøndelag Fault Complex) inherited from earlier phases of tectonic compression and extension, as well as to the onshore geology.
The presence and probable reactivation of deep-seated Palaeozoic detachments has been stated by several previous studies in the northern North Sea (e.g. Gabrielsen et al., 1999; Fossen et al., 2000; Odinsen et al., 2000). Furthermore, the dominant N-S and NE-SW striking fault trends that can be observed offshore have been considered to resemble the orientation of Palaeozoic fault patterns onshore Norway, and it is likely that these trends were reactivated during subsequent phases of rifting (Doré et al., 1997, Roberts et al., 1999). However, the nature of this proposed reactivation has not been investigated in detail to date and remains obscure.
To address these issues, an array of major faults and seismic facies boundaries were mapped along with key seismic-stratigraphic horizons; the ages of which are constrained by biostratigraphically-constrained well data.Preliminary results indicate that core data and seismic facies variability have the potential to differentiate basement types. As such, this study will use detailed quantitative fault analysis techniques such as throw-length and throw-depth plots to constrain the geometry and characteristics of fault populations (e.g. average fault lengths, spacing, propagation, slip rates and timing) that developed within or above different basement types. The results of this study will provide a fundamental understanding about fault growth and reactivation in heterogeneous crust and how these different basement domains influenced rift evolution in general.