Mechanisms of overburden deformation associated with the emplacement of the Tulipan sill, mid-Norwegian margin
By T. Schmiedel, S. Kjoberg, S. Planke, C. Magee, O. Galland, N. Schofield, C. A. L. Jackson, and D. A. Jerram.
Seismic expression of the Tulipan sill. (a) The 3D visualization of the saucer-shaped geometry of the top Tulipan sill horizon. Radial magma flow indica- tors mark edges of reflection segments representing upward, outward trans- gressing, igneous inclined sheets (Schofield et al., 2012b; Magee et al., 2014), examples of these are highlighted as lobes and cross referenced to profile P2- P2′ in (b). (b) Seismic profiles show the cross-sectional expressions of the Tulipan sill (see [a] for the location). P1-P1′ highlights the picked Tulipan sill top and base, whereas P2-P2′ visualizes the segmented character of the Tulipan sill reflection and indicates an underlying sill (S) below the Tulipan sill (Tulipan top — dashed white line; dashed black line tentatively interpreted as the sill base; lobes high- lighted in [a] are also indicated).
The emplacement of igneous intrusions into sedimentary basins mechanically deforms the host rocks and causes hydrocarbon maturation. Existing models of host-rock deformation are investigated using high-quality 3D seismic and industry well data in the western Møre Basin offshore mid-Norway. The models include syn- emplacement (e.g., elastic bending-related active uplift and volume reduction of metamorphic aureoles) and postemplacement (e.g., differential compaction) mechanisms. We use the seismic interpretations of five hori- zons in the Cretaceous-Paleogene sequence (Springar, Tang, and Tare Formations) to analyze the host rock deformation induced by the emplacement of the underlying saucer-shaped Tulipan sill. The results show that the sill, emplaced between 55.8 and 54.9 Ma, is responsible for the overlying dome structure observed in the seismic data. Isochron maps of the deformed sediments, as well as deformation of the younger postemplace- ment sediments, document a good match between the spatial distribution of the dome and the periphery of the sill. The thickness t of the Tulipan is less than 100 m, whereas the amplitude f of the overlying dome ranges between 30 and 70 m. Spectral decomposition maps highlight the distribution of fractures in the upper part of the dome. These fractures are observed in between hydrothermal vent complexes in the outer parts of the dome structure. The 3D seismic horizon interpretation and volume rendering visualization of the Tulipan sill reveal fingers and an overall saucer-shaped geometry. We conclude that a combination of different mechanisms of overburden deformation, including (1) elastic bending, (2) shear failure, and (3) differential compaction, is responsible for the synemplacement formation and the postemplacement modification of the observed dome structure in the Tulipan area.