3D Structure and formation of hydrothermal vent complexes at the Paleocene-Eocene transition, the Møre basin, Mid-Norwegian margin
By S. Kjoberg, T. Schmiedel, S. Planke, H. H. Svensen, J. M. Millette, D. A. Jerram, O. Galland, I. Lecomte, N. Schofield, Ø. T. Haug, A. Helsem.
Schematic model displaying key development stages during vent formation. A) Emplacement of intrusion promotes fluid generation and overpressure causing overburden failure and explosive hydrothermal venting which blankets the surrounding area with vent material and older sediments. Large volumes of carbon outgassed into the water column and atmosphere. B) After the initial high energy venting, activity gradually wanes with long-lived gas seepage occurring over many thousands of years and periodically promoting small-scale sediment eruptions, which fill the crater and build up a shallow angle dome. C) Post venting sedimentation blankets the dome and builds up a potentially sealing cover over thousands to millions of years. Compaction of surrounding strata may exceed that of the hardened or potentially over- pressured vent material resulting in differential compaction and the accentuation of the dome feature.
The mid-Norwegian margin is regarded as an example of a volcanic-rifted margin formed prior to and during the Paleogene breakup of the northeast Atlantic. The area is characterized by the presence of voluminous basaltic complexes such as extrusive lava and lava delta sequences, intrusive sills and dikes, and hydrothermal vent complexes. We have developed a detailed 3D seismic analysis of fluid- and gas-induced hydrothermal vent complexes in a 310km2310 km2 area in the Møre Basin, offshore Norway. We find that formation of hydrothermal vent complexes is accommodated by deformation of the host rock when sills are emplaced. Fluids are generated by metamorphic reactions and pore-fluid expansion around sills and are focused around sill tips due to buoyancy. Hydrothermal vent complexes are associated with doming of the overlying strata, leading to the formation of draping mounds above the vent contemporary surface. The morphological characteristics of the upper part and the underlying feeder structure (conduit zone) are imaged and studied in 3D seismic data. Well data indicate that the complexes formed during the early Eocene, linking their formation to the time of the Paleocene-Eocene thermal maximum at c. 56 Ma. The well data further suggest that the hydrothermal vent complexes were active for a considerable time period, corresponding to a c. 100 m thick transition zone unit with primary Apectodinium augustum and redeposited very mature Cretaceous and Jurassic palynomorphs. The newly derived understanding of age, structure, and formation of hydrothermal vent complexes in the Møre Basin contributes to the general understanding of the igneous plumbing system in volcanic basins and their implications for the paleoclimate and petroleum systems.