Отправлено: 01.10.20 03:51. Заголовок: Modelling hydrothermal venting in volcanic sedimentary basins

Modelling hydrothermal venting in volcanic sedimentary basins:
Impact on hydrocarbon maturation and paleoclimate
Karthik Iyer a,b,∗, Daniel W. Schmid a,c, Sverre Planke d,e, John Millett d,f

Vent structures are intimately associated with sill intrusions in sedimentary basins globally and are
thought to have been formed contemporaneously due to overpressure generated by gas generation during
thermogenic breakdown of kerogen or boiling of water. Methane and other gases generated during this
process may have driven catastrophic climate change in the geological past. In this study, we present
a 2D FEM/FVM model that accounts for ‘explosive’ vent formation by fracturing of the host rock based
on a case study in the Harstad Basin, offshore Norway. Overpressure generated by gas release during
kerogen breakdown in the sill thermal aureole causes fracture formation. Fluid focusing and overpressure
migration towards the sill tips results in vent formation after only few tens of years. The size of the vent
depends on the region of overpressure accessed by the sill tip. Overpressure migration occurs in selfpropagating waves before dissipating at the surface. The amount of methane generated in the system
depends on TOC content and also on the type of kerogen present in the host rock. Generated methane
moves with the fluids and vents at the surface through a single, large vent structure at the main sill
tip matching first-order observations. Violent degassing takes place within the first couple of hundred
years and occurs in bursts corresponding to the timing of overpressure waves. The amount of methane
vented through a single vent is only a fraction (between 5 and 16%) of the methane generated at depth.
Upscaling to the Vøring and Møre Basins, which are a part of the North Atlantic Igneous Province, and
using realistic host rock carbon content and kerogen values results in a smaller amount of methane
vented than previously estimated for the PETM.

Our study, therefore, suggests that the negative carbon
isotope excursion (CIE) observed in the fossil record could not have been caused by intrusions within the
Vøring and Møre Basins alone and that a contribution from other regions in the NAIP is also required to
drive catastrophic climate change.