Geothermal convection of seawater cools the margins of carbonate platforms, warming the interior. Previous RTM studies suggested this process can drive dolomitisation in the platform interior at depth at >50oC. However, extrapolation from short (0.1 Myr) simulations suggested complete dolomitisation requires at least 30-60 Myr. Our more extended (30 M.y) TOUGHREACT simulations indicate significant non-linearities in the system, with complete dolomitisation within 15 Myr. Reactions rapidly become flux controlled, forming a shallower wedge-shaped dolomite body which thins from the margin to the interior temperatures of 20-30oC. Geothermal dolomitisation is relatively insensitive to changes in boundary conditions such as relative sea-level and platform geometry, but is slower in radial than linear platforms. Sediment permeability and reactive surface area (RSA), often inversely related, are key controls. Low fluid flux limits dolomitisation to the platform margin of low permeability muddy platforms despite high RSA. Dolomitisation of more permeable grainy platforms is limited by RSA, and occurs only in the platform core due to widespread platform cooling. Layering of sediment types produces a complex vertical diagenetic stratigraphy, favoring more reactive beds at shallow depth where permeability is not limiting, but switching to more permeable beds at depth. Bank-marginal fracturing limits dolomitisation of the interior, irrespective of whether the fractures are open or sealed.
|Translated title of the contribution||Geothermal convection: a viable mechanism for early burial dolomitisation of platform carbonates|
|Title of host publication||Tough Symposium 2009, Berkley California|
|Publication status||Published - 2009|
Bibliographical noteConference Proceedings/Title of Journal: Proceedings of the TOUGH Symposium 2009
Conference Organiser: Lawrence Berkeley National Laboratory