Fault-associated dolomites in the benicàssim area, Maestrat Basin, E. Spain: macro- to micro-scale fluid flow in carbon

Partial dolomitization of the middle to late Aptian carbonate succession from the SE Maestrat Basin (E. Spain) occurred during shallow burial in relation to the circulation of high temperature fluids (>60° C) through regional extensional faults and most permeable host limestone facies. The timing of replacement is constrained between the early Albian (syn-rift) and the Campanian (post-rift). Analytical data suggest that most likely dolomitizing fluid is evolved Aptian/Albian seawater, probably mixed with basinal waters. The resulting replacive dolomite texture has very low porosity, mainly of vuggy type, that was successively enhanced by dissolution and occluded by burial dolomite and calcite cementation during Late Cretaceous. Dolomite hosted Mississipi Valley-type ore deposits, and associated saddle dolomite, formed due to hydrothermal alteration through large-scale faults during the onset of the Tertiary. Later Alpine uplift and fracturing promote meteoric calcite cementation and dedolomitization through fractures and fault zones. Porosity and permeability data evidence a very bad potential reservoir quality of the host limestone, being only slightly higher in the dolomites due to the reported pervasive burial calcite cementation. Results provide a new case study of partial dolomitization that can be used in the characterization of equivalent hydrocarbon reservoirs worldwide.