Fracture-Related Dolomitization Affecting Late Jurassic—Lowermost Cretaceous Syn-rift Deposits (Maestrat Basin, Southern Iberian Chain, Eastern Spain)

Abstract

Late Jurassic-lowermost Cretaceous limestones and dolomites are oil reservoirs in the offshore Mediterranean field. Because the same dolomitization process exists in the neighboring onshore Maestrat basin, a thorough understanding of the dolomitization model will help greatly in understanding the reservoir properties. The studied dolomites are Ca-rich, Mn, Sr and Na-poor, with a variable content of Fe, and are attributed to multiple dolomitization events at various temperatures and/or from fluids with variable d18 OSMOW values. The fluid inclusions indicate the contribution of deep basin brines. Mg was provided by partial dissolution of Triassic and Liasic carbonates and evaporites, together with the expulsion of crystallization water from clay minerals. Dolomitization occurred in still porous and poorly compacted limestones, simultaneous with the earliest Cretaceous syn-rift re-structuration, giving rise to a significant subaerial exposure of the uplifted blocks, with the development of a well developed erosive surface on top of the Berriasian successsion.