5/31/2023 0 Comments Dark fracture platformsDuring the Early to Late Jurassic, the western margin of Morocco was a passive margin, and carbonate deposition in the basin took place in a subtropical to arid climate 9, 10. The Essaouira–Agadir Basin (EAB) is located in south-western Morocco (Fig. It provides a unique opportunity to map dolomite body geometries and their associated dolomitization fronts in a single location in order to: (1) decipher the controls on the position of dolomitization fronts (2) understand the potential control of salt-related deformation to dolomitization (3) explore the relationship between reaction fronts, mechanical deformation and diagenesis in a partially dolomitized carbonate platform. This study is based on a Lower Jurassic carbonate platform that outcrops in part in the salt-cored Amsittene Anticline, Essaouira-Agadir Basin (EAB), Western Morocco (Fig. Nevertheless, the controls on their occurrence and position have received remarkably little attention. Previous studies have demonstrated that these reaction fronts can control the spatial variability of porosity 5, 6 and the accumulation of ore minerals 7, 8. These bodies can have distinct dolomite–limestone reaction fronts 2, 3, 4, 5. These findings have implications to the prediction of structurally controlled diagenetic processes and the exploration of naturally fractured carbonate reservoirs for energy exploration globally.ĭolomitization can lead to the formation of distinct dolomite bodies which can influence the storage capacity and heterogeneity of hydrocarbon, ore and CO 2 storage reservoirs. These events modified rock properties in such a way that fluid flow was repeatedly focused along the original dolomite-limestone boundary, overprinting much of its original signature. The results demonstrate that an apparently simple reaction front can have a complex history, governed by the inheritance of prior diagenetic events. Karstification subsequently exploited these fracture corridors, widening fractures and leading to localized collapse and brecciation. The fracture corridors are interpreted to exploit dolostone-limestone boundaries, forming prior to a later, higher temperature, hydrothermal dolomitization event, which coincided with the formation and growth of the anticline. The termination of dolomite formation is therefore interpreted to be associated with a decrease in the capacity of the magnesium-rich fluids to dolomitize the rock, as indicated by the presence of non-stoichiometric and poorly ordered dolomite at the reaction fronts. The stratabound dolomite bodies apparently terminated at a fracture-bound contact, but the presence of dolomite fragments within the fracture corridor suggests that fracturing post-dated the first dolomitization event. These patterns, coupled with a decrease in porosity, increase in ∆ 47 temperature and δ 18O water values indicate multiphase recrystallization and stabilization by warm, Mg-rich fluids. Here, consistent patterns of increasing dolomite stoichiometry and ordering, along with a change from seawater-derived, fabric-retentive dolomite to fracture-controlled, fabric-destructive hydrothermal dolomite are observed vertically across the stratabound dolomite bodies. This paper provides a detailed documentation of reaction front evolution in a tectonically active salt basin and reveals a high level of complexity, associated with multiple fluid flow and tectonic events. Recent work has demonstrated the significance of paleo-reaction fronts to decipher multiphase recrystallization processes and provide high porosity zones. They have not been extensively studied, perhaps because they appear simple in outcrop. Diagenetic boundaries are paleo-reaction fronts, which have the potential to archive the termination of metasomatic processes in sedimentary rocks.
0 Comments
Leave a Reply. |