Saddle dolomite and calcite cements as records of fluid flow during basin evolution: Paleogene carbonates,United Arab Emirates |
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| Institution: | 1. ADCO, P.O. Box 270, Abu Dhabi, United Arab Emirates;2. Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada;3. Department of Petroleum Geosciences, The Petroleum Institute, P.O. Box 2533, Abu Dhabi, United Arab Emirates;4. Department of Geology, United Arab Emirates University, Al Ain, United Arab Emirates;5. Ingrain Company, Abu Dhabi, United Arab Emirates;6. Department of Earth Sciences, University of Oslo, Oslo, Norway;7. Soran University, Faculty of Science, Department of Petroleum Geosciences, Iraq;1. College of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan, China;2. PetroChina Southwest Oil and Gas Field Company, Chengdu 610051, Sichuan, China;1. College of Earth Science & Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China;2. Exploration and Development Research Institute, PetroChina Southwest Oil & Gas Field Company, Chengdu, Sichuan 610041, China;3. Chuanzhong Division of PetroChina Southwest Oil & Gas Field Company, Suining, Sichuan 629000, China;1. Departament de Geologia, Facultat de Ciències, Universitat Autònoma de Barcelona, Edifici Cs s/n, 08193 Bellaterra, Cerdanyola del Vallès, Spain;2. Departamento de Cristalografía y Mineralogía, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, c/ José Antonio Novais s/n, 28040, Madrid, Spain |
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| Abstract: | Field observations indicate that tectonic compression, anticline formation and concomitant uplift events of marine Paleogene carbonates in eastern United Arab Emirates, which are related to the Zagros Orogeny, have induced brecciation, karstification, and carbonate cementation in vugs and along faults and fractures. Structural analysis, stable isotopes and fluid inclusion microthermometry are used to constrain the origin and geochemical evolution of the fluids. Fluid flow was related to two tectonic deformation phases. Initially, the flux of moderately 87Sr-rich basinal NaCl–MgCl2–H2O brines along reactivated deep-seated strike-slip faults have resulted in the precipitation of saddle dolomite in fractures and vugs and in dolomitization of host Eocene limestones (δ18OV-PDB ?15.8‰ to ?6.2‰; homogenization temperatures of 80–115 °C and salinity of 18–25 wt.% eq. NaCl). Subsequently, compression and uplift of the anticline was associated with incursion of meteoric waters and mixing with the basinal brines, which resulted in the precipitation of blocky calcite cement (δ18OV-PDB ?22‰ to ?12‰; homogenization temperatures of 60–90 °C and salinity of 4.5–9 wt.% eq. NaCl). Saddle dolomite and surrounding blocky calcite have precipitated along the pre- and syn-folding E–W fracture system and its conjugate fracture sets. The stable isotopes coupled with fluid-inclusion micro-thermometry (homogenization temperatures of ≤50 °C and salinity of <1.5 wt.% eq. NaCl) of later prismatic/dogtooth and fibrous calcites, which occurred primarily along the post-folding NNE–SSW fracture system and its conjugate fracture sets, suggest cementation by descending moderately 87Sr-rich, cool meteoric waters. This carbonate cementation history explains the presence of two correlation trends between the δ18OV-PDB and δ13CV-PDB values: (i) a negative temperature-dependent oxygen isotope fractionation trend related to burial diagenesis and to the flux of basinal brines, and (ii) positive brine-meteoric mixing trend. This integrated study approach allows better understanding of changes in fluid composition and circulation pattern during evolution of foreland basins. |
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| Keywords: | Fracture-filling carbonates Hot basinal brines Fluid flow Dolomitization Tectonic evolution |
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