Fracturing and calcite cementation controlling fluid flow in the shallow-water carbonates of the Jandaíra Formation,Brazil |
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| Institution: | 1. Faculty of Earth and Life Sciences, Sedimentology and Marine Geology Group, VU University Amsterdam, De Boelelaan 1085, Amsterdam 1081HV, The Netherlands;2. Department of Geoscience and Engineering, Delft University of Technology, Stevinweg 1, Delft 2628CD, The Netherlands;3. Departamento de Geologia, CCET, Federal University of Rio Grande do Norte, Natal, RN, 59078-970, Brazil;4. Petrobras Research and Development Center, CENPES, Av Horácio de Macedo 950, Cidade Universitária, Rio de Janeiro, Brazil;5. Max Planck Institute of Chemistry, Hahn-Meitnerweg 1, 55218 Mainz, Germany;6. King Fahd University of Petroleum and Minerals, College of Petroleum Engineering and Geosciences, Dhahran 31261, Saudi Arabia;1. University of Brasília, Institute of Geosciences, Campus Universitário Darcy Ribeiro, Brasília, CEP 70.910-900, DF, Brazil;2. PETROBRÁS – Centro de Pesquisa e Desenvolvimento, Ilha do Fundão, Rio de Janeiro, CEP: 21949-900, RJ, Brazil;3. The Natural History Museum, Cromwell Road, SW7 5BD, London, UK;4. Federal University of Rio de Janeiro, Department of Geology, Av. Brigadeiro Trompowski s/n, Rio de Janeiro, CEP 21914-900, RJ, Brazil;5. School of Earth Sciences and Resources, China University of Geosciences, Xueyuan Road, Haidian Distirct, Beijiing, 100083, China;1. Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK;2. Department of Sciences, University of Basilicata, Italy;3. Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari Aldo Moro, Italy;1. Programa de Pós-graduação em Análise de Bacias e Faixas Móveis, Universidade do Estado do Rio de Janeiro (UERJ), Faculdade de Geologia, Rua São Francisco Xavier, 524, sala 2032A, 20550013, Maracanã, Rio de Janeiro Brazil;2. Programa de Pós-graduação em Geologia, Universidade Federal do Rio de Janeiro (UFRJ), Departamento de Geologia, Laboratório de Macrofósseis, Av. Athos da Silva Ramos, 274, 2194191, Ilha do Fundão, Rio de Janeiro, Brazil;3. Universidade Federal do Rio de Janeiro (UFRJ), Departamento de Geologia, Laboratório de Macrofósseis, Av. Athos da Silva Ramos, 274, 21941916, Ilha do Fundão, Rio de Janeiro, Brazil |
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| Abstract: | The shallow-marine carbonate rocks of the Jandaíra Formation have been subject to significant permeability variations through time due to various events of fracturing and calcite cementation. As a consequence, the Jandaíra Formation accommodated fluid flow only during specific moments in time. We reconstructed these episodes of fluid flow based on isotope characterizations and microscope characteristics of calcite veins and host rock cements. The Jandaíra Formation, which belongs to the post-rift sequence of the Potiguar Basin in northeast Brazil, was deposited from the Turonian onward until a marine regression exposed it in the Campanian. Due to the subaerial exposure, meteoric waters flushed out marine connate waters, leading to an event of early diagenesis and full cementation of the Jandaíra Formation. Fluid flow through the resulting impermeable carbonate formation appears to be closely related to fracturing. Fracturing in the Late Cretaceous induced a drastic increase in permeability, giving rise to extensive fluid circulation. Host rock dissolution associated to the circulating fluids led to calcite vein cementation within the fracture network, causing it to regain an impermeable and sealing character. In the research area, fluid flow occurred during early burial of the Jandaíra Formation at estimated depths of 400–900 m. This study documents the first application of fluid inclusion isotope analysis on vein precipitates, which allowed full isotopic characterization of the paleo-fluids responsible for calcite vein cementation. The fluid inclusion isotope data indicate that upwelling of groundwater from the underlying Açu sandstones provided the fluids to the fracture network. In Miocene times, renewed tectonic compression of a lower intensity created a secondary fracture network in the Jandaíra Formation. The density of this fracture network, however, was too low to induce a new episode of fluid circulation. As a result, this tectonic event is associated with the development of barren extensional fractures. |
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| Keywords: | Geochemistry Fluid inclusion isotope analysis Fracturing Calcite cementation Fluid flow Permeability Jandaíra formation Potiguar basin |
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