Revista Mexicana de CienciasGeochemistry Geológicas, v.of25, núm. 2, 2008,limestones, p. 225-235Bhima basin, Karnataka, India Neoproterozoic
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Carbon and oxygen isotope geochemistry of Neoproterozoic limestones of the Shahabad Formation, Bhima basin, Karnataka, southern India
Ramasamy Nagarajan1,2, Alcides N. Sial3, John S. Armstrong-Altrin4,*, Jayagopal Madhavaraju5, and Raghavendra Nagendra1 Department of Geology, Anna University, Chennai-600 025, India. Present Address: School of Civil Engineering, SASTRA University, Thirumalaisamudram, Thanjavur – 613 402, India. 3 Núcleo de Estudos Geoquímicos - Laboratório de Isótopos Estáveis (NEG - LABISE), Departmento de Geologia, Universidade Federal de Pernambuco, C.P.7852, Recife, PE, 50670-000 Brazil. 4 Universidad Autónoma del Estado de Hidalgo, Centro de Investigaciones en Ciencias de la Tierra, Ciudad Universitaria, Carretera Pachuca-Tulancingo Km. 4.5, 42184 Pachuca, Hidalgo, Mexico. 5 Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, Apartado Postal 1039, 83000 Hermosillo, Sonora, Mexico. *
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ABSTRACT Petrography, major (including four trace elements), stable isotopes (carbon and oxygen), and Sr/86Sr geochemistry of limestones of the Shahabad Formation, Bhima basin, Karnataka, southern India are reported. These limestones show a narrow range of δ13C (~1.34−1.96‰) and δ18O (~ -6.04 to -7.61‰) values. The petrographic study reveals the presence of microsparite and micro- and macrostylolites. The δ13C and 87Sr/86Sr values indicate that these limestones were deposited during the late Neoproterozoic age and the δ18O values also are very similar to the average Proterozoic carbonate values. Mn and Sr concentrations and low Mn/Sr ratio (
