Geochemistry of Neoproterozoic shales of the Rabanpalli Formation, Bhima Basin, Northern Karnataka, southern India: implications for provenance and paleoredox conditions

  • Ramasamy Nagarajan Department of Geology, Anna University, Chennai 600025, India. Present address: School of Civil Engineering, SASTRA, Deemed University, Thirumalaisamudram, Tanjavur, India.
  • Jayagopal Madhavaraju Estacion Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, Apartado postal 1039, 83000 Hermosillo, Sonora, Mexico.
  • Raghavendra Nagendra Department of Geology, Anna University, Chennai 600025, India.
  • John Selvamony Armstrong-Altrin Centro de Investigaciones en Ciencias de la Tierra, Universidad Autónoma del Estado de Hidalgo, Ciudad Universitaria, Carretera Pachuca-Tulancingo km. 4.5, 42184 Pachuca, Hidalgo, Mexico.
  • Jacques Moutte Centre SpiNC, Ecole des Mines, 158 cours Fauriel, F 42023, Sant-Etienne, France.
Keywords: geochemistry, shale, provenance, paleo-oxygenation conditions, Rabanpalli Formation, Bhima Basin, India.

Abstract

The Rabanpalli Formation exhibits two types of shales, viz. grey and calcareous shales. These shales (grey and calcareous) have been analysed for major, trace, and rare earth elements to find out their source rocks characteristics and paleo-oxygenation conditions. The grey shales have higher concentration of SiO2, Al2O3, Fe2O3, K2O, Zr, Th, U, V, Cr, La, Ce, and Y than calcareous shales, whereas calcareous shales are enriched in CaO, Mn, Sr, Ba, Cu, and Zn, which indicate that the carbonate phase minerals are higher in calcareous shales. The positive correlation of K2O with other elements, and abundance of Al2O3, Ba, Th, and Rb suggest that these elements are primarily controlled by the dominant clay minerals. La/Sc, Th/Sc, Th/Co, Th/Cr, and Cr/Th ratios of shales were compared with those of sediments derived from felsic and basic rocks (fine fraction), upper continental crust (UCC) and post-Archean Australian average shale (PAAS) ratios, which reveal that these ratios are within the range of felsic rocks. The La/Sc vs. Th/Co plot also suggests the felsic nature of the source rocks. The shales show slightly light rare earth element (LREE) enriched and flat heavy rare earth element (HREE) patterns with negative Eu anomaly, and are similar to the granitoids from Dharwar Craton, which suggest that the Archean Dharwar Craton contributed the sediments to the Bhima basin. The geochemical parameters such as U, authigenic U, U/Th, V/Cr, Ni/Co, and Cu/Zn ratios indicate that these shales were deposited under oxic environment.

Published
2018-02-09
Section
Articles