Petrography, carbon (δ13C) and oxygen (δ18O) isotope geochemistry of the Proterozoic Sirban Limestone Formation, NW Himalaya, India

Abstract

The Sirban Limestone Formation (SLFm) dolostones cropping out in the Riasi Allochthon (NW Himalaya, Jammu, India) show a range of δ¹³C (−1.08 to 0.73‰) and δ¹⁸O (−11.50 to −7.82‰) values and the mean values of 0.15‰ and −9.12‰ Pee Dee Belemnite (PDB), respectively. The δ¹³C values indicate that these dolostones were deposited during Neoproterozoic, and the δ¹⁸O values also are very close to the average Mesoproterozoic carbonate values obtained from the coeval carbonates. The characteristic δ¹³C values have the potential to provide an age constraint for the SLFm, and the mean δ¹⁸O value is comparable to the ‘best preserved’ δ¹⁸O mean value (−7.5 ± 2‰) reported for most of the Meso-Neoproterozoic to Early Cambrian carbonates. δ¹³C vs. δ¹⁸O plot for the SLFm suggests normal marine origin with late-stage cementation. In the present study, stable isotope geochemistry of the SLFm dolostones is attempted. Preliminary data on the major-and-minor elemental composition of SLFm has also been presented. In addition, several petrographic facies identified in the SLFm have also been documented here. Diagenesis characterisation of these facies show dolomitization represents an important phase in the early diagenesis process. The subsequent diagenetic stages range from early seafloor cementation to late-stage tectonic stylolitisation, which have obliterated the original textures to dominant diagenetic textures, also reflected in the δ¹³C and δ¹⁸O values. Similar isotope profiles can be potentially significant for the chemostratigraphic correlation of different sections within the Riasi Allochthon and coeval equivalents regionally and globally.