6533b831fe1ef96bd1298d7a

RESEARCH PRODUCT

Carbon isotope geochemistry and geochronological constraints of the Neoproterozoic Sirohi Group from northwest India

subject

description

a b s t r a c t The early Neoproterozoic carbonates of the Sirohi Group, northwestern India, were studied for geochronology as well as for oxygen and carbon isotopes across three different sections to understand their relationship with contemporaneous global events. New single zircon Pb-Pb evaporation data con- strain the age of the Sirohi Group between ca. 920 and ca. 820 Ma, though actual span for deposition of the carbonates may be little shorter taking into allowance the time for peneplanation. Narrow range in variation of 18O values is generally observed in the carbonate which is consistent with generally well-preserved original compositions. Two sections (SA and SS) out of the three that were studied had similarly small variations in 18 O (about 2‰), whereas the third section (SN) had a slightly wider range of 18O (around 5‰). The 18O values of the SN section varied between −11.9 and −17.6‰, which can be attributed to marginal modifications in primary composition caused by contact metamorphism which is evident by the occurrence of wollastonite in the carbonates. The 13 Ccarb values of these carbonates varied between −4.1 and +4.7‰ in all sections. Positive and near-zero 13Ccarb values are from SA and SS sections which are least affected by the metamorphism. The 13 Ccarb values of these two sections are interpreted as primary and can be correlated with contemporary sea-water compositions. The SN section showed negative 13