STABLE ISOTOPIC VARIATION OF THE GANGOLIHAT AND DEOBAN FORMATIONS IN GARHWAL-KUMAUN, NORTHWESTERN INDIA: IMPLICATIONS FOR THE CORRELATION OF THE LOWER LESSER HIMALAYAN STRATIGRAPHY

In northwest India, the age and stratigraphic correlations between two carbonate formations in the lower Lesser Himalayan stratigraphy, the Gangolihat in Kumaun, and Deoban in the Tons Valley of Garhwal, are controversial because fossil evidence is inconclusive. In this study, we report 50 new measurements of carbon and oxygen isotope abundance, and lithofacies variations in carbonate successions. Gangolihat carbonate sequence from Kumaun reveal δ¹³C values range between -2.6 and 1.1 ‰ with a mean of 0.4‰; whereas, in the Tons Valley the Deoban δ¹³C values are more positive, range between 1.4 and 5.6 ‰ with a mean of 3.7‰. δ¹⁸O values of Gangolihat Formation from Kumaun are ranging between -13.9 and -5.9 ‰ with a mean of -9.9 ‰; whereas, in the Deoban Formation from the Tons valley, the values range between -11.2 and 3.7 ‰ with a mean of -7.9 ‰. Clearly, the Gangolihat and Deoban Formations are two different chemostratigraphic units. The near 0‰ δ¹³C value of Gangolihat Formation (0.4‰) suggests that it is certainly older than ca. 1300 Ma, and likely Paleoproterozoic in age. The positive δ¹³C values of the Tons valley Deoban Formation suggest that it is probably younger than the Gangolihat Formation. In the Tons Valley, the Deoban Formation is underlain by ca. 1800 Ma Dhargad Quartzite (equivalent to the Berinag Formation); whereas, in Kumaun, the Gangolihat Formation is overlain by ca. 800 Ma quartzite.Carbonate isotope signatures of these two formations are markedly different than the extensively studied Neoproterozoic Krol Formation, which preserve large negative and positive δ¹³C values. Thus, in northwest India, the Deoban and Gangolihat Formations must be mapped as separate formations and not continuous along strike, and they are not equivalent to the Krol Formation.