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Clumped isotope studies of cap
carbonate rockes overlying Pc-C
glacial diamictites of Blaini
Formation, Lesser Himalaya, India:
Evidence for amelioration and post
depositional alteration
MIKHAIL V. VASILIEV,1 PROSENJIT GHOSH,1 R. SRINIVASAN2,
R. ISLAM3, KESAR SINGH3 AND ANIL K. GUPTA3
1
Devicha Centre for Climate change, Indian institute of
Science, Bangalore, India
2
Centre for Atmospheric and Oceanic Sciences, Indian
Institute of Science, Bangalore
3 Wadia Institute of Himalayan Geology, Dehradun, India
Drastic release of methane into atmosphere is considered as
an important factor for green house warming that terminated
Neoproterozoic “Snowball Earth” event Ca. 635 Ma. Highly
depleted 13C signature in post-glacial cap dolostones is
interpreted as a product of methane oxidation at the time of
precipitation. Application of carbonate clumped thermometry
to the cap carbonates provides new constraints on the origin
of the carbonate bodies which have been subjected to post
depositional diagenetic or metasomatic alterations. This
thermometer can be used to estimate the temperature of
carbonate precipitation and the 18O of the fluids from which
carbonates grew. In this work, we have analyzed carbonate
samples from the cap dolomites that immediately overlie the
Blaini glaciogenic diamictites of Mussoorie syncline of the
Lesser Himalaya which are considered to represent glaciation
event during PC-C transition in Indian geology. The cap
carbonate rock is dominantly micritic with veins of sparry
carbonate. Micritic part of the samples yield 47 values
ranging from 0.518‰ to 0.207‰. The sparry carbonate from
the veins yield 47 in the range from 0.3 to 0.1‰.
Temperatures calculated for micritic carbonates following
Ferry et al [1] vary from 40o to 209°C and for vein carbonate
the range is between 120oC to 300oC. The 18O of fluids
responsible for the micritic carbonate precipitation show
variability between -5 to 0.6 ‰, which reflects signature of
glacial or meteoric water. The 13C signature recorded ranges
between –1.5 to –2.5 ‰ and is in agreement with data from
the previous workers [2], [3]. Higher temperatures recorded
in some of our carbonate samples point to two possible
processes like disequilibrium precipitation during late
diagenesis or high temperature fluid interaction at the time of
Himalayan orogeny.
[1] Ferry et al., Geology, 39(6) 571-574 (2011). [2] Kaufman
et al., Precambrian Research 147 (2006) 156–185. [3]
Bristow et al., 2011; Nature10096.