PALEOCLIMATE AND PALAEOVEGETATION IN CENTRAL INDIA DURING THE UPPER CRETACEOUS BASED ON STABLE-ISOTOPE COMPOSITION OF THE PALEOSOL CARBONATES

The oxygen isotope compositions of the pedogenic carbonates formed on the sediments of the Lameta Formation of Central India during the Upper Cretaceous range from -6.7 to -8.9 parts per thousand. Estimates of the oxygen isotope composition of the soil-water in equilibrium with the carbonates suggest average meteoric water composition of -8 parts per thousand. This value is considerably lighter compared to the modern precipitation in Central India (-3 parts per thousand). The lighter oxygen isotope composition can be explained in terms of cumulative effects of highly seasonal (monsoon-like) climatic regime in a rain shadow zone and a more pronounced ''continental effect'' due to a bigger size of Cretaceous India. The carbon isotopic compositions of the Lameta carbonates range from -7.1 to -10.7 with an average of -9.1 parts per thousand suggesting pedogenesis in soils dominated by C-3 type of vegetation. The estimated average composition of the vegetation is about 3 parts per thousand enriched compared to the modern day C-3 vegetation. This is probably due to atmospheric influence contributing about 15% of the total CO2 in the soil. An analysis of this contribution using the model of Cerling (1991) indicates that the partial pressure of CO2 in the Late Cretaceous atmosphere was 800-12,000 ppmV.