Palaeoclimate and palaeovegetation in central India during the Upper Cretaceous based on stable isotope composition of the palaeosol carbonate

Abstract

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‰. Estimates of the oxygen isotope composition of the soil-water in equilibrium with the carbonates suggest average meteoric water composition of -8‰. This value is considerably lighter compared to the modern precipitation in Central India (-3‰). 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‰ suggesting pedogenesis in soils dominated by C₃ type of vegetation. The estimated average composition of the vegetation is about 3‰ enriched compared to the modern day C₃ 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.