CARBON-ISOTOPE SIGNATURE OF ENVIRONMENTAL-CHANGE FOUND IN FOSSIL RATITE EGGSHELLS FROM A SOUTH ASIAN NEOGENE SEQUENCE

A > 10-m.y.long sequence of ratite (e.g., ostrich) eggshells from Siwa lik Group sedimentary deposits of northern Pakistan and India shows a dramatic (approximately 8 parts per thousand) increase in the deltaC-1 3 in biomineralogic calcite by approximately 4 Ma. Values of deltaC-13 from ratite eggshell carbonate older than 7 Ma are about the same as those from carbonate from contemporaneous fossil mammal tooth enamel a nd paleosols. However, after 4 Ma, the ratite eggshell carbonate delta C-13 values are approximately 5 parts per thousand less than these coe xisting materials. These findings are evidence of the development of a C3-C4 vegetative mosaic probably mirroring the sedimentologic-edaphic mosaic of the aggrading alluvial plain of the Siwalik depositional sy stem.