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摘要
A mid-Pliocene fauna (4.2-3.1 Ma) was recently uncovered in the Zanda (Zhada) Basin in the southwestern Himalaya, at an elevation of about 4200 m above sea level. These fossil materials provide a unique window for examining the linkage among tectonic, climatic and biotic changes. Here we report the results from isotopic analyses of this fauna and of modern herbivores and waters as well as paleo-temperature estimates from the Zanda Basin. The delta C-13 values of enamel samples from modern wild Tibetan asses, and domesticated horses, cows and goats in the area are -9.4 +/- 1.8 parts per thousand, which indicate a diet comprising predominantly of C-3 plants and are consistent with the current dominance of C-3 vegetation in the region. The enamel-delta C-13 values of the fossil horses, rhinos, deer, and bovids are -9.6 +/- 0.8 parts per thousand, indicating that these ancient mammals, like modern herbivores in the area, also fed primarily on C-3 vegetation and lived in an environment dominated by C-3 plants. The lack of significant C-4 plants in the basin suggests that the area had reached high elevations (>2.5 km) by at least the mid-Pliocene. Taking into account the changes in the delta C-13 of atmospheric CO2 in the past, the enamel-delta C-13 values suggest that the average modern-equivalent delta C-13 value of C-3 vegetation in the Zanda Basin in the mid-Pliocene was similar to 1-2 parts per thousand lower than that of the C-3 biomass in the basin today. This would imply a reduction in annual precipitation by about 200-400 mm in the area since then (assuming that the modern C-3 delta C-13-precipitation relationship applied to the past). Consistent with this inference from the delta C-13 data, the enamel-delta O-18 data show a significant shift to higher values after the mid-Pliocene, which also suggests a shift in climate to much drier conditions after similar to 4-3 Ma. Paleo-temperature estimates derived from a fossil bone-based oxygen isotope temperature proxy as well as the carbonate clumped isotope thermometer for the mid-Pliocene Zanda Basin are higher than the present-day mean annual temperature in the area. After accounting for late Cenozoic global cooling, these paleo-temperature estimates suggest that the paleo-elevation of the Zanda Basin in the mid-Pliocene was similar to or slightly (less than similar to 1 km) lower than its present-day elevation, which is consistent with the inference from the delta C-13 data.
- 出版日期2013-8-15
- 单位中国科学院古脊椎动物与古人类研究所
