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灵台红粘土-黄土剖面钙质结核的碳同位素记录表明:在东亚季风区,C_4植被至少在7.0Ma时已经存在;从4.0Ma开始,C_4植被逐渐扩张,但并未达到主导地位。与低纬地区相比,本区C_4植被的扩张滞后约3.0 Ma;晚中新世以来北美北纬37°以北地区C_4植被扩张要滞后于北纬37°以南地区,在东亚大陆区,此分界线似乎要更加靠南。从约2.0 Ma以来,黄土高原C_4植被又明显减少,这说明除CO_2含量和温度变化外,可能还有其他因素在对C_3/C_4植被的转换起一定作用。
Carbon isotope records of the calcareous nodules in the Lingtai red clay-loess section indicate that C_4 vegetation existed at least at 7.0 Ma in the East Asian monsoon region. From 4.0 Ma, the C_4 vegetation gradually expanded but did not reach the dominant position. Compared with the low latitude region, the C_4 vegetation in this area has a lag of about 3.0 Ma. Since the Late Miocene, the expansion of C_4 vegetation in north latitude 37 ° north latitude lags behind that of the south 37 ° north latitude. In East Asia, The border seems to be more south. From about 2.0 Ma, the C_4 vegetation in the Loess Plateau decreased obviously again, indicating that besides the CO_2 content and the temperature change, there may be other factors that play a role in the conversion of C_3 / C_4 vegetation.