新疆天山北坡地区中晚全新世古生物多样性特征

PALAEO-BIODIVERSITY AT THE NORTHERN PIEDMONT OF TIANSHAN MOUNTAINS IN XINJIANG DURING THE MIDDLE TO LATE HOLOCENE

选择新疆天山北坡不同海拔高度、不同植被带和不同沉积年代的大西沟、桦树窝子、小西沟、东道海子和四厂湖剖面计算孢粉复合分异度指数,并根据已发表的有关文献中关于粒度、磁化率、烧失量等多项分析的数值整合结果探讨了本区中晚全新世以来生物多样性的时空变化和环境特征。森林草原过渡带的古生物多样性远高于高山、亚高山草甸带和荒漠带,孢粉复合分异度较高,鉴定的孢粉科属数较多。3600～3200aB.P.、1700～1400aB.P.、1000～600aB.P.和450aB.P.以来4个时段的生物多样性偏高。大西沟地区3600～3200aB.P.期间和四厂湖地区中世纪期间气候均较湿润,其古生物多样性也较高,可见古环境演变和古生物多样性的动态变化具有相对一致性,孢粉复合分异度指数在一定程度上可以反映气候与环境的变化。但由于孢粉鉴定的精确度较差、受外来花粉的干扰等多种因素影响,使得孢粉多样性指数在反映生物多样性和古环境方面存在一定的偏差。

Palaeo-biodiversity and environmental characteristics in the Mid- and Late Holocene were investigated in five profiles from Daxigou, Huashuwozi, Xiaoxigou, Dongdaohaizi and Sichanghu, which are located at different elevations and in different vegetation zones on the northern piedmont of Tianshan Mountains, Xinjiang. Selected profiles were located at three vegetation zones. The first was the .alpine and sub.alpine meadow vegetation zone （2 700- 3 400 m）. Thirty-eight genera and families were identified in the Daxigou profile （3 450 m）. Pollen Simpson index was 2.72 -7.67 with a mean value of 4.84. The forest-steppe ecotone was from 1 200 - 1 600 m elevation. Forty-two pollen genera and families were identified in the Huashuwozi profile and 39 in the Xiaoxigou profile at this vegetation zone. The pollen Simpson index of Huashuwozi profile was 4.2- 12.4 with a mean value of 7.8, and that of Xiaoxigou profile was 4.13 - 12.06 with a mean value of 6.89. The last two profiles were located in the typical desert zone （400- 600 m）. Thirty-two pollen genera and families were identified in Dongdaohaizi profile and 35 in Sichanghu profile. The pollen Simpson index of Dongdaohaizi profile was 1.8 - 18.8 with a mean value of 6.62. The pollen Simpson index of Sichanghu profile was 4.1 - 9.0 with a mean value of 5.55. These results showed that Holocene biodiversity and the pollen Simpson index were the highest in profiles from the desert-steppe vegetation zone. Our analysis also showed that four periods （3600 - 3200 aB. P., 1700 - 1400 aB. P., 1000 - 600 aB. P., and 450 aB. P. ） had the highest pollen Simpson index and highest biodiversity on the northern piedmont of Tianshan Mountains in Xinjiang. Thus, the pollen Simpson index reflects climatic and environmental changes to a certain extent. However, biases exist due to the influence of buried pollen assemblages, low precision in pollen identification - to genera and family levels only, influx of exotic pollen and human disturbances. Pollen that had low representation in the profiles was not taken into account in calculating the biodiversity index, which might underestimate overall palaeo-biodiversity. Due to different abilities of pollen dispersal and transportation, there is high spatial variation in the number of pollen taxa at different sites within the same research district. In addition, sediment composition, strata chronology and human activities have great impacts on pollen preservation, which also affect our ability to estimate palaeo-biodiversity. All in all, this research showed that the pollen Simpson index is an important index of palaeo-biodiversity and the paleoenvironment, but more research is needed.