新疆孔雀河北岸72～51 ka BP湖相沉积物的孢粉植物群初步研究

Palynoflora of lacustrine sedimentation in the northern margin of the Kongqi River,Xinjiang from 72-51 ka BP

对新疆孔雀河北缘的LX02剖面湖相沉积物开展了OSL测年和孢粉记录研究。结果显示:该剖面湖相沉积自72. 4 ka BP延续到51. 0 ka BP。这一期间,研究区为针叶、阔叶混交林植被,林下生长灌木和草本,低洼潮湿的地方生长蕨类孢子和藻类。植被的主要类型有松(Pinus)、栎(Quercus)、栗(Castanea)、榛(Corylus)、莎草(Cyperaceae)、蒿(Artemisia)、藜(Chenopodiaceae)、水龙骨科(Polypodiaceae)等,同时还含有少量的山核桃(Carya)和枫杨(Pterocarya)等亚热带的孑遗植物花粉。具体来说,组合带Ⅰ(72. 4~66. 8 ka BP)、Ⅲ(56. 1~51. 0 ka BP)对应的沉积期间,研究区阔叶树花粉含量低而灌木和草本花粉含量高;组合带Ⅱ(66. 8~56. 1 ka BP)对应的沉积期阔叶树花粉含量都较高,而灌木和草本花粉相对较低,揭示72. 4~51. 0 ka BP研究区气候总体上呈现冷干—暖湿的气候波动特征。这与粘土矿物和地球化学特征所反映的古气候特征及其变化一致,亦与柴达木盆地东部介形类丰度特征研究、柴达木盆地东部古湖泊高湖面光释光年代学研究、北京平原区有机碳同位素研究等结果吻合较好,然而,这一气候变化规律的内部驱动机制还有待进一步的深入研究。

In this paper, the author chose LX02 section of the lake sedimentary with a thickness of 5.4 meters which located at the north margin of the Kongqi River in south Xinjiang, China, as the research object. From the top down to the bottom, six Optically Stimulated Luminescence （OSL） ages were achieved as follows 53.1 ± 4.4 ka BP at0.18 m,56.1± 3.2kaBPatl.19m,57.9±3.3kaBPat2.21m,60.5±4.0kaBPat3.10m,67.0±6.0ka BP at 3.71 re,and 71.0 ±3.6 ka BP at 4.69 m. The chronology sequence of the LX02 section was established on 60SL age results from 72 ka BP to 51 ka BP. In the meanwhile ,80 pollen samples were analyzed and 13 541 grains of pollen and spores were identified （ 169 grains/sample on average）. A total of 47 spore and pollen types were identified. On the whole, arboreal pollen taxa were dominant in most of the samples, ranging from 18.91% to 91. 03% in abundance with an average of 58.20%. Shrubs and herbs were less dominant,fluctuating between 8.97% and 60.12% in abundance and averaging at 35.02%. Fern spores and algae ranged from 0.00% to 13.64% in content and had a mean of 6.78%. These indicated that, during the deposition of this section, the study area was generally covered continuously by coniferous and broadleaved forests, under which various shrubs and herbs grew vigorously. Ferns and algae mainly distributed in some low-lying humid places within the study area. The main vege- tational types included Pinus, Quercus, Castanea, Corylus, Cyperaceae, Artemisia, Chenopodiaceae, and Polypodiace- ae. There were also some Carya and Pterocarya, and these subtropical types occurred commonly with low and erratic percentages. Specifically, the palynoflora of section was divided into three stages according to the variation of major pollen type and B. T. P. / （ S. 19. ＋ H. P. ） ： in zones Ⅰ （72.4 - 66.8 ka BP）, Ⅲ （ 56.1 - 51.0 ka BP）, the broadleaved arboreal pollen was always low in abundance while the shrub and herb pollen was usually high. In zone Ⅱ （66.8 -56.1 ka BP） ,the broadleaved tree pollen was generally high and the shrub and herb pollen was low on the whole. This indicated the characteristics of climate fluctuate in the study area between dry-cold and humid-warm patterns during the Late-Pleistocene period. This mode of climate change in the study area is not only well correlated with the changes of weathering intensity revealed by the character of clay mineral and geochemistry, but also well matched with the Ostracoda abundance in upper well Dacanl located in the southeast Qaidam Basin, Luminescence Chronology of High Lake levels of Paleolakes in the Late Quaternary eastern Qaidam Basin, Organic Carbon Isotopic characteristics of Beijing Plain. Nevertheless, the internal forcing mechanism for this mode of climate changes in the study area remains unclear up to now and deserves further investigation.