洞穴石笋沉积旋回主要特征的古气候环境研究

A Paleoclimate Environment Study on the Main Characteristics of Sedimentary Cycles in Stalagmite

通过对我国南方大型石笋组分、结构构造的观测和董哥洞10号（D10）石笋210件碳、氧同位素组成、20个U系测年数据,以及部分微（痕）量元素的分析对比,概述了石笋沉积旋回性特征、旋回界面类型和相关的气候、环境、地质意义。以组成D10石笋的碳酸盐含碳质、黏土矿物,呈黑灰、灰黄、灰白、灰等色泽匹配、纹层厚及组合、层面呈拱形或平直分别组合或转变、构造类型、碳氧同位素组成及其组合,呈协调平行、不协调同向、不协调反向变化三类型若干亚类等,旋回性特征,确定了19个沉积旋回。根据δ^13C平均值为-3.91‰PDB、δ18O为-6.97‰PDB分别为冷暖气候演变的临界（阀）值,δ^13C或δ^18O〉临界值者的偏重是冷,〈临界值的偏轻是热。以δ^13C、δ^18O组成（表1）和组合变化类型和上述旋回性特征,结合层面构造呈渐变过渡或突变,以及20个同位素年龄数据,初步认定荔波地区352 930-99 410年间沉积的19旋回,是一个较完整的冰期气候演化过程,属我国第四纪冰期系列的第五冰期,10旋回顶180 695年（推算）-15旋回顶129 890年,约5万多年是连续严寒的盛冰期,①、16分别可能是冰期早、晚时段相对温暖的间冰期。 期间冷暖变化有5万年级的、10万年级的气候旋回。论证了荔波地区35～10万年间是冰期气候环境，前期17万年寒冷的气候环境，期间35万年、25万年前后更严寒，但生态基本保持正常演变的面貌，中期5万多年为极寒冷的气候环境，生态向适应冷气候环境演化，晚期3万多年为冷暖频繁突（跃）变的恶劣气候，期间生态面貌复杂，正常演替与残存、突变演替并存。

We summarize the characteristics of sedimentary cycles,cycle interface types of some stalagmites and related significances in climatic,environmental and geological sciences.Before that,the components and structures of some typical large stalagmite in southern China were studied.Also 210 isotopic samples of δ13C,δ18O,20 samples for U series dating in D10 and some related trace elements were analyzed comparatively.According to the colors reflected by different impurities in carbonate,the lamina features and isotopic components of stalagmite in DIO, three cycling features which are accordant parallel,unaccordant parallel and unaccordant unparallel can be divided. 19 sedimentary cycles can be identified. The average δ^13C, δ^18O value -3.91‰PDB and -6.97 ‰PDB respectively represent the threshold values which indicate the evolution of cold and warm climate. Consequently, if the isotopic value is higher than the threshold value, it means the climate is in favor of cold conditions. According to the isotopic and cycle characteristics of the sedimentary, it is considered preliminarily that the 19 cycles deposited during the years from 352 930 to 99 410 in Libo area indicate a relatively complete process of the climate evolution in the fifth Ice Age of the Quaternary Ice Age series in China. The 50 000 years which is calculated from cycle 10 to cycle 15 is surmised as a continuous freezing glacial maximum. The cycle 1 and cycle 16 represents probably interglacial period which was relative warmer. Furthermore, there also existed 50 000 or 100 000 years scale climatic cycle during the period. It is demonstrated that there was glacial period in Libo area from 350 000 to 100 000 years ago. The prophase about 170 000 years was frigid climate, and during 3,50 000 years and 250 000 years period was even more frigid, however the ecological environment evolved normally. The metaphase about 50000 years was extremely frigid and the ecological environment evolved in favor of the arctic weather. The late stage about 30 000 years represented an extreme climate in which the abrupt change between cold climate and warm climate occurred frequently, the normal and mutational succession coexisted.