柴达木盆地全球末次冰期介形类动物群的演变

EVOLUTION OF OSTRACODA OF THE GREAT ICE AGE OF LAST GLACIAL STAGE IN QAIDAM BASIN

晚更新世晚期 ,柴达木盆地达参 1井井深 4 6m以下的沉积物内 ,水生生物化石有很高的丰度和分异度。介形类为Cyprideistorosa- Ilyocyprisinermis组合 ,伴生有轮藻类、腹足类、双壳类、植物和鱼类等化石。井深 4 6～ 10m ,为全球末次冰期盛冰阶 (2 5～ 10kaB P )沉积 ,当时气候极端干冷 ,出现干盐湖地质事件 ,沉积物由湖相泥岩迅速演变为石盐层 ,生物化石罕见 ,几近绝迹。平均 4 0m厚的石盐沉积遍及三湖 (台吉乃尔湖、达布逊湖和霍布逊湖 )地区 ,形成了该区天然气赖以保存的最后一道屏障———天然气藏的盖层。井深约10m以上 ,为全新世暖期或称现代间冰期沉积物 ,渐变为浅湖相泥岩和粉砂岩夹膏盐沉积。当时处于氧同位素阶段 1,湖水盐度逐渐降低 ,水生生物丰度和分异度再度增高 ,介形类更替为半咸水—淡水Candonaneglecta- Candoniellalactea组合 ,伴生有丰富的轮藻、腹足类、双壳类等。直到现代 ,台吉乃尔湖、达布逊湖和霍布逊湖以南由于受昆仑山充足的淡水补给影响 ,水生生物丰富。三湖以北 ,远离主要淡水补给区 ,水体较咸 ,介形类则为典型的盐湖介形类Eucyprisinflata所替代 ,膏盐沉积比三湖以南明显增多。

The aquatic biota from the late Late Pleistocene was sampled below 46 m in the Well Dacan 1 of Qaidam Basin.They showed a high abundance and high diversity. The ostracoda was Cyprideis torosa-Ilyocypris inermis assemblage and associated with Charophyta, Gastropoda, Pelecypoda, plants and fishes. The sediments from 46～10 m depth in Well Dacan 1 were deposited in the Great Ice Age of the Last Glacial Stage. In that time, the climate was rather arid and icy, so the playa occurred. The sediments rapidly developed from lake facies mudstone to halite. It was hard to find fossils,and most of biota disappeared completely. The Three-Lake Depression (Taijinaier Lake,Dabuxun Lake and The Huobuxun Lake ) was entirely covered by about 40 m of salt bed, which acted as the last cap layer for natural gas, namely the cover of the gas reservoir.The sediments above 10 m in the Well Dacan 1 were gradually changed into shallow lake mudstone and siltstone gypsiferous salt,which were formed in the Holocene warm stage (modern interglacial stage), or the first stage of oxygen stable isotope. In this stage the salinity of the region decreased and the abundance and diversity of the biota increased again. The ostracoda was replaced by an assemblage of Candona neglecta-Candoniella lactea, which was adapted to the environment of the slight brackish and fresh water. It was also associated richly with Charophyta, Gastropoda, Pelecypoda,etc.Up to now, there has been abundant aquatic biota in the south of Taijinaier Lake,Dabuxun Lake and Huobuxun Lake because of the supply of freshwater from Kunlun Mountains. However, the water is relatively salty in the north of Taijinaier Lake,Dabuxun Lake and Huobuxun Lake owing to the great distance away from the main supply of freshwater. The ostracoda was replaced by the typical salty-lake ostracoda Eucypris inflata. assemblage. The distribution of gypsum-halite beds in the north is obviously more than that in the south of Taijinaier Lake,Dabuxun Lake and Huobuxun Lake.