天山北缘安集海河组湖相灰岩氧碳同位素变化的古环境意义
李骞+田孝茹+胡瀚文+郭召杰
摘要：渐新统安集海河组代表了天山新生代快速隆升之前北缘的湖相沉积，其顶部至上覆沙湾组沉积相变反映了天山隆升对周缘地区环境的影响。对安集海河剖面进行了实地测量，并对安集海河组湖相灰岩夹层进行系统采样，通过沉积相分析、氧碳同位素测定，还原安集海河组时期湖泊环境特征及末期的演变。结果表明：安集海河组整体属于典型的深湖和半深湖亚相沉积，顶部为滨湖沉积；该组δ18O值与δ13C值整体较高，δ18O值在中部偏高，下部和上部相似而较中部稍低，顶部显著偏负，δ13C值在中部明显偏负，下部变化较大但比中部稍高，上部显著偏正；区域气候资料与大气环流模拟表明，该时期氧碳同位素变化不受降水来源和季风等因素的影响。综合沉积相分析与氧碳同位素试验结果，安集海河组大部分时期气候以温暖湿润为主，末期接近沙湾组时期气温出现明显下降，气候变为干旱寒冷；全球平均气温在安集海河组末期未出现显著变化，因此，这一区域气候变化可能更多地与印度—亚欧板块碰撞远程效应导致的天山活化隆升有关。
关键词：古环境变化；安集海河组；新生代；湖相灰盐；氧碳同位素；沉积相；构造隆升；天山
中图分类号：P66；X141 文献标志码：A
Abstract： Oligocene Anjihaihe Formation in northern Tianshan represents lacustrine sedimentary before the rapid uplift of Tianshan in Cenozoic. The variation of sedimentary facies at the top of Anjihaihe Formation and overlying Shawan Formation indicates the influence of the uplift of Tianshan. Field measurement was carried out in Anjihaihe section， and lacustrine limestone was sampled from Anjihaihe Formation for sedimentary facies analysis and oxygen and carbon isotopes analysis. The lacustrine environment during Oligocene was reconstructed. Results reveal that Anjihaihe Formation is mostly formed in semi-deep to deep lacustrine environment and in shore environment at the top. δ18O values and δ13C values in Anjihaihe Formation are relatively higher than normal lakes； δ18O values of the middle part are slightly higher than those of lower and upper parts； at the top of Anjihaihe Formation， δ18O values drift negatively significantly. On the other hand， δ13C values are much higher in the upper and top than those in the middle and lower parts with few exceptions. Regional climatic data and simulation of atmospheric circulation indicate that the variation of isotope in Oligocene is not the result of air mass change and monsoons. Given the data of oxygen and carbon isotopes， along with sedimentary facies analysis， it is concluded that Anjihaihe Formation is characterized by a worm and humid environment while the subsequent top part witnesses an obvious fall in temperature and the climate turns cool and dry. Considering that global climate showes no distinct change at the end of Anjihaihe Formation， this regional change may be to a large degree relate to the active uplift of Tianshan caused by the far field effect of India-Eurasia Plate collision during Cenozoic.
Key words： paleoenvironment change； Anjihaihe Formation； Cenozoic； lacustrine limestone； oxygen and carbon isotopes； sedimentary facies； tectonic uplifting； Tianshan
0 引 言
摘要：渐新统安集海河组代表了天山新生代快速隆升之前北缘的湖相沉积，其顶部至上覆沙湾组沉积相变反映了天山隆升对周缘地区环境的影响。对安集海河剖面进行了实地测量，并对安集海河组湖相灰岩夹层进行系统采样，通过沉积相分析、氧碳同位素测定，还原安集海河组时期湖泊环境特征及末期的演变。结果表明：安集海河组整体属于典型的深湖和半深湖亚相沉积，顶部为滨湖沉积；该组δ18O值与δ13C值整体较高，δ18O值在中部偏高，下部和上部相似而较中部稍低，顶部显著偏负，δ13C值在中部明显偏负，下部变化较大但比中部稍高，上部显著偏正；区域气候资料与大气环流模拟表明，该时期氧碳同位素变化不受降水来源和季风等因素的影响。综合沉积相分析与氧碳同位素试验结果，安集海河组大部分时期气候以温暖湿润为主，末期接近沙湾组时期气温出现明显下降，气候变为干旱寒冷；全球平均气温在安集海河组末期未出现显著变化，因此，这一区域气候变化可能更多地与印度—亚欧板块碰撞远程效应导致的天山活化隆升有关。
关键词：古环境变化；安集海河组；新生代；湖相灰盐；氧碳同位素；沉积相；构造隆升；天山
中图分类号：P66；X141 文献标志码：A
Abstract： Oligocene Anjihaihe Formation in northern Tianshan represents lacustrine sedimentary before the rapid uplift of Tianshan in Cenozoic. The variation of sedimentary facies at the top of Anjihaihe Formation and overlying Shawan Formation indicates the influence of the uplift of Tianshan. Field measurement was carried out in Anjihaihe section， and lacustrine limestone was sampled from Anjihaihe Formation for sedimentary facies analysis and oxygen and carbon isotopes analysis. The lacustrine environment during Oligocene was reconstructed. Results reveal that Anjihaihe Formation is mostly formed in semi-deep to deep lacustrine environment and in shore environment at the top. δ18O values and δ13C values in Anjihaihe Formation are relatively higher than normal lakes； δ18O values of the middle part are slightly higher than those of lower and upper parts； at the top of Anjihaihe Formation， δ18O values drift negatively significantly. On the other hand， δ13C values are much higher in the upper and top than those in the middle and lower parts with few exceptions. Regional climatic data and simulation of atmospheric circulation indicate that the variation of isotope in Oligocene is not the result of air mass change and monsoons. Given the data of oxygen and carbon isotopes， along with sedimentary facies analysis， it is concluded that Anjihaihe Formation is characterized by a worm and humid environment while the subsequent top part witnesses an obvious fall in temperature and the climate turns cool and dry. Considering that global climate showes no distinct change at the end of Anjihaihe Formation， this regional change may be to a large degree relate to the active uplift of Tianshan caused by the far field effect of India-Eurasia Plate collision during Cenozoic.
Key words： paleoenvironment change； Anjihaihe Formation； Cenozoic； lacustrine limestone； oxygen and carbon isotopes； sedimentary facies； tectonic uplifting； Tianshan
0 引 言
