泸沽湖沉积物中的铁元素和有机分子记录及其古气候/环境意义  

IRON AND n-ALKANES RECORDS AND THEIR ENVIRONMENTAL SIGNIFICANCE OF LUGU LAKE, SOUTHEASTERN TIBETAN PLATEAU

作　　者：王自翔[1,2,3] 王永莉[2,3] 孟培[1,2,3] 汪亘[1,2,3] 孙丽娜[1,2,3] 孙则朋 徐亮[1,2,3] 吴保祥[2,3] 

机构地区：[1]中国科学院大学,北京100049 [2]甘肃省油气资源研究重点实验室(中国科学院地质与地球物理研究所兰州油气资源研究中心),兰州730000 [3]中国科学院油气资源研究重点实验室,兰州730000

出　　处：《第四纪研究》2015年第1期131-142,共12页Quaternary Sciences

基　　金：中国科学院战略性先导科技专项项目（批准号：XDB03020405和XDB01030403）、国家自然科学基金项目（批准号：41172169）、西部之光计划联合学者项目和甘肃省重点实验室专项项目（批准号：1309RTSA041）共同资助

摘　　要：通过泸沽湖沉积物样品的年代学、穆斯堡尔谱学和有机分子地球化学分析,研究了泸沽湖三万年以来的铁元素与正构烷烃记录,及其古气候/环境变化特征.泸沽湖沉积速率稳定,平均沉积速率为0.28mm/a.沉积物中Fe2＋相对含量低于Fe3＋,Pr/Ph为0.54～1.48,平均为1.04,表明泸沽湖总体属于弱氧化环境.正构烷烃碳数分布在C11～C33之间,呈双峰分布形式,∑C21-/∑C22＋为0.12～2.66、CPIh为1.20～ 4.37、ACLh为25.68～27.97以及Paq为0.25～0.63,指示泸沽湖沉积有机质母质既有高等植物也有水生生物.泸沽湖沉积物中总铁相对含量（Tot-area）、Fe2＋/Fe3＋比值与生物标志化合物参数（Pr/Ph、∑C21-/∑C21＋、CPIh、ACLh和Paq）相关性较强,均是指示古气候/环境变化的有用指标：沉积物中总铁相对含量（Tot-area）与湖区降水量成负相关;Fe2＋/Fe3＋不仅能指示湖泊沉积环境特征,而且与古气温成负相关.利用上述指标重建了三万年以来泸沽湖湖区的古气候/环境,将泸沽湖湖区古气候分为3个阶段：30～20cal.ka B.P.寒冷干燥期、20～ 5cal.ka B.P.温暖潮湿期和5～0cal.kaB.P.寒冷干燥期.其中在12cal.ka B.P.左右出现气候突变为干冷,应为新仙女木冷期.Lugu Lake, located at the southeastern Tibetan Plateau （27°40＇- 27°44＇N, 100°46＇-100°55＇E）, is the second largest deep plateau-lake in Yunnan-Guizhou Plateau. A 880cm long core （at 27°40＇49＂N, 100°48＇00＂E） taken from water to a depth of 44.5 meters shows that its sediments are rich in organic matters with leaf remains but without distinguishable physical features. The age-depth model of the Lugu Lake core is established from 16 AMS14C dates. This paper presents iron and n-alkanes evidences for reconstructing paleoclimate of Lugu Lake region during the past 30, 000 years. 16 samples from the core spanning the last 30ka have been studied, combining with chronology, 57Fe Mtissbauer spectroscopy （MBS） and gas chromatography-mass spectrometry. The rate of sedimentation in Lugu Lake is stable, and its average value is 0.28mm/a . Two species of Fe were identified as paramagnetic Fe3＋ and paramagnetic Fe2＋ by MBS, and the Fe2＋/Fe3＋ radio〈 1. At the same time, the ratio of Pr/Ph is 0.54- 1.48 with an average of 1.04. Both above two indexes indicate that the oxidation-deoxidation environment of Lugu Lake is weak oxidation environment. The total percentage composition of iron （Tot-area） shows a strong linear relationship with the ratio of Fe2＋/Fe3＋ in the samples, which suggest that the change of paleo-climate and sedimentary environments not only affect the chemical forms and oxidation states of iron but also relative content of iron. A series of n-alkanes were identified in Lugu Lake sediments range from C11 to C33 and show a double-modal distribution pattern. The n-alkanes indexes of ∑C21 /∑C2^2＋ , CPIh, ACLh and Paq are 0. 12-2.66, 1.20 - 4.37, 25.68- 27.97 and 0.25 - 0.63, respectively, suggesting that the organic matters in the lake sediments were mainly derived from higher terrestrial plants and the lower aquatic organism. Both of total iron （Tot-area） and Fe2＋/Fe3＋ radio in this core has a strong correlation with n-alkanes indexes （∑C21-/∑C22＋

关 键 词：泸沽湖 铁元素 正构烷烃 氧化还原环境 古气候 

分 类 号：P534.63[天文地球—第四纪地质学] P941.78[天文地球—古生物学与地层学]