Dissolvable Organic Composition and Its Paleoclimatic and Environmental Significance in Sediments of the Gucheng Lake

Abstract

通过江苏固城湖GS1钻孔中可溶有机质成分的全面分析,揭示了可溶有机质中正烷烃、脂肪酸、醇类等生物标志化合物的组成与剖面变化特征,探讨了该湖泊生物输入状况、沉积环境以及沉积物物源的变化.研究表明,固城湖沉积物中有机质以外源高等植物输入为主,湖区12.2kaBP以来古气候总体呈升温趋势,并且暖期对应于湖泊内源藻类、细菌类的繁盛和湖泊生产力的提高.此外,固城湖12.2kaBP以来基本为还原环境.并且在某些时段达到较高的还原程度.;The Gucheng Lake is located in Gaochun County, Jiangsu Province(31°14'36''N-31°19' 28''N，118°51'34''E ~ 118°57'56''E). It lies in the southeast monsoon climate area. For studying the palcoclimatic of the environmental change of the lake area since Late Ice Age and clarifying the evolution of the southeast monsoon. a core of 20 meters (GSl) was drilled at the center of the lake in November，1992. Based on the analyses of dissolvable organic compound of the GSl core，this paper gives out the composition and character of these compounds.Concentrations of hydrocarbons range from 0. 89 to 32. 80 ug/g of dry sediment, and range of the carbon number is from C15 to C34. Carbon preference index for hydrocarbons (CPI) varies from 1. 32 to 5. 92, and range of the OEP is from 1. 2 to 5. 99. The former Pr/ Ph ratios are 0. 01-0. 80，and L/H ratios are 0. 03-0. 50.Normal C15-C34 FAs，branched-chain C15-C18 were detected in the samples. Concentrations of total FAs range from 4. 4 to 279 pg/g of dry sediment, with maximum in 3. 4-4. 5m at depth. Carbon preference index (CPIA) varies from 2. 16 to 12. 08. Normal saturated fatty acids display even numbered predominance and bimodal distribution model with major peaks at C16-C18 and C28-C30. Unsaturated FAs detected are n-C16:l，N-C18:1. Total unsaturated FAs contents are from 10. 88 to 265. 38 pig/g of dry sediment. The vertical variations of these unsaturated FAs are similar to those of total FAs.Alcohols contents are from 18. 7 to 318. 6 ug/g of dry sediment. Ranges of the carbon number arc C14-C32. The distribution model shows the character with major peak at C24-C28. The EOP values are 1. 09-16. 3, and ratios of the ∑C19^-/∑C20⁺ are 0. 03-0. 50.These studies made it clear that organic matter in the sediments of the Gucheng Lake mainly camc from terrestrial plants and the paleotemperature in the basin rose up since 12-2kaBP. During the warm stage, the lake productivity was high and the bacteria and algae in lake flourished. Since 12. 2kaBP，the lake showed some reductive character with certain stages of high reductive environment.