脂肪酸在古土壤层和黄土层中的分布差异及其环境指示意义

Distribution Differences of Fatty Acids in Paleosol and Loess Layers and their Paleoclimate Significances in Luochuan of Shannxi

陕西洛川黄土剖面中的黄土层（１６号样品，Ｌ２层）及古土壤层（２３号样，Ｓ２层）中脂肪酸存在显著差异：黄土层中的正构脂肪酸以不对称的双峰分布（Ｃ（１０）－Ｃ（２１）和Ｃ（２２）－Ｃ（３３）），前峰高于后峰，Ｃ（１６）：０为主峰；古土壤层中，脂肪酸以三组峰分布（Ｃ７－Ｃ（１１）、Ｃ（１２）－Ｃ（２１）和Ｃ（２２）－Ｃ（３６）），Ｃ９、Ｃ（１６）、Ｃ（２８）近乎相等；古土壤层中的异构脂肪酸有ｉＣ（１７）、ｉＣ（１９），反异构脂肪酸有ａｉＣ（１４）、ａｉＣ（１５）、ａｉＣ（１７）、ａｉＣ（１９）、ａｉＣ（２０）等，黄土层中几乎不见它们；均含有Ｃ（１６：１）、Ｃ（１８：１）不饱和脂肪酸，其中Ｃ（１８：１）含量高。Ｌ２、Ｓ２的脂肪酸差异反应了它们生成环境的不同。

Careful researches on the GC--MS metklestified fatty acids isolated from the loess samples(L,)and paleosol samples (S,) in Luochuan loess section, Shannxi, manirest that there exist distinguished differences in two layers. In paleosol layer(S,), fatty acids is trimodally distributed in which C, is the mgximum peak value form C, to Cll without even or odd predominance. C,, is the maximum peak vine from C12 to C21,with a predominance medium carbon numbered compounds with the CPI value (C,,-C,,) of about 4. 2. Among C,, --C,,,C,8 is the maximun peak value with CPI values of about 2. 6. In loess layer (L, ),fatty acids distribute in bimodal type with two maximal values (C,,,C,,) in the ranges C,, to CZI and C22 to C31. The front peak with CPI value 13. 3 is obviously higher than latter peak with CPI value 2. 73 in GC--MS. Some iso-,antiso--,fatty acids also have been found in SZ, iCI,, iC,,,iC,9,aiC14 aiC15,aiCI,,aiC2,, but without iso- or antisofatty acids found in LZ layer. The monounsaturated fatty acids of C16, ] and C18: I was found in SZ and LZ layers in which C18: 1 is higher in content. All of these indicate that formating environments of the two layers are rather different. During paleosol stage, the climate is warm and humid suitable for almost every kinds of organisms especially bacteria and high plants, which may belong to frost and parair environment, whereas during loess development stage, climate is cold and dry only suitable for some organisms suck as algae and mosses grown, which may belong to a parair environment.