Molecule Characteristics In Chinese Temperate Soils And Their Significant Biomarker Changes In Loess-red Clay Sequence

Topics of the formation and development of Asian monsoon, drying of Asian inland, and vegetation evolution and soil erosion on the Loess Plateau have been more and more gain scientific and social attention. The thick and continuous loess-red clay sequence on the Chinese Loess Plateau records in detail the evolution of Asian monsoon and its related dust provenance variation. Application of numerous inorganic proxies to this sequence has contributed to considerable progresses in monsoonal evolution. However, less organic proxies are involved.Biomarkers have be used as proxy for the re-construction of paleoenvironments and paleoclimate in the study of marine sediments, lake and peat deposits. However, the biomarker record so far obtained from CLP only spans narrow time, and the detailed information on the red clay has not been reported to our knowledge. This thesis systemically investigated molecule characteristics of Chinese modern soils collected from tempetate zones in response to modern environmental changes. Based on this, loess-red clay samples collected from complete Chaona section spanning the last 8.1 Ma are analyzed to discuss in details the vegetation and biological evolutions with these molecule varied with monsoon climate on the Loess Plateau. The results provide strong organic geochemical evidence for the scientific topics above. Following conclusions are obtained:1. Besides n-alkane, n-alkan-2-ones and n-fatty acid, eleven pseudohomologous families of branched alkanes with quaternary substituted carbon atoms (BAQCs), 2,2-DMAs, 7,7-, 6,6-, 5,5-, and 3,3-DEAs, 3-E-3-MAs, 5-E-5MAs, 5-B-5-EAs, 6-B-6-EAs, 3,3, ω3, ω3-TEAs, and 5,5,ω5, ω5-TEAs, as well as hitherto unreported n-alkan-3-ones, were observed in Chinese modern soil samples and loess-red clay samples from the Chaona section. The relative abundances of LMW (C₁₈-C₂₂) and HMW (C28-C33) BAQCs seem to covary with climate zones and change s with age in loess-red clay samples, suggesting that the source organisms of BAQCs, present in soils, can express different lipid distributions in response to environmental constraints.2. Their distribution and CPI(h> and C15-21/C22-35 ratios changes with climate zones, their lower molecular weight components(Ci5-C2i) dominate in southeast China, while the higher molecular weight ones (C23-C33) dominate in cold, arid northwest China. The distributions of ?-Alkan-2-ones, n-alkan-3-ones and 5,5-DEAs exhibit strong regional variations, correlated with the spatial distributions of climate and vegetation.This study is the first biomarker record from complete Chaona section (8.1Ma). Significant fluctuations were observed in the patterns of ?-alkanes and w-alkan-2-ones, as well as several biomarker ratios, which are related to changes in lithology/paleoclimate. These records revealed the important environment changes at about 5.48, 3.6 and 2.6Ma, characterized by the occurrence of deciduous trees and the enhanced degradation and diagenesis of organic matter associated with enhanced precipitation between 8.1-2.95Ma, and the onset of the Asian monsoon and aridification between -7.28-5.48Ma;4 4an intensification of Asian summer monsoon between the warmest period ⁵.48-3.54Ma, characterized by increases of woody plant, enhanced microbial activity and the highest soil humidity;and an intensified Asian winter monsoon with a dry and cool climate at 3.6Ma, resulting in continued aridity in China and occurrence of grassy vegetables grasses with increasing intensification and fluctuation since 2.6Ma over CLP. They support the similar evolution of the Asian Monsoon revealed by inorganic indices, which were in broadly consistent with those given by some other inorganic proxies.4. This work evaluated the potential of using different biomarker indices and as proxies for the environmental change, which could reveal the source organisms, microbial degradation and diagenesis of organic matter in response to evolution of the Monsoon. With analyse of other biomarkers, we could reveal the more comprehensive history of evolution of the Monsoon.