【作者】 谢远云；

【导师】 殷鸿福； 李长安；

【作者基本信息】 中国地质大学 ， 第四纪地质学， 2004， 博士

【摘要】 江汉平原是典型的由河间洼地组成的洪泛平原,这些洼地积水就成为河间洼地湖或沼泽。江汉湖泊多属于这种类型的洼地湖。平原的第四系沉积是河湖交替演变的产物,河床相、洪泛相、湖相及沼泽相沉积层交替出现,反映了第四纪以来江汉平原河湖交替的环境演化格局。因此这些河湖沉积物是研究江汉平原全新世以来气候环境变迁的良好地质体。江汉平原江陵剖面厚约6 m 的河湖沉积物提供了该地区9 kaBP 以来完整而连续的气候环境记录。通过总有机碳(TOC)、总氮(TN)、C/N 比值、有机碳稳定同位素(δ13C)、粒度、孢粉等多项气候替代性指标,重建了江汉平原9 kaBP 以来的气候环境演化,并进行了海陆气候对比、区域及远程气候对比。相比较长江下游及长江三角洲等中国东部地区而言,长江中游特别是江汉平原中晚全新世以来的气候环境变化研究较为薄弱。同时,全新世作为衔接地质时期与历史时期的一个重要时段,其气候与环境变化过程和规律对预测未来可能出现的全球气候环境变化,起重要的借鉴作用。因此此项研究不仅对全球气候变化研究具有重要的意义,而且对人类的生存环境和社会的可持续发展也具有一定的意义。通过理论分析和相互对比印证,基本上找到了各项指标的气候指示意义。有机指标中采用了TOC、TN、C/N 值和δ13C 四项指标。TOC 和TN 含量与湖泊流域内的植被覆盖度、陆源有机质输入、湖泊生物量有关。当气候暖湿时,湖泊生产力和生物量较大,并且流域内植被覆盖度高,陆源有机质随地表径流大量汇入湖盆,因而使得TOC 和TN呈上升趋势;相反在气候干冷时期,湖泊生产力和陆源有机质的输入均呈下降趋势,造成TOC和TN 含量降低。因此TOC 和TN 的升高指示气温的增加,降低代表温度的下降。沉积物有机质的C/N 比值可以提供有机质来源信息,可有效指示湖泊沉积物有机质的来源。C/N 比值的高值指示陆源有机物质的贡献较大,又进而指示地表径流和区域降水量的增加。江陵剖面311～386 cm 层位的泥炭层的TOC 和TN 含量极高,而其它层位的TOC 和TN 含量极低。江陵剖面的δ13C 值较偏负,波动幅度小,在311～386 cm 段为一明显的谷值,且与TOC 和TN成反相关关系。因此江陵剖面沉积物中的有机碳同位素表现为暖期偏负,冷期偏正的特点。江汉平原河间洼地的下垫面的地貌特征,使其有利于地表径流将周边高地冲刷而下的陆源粗颗粒物质在这些洼地湖泊内沉积下来。控制地表径流发育程度的湖盆流域降水量的变化是控制江陵剖面积水洼地湖沉积物粒度的主要因素。通过对江陵剖面湖泊沉积物多环境指标的综合对比及相互印证,揭示出湖泊沉积物粒度的另一种气候解释:粗粒沉积物指示降水量较大的湿润气候,细粒沉积物则对应降水量相对较少的干旱气候。对于冲积物粒度的气候解更多还原

【Abstract】 Jianghan Plain is typical flood plain, composed of much of interfluvial lowlands, which become interfluvial lowlands lake or marsh after storing water. Quarternary sediments of plain areas are results of alternate fluvial and lacustrine evolvement, and bed phase and flooded and lacustrine facies sedimentary deposits occur alternately, and these reflect environmental evolvements of alternate fluvial and lacustrine variances in Jianghan Plain over Quarternary. Therefore, the fluvial and lacustrine sediments are good geologic body in the research on climatic and environmental changes since Quaternary in JianghanPlain. The fluvial and lacustrine sediments 6 m thick from Jiangling profile in Jianghan Plain offer continuous and complete climatic and environmental records over 9 kaBP in study region. Through abundant climatic carriers, included total organic carbon, total nitrogen, C/N ratio, organic carbon stable isotope, grain size and pollen, the article reconstruct the climatic and environmental evolvements since 9 kaBP at Jianghan Plain, and also carry out the comparison of sea and land climate, of regional climate, of long-range climate. Comparison with East China areas, such as the lower reaches and delta of the Yangtze River, The researches on climatic and environmental changes since middle-late Holocene, in the Middle reaches of Changjiang River, and especially in Jianghan Plain, are relatively weak. At one time, Holocene, which is important time interval in joining geological period to historical period, its climatic evolvement course and rule play an important roles to forecast coming global climatic changes. And so, the research is not only of significant value to global climate change research, but also to human living environment and social sustainable development. With the help of theoretical analysis and correlation of each other, the significance of each climatic indicator is basically found. The organic index, comprised of TOC、TN、C/N ratio、δ13C, is analyzed in the paper. The content of TOC and TN is in relation to vegetational cover in drainage area and import of terrestrial organic matter and lacustrine biomass. When climate is warm and humid, lacustrine productivity and biomass is massive, and that, vegetational cover in drainage area is high, and terrestrial organic matter come into lacustrine basin in large amounts with surface runoff, therefore, TOC and TN value show itself upward trend. However, when climate is dry and cold, lacustrine productivity and input of terrestrial of organic matter come into downtrend, as a result, content of TOC and TN reduce. Therefore, rise of TOC and TN value indicate rise of temperature, however, reduce represent reduce of temperature. The ratio of C to N can offer information about the origins of organic substances, and is an effective method of identifying the resource of organic substances. The high value of C/N reflect that contribution of terrestrial organic matter is biggish, and the increase of surfare runoff and regional precipitation. The content of TOC and TN in peat bed, 311 to 386 cm position in Jiangling profile, is relatively high, however, other is relatively low. Theδ13C value in Jiangling section is lower, and has an little fluctuation range, and theδ13C value in 311 to 386 cm section is an evident low value, and moreover is in reverse relation to TOC and TN value. Therefore, the lowerδ13C value correspond to warmer climate, and vice versa. It is topographic feature of underlaying surface of interfluvial lowland that be of great advantage to terrestrial coarse grain substances, eroded from surrounding highland by surface cutoff, deposit into the lowland lake. The variation of precipitation at lake basin drainage area, dominating developmental degree of surface cutoff, is main factor of controling grain size of sediments from daya lake for Jiangling section. On the basic of the complex comparison among environmental index from lacustrine sediments in Jiangling section, the article results show that coarse particle size correspond to humid climate when precipitation is high, at the same time, fine particle size correspond to arid climate when precipitation is low. The climatic significances of alluvial deposit grain size is primarily discussed. If changes of grain size of offchannel alluvial deposit are mainly dominated by flood frequency and levee break times, the grain-size changes may be in relation to climatic changes. By now, the increase of coarse grain content may indicate dry and cold climate, but the increase of fine grain content probably reflect warm and humid climate. In such a case, there are fourteen floodwater event records between 311 to 0 cm period of time. Through comparison of grain size characters between fluvial alluvium in 0 to 311 cm section and lacustrine bog sediments in 311 to 386 cm section, it is found that there are obvious difference in grain size characteristic between the two kind of sediments, and they can be distinguished with the use of distribution scatter diagram, and grain size images, and Q1-Md-Q3 grain fineness. The seven thousand one hundred forty two pollen have been in fifty two samples at Jiangling section, and respectively belong to one hundred forty five family and genus. The total features of pollen are that pollen species is relatively plentiful, and that dominant species isn’t very obvious, and that xylophyta and herb and fern all are existent. The volume of xylophyta pollen is between 17.54%～59.4%, with an average of 36.38%, and herb pollen is 16.26%～66.67%, 35.92%, and fern pollen is 0～56.14%, 27.7%. Based on pollen concentration and percentage content, and combined with geochemical parameter and lithology change, the section is divided into three spore belt and six subzone. The spore assemblage, since 9 kaBP, show that the vegetation appearance of the study region mainly is subtropical grassland vegetation with sparse conifer and broadleaf. Pinus pollen is main needle leaved plant, and broadleaf plant primarily comprise Betula、Ulmus、Juglans、Quercus、Q.gilliana、Castanea/Castanopsis, and herb plant is mainly comprised of Gramineae、Cyperaceae and Artemisia, and fern plant consist of Psilamonoletes and Adiantum. Based on the above statement, four main phases of climate fluctuation were shown in the past 9000 years: 9.0—6.0kaB.P. , warm and wet; 6.0—4.6kaB.P. , cold and aridity; 4.6—2.5kaB.P. ,warm and wet; 2.5kaB.P.—present, cold. The climatic changes over 9kaBP in Jiangling area are coincident with large numbers of research information from domestic, moreover, many obvious climatic events are in good agreement with many international study result. It is showed that climatic change in Jiangling region is characterized by globality. There are eighteen floodwater records in the last 2870 aBP in Jiangling area. Based on the power spectrum analysis of paleo-floodwater records, it is found that the floodwater events is of cycle of 26、36、43、52、79、110a, and but 43、79、110a periods is most evident. The periods is the response to solar activity cycle.更多还原