Yuan Daoxian Qin Jiaming Lin Yushi

Zhang Meiliang Li Bin

It is difficult to forecast the long term climatic changes on the basis of the instrument records because of their short time series. Accordingly, how to apply the geological and phenological records to reconstruct paleo-environmental changes, particularly up to 200, 000 years B. P. is very important for studying the global changes. Besides deep-sea sediments, ice cores, lake sediments, loess and so on, karst sediments have been widely used in the recent years around the world, especially in the regions without other geological records. There are the karst regions with a total area of 540,000 km² in south China which is located at a special climatic zone under the joint control of the Asia monsoon, the Indian Ocean monsoon and the subtropical anticyclone. In order to study the mechanism of the changes in atmospheric circulation, it is very important to obtain high resolution and long period paleo-climatic data. According to this idea, we did the basic researches to reconstruct the paleo-environment in Guilin area, which has not only provided the high resolution paleo-environmental records, but also tested and improved various new techniques and methods.

    The Project "High Resolution Paleoenvironmental Reconstruction up to 200, 000 Years B. P. With Speleothems From Guilin" was supported by the National Natural Science Foundation of China (No. 49472170). Meanwhile, additional support was provided by the Natural Science Foundation of Guangxi. Under the joint efforts of the members of the Karst Dynamics Laboratory, and the cooperation of many scientists at home and abroad for about 4 years, the scientific objectives have been achieved. This book is based on the Project's scientific results.

    The book includes 6 chapters, that is, the initiation of the Project, the geological background of the cave formation, the speleology, the records of the paleo-climatic changes up to 200, 000 years in Guilin, the basic pattern of the climatic changes and its correlation with the global changes, and conclusion. It totals about l00, 000 Chinese characters, 22 Figures and 23 Tables.

    The book gives a detailed discussion on the geological background of the cave formation and the development history of the cave. Four stalagmites were selected including No. 1 stalagmite from Shuinan cave in Guilin, the No. I stalagmite from Xiangshui cave at Guanyang county, the No. 1 stalagmite from Panlong cave in Guilin, and the No. 4 stalagmite from Fengyu cave at Lipu county. On the basis of detailed sedimentological studies, the four stalagmites were used as a composite profile to reconstruct the paleo-climatic changes up to 200, 000 years B. P. Several new techniques were used in the works, including some up-to date dating techniques such as AMS ¹⁴C, TIMS U-series and ²¹⁰ Pb dating methods. Oxygen and carbon isotopes were taken as the major climatic proxies, and luminescence technique and trace element geochemical technique were as supplementary climatic proxies. To solve some difficult problems such as the dating technique for the samples with low uranium content, the reliability of ¹⁴ C dating and the interpretation basis of isotopic records, we did some methodological researches and put forward some new methods or ways which will be useful for future work. The major results are as follows:

1.Two big stalagmites back to 40,000 years B. P. , with continuous profile of clear annual growth laminae for studying the paleo-climatic changes since the last glaciation, were first found in Guilin area. In addition, a continuous profile from 100,000 to 200,000 years B. P. were also found. The laminae composed of calcite are suitable to applying AMS ¹⁴C and TIMS U-series dating methods to get reliable and high resolution ages compatible with other materials such as lake or marine sediments. Therefore, to the geochronology study since the late Pleistocene Epoch, stalagmites may have vast vistas.

2.Applying high resolution and sensitive AMS ¹⁴C and TIMS U-series dating methods, as well counting and a- counting U- series dating methods, 4 stalagmites were systematically dated, and a reliable chronogical order was set up, which provided effective time marks for the paleo-climatic studies.

3.The systematical studies of the oxygen and carbon isotopes of the calcite of the last glaciation and Holocene stalagmites (including the present deposit), as well as the studies of the correlativity between the precipitation and the various climatic factors show that the & values of the oxygen and carbon isotopes in stalagmite calcite have a negative correlation with the annual mean surface air temperature. The result is different from that in Europe and America, and suggests a new interpretation basis for the isotopic records.

4.On the basis of the systematical studies of the oxygen and carbon isotopes of the four stalagmites, a basic paleo-climatic change pattern up to 200,000 years in Guilin area was set up. The cycles A, B, C (including the more detailed stages 1-6) can be correlated with the oxygen isotopic records of the deep sea sediments. Furthermore, some millennium and centennial cold events, e.g. 11.0-10.7ka, 12.6-13.0ka, 15.8-16.7ka, 17.5-20.2ka, 22.5-25.6ka, 43-43.8ka, 103.5-114.0ka, 126.3-136.0ka, and 139-142.7 ka, were recorded, which filled in the gaps in the fields of the global change studies in south China.

5.The parallel studies of two stalagmites up to 44,000 years B. P. gave identical results. The results show that there are 3 climatic cycles and 7 climatic stages which can be correlated with the records in the loess in north China.

6.The study of microlayer luminescence spectral characteristics on the sample from the lower part of No.1 stalagmite from Panlong cave shows that there is a good correlation between luminescence spectral records and d ¹⁸O records. The results also show that the luminescence spectral records may give a higher resolution.

7.To a certain extent, the colour index and the structure of laminae may reflect the environmental changes. Thin laminae with dark colour may reflect a cold and dry climate, and thick laminae with bright colour may reflect a warm and humid climate. The rate of sedimentation may also reflect climate changes. In addition, the meanings of characteristic element contents and element ratios were also tested. Because this research was the initial attempt to reconstruct the paleo-environment with high resolution by using big stalagmite of 1. 2 -2. 4 m high in China, there might be some imperfect or problems, any comments will be welcome gratefully.

Contents

Preface

Chapter 1. The initiation of the Project
1.1 Objectives
1.2 Origin of the Project
1.3 Status quoante
1.4 Technical methods
1.5 Accomplished work

Chapter 2. Geological and environmental background of cave formation
2.1    Introduction to regional geology and hydrogeology
2.1.1 Physical geography
2.1.2 Stratigraphy and lithology
2.1.3 Geological structures
2.1.4 Hydrogeological settings
2.2   Development conditions of caves
2.2.1 Parent rocks of caves and Hydrological catchment
2.2.2 Fractures, fissures and their structure background
2.2.3 Lithology and associated features
2.2.4 Climate

Chapter 3. Speleogical background
3. 1. Panlong cave system
3. 2. shuinan cave system
3. 3. Xiangshui cave system
3. 4. Fengyuyan cave system

Chapter 4. Records of paleoclimatical changes up to 200ka B. P. in Guilin
4. 1. Sampling and Analysis methods
4. 1. 1 Sampling
4. 1. 2 Analysis methods
4. 2. The records of deposit ages and the growth rate of stalagmites
4. 2. 1 The records of stalagmite deposit ages
4. 2. 2 The growth rate of stalagmites
4. 3. The Records of the carbon and oxygen isotopes of stalagmites
4. 3. 1 Equilibrium check of isotopic deposit
4. 3. 2 Environmental interpretation of carbon and oxygen isotopes
4. 3. 3 The records of the carbon and oxygen isotopes
4. 4. Other environmental information of stalagmites
4. 4. 1 Correlative with deposition cycles of stalagmites
4. 4. 2 Climatic indicator of some chemical components of stalagmites
4. 4. 3 Luminescence and its paleoenvironmental records in a stalagmite

Chapter 5. Main characteristics of climatic changes over the past 200ka in Guilin area and Its correlation with global changes
5. 1 The regularity of climatic evolution
5. 2 Climatic stages and chief events
5. 3 Carbon isotopic event

Chapter 6. Conclusions
6. 1 Work methods
6. 2 Technical methods
6. 3 Comparison with the same work at home and abroad
6. 4 Main study results
6. 5 Problems

References

Abstract