|
High Resolution Paleoenvironmental Reconstruction up to 200,000 Years B.
P. with Speleothems from Guilin
Yuan Daoxian Qin Jiaming Lin Yushi
Zhang Meiliang Li Bin
Abstract
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 ß-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 quo ante |
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 |
|