『Abstract
Numerous authors have utilised physical properties of Chinese
loess and red clay deposits to develop apparently detailed and
continuous past climate records from the Miocene into the Holocene.
Many of these studies have further suggested that the principal
climatic agent responsible for the aeolian emplacement and diagenesis
of Chinese loess, the East Asian Monsoon, has fluctuated rapidly
on millennial to sub-millennial timescales, in concert with dramatic
changes in the North Atlantic (Dansgaard-Oeschger cycles and Heinrich
events) and the western Pacific (El Nino(後のnの頭に〜)
Southern Oscillation). Much of this evidence is based on reconstructions
and age models that are tied to assumptions concerning the nature
of loess sedimentation and diagenesis, for example, the belief
that loess sedimentation can be viewed as essentially continuous.
Some authors have however, cast doubt on these assumptions and
suggest that the application of radiometric techniques may be
required to determine their validity. Recent studies utilising
Optically Stimulated Luminescence (OSL) methods have reinforced
these doubts and here, OSL dates obtained at 10 cm intervals from
three sites along a transect across the Chinese Loess Plateau
have been used, in combination with climate proxy evidence, to
test the existing assumptions that underpin many palaeoclimatic
reconstructions from loess. In this way, the first time-continuous
and independently dated late quaternary climate reconstruction
is developed from loess. The data indicate that sedimentation
is episodic and that once emplaced, loess is prone to pedogenic
disturbance, diagenetic modification and in some cases erosion.
The relationships between proxies and sedimentation rates are
also assessed and climatic interpretations based o different age
models compared. The implications of these findings for reconstructions
of climate from loess are explored and comparisons are made between
the developed palaeoclimate records and evidence from ice and
ocean cores. This exercise also highlights important information
concerning the relative influence of forcing mechanisms behind
East Asian Monsoon change over the late quaternary.
Keywords: luminescence dating; Chinese loess; Quaternary; East
Asian Monsoon; sedimentation; diagenesis』
1. Introduction
2. Proxy records in loess
2.1. Dating the Chinese loess record by proxy
2.2. Assessing loess proxy chronologies
3. Independent dating of loess
3.1. Non-radiometric independent dating of the Chinese loess
record
3.2. Radiometric dating of the Chinese loess record
3.3. Luminescence dating
3.4. OSL applications to the Chinese loess record
4. Analysis of loess sections at Shiguanzhai, Xifeng and Beiguoyuan
4.1. Patterns of sedimentation, preservation and disturbance
4.2. OSL age and proxy variation
4.3. Interpretation of the proxy record changes
4.4. Discrepancies in previous age models
5. Reinterpretation of the loess record
6. Summary and implications
Acknowledgements
References