『Abstract
Palaeoclimatic interpretation of the Red Clay in the Chinese
Loess Plateau is particularly important for understanding of the
East Asian monsoon evolution from Pliocene to the Quaternary.
In this study, a N-S transect involving five loess-Red Clay sections
across the Loess plateau was selected for detailed investigation
with analyses of grain size and major element geochemistry, in
order to address the spatial pattern. Results indicate that the
Red Clay contains large amount of coarse (＜6φ, i.e.＞16μm) fraction
and shows prominent N-S decreasing gradient much similar to that
of the overlying loess, suggesting that the dust transport was
dominantly by low-level northerly/northwesterly winds. Compared
with overlying loess, the Red Clay is markedly fine and rather
constant through all the sections, implying a distant and steady
dust-source area about 200 km further north during most of the
Pliocene time. Pedogenic leaching intensities inferred from geochemical
data display a clear decreasing trend from south to north both
for the Red Clay and the loess, suggesting that the modern spatial
pattern of the East Asian monsoon regime has been maintained at
least for the past 5 Ma. The N-S spatial gradient, however, might
be smaller during the Pliocene than the Quaternary period. Temporally,
two short periods of climatic deterioration implied by marked
grain-size coarsening and low weathering intensity occurred at
5.3 and 3.5 Ma, respectively, which divide the Pliocene into two
major stages. The 5.3-3.5 Ma stage is characterized by a steady
state climate through the entire region, consistent with other
records. In the 3.5-2.7 Ma stage, the Red Clay in the Jingbian
section shows a noticeable coarsening in grain size than the previous
stage, indicating some southward extension of the desert, in agreement
with mass accumulation rate record in the north Pacific. But the
eolian dust deposition remained relatively stable in major part
of the Loess Plateau until 2.7 Ma. The Red Clay deposition was
then terminated by massive and coarse loess deposition in the
entire region, suggesting dramatic intensification of the winter
monsoon in response to the onset of extensive glaciation of Northern
Hemisphere.』
1. Introduction
2. Study sections and age constraints
3. Samples and laboratory measurements
3.1. Grain size analysis
3.2. Major elements
4. Results and discussion
4.1. Grain size variations through profiles
4.2. Spatial variation of grain size distribution and implications
of deposition environment
4.3. Major element abundances of the Red Clay through profiles
4.4. Spatial pattern of major element abundances
4.5. Post-depositional weathering intensities
4.6. Palaeoclimatic implications
5. Conclusions
Acknowledgments
Appendix A
References