(A) Geochemical and isotopic characterization of
the Pliocene red clay formation from the Chinese Loess Plateau:
1. Geochemical proxies in the loess-paleosol
sequences: Late Tertiary to Quaternary loess-paleosol sequences provide
invaluable record of the changing environment in continental areas
during that time interval. Loess source proxies include quartz
morphology, heavy minerals assemblages, oxygen isotope geochemistry of
quartz, major and trace elements and Sr-Nd isotopic compositions.
2. Current target area: We have been studying various
loess-paleosol sequences in the Chinese Loess Plateau. To executive this
subproject, we extended our area of investigation from to the Central
Asia loess, with the southern Tajikistan as a key target. The
Chashmanigar loess section (38°23'32”N, 69°49'57”E) section was chosen
because some detailed stratigraphic and magnetic susceptibility data
have been published. To be able to fully compare the magnetic and
geochemical data, we use the samples collected by these authors. This
section is about 200 m thick and consists of an alternation of loess and
paleosol layers (pedocomplex, strictly speaking). The basal age of the
section is about 1.77 Ma.
3. Scientific interests: This study is aimed to answer
the following questions and to test some hypotheses.
(a) What are the source areas of the Tajik loess? Have
these source(s) changed in response to tectonic or climatic events?
(b) What is the most appropriate tracer to be used in
unraveling the loess sources(s) and their weathering history?
(c) Are the high mountain regions the ultimate source
of the loess material? What is the turnover time required between
physical erosion of particles in these areas and incorporation into
loess deposits? What the relationship between this time and the mean
erosion rate in these areas?
(d) Are the climatic proxies we established on Chinese
loess sequences still valid in Central Asia ? Can we go further and be
able to reconstruct paleorainfall levels by combining chemical analysis
and magnetic susceptibility data?