Sl. Yang et al., Pedogenic carbonate isotope record of vegetational evolution since late Miocene in Loess Plateau, CHIN SCI B, 44(11), 1999, pp. 1034-1038
Isotopic analyses for paleovegetational evolution have been carried out on
samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence a
t Lingtai (35 degrees N), the Loess Plateau. Stable carbon isotopic composi
tion indicates that (i) C-4 plants might be present at least by 7.0 Ma; (ii
) C-4 plants expanded gradually between similar to 4.0 and similar to 3.2 M
a, and their biomass fraction was up to 50%; and (iii) the biomass of C-4 v
egetation since similar to 2.0 Ma seems to have been decreased to the level
(about 20%) before 4.0 Ma. C-4 plant expansion at Lingtai cannot be fully
understood with the "global C-4 expansion" model because it occurred much l
ater up to 3.0 Ma than in Pakistan, which indicates that some changes in th
e regional climatic system may also contribute to C-3/C-4 shift except chan
ges in atmospheric CO2 concentrations and temperature. The latitudinal zone
for C-3/C-4 transition seems to move southwards slightly in East Asia, com
pared with the case in North America where 37 degrees N is the ideal bounda
ry for the C-4 expansion.