1 research outputs found
Magneto- and cyclostratigraphy in the red clay sequence:New age model and paleoclimatic implicationfor the eastern Chinese Loess Plateau
The Chinese Loess Plateau red clay sequences display a continuous alternation of sedimentary
cycles that represent recurrent climatic fluctuations from 2.58 Ma to the Miocene. Deciphering such a
record can provide us with vital information on global and Asian climatic variations. Lack of fossils and
failure of absolute dating methods made magnetostratigraphy a leading method to build age models for
the red clay sequences. Here we test the magnetostratigraphic age model against cyclostratigraphy. For
this purpose we investigate the climate cyclicity recorded in magnetic susceptibility and sedimentary grain
size in a red clay section previously dated 11 Myr old with magnetostratigraphy alone. Magnetostratigraphy
dating based on only visual correlation could potentially lead to erroneous age model. In this study the
correlation is executed through the iteration procedure until it is supported by cyclostratigraphy; i.e.,
Milankovitch cycles are resolved in the best possible manner. Our new age model provides an age of
5.2 Ma for the Shilou profile. Based on the new age model, wavelet analysis reveals the well-preserved
400 kyr and possible 100 kyr eccentricity cycles on the eastern Chinese Loess Plateau. Further, paleomonsoon
evolution during 2.58β5.2 Ma is reconstructed and divided into three intervals (2.58β3.6 Ma, 3.6β4.5 Ma,
and 4.5β5.2 Ma). The upper part, the youngest stage, is characterized by a relatively intensified summer
monsoon, the middle stage reflects an intensification of the winter monsoon and aridification in Asia, and
the earliest stage indicates that summer and winter monsoon cycles may have rapidly altered. The use
of cyclostratigraphy along with magnetostratigraphy gives us an effective method of dating red clay sequences,
and our results imply that many presently published age models for the red clay deposits should be
perhaps re-evaluated