Magnetostratigraphy and Sedimentology of the Eolian Deposits Since the Late Miocene in Northern China and the Paleoclimatic Implications

doi:10.7523/j.issn.2095-6134.2002.2.019

Abstract

Abstract:

In this study, two thick loess-red clay sequences located at Lingtai and Jingchuan, the Chinese Loess Plateau, are studied with emphases on magnetostratigraphy and sedimentology. Paleomagnetic measurements show that the Jingchuan red clay has a basal age of 8.0 Ma, which is one million years older than the previously studied Lingtai section. Field observations and grain size analyses both suggest an eolian origin of the red clay sediments at Lingtai and Jingchuan, thus extending available records of the eolian deposits in the Loess Plateau from 2.6 Ma back to 7.0～8.0 Ma. Correlation of five red clay sections in the Loess Plateau suggests that the Lingtai red clay sequence has a relatively continuous nature of sedimentation and can be regarded as the type-section of the Tertiary red clay deposits in northern China. On the basis of spatial changes in the grain size of one northwest-southeast loess transect, several semiquantitative models of grain size parameters versus the minimum distance from the source region to depositional areas were developed. According to these models, the estimated southeastern margin of the desert in northern China during the Tertiary red clay development is similar to that of the present Badain Jaran desert. To reconstruct the long-term East-Asia monsoon history from the celebrating eolian red clay-loess deposits, the ratios of CBD-extractable Fe₂O₃ to totalFe₂O₃ concentrations in the Lintai red clay-loess sequence, the proxy indicator for the summer monsoon changes, were measured. The LingtaiFe₂O₃ ratio record indicates that the East-Asia summer monsoon has experienced a non-linear evolution over the past seven million years. The strongest East Asia summer monsoon may occur between 4.1 and 4.8 Ma, which may be causally related to the relatively small ice volume and high global temperature during the early Pliocene.

Key words: loess, red clay, eolian deposits, grain size, paleomonsoon

CLC Number:

P535
P532

YANG Shi-Ling, DING Zhong-Li. Magnetostratigraphy and Sedimentology of the Eolian Deposits Since the Late Miocene in Northern China and the Paleoclimatic Implications[J]. , 2002, 19(2): 202-208.

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