Abstract
The red-clay sequence on the Chinese Loess Plateau (CLP) was deposited during the late Miocene-Pliocene and is encoded with important information of past climate changes. However, it has received much less study in comparison to the overlying Pleistocene loess-paleosol sequence. In this paper, we review recent progress in characterizing the environmental magnetic parameter-based paleoclimate history recorded by the red-clay sequence. Several key conclusions are as follows. 1) the red clay and the loess-paleosol sequences have similar magnetic enhancement mechanisms but magnetic minerals in the red clay sequence have experienced a higher degree of oxidation than in the loess-paleosol sequence. 2) The CLP experienced a cooling and wetting trend from 4.5 to 2.7 Ma, caused by ice sheet expansion and East Asian summer monsoon intensification, respectively. 3) The above conclusions benefit from backfield remanence curve unmixing and comparison of magnetic grain size/concentration records, which are particularly useful in separating the temperature from the precipitation signal. A clear need in future studies is to explore the concentration and the grain size variations of hematite and goethite in the red-clay sequence and their formation mechanisms. The payback would be a clear understanding of climate history during the late Miocene-Pliocene, a possible analog for future warmer climate.
Highlights
Loess sediments on the Chinese Loess Plateau (CLP) are products of inland Asian aridification and global cooling (Liu, 1985; Heller and Evans, 1995) and recent studies reveal that recycled northeastern Tibet-originated sediments brought by the Yellow River are important sources for the CLP (Stevens et al, 2013; Nie et al, 2015)
Most researchers agree that loess sediments younger than 6 Ma are eolian with little modification from fluvial processes (Ding et al, 1998; Sun et al, 1998; An et al, 2001; Lu et al, 2001)
We found that the ferrimagnetic grains responsible for enhancement of χ in the red-clay sequence and the loess sequence have a consistent grain size distribution (Nie et al, 2007, 2008d, 2013a)
Summary
Loess sediments on the Chinese Loess Plateau (CLP) are products of inland Asian aridification and global cooling (Liu, 1985; Heller and Evans, 1995) and recent studies reveal that recycled northeastern Tibet-originated sediments brought by the Yellow River are important sources for the CLP (Stevens et al, 2013; Nie et al, 2015). Less rock magnetic work has been done on the red-clay sequence on the CLP (Liu et al, 2003; Nie et al, 2007, 2008d, 2010; Song et al, 2007).
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