Abstract
A high-resolution environmental magnetic investigation has been carried out on a 186.3-m-thick sequence of fluvial sediments from the Tianzhu borehole in the Beijing Plain. Magnetic stratigraphic analysis revealed that the sediment sequence spans the last 800 ka without significant hiatuses. Comparison of the magnetic susceptibility (k) with pollen records suggests that the magnetic susceptibility serves as a good proxy for climate changes. The high k values of the sediments reflect warm climate conditions, and the low k values match cold periods. Magnetic susceptibility records correlate well with the ODP 677 oxygen isotope proxy, with high/low k values corresponding to the interglacial/glacial stages, implying a climate alternation of glacial-interglacial cycles in the Beijing Plain. The lithologic analysis of the Tianzhu borehole cores suggests that climate change was the primary factor in controlling the fluvial sedimentary cycles in the studied area. A fluvial sedimentary model in which precipitation affected the fluvial sediment by controlling the discharge and transport capacity of rivers in different stages may be applied to our research. The rock magnetic records of the Tianzhu fluvial sequence display two extreme events at 750–720 ka and 270–250 ka, respectively, which are regarded as a two-period cycle of aridification and cooling in the Asian interior. The extreme event at 750`-720 ka likely resulted from the fast uplift of the Himalayan-Tibetan Plateau and the expansion of Arctic ice-sheet.
Highlights
The initial desertification of the Asian interior is considered to be one of the most prominent climate changes that occurred in the northern hemisphere during the Cenozoic era (Ruddiman and Kutzbach, 1989; Manabe and Broccoli, 1990; Ramstein et al, 1997; An et al, 2001)
By comparing magnetic susceptibility records and lithology with the ODP 677 δ18O proxy, we demonstrate that sediments in the interglacial periods were predominated by coarse grain-size sands and silts with a relatively high magnetic susceptibility
We conclude that climate change was the main factor in controlling the fluvial sedimentary cycles in the study area
Summary
The initial desertification of the Asian interior is considered to be one of the most prominent climate changes that occurred in the northern hemisphere during the Cenozoic era (Ruddiman and Kutzbach, 1989; Manabe and Broccoli, 1990; Ramstein et al, 1997; An et al, 2001). Desert loess is a valuable indicator of aridification and cooling evolution in Asia (Kalm et al, 1996; Gu et al, 1999; Sun and Liu, 2000; Chen et al, 2001; Guo et al, 2004; Ding et al, 2005; Deng et al, 2006)
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