Late Miocene-Pliocene development of Asian aridification as recorded in the Red-Earth Formation in northern China

摘要

In northern China, the Late Miocene-Pliocene Hipparion Red-Earth Formation in the eastern Loess Plateau fills a gap of climate records between the well-known loess-soil sequences of the last 2.6 Ma and the Miocene loess-soil sequences from the western Loess Plateau. Earlier studies on type sections indicate that a major part of the Red-Earth Formation is also of windblown origin, covering the period from ～ 7-8 to ～2.6 Ma BP. Because the eolian dust deposited in the region originated from the Asian desert lands, the Red-Earth must contain a record of the aridification history of the Asian interior. In this study, the Xifeng type section in the eastern Loess Plateau is studied to assess the development of Asian aridification during Late Miocene-Pliocene time. Eolian dust deposition continued at the central Loess Plateau since ～ 6.2 Ma BP, indicating that sizable desert lands in the interior of Asia and the Asian winter monsoon must have been constantly maintained during Late Miocene-Pliocene time, and were able to provide a significant amount of eolian dust. The aridity in the source areas was stronger from ～ 6.2 to ～ 5 Ma BP and weaker from ～ 5 to ～ 3.6 Ma BP. Two major aridification steps are observed at ～ 3.6 and ～ 2.6 Ma BP, respectively. The intensification of eolian deposition at ～3.6 Ma BP is synchronous with a suggested uplift of portions of the Tibetan Plateau. The general aridification history is also highly consistent with the ongoing high-latitude cooling and the consequent expansion of Arctic sea-ice/ice sheets during this interval. Our results therefore suggest that both Tibetan uplift and ice-building processes in the northern hemisphere were two prominent driving forces behind the long-term desertification in the interior of Asia during Late Miocene and Pliocene time.