Abstract. An almost 300m thick eolian sequence of Late Cenozoic sediments, which includes 162.5m of Quaternary loess-paleosols and 126m of Late Tertiary eolian Red Clay from the central part of the Chinese Loess Plateau, was investigated to determine the magnetostratigraphy. The results show that colJan dust accumulation, and by inference the related East Asia palcomonsoon, had begun by 7.2Ma. As palcomonsoon are largely controlled by the Tibetan Plateau, this implies that the Plateau had reached some critical elevation by 7.2Ma. The section also documents a rapid increase in eolian dust accumulation in the Late Cenozoic at 3.2Ma that is probably due to the influence of global ice volume on the East Asian monsoon.

[1] The Matuyama-Brunhes (M/B) boundary, termination of Jaramillo normal subchron (J/M) as well as three young geomagnetic excursions has been revealed in the Weinan loess section [Zhu et al., 1994[Zhu et al., , 1998[Zhu et al., , 1999. Recently, we carried out further paleomagnetic directional studies on the same section and recovered the onset of the Jaramillo normal subchron (M/J) and four geomagnetic excursions, two in the Brunhes and two in the late Matuyama. The fact that all seven excursions found in this section are in loess units and expected excursions in paleosols are not found suggests that short-lived geomagnetic signals could be only recorded in loess units, and may have been fully smoothed or wiped out in paleosol units by strong pedogenesis. Constrained by a new astronomical timescale (HLD 00 ), ages of the geomagnetic excursions and reversal boundaries have been estimated. We tentatively correlated these excursions with previous results, indicating that a large lock-in model may not be correct for the whole loess profile, although some apparently big positive age discrepancies were observed for the main boundaries.

Tibetan Plateau uplift has been suggested as the main driving force for mid-latitude Asian inland aridity (AIA) and for deposition of thick aeolian sequences in northern China since the Miocene. However, the relationship between earlier AIA and Tibetan Plateau mountain building is uncertain because of a lack of corresponding thick aeolian sequences with accurate age constraints. We here present results for a continuous aeolian sequence that spans the interval from >51 to 39 Ma from the eastern Xorkol Basin, Altun Shan, northeastern Tibetan Plateau. The basal age of the studied sequence postdates initial uplift of the Tibetan Plateau by several million years. Our results indicate that the local palaeoclimate was teleconnected strongly to the overall global cooling pattern, so that local enhanced aridification recorded by the studied aeolian sequence is dominantly a response to global climatic forcing rather than plateau uplift.