Link West China and N Pacific Ocean—Miocene dust event in the lower reaches of the Yangtze River, China

Advances in the Miocene aeolian sequence in West China, have enhanced our understanding of long-term aeolian dust evolution and the monsoon climate changes in central Asia(Guo, et al, 2002). Early study on the ODP boreholes in North Pacific region indicated the dust sedimentation flux increased obviously in Miocene, especially in (Rea, 1985). Is the region between the West China and the North Pcific existing Miocene aeolian deposit? A new discover of the Miocene aeolian deposits in the lower reaches of the Yangtze River, China is interesting. Lavas of the basalt hills covered on the ancient sediments in Lingyan hill, north Nanjing suburb. The section in Lingyan Hill was an abandoned sand mining site. The depth of aeolian sediments is about 4.2 meters in the top layer of the loose deposits. Multi-environmental proxies of the samples from the aeolian layer were analyzed, including the magnetic susceptibility, Quartz shape (by SEM), elements (by ICP-MS), grain size (by Malvern 2000). The characteristics of the quartz grain photos indicate the grains were not transported by river. The main feature of the quartz grains are angular and sub-round, and the surface of the quartz have few strike marks. Some of the grains have the chemical erosion shallow holes the silicon deposits on the surface. The magnetic susceptibility,element composition, as well as the REE, are similar to the aeolian loess in China. The basalt lava was dated by K-Ar method and indicated the eruption time was 12.17 Ma. So the aeolian deposits in Lingyan Hillis older than that time. The 4.2 meters long aeolian deposits in the lower researches of the Yangtze River is not enough to reconstruct the long-term environmental changes. The event significance is obvious. In West China and the N Pacific the dust flux rapidly increased in from 16-14Ma or even later time (An et al,2006). Accoding to the basalt lava eruption time (12.17Ma), the aeolian deposits from Lingyan Hill section may indicate the dust deposit belonged to the Miocene strong dust flux event mentioned above. This paper provides new evidence in the north hemisphere about the Miocene dust event in 16-14Ma and that may indicate a global abrupt climate change during that time. Acknowledgement Thanks to the NSFC financial support (No 40676052).