Ti CONTENTS IN STILL-WATER DEPOSITS AND ITS RESPONSE TO DRY-WET ENVIRONMENTAL CHANGES: A CASE STUDY AT ZHONGBA, CHONGQING

Rb/Sr ratios as an important proxy to reveal dry-wet climatic variation have been applied in many fields, and the method is comparatively mature. However, some literatures documented that it seemed not too precise enough for the records in a short time scale, 1ka for instance. Therefore, we require a new proxy for short time studies.
The Zhongba Site in Chongqing has remained a continuous sequence since 5 kaBP. From the stratigraphical sequences it is expected to extract more information to reveal the local palaeo-environment evolution. Ti is an inactive element which exists in oxides in nature, the authors measured Ti contents of each layer by Inductively Coupled Plasma Atomic Elelectronic Spectrometer. For comparison, Rb and Sr contents in relevant layers were also measured with X-ray fluorescent. Results show that it is correlative between Ti values and Rb/Sr ratios. It suggests that Ti may become an environmental proxy.
Ti is usually endowed with hornblende, biotite, sphene, and ilmenite etc. When weathered, Ti and its oxides is hard to be transported, and little will be leached, although Nesbitt W H(1984) suggested that Ti would be hydrolyzed when index of chemical alteration(CIA) exceeding 90. However, CIA of each layer in this study is less than 85.69, consequently, it excludes the possibility of chemical weathering which will influence Ti variations. Through measuring the contents of TOC in layers, it is found that a Ti-enriched layer is consistent with low organic materials, and vice versa. In contrast with Rb/Sr ratios, Ti variation has relatively larger ranges and higher frequency that can be used to delineate climatic changes distinctly and precisely. In addition, the Ti content variation at the Zhongba Site suggests more climatic cycles than Rb/Sr ratios do, especially during the interval from 2.5ka~2.6kaB.P.