Hydrochemical Control Factors Of Travetine Precipitation And The Significance Of Laminated Travetine As Archives Of Climate And Environment

Hydrochemical control factors of travetine precipitation is the basic condition forthe deposition of travertine. In order to better understand the impact of travertinedeposition control factors, water samples of23hot spring collecting from thehydrothermal activities areaes of Guangxi, Yunnan, Tianjin and Tibet of China.Around18hot springs have travertine deposition, and the rest have no travertinedeposition. We analized temperature, pH, TDS, contents of Ca²⁺, HCO₃^-, Mg²⁺, Na⁺,K⁺and SO2-4, percentage content of Ca²⁺and HCO₃^-, and Mg/Ca ratios of these springs.Hot springs with deposition of travertines have a wide temperature range and higherP1.29C O2, the average was10-atm, variation range of TDS in most springs are from1to3g/L, and calcite saturation indices （SIc） and aragonite saturation indices （SIa） aresaturated. At the same time, contents of HCO₃^-are very high, of which the vastmajority are greater than470mg/L. when percentage content of the HCO₃^-close toor greater than30%of the anions total, and equivalent of Ca²⁺and HCO₃^-have a verygood match with each other, springs are most probably proned to deposite travertines.We present a continuous about30-year-long （1978to2006） high-resolutionrecord of trace element （Mg, Sr, Ba） and stable isotope (δ¹³C, δ¹⁸O) variations in amodern laminated travertine from Wangsi Well, Tianjing. Sr and Ba along thetravertine section show high-positive correlation, which have a good negativecorrelation with Mg. Sympathetic variations in δ¹³C and δ¹⁸O of travertine werediscovered. Variations of δ¹³C and Mg/Ca are involved in physical characteristics（thickness, color, crystallinity） of the laminated travertine, and they relate to climatechanges. When travertine micro-layer is a thick, brown, loose layer, and which have alow Mg/Ca ratios and high values of the δ¹³C and δ¹⁸O, reflecting the cold and dryclimate conditions; Conversely, when the travertine micro-layer is a thin milky denselayer, and have a high Mg/Ca ratios and low values of the δ¹³C and δ¹⁸O, reflectingthe warm and humid climatic conditions.U-series dating of9travertine samples depositing near Rongma hot springs inthe northern Tibet was used. The results show that the U contents of the travertinesamples are as high as0.298-1.363ppm, and variation range of the234U/238U are from1.475to1.700. The uranium-series ages of the travertine samples range from11,500to4,600a, falling within the first stage of the warmest period of the marine oxygenstable isotope （MIS1）, high-resolution δ¹⁸O values record of the speleothems in Hulu Cave and Guliya Ice core, respectively, reflecting a warm and wet period duringthe deposition of the travertines in the study area. Combination of the high water levelof the lake and the prosperous Charophyta flora at the Taicuo ancient lake of Tibetand strong summer monsoon influence imply a warm and wet climate during the sameperiod. High-resolution hot spring travertine dating establishs a continuous, reliabletime scale of the study area. It is significance for the reconstruction of paleoclimateand palaeohydrology in the study area.