Study On The Geochemistry Factor Of Travertine And The Environment Control Mechanism Of This Deposition

The method of combining of hydrogeochemical automatic data logging,in-situ perennial observation and analytic sampling in lab was used to study the rule of hydrogeochemistry,trace element and carbon and oxygen stable isotopes and varity of spring water,pool water and channel water.And combing the result of analysing for carbon and oxygen stable isotopic modern travertine deposited in pool and channel and the rainfall in baishuitai area and oxygen and deuterium stable isotopes of rain, we can gain some relationship between the environment and the travertine. At the same time,the message of environment temperature and rainfaull involeved in paleoenvironment reconstruction with carbon and oxygen isotopes of the travertine is discussed.Through analysing of the data in No.1 spring which is the source of the pond water, we can find that No.1 spring didn't have the charicterictics of variations of typical epikarst springs.The temperature of this spring is so stable in the whole year. The pressure of CO₂ is up to about 70000 ppmv. And the concentration of Ca²⁺ and HCO3- is above 190mg/L and 720mg/L. These all are the basic chemistry background which is applied for travertine. Compareing the automatic temperature data of pool and man-made channel, it can be found that pool water and channel water have various changing temperature day and night.It means that pool water and channel water are both influenced by temperature.And because of the velocity and flux of flow,the temperature fluctuations in pool is more than one or two times above in channel.Rapid CO₂ degassing from the water is triggered by the higher partial pressures than that of the surrounding air.Cosequently,as the water flows downstream of the spring the CO₂ partial pressures gradually decreases,the pH increased.The water becomes supersaturated with respect to calcite,and travertine is deposited, which brings on the decrease of concentration of calcium and bicarbonate.As the water flows from the middle to the end, the CO₂ partial pressures become to be stable and decrease appreciably.This is the result of new balance of deposited travertine.The travertine in pool has the similar rule.When in monsoon,the concentration of Ca²⁺,Mg²⁺,HCO₃^-,SO₄^2- and Sr in channel water and No.1～5 pool water which is derived from channel water is decreased by the rainfall except of K+.It is a good linear negative correlation betweent the concentration of Sr in water and the total of rainfall.It is reflected the total of the rainfall at a certain extent.but for the spring,it is so stable in hydrogeochemistry and trace element.Becauce of the influence of the stable spring,the rain effect in No.6～10 pool is not obviously.The pool water and channel water also has the space diversification.As the Sr for example,it is decreased from upstream to downstream.the reason is Sr is adsorbed by CaCO₃ when the travertine is deposited.Diluted effect of rainwater not only impacts the elements in water but also affects stable isotopes in water and travertine. Through analyzing oxygen and deuterium stable isotopes of the rain we work out Local Meteoric Water Line in baishuitai area. Comparing with Global Meteoric Water Line, the slope and intercept of Local Meteoric Water Line is 12.56 and 54.88. It is higher than the Global Meteoric Water Line which is 8 and 10. The value of deuterium excess shows that the precipitation source in baishuitai area is coming from oceanic air mass by monsoon. And the evaporation effect of oxygen isotopes in water is not obviously. It is show a good negative correlation betweent the oxygen isotopes in rainwater and rainfall. When the total of the rain is increasing, the oxygen isotopes of the rain is decreased. It affects the channel water and pool water which is replenishment from rainwater. The oxygen isotopes in channel water and pool water is decreased.and the rule of travertine deposited has the similar rule--- linear negative correlation betweent the oxygen isotopes in travertine and rainfall. The carbon isotopes in water and travertine is decreased by Diluted effect of rainwater. And variation of carbon and oxygen isotopes in travertine is synchronization.it is show the similar controlled mechanism.The stable isotopes in channel water, pool water and travertine has not only the rule of temporal variety,and also has thr rule of space variety.Carbon isotopes of travertine in channel and pool in baishuitai area gradually increased along the flow path.the main reason is that as the CO₂ degasses from water,isotope fractionation happens.The carbon isotopes is enriched in water.And when the travertine is deposited,the carbon isotopes is enriched in travertine.It is means that the heavy carbon isotopes is enriched twice.In a word, the base of theoretics and experimentation for paleoenvironment reconstruction from travertine is applied by the correlation between the trace element of Sr in water, oxygen stable isotopes in travertine and rainfall.But we should do more sample and symbolic Statistic analyzed in order to use this correlation for paleoenvironment reconstruction.