A Study Of The Elements And Formation Of The Travertine Laminas From Thermal Groundwater At The Wang4Well In Baodi District Of Tianjin

Our country has much distribution of karst area and considerable tufa deposition.Predecessors have made certain progress in aspects of tufa reserching. The reach reports rangesfrom deposition patterns, depositional mechanism to the guiding significance in the reconstructionof paleoclimate and paleoenvironment. These results focus on the tufa which is deposited by coldwater. So what about the travertine? Especially the micro-layers in travertine whether have similarfactors in deposition as tufa? Such as influence of climate and environment play on the travertinelayers forming. Domestic results haven't relevant reports. Taking Wangsi Wells for example todemonstrate the effect for climate factors exerted on travertine's laminas which deposited by themidder or low temperature springs and micro-layers' indicative significance. Wangsi Wells locatedin south of yinjiapu village which is in tianjin baodi. It was dug in1978and deposited about half ametre thick travertine with considerable layers along the outside wall of well until2005.Through field sampling,21travertine laminas had been selected for study. We described thephysical characteristics of each laminas and made flakes before selected99test points.49elements with major, trace and rare earth elements had been tested by electronic probe andLA-ICPMS. Electron probe analysis shows that the main compositions in the sample are CaO:52.27%-55.21%with an average content of53.55%. The rest of the Lord measured is low exceptabout1.19wt%of MgO and0.75%of SrO. LA-ICPMS accurately determined most metal elementin the samples. Test resulets show that38.33%of Ca,0.55%of Mg and1.25%of Sr. The rest ofthe other elements elements are no more than0.1%.By analysis of physical characteristics of travertine laminas, study of the change of itschemical composition among laminas and comparison of mutual relations of various change laws,it is found that certain change laws are shown in physical characteristics of travertine laminas.Temperature rise leads to the increase of travertine sedimentation rate and of relevant laminathickness from initial13mm to18mm; Mg/Ca ratio between change of physical characteristics(e.g. lamina thickness, density) and travertine lamina also has corresponding fluctuation ofhigh-low values. Mg/Ca ratio is lower when thickness is larger and the lowest value is0.5×10-3,and higher when lamina is thinner and normally is around0.02; Mg/Ca ratio has no necessaryconnection with season change of climate environment and is not sensitive to response of climatechange. The indicative meaning of travertine laminas of hot water sedimentation to climate changehas yet to be considered carefully. Contents of trace element of Sr and Mg, Sr and Ba in travertinelaminas show apparent inverse correlation and positive correlation respectively; total content ofrare earths is low and varies greatly with each lamina from0.0136to14.2965ug/g, the meanvalue of which is0.47ug/g. The total content of rare earths increases with the progress ofsedimentation, which indicates that there has been certain change in travertine source areas andinterconnection among aquifers or their mixing effect has been enhanced; there is obviousdifferentiation between light and heavy rare earth element and the light rare earths are relativelyenriched.