Study On Layers Of Stromatolites Of Tieling Formation At Jixian Section In Tianjin

Stromatolite laminations,as biological sedimentary structure,contain a large amount of information on the forming environment.The obvious sedimentary rhythm is the characteristic of Stromatolite,but at this stage the meaning in time represented by each couple laminations is still in discussion.Jixian Section in Tianjin is the standard section of Middle-upper Proterozoic Erathem in China,of which Tieling Formation contains a lot of Stromatolites,which can provide a large amount of desirable samples for research.Thus the paper chooses Tieling Formation as the research area and Stromatolite laminations as the research object,in order to explore the characteristics of sedimentary environment and the time meaning indicated by the Stromatolite laminations.In order to finish the paper,I have read a lot of literatures and made several field investigations.The samples were obtained from Tieling Formation and experienced a series of processes including grind,polish,making wafers and pelletized powder samples.Besides,the statistical analysis on laminations was developed through observing the polishing sample.In addition,powder samples were pelletized to make carbon and oxygen isotopes tests and the analysis of the whole rock composition.The statistical analysis results on laminations show that the part Stromatolite sample contains a total of 21 Lamina groups and 249±5 laminations.The diameters of laminations have an obvious change of getting longer after being shorter.The carbon and oxygen isotope tests indicate that the value of?¹³C has an overall tendency to increase along the growth direction of Stromatolite,while the value of?¹⁸O?V-PDB?has an overall tendency to decrease.The whole rock composition analysis shows that the contents of CaO in the thicker Stromatolite laminations are higher than that in fine laminations.On the basis of reading literatures,field investigation and indoor analysis,the paper draws some conclusions with the guide of previous research results and theories.In terms of sedimentary environment,this paper believes that the location of Tieling Formation has changed comparing with its original sedimentary area which should be in tropical and subtropical region.Besides,the formation period of the Stromatolite samples should be in the rise period of sea level which belongs to Transgression systems tracts,while the seawater temperature in sedimentary period in general has a tendency to rise.In aspect of exploring time significance indicated by the Stromatolite laminations,we approve that each couple Stromatolite laminations represent a year and have found some evidences to prove it.In addition,we hypothesized that the periodic thicker Stromatolite laminations may be associated with sunspot activities.