Study On Cyanobacteria Fossils And Mats Of Stromatolites Of Mesoproterozoic Tieling Formation At Jixian In Tianjin

Stromatolite laminations as special biological sedimentary structure,the internal structure of stromatolite is affected by the biological community,external structure is under the control of the surrounding sedimentary environment.Thus stromatolite macroscopic features can be used as a reference index to study the effects of environmental change,has certain research value.Unfortunately,it is hard to constitution in the Precambrian carbonate stromatolite soft cyanobacteria fossils preserved intact in the long term diagenetic process.As a result,how the Precambrian stromatolites are formed and why it is difficult to find cyanobacteria fossils in stromatolites of the Precambrian strata,Riding(1994)called them Precambrian enigma.In China,there are abundant stromatolites in the middle-upper Proterozoic standard stratigraphic section,especially the top of Tiling Formation,which located in Ji County,Tianjin City.So based on the stromatolites in the top of Tiling Formation,this study recorded the column morphological features of stromatolite by taking pictures and we processed the stromatolite samples by polishing,grinding and then,observed the stromatolite chips under microscope.This thesis describes the microcosmic and macroscopic form characteristics of stromatolites.Meanwhile the quantitative analysis of the element composition of the light and dark stromatolite laminations was carried out,and to study the form and forming process of cyanobacteria fossils in stromatolites,the process of microbial mats build the stromatolite,establish depositional environment of the stromatolites in the top of Tiling Formation.this thesis gets some recognition as follows.1.The sedimentary environment of stromatolite in upper Tieling Formation is likely to marine upper subtidal sedimentary environment which hydrodynamic energy medium.Besides,the formation period is in the rising period of sea leveland also make the sedimentary environment distribution pattern figure of this region.2.Stromatolitic microstructure characteristics of stromatolites classification and stromatolites genera and species identification has a guiding significance and types ofmicro structural characteristics are relative to microbial mats of stromatolites,diagenesis and deposition rate.And has carried on the detailed description,3.Suspected fossil of globular cyanobacteria and suspected filamentous cyanobacteria are fund between boundaries of light and dark stromatolite laminations in stromatolite in upper Tieling Formation In jixian area.the fossil of filamentous cyanobacteria was named as the "Calcium sheath fossil ".The origin and the significance of the ancient environment of the "Calcium sheath fossils" are analyzed in detail,it provides a very favorable evidence of biogenic stromatolites in the Precambrian strata.4.Both the light and dark stromatolite laminations in stromatolite,the Calcium ion concentration is very high,and the content of ferrous iron in dark stromatolite laminations is higher than in light stromatolite laminations which Description of the dark stromatolite laminations are formed in the micro-reducing sedimentary environment.The growth of stromatolite reflects changes in the seasonal cycle of grade,at last made the light and dark stromatolite laminations formation pattern.