A radical reinterpretation of the growth and form of the stromatolite Conophyton lituus(Maslov)from evidence of syngenetic biofilm mineralisation  

作　　者：Robert V.Burne 

机构地区：[1]Research School of Earth Sciences,The Australian National University Canberra,ACT 0200,Australia [2]School of Earth and Environmental Sciences,The University of Queensland,Brisbane,QLD 4072,Australia

出　　处：《Journal of Palaeogeography》2022年第1期69-84,共16页古地理学报（英文版）

摘　　要：Conophyton(Maslov)is a cylindroidal stromatolite form-genus characterized by nested conical laminae.Well-preserved Conophyton,up to 4 m tall and with basal diameters of up to 50 cm,are exposed in the Proterozoic Atar Formation of Mauritania,where many occur together,in growth position,as fields of individual columns spaced between 5 and 70 cm apart.The uniformity of these forms and their regular distribution suggest that they grew in quiet-water environments below wave base.Evidence for their penecontemporaneous organomineralization is indicated by nearby toppled examples of undeformed Conophyton forms alongside eroded lithified Conophyton fragments in carbonate breccias.Two characteristics of Conophyton have been used to classify the structures-the form of the lamination and the nature of its axial structure.A mathematical/physical model provides an explanation for the growth pattern of Conophyton.It predicts that coniform structures with thickened axial zones form when upward organic growth of a biofilm moderately exceeds the rate of its mineralization.The varying characteristics of these features between different forms of Conophyton are thought to reflect biomineralization of the decaying biofilm rather than differences in the composition of microbial communities.A modern example of a syngenetic mineralization process capable of producing similar structures has been observed in the contemporary sediments of Lake Preston,Western Australia,where benthic microbial mats are being transformed into coniform lithified crusts.The initial biomineralization of the coniform mat forms magnesium silicate that first coats and permineralizes web-like microbial extracellular polymeric substances(EPS)and then coalesces into a uniform mass that provides mechanical strength to the cones.At a later stage,massive carbonate crystal growth occurs that over-prints much of this texture,leaving only small,remnant areas of the magnesium silicate phase.Many fossil Conophyton are composed of dolomite,and the remains of the microbial comm

关 键 词：Conophyton Morphogenesis PROTEROZOIC STROMATOLITE MICROBIALITE Mineralisation BIOFILM Lake Clifton Lake Preston Maslov 

分 类 号：Q914.2[天文地球—古生物学与地层学]