Microbial Fossils And Micro Structures From The Early Cambrian Kuanchuanpu Biota

Microorganism is a crucial component of ecosystem and their metabolic activities are closely related with the macro/micro-environments.The researches of fossil microbes and relevant micro structures can not only reveal the face of ancient biosphere,but also provide unique information on the co-evolution of life and the Earth.The early Cambrian is a key transition during geological history and those early Cambrian phosphatized fossil Lagerstatten in China have been intensively studied.However,previous researches mainly focused on microfossils of animals or plants and fossilized microorganism have been somehow overlooked.And such studies are usually restricted on cyanobacteria and their morphologies,while the relationship between of microbes and other geological processes,which is important issue of modern research,has not been fully demonstrated.This study based on the new materials of microorganisms and relevant micro structures with large amount of information on morphology,taphonomy and the interaction of microbes and other animal fossils.These allow us to investigate such microorganism from some new perspectives,such as taphonomic mechanism,living environment of microbial and their behaviors,fossil ultra-micro structures and chemical compositions.The main research contents include:1)Endolithic microorganisms versus ambient inclusion trails(AITs): analysis of both morphology and taphonomy of these 3 micro tubular structures;discovey of a new type of AITs carbonaceous terminal propelled grains;discussions on an intriguing AITs spiral distribution pattern on protoconodonts and its significance.2)Microbial pseudomorphs of non-mineralized animal,along with the comparsions with the results of modern taphonomic experiments.3)Supplemental features of some known cyanobacteria: preservation of the trichomes tips and cellular structures of Cambricodium and the varied preservation types of Girvanella.The results are summarized as follow:1)Endolithic cyanobacteria,endolithic fungi and AITs are essentially different in morpholo-gical features,formation stages and mechanism of preservation,which clarifies the ambiguity of their recognition eventually with a complete model.Carbonaceous AITs terminal grains provide new explanations of the diversity of AITs morphology and forming mechanism.Raman geothermometry of these carbonaceous materials indicates the Kuanchuanpu Fm.in this area underwent very low-grade metamorphism,with a peak metamorphic temperature estimated at 232~261°C.This implies that the fossils are mostly free from metamorphic overprints,and roughly constrains the upper limits of AITs formation.Through the analysis of the requirements for forming spiral AITs pattern,the original chemical composition of Early Cambrian protoconodont spines should be mainly recalcitrant organic materials.2)In Kuanchuanpu Biota,there are 4 types of complete microbial pseudomorphs and 1 types of incomplete microbial pseudomorph.The formation of complete pseudomorphs can be subdivided into 2 mechanisms: A,casting and replacement of microbial cells;B,biofilm stabilization.Pseudomorphs process great potential to preserve non-mineralized soft tissues.3)The gradually tapering tips of cyanobacteria Cambricodium filaments and the strings of flaten cells suggest a close affinity with mordern Rivulaiaceae,especially Gardnerula.While Girvanella may appear various preservational types depends on different degrees of calcification of their sheaths.These new findings emphasize that the study of cyanobacteria fossils,which largely rely on morphological information,should be more concerned about taphonomic factors.