The Study Of Sedimentary Characteristics And Biofacies Of Terrestrial Hot Spring Sinter At Gumingquan And Yanjingquan,Tengchong,Yunan Provence

The Rehai geothermal field is one of the largest geothermal fields in the Tengchong volcanic geothermal area,located between the Indian and Eurasian plates and frequently develop volcanic hot-spring activities.The research sites are mainly high-temperature??>85???hot spring environments,composed of alkali chloride type?Na-HCO₃-Cl;p H?9?hot spring water and around the hot spring vents deposited siliceous sinter.The siliceous hot spring deposition entombs microbes that growth in high-temperature water,and plant debris,form unique biosignature associated with sinter biofacies.This sinter texture provides a unique opportunity to understand how to the preservation of fossil at extreme paleo-hot spring system.Hence,we mainly focus on the sedimentary characteristics of hot spring sinter,including a detailed description of petrological mineralogy,hydrochemistry.Combine with typical biosignature data,systematically analyze the relationship between hot spring,sinter and microbe and explore the factors that affect the quality of preserved biological characteristics in sinter,providing a supplement to study early life at extreme environments.At first,this study identified three sedimentary temperature gradient facies environments and nine sinter texture;the temperature gradients include high-temperature hot spring environment?>75??;mid-low temperature environment??75?-45??;lower temperature distal apron environment?<45??.We tested the basic parameters of hydrothermal fluids at the field and sampled the water samples to hydrochemical analysis.An integrated study analysis that XRD?X-ray powder diffraction??SEM?scanning electron microscopy?and EDS?Energy Dispersive Spectrometer?was undertaken at the Gumingquan and Yanjingquan hydrothermal system to appraise the petrological and mineralogical characteristics of the hot-spring deposits.Besides,the preserved biosignature in siliceous sinter can be detailed by scanning electron microscopy.The main results are as follows:?1?The hot water sampled at Gumignquan and Yanjignquan is a high temperature?>80??,alkali chloride type?Na-HCO₃-Cl;p H?9?,and abundant HCO₃^-?Cl^-?Na⁺?K⁺ion.?2?The sinter at the high-temperature vent area is dominated by spicular sinter,?pseudo?columnar sinter;however,distal apron deposited by“palisade fabrics”sinter,indicated that the difference of sinter“biofacies”,this phenomenon is the result of changes of hydrothermal fluids,temperature,microbial activities.?3?The quality of the preservation of biosignature mainly controls by diagenesis,with the gradual increase of sedimentary-diagenesis maturation,part of microbial-associated morphological features will gradually disappear.?4?Compared with other typical modern siliceous diagenesis,at Gumignquan and Yanjignquan,only recognizes Opal-A and crystalline quartz silica phase,lacks Opal-C and Opal-CT,this lack of silica phase in a short time will make it difficult to identify the biological characteristics.?5?The siliceous deposits in the study area continuously subjected to acidic steam,form clay minerals?kaolinite,mica,etc.?.This hydrothermal alteration occurs at the Opal-A deposition periods and the surface of the crystalline quartz,indicating that the lack of biological characteristics caused by hydrothermal alteration is likely to occur at the earliest stage of silica deposition and continues throughout the diagenesis-burial stage.Compared with the typical hydrothermal environment in the world,the alteration produced in the study area is stronger than other places.In this study,based on the division of the temperature gradient facies at Gumingquan and Yanjingquan,detailed not only the characteristics of the lithofacies of sinter and preserved biosignature in siliceous deposits,but also explain the factors that affect the quality of silicified biological preservation characteristics.Comparison of this study with siliceous deposits in typical regions provides evidence for the paleoecological studies at hot spring systems.