Application of organic matter laser Raman spectroscopy thermometry:A case study of Dengying Formation in Western Hubei
Raman spectroscopy is a rapid,simple,and non-destructive analytical method that has significant advantages in assessing the thermal evolution history of carbonaceous materials in deep-time geological samples.However,its usage re-mains controversial and disputed.This study,taking the Dengying Formation carbonates in western Hubei region as an ex-ample,conducted batch Raman spectroscopy tests and calculated the average temperature to be 201℃ to 226℃.This temperature variation falls within an acceptable range.The Raman temperatures of dolomite in the Baimatuo and Hama-jing Members are relatively high and stable,whereas the Ramen temperature range within individual limestone samples from the Shibantan Member is large(180-230 ℃).The Raman spectral characteristics vary significantly with different de-grees of organic matter enrichment,and the temperature fluctuations are also evident vertically.The I135o/I16oo ratio(0.5-1.5)in Shibantan memeber exhibits a similar distribution pattern,but there is no correlation with organic carbon isotope ratios(δ13Corg)and total organic carbon(TOC).These results indicate that the organic matter Raman thermometer has substantial potential for evaluating the burial metamorphic temperature of deep-time samples.When employing this meth-od,the highest metamorphic temperature should be considered in the same basin,and increasing the number of sampling points within a single sample can reduce errors.The heterogeneity in the Raman temperatures of organic matter in the Dengying Formation is due to uneven metamorphism related to varying degrees of organic matter enrichment.The Dengy-ing Formation is under ultra-low-grade burial metamorphic temperature conditions,which is conducive to the preservation of Ediacaran metazoan fossils.
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