he Strontium Isotopes of Deep-sea Siliceous Rocks from Earlier Carboniferous to Earlier Permian,Qinzhou,Guangxi

Key words: 
• Qinzhou basin /
• deep-sea siliceous rock /
• st rontium isotopes /
• global eustasy

Abstract: The carbon,oxygen and strontium isotope composition of marine carbonate is mainly controlled by global events,such as relative amount of organic accumulation and oxidation,orogenic events,glacial activity,changes in seafloor spreading rate and palaeoclimate variation.The evolution tendency of isotopes with the same stratigraphy interval is similar.This is the fundamental principle of isotope stratigraphy.However,carbonate sediments are normally absent in deep sea environment,we could not obtain the data of carbon and oxygen isotopes,but the deep sea sediments with few fossils specially need the supports of isotope stratigraphy.For this reason,we collected siliceous rock samples from deep sea environment,researched their strontium isotope and set up evolution curves to seek after their application foreground in isotope stratigraphy. The deep sea siliceous rock samples studied here were collected from the sedimentary section from Earlier Carboniferous to Earlier Permian,Qinzhou,Guangxi.Based on the analysis of X ray diffraction and cathodoluminescence of the collected samples,they should be chemical precipitation from seawater.After age correction based on the Rb/Sr ratio,we obtained the original ⁸⁷Sr/⁸⁶Sr values and set up the evolution curve which is similar to that of shallow water carbonate from the same age in Upper Yangtze Platform.It supports the notion of a global consistency in strontium isotope composition of marine interior sediments.However,because we could not eliminate effect from terrigenous clastics with higher 87 Sr content,the average of ⁸⁷Sr/⁸⁶Sr values form siliceous rocks is observably higher than that from carbonate rocks.Additionally the lower ⁸⁷Sr/⁸⁶Sr ratio record of carbonate in Earlier Permian was probably caused by substantial basalt eruptions on Upper Yangtze Platform at the time.The strontium data exhibit three intervals of relatively low ⁸⁷Sr/⁸⁶Sr ratio in Earlier Carboniferous,earlier stage of Late Carboniferous,and Earlier Permian,corresponding to global eustatic high sea level stands.The strontium data exhibit one intervals of relatively high ⁸⁷Sr/⁸⁶Sr ratio in Late stage of Late Carboniferous corresponding to global eustatic lower sea level stands.