The Strontium Isotopic Composition Of Marine Cabonate From The Huaying Mountain, Eastern Sichuan

Strontium isotope stratigraphy (SIS) has became a important part of Chemistry Stratigraphy at present, and also became increasingly a effect method for the global geological events and marine sediment's age research. In order to know the strontium isotopic composition of marine cabonate rocks from the Huaying Mountain, Eastern Sichuan, we have researched on the stratigraphy, sedimentology and strontium isotope stratigraphy, base on the observation, survey and sampling for the field outcrops.Most of the samples have original microlite texture and much-dark, dark cathodoluminescence, only less than 20 percent samples have middle or more brighter cathodoluminescence. And they also have lower Mn content (mean content is 224 ppm for all samples) and higher Sr conent (mean content is 627 ppm for all samples), their Mn/Sr ratio are also small (mean Mn/Sr ratio is 0.65 for all samples). Base on the samples' microfabric, cathodoluminescence, Mn content, Sr content and Mn/Sr ratio, eliminate several samples which have been suffered more stronger diagenesitic alteration and could be not represented for the seawater. So the most of marine carbonate samples only have been suffered limited diagenesitic alteration, and could be represented for the seawater from the Huaying Mountain, Eastern Sichuan, the later strontium isotope analysis result also prove it.The strontium isotopic variation curve for the marine cabonate rocks from the Huaying Mountain, Eastern Sichuan could subdivision to five phases: strontium isotopic variation for the Feixianguan Formation (early Lower Triassic) is comparative stable (first and second phase), and then the strontium isotopic variation for the Jialingjiang Formation (late Lower Triassic) ascend quickly in the short interval and arrive the maximum strontium isotope ratio for the Triassic seawater (third and fourth phase), at last the strontium isotopic variation for the Leikoupo Formation (early Middle Triassic) descend quickly in the short interval (fifth phase). So the strontium isotopic variation curve for the marine cabonate rocks from the Huaying Mountain, Eastem Sichuan is similar to other pioneering studies, and explain that global geological events are the mostly dominative fators for the strontium isotopic variation of the samples.The ages for the samples near several key stratigraphic boundaries of the marine Triassic from the Huaying Mountain, Eastern Sichuan are calibrated, according to the strontium isotope - age databases for the Triassic seawater from other pioneering studies. The ages calibrated for the samples near the Permian/Trassic boundary are about 245.30 Ma, 253.18 Ma or 252.60 Ma (corresponded different databases, respectively), the samples near the Feixianguan Formation/Jialingjiang Formation boundary are about 244.95 Ma, 252.67 Ma or 251.62 Ma (corresponded different databases, respectively), the samples near the Jialingjiang Formation/Leikoupo Formation (Lower Triassic/Middle Triassic) boundary is between 241.9 and 242.2 Ma, and the samples near the Triassic marine and non-marine sediment boundary are about 240.08 Ma or 237.50 Ma (corresponded different databases, respectively).