Carbon and Strontium Isotopes of Late Palaeozoic Marine Carbonates in the Upper Yangtze Platform,Southwest China

238 marine carbonate samples were collected from seven sedimentary sections ofthe entire late Palaeozoic (Permian, Carboniferous and Devonian) in the Upper Yangtze Plat-form, southwest China. Based on the absence of cathodoluminescence and very low Mn (gener-ally<50 ppm) contents of the samples, it is thought that they contain information on the orig-inal sea water geochemistry. The results of isotopic analyses of these samples are presented interms of δ~(13)C and ~(87)Sr/~(86)Sr ratios versus geological time. The strontium data, consistent withother similar data based on samples from North America, Europe, Africa and other areas inAsia, support the notion of a global consistency in strontium isotope composition of marinecarbonates. The strontium data exhibit three intervals of relatively low ~(87)Sr/~(86)Sr ratios in thelate Middle Devonian to early Late Devonian, Early Carboniferous and Early Permian, corre-sponding to global eustatic high sea level stands. The lowest ~(87)Sr/~(86)Sr ratio recorded in theLate Permian was probably caused by substantial basalt eruptions in the Upper Yangtze Plat-form at the time. Three corresponding periods of relatively high δ~(13)C values at roughly the samethe intervals were caused by a relatively high rate of accumulation of organic carbon duringsea level rises at these times. The deposition of coal was probably responsible for the increaseof sea water δ~(13)C at other times. The δ~(13)C values drop dramatically near theDevonian/Carboniferous, Carboniferous/Permian and Permian/Triassic boundaries, con-sistent with other similar data, which further support the notion that geological time boundariesare associated with mass extinction and subsequent rejuvenation.

Carbon and Strontium Isotopes of Late Palaeozoic Marine Carbonates in the Upper Yangtze Platform,Southwest China

238 marine carbonate samples were collected from seven sedimentary sections of the entire late Palaeozoic (Permian, Carboniferous and Devonian) in the Upper Yangtze Platform, southwest China. Based on the absence of cathodoluminescence and very low Mn (generally < 50 ppm) contents of the samples, it is thought that they contain information on the original sea water geochemistry. The results of isotopic analyses of these samples are presented in terms of δ¹³C and ⁸⁷Sr/⁸⁶Sr ratios versus geological time. The strontium data, consistent with other similar data based on samples from North America, Europe, Africa and other areas in Asia, support the notion of a global consistency in strontium isotope composition of marine carbonates. The strontium data exhibit three intervals of relatively low ⁸⁷Sr/⁸⁶Sr ratios in the late Middle Devonian to early Late Devonian, Early Carboniferous and Early Permian, corresponding to global eustatic high sea level stands. The lowest ⁸⁷Sr/⁸⁶Sr ratio recorded in the Late Permian was probably caused by substantial basalt eruptions in the Upper Yangtze Platform at the time. Three corresponding periods of relatively high δ¹³C values at roughly the same time intervals were caused by a relatively high rate of accumulation of organic carbon during sea level rises at these times. The deposition of coal was probably responsible for the increase of sea water δ¹³C at other times. The δ¹³C values drop dramatically near the Devonian/Carboniferous, Carboniferous/Permian and Permian/Triassic boundaries, consistent with other similar data, which further support the notion that geological time boundaries are associated with mass extinction and subsequent rejuvenation.