西南地区晚二叠世氧、碳稳定同位素的古地理意义

PALEOGEOGRAPHIC SIGNIFICANCES OF CARBON AND OXYGEN ISOTOPES IN LATE PERMIAN ROCKS OF SOUTHWEST CHINA

对西南地区的１９个晚二叠世碳酸盐岩型煤系剖面进行了碳酸岩稳定同位素的测定，探讨了其“年代效应”的校正及古盐度与古温度计算问题。结果表明：在兴文、贵阳、金沙、南桐、重庆一线以西的地区，Ｚ值＜１２０，δ１３Ｃ值明显低于此线以东的地区，但与Ｓｃｈｏｐｆ给出的淡水石灰岩的δ１３Ｃ范围相比偏高，说明为海陆过渡相沉积；而此线以东的地区Ｚ值＞１２０，δ１８Ｏ、δ１３Ｃ均说明为海相沉积，与以前的沉积环境研究结论一致。用校正后的δ１８Ｏ计算出碳酸盐岩形成时的介质古温度为１４．８－５０．９℃，且大多在２３－３１℃，说明当时该区为温暖－炎热的气候，与古地磁资料显示的当时该区处于赤道附近的热带地区的结论基本一致。

The 18O and 13C values of carbonate from nineteen coal-bearing sections of Late Permian in Southwest China are determined. The correction of“age effect”and the calculation of paleotemperature and paleosalinity are discussed in this paper. The results show that Z values are less than 120 in the areas to the west of the line of Xingwen, Guiyang, Jinsha, Nantong and Chongqing, which are much smaller than those in the areas to the east of the line and larger than those of the freshwater carbonate. These facts mentioned above suggest that the sedimentary rocks in these areas deposited in marine-continent transition environment. The Z(> 120), 18O and 13C values in the areas to the east of the line show that the sedimentary rocks deposited in marine environment, which is corresponding to the results of sedimentary environment studies obtained earlier. The paleotemperatures of the seawater, when the carbonate deposited, were in the range of 14.8-50.9℃ , mostly in 23-31℃, which were calculated using the corrected 13C values. The paleotemperature suggests that those areas were wanm and hot at that time, being in accord with the paleomagnetism data indicating that the areas were near the equator in Late Permian.