碳酸盐岩中稳定同位素对古气候的表征

An expression of palaeoclimate by stable isotopes in Carbonate sedimentary rocks.

碳酸盐岩中稳定同位素组成对古气候和古环境具有较为明显的表征意义。根据对广泛分布于塔里木盆地的下古生界碳酸盐岩的碳、氧稳定同位素分析，绘出了浅水台地相的柯坪剖面和深水盆地相的库鲁克塔格剖面寒武系底部至奥陶系顶部稳定同位素地层曲线。经过两地的对比并结合稳定碳、氧同位素组成特点，认为：在塔里木地区，晚震旦纪晚期至寒武纪早期有陆地冰川发育，海水温度较低，利于有机质的保存，应为烃源岩发育期，台地相碳酸盐岩与盆地相页岩均可成为良好的烃源岩；早寒武世晚期至早奥陶世，浅水台地区有机质埋藏率下降，但深水区有机质的埋藏率增加；中、晚奥陶世是又一个烃源岩广泛发育期。图３ 参７（王大锐摘）

Depending on the stable isotopic carbon and oxygen compositions in the carbonates of Lower Paleozoic group which are widely distributed within the Tarim basin, the stable isotopic stratigraphic curves can be shown clearly on both sections of Keping (shallow water platform facies) and Kuluketage (deep water basinal facies). Based on the comparison of carbon and oxygen isotopic compositions on both sections, it is suggested that land glacial developed in the episode from Later Sinian to Early Cambrian in the Tarim area when the temperature of sea water was relatively lower and organic matter could be easily preserved, so that should be a developing time of hydrocarbon source rocks. The carbonates of platform facies and shale of basin facies could become the good source rocks sedimented in this episode; the Middle Late Ordovician could be another episode for the wide development of source rocks; the buried rate of organic carbon decreased in the platform facies but increased in the deep water basinal facies during the Early Cambrian to Early Ordovician.