贵州独山地区上二叠统合山组C、O同位素特征、沉积环境分析

Characteristics of carbon and oxygen isotopes and sedimentary environments of Upper Permian Heshan Formation in Dushan area,Guizhou

合山组的沉积环境在不同地区存在较大差异,前人未有关于独山地区上二叠统合山组沉积环境及C、O同位素的报道。为了查明贵州独山地区合山组沉积环境及C、O同位素特征,在分析合山组沉积组合和沉积相的基础上,进一步分析了合山组26件碳酸盐岩样品的C、O稳定同位素特征,以及沉积环境演化过程。结果表明,贵州独山地区合山组主要发育了局限台地、开阔台地、台地边缘浅滩和台盆4种沉积环境;δ^(13)C(PDB)值变化在-1.1‰~5.0‰之间,平均值为3.1‰,δ^(18)O(PDB)值变化在-8.8‰^-2.1‰之间,平均值为-5.6‰;δ^(13)C值与海平面的变化呈正相关,δ^(18)O值主要受海平面变化影响,与之呈负相关;研究区古盐度Z值主要介于120.3~132.4之间;根据δ18O计算出的古温度在13.7℃~47℃,平均温度为30.2℃,代表了热带气候。在晚二叠世,独山地区合山组早期沉积环境是由局限台地、开阔台地、台地边缘浅滩迅速变为深水台盆沉积,之后海水变浅,中期经历了由局限台地迅速变为台盆沉积的演化过程,晚期为局限台地环境沉积。

The sedimentary environments of Heshan Formation are different in different regions,and there were no previous reports about the sedimentary environments and C,O isotopic characteristics of Upper Permian Heshan Formation. Based on the analysis of the sedimentary association and sedimentary facies of Heshan Formation,we made further analysis of the C,O isotopic characteristics and sedimentary environment evolution process of the 26 carbonate rock samples from Heshan Formation. The results showed that,Heshan Formation mainly developed 4 sedimentary environments,including restricted platform,open platform,platform margin shoal and inter-platform basin. δ^13C（ PDB） ranged from-1. 1 ‰ to 5. 0 ‰,with the average value of 3. 1 ‰; δ^18O（ PDB） ranged from-8. 8 ‰ to-2. 1 ‰,with the average value of-5. 6 ‰. There was a positive correlation between the δ^13C value and the change of sea level,and the value of δ^18O was mainly influenced by sea-level change and was negatively related to it. The Z value of salinity in the area ranged from 120. 3 to 132. 4. The paleotemperature calculated according to δ^18O was from 13. 7 ℃ to 47 ℃,and the average temperature was 30. 2 ℃,representing tropical climate. In the Late Permian,the early sedimentary environments of Heshan Formation changed rapidly from restricted platform,open platform and platform margin shoal into deep-water basin. Then the sea shallowed,and restricted platform quickly became sedimentary basin. The late sedimentary environments were mainly restricted platform.