摘要
通过比对四川广元上寺剖面二叠系栖霞组碳同位素值变化,探讨了该区烃源岩发育的古生态环境。由于二叠纪高CO2浓度背景使得古海洋海水中相对富集13C,因此二叠纪海相沉积的四川广元上寺剖面栖霞组碳酸盐岩碳同位素均为正值。广元上寺剖面从栖霞组底部向上碳酸盐岩碳同位素逐渐正偏,显示从栖霞组底部沉积时期开始海平面逐渐上升,向相对缺氧沉积环境过渡。栖霞组中部古海洋生产力增高,使得总有机碳同位素正偏。受总有机碳同位素波动的影响,碳同位素分馏值(∈TOC)在整个栖霞组波动频繁。根据平衡状态下碳循环有机碳埋藏分数模型,计算了整个栖霞组有机碳埋藏分数,结果显示有机碳埋藏分数(forg)在整个栖霞组都较高,符合二叠纪的碳埋藏在整个显生宙处于最高阶段的地质背景。栖霞组中部高TOC含量层位对应forg逐渐增高,反映forg与有机碳沉积的保存环境密切相关,说明利用古海洋生产力和forg的变化,可在一定程度上指示原始碳埋藏量的变化。
By comparing the change of carbon isotope,the paleoecological environment of source rocks at Shangsi section in southern China was discussed. Paleo-ocean was enriched with 13C due to high CO2 concentration during the Permian. All of the δ13Ccarb values were greater than 0 at Shangsi section during the Permian. A positive excursion in carbonate isotope from the bottom to top of the Qixia Formation showed sea-level rising. It formed an anoxic sedimentary environment. Paleoproductivity increasing led to a positive excursion in total organic carbon isotope records in the middle part of Qixia Formation. Affected by organic carbon isotope variation, the carbon isotope fractionation between inorganic and organic carbon varied frequently in the Qixia Formation. Using the mass-balance model carbon cycle, the fraction of organic carbon burial（forg） was calculated. In this section, the results show that high forg value accorded with the high value forg during the whole Permian. The gradually increasing value of forg corresponded with high TOC content in the middle part of Qixia Formation. It indicates that the forg is related to the redox conditions, and using changes of paleo-ocean productivity and forg, the variation of original carbon burial quantity can be estimated.
出处
《古地理学报》
CAS
CSCD
北大核心
2010年第3期301-306,共6页
Journal of Palaeogeography：Chinese Edition
关键词
碳酸盐岩碳同位素
总有机质碳同位素
有机碳埋藏
二叠系
栖霞组
carbonate carbon isotope
total organic carbon isotope
organic carbon burial
Permian
Qixia Formation
