松辽盆地松科1井上白垩统烃源岩有机碳含量与沉积速率的关系*

与海相盆地相比,陆相湖盆沉积物TOC和沉积速率关系的研究尚处于探索阶段,尤其是在沉积作用对TOC的控制机理研究方面还有待深入。首先运用旋回地层学方法,识别了松科1井南孔上白垩统天文周期,并利用滑动窗口频谱分析方法计算了各窗口的沉积速率及对应的TOC值。以姥鲛烷和植烷(Pr/Ph)比值作为氧化还原条件的指标,以介形虫壳体的δ¹³C作为古生产力大小的指标,对不同环境和不同古生产力条件下TOC和沉积速率的关系进行了探讨。研究表明: 在还原环境下,TOC主要取决于古生产力高低,而沉积速率的影响相对较小,当古生产力较高时,TOC值一般大于1%;反之,TOC值小于1%。但在氧化环境、低古生产力条件下,TOC随着沉积速率先增大后减小,其临界值为11,cm/ka。

Relationship between total organic carbon content and sedimentation rate of the Upper Cretaceous source rocks in Well CCSD-SK-I in Songliao Basin

Compared with study in marine basins,study on the relationship between total organic carbon (TOC) content and sedimentation rate(SR)in continental lacustrine sediments is still in exploration phase,and the controlling mechanism of sedimentation on TOC especially needs intensive study. In this paper,astronomical cycles of the Upper Cretaceous in the southern borehole of Well CCSD-SK-1 were firstly identified with the cycle stratigraphy method; and then SR and the corresponding TOC of each window was calculated by moving-window spectral analysis method. Taking the Pr/Ph ratio as a redox condition index and δ¹³C of the ostracod shell as a paleo-productivity index,the relationship of SR and TOC in different environments and different paleo-productivity conditions in detail was discussed. Analyses show that TOC is mainly controlled by palaeo-productivity while the influence of SR is very little; in a high palaeo-productivity environment the TOC value is larger than 1% and less than 1% in contrast. But under the oxidation and low palaeo-productivity conditions,the TOC value tends to increase with SR when SR is less than 11,cm/ka and then decreases in a higher SR background.