摘要：

羌塘盆地中侏罗统黑色岩系因富含有机质而成为重要烃源岩之一。选择毕洛错剖面为研究对象,以古生物地层学为基础,依据TOC含量和碳氧同位素变化,深入分析该剖面中侏罗统巴通阶—卡洛夫阶(Bathonian-Callovian)黑色岩系的碳氧同位素时空分布规律,探讨该时期的古环境、古气候等特征。 结果显示: 研究区中侏罗统黑色岩系的TOC含量为0~1.5%,δ¹³C_org值为-24‰~-26‰(PDB),δ¹³C_carb值为-4.819‰~2.323‰(PDB)(平均值为-0.659‰),δ¹⁸O值为-13.96‰~0.66‰(PDB)(平均值-7.37‰)。通过全球碳同位素地层对比,认为巴通期底部δ¹³C_carb负偏与早—中侏罗世海退事件驱动的陆源输入增强相关; 中—晚巴通期至早卡洛夫期δ¹³C_carb正向偏移对应海洋初级生产力激增事件; 卡洛夫期至早牛津期,沙特阿拉伯、巴黎盆地、波兰喀尔巴阡山脉以及羌塘盆地δ¹³C_carb普遍发生了正偏移现象,且与高TOC页岩层段相对应,表明富有机质黑色岩系的发育与大规模海侵有关,并受控于全球海平面上升背景下有机质埋藏通量的增加。另外,古生物学、岩石学以及氧化还原指标(V/(V+Ni)、V/Cr、Ni/Co等)显示,该套黑色岩系形成于较还原的沉积环境中。上述成果揭示了羌塘盆地中侏罗统黑色岩系碳氧同位素时空分布具有全球性,而且受控于还原条件、海平面上升等多种因素的控制。

关键词: 碳氧同位素, 全球对比, 海平面变化, 黑色岩系, 中侏罗统, 羌塘盆地

Abstract:

The Middle Jurassic black rock series in the Qiangtang Basin serve as significant hydrocarbon source rocks due to their high organic matter contents. The Biluo Co section was chosen as the research target. Based on paleontological stratigraphy and by analyzing the total organic carbon(TOC)contents as well as variations in carbon and oxygen isotopes,this study discussed the spatio-temporal distribution patterns of carbon and oxygen isotopes from the black rock series of the Bathonian-Callovian stages(Middle Jurassic),and the characteristics of the paleoenvironment and paleoclimate during this period. Results show that the TOC contents range from 0 to 1.5%,δ¹³C_org,δ¹³C_carb and δ¹⁸O values vary between-24‰ and-26‰,-4.819‰ and 2.323‰(mean values of-0.659‰),-13.96‰ and 0.66‰(mean values of-7.37‰),respectively. According to the global carbon isotope correlations,the negative inorganic carbon excursions in the early Bathonian is associated with the enhanced terrigenous input triggered by the Early-Middle Jurassic regression event. The positive shifts of δ¹³C_carb from the Middle-Late Bathonian to the Early Callovian correspond to the event of a substantial surge in marine primary productivity. During the Callovian-Early Oxfordian,a widespread positive carbon isotopes anomalies and high TOC contents of shales occurred in regions such as the Qiangtang Basin,Saudi Arabia,Paris Basin,and Polish Carpathians,which shows that the organic-rich black rock series are closely related to large-scale marine transgressions and primarily driven by the increase in the burial flux of organic matters under the backdrop of global sea-level rise. Moreover,paleontological and petrological characteristics,and redox-sensitive proxies(e.g.,V/(V+Ni),V/Cr,Ni/Co ratios) suggest that the black rock series deposited in a relatively reducing sedimentary environments. This study highlights that the carbon and oxygen isotopes of Middle Jurassic black rock series have the global distribution patterns influenced by multiple factors,including redox conditions,sea-level fluctuations, burial dynamics of organic matters, and so on.

Key words: carbon and oxygen isotope, global correlation, sea-level changes, black rock series, Middle Jurassic, Qiangtang Basin

中图分类号: 

• P597