【摘要】 本研究利用大庆油田在松辽盆地中部的岩心样品进行了青山口组有机碳稳定同位素的测试,通过化学地层和生物地层研究提出了青山口阶的顶底标志。在青山口组底部同位素值最低,为- 32 .2‰,与介形虫Cypridea elliptica的消失界面吻合。同位素值随后迅速上升,形成底界之上的第一个峰值,为- 2 8.1‰。随后的4个峰值自下而上分别是- 2 8‰、- 2 7.8‰、- 2 7.3‰和- 2 6 .6‰,相间的低峰值一般处于- 30‰～- 2 9‰左右。最为重要的是,有机碳稳定同位素值在青山口组顶部出现一个明显的异常,由- 2 9.5‰急剧升为- 2 3.1‰,随后又迅速降为- 30 .12‰,形成一个明显的正向峰值。这一正向偏移的位置与介形类Cypridea panda和Triangulicyprisfusiformis的消失界面基本吻合,并与全球Cenom anian- Turonian界线稳定同位素事件表现一致。据此,将这一稳定同位素正向偏移确定为青山口阶顶界的化学标志。通过这一标志可以将青山口阶的顶界与海相Cenom anian阶顶界进行对比。研究结果表明,化学地层标志是陆相与海相地层的对比的渠道。青山口阶的有机碳稳定同位素值具有全球一致的意义,与我国西藏南部海相地层,乃至全球重要地区Cenomanian- Turonian阶稳定同位素界线均具有可比性。更多还原

【Abstract】 The Songliao Basin is a big lake during mid-Cretaceous, where a group of bituminous sediments are well deposited. The biostratigraphy has been well studied, but little has been done on the correlation between lacustrine sediments with standard marine sequence. The present isotopic measurement is focused on the Qingshankou Fourmation, and in the hope to find a way for correlation. Fifty-nine core samples were collected from a borehole in central part of the basin, where the Qingshankou Fourmation is contacted conformably with underlying Quantou and overlying Yaojia Formations. Bulk rock organic carbon isotopic data were measured. The profile shows the values varying from -32.2‰ to -23.1‰. The lowest value appears at the base of Qingshankou Formation, which matches with the disappearance of ostracods assemblage Cypridea elliptica-Cypridea deformata. Six peaks occur upwards, their values are -28.1‰, -28‰, -27.8‰, -27.3‰, -26.6‰, and -23.1‰. The most important is the uppermost peak that is the maximum of the profile and occurs at the boundary of Qingshankou /Yaojia Formations. The ostracods assemblage Cypridea panda-Triangulicypris fusiformis disappeared 4 miters underneath the peak. As in other parts of the world, large amount of organic carbon burial caused the positive excursion in δ13C values between Cenomanian/Turonian boundary (Kuhnt et al. 1997; Caron et al. 1999; Meyers et al, 2001; Prokoph et al. 2001; Wan et al, 2003b). The positive excursion also happened in non-marine environments (Hasegawa, 2003; Tsikos, et al, 2004) under one paleo-atmospheric system of same time. The strength and stratigraphic restriction of the δ13C signal at the boundary between Qingshankou—Yaojia Formations are well coincident with global distributed positive excursion. By the chemostratigraphic study, therefore, the Qingshankou Formation can be correlated with the Cenomanian stage.更多还原