摘要
根据中国湖北黄陵背斜周缘11条奥陶纪、志留纪地层剖面的笔石,几丁虫和虫牙反射率的研究,结合相同或邻近层位牙形石色变指数(CAI)和分散有机质成熟度的红外光谱鉴定,进一步证明:笔石、几丁虫和虫牙的反射率具有随成熟度增加而增加的特点以及各自不同的反射率径迹,因此,在不含镜质组的前泥盆纪地层中,它们可以作为热成熟度的指示。笔石具有明显的各向异性的光学特点,在平行层面所切笔石光面上测量笔石最大油浸反射率,对确定含化石母岩的成熟度最为合适。几丁虫和虫牙具有各向同性的光性特点,因而它们的光面仅显示反射率而无双反射率。笔石、几丁虫和虫牙反射率分布趋势的分析表明,可以将本区奥陶系与志留系划分为3个成熟度区。并对各区形成油气的潜在可能性进行了讨论,其结果与牙形石色变指数和有机质红外光谱分析,所证明的区域有机质成熟度分布模式基本一致。
Based on studies of the reflectance of Ordovician and Silurian zooclasts from 11 sections around the Huanglin Anticline, Hubei, China, combined with determination of the conodont colour indices (CAI) and of infrared spectroscopy of dispersed organic matters from the same or adjacent horizons, it is further proved that reflectances of graptolites, chitinozoans and scolecodonts, like vitrinke and natural bitumen, increase with increasing maturation, but follow different reflectance paths. They may be used, therefore, as thermal maturation indicators for vitrinitefree pre-Devonian strata.Graptolites display optically strong anisotropy. The maximum reflectance measured from graptolites on polished section cut parallel to the bedding plane is the most suitable for determination of maturation of their host rocks. In polished section chitinozoans and scolecodonts show reflectance, but no bireflectance due to their isotropy. The random reflectance of chitinozoans is higher than that of scolecodonts in the cse of the same maturity. Weathering, however, may interfere with the reflectance measured from the sample. Comparing with the reflectivity of those zooclasts the reflectance of solid bitumen appears to be not very unreliable.By analysing the distribution trends of graptolite, chitinozoan and scolecodont reflectances three areas of maturation can be recognized: the Yichang-Xingshan, Yuanan and Yidu-Changyang areas. This result coincides with the distribution pattern of regional maturation presented by CAI and infrared spectroscopic determination of organic matter. The maximum reflectances of Ordovician and Silurian graptolites range from 2.04 to 2.92% in the Yichang-Xingshan area, corresponding to the equivalent vitrinite reflectance of 1.0-1.1%. This result shows that this area has passed the oil generation phase, belonging to the maturity to early high maturity stages and has a potential for the formation of wet gas rather than for oil generation. In the Changyang-Yidu area (excluding the area south of Pinluo of Changyang to Tizikou of Yidu) the maximum reflectances of graptolites range from 3.15 to 3.45% (Tab.1, Fig. 5), corresponding to the equiva- lent vitrinite reflectance of 1.3—1.6%. The vitrinite reflectance in the Yuanan area is estimated to be from 1.4 to 1.7% according to the CAI value (3—3.5). In both areas they are in the early high maturity stage and probably have a potential for dry gas generation The vitrinite reflectance is estimated to be above 2% south of Pinluo of Changyang to Tizikou of Yidu, belonging to the late high maturity stage with little potential for gas generation. Based on studies of reflectance of bitumen (1.63—1.85%) and equivalent vitrinite reflectance (1.4%) (Tab.1) obtained from an infrared spectrum analysis of organic matter in Fujunmiao of Xintan, Zigui, it is noteworthy that the organic maturity there is a little higher than that in the Yichang-Xingshan area and lower than that in that Yidu-Changyang area. Whether another maturity area is present between the Yichang-Xinshan and Yidu-Cbangyang areas needs to be proved.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1992年第3期269-279,共11页
Acta Geologica Sinica
基金
联邦德国大众汽车基金
中华人民共和国地质行业科学技术发展基金
关键词
笔石
几丁虫
虫牙
反射率
探油
graptolite, chitinozoan, scolecodont, reflectance
