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近年来,四川盆地上三叠统是陆相还是海相的争议越来越多。正确认识该问题不仅是正确解读印支运动和四川盆地形成的关键,更是预测须家河组天然气勘探潜力的关键。晚三叠世四川盆地物源、沉积构造、黏土矿物、硼钾比和有机地球化学5个方面的证据证实,须家河组须一段—须三段为海相沉积,须四段—须六段沉积时期,由于龙门山南段的隆升,四川盆地与外海逐渐失去联系,但仍受到海侵作用的影响。①1000多口单井岩石薄片资料分析表明,须四段—须六段沉积时期,龙门山南段尚未抬升或仍为水下隆起,四川盆地与外海依旧相连;②不仅须一段—须三段岩心和露头中发育大量潮汐成因沉积构造,须四段—须六段也非常发育,表明该时期仍然受到潮汐作用的影响;③须四段—须六段高岭石开始出现,但仍有大量伊利石和绿泥石存在,表明该时期酸性古水介质虽开始出现,但仍受到盐碱性古水介质的影响;④硼钾比分析表明,须三段沉积时期古水体盐度开始降低,但仍远远大于正常淡水湖泊水体盐度(平均值为0.5‰),表明该时期仍有大量咸水的注入;⑤有机地化分析表明,须四段—须六段姥植比(Pr/Ph)明显较低,烃源岩的饱和烃十分特殊,甲基甾烷丰富,烃源岩芳烃组成具有明显的特殊性,反映该时期明显受到海侵作用的影响。
In recent years, there are more and more controversies that the Upper Triassic in the Sichuan Basin is continental or marine. Correct understanding of this issue is not only the key to correctly interpret the Indosinian movement and the formation of the Sichuan Basin, but also predict the potential for natural gas exploration in the Xujiahe Formation. Evidence from provenance, sedimentary structure, clay mineral, boron-to-potassium ratio and organic geochemistry in the Late Triassic Sichuan Basin confirms that the Xujiahe Formation of Xujiahe Formation should be marine sediment, During the sedimentary period, due to the uplift of the southern segment of Longmen Shan, the Sichuan Basin and the outer sea gradually lose contact, but are still affected by transgression. ① The data of more than 1000 single well rock slices shows that the sedimentary period of the fourth member to the sixth member of the Seishan segment has not yet been uplifted or is still subducted in the south of Longmen Shan, And the outcrops developed a large number of tidal sedimentary structures, the fourth member - to be six sections are also very developed, indicating that the period is still subject to the impact of tidal effects; ③ four to four - to be six kaolinite began to appear, but there are still a large number of Erie The existence of the rocks and the chlorite indicates that although the acidic palaeo-media began to appear during this period, it was still affected by the saline alkaline palaeosol medium. (4) The analysis of B and K ratios showed that the salinity of the Paleo-Sediment began to decrease, Which is much larger than the salinity of normal freshwater lakes (average 0.5 ‰), indicating that there is still a large amount of salt water injected during this period. (5) Organic geochemical analysis shows that Pr / Ph It is obviously lower. The saturated hydrocarbons in the source rocks are very special and the methylstestanes are abundant. The composition of aromatics in the source rock is obviously peculiar, reflecting the obvious influence of transgression during this period.