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(一) 火山岩系与正常沉积岩系的形成过程有很大的差异。即使以火山岩系而论,陆相火山岩的堆积又不同于海相火山岩。由此可见,在地层工作中应特别注意它们各自的特殊性。陆相火山岩系主要由火山喷发的熔岩流、各种超浅成次火山岩体、火山碎屑岩、火山喷发间隙期的洪积、坡积碎屑岩、火山宁静期的河湖相沉积组成。由于火山活动的形式具有多样性,火山岩系的堆积方式随火山活动形式的不同亦有变化。火山活动受上地幔与下地壳内岩浆生成、发展和演化的制约。它在堆积物中表现为岩石化学成份的变化和岩石组合特征的差异等。以此为主要标志,可将火山岩系划分为一些旋回。旋回之间具有对比性。
(A) The formation of volcanic rocks and normal sedimentary rocks are very different. Even in terms of volcanic rocks, the accumulation of continental volcanic rocks is different from that of marine volcanic rocks. Thus, we should pay special attention to their particularities in stratigraphic work. The continental volcanic rocks are mainly composed of lava flows erupted from volcanoes, various super-shallow subvolcanic volcanic rocks, volcaniclastic rocks, alluvial deposits of volcanic eruption gap period, sedimentary clastic rocks and sediments of volcanic and lacustrine sediments. Due to the diversity of the forms of volcanic activity, the volcanic rock accumulation also varies with the volcanic activity. Volcanic activity is controlled by the formation, development and evolution of the magma in the upper mantle and the lower crust. It is manifested in the sediment changes in petrochemical composition and rock composition characteristics of the difference. As the main symbol, volcanic rocks can be divided into some cycles. There is contrast between cycles.