浙江长兴煤山地区晚二叠世末、早三叠世初的火山活动

<正> 近年来,不少学者分别从生物地层(赵金科等,1981;盛金章等,1983;王义刚,1984;Sheng Jinzhang et al.,1984),事件地层(孙亦因等,1984;何锦文,1985),岩相、生物相(杨万容等,1981;芮琳等,1984),粘土矿物(何锦文,1981),元素地球化学特征(柴之芳等,1986),构造岩浆活动(周瑶琪,1986)以及碳同位素(陈锦石等,1984)等方面对浙江

The latest Permian and earliest Triassic volcanic activities in the Meishan area of Changxing, Zhejiang

Recently, a great number of crystals of α-quartz with a hexagonal dipyramidal habit were discovered in the mixed faunal beds 1-3 of sections A, B, D and Z in the uppermost Permian and lowermost Triassic of Meishan, Changxing of Zhejiang, i.e, beds, 2,3, 5 and 11 of section Z; beds 22, 23 and 25 of section D; beds 5, 6 and 8 of section B and beds 11 and 12 of section A (Fig. 1). It is generally believed that quartz crystal with a hexagonal dipyramidal is typical of phenocrystal in acidic eruptive rocks and always occurs in rhyolite and dacite. Judging from the vertical and lateral distribution of the hexagonal dipyramidal quartz crystals, the Meishan area might have been influenced at least by three phases of volcanic eruption during the latest Permian and earliest Triassic time. The first volcanic eruption might have beguan at the end of Permian and completed at the beginning of Triassic, experienced quite a long period, correspongmg approximately to the sedimentation of the mixed faunal bed 1 including the boundary clay below and greyish black mudstone above, i.e, beds 11, 12 of section A; beds 5, 6 of section B; beds 22, 23 of section D and beds 5, 6 of section Z, with the height stage of the eruption happening at the end of the Permian period. The second volcanic eruption took place-during the earliest Triassic period corresponding to the deposition of the lowermost part of mixed faunal bed 3, i.e. bed 8 of section B, bed 25 of section D and bed 5 of section 2. The third volcanic eruption has happened during the earliest Triassic Period, corresponding to the sedimentation of the uppermost part of the mixed faunal bed 3, i.e. bed 11 of section Z. It is interesting to note that three phases: of volcanic eruption coincide approximately with the time of mass extinction of Permian marine invertebrate faunas, and origin and extinction of the Permian-Triassic mixed fauna. The volcanic effects may be one of the causes of the mass extinction of the Permian marine invertebrates at the end of Permian.