四川省若尔盖县巴西—吉求地区晚三叠世遗迹化石及遗迹相

    FEATURES AND DISTRIBUTION OF VOLCANIC ROCK ASSOCI ATIONS OF VARIOUS AGES IN THE BEISHAN AREA, GANSU

    • 摘要: 四川若尔盖巴西—求吉地区晚三叠世首次发现了丰富的遗迹化石,经鉴定有22个遗迹属、34个遗迹种。根据不同遗迹属在不同层位中的相对丰度,建立了4个遗迹组合:(1)Helminthop sis—Phycosiphon组合;(2)Dendrotichnium—Neonereites组合;(3)Paleodictyon组合;(4)Taenidi um—Cosmorhaphe组合。上述遗迹组合大致相当于Seilacher的Zophycos遗迹相和Nereites遗迹相。依据遗迹化石进行了沉积环境分析,认为该区晚三叠世的沉积环境经历了大陆斜坡中下部—大陆斜坡下部—深海盆地的演变。

       

      Abstract: On the basis of a large amount of data combined with field work in some ore districts and petrochemical work, the authors have compiled a map of volcanic rock associations and their distribution in the Beishan area, summarized the features of volcanic rock associations of various ages and their distribution in the Beishan area. It is suggested that the volcanic rocks in most horizons belong to the successively differentiated rock association of normal K Na type and dominantly calc alkaline, intermediate to acid compositions, while basic and bimodal volcanic rock associations of the tholeiite series are only developed in Proterozoic, Middle Ordovician, Upper Ordovician and Lower Permian strata. The alkaline series is scanty and no alkaline rocks (σ>9.0) occur in the study area. Intermediate acid rocks of the potassic type may appear in some ore districts such as Baishantang, Gongpoquan and Langwashan. The features of volcanic rocks reflect the tectonic evolution history of multiple "openings" and "closings" in the Beishan.

       

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