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首页> 外文期刊>International Journal of Earth Sciences >Mesozoic (Lower Jurassic) red stromatactis limestones from the Southern Alps (Arzo, Switzerland): calcite mineral authigenesis and syneresis-type deformation
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Mesozoic (Lower Jurassic) red stromatactis limestones from the Southern Alps (Arzo, Switzerland): calcite mineral authigenesis and syneresis-type deformation

机译：来自南阿尔卑斯山（瑞士阿尔佐）的中生代（下侏罗统）红色层间质灰岩：方解石矿物的成矿作用和干缩型变形

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摘要

The Broccatello lithological unit (Lower Jurassic, Hettangian to lower parts of Upper Sinemurian) near the village of Arzo (southern Alps, southern Switzerland) is a mound-shaped carbonate deposit that contains patches of red stromatactis limestone. Within the largely bioclastic Broccatello unit, the stromatactis limestone is distinguished by its early-diagenetic cavity system, a relatively fine-grained texture, and an in-situ assemblage of calcified siliceous sponges (various demosponges and hexactinellids). A complex shallow subsurface diagenetic pathway can be reconstructed from sediment petrography in combination with comparative geochemical analysis (carbon and oxygen isotopes; trace and rare earth elements, REE + Y). This pathway includes organic matter transformation, aragonite and skeletal opal dissolution, patchy calcification and lithification, sediment shrinkage, sagging and collapse, partial REE remobilization, and multiple sediment infiltration. These processes occurred under normal-marine, essentially oxic conditions and were independent from local, recurring syn-sedimentary faulting. It is concluded that the stromatactis results from a combination of calcite mineral authigenesis and syneresis-type deformation. The natural stromatactis phenomenon may thus be best explained by maturation processes of particulate polymer gels expected to form in fine-grained carbonate sediments in the shallow subsurface. Conditions favorable for the evolution of stromatactis appear to be particularly frequent during drowning of tropical or subtropical carbonate platforms.
机译：Broccatello岩性单元（下侏罗纪，Hettangian到上Sinemurian的下部）靠近Arzo村（瑞士南部，阿尔卑斯山南部），是一个丘状的碳酸盐矿床，其中含有红色的层间层石灰岩。在具有大量生物碎屑的布罗卡塞洛单元中，层间层灰岩的特征是其早成岩的空洞系统，相对细颗粒的质地以及钙化硅质海绵的原位组合体（各种海绵体和十六碳体）。可以通过沉积物岩石学和比较地球化学分析（碳和氧同位素；痕量和稀土元素，REE + Y）来重建复杂的浅层地下成岩途径。该途径包括有机物转化，文石和骨骼蛋白石溶解，片状钙化和石化，沉积物收缩，下陷和塌陷，部分REE迁移以及多种沉积物渗透。这些过程发生在正常海洋条件下，基本上是有氧条件，并且独立于局部，反复的沉积沉积断层。结论是，层间震源于方解石矿物的成因作用和脱水型变形的结合。因此，自然层间触觉现象可以用预计在浅表层下的细粒碳酸盐沉积物中形成的颗粒状聚合物凝胶的成熟过程来最好地解释。在热带或亚热带碳酸盐岩台地溺水期间，有利于层间触目演化的条件似乎特别频繁。

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