THE ORIGIN AND SIGNIFICANCE OF ZIGZAG MICROSTRUCTURE IN LATE PALEOZOIC LOPHOPHYLLIDIUM (ANTHOZOA, RUGOSA)
THE ORIGIN AND SIGNIFICANCE OF ZIGZAG MICROSTRUCTURE IN LATE PALEOZOIC LOPHOPHYLLIDIUM (ANTHOZOA, RUGOSA)
复制标题
晚古生代垂叶草（ANTHOZOA，RUGOSA）之字形微结构的起源及其意义
作者：
J. E. Sorauf;G. Webb
摘要：在晚古生代孤立的 Rugosa 中，Schindewolf (1942) 定义的锯齿形微观结构与生物方解石（中镁方解石，IMC）中镁含量的升高及其随后在成岩过程中因微溶解和新变质而损失有关。这种特殊的微观结构仅在一些石炭纪和二叠纪皱纹珊瑚（例如 Lophophyllidium spp.）中得到确定。这些珊瑚的隔膜和其他骨骼微结构主要是（斜）倾斜片状，这也被解释为成岩起源。两个方向的倾斜片层通常出现在加厚的骨架单元中，形成 V 形，构成锯齿形微结构，其方向由骨架方解石内微白云石气泡的存在决定。对阿肯色州密西西比伊莫组珊瑚、俄克拉荷马州宾夕法尼亚州鹿角沥青和肯塔基州宾夕法尼亚州肯德里克页岩的珊瑚的地球化学研究都表明，珊瑚骨架方解石中的镁含量升高，最高可达 6 至 8 摩尔% CaCO3 附近，从而形成中间镁方解石。具有这种锯齿状微观结构的珊瑚显然只出现在晚古生代的“文石海”时期；因此，皱纹珊瑚的这种成岩行为可以作为海洋化学和/或气候长期变化的代表。
Abstract In late Paleozoic solitary Rugosa, the zigzag microstructure as defined by Schindewolf (1942) is related to presence of an elevated magnesium content within biogenic calcite (intermediate magnesian calcite, IMC) and its subsequent loss during diagenesis by microdissolution and neomorphism. This particular microstructure has been recognized with certainty only in some Carboniferous and Permian rugose corals (e.g., Lophophyllidium spp.). Septal and other skeletal microstructures in those corals are dominantly (oblique) sloping- lamellar, which is also interpreted as diagenetic in origin. Two directions of oblique lamellae commonly occur in thickened skeletal elements, forming chevrons that make up zigzag microstructure with its orientation determined by presence of microdolomite blebs within skeletal calcite. Geochemical studies of corals from the Mississippian Imo Formation of Arkansas, the Pennsylvanian Buckhorn asphalt of Oklahoma and Pennsylvanian Kendrick Shale of Kentucky all indicate that magnesium content in skeletal calcite of the corals was elevated, with a maximum in the neighborhood of six to eight mole percent CaCO3, thereby forming intermediate magnesium calcite. Corals with this zigzag microstructure apparently only occurred during the late Paleozoic interval of “aragonite seas”; as a result, this diagenetic behavior of rugose corals can serve as a proxy for secular change in marine chemistry and/or climate.