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首页> 外文期刊>Facies >Calcitization of aragonitic bryozoans in Cenozoic tropical carbonates from East Kalimantan, Indonesia
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Calcitization of aragonitic bryozoans in Cenozoic tropical carbonates from East Kalimantan, Indonesia

机译：来自印度尼西亚东加里曼丹的新生代热带碳酸盐中古生孢子虫的钙化作用

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Aragonite is commonly lost during the diagenesis of carbonate rocks, producing a significant bias in the fossil record. However, taphonomic loss of aragonitic biota can be nullified when skeletal aragonite is replaced by calcite. Here we report calcification of the originally aragonitic skeletons of two cheilostome bryozoan taxa-Reussirella sp. and Reptadeonella toddi-in muddy reefs from the Miocene of East Kalimantan. The calcitic composition of these Miocene fossils is shown using Raman spectroscopy, which enabled precise in situ analysis of skeletal walls without contamination from sediment or chamber-filling cement. Compared with Recent and fossil relatives preserved in original acicular aragonite, the calcitized bryozoans have skeletons with blocky microstructures, undulose extinction patterns, and small patches of highly birefringent acicular crystals that may be aragonite relics. Calcitization of the bryozoans as well as scleractinian corals in the East Kalimantan Miocene reefs was probably made possible because of the high input of fine-grained clastic sediments that partially sealed the buried skeletons, although other factors must be invoked to explain the lack of calcitized molluscs in the same reefs. A general conclusion from this study is that not all bryozoans preserved in deposits from which aragonitic molluscs have been lost through diagenetic dissolution possessed original skeletons of calcite. The potential for selective loss of molluscs but not bryozoans and corals must be taken into account during biofacies analysis.
机译：文石在碳酸盐岩的成岩过程中通常会丢失，从而在化石记录中产生明显的偏差。但是，用方解石代替骨架文石时，可以消除古生物群的菌落丧失。在这里，我们报告两个cheilostome bryozoan类群-Reussirella sp的原始文石骨架的钙化。以及东加里曼丹中新世的泥沼里的小假单胞菌Toddi。这些中新世化石的钙化成分是通过拉曼光谱法显示的，该光谱法能够对骨骼壁进行精确的原位分析，而不会受到沉积物或充填水泥的污染。与原始的针状文石中保存的近代和化石亲属相比，钙化的苔藓虫的骨架具有块状微结构，无节状消光模式和小块的高双折射针状晶体，可能是文石遗迹。东加里曼丹中新世珊瑚礁的苔藓虫和巩膜珊瑚的钙化可能成为可能，因为大量输入的细碎碎屑沉积物部分封闭了被掩埋的骨骼，尽管必须引用其他因素来解释缺乏钙化的软体动物的原因。在同一个礁石中。这项研究的总体结论是，并非所有保存在沉积物中的苔藓动物都具有方解石的原始骨架，而沉积物中的古生动物软体动物因成岩作用溶解而从中丢失。在生物相分析中，必须考虑选择性损失软体动物而不是苔藓动物和珊瑚的可能性。

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