Patterns of silicification in Permian pelecypods and brachiopods from Wyoming
Patterns of silicification in Permian pelecypods and brachiopods from Wyoming
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DOI：
10.1306/212f7e91-2b24-11d7-8648000102c1865d
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发表时间：
1981-12
影响因子：
2
通讯作者：
J. Schmitt;D. W. Boyd
中科院分区：
文献类型：
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作者：
J. Schmitt;D. W. Boyd
摘要硅化的翼足类和腕足类在怀俄明州中西部的二叠纪公园城组的埃尔韦、弗兰森和宏伟的成员中很常见。对成百上千个这样的化石的研究已经认识到了硅化的五种模式。模式I的特征是巨型石英晶体从骨骼边界向内突出并垂直于骨骼边界，而模式II的化石由同心的玉髓石英纹层组成。在模式III中，微晶石英的外层突然向内分级为层状玉髓石英，而层状玉髓石英又突然向内分级为巨型石英。显示模式IV的贝壳包括平行于骨骼边界排列的巨型石英晶体，并与贝克石圆盘相邻。图案V由平行于骨骼边界排列的巨型石英晶体组成。在腕足类中，这些晶体通常表现出残留的骨骼微结构。最初由文石构成的翼足类壁层的特征是I、II、III和IV。模式V描述了所有腕足类和原始钙化层的翼足类。模式I、II、III和IV被解释为填充了骨架碳酸盐溶解产生的空隙。V型是碳酸盐溶解和二氧化硅沉淀共同作用的结果。
ABSTRACT Silicified pelecypods and brachiopods are common in the Ervay, Franson, and Grandeur Members of the Permian Park City Formation of central and western Wyoming. Study of hundreds of these fossils has resulted in recognition of five patterns of silicification. Pattern I is characterized by megaquartz crystals projecting inward from and perpendicular to the skeletal boundary, whereas fossils exemplifying Pattern II consist of concentric laminae of chalcedonic quartz. In Pattern III, an outer lamina of microcrystalline quartz grades abruptly inward to laminated chalcedonic quartz which in turn grades abruptly inward to megaquartz. Shells demonstrating Pattern IV involve megaquartz crystals aligned parallel to the skeletal boundary and lying adjacent to beekite discs. Pattern V consists of megaquartz crystals aligned parallel to the skeletal boundary. In brachiopods, these crystals typically exhibit relict skeletal microstruture. Pelecypod wall layers constructed originally of aragonite are characterized by Patterns I, II, III and IV. Pattern V characterizes all brachiopods and originally calcitic layers of pelecypods. Patterns I, II, III and IV are interpreted to result from filling of voids created by dissolution of skeletal carbonate. Pattern V results from concurrent carbonate dissolution and silica precipitation.