Precipitation of Lime Mud in Coral Reef Environments of the Ryukyu Arc

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The objective of this research is to clarify the origin of lime mud in coral reef environments, because the lime mud may be lithified as micrite in ancient limestone.The lime mud contains such carbonate minerals as HMC(high-Mg calcite) and aragonite ; however, the Mg/Ca and Sr/Ca ratios in these minerals contained in lime mud are lower than those ratios in coarse carbonates. This may signify that Mg and Sr from these carbonate minerals may be leached out during fining processes in the environments.Lime clay was first discovered during this research. Lime clay is contained as pathes in coral skeletons or coral reef limestones. Mineralogically, lime clay is enriched with HMC.In conclusion, this lime clay patch may be formed as micrite envelope in the limestone. In other words, organisms may bore the limestones and coral skeletonsand HMC and other carbonates may be precipitated in this bored space in the coral reef limestone.