Sea-level and Climate Changes Recorded in Carbonate Diagenesis

浅海碳酸盐沉积物由于其化学性质，在近地表环境中会发生各种类型的成岩作用。因此，环境变化，特别是海平面和气候变化，不仅影响生物碳酸盐岩的沉积作用，而且控制其成岩作用。因此，委员会认为，成岩特征记录在浅层-水碳酸盐岩是环境变化的良好指示剂。本研究的目的是根据沉积岩石学观察和碳、氧稳定同位素组成，阐明琉球群岛全新世-更新世碳酸盐岩沉积中早期碳酸盐岩成岩作用的时间尺度和机制，并认识记录的海平面和气候变化。根据沉积岩石学观察和碳、氧稳定同位素组成的结果，认为琉球群岛全新世-更新世碳酸盐岩沉积中的碳酸盐岩是环境变化的良好指示剂。根据沉积岩石学观察和碳、氧稳定同位素组成的结果，提出了琉球群岛全新世-更新世碳酸盐岩沉积中早期碳酸盐岩成岩作用的时间尺度和机制，并探讨了琉球群岛全新世-更新世碳酸盐岩沉积中记录的海平面和气候变化对琉球群岛晚第四纪碳酸盐沉积物的研究表明，矿物和碳、氧同位素组成的成岩蚀变发生在沉积后约4,000年内，而早期成岩作用使同位素和矿物组成在约数万年内发生了较原始值的严重变化。特别指出，与相对海平面变化有关的陆上暴露的大气成岩作用使同位素组成发生了急剧变化。对南内海-大东岛上更新统大东组成岩作用的研究表明，该组原生沉积物经历了与相对海平面变化有关的两次白云石化作用，成岩流体为海水或近海水。此外，对一种典型的陆源碳酸盐沉积物石笋的初步研究表明，石笋的δ^<13>C和δ^<18>O可能记录了陆地上的气候变化，如水温等，这对精确重建数万年来的古气候是有用的。

Shallow-marine carbonate sediments are subjected to various types of diagenesis in near-surface environments because of their chemistry. Therefore, environmental changes, especially sealevel and climate changes, do not only influence the sedimentation of biogenic carbonates, but also control their diagenesis. Consequently, diagenetic features recorded in shallow-water carbonates are good indicators of environmental changes.The objectives of this research are to clarify the time scale and mechanism of early carbonate diagenesis and to recognize sealevel and climate changes recorded in the Holocene to Pleistocene carbonate sediments of the Ryukyu Islands on the basis of sedimentary petrographical observations and carbon and oxygen stable isotopic compositions.As a result of examinations of the Late Quaternary carbonate sediments of the Ryukyu Islands, diagenetic alteration on mineral and carbon and oxygen isotopic compositions are within about 4,000 years after the deposition, and serious changes of isotopic and mineral compositions from primary values occur within about a few ten thousand years by early diagenesis. Especially, it is pointed out that isotopic compositions are drastically changed by meteoric diagenesis related to subaerial exposure associated with relative sealevel changes. The study on diagenesis of the Plio-Pleistocene Daito Formation, Minaimi-Daito-jima Island, made clear that primary sediments of the formation were dolmiteized twice associated with relative sealevel changes, and that the dolomitizaing fluids were marine or near-marine water. Further, a preliminary research on a stalagmite, which is a typical terrestrial carbonate sediment, suggests a possibility that δ^<13>C and δ^<18>O of a stalagmite record climate changes on land, such as water temperature and so on, and that it is useful for precise reconstruction of paleoclimate within past a few ten thousand.