Temperature regimes during formation of Miocene island dolostones as determined by clumped isotope thermometry: Xisha Islands, South China Sea

Carbonate dumped isotope thermometry is a relatively new type of analysis that has been used to obtain a better understanding of the temperature and salinity of the water that mediated the development of dolostones in the Cenozoic successions of isolated oceanic islands. There is, however, still some uncertainty about the factors that could modify the clumped isotopes even in shallow burial conditions and thereby affect the temperatures and salinities derived from them. Here, focus is placed on a 210.5 m thick succession of Miocene dolostones that is found on the Xisha islands in the South China Sea that have experienced rapid subsidence since the Early Miocene. These dolostones are typically formed of crystals that have a dirty core that is encased by a clear outer rim. The formation of the dirty cores, the primary replacement dolomite, was probably mediated by normal seawater in near-surface conditions, whereas the later cements formed at higher temperatures from slightly evaporated seawater. Given that it is impossible to separate the dirty cores from the dear rimes for analytical purposes, it must be recognized that the clumped isotopes and other geochemical data (e.g., delta O-18, Sr-87/Sr-86) are averages of these two types of dolomite. This also means that the development of dolomite in these dolostones involved two successive stages of dolomite development that was probably related to sealevel cycles. Despite these issues, clumped isotope thermometry can still provide valuable temperature and salinity information for understanding the dolomitization processes that led to the development of island dolostones. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

Carbonate dumped isotope thermometry is a useful technique for studying the temperature and salinity of water that influenced the development of dolostones on isolated oceanic islands. This study focuses on a thick succession of Miocene dolostones found on the Xisha islands in the South China Sea. Despite the challenges of analyzing mixed dolomite types, clumped isotope thermometry can still provide valuable information about the dolomitization processes.