Constraining dolomitization by M g isotopes: A case study from partially dolomitized limestones of the middle C ambrian X uzhuang F ormation, N orth C hina

作者：Yang Peng, Bing Shen, Xianguo Lang, Kang‐Jun Huang, Jitao Chen, Zhen Yan, Wenbo Tang, Shan Ke, Haoran Ma, Fang‐Bing Li · 发表于：Geochemistry Geophysics Geosystems · 年份：2016 · DOI：10.1002/2015gc006057 · 被引用次数：47 · 研究领域：Geology and Paleoclimatology Research、Paleontology and Stratigraphy of Fossils、Isotope Analysis in Ecology

Abstract The “dolomite problem” refers to the rare dolomite formation in modern oceans that is in sharp contrast to the widespread ancient dolostone in rock record, as well as failure of laboratory inorganic dolomite precipitation at near Earth‐surface temperature. Novel Mg isotope systematics provides a promising tool in resolving the “dolomite problem”. Here, we develop a protocol to place constraints on the dolomitization process by using Mg isotopes. In this study, we measured Mg isotopic compositions ( ) of two batches of partially dolomitized limestone samples from the middle Cambrian Xuzhuang Formation in North China. varies between −0.55‰ and −3.18‰, and shows a negative linear correlation with , suggesting that can be described by a binary mixing between the calcite and dolomite components. Mg isotopic composition of the dolomite component ( ) for the lower sample set that is collected from a 4 m stratigraphic interval containing three high‐frequency ribbon rock‐packstone cycles is −1.6‰, while for the upper sample set (from a thick sequence of ribbon rock) is significantly higher (−0.3‰). However, neither mineralogical and elemental compositions, carbon and oxygen isotopes, nor crystal morphologies of dolomite provides diagnostic criteria to differentiate these two batches of samples. of the Xuzhuang limestone is simulated by the Advective Flow (AF) and the Diffusion‐Advection‐Reaction (DAR) models. The AF model assumes that Mg is transported by advective fluid flow...