The “dolomite problem” is a long‐standing puzzle in sedimentology and mineralogy. Previous studies have shown that some dolostones are formed by microbes or in hydrothermal–burial environments. Here, we provide a different case in which an abiotic and Ca‐rich dolomite layer precipitated in Lake Sayram, Central Asia, during the early Holocene. The 12‐cm‐thick layer consists of abundant partially ordered dolomite crystals (mean > 50 wt% and maximum = 81 wt%) which have euhedral and rhombohedral shapes and weak cation ordering. Transmission electron microscopy reveals that even in a single crystal, compositions vary among different domains. Mineralogical and isotopic evidence suggests that these dolomites are of primary and abiotic origin. We infer that this dolomite layer might be the product of day and night temperature cycling of shallow lake water under local warming trend. This study provides evidence for abiotic dolomites forming at ambient temperature.
The "dolomite problem" is a long-standing puzzle in sedimentology and mineralogy. Previous studies have shown that some dolostones are formed by microbes or in hydrothermal-burial environments. Here, we provide a different case in which an abiotic and Ca-rich proto-dolomite layer with weak cation ordering precipitated in Lake Sayram, Central Asia, during the Early Holocene. The 12-cm-thick layer, with abundant proto-dolomite (mean 50 wt% and maximum=81 wt%), consists of euhedral and rhombohedral grains. The similarδ18O values of proto-dolomites and ostracods at the same depth demonstrate that the former are authigenic. Morphologic and isotopic features of these proto-dolomites are distinct from those of microbial dolomites, suggesting an abiotic origin. We infer that this proto-dolomite layer is the product of a warming and arid climate, which is supported by regional climatic records. This study provides evidence for previous studies that dolomite can precipitate directly in "dolomite seas" at ambient temperature.
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