An Early Holocene Primary Dolomite Layer of Abiotic Origin in Lake Sayram, Central Asia

Abstract

AbstractThe “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.