An Early Holocene primary proto-dolomite layer of abiotic origin in Lake
Sayram, Central Asia
Abstract
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.