资源环境科技发展态势分析平台

Paleozoic and Precambrian sedimentary successions frequently contain massive dolomicrite [CaMg(CO3)(2)] units despite kinetic inhibitions to nucleation and precipitation of dolomite at Earth surface temperatures (<60 degrees C). This paradoxical observation is known as the "dolomite problem." Accordingly, the genesis of these dolostones is usually attributed to burial-hydrothermal dolomitization of primary limestones (CaCO3) at temperatures of >100 degrees C, thus raising doubt about the validity of these deposits as archives of Earth surface environments. We present a high-resolution, >63-My-long clumped-isotope temperature (T-Delta 47) record of shallow-marine dolomicrites from two drillcores of the Ediacaran (635 to 541 Ma) Doushantuo Formation in South China. Our T-Delta 47 record indicates that a majority (87%) of these dolostones formed at temperatures of <100 degrees C. When considering the regional thermal history, modeling of the influence of solid-state reordering on our T-Delta 47 record further suggests that most of the studied dolostones formed at temperatures of <60 degrees C, providing direct evidence of a low-temperature origin of these dolostones. Furthermore, calculated delta O-18 values of diagenetic fluids, rare earth element plus yttrium compositions, and petrographic observations of these dolostones are consistent with an early diagenetic origin in a rock-buffered environment. We thus propose that a precursor precipitate from seawater was subsequently dolomitized during early diagenesis in a near-surface setting to produce the large volume of dolostones in the Doushantuo Formation. Our findings suggest that the preponderance of dolomite in Paleozoic and Precambrian deposits likely reflects oceanic conditions specific to those eras and that dolostones can be faithful recorders of environmental conditions in the early oceans.