白云石非经典结晶演化机制实例:从成核到完全有序的微观记录OA

Dolomite serves as an important reservoir rock for oil and gas,and its genesis has long been a contro-versial topic in sedimentology and petroleum geology.The core contradiction lies in that highly ordered dolomites are widely developed in strata throughout geological history,but rarely found in modern sedimentary environ-ments,and they are difficult to be directly synthesized under near-surface conditions.To reveal the crystallization mechanism of ordered dolomites,particularly their evolution pathway at the nanoscale,dolomites from the Edia-caran Dengying Formation at the Yangba section of the Sichuan Basin were taken as the research object.The microstructural characteristics of dolomites were systematically analyzed through rock thin-section observations,scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS),and in situ Raman spectroscopy.The results showed that dolomites from the second member of the Dengying Formation at the Yangba section were mainly composed of stromatolite dolomites and thrombolite dolomites.SEM observations revealed four types of nanoscale aggregates with special morphologies,including spherical-subspherical,rod-shaped,bouquet-like,and petal-like forms.EDS analyses confirmed that these aggregates were authigenic carbonates rather than exoge-nous contaminants.These aggregates were formed by the attachment and assembly of nanoparticles and exhibited typical characteristic morphologies of metastable intermediates in a nonclassical crystallization process.They were key and ubiquitous precursors in such crystallization pathway.Microbial activities and organic molecules had a significant controlling effect on the formation and preservation of these aggregates.Localized dissolution was observed in these nano-aggregates,and regular rhombic crystal structures gradually developed at their bounda-ries.This recorded the complete transition process of the aggregates to thermodynamically stable phases through dissolution-reprecipitation,and ultimately to the formation of rhombic euhedral ordered dolomites.This study clarifies a complete pathway of dolomite formation at the microscale,during which dolomites form as a metastable intermediate phase via nonclassical crystallization and subsequently evolve into an ordered structure through dis-solution-reprecipitation.The findings offer a new theoretical framework for understanding the formation mecha-nism of dolomites under natural conditions.