The chemistry of eolian quartz dust and the origin of chert

Abstract

Among the numerous models that have been suggested for the primary and predominant source of silica for chert, we suggest that eolian dust is worthy of further considerations. Such considerations are supported by the common association of Phanerozoic chert with evaporites, limestones, dolomites, or other strata that were deposited within or near arid paleoclimates. This association suggests a direct or indirect causal link between aridity and chert formation. In addition, eolian processes export large quantities of quartz-rich dust from arid climate ergs or loess lands. The chemistry of abraded quartz particles derived therefrom is consistent with chert formation. Abrasion of quartz particles produces an amorphous surface layer and underlying lattice disorder. An inverse relation between particle size distribution (, 64 lm) and the enthalpy of solution of abraded quartz is indicative of the degree of lattice disorder; as particle size decreases, the enthalpy of solution increases. The amorphous surface layer and underlying lattice disorder enhance both the rate and amount of dissolution of quartz dust particles; the solubilized silica can then be reprecipitated and diagenetically altered to the various silica polymorphs that occur in chert. An eolian supply and the chemistry of eolian abraded quartz particles may account for chert formation in disparate depositional environments that encompass deep-sea chert, chert in epicontinental seas including shallow shelves, and chert that formed in continental eolinites, lakes, and soils (arid climate silcretes).