PALEOCLIMATE, AEOLIAN DUST, AND THE ORIGIN OF PALEOZOIC CHERT IN THE CONTERMINOUS UNITED STATES
Mechanical aeolian abrasion of quartz induces lattice disorder, which increases as grain size decreases as does chemical reactivity. The chemical properties of fine quartz leads to flocculation of clay-size quartz dust in marine environments, which may explain the long-held view that syngenetic sedimentary chert formed from siliceous gels. The ≤10μm size of microcrystalline quartz comprising chert is equivalent to very fine silt and clay-size quartz in dust. Lattice disorder in this fine size fraction may contribute to the undulose extinction of microcrystalline quartz that comprises most chert. Lattice disorder likely exacerbated corrosion of detrital monocrystalline quartz dispersed in microcrystalline quartz matrices.
The stratigraphy and petrology of bedded Paleozoic chert is consistent with silica deposited by aeolian processes as follows: 1) grain size of monocrystalline detrital particles in chert may indicate the magnitude of dust storms, or the proximity to dust sources (or both) because of particle size sorting by wind, 2) silt- and sand-bearing chert beds may have formed in more proximal settings, whereas very fine-grained vitreous chert beds may represent deposition in distal settings where dust was mostly clay-size quartz, 3) variations in the chemical and mineralogical composition of dust are consistent with variations in the composition of chert deposits, 4) dust provides a readily available primary source of dissolved silica for silica secreting organisms. Finally, Paleozoic sedimentary chert in the US formed under inferred warm-arid paleoclimates where copious amounts of aeolian dust were likely exported from desert environments.