Rock varnish in New York: An accelerated snapshot of accretionary processes

摘要: Abstract Samples of manganiferous rock varnish collected from fluvial, bedrock outcrop and Erie Barge Canal settings in New York state host a variety diatom, fungal bacterial microbial forms that are enhanced manganese iron. Use Dual-Beam Focused Ion Beam Scanning Electron Microscope to manipulate the situ reveals would not have otherwise been identified. The relative abundance Mn–Fe-enriched biotic samples is far greater than varnishes warm deserts. Moisture availability has long noted as possible control on growth rates, hypothesis consistent with Mn-enhancing bioforms. Sub-micron images incipient formation reveal varnishing probably starts mortality microorganisms Mn bare mineral surfaces; death results adsorption Mn-rich sheath onto form filamentous networks. Clay minerals then cemented by remobilization material. Thus, previously unanswered question what comes first – clay deposition or enhancement can be answered because faster rate growth. In contrast, very slow rates seen deserts, microns per thousand years, make it less likely will accretionary processes fast-accreting moist settings.