A Critical Assessment of Anthropogenic Slags and Petroleum Pyrogenetic Glasses in the Southeastern United States: Petrology and Misidentification as Natural Melts

Session: Myths and Misrepresentations surrounding Cosmic Impact claims in Paleoclimatology, Paleontology, Paleoecology, Geoarchaeology, and Quaternary Research

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Many of the controversial claims that have been published over the last two decades regarding evidence of impacts or airbursts at the Younger Dryas Boundary have cited and relied upon comparisons to melt breccias collected around Blackville, South Carolina, described by Bunch et al. (PNAS, 2012). As someone acknowledged by those authors as providing “critical” samples (and as a co-author of the Firestone et al. (2007) YDB article), I am uniquely qualified to give testimony that those glasses are slags from an abandoned railroad. The lead authors were aware of the clear evidence of that before publication.

I could argue that to the extent subsequent claims of YDB glasses, and other more recent Holocene samples, convincingly demonstrate similarities to the Blackville slags, those claims of impacts or airbursts that rely on the comparison, properly should be retracted. Remarkably, many of the Bunch at al. (2012) authors joined with Bindi et al. (2026) seemingly to endorse the conclusion, after fifteen years of saying otherwise, that they are uncertain whether the glasses were, “…produced by natural processes or anthropogenesis.”  But how can there can be any doubt when the coordinates of the sample studied by Bindi (2026) map to the center of a railroad berm composed largely of construction aggregate.

No amount of circumspection prevented many of the authors from drawing on Bunch at al. (2012) to make definitive assertions of a YDB impact near Perkins, Louisiana (Fitzenreiter et al., 2025). I was asked by one author to examine samples from the site in advance of publication. My preliminary petrography suggested quench rates slower than those typically observed for small-scale impacts or short-duration airbursts. I reported that they either were anthropogenic or, less likely but plausibly, might be ejecta eroded from older impact strata that do occur up-gradient. However, a subsequent tour of the site and additional samples graciously provided by the lead author, revealed evidence that these glasses are most like those produced by petroleum fires. The Perkins site, in fact, sets in the middle of an area with abundant pimple mounds, which have been linked to gas extrusions.   

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