Hot atmospheric formation of carbonate accretionary lapilli at the Cretaceous-Paleogene boundary, Brazos River, Texas, from clumped isotope thermometry

Abstract The Chicxulub impact (in the northern Yucatan Penninsula, Mexico) marks Cretaceous-Paleogene (K-Pg) boundary and is implicated in one of five major extinctions. Researchers have examined ejecta from impact, most recently a drill core crater itself, yet processes chemical reactions occurring vapor plume are poorly constrained. Rounded carbonate particles, identified as accretionary lapilli, been found thousands kilometers may be unique record conditions. We present carbon (?13C), oxygen (?18O), clumped (?47) isotope ratios lapilli Brazos River, Texas (USA), well foraminifera mudstone. Unaltered ?13C ?18O values covary, ranging ?9.38‰ to ?2.10‰ ?7.72‰ ?5.36‰, respectively, they distinct mudstones, foraminifera, secondarily altered same section. Clumped temperatures [T(?47)] range 66 °C 539 average 155 ± 46 (1 standard deviation), with sedimentary fossil carbonates recording clement, shallow ocean–like T(?47). These data consistent petrography hypothesized formation, we argue that result target rock decarbonation. Atmospheric >100 extending >1800 km imply an uninhabitable zone within seconds minutes was 10× larger diameter than itself.