The petrography and chemical composition of carbonate accretionary particles of Chicxulub impact origin are described from Cretaceous-Paleogene boundary deposits at Brazos River, Texas, and Bass River borehole, New Jersey. The particles consist of lapilli and lapilli fragments ranging in size from 0.05 to 0.3 cm; they are white in color, have an accretionary fabric at several scales, and are composed of micrometer-sized microspar of low-Mg calcite with an elevated sulfur content. The internal aggregate microfabric indicates that they formed by accretion of small solid particles, suggesting an origin from carbonate crystals generated within the vapor plume of the Chicxulub impact. Carbonate accretionary lapilli occur with altered glass spherules in Cretaceous-Paleogene boundary deposits at sites in Texas and northern Mexico and in the spherule layer in New Jersey, indicating that a large amount of particulate carbonate was present within the impact plume.

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