DIFFERENTIATING COPPER AND DIAMOND IN SEDIMENT-EXTRACTED NANOPARTICLES FROM BULL CREEK, OK

The Younger Dryas impact hypothesis (YDIH) proposed that an extraterrestrial object exploded as it entered earth’s atmosphere, triggering the climate reversal 12,900 years B.P. To test this hypothesis, many research groups have searched for impact evidence in sediments corresponding to the Younger Dryas boundary (YDB), including nanodiamonds. Natural nanodiamonds are present in meteorites and form terrestrially during impact events through chemical vapor deposition (CVD) and shock metamorphism. Nanodiamonds have been identified at 24 Younger Dryas sites, including in Bull Creek, OK. However, one research group suggested nanoparticles identified as ‘n-diamond’ are copper-based phases rather than diamond.

Differentiating copper and diamond on the nanoscale via transmission electron microscopy (TEM) presents challenges. The diffraction structures of copper and n-diamond are very similar, both copper and carbon are present in the background system, and the analytical volumes for energy-dispersive X-ray analysis (EDXA) are extremely small. To overcome this, we used a low-background beryllium TEM holder, copper-free TEM grids, and compared the sample results to control sample blank grids. Samples included sediment digest extracts from the surface layer at Bull Creek, OK, previously shown to have relatively abundant nanoparticle populations, along with control samples of laboratory produced copper and diamond nanoparticles.

Our initial findings show higher amounts of carbon on sediment-extracted nanoparticles compared to blank grids with small amounts of copper that may be attributed to background column secondary x-rays. These findings are consistent with previous data from this site and are the first step in confirming the characterization of nanoparticles from the Younger Dryas. This study advances the understanding of nanoparticles from Bull Creek, OK and contributes to interpretations and methods for the analysis of nanoparticles from the YDB, along with our understanding of sediment-hosted nanoparticles in the geologic record.