High-pressure phase of natural fullerene C₆₀ in iridium-rich Cretaceous-Tertiary boundary layers of Deccan intertrappean deposits, Anjar, Kutch, India

Abstract

We report here for the first time the presence of the natural, toluene-soluble C₆₀ and the toluene-insoluble high-pressure and temperature phase of fullerene C₆₀ in the carbonaceous matter extracted from the iridium-rich layers of the intertrappean sediments of Anjar, India. The toluene-insoluble form of fullerene is formed at high-temperature and pressure (HPT) and is distinguished from normal fullerene by UV-visible and Fourier-transform infrared (FT-IR) spectroscopic techniques. The C₆₀ fullerene has been identified by high-resolution electron-impact ionization mass spectrometric analysis, as well as by Fourier-transform infrared (FT-IR), UV-visible, and ¹³C-nuclear magnetic resonance (NMR) spectroscopy. In iridium-poor horizons of this section, fullerenes are absent, but complex hydrocarbons are sometimes present. The FT-IR spectroscopic studies on the insoluble fullerenes show strong absorption peaks at about 740 and 509 cm^-1 and a number of weak peaks at 1380, 1300, 1205, 1120, 1000, 608, 554, and 441 cm^-1, which are characteristic of a high-pressure and temperature C₆₀ fullerene. The UV-visible spectra of the toluene-soluble fullerene, as well as the insoluble fullerene, show strong absorption bands at 270 and 348 nm, which are characteristic of pristine fullerene C₆₀. The toluene-insoluble carbon-rich residue shows additional absorption bands at 710, 640, and 395 nm. These UV-visible bands independently confirm the presence of the high-pressure-temperature (HPT) phase of fullerene C₆₀. Conditions of high-pressure and temperature required for formation of the HPT fullerene phase can be created by an energetic impact event. Therefore, the presence of HPT fullerene in the KT boundary layer at Anjar is linked to the impact event at the KT transition.