什么是 Clumped isotopes？

Clumped isotopes are molecules or groups that contain two heavy isotopes bonded together. In carbonates, $\Delta_{47}$ is the excess, in per mil, of the abundance of $^{13}\mathrm C^{18}\mathrm O^{16}\mathrm O_2$ groups, measured as mass-47 carbon dioxide, over a random distribution of the isotopes.