  Recent dynamical models of Solar System evolution and isotope studies of
rock-forming elements in meteorites have suggested that volatile-rich asteroids
formed in the outer Solar System beyond Jupiter's orbit, despite being
currently located in the main asteroid belt. The ambient temperature under
which asteroids formed is a crucial diagnostic to pinpoint the original
location of asteroids and is potentially determined by the abundance of
volatiles they contain. In particular, abundances and 13C/12C ratios of
carbonates in meteorites record the abundances of carbon-bearing volatile
species in their parent asteroids. However, the sources of carbon for these
carbonates remain poorly understood. Here we show that the Tagish Lake
meteorite contains abundant carbonates with consistently high 13C/12C ratios.
The high abundance of 13C-rich carbonates in Tagish Lake excludes organic
matter as their main carbon source. Therefore, the Tagish Lake parent body,
presumably a D-type asteroid, must have accreted a large amount of 13C-rich CO2
ice. The estimated 13C/12C and CO2/H2O ratios of ice in Tagish Lake are similar
to those of cometary ice. Thus, we infer that at least some D-type asteroids
formed in the cold outer Solar System and were subsequently transported into
the inner Solar System owing to an orbital instability of the giant planets.
