One possibility would be that if the calcium already existed in the asteroid along with ice. The ejecta could somehow retain some water along with the original

One possibility would be that if the calcium already existed in the asteroid along with ice. The ejecta could somehow retain some water along with the original organisms the sudden relocation to space would preserve the structure (if it hadn't been vaporized first). The water would turn to ice. If this asteroid then came near the Sun, the ice would presumably melt by the ambient heat (and if deep inside, wouldn't immediately sublimate). The moisture will then aid in the fossilization. That's purely speculation, of course.