The environmental situation on Mars does not allow a buried corpse to decompose. Lack of microbes on the martian surface means that decomposition of organic material (i.e. dead bodies) is not possible. To avoid an exponential growth of number of tombs, a different kind of funeral will be required.
How the Swedish do it
Dead bodies are freeze-dried with liquid nitrogen, then powdered by a vibration mechanism and finally buried on the cemetery, not too far beneth the surface. The roots of plants grow into the powder and bring the substances of the powder into the circles of eternity. This funeral technology has an ethical aspect: If the grandchild asks "Where has my grandma gone?" you can tell him "She has turned into a beautiful rose...".