Here’s a bit from the US Bishops:
Thus, while “cremation is now permitted, it does not enjoy the same value as burial of the body…The Church clearly prefers and urges that the body of the deceased be present for the funeral rites, since the presence of the human body better expresses the values which the Church affirms in its rites.” (413) However, “when extraordinary circumstances make the cremation of a body the only feasible choice, pastoral sensitivity must be exercised by all who minister to the family of the deceased.” (414)
The rites of burial for the cremated remains of a body may be found in the appendix to the Order of Christian Funerals. This appendix recommends that when cremation is chosen, the body be cremated after the Funeral, thus allowing for the presence of the body at the Funeral Mass. When pastoral circumstances require it, however, cremation and committal may take place even before the Funeral liturgy.
Any catechesis on the subject of cremation should emphasize that “the cremated remains of a body should be treated with the same respect given to the corporeal remains of a human body. This includes the use of a worthy vessel to contain the ashes, the manner in which they are carried, the care and attention to appropriate placement and transport, and the final disposition.” (416)
While cremated remains may be buried in a grave, entombed in a mausoleum or columbarium or even buried at sea, “the practice of scattering cremated remains on the sea, from the air, or on the ground, or keeping cremated remains in the home of a relative or friend of the deceased are not the reverent disposition that the Church requires.” (416) The cremated remains of the body may be properly buried at sea in the urn, coffin or other container in which they have been carried to the place of committal. When a body, or the cremated remains of a body are buried at sea, the Committal prayer found at number 406 § 4 is used:
more]
Here’s
more information from the bishops:
Why does the Church prefer the burial of the actual body of the deceased? There are many reasons that I can think of for the burial of simply the cremated remains.
The Church has always held a preference for corporeal body. The body of a deceased loved one forcefully brings to mind the mystery of life and death and our belief that our human bodies are temples of the Holy Spirit and destined for future glory at the resurrection of the dead. In addition, the body which lies in death recalls the personal story of faith, the past relationships, and the continued spiritual presence of the deceased person.
This is the body once washed in baptism, anointed with the oil of salvation, and fed with the bread of life. This is the body whose hands clothed the poor and embraced the sorrowing. The human body is so inextricably associated with the human person that it is hard to think of a human person apart from his or her body. Thus, the Church’s reverence and care for the body grows out of a reverence and concern for the person whom the Church now commends to the care of God.
[Edited]