Dead Marshes

[Finwe]

As for elven bodies decaying, i don't remember where i read it but there seemed to be a case of an elf dying and his body disintegrated into light and travelled west

I believe you're talking about the body of Fëanor. His fëa was so fiery, that when he died (after getting his arse completely kicked black and blue by a bunch of Balrogs), his body disintegrated into ashes, and presumably blew away in the wind. His fëa still reached the Halls of Mandos, and it remains there until the End of Days, in atonement for its misdeeds (Rebellion against the Valar, Kinslaying at Alqualondë, betraying Fingolfin and the Burning at Losgar, etc.).