Just yesterday had to deal with some putrid crud <shivers>
some temp had parked a dumpster overfilled with food debis in a corner some time ago. It had gone unseen by all, when discovered the barrel was topped of with rainwater... and we've had two weeks of sunshine minimum.
Not really dead meat smell yet, due to the anaerobic conditions from the water, but sour and foul none the less.
You a biologist Chtulu, or just a fascination with the macabre?
sorry spam. I'll try to rectify it with some relevant biotech babble.
Anyhow You are right to point out the rotting imp in magma, it should by logic just decay without smell or melt. ...on the other hand, if it floats, convection would enable smoke etc to dissipate from the corpse...smell of burning chitin..hmmm. noxic smoke: fumes from some smoldering fire retardant materials can actually be quite toxic. unsure if carbon monoxide and similarly reducing anoxic fumes are an issue with magma...in open air oxygen supply is no problem, but in a cave?