If protein can sometimes be preserved in fossils, could infectious prions also be fossilized and pose a danger to researchers. The probability of that happening could be extremely small, but could it be possible. Also, if sound makes ripples on very thin exposed mud, and then that gets immediately covered, can it be later decoded with our modern technology to recreate ancient sounds?

most unlikely - fossilisation of proteins especially small ones like prions is very poor even in bone. to occur in brain tissue which never fossilises is almost impossible.