Hi.

Could it bhe possible that instead of just causing a 'tsunami' that this comet you are talking created a Mega Tsunami. Also there are several cases around the world of fossilised marine creatures been found on mountain tops. One thing that could also account for this is the formation of the miuntain itself where two plates push together and are forced together. So what was once on the ground now lies on the surface.
These are only ideas maybe of some use to you I dont know.
Anyway Thanks for reading this

Andrew