Marine fossils on hilltops

Adam Vonk explains how it is possible that we can find a marine fossil – remnants of an organism that lived in the sea – on the top of a hill. Originally, the fossil would have been deposited on the sea floor, and the organism would have been compacted and became fossilised. Then the rock that the fossil sits in was uplifted. In the Taranaki basin in the North Island of New Zealand that Adam has studied, there has been a great deal of uplift, with the greatest uplift occurring in the centre of the island.

Jargon alert

Each field of science has its own language – here is a term Adam uses:

• Uplifted – upheaval and lifting of the Earth’s crust, which is typically caused by tectonic plates moving and pushing each other.

Transcript

ADAM VONK If we find a fossil at the top of the hill, immediately the question is, well, marine fossils don't naturally occur on the top of hills. So the logical sort of explanation for that is that marine fossil had to accumulate in the sea. The only way a fossil can actually be on the top of the hill is that the rock that the fossil accumulated in has been uplifted and eroded. The whole of the North Island has been uplifted. Generally, the greatest amount of uplift is in the centre of the island, and it tapers away to the edges of the island. So, we can actually work out how much the rock has been uplifted and how much rock has gone off the top and been eroded away.

Acknowledgements: Lloyd Homer – GNS Science