So today we are at Curio Bay on the very far south coast of the South Island of New Zealand.
And Curio Bay is a special place because it's on the wild coast and there are rocks here
that date back from the Middle Jurassic about 170 million years ago. And what's particular
about this location is that when we look closely at the wave cut platform that has been eroded
flat by the sea, on this platform there are many many tree stumps and logs that have been
preserved and turned from wood into silica which makes them very very hard. So it is
believed that the rocks around these tree stumps and logs are sandstones that were washed
off the slopes of a big volcano somewhere nearby here way back in the distant past,
and the trees and the vegetation were overwhelmed by this volcanic mud flow and preserved so
that we can see them today. So what we're going to do now is going to go down and explore
this shore platform and see what we can find.
So right at the bottom of the steps we have this huge tree trunk which would have been
washed down with the debris in the mud flow from the volcano. You can see that this is
not wood anymore, it's really really hard silica rock. So that's why it's been preserved
for so long - it hasn't decayed away. So what happens is when the tree dies and is buried
in this very silica rich sediment, slowly the liquid percolates into the gaps in the
cells in the wood and deposits the silica. So the silica gradually if you like fits into
the spaces within the wood and becomes solid and that's how the log becomes silicified,
and the original wood may or may not remain for a while or it might decay away. Now at
the time that this forest was living there were no flowering plants, so these trees are
conifers and tree ferns.
So here we've got a a quite a big chunk of a tree stump - you can actually see the growth
rings of the tree preserved. And studying these growth rings has shown that at this
time in the Middle Jurassic where this forest was quite close to the Antarctic Circle, at
that time there was no ice in Antarctica, so it was quite a warm climate on planet earth.
And the alternation of these growth rings has shown that there were actually kind of
seasonal periods of rapid growth and less growth at that time. And here you can see
the black carbon rich layer that was probably the floor of the forest at the time. So when
we go to the back of the beach we can see that actually this was not just a single event
with one flood burying one forest, because it looks like here we have a dark carbon rich
layer which represents a forest floor, then we have the volcanic sandstone on top and
then above it we see yet another black layer which is another forest regrowing after that
first event. As we go up the cliff you can see multiple layers so it looks like the forest
regrew and then was flooded over again and re-grew another time and so on multiple times.
If we explore around this area where we have these dark carbon-rich layers sometimes we
can find fossil remains of the plant material and this is an example of some fern leaves
and another example here with more bits of a fern frond - telling us a little bit about
the ecology of this forest at the time. One thing to remember is that this is a special
scientific site and it's really important that anything that we find in terms of wood
fragments or fossils must be left here and not taken away.
This is a particularly fine example of one of the tree stumps over half a metre across
and you can see those growth lines really clearly.