Deep in the heart of Damaraland, a
dry rugged area of Northern Namibia, can be found the
Petrified Forest. Here you can see the fossilized trunks of trees
that are estimated to be about 280 million years old. They were members of
the early Cordaites family of trees (Dadoxylon arberi Seward, classified as
a gymnospermopsida) that grew to heights of over 40m and were the ancient
ancestors of our present day conifers and ferns.
There are large tree
trunks and sections of trunks scattered over the site. The
mineralization of the wood has produced some colourful examples where the
detail of wood grain of the trees along with knots and bark can clearly be
seen and
make for some interesting photographs for your collection.
How Did This Happen?: During the
Permian Period, Namibia formed part of the ancient continent of Gondwana
and was situated further south towards the polar region. From about 320 to
270 million years ago the southern regions of the continent were gripped in
what is known as the Great Gondwana Ice Age and was covered in ice
fields and glaciers. Eventually the climate began to warm and a great thaw set-in causing floods of melt water
to wash over the land that carried with them
ice, rock debris and silt. There were occasions when the melt water
would become excessive and would rush across the land tearing up and
carrying with it virtually everything in its path. It was such a flood that
ripped through the ancient forest where these trees grew with such force
that many of the tree trunks literally snapped off and were carried to their final resting place from far
away and almost immediately buried under a thick layer of sand and
rubble. Sealed in this airtight grave the wood was not subjected to
the ravages of insects and normal decomposition that vegetable matter
is normally subjected to. The site experienced further sedimentation
over periods of many millions of years until the trees were buried under
hundreds of metres of overburden. The immense pressures caused the
quartz present in the sediments to dissolve. The silica rich solution
in turn permeated into the wood. The acidity of the solution was
sufficient to dissolve the organic matter and thus it was replaced
with crystalline quartz. Over the following 280 million years this
area was subjected to changes of cataclysmic proportions. The ancient
continent of
Gondwana eventually divided and the surface levels arose. Ice
ages came and went and erosion by water wash and later desert winds
eventually uncovered the tree trunks and they were once again exposed
above ground level.
Acknowledgements and further reading: G1, G2, G3, H12, P1
