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The Murchison Gorge
The meandering, water-sculptured Murchison Gorge is a very
young feature compared with the ancient rocks that cover
much of Kalbarri National Park.
The red and white-banded layers of the Tumblagooda Sandstone were deposited by
rivers and on tidal sandflats between 450 and 480 million years ago, a time when
life was just venturing onto land.
The rivers flowed westward, crisscrossing a broad plain that merged with the
tidal flats bordering the coast.
In places, deltas built out from this coastline, separated by large bays.
The river deposits now form mostly thick beds of cross-bedded sandstone, whereas
the tidal deposits form thin beds of sandstone and siltstone.
Fossilized burrows created by worm-like animals are found
throughout the rocks.
Around 130 million years ago, the ancestral Murchison River
began to cut down through the Tumblagooda Sandstone, creating
a broad and gentle valley in its wake - the same valley that
one drives through to visit most lookouts.
Then, about 10 million years ago, the whole area around Kalbarri
was uplifted and the river further incised the rock layers,
carving the deep Murchison Gorge that we see today.
Over 2'500 million years ago, this
was the sea floor.
Layers of silica (white and red) and iron
oxide with silica (dark grey) built up over time, squeezing
out the water to form tough, well-bedded rock.
Colliding continental plates caused these rocks to buckle and develop numerous
vertical cracks before being lifted up to form dry land.
Erosion over millions of years has sculptured the rocks you see into the present
The steep cliffs of layered rocks that rise from the sea
are made of 480 million-year old Tumblagooda Sandstone.
These were deposited as layers of sand and silt were piled up by rivers on tidal
The rubbly white rocks that form the upper part of these cliffs are made of the
much younger Tamala Limestone.
This was deposited during the last 2 million years; wind-blown sand dunes that
were later converted to limestone.
Structures like the Natural Bridge are formed by the wave
action eroding the softer layers of rock ultimately undermine
Eventually it will lead to their collapse.