WEST KIMBERLEY PLACE REPORT - Department of Sustainability ...

GEOLOGICAL HISTORY
Geologists explain the formation of the Kimberley in terms of physical forces which
have shaped present landforms over thousands of millions of years: the movement of
continental plates; shifts in climate and sea level; and the action of wind, water and
ice on rock. Geologists situate change in geological periods, which are defined with
reference to global geological and evolutionary developments. These explanations are
published in written form, are sometimes disputed, and may be revised or refined over
time on the basis of new evidence, or new methods of interpreting existing evidence.
The geological origins of the Kimberley reach back to a period when life was first
evolving in Earth's oceans, before the appearance of multicelled organisms.
Geologists believe that the oldest rocks in the west Kimberley, which now lie in the
Lennard Hills, were formed between 1,920 and 1,790 million years ago (Tyler 2000).
During much of this time, a significant portion of the west Kimberley was part of a
separate, larger continent located to the north of what would become the Australian
continent, but drifting towards it.
About 1,880 million years ago, these two continents collided in an event now known
as the Hooper Orogeny, causing major upheavals in Earth's crust and forming a
mountain range – the King Leopold orogen – not unlike the modern Andes. Today,
rocks which were part of the Hooper Orogeny are spectacularly exposed along the
Kimberley coastline. The collision produced huge volumes of molten rock (magma).
Much of this magma spewed as lava from erupting volcanoes, while some remained
within the crust and over time solidified to form granite and gabbro. The tremendous
forces created by the collision were enough to buckle rocks into folds and break them
along faults. Some rocks were buried deep in the crust, where the intense pressure and
temperature transformed them into minerals such as garnet and mica. Where
conditions were most intense, the rocks melted. Over time, the mountain range
created by this collision was weathered by wind and rain. Huge amounts of sediment
washed or blown into the shallow seas and rivers of the Kimberley Basin hardened
through temperature and pressure into extensive sedimentary rocks (Tyler 2000;
Maher and Copp 2009).
Around 1,000 million years ago, the southern edge of the ancient Kimberley landmass
(represented by the rocks of the greater Kimberley Plateau) moved south against the
Pilbara Craton, heating, folding and faulting rocks. The renewed contact again led to
the formation of a series of mountains. Rocks showing evidence of this event can be
seen on Yampi Peninsula.
From around 850 to 630 million years ago, during the 'Cryogenic' period of the
Neoproterozoic era, a series of intense ice ages gripped much of Earth, interspersed
with episodes of runaway greenhouse conditions. Glacial deposits from approximately
700 million years ago are well preserved in the Kimberley. About 630 million years
ago at the beginning of the Ediacaran period, the glaciers thawed. An array of
complex multicelled organisms is preserved in rocks from this period, known as the
Ediacara biota. The Ediacara biota bore almost no resemblance to modern organisms;
it appears to have been dominated by soft-bodied animals resembling segmented
worms, fronds, disks, and immobile bags. The fossil remains of these organisms have
been found in all parts of the world. As waves of evolutionary change were washing
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