WEST KIMBERLEY PLACE REPORT - Department of Sustainability ...

(Playford et al. 2009). The features they preserve are diverse, and include shores and
inlets, islands and archipelagos, platforms and atolls (Johnson and Webb 2007). The
Lennard and Fitzroy rivers expose spectacular reef cross sections at Windjana and
Geikie gorges (Long 2006). The Proterozoic rocks of the Oscar Range, an outlier of
the King Leopolds, was an archipelago during the late Devonian, and preserves many
reef features in intricate detail (Johnson and Webb 2007).
As well as providing a sense of the grandeur of the Devonian reef system, fossils also
preserve intimate and exact details of the individual organisms that built and occupied
these reefs and the shallow seas that supported them. In particular the Gogo
Formation, a limestone formation of the Lennard Shelf, contains spectacular and
abundant fossils of fish that lived in deeper water, seaward of the reefs. Nearly 50
species have been described so far, and work is ongoing. The fish fossils mostly occur
below the surface of the formation within 'Gogo nodules' that sometimes become
exposed when the surrounding rock is weathered out (Playford et al. 2009). The
preservation of these fish is exceptional: their fossils are near-complete, with threedimensional
skeletons. Soft tissue features of the fish have been preserved here,
intact, for over 300 million years.
Following sea level retreat around the world, between 310 and 270 million years ago
glaciers of the Permo–Carboniferous ice age, which covered much of Earth in sheets
of ice, buried the remains of the Devonian reef and laid down sedimentary rocks in
the Canning Basin. As sub-glacial ice melted, water reacted with the carbonate
structures of the reef and began to hollow out the maze of caves and tunnels which
now form the extensive karst systems of the Kimberley limestone ranges. The reef
was buried under glacial sediments for millions of years, before uplift eventually
exposed it once more.
The end of the Permian is defined by a mass extinction of an unprecedented scale,
informally known as 'the great dying'. More than 90 per cent of all marine species
disappeared from the fossil record and 70 per cent of terrestrial vertebrate species.
However, it ushered in the Mesozoic era, the 'age of dinosaurs'. By the Triassic
period, beginning around 245 million years ago, the grip of cold, arid glacial
conditions had given way. From around 200 million years ago, in the early Jurassic
period, the Kimberley Plateau once again formed part of a large island landmass,
separated from the Northern Australian and Pilbara cratons by an inland sea. During
the Cretaceous period, many species of dinosaurs occupied the area. As dinosaurs
walked over swampy ground about 130 million years ago, they left tracks, some of
which are preserved as fossils in the Broome Sandstone and exposed along the west
coast of Dampier Peninsula. Fossilised remains of plants and pollens are found along
with the tracks, which allow geologists to estimate their age. Plant remains and
depositional features of the sandstone show the range of environments that these
dinosaurs inhabited, which included rich lagoonal forests, estuaries, swamps and
riverine areas.
The early Cretaceous coastal plain and drainage were roughly parallel to the existing
Dampier Peninsula coastline: 'on the landward (eastern) side of the coastal plain a few
small lakes and swampy areas intervened among groves of ferns, while on higher
ground there was open forest dominated by cycads. In a few places there were
stretches of flood debris (pebbles and boulders) and sheets of sand blown out from the
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