Reflections - a river cascades down Weano Gorge. The with sunlight ablaze red cliffs reflect in the water and give it an orange to bronze colour. Weano Gorge, Hamersley Range, Karijini National Park, Pilbara, Western Australia, Australia. Rocks exposed at the gorges in Karijini originated as fine grained sediment which accumulated on an ancient sea floor 2500 million years ago. At this time the atmosphere contained much less oxygen and the only forms of life were simple bacteria and algae. Many of these sediments laid down in the oceans were rich in iron and silica. Over hundreds of millions of years; the iron-rich deposits were transformed by the pressure of further sediments laid down over them; and the gradually turned into tough well-bedded rock. The gorges were eroded when a sharp drop in sea level caused the rivers to downcut rapidly-a process enhanced by the onset of a more arid climate; which depleted the protective vegetation cover on the valley sides.