DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Stratified quartzite, a metamorphic rock derived from sedimentary sandstone, at Brachina gorge in the Flinders Ranges, South Australia. These rocks form part of the Adelaide Geosyncline, an elongated downwarp in the earth's crust whose bottom has subsided beneath accumulating sediments. The pre-Cambrian sedimentary rocks which were formed in its development (around 750 million years ago) subsequently metamorphosed into the quartzite seen here. The strata have also undergone deformation associated with a period of mountain building that occurred about 50 million years ago.
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