The ‘Great Inland Sea’ that so many Australian explorers went looking for did actually exist. Unfortunately, the explorers were a few hundred million years too late. Evidence for an inland sea can be found in the rocks of the Flinders Ranges, in South Australia, where the sand, silt and shell fragments on the ancient sea floor have been compressed into layers of sandstone, siltstone, limestone or quartzite; then all tilted at about 30 degrees.
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Travelling east to west along Brachina Gorge you travel through 50 million years in time; starting from rocks that are over 600 million years old. The oldest reefs were made of blue-green algal stromatolites, which are still growing today at Shark Bay, in Western Australia. The rock boundary between the Pre-Cambrian Ediacaran Period with the earliest marine animal fossils, such as Dickinsonia, and those at the start of the explosion of life in the Cambrian Period is 540 million-years-old. Early Cambrian reefs were made of ancient sponges. The youngest rocks were limestone, with lots of fossil trilobites (extinct crustaceans), brachiopod and mollusc shells, and sea tulips – all ancestors of similar animals that live in our oceans today.
An ancient beach in the nearby Ediacara Hills is not famous for its terrific surf, but for the earliest animal life forms fossilised there 575-540 million-years-ago. When storms swept over the beach, the whole community of soft bodied animals that lived there was smothered with layers of sand and silt – fossilising them – and later transformed into hard quartzite. The fossils were discovered in 1946 but it took years for their importance to be realised. The animals include ancestors of existing colonial soft coral sea pens, jellyfish, sea anemones, segmented wormlike animals, as well as other segmented and tri-radial animals which have no descendants today.
Most species are unique to the Ediacara Hills, which has given its name to the Geological Period (the newest and only Period named from Australia). Some of the animals have been found in other parts of the world, such as a Dickinsonia recently found in Russia. Cholesterol has been extracted from this fossil, providing the earliest evidence of animal life on earth.
It was awe inspiring to be able to walk on such an ancient beach, and see and touch the perfect imprints of those inhabitants of the ancient ocean.
To learn more about what lives in our oceans today, and to see what activities are planned for the next school holidays in the local area, check the Nature Coast Marine Group's website www.ncmg.org.au