Fossil corals, brachiopods, bivalves, and crinoids, from ancient seas 400 million years ago, survive in the limestone of the Chillagoe District, Queensland, Australia. An abundance of these Silurian marine invertebrate fossils are preserved in the rocky outcrops in the area and easy to spot. You can see them on the natural rough surfaces of the cliff-like sides to the karst towers or bluffs. You can also see them in the cut sections of adjacent boulders where the marble quarrymen have been exploring the commercial potential of new sites.
I didn’t see all the types of fossil known to occur here; neither can I now put a scientific name on the specimens I discovered. I noted cross and longitudinal sections of solitary corals – some quite large. There seemed to be a lot of colonial pipe corals – transverse sections of them en masse and lengthwise views of individual pipes. There were crinoid or sea lily stems too. In life, these resemble flowers but are really multi-armed animals of the starfish family which attach to the sea bed by a long jointed, flexible stalk. It is mostly small pieces, or a series of pieces, of the articulated stalk that have been preserved in the rock.
Large bivalved mollusc shells, some still joined together in the pair, were the most numerous fossils – and there were many brachiopods as well. These occurred as distinct shelly layers in the way they had been deposited in the sea-bed sediments so long ago. However, major upheavals and folding of the compacted deposits during later geological periods has resulted in these layers of fossils being re-oriented from the original horizontal to an almost vertical alignment.
Rocks and Landscapes of the Chillagoe District by W. F. Wilmott and D. L. Trezise, 1989, Queensland Department of Mines, Queensland Department of Natural Resources, Mines and Energy, ISBN 0 7345 2486 2, QNRME04050, pp 3-7, gives details of the sediment deposition off the edge of the continent between the Silurian and Devonian Periods – when the Chillagoe fossils were formed.
COPYRIGHT JESSICA WINDER 2012