University Of Tasmania
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The Ordovician system in the Ida Bay area

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posted on 2023-05-27, 11:40 authored by Christopher SharplesChristopher Sharples
Ordovician sedimentary rocks in the Ida Bay area occur in a north-south trending Tabberabberan anticline, and in some further outcrops having doubtful structural relationships. Early Ordovician quartzites containing gastropods are overlain on Marble Hill by 350 metres of limestone ranging in age from Late Chazyan to Trentonian. Ten lithofacies are distinguished in the limestones on Marble Hill, most of which represent sediments deposited in depositional regression cycles in a prograding tidal flat environment. While the lower 240 metres of limestones represent supratidal-intertidal conditions, the upper 110 metres represent intertidal-subtidal conditions. Siliceous sediments on Coal Hill, north of the Lune River, appear to represent Ordovician Limestones which have been completely silicified, probably by a process related to silcrete horizon formation. A primary Ordovician magnetisation is no longer present in the limestones on Marble Hill; instead a secondary magnetisation of mid-Cretaceous age has overprinted previous magnetisations in the limestone, probably as a result of burial and increased heat flow related to the rifting of the Tasman Sea.


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