Book contents
- Frontmatter
- Contents
- Colophon
- Preface
- Acknowledgements
- Maps
- Units of measurement and abbreviations
- 1 Geology: An Australian perspective
- 2 The Earth: A geology primer
- 3 Telling geological time: The great canvas
- 4 The cratons: Building the core of Precambrian rocks
- 5 Mountain building: Paleozoic orogenic rock systems
- 6 Warm times: Tropical corals and arid lands
- 7 Icehouse: Carboniferous and Permian glaciation
- 8 Mesozoic warming: The great inland plains and seas
- 9 The birth of modern Australia: Flowering plants, mammals and deserts
- 10 Fossils: The Australian record of past life in context
- 11 The land stirs: Volcanoes and the eastern highlands
- 12 The outline and submerged terrace: Building the continental shelf and coastlines
- 13 The coral reefs: Unique parts of the continental shelf
- 14 Patterns of change: Cycles in Australia's journey
- Epilogue
- Sources and references
- Index
- References
14 - Patterns of change: Cycles in Australia's journey
- Frontmatter
- Contents
- Colophon
- Preface
- Acknowledgements
- Maps
- Units of measurement and abbreviations
- 1 Geology: An Australian perspective
- 2 The Earth: A geology primer
- 3 Telling geological time: The great canvas
- 4 The cratons: Building the core of Precambrian rocks
- 5 Mountain building: Paleozoic orogenic rock systems
- 6 Warm times: Tropical corals and arid lands
- 7 Icehouse: Carboniferous and Permian glaciation
- 8 Mesozoic warming: The great inland plains and seas
- 9 The birth of modern Australia: Flowering plants, mammals and deserts
- 10 Fossils: The Australian record of past life in context
- 11 The land stirs: Volcanoes and the eastern highlands
- 12 The outline and submerged terrace: Building the continental shelf and coastlines
- 13 The coral reefs: Unique parts of the continental shelf
- 14 Patterns of change: Cycles in Australia's journey
- Epilogue
- Sources and references
- Index
- References
Summary
The Earth is dynamic, its continents wandering great distances over time, repeatedly coming together and splitting up as oceans close and open. Australia is an old and complex continent, subject to ever-changing global lithosphere dynamics, and still slowly evolving. Its history is written in its rocks. It was periodically subjected to compressional events as the supercontinents were assembled and tensional events as the supercontinents disintegrated. A convergent plate boundary lay immediately to the east of Australia for much of its more recent, post-Precambrian history. The dynamics of this boundary built much of the eastern Australian crust. Climate affecting Australia fluctuated considerably, with episodes of icy conditions separated by longer intervals of warmth. There were massive extinction events that shaped life on the Earth. The last of these occurred when Australia was progressing to be an island continent. This event, and the isolation that followed, resulted in the distinctive animals and plants that characterise Australia.
GLOBAL WANDERING
The story of Australia is about the journey of a landmass wandering across the globe through geological time. The more recent part of the journey, over the last 100 million years or so, back to the Cretaceous, is well established. This is because the seafloor spreading history of the oceans is known back to this time, recorded by the striped pattern of magnetic anomalies symmetrical about the mid-ocean ridges. By progressively removing the strips of ocean crust, from the youngest back to the oldest, we can project movements of the ocean-bordering continents back through time.
The earlier journey, preceding the Cretaceous, is less securely known and increasingly so the further back we go. Knowledge of it depends on paleomagnetic data, which tells us where rock bodies of various ages were located with respect to the Earth's magnetic field at their time of formation. By implication, they give a ‘fix’ for the location of a continent at that time. However, the ‘fix’ is only in terms of paleolatitude and is unconstrained for paleolongitude. This deficiency is reminiscent of the riddle that plagued ancient mariners. Doubtless we will have misplaced Australia in global reconstructions for the distant reaches of geological time, just as many ancient mariners misplaced the longitudinal position of their vessels, sometimes with disastrous consequences.
Continental geology provides important indications of how the jigsaw of continental configurations may have looked in the past.
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- The Geology of Australia , pp. 327 - 346Publisher: Cambridge University PressPrint publication year: 2016