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Sub-surface data in Taranaki provides new insights into the break-up of Gondwana supercontinent - 28/09/2017

A recently completed study of the geological history of New Zealand’s offshore northwestern region has revealed new insights into the break-up of the Gondwana supercontinent during the time of the dinosaurs.

The study is believed the be the first to recognise two distinct phases of rifting based on seismic data across an extensive part of Gondwana– where the Earth’s crust is stretched and breaks up.

It will help geologists better predict where and when coal-bearing rocks – from which oil and gas can form – were deposited in the Earth’s crust. This will help in the search for new accumulations of oil and gas in New Zealand.

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Typically, after five years, all privately acquired petroleum exploration data in New Zealand becomes freely available and this gives scientists access to a large amount of high-quality data to investigate a wide range of earth processes, including natural hazards and climate history 

Dr Dominic Strogen

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The study also provides additional insights into how continents break-up and how ocean basins form.  Such separation of continents and can be seen actively occurring today in the Great Rift Basin in Africa and the Red Sea of Arabia, and is a fundamental Earth process that continues to influence the topography of New Zealand to this very day.

Lead author Dominic Strogen, of GNS Science, said the study was a great example of how scientists can obtain benefits from geological data gathered and paid for by petroleum exploration companies and the New Zealand Government as part of petroleum exploration.

“Typically, after five years, all privately acquired petroleum exploration data in New Zealand becomes freely available and this gives scientists access to a large amount of high-quality data to investigate a wide range of earth processes, including natural hazards and climate history,” Dr Strogen said.

The scientists analysed subsurface seismic data from the Taranaki and Reinga-Northland sedimentary basins. They also had access to information from dozens of drillholes drilled over the past 50 years.  

For several hundred million years, the continental crust that would eventually become Zealandia lay along the eastern side of the Gondwana supercontinent. Australia and Antarctica, also part of Gondwana at that time, were essentially Zealandia’s next-door neighbours.  

About 105-million-years-ago — for reasons that remain uncertain — Gondwana began to break apart.  The powerful tectonic forces associated with the break-up of the supercontinent stretched the continental crust around the New Zealand region to breaking point, and by 83-million-years-ago Zealandia separated from Gondwana, with new ocean basins forming between the two continents.

The Tasman Sea was formed during this process, and the region that would eventually become New Zealand looked vastly different to what it does today.

The scientists have called the first of the two distinct rifting phases the “Zealandia rift phase” and it occurred between 105–83-million-years ago.

It created a series of north–northwest-trending sedimentary basins (depressions, or low points on Earth’s surface) in the Taranaki-Northland-Reinga region, in the initial phases of separation of Zealandia from Gondwana.

The researchers found that sedimentary basins were also formed in many other parts of Zealandia at this time, such as in the Canterbury and Otago regions.

A short-lived period between 83–80-million-years-ago saw uplift and erosion occur across much of what now comprises the offshore Taranaki and northwest Nelson regions.

This period of uplift was quickly followed by a second phase of rifting and thinning of the continental crust in a zone up to 150km wide through the West Coast–Taranaki region between 80–55-million-years-ago.  

This second period of rifting also formed sedimentary basins, into which organic matter-rich sediments were deposited that later formed many of the famous West Coast coal seams.

The study was undertaken by GNS Science geologists Dominic Strogen, Hannu Seebeck, and Peter King, along with Professor Andy Nicol from the University of Canterbury.

It was recently published in the prestigious Journal of the Geological Society, London under the title

‘Two-phase Cretaceous–Paleocene rifting in the Taranaki Basin region, New Zealand; implications for Gondwana break-up.’ 

Caption for image: A series of maps depicting how the greater Taranaki Basin region may have looked in the ancient past.  Grey and green colours show land, pale-yellow and blue colours show marine environments (darker blue colours indicate progressively deeper water).  The 98 million-years-ago map represents the first “Zealandia” phase of rifting, the 82 million-years-ago map shows the short-lived period of uplift and erosion, and the 77 and 62 million-years-ago maps show the second phase of rifting.  Of note is how vastly different the geography of the Taranaki Basin area was to that we see today.

A series of maps depicting how the greater Taranaki Basin region may have looked in the ancient past.  Grey and green colours show land, pale-yellow and blue colours show marine environments (darker blue colours indicate progressively deeper water).  The 98 million-years-ago map represents the first “Zealandia” phase of rifting, the 82 million-years-ago map shows the short-lived period of uplift and erosion, and the 77 and 62 million-years-ago maps show the second phase of rifting.  Of note is how vastly different the geography of the Taranaki Basin area was to that we see today.