New Zealand’s offshore sedimentary basins hold the ‘missing pages’ of Zealandia’s history
Over millennia, the surface of our continent, Zealandia, has changed significantly, driven by tectonic forces, erosion, ocean currents, volcanism, and even flora and fauna, continuously altering its appearance and often shrouding the history of what came before.
Untangling Earth's geological record is like piecing together a collection of shuffled books, scattered chapters, and missing pages - for geologists, organizing this library requires a range of expertise.
Imagine sedimentary basins as sections within the Earth's library, each containing a unique collection of books in the form of geological records. These ‘books’, comprising layers of sedimentary rocks, are like volumes of Earth's history, preserving stories of ancient landscapes, climates, and ecosystems.
Now, picture these basin "sections" scattered across the Earth's surface, akin to various sections in a vast library. Some basins may be found beneath the deep ocean floor, on continental shelves, while others are nestled deep within the interiors of continents.
Each basin holds a wealth of information, like fragments of a giant puzzle. By piecing together geological records from these basins, scientists can delve into the Earth's past to uncover chapters of ancient climates, ecosystems, and geological processes.
A recently published paper, ‘New Zealand’s Offshore Sedimentary Basins’, led by a team of GNS researchers, presents new interpretations and mapping that define the distribution, extent, and sediment thickness of 25 primarily offshore sedimentary basins within New Zealand’s Exclusive Economic Zone (EEZ) and Extended Continental Shelf (ECS). The paper forms the culmination of a significant and highly productive period of sedimentary and basins research, decades long and involving hundreds of New Zealand and international geoscientists. These results help provide a ‘whakapapa’ for the Zealandia continent.
These basins cover ~1.64 million km² of the ~5.8 million km² (~28%) of New Zealand’s offshore territory. Much of the work in this paper was undertaken as part of the multi-year Government-funded and GNS-led Atlas of Petroleum Prospectivity (APP) research programme. Another significant contribution was from research leading to the establishment of our maritime borders with Australia and France (through New Caledonia), thereby allowing each nation exclusive rights to the sea floor and below within their territories.
The sands of time
This paper is the first time that the stories from all New Zealand’s offshore basins have been compiled. The rocks studied, up to 110 million-years-old, reveal how Zealandia was formed, how it has drifted across Earth’s surface, and how the region’s climate has repeatedly warmed and cooled over time.
For example, the image below shows a reconstruction of Zealandia 48 million years ago, when the continent had a very different shape. The present-day coastline, shown in black, reveals how the present-day landmasses have moved since this time. The map shows how New Zealand’s sedimentary basins reflect different aspects of Zealandia’s geological evolution. The basins in green formed along the eastern edge of the Gondwana supercontinent, whereas the pale-yellow basins primarily formed during the time Zealandia was breaking away from Gondwana, before and during the opening of the Tasman Sea. The brown basins formed during the early phase (40–20 million years ago) of formation of the tectonic plate boundary that now bisects New Zealand, and the blue basins relate to more recent tectonic plate boundary formation since 20 million years.
Of particular interest to the biological science community, the study of New Zealand sedimentary basins also provides information on biodiversity through time, revealing where landmasses lay, what plants and animals have lived here previously, how species have evolved, and how their populations have changed and moved through time.
This assessment of NZ’s basins has been built upon the shoulders of many, many excellent geoscientists, and we hope that this paper is an appropriate recognition for their insights and contributions.
Future opportunities
New Zealand’s sedimentary basins are candidates for new and emerging technological uses, such as Geological Energy Storage, and Carbon Capture and Storage (CCS), the latter involving the capture of CO² from large sources such as electricity generation plants and then permanently storing it underground to reduce emissions and aid in the challenges of climate change.
Other forms of underground energy storage, such as storing compressed air or surplus hydrogen generated from green electricity, could be considered as a way of dealing with times of electricity shortage.
This paper will act as a great framework for further studies in the future, such as understanding the thickness and properties of the sediments in the basins to know how seismic waves from earthquakes will move through the earth. Knowing the depth to the harder 'basement' rocks beneath the sedimentary basins is also important for seismic hazard assessments, given how those rocks can reflect and refract seismic waves. It's also possible that these basins contain minerals and other critical materials that may be important to helping NZ's economic development and a transition to a low-carbon economy.
The paper ‘New Zealand’s Offshore Sedimentary Basins’ Bland KJ, Strogen DP, Arnot MJ, Viskovic GPD, Sahoo TR, Seebeck H, Kellett R, Bull S, Thrasher GP, Kroeger KF, Lawrence MJF, Griffin AG. 2024 is available here.(external link)
Contributions to the paper have come from many across the decades but in particular Peter King, Mike Isaac, Greg Browne, Chris Uruski, Rob Funnell, Nick Mortimer, Ray Wood, Rick Herzer, and Brad Field.