Taranaki Basin facts for kids
The Taranaki Basin is a large area of land and sea on the west coast of New Zealand's North Island. It's like a giant bowl filled with layers of rock and sediment. This basin is super important because it holds most of New Zealand's oil and gas! Scientists have drilled over 400 wells here and found about 20 oil and gas fields.
This basin started forming a long, long time ago, during the Cretaceous period, when the supercontinent Gondwanaland began to break apart. This pulling apart created a "rift," which is like a big crack in the Earth's crust. Later, the Pacific Plate started sliding under the Australian Plate, a process called subduction, which also shaped the basin. The Taranaki Basin covers about 100,000 square kilometers, and most of it is under the sea. It's mostly filled with sediments from the ocean, but also some from land, especially from the Late Cretaceous to the Eocene periods.
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What is the Taranaki Basin?
The Taranaki Basin is located on the west coast of the North Island, in the Taranaki Region. It's about 400 kilometers west of where the Pacific and Australian plates meet today. This huge basin is about 100,000 square kilometers big and contains up to 9 kilometers of sediment!
The basin has two main parts:
- The Western Platform: This part is pretty stable and hasn't changed much over time. It has between 2,000 and 5,000 meters of sediment, from the Late Cretaceous period until now.
- The Eastern Mobile Belt: This part is more active and has many features like "grabens" (sunken blocks of land) and "faults" (cracks in the Earth's crust where rocks have moved).
These two parts are separated by a major fault zone called the Cape Egmont fault zone.
Animals Living in the Taranaki Basin
The waters of the Taranaki Basin are home to amazing sea creatures.
- The huge Blue whale uses this area as a place to breed.
- The Southern right whale also lives here.
- The critically endangered Māui dolphin lives near the Taranaki coast. It's one of the rarest dolphins in the world!
How the Taranaki Basin Formed
The Taranaki Basin's story is all about how the Earth's plates moved and changed over millions of years.
Early Rocks (Basement Structure)
Before the basin even started to form, there were older rocks deep underground. These are called "basement rocks." They are a mix of different types of rocks, including some from the original supercontinent Gondwana.
When the Earth Ripped Apart (Rifting)
The Taranaki Basin began to form in the Late Cretaceous period. This was when Australia and a landmass called Zealandia started to pull away from each other. This pulling apart was part of the breakup of Gondwanaland. This event created the Tasman Sea and also caused big cracks, or "rifts," to form in the land that would become New Zealand. The Taranaki Rift was one of these cracks, and it eventually grew into the Taranaki Basin.
As the land pulled apart, sediments like sand, silt, and coal were deposited in the sunken areas. These layers show how the Earth was stretching during this time.
After the Rifting (Drift)
After the pulling apart stopped in the Late Cretaceous, the Taranaki Basin became a "passive margin." This means it was no longer actively being pulled apart. The land slowly sank, allowing huge amounts of sediment to build up during the Paleocene and Eocene periods. These sandstone layers from the Paleocene and Eocene are where most of the oil and gas in the basin are found today! Over time, less sediment was deposited, and the layers became thinner.
Layers of Rock (Stratigraphy)
The Taranaki Basin is made up of many different layers of rock, each telling a story about the Earth's past. Here are some of the main groups of rocks, from oldest to newest:
Pakawau Group
These are the oldest sediments in the Taranaki Basin, laid down between the Late Cretaceous and Paleocene. They include sandstones from rivers and oceans. In some places, this group is more than 2,000 meters thick!
Kapuni Group
This group contains several important layers from the Paleocene and Eocene periods. These include:
- Farewell Formation: Mostly sandstone from rivers.
- Kaimiro Formation: Sandstones from rivers and coastlines.
- Mangahewa Formation: Sandstone, siltstone, mudstone, and coal. This layer has good rocks for holding oil and gas.
- McKee Formation: Easily recognized by its coarse, well-sorted sandstones.
Tikorangi Limestone
This layer is mostly sandy limestone from deep water, with some mudstone and sandstone mixed in. It's found above the Kapuni Group.
Mahoenui Group
This group has mudstones with thin layers of sandstone, siltstone, and limestone. These sediments were deposited during the Late Oligocene and Early Miocene.
Mokau Group
This group is made of sandstones from shorelines, with some siltstones. You can also find layers of river gravel and coal here. These rocks formed in the Early Miocene.
Wai-iti Group
This group includes:
- Mohakatino Formation: Mudstones with volcanic sandstones.
- Mt Messenger Formation: A very thick sandstone layer.
- Urenui Formation: A silty mudstone.
Matemateāonga Formation
This layer has shellbeds, siltstones, and sandstones. It formed during the Late Miocene and Early Pliocene.
Newer Deposits
Volcanic activity, like the eruption of Mount Taranaki, started in the basin during the Miocene and continues to this day!
Oil and Gas in the Taranaki Basin
The Taranaki Basin is where most of New Zealand's oil and gas comes from. Over 1.8 billion barrels of oil and gas have been found here, with about 70% of that being natural gas. More than 400 wells have been drilled in about 20 different oil and gas fields.
The basin's complex history has created many different types of "traps" that hold the oil and gas. These traps are often formed by faults (cracks in the rock) or by folds in the rock layers.
Source Rocks for Oil and Gas
Most of the oil found in the Taranaki Basin comes from coal and marine shales (a type of rock) that formed in the Late Cretaceous and Paleogene periods.
Oil and Gas Fields in the Taranaki Basin
Here are some of the main oil and gas fields found in the Taranaki Basin:
- Mangahewa Field
- Maui Field
- Kapuni Field
- Cardiff/Radno Field
- Turangi/Ohanga Field
- Pohokura Field
- McKee Field
- Tuhua Field
- Tui oil field
- Kupe Field
- Rimu Field
- Maari Field
- Kaimiro Field
- Cheal Field
- Moturoa Field
- Karewa Field
- Ngatoro Field
- Waihapa Field
- Toko Field
