Stratigraphy of New Zealand facts for kids
This article is about the different types of rock layers found in New Zealand. Geologists (scientists who study rocks) give special names to these rock layers. As they discover more about how rocks are formed, new names are sometimes created, and old ones might become less common. This list is based on the official New Zealand rock naming guide from 2014. However, some older names that are still used are included to help you understand.
Each rock unit has two parts to its name: a main name, which is usually a place where the rock is found (like the Waitematā area), and a rank, like "Group." Rocks are organized in a hierarchy, from smallest to largest:
- Beds: Individual layers of rock.
- Members: Groups of beds.
- Formations: Groups of members.
- Subgroups: Groups of formations.
- Groups: Groups of subgroups.
- Supergroups: Groups of groups.
- Terrains: For very old "basement" rocks, these are large blocks of rock that formed in different places and then joined together.
Sometimes, not all these levels are used for every rock type. Many New Zealand rocks also have names based on what they are made of, like the Wooded Peak Limestone (a rock made mostly of calcium carbonate) or the Hawks Crag Breccia (a rock made of broken, angular pieces).
Contents
New Zealand's Main Rock Groups
New Zealand's rocks are often divided into two big "megasequences" or super-groups. Think of these as two main chapters in New Zealand's geological story.
Austral Superprovince: The Oldest Rocks
The Austral Superprovince includes all the very old "basement" rocks. These rocks formed between the Cambrian period (about 541 million years ago) and the Cretaceous period (about 66 million years ago). This superprovince is split into two main areas:
- Eastern Province: This area has seven different rock blocks called terranes.
- Western Province: This area has two terranes.
Zealandia Megasequence: Younger Rocks
The Zealandia Megasequence includes all the younger rocks that formed on top of the basement rocks. These rocks are from the Cretaceous period (starting about 145 million years ago) up to the Holocene (our current time). This megasequence is divided into five supergroups, from oldest to youngest:
- Momotu Supergroup
- Haerenga Supergroup
- Waka Supergroup
- Māui Supergroup
- Pākihi Supergroup
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Basement Rocks: Austral Superprovince
These are the oldest rocks in New Zealand, forming the base of the land. They are divided into different terranes, which are like puzzle pieces that came together over millions of years.
Takaka Terrane
The Takaka Terrane is home to some of New Zealand's very oldest rocks.
- Haupiri Group: These rocks are from the Cambrian period and are found in Tasman. They are made of conglomerate (rocks with rounded pebbles) and siltstone.
- Mount Arthur Group: Found in Tasman, these rocks include marble and mudstone. The famous Harwoods Hole cave is formed in the Mount Arthur Marble.
Buller Terrane
The Buller Terrane contains rocks that were once thought to be the oldest in New Zealand.
- Greenland Group: These rocks are found in Westland, Tasman, and Fiordland. They are marine (ocean-formed) volcanic sandstones and siltstones.
Dun Mountain-Maitai Terrane
The Dun Mountain-Maitai Terrane is known for its unique rock types.
- Dun Mountain Ultramafics Group: These rocks are found in the South Island and are the source of pounamu (New Zealand jade), a very special stone.
Torlesse Composite Terrane
The Torlesse Composite Terrane makes up a large part of the South Island.
- Rakaia Terrane: These greywacke rocks are the main type found in the Southern Alps, New Zealand's largest mountain range.
Cover Sequence: Zealandia Megasequence
These younger rocks sit on top of the older basement rocks. They tell the story of New Zealand's more recent geological past, including volcanic activity and changes in sea level.
Momotu Supergroup
This supergroup includes rocks from the Cretaceous period.
- Pororari Group: Found on the West Coast, this group includes the Hawks Crag Breccia, which is known for having uranium.
- Mount Somers Volcanics Group: These volcanic rocks are found in Canterbury and include different types of volcanic flows.
Haerenga Supergroup
This supergroup includes rocks from the Eocene and Oligocene periods.
- Te Kuiti Group: Found in Waikato, Northland, and Auckland, these rocks include sandstone, coal, and limestone.
- Tinui Group: In Wairarapa and Gisborne, these mudstone and sandstone rocks are famous for containing Dinosaur fossils.
- Onekakara Group: Found in Otago and Canterbury, these siltstone rocks are where the amazing Moeraki Boulders were formed.
Waka Supergroup
This supergroup includes rocks from the Oligocene and Miocene periods.
- Te Kuiti Group: These rocks, found in Waikato, Northland, and Auckland, are the host rocks for the famous Waitomo Caves and the "hole in the rock" at Piercy Island.
- Nile Group: Found in Westland, these limestones form the unique Punakaiki Rocks (Pancake Rocks) and the Oparara Basin Arches.
- Alma Group: In Otago and South Canterbury, this group includes the Oamaru Stone limestone, used for building.
Māui Supergroup
This supergroup includes rocks from the Miocene and Pliocene periods, often linked to volcanic activity.
- Coromandel Group: These volcanic rocks on the Coromandel Peninsula are where hard rock gold mines are found.
- Waitakere Group: Found in Auckland, these volcanic rocks include the famous Lion Rock at Piha Beach.
- Waitemata Group: These marine rocks are found around Waitematā Harbour and form its sea cliffs.
- Banks Peninsula Volcanic Groups: Several groups like Diamond Harbour, Mount Herbert, Akaroa, and Lyttelton Volcanic Groups form the Banks Peninsula Volcano near Christchurch.
- Dunedin Volcanic Group: These volcanic rocks formed the Dunedin Volcano and make up the Otago Peninsula.
- Manuherikia Group: Found in Otago and Southland, these river sediments contain New Zealand's only fossilized land mammals, known as the (Saint Bathans Fauna).
Pākihi Supergroup
This supergroup contains the youngest rocks, from the Pleistocene and Holocene periods, often related to recent volcanic activity and sand dunes.
- Karioitahi Group: Found in Northland and Auckland, these are modern sand dunes, including the west coast ironsands.
- Kerikeri Volcanic Group: These basaltic flows and scoria cones form the Auckland Volcanic Field and the Wairere Boulders.
- Taupo Group: These volcanic rocks, including tephra (ash) and ignimbrite, come from the Taupo Volcano.
- Okataina Group: Part of the Taupo Volcanic Zone, these rocks include tephra and lava domes.
- Onoke Group: Found in Wellington and Wairarapa, these marine mudstone rocks form the unique Putangirua Pinnacles through erosion.
- Hawkdun Group: In Otago, these gravels are one source of alluvial gold.
Images for kids
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A simple picture showing the layers of rock under New Zealand. Scientists have removed the effects of recent earth movements to make it clearer.
