Geology of New South Wales facts for kids

New South Wales, a state in Australia, has a fascinating geology! Its land is made up of seven main areas, each with its own unique rocks and history. These areas are like giant puzzle pieces: the Lachlan Fold Belt, the Hunter-Bowen Orogeny (also called the New England Orogen), the Delamerian Orogeny, the Clarence Moreton Basin, the Great Artesian Basin, the Sydney Basin, and the Murray Basin.

Some of these big areas have smaller parts too. For example, the Great Artesian Basin includes the Eromanga Basin and the Surat Basin. The Sydney Basin stretches north into the Gunnedah Basin and then the Bowen Basin. These basins are like huge bowls in the Earth's crust that have filled up with layers of rock over millions of years. New South Wales is also important for mining, with places like Broken Hill known for its rich minerals, and coal mines in the Hunter and Illawarra regions.

Lachlan Fold Belt: Ancient Mountains and Rocks

The Lachlan Fold Belt is a huge area of old rocks found in the central and southeastern parts of New South Wales. It also lies deep beneath the Great Artesian Basin, Sydney Basin, and Murray Basin. This region was once much wider, stretching for thousands of kilometers!

It formed about 450 to 340 million years ago during the Middle Paleozoic era. Imagine the Pacific plate (a giant piece of Earth's crust) slowly sliding under the Australian continent. This movement squeezed and folded the ocean floor sediments, creating the rocks we see today. The Australian Capital Territory is actually located right in the middle of the Lachlan Fold Belt.

Hunter-Bowen Orogeny: A Volcanic Past

The Hunter-Bowen Orogeny, also known as the New England Orogen, is another important geological area. It contains rocks from the Late Paleozoic to early Mesozoic times. This region formed when the Pacific Plate was sliding under Australia, creating a chain of volcanoes and a special zone where volcanic materials and sediments built up.

Darling and Barka Basins: Stretched Earth

The Darling Basin started forming a very long time ago, in the early Devonian period. The Earth's crust in this area began to stretch, creating deep valleys called basins (like the Cobar Basin) and flatter areas called shelves. Over time, these areas filled up with sediment and volcanic rocks.

Later, these rocks were pushed upwards, and rivers deposited more sand and silt, forming the Barka Basin. Most of the rocks here are made of quartz sand.

Sydney Basin: Home to Sydney's Rocks

The Sydney Basin is where you find the rocks that make up the land around Sydney. It stretches from Newcastle down to Batemans Bay. This basin is made of Permian and Triassic sedimentary rocks, which are rocks formed from layers of sand, mud, and other materials.

The rocks here tell a story of ancient seas and rivers. The first rocks formed in the Permian period came from volcanoes in the Hunter region. Later, coal seams formed from ancient plants in swampy areas. The basin then sank, and seawater covered much of the land, depositing more layers.

A famous rock in Sydney is the Hawkesbury sandstone. You can see it in many cliffs and buildings around the city. Above this, you find the fine sandstone of the Mittagong Formation and the Wianamatta shale. Millions of years ago, the basin was buried under even more layers of rock, but these have since worn away.

Great Artesian Basin: Australia's Underground Water Supply

A large part of the Great Artesian Basin is located along the northern border of New South Wales, extending into Queensland. This huge basin covers about one-fifth of New South Wales! It formed during the Jurassic and Cretaceous periods.

This basin is like a giant underground sponge, holding vast amounts of water. The oldest rocks in the basin are sandstones and shales from the Jurassic period. Later, during the Cretaceous period, seawater entered the basin, depositing more layers of shale. Today, much of the basin is covered by younger sediments from rivers and lakes.

Because it holds so much water, many artesian wells have been drilled here, allowing us to learn a lot about its deep structure and underground temperatures.

Clarence Moreton Basin: Northeastern Riches

The Clarence Moreton Basin is in the far northeast of New South Wales, around Lismore and Grafton. It also extends into Queensland. This basin formed as the Earth's crust stretched, creating a space that filled with continental deposits.

The basin contains Triassic volcanic rocks and sedimentary layers, including important coal beds. Most of the rocks here are Jurassic and Cretaceous sedimentary rocks. The basin was named after the Clarence River because it was discovered that the Clarence Basin and the Moreton Basin in Queensland were actually one big structure.

One interesting feature is the Blaxland Fossil Wood Conglomerate Member, where you can find fossilized tree trunks up to 18 meters long! These ancient trees have turned into rock over millions of years.

Murray Basin: A History of Seas and Lakes

A cross-section showing the layers of the Murray Basin

The Murray Basin formed after Australia separated from Antarctica. Over time, this basin slowly sank and filled with up to 600 meters of sediments during the Cenozoic Era (the last 66 million years).

In ancient times, the western part of the basin was flooded by seawater, leaving behind layers of sand, silt, and clay. The sea level rose and fell many times, creating different layers of rock like marl and limestone.

Around 2.5 million years ago, during the Pleistocene Ice Age, the Murray River was blocked by rising land in Victoria. This created a huge freshwater lake called Lake Bungunnia, which covered an area of 40,000 square kilometers! This lake eventually dried up, leaving behind salt lakes that you can still see today. The Murray River then carved a new path to the sea.

Today, most of the surface of the Murray Basin is made of deposits from the Quaternary period, including river deposits and sand layers that hold underground water.

Oaklands Basin: Hidden Coal Deposits

The Oaklands Basin is a hidden basin in the Riverina district of southern New South Wales. It's covered by the Murray Basin. This basin is about 3,800 square kilometers and contains very thick layers of sediment, over 1,000 meters deep!

It was first discovered in 1916 when people drilling for water found coal. Since then, most of the exploration in this basin has been for coal.

Volcanic Rocks: Fiery Past

New South Wales has many areas with volcanic rocks, covering about 26,000 square kilometers! These rocks are from the Cainozoic period (the last 66 million years). You can find major volcanic areas in the northeast, including the Liverpool Range, Barrington Tops, Nandewar Range, the Warrumbungles, and the famous Tweed Volcano. These are all reminders of a fiery past when volcanoes erupted across the landscape.

Geological History: How New South Wales Formed

Millions of years ago, in the Cambrian period, only the far west of New South Wales existed in its current form. It was part of a giant supercontinent called Rodinia, connected to what is now North America!

Later, North America broke away, and the Pacific Ocean began to open. In the Ordovician and Silurian periods, sediments built up on the new seafloor. Then, a chain of volcanoes formed, and the land behind them was pushed onto the east coast of Australia, creating the Lachlan Fold Belt. This process shaped the land, which is why many rivers and mountain ranges in New South Wales run from north to south.

Fossils: Clues to Ancient Life

New South Wales is a treasure trove of fossils, which are the preserved remains of ancient life.

• At Lightning Ridge, you can find amazing opalized fossils that are about 100 million years old. These are fossils that have turned into precious opal!
• The Wellington Caves contain fossils of huge animals, called megafauna, that lived between 4 million and 30,000 years ago. These include the fearsome marsupial lion and giant kangaroos.
• Canowindra is home to one of the most important fish fossil sites in the world! It dates back 360 million years to the Devonian period and includes unique fish like Groenlandaspis and Canowindra grossi. There's even a museum there called the Age of Fishes Museum.
• At Cuddie Springs, you can find fossils of the giant Diprotodon and the enormous Thunder Bird.
• The Griman Creek Formation also holds Cretaceous dinosaur fossils.

Economic Geology: Mining and Minerals

Mining: Digging for Riches

New South Wales is rich in minerals, and many mines operate across the state:

• Broken Hill Ore Deposit is famous as one of the world's richest zinc and silver mines.
• The Cadia-Ridgeway Mine near Orange and Lake Cowal Campaign and Barrick Gold near Parkes are important gold mines.
• The CSA Mine and Endeavour Mine near Cobar extract copper and zinc.
• Mineral sands, containing valuable minerals like rutile, zircon, and ilmenite, are mined at places like the Ginko Mineral Sand Deposit.

Disasters: Nature's Power

New South Wales has also experienced natural geological events:

• The oldest coal seam fire in the world has been burning for about 6,000 years at Burning Mountain near Wingen, New South Wales. This is a fascinating natural phenomenon!
• The Newcastle earthquake on December 28, 1989, was a significant event that affected the city.

Images for kids

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  A book about copper mining in New South Wales from 1899.