Geology in the MacleayGeology excursion for Stage 3

General

Most of the rocks in the Macleay Valley are very old.

They were formed at the bottom of a sea 250 million years ago in the Permian age. To put that in perspective at the time these rocks were formed there were no humans, no mammals, no reptiles, no birds, and no flowering plants.

They were formed before the dinosaurs when the only life on Earth was in the sea or amphibians and insects on the land.

Geology Map of Macleay valley

Where to see Rocks

We can see these rocks in road cuttings and along the Macleay River where it has dug into the rock.

Rocks

The predominant rock type in the Macleay Valley is sedimentary. Usually mudstone or siltstone, with some sandstone, conglomerate and limestone.

Mudstone Sandstone Conglomerate Limestone

The formation of the Great Dividing Range pushed the layers of sedimentary rocks from horizontal to many different folds and angles.

Sedimentary Folding

This can be seen here along the cuttings of Armidale Rd where the rock is at a steep angle.

Landslides

The angle of these rocks means that layers slip off frequently during wet weather causing landslides.

SlateSlate is a metamorphic rock caused by heat and pressure

being applied to mudstone. It can be seen on Armidale Rd at this cutting near Nook Ck. Slate can be used for roofs and floors.

Anderson's Sugarloaf/ Barralbalayi

Anderson's Sugarloaf or Barralbalayi dominates the landscape in the Upper Macleay. It is an example of some the youngest rocks in the valley. It's cap is made of basalt formed by the Ebor Volcano 20 million years ago.

ConglomerateOn the road down to the Macleay River at Bellbrook can be

seen an interesting example of conglomerate. Conglomerate is formed by a river laying down rocks and silt. In this example you can see the layers caused by successive floods.

Conglomerate

A closer look at the conglomerate shows the rounded pebbles caused by rolling in the river.

Macleay RiverAt the Macleay River the predominant stones on the

riverbed are basalt and granite. The nearest source of both these stones is 50-100 km away but they have been carried here by the river. The local rock is not seen because mudstone and siltstone are rapidly ground down to mud and silt.

http://youtube.com/v/5tpnJDzZVRY

Basalt and Granite

Basalt and granite are igneous rocks formed by volcanoes. The basalt has come down from the basalt lava flow of the Ebor Volcano on the New England Tableland.The granite has come from a much older volcanic intrusion at Five Day Creek and Dyke River.

Riverbank walk

In this photo the presence of the conglomerate above the mudstone shows that it is younger rock.

Inclination

This photo shows the angle of the mudstone and its layers.

Limestone

A limestone outcrop can be seen at Willi Willi. It was formed from coral in a shallow sea about 280 million years ago. Sometimes coral can be seen in the rock.

Limestone is used to make concrete.

Limestone Caves

Limestone is permeable to water which dissolves the calcium in it and forms caves. There are many caves at Willi Willi but they are on private property and require a NPWS permit to visit.

Erosion

This view from the Carrai Plateau shows how deeply the Macleay River has carved away the rocks forming valleys.

Rocks at the CemeterySandstone, granite and marble can be seen in headstones

at the West Kempsey Cemetery.

Uses of Rocks in Kempsey

Kemps Pinnacle

Science Syllabus Stage 3 Content

Earth and its Surroundings

The Earth is part of a changing system. It is also itself a changing system. In order to preserve life on Earth, there is a growing need to develop understanding of the Earth’s characteristics and how people interact with their environments.

The Earth and its Surroundings strand is concerned with:

• natural changes that occur, such as soil erosion, volcanic eruption, climatic changes and movement of water

•the variety and characteristics of naturally occurring materials

• the methods people use to obtain and process materials

•the methods people use to manage natural resources

•limitations to resources available on Earth • renewable resources.