GEOLOGY OF THENEWCASTLE COASTLINE

NEW SOUTH WALES

www.resourcesandenergy.nsw.gov.au

The coastal cliffs in the Newcastle area are made of the Newcastle Coal Measures – one part of the Sydney Basin. These sedimentary rocks were formed from sediments deposited in rivers and swamps in the late Permian approximately 255 million years ago. Subsequent uplift and erosion has resulted in the topography we know today – the headlands, the beaches and the rock platforms along The Bathers Way and beyond.

This map and brochure explains some of the features that make up our beautiful coastline.

Aboriginal tools

The rocks of the Newcastle Coal Measures were mined long before European settlement.

The Nobbys Tuff consists of thin layers of volcanic ash. This ash originated from volcanic eruptions that would have covered the landscape, and in some places rivers redistributed the ash. Some tuff layers are very fine grained, hard and chert-like, due to silica enrichment by chemical weathering. The rock breaks with a conchoidal (curved) fracture to produce very sharp edges. Local Awabakal and Worimi people used small boulders of the rock at the foot of cliffs at Merewether and Glenrock to make cutting and scraping tools.

Coal

Europeans discovered coal near Newcastle in 1791, before Lieutenant Shortland explored and named the Hunter River and noted abundant coal in 1797. One of the early names for Newcastle was Coal River, and coal became the first export commodity of the fledgling New South Wales colony.

Coal from Newcastle quickly made a name as a top quality coking (or metallurgical) coal – the Victoria Tunnel Seam is regarded as one of the best in the world due to its low ash and sulfur content. Thermal coal from the area is used to generate electricity.

The Port of Newcastle is the biggest coal export harbour in the world, with 142 million tonnes shipped in 2012–13. The coal monument in Parnell Place was dedicated in 1910 as a tribute to coal exports.

Linking Newcastle to Gondwana

The Newcastle Coal Measures contain many plant fossils that represent late Permian forests. The most common are leaves of Glossopteris, a woody seed-bearing plant. They are found in shale (e.g. south of Merewether Baths) and near the Bogey Hole . Glossopteris fossils are found in South Africa, India, South America – and also in Antarctica. As the seeds of Glossopteris were heavy and could not have been transported far by wind or water, all of these places must have been near each other in the late Permian – when continents were joined together in the supercontinent Gondwana.

Pumice

Pumice fragments are often found on the beaches of eastern Australia . Pumice is a very light rock formed from glass and crystals in frothy lava that has been explosively erupted from volcanoes. But where does it come from?

In July 2012 a raft of pumice was observed floating over the Kermadec Trench between New Zealand and Fiji. This pumice was erupted from an underwater volcano (known as a seamount). Over the next few months, this raft of pumice gradually floated over the Tasman Sea and washed up on beaches of eastern Australia. The size and abundance of the pumice is unusual – with some lumps as big as footballs. Animals such as shellfish and crabs hitch a ride on the pumice as it floats. This is one way early life would have been transported around our planet.

Building a city

The development of Newcastle has been dependent on the local geology. The initial settlement relied on fresh water springs on The Hill. Small communities developed as coal mines opened, such as at Wallsend, Lambton and Charlestown. Major drainage and reclamation work in the 20th century allowed development of suburbs on the floodplain such as Hamilton and Broadmeadow . Local resources have been used for construction such as the Waratah Sandstone, clay in the Thornton area for brick-making, quartz-rich sand for construction and glass making, and titanium-bearing minerals from Stockton Bight . Carboniferous volcanic rocks (e.g. near Karuah, Paterson and Seaham) are quarried for use as aggregate, including as road and railroad ballast.

Our ever-changing coastline

Our coastline is constantly changing! Some of these changes are man-made. For example, Nobbys Beach has only formed since Macquarie Pier joining Nobbys to the mainland was completed in 1846.

Other changes are natural. The sand on our city beaches is constantly shifting, with single storm events capable of eroding and redepositing masses of sand. And some changes are a combination. Erosion along natural jointing surfaces in rocks is common in the area. Care needs to be taken during construction to allow for these surfaces, so that rock falls do not occur.

What’s under the ocean?

Geology doesn’t end at the coast. In fact the rocks of the Newcastle Coal Measures extend out under the sea up to 50 km off Newcastle! Coal mining has taken place out to sea from onshore operations, including at Burwood Colliery. The continental shelf at Newcastle is about 50 km wide with water depth mostly less than 200 m. The continental shelf is cut by canyons where rivers like the Hunter River cut across them. Parts of the shelf would have been exposed during glacial periods – when sea level was much lower than present levels. The narrowness of the continental shelf is one of the reasons whales are commonly seen along our coastline on their annual migration.

Records of climate change

The rocks of the Newcastle area tell us about past climates and landscapes. During the Late Carboniferous and early Permian, Newcastle was much closer to the south pole, and the climate was very cold. Evidence of glaciation includes the varved shales (e.g. at Seaham) that formed from seasonal melting, tillites and dropstones (e.g. near Raymond Terrace) and striations where rocks carried in glaciers carved grooves into bedrock (e.g. near Tocal).

In the last interglacial, about 120 000 years ago in the Pleistocene, the sea level was about 2–5 m higher than it is now. Bivalve fossils near Largs represent a raised beach, and shallow marine, estuary-like conditions covered much of the lower Hunter Valley. Since then, sea level has fluctuated. Around 20 000 years ago, during the last glacial maximum, the sea level was >100 m lower than today. The beach would have been about 25 km to the east. The sea level has been at present levels for ~6500 years. The flat-lying rock platforms along the coastline probably formed during this period.

Dykes

Dykes are subvertical intrusions of molten rock. Basalt or dolerite dykes occur through the Newcastle Coal Measures. They usually intrude along pre-existing weaknesses such as joints in the rock. The dykes are about 90 million years old (Late Cretaceous) – approximately 160 million years younger than the Newcastle Coal Measures they intrude! The dykes were probably intruded during stretching of the Earth’s crust prior to rifting and seafloor spreading that created the Tasman Sea. Joints opened up allowing molten basalt to squirt up into the crust, where it cooled.

Excellent examples occur at Nobbys , on the northern side of the Cowrie Hole , and in the cliff section at Newcastle South. The dyke at Newcastle South is a teschenite comprising plagioclase, analcime and augite minerals.

Fossilised forests, weathering and concretions

The rock platforms along the Newcastle coast are full of geological surprises! Petrified tree remains including stumps, trunks and branches of Glossopteris flora occur near the Cowrie Hole , Dudley, and Swansea. Some were flattened by a volcanic eruption, others were drowned and buried. The wood of these plants was like that of modern Hoop and Norfolk pines.

Honeycomb weathering of sandstone occurs when salt crystallises in the pore-space of rock, causing the mineral grains to separate. Sand is then swirled around causing erosion and creating the honeycomb effect. Tessalated pavement occurs by weathering along joints. Red–brown concretions are common where colloidal limonite (hydrated iron oxide, rust) has accumulated along weaknesses in the rock such as bedding planes or joints, or around pebbles or fossils. The concretions are prominent as they resist weathering. Other sedimentary features include scour and fill, meandering stream channels and limonite boxworks.

Earthquakes

The Lower Hunter Valley has a long history of earthquakes. Since European settlement earthquakes have been recorded frequently in the Newcastle area. The first recorded earthquake in Newcastle was in 1837. In recent times, Newcastle was shaken by an earthquake of magnitude 5.6 on the Richter scale on 28 December 1989.

The focus of the earthquake was under Boolaroo, approximately 15 km southeast of Newcastle, at a depth of 10 to 12 km.

Although damage was widespread, the greatest damage occurred in the inner parts of Newcastle built on reclaimed floodplains of the Hunter River, particularly where older buildings were concentrated.

Further reading

England B. 1982. The Hunter Valley, N.S.W. Gemcraft Publications, Victoria.

Hunter C. 1991. The earth was raised up in waves like the sea. Earthquake tremors felt in the Hunter Valley since white settlement. Hunter House Publications, Newcastle.

Kerr R. 2000. The Bathers Way Geology and Landscape. Report to Newcastle Tourism/City Strategy, Newcastle City Council. NCC library reference Q559.442/KERR.

Geological timescale

PeriodAge*(Ma) Geological feature

Quaternary 2.6 Development of Hunter River floodplain

Neogene 23

Paleogene 66

Cretaceous 145

Jurassic 201

Triassic 252

late Permian Newcastle Coal Measures: terrestrial fossils

early Permian 299Maitland Group: shallow marine fossilsDalwood Group: shallow marine fossils

Carboniferous 359 Volcanism and glacial activity

* Age at beginning of period

Acknowledgements

Compiled by Phil Gilmore (Geological Survey of New South Wales, NSW Trade & Investment) in 2014.

Special thanks to Brian England and Roslyn Kerr for review, and to Robin Offler, Ron Evans, Ron Boyd, Peter Roy, John Whitehouse, Scott Bryant and Geoscience Australia for geological input. Graphic design by Carson Cox. Cartography by Kate Holdsworth. Photography by Phil Gilmore and Brian England. Editing by Simone Meakin.

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