Download Geology of the Newcastle Coastline

Aboriginal tools
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.
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. 1
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.
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 3 . 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.
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. 2
Pumice
Pumice fragments are often found on the beaches of eastern
Australia 4 . 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 5 . Local
resources have been used for construction such as the
Waratah Sandstone, clay in the Thornton area for brickmaking, quartz-rich sand for construction and glass making,
and titanium-bearing minerals from Stockton Bight 6 .
Carboniferous volcanic rocks (e.g. near Karuah, Paterson and
Seaham) are quarried for use as aggregate, including as road
and railroad ballast.
Geological timescale
Period
Age*
(Ma) Geological feature
Quaternary
2.6
Neogene
23
Paleogene
66
Cretaceous
145
Jurassic
201
Triassic
252
late Permian
Development of Hunter River floodplain
Newcastle Coal Measures: terrestrial fossils
early Permian
299
Maitland Group: shallow marine fossils
Dalwood 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.
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. 7
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! 8 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 9 , on the northern side
of the Cowrie Hole 10 , and in the cliff section at Newcastle
South. 11 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 12 , 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.
GEOLOGY OF THE
NEWCASTLE COASTLINE
NEW SOUTH WALES
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. 13
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.
www.resourcesandenergy.nsw.gov.au
Sheperds
Hill Fort
Murdering Gully
Merewether
Surf Club
Hickson Street
70
Dixon Park
Surf Club
60
Bar Beach
Surf Club
Anne Feneley
Lookout
Newcastle
Surf Club
Fort Scratchley/Signal Hill
The Cliff
50
(Metres)
Strezlecki
Lookout
Tuff
Nobbys
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30
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Horizontal scale
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Image © Land and Property Information 2014
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