Download Geology of the Newcastle coastline, New South Wales

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.
Around 255 million years ago the climate and
landscape around Newcastle were very different to
today. Large rivers flowed across the land, with
sand, silt and mud transported and deposited in
extensive floodplain systems. The sediments were
later compacted to form the sandstone, siltstone
and mudstone we see along the rock platforms and
cliffs today. Large forests included the fern-like
Glossopteris and Dadoxylon trees. Fossilised plant
remains are common along the rock platforms.
Some plants rotted in swamps and with time were
buried and compacted to form the coal seams of the
Newcastle Coal Measures. Insects lived in the forests
– fossilised insects and trees have been found
together near Belmont. From time to time, huge
volcanic eruptions covered the land in ash that
formed tuff horizons throughout the coal measures.
The eruptions were so violent that huge swathes of
forest were knocked over by some blasts. Rocks
were gently folded by tectonic processes to produce
the undulating surfaces we see in cross-section. As
the Tasman Sea opened up around 90 million years
ago, hot magma from the mantle was injected into
the coal measures – these dykes are seen along
the coastline.
This map and brochure explains some of the
features that make up our beautiful coastline.
Aboriginal tools
Coal
Building a city
Linking Newcastle to Gondwana
The rocks of the Newcastle Coal Measures were mined long
before European settlement.
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.
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 3 . 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 4 .
Carboniferous volcanic rocks (e.g. near Karuah, Paterson and
Seaham) are quarried for use as aggregate, including as road
and railroad ballast.
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 Ocean Baths 5 ) and near the
Bogey Hole 6 . 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 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 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 150.5 million tonnes shipped in 2013. The coal
monument in Parnell Place was dedicated in 1910 as a tribute
to coal exports 2 .
Geological timescale
Period
Age*
(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
299
Maitland Group: shallow marine fossils
Dalwood Group: shallow marine fossils
Carboniferous
359
Volcanism and glacial activity
* Age at beginning of period. Ma = millions of years.
Acknowledgements
Looking south at the Nobbys Tuff, King Edward Park.
The Victoria Tunnel Seam at Little Redhead Point.
Waratah Sandstone used for construction of Macquarie Pier, Nobbys Beach.
Glossopteris leaf fossils.
Compiled by Phil Gilmore (Geological Survey of New South
Wales, NSW Department of Industry) in 2014, updated 2015.
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, Brian
England and Roslyn Kerr. Editing by Simone Meakin and
Geneve Cox.
Cover photograph: the Bogey Hole.
This Inspiring Australia initiative is supported by the
Australian Government as part of National Science Week.
Looking north at Shepherds Hill and Susan Gilmore Beach.
Our ever-changing coastline
What’s under the ocean?
Records of climate change
Dykes
Fossilised forests, weathering and concretions
Earthquakes
Our coastline is constantly changing! Some of these changes
are man-made. For example, Nobbys Beach has only formed
since Macquarie Pier joining Nobbys Head to the mainland
was completed in 1846 7 .
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.
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 shale (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).
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.
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. Their
wood was like that of modern Hoop and Norfolk pines.
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, the city was shaken
by an earthquake of magnitude 5.6 on the Richter scale on
28 December 1989.
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. Tessellated
pavement occurs by weathering along joints. Red–brown
concretions are common where colloidal limonite (hydrated
iron oxide, rust), probably originally siderite, 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 structures, meandering channel
deposits and limonite boxworks.
The focus of the earthquake was under Boolaroo, approximately
15 km southwest of Newcastle, at a depth of 10 to 12 km.
Humpback whale breaching off Newcastle.
Top: Varved shale at Seaham. Bottom: Glacial deposits near Seaham.
Late Cretaceous dyke at the Cowrie Hole.
Top: Tessellated pavement. Bottom: Honeycomb weathering.
NEW SOUTH WALES
Please note
The following suburbs of Greater Newcastle are mentioned in
the text but not identified on the maps: Belmont, Boolaroo,
Broadmeadow, Charlestown, Dudley, Hamilton, Lambton
and Wallsend.
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.
L
EASE
TA
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Top: The Pasha Bulka on Nobbys Beach, 2007.
Bottom: Pumice deposits at the Cowrie Hole.
Excellent examples occur at Nobbys 9 , north of the Cowrie
Hole 10 , and in the cliff section at the southern end of
Newcastle Beach 11 . The dyke at Newcastle Beach is teschenite
comprising plagioclase, analcime and augite minerals.
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
N
Pumice fragments are common on the beaches of eastern
Australia 8 . This very light rock formed from glass and
crystals in frothy lava explosively erupted from volcanoes.
In July 2012 a raft of pumice was found floating over the
Kermadec Trench between New Zealand and Fiji. This
pumice erupted from an underwater volcano (or seamount).
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. Shell 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 but the rock platforms along
the coastline probably formed at slightly higher sea levels.
GEOLOGY OF THE
NEWCASTLE COASTLINE
P
Other changes are natural. The sand on our beaches is
constantly shifting, with single storm events 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 prevent rock falls.
KE O
www.resourcesandenergy.nsw.gov.au
Cross-section (shown on map with red line)
Shepherds
Hill Fort
Murdering Gully
Merewether
Surf Club
Hickson Street
70
Dixon Park
Surf Club
60
(metres)
Anne Feneley
Lookout
Newcastle
Surf Club
Fort Scratchley/Signal Hill
The Cliff
50
Tuff
Newcastle Coal Measures
30
A
10
B
Nobbys
Head
Tuff
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Nobbys
Surf Club
Nobbys
Nobbys
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Sea level
Strzelecki
Lookout
Cooks Hill
Surf Club
End of breakwater
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1 cm = 130 m
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1 cm = 20 m
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Newcastle
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Surf Club
Merewether
Surf Club
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Surf Club
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King Edward
Park
Susan Gilmore
Beach
Merewether
Ocean Baths
D
6
Newcastle
Surf Club
Cowrie Hole
Newcastle
Ocean Baths
Bogey Hole
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Nobbys
Surf Club
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Macquarie
Pier
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Nobbys
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Image © Land and Property Information 2015
Dudley
Tuff
bys
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Nobbys Seam
Seam
Bar Beach formation
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d l e
D u
D u d l ey S e am
Bogey Hole formation
m
S e a
B o gey Ho
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f o r ma t i o n
Paterson
Tocal
Seaham
Karuah
Largs
Victoria
Tunnel Seam
Maitland
Dudley
Seam
(upper)
Nobbys
Thornton
Raymond
Terrace
Legend
Tu f f
Roads
Newcastle
Quaternary
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fau
Nobbys
Tu f f
Victoria
Tunnel Seam
E
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Nobbys Seam
Victoria Tunnel Seam
Nobbys Tuff
Nobbys Seam
D
Merewether
Conglomerate
k
Victoria Tunnel Seam
C
Merewether Conglomerate
y
B
Merewether
Conglomerate
d
A
Triassic
late Permian
Swansea
0
10
20 km
early Permian
Carboniferous