Road World Championship: Wollongong 2022, Australia

Hello, and welcome back to GeoTdF.org! On this site, we will give you a brief overview of the beautiful geology, and more, along the UCI World Championships parcours of Wollongong 2022!

Along the parcours, we have indicated 8 points that you can see during the race, of which we provide you with some background information, so check it out!

View of the Illawara coast, from Stanwell Tops

Before we dive into geology, we first acknowledge the Dharawal people, the Traditional Owners and Custodians of Country throughout Australia and their connections to land, sea and community. The land on which the UCI Wollongong is taking place is that of the Dharawal people. We recognise and respect their cultural heritage and beliefs and we pay our respect to their Elders, past present and future, and extend that respect to all Aboriginal and Torres Strait Islander peoples today.

The Dharawal people lived in the coastal areas of the greater Sydney region. The Bass Point campsites (Shellharbour area) may be the oldest dated coastal campsite in New South Wales with occupation going back 17,000 years.

The name Wollongong is said to originate from the Aboriginal word Wollonyuh or Wollonga, which means sound of the sea or hard ground near water.  The UCI Wollongong is taking place within the Illawarra region, named after the aboriginal words Elourera or Allowrie, meaning high place near the sea.

In the Illawarra region, signs of Aboriginal occupation and activity can be found in rock platforms and rock shelters, which were used as tool making, cooking, and camping places. The abrasive qualities of sandstone, the rock that makes up the scenic cliffs and rugged coastline along the race, were excellent for sharpening tools. There are numerous so-called ‘middens’: ​​accumulations of shell produced by Aboriginal people collecting, cooking and eating freshwater shellfish, as well as quarry sites in the region, and stone arrangements and engravings.

Helensburg elite start: Permian and Triassic sandstones, coal deposits, and mass extinction

The elite riders will start their race riding along the Illawara coast that consists of cliffs and embayments. One of the first cliffs carries the name ‘Coal Cliff’, which already tells you what you’re going to find there. These coal deposits formed from lush vegetation where by the amount of plant remains that fell in shallow water was so high that all oxygen needed for decay was used up. As a result, first peat formed, which became compressed further when the deposits were buried below thick piles of sand, and eventually coal formed.

The coals here formed in Permian to Triassic times, between about 300 and 210 million years ago. Australia then formed the northeastern part of the continental landmass that made up southern Pangea: Gondwanaland, which had existed as a giant continent since late Precambrian times, about 550 million years ago, and which included Australia, Antarctica, India, Arabia, Africa, and South America, and smaller continental fragments that now make up parts of Indonesia, Tibet, Afghanistan Iran, Turkey, Greece, the Balkan, and Italy. Australia was located at more temperate latitudes, closer towards the south pole.

The coal deposits are part of the Sidney Basin: a vast area occupied by rivers, lakes, swamps, and shallow seas, in which large amounts of sand were deposited. The sand was derived from a large mountain belt that at the time was forming along the eastern margin of Australia. For much of the last hundreds of millions of years, large oceanic plates from the Pacific ocean have been subducting below the surrounding continents. Today, that subduction zone, and the associated volcanoes that make the famous Pacific Ring of Fire, is located offshore, from New Zealand to the islands of Tonga and Fiji. But in Permian and Triassic times, the subduction zone was located along the Australian continental edge, from Tasmania to Cape York, and made mountains and volcanoes that were glaciated. Meltwater produced rivers that dumped sediments in the Sidney Basin. There are sedimentary rocks near Kiama, about 25 km to the south of Wollongong, that contain traces of permafrost, and if you want to get an idea what the mountain belt looked like, tectonically, geographically, and climatically, you’d have to imagine something like western Canada and Alaska today.

The coal swamps were dominated by trees known as ‘Glossopteris’: middle- to high-latitude lowland vegetation characteristic of Gondwanaland. In the coals, you can still beautifully see the plant remains, of 300 million years ago! They are visible at Bulli (location 4), at Sea Cliff Bridge (location 2), and at Austinmer Beach (location 3).

The Permian-Triassic extinction horizon at Sea Cliff Bridge

Perhaps the most surprising part about the Glossopteris coals is that they formed in the Permian as well as in the Triassic. The divide between the two was the Permian-Triassic Boundary Mass Extinction, 251.9 million years ago. This extinction is the worst in Earth History, and is also known as the Great Dying. 95% of marine species, and 70% of land species disappeared, probably because of extreme climate change due to massive volcanism in Siberia. But surprisingly, the land plants of the eastern Gondwana escaped extinction, and lived happily ever after. Or well into the Triassic anyway is Earth’s most severe extinction event. It formed the boundary between the Permian and Triassic geologic periods around 252 million years ago. 

The Permian-Triassic extinction is in the rock record preserved as a simple layer. Below that horizon, abundant fossils are present that never returned in the layers above, an impressive sight. This layer is exposed under Sea Cliff Bridge (Locatoin 2), where the top of Bulli Coal Measures is capped by a distinct layer that marks the extinction event (Fig. 6). Above this layer, the Nepean and Hawkesbury sandstones crop out.

Mount Keira and Mount Kembla

The Mount Keira Loop goes through Mount Keira (location 6) and Mount Kembla (location 7), which form the hilly area west of Wollongong.  Mt Keira is believed to come from the Dharawal word Djeera, meaning wild turkey, and is known as the women's mountain, a teaching place. Mt Kembla, on the other hand, is believed to come from the word "Jum-bulla" or "Djenbella" meaning a place to hunt wallabies (medium-sized marsupials), and is considered Dharawal men's mountain. Mt Kembla and Mt Keira are considered to be sisters.

The  Mount Keira Loop starts from the coastal area in Wollongong and ascends topographically to the west, towards Mt Keira and Mt Kembla. The coastal region near Wollongong consists of geologically recent sand and river deposits. Along Gipps Road and Mt Keira Road, the route then goes through the Permian sedimentary and volcanic rocks, as well as the Illawarra coal measures that we’ve seen along the Illawara coast route.  But as the road starts climbing towards Mt Keira, the geology transitions to younger, Triassic (about 240 million years ago), sedimentary rocks that includes the famous Hawkesbury Sandstone.  This sandstone has been extensively used as building material, for instance to build Sidney, and preserves many Aboriginal rock carvings and drawings. The durable sandstone layer formes the cap rock of the softer underlying sediments and generated the prominent Illawarra escarpment, to which Mt Keira and Mt Kembla belong.

Geologic history of the Illawarra escarpment and the Hawkesbury Sandstone

The Illawarra Escarpment marks a spectacular change in elevation in the coastal sea cliffs. From north to south it rises from 300 metres to 700 m and can be followed for 120 km parallel to the coast. The Illawara escarpment is easy to spot, forming straight, wall-like cliffs west of Wollongong. Because the escarpment is so straight, geologists first thought that the escarpment was a large fault that would have uplifted the mountainous area west of Wollongong. and subsided the coastal lowland, where Wollongong is located. But when they started to map the region in detail, they found no evidence of a large fault. Instead, the escarpment is the product of erosion, combined with landsliding, for a long period of time, at least 25-30 million years. 

The Hawkesbury sandstone is hard and difficult to erode, whereas the overlying and underlying sedimentary rocks are softer and wash away easier. So once rain and rivers eroded overlying rocks lays the Hawkesbury sandstone bear, it takes a long time before that sandstone is eroded away. But as soon as there is a hole through that sandstone, the underlying strata are eroded easily. This is the recipe to form steep cliffs: at the eastern edge, just west of Wollongong, the Hawkesbury Sandstone has been eroded and the topography that the riders have to climb has been developed. There underlying soft sediments are carved away below the durable sandstone layer, and the Hawkesbury Sandstone breaks along a fractures, and large blocks collapse that you’ll find scattered on the slopes of Mt Keira and Mt. Kembla.

The Hawkesbury Sandstone had a famous name giver: In 1844, Charles Darwin named the sandstone after the Hawkesbury River, where it is most common. The Hawkesbury Sandstone originated as floodplain deposits of a huge, braided river system in the Middle Triassic (approximately 240 million years ago). The Hawkesbury Sandstone is yellowish brown in colour, and consists primarily of quartz, clay minerals, and siderite (iron carbonate). The Hawkesbury Sandstone was used a building material for many of the great, classic buildings of Sydney, such as St Mary’s Cathedral, Sydney Town Hall, the Martin Place General Post Office, the Art Gallery of New South Wales, and the early parts of the University of Sydney. In the early days, the sandstone was primarily extracted from quarries located in what is now Sydney Central Bisiness District, and specifically from Pyrmont and Ultimo areas. Paradise, Hell Hole, and Purgatory are some of the larger mines that provided building stones.  It is estimated that between the 1860s and 1930s more than half a million cubic yards may have been extracted by Pyrmont and Ultimo areas.

Wollongong City Circuit: Flagstaff Point: Icebergs and dropstones

The Wollongong City Circuit passes along Flagstaff Point, a small peninsula north of the Wollongong City Beach, home to the Wollongong Lighthouse. The Lighthouse is built on top of the Permian sandstones that we find along much of the coast. Where Australia’s east coast has a subtropical climate today, geological features in the sandstone show that the sediments were deposited at near-freezing temperatures (< 4˚C). This is no wonder: the sandstones were deposited when Gondwanaland that was organized around the South Pole and that contained an icecap. Indications for the cold environment are the occurrence of a rare mineral called glendonite (for the mineral freaks among you: that is a stellar pseudomorph of calcite after ikatite), and the presence of large glacial ‘dropstones’ within the sandstone.  Dropstones are funny rocks: they are isolated fragments of rock that are entirely foreign to the marine rocks they are part of. Like a big block of granite that suddenly ends up in the middle of sediments of a sea floor, as if they were dropped there from a ship. The ship in question was…an iceberg. When glaciers move over rock surfaces, they incorporate blocks and debris in the ice. Icebergs that break off the glaciers as they enter the sea thus contain rocks, and when they melt, the blocks sink to the sea floor. Add to that 260 million years of plate tectonic motions, and the drop stones are now located at the subtropical beaches of Wollongong.

The sandstones at Flagstaff Point were deposited on top of beautiful lavas known as the Bumbo Latites, which are bestexposed at the Bombo headland and quarry, about 25 km south of Wollongong. The Bumbo Latite formed 265 million years ago (late Permian), and is characterised by hexagonal columns with large crystals of plagioclase, pyroxene and iron-titanium oxide in a groundmass of plagioclase, pyroxene, iron-titanium oxide, olivine, K-feldspar and traces of apatite. The Bumbo Latite lavas flowed into a shallow, circum-polar sea environment.

Natural hazards on Australia’s East Coast

We already mentioned that the Illawara Escarpment is prone to landsliding. Earlier this year, exceptionally high amounts of rain and floodwater have mobilised landslides which cut off communities and caused major damage to infrastructure around the Illawarra and the coast south of Sydney. Mount Keira, was once again scarred with a landslide on the southern side of the 463-metre-tall mountain.

But landsliding also occurs below sea level, and even though that will not directly destroy buildings down-slope, they come with the major risk of tsunamis. And because 85% of Australia’s population lives within 50 km of the coast, Australian geoscientists intensively study where such submarine landslides occurred in the past. 

Submarine landslides are underwater landslides, often triggered by earthquakes, where seafloor sediments or rocks move down a slope towards the deep seafloor, a process known as mass wasting. Moving such large quantities of rock, they also move large quantities of water, and this can generate tsunamis, like in Sulawesi, Indonesia, in 2018.  However, because these features are offshore and under water, we do not have a detailed image of them. A team of researchers sailed on Australia’s research vessel Southern Surveyor in 2013. Using the ship’s multibeam sonar they mapped the ocean floor in unprecedented detail and found huge scars along the coast offshore Wollongong, Sydney, Byron Bay and Sydney. These features are locations where sediment along the shelf has collapsed and formed submarine landslides up to several tens of kilometres across. Models of tsunamis generated

by submarine landslides suggest that these potentially represent a future tsunami risk for Australia’s east coast. Further research is needed to understand past and potential future slides and their tsunami-generating potential.

Geoscience in Australia

Australia hosts some of the best Geoscience departments in the world. If you consider studying geology or related fields in Australia, check out some of these departments!

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I am a Senior Lecturer in Geology, in the School of Geosciences at the University of Sydney. My research activities primarily focus on developing a better understanding of the structure, deformation and rheology of the Earth’s lithosphere, as well as on improving our knowledge of the subsurface in urban areas (Urban Geology). My research finds applications in mapping deep mineral systems, assessing seismic risk, and urban planning. Read more about Vasileios Chatzaras.

Vasileios Chatzaras

I am a lecturer at the University of Queensland. My research evolves around tectonics and the evolution of Earth's lithosphere at various spatio-temporal scales. I apply a combination of field-based methods with laboratory analyses (geochronology, paleomagnetism) to reconstruct subduction, accretion and exhumation. Read more about Derya Guerer.

Derya Guerer

I am a geologist at the University of Utrecht, The Netherlands, and I study plate tectonics and the driving mechanisms in the Earth’s mantle, mountain building processes, and the geography of the geological past. I enjoy geological fieldworks all over the world, and translating the results to science and to a broad public. Check out Douwe van Hinsbergen and the others of the team.

Douwe van Hinsbergen