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Tongarra coal seam at Austinmer Beach

 The Sea Cliff Bridge
Basalt dyke about 40cm wide
The Tongarra Seam exposed in northern headland of Austinmer Beach
Close up of the Tongarra Seam at Austinmer Beach

Illawarra Coal Measures

Latitude -34.223817 Longitude 150.996652

Located in the Illawarra Region of NSW, nearest town Wollongong

Source:: Field Geology of New South Wales

Link to Detailed Map

The Illawarra Coal Measures are a group of sedimentary rocks which include: shale, quartz-lithic sandstone, conglomerate, chert, sporadically carbonaceous mudstone, coal and torbanite seams formed in the late Permian 253-263mya. They are part of the Sydney Basin which is a part of the much larger Sydney-Gunnedah-Bowen Basin that extends from coastal southern NSW to central Queensland. The coal measures have been an important economic resource in the development of NSW. Their proximity to the coast at Port Kembla has been an important factor supporting the export of coal and the import of iron ore.

In 1839, the respected geologist Reverend William Branwhite Clarke explored the Illawarra coal seams as part of his geological survey of the colony. This exploration was crucial to the subsequent development of coal mining in the Illawarra region as it demonstrated the available coal reserves, thus paving the way for such reserves to be extracted.

In the Illawarra there have been more than 60 known sites of coal mining since the mid-nineteenth century, several of which are still producing today. Coal mining in the Illawarra began in 1848 at Mount Keira and the first coal export from the Illawarra left Wollongong harbour in 1849, destined for the Sydney market.

To get a good overview of the Wollongong Coal Measures start at the Lawrence Hargrave Lookout at Bald Hill. You can access this via Lawrence Hargrave Drive which leads off the Southern Freeway (take the Stanwell Park turnoff) or from Lady Wakehurst Drive which leads from the Royal National Park. On most occasions you will also see the spectacle of hang-gliders spiralling through the thermal updrafts. As you travel down Lawrence Hargrave Drive there are plenty of opportunities to stop for coffee, a snack or lunch at one of the cafes. As well, you can drive the 660 metres of the unique Sea Cliff Bridge, one of the few ocean bridges in the world and you can park the car and take a stroll on the bridge's pedestrian walkway.

View looking south from Lawrence Hargrave Lookout

You can identify the various landforms from the photo above. Note the ancient landside where the railway cutting is marked on the photo. Descend Lawrence Hargrave Drive to the south and you will pass The Illawarra Coke Company, which mines the Bulli Seam, at Coalcliff. It has a large washery for cleaning the coal after extraction. Waste from the washery has formed a large dump (now grassed).

The Sea Cliff Bridge blocks views and access to the unstable cliff at Coalcliff and you can no longer see as much of the Illawarra Coal Measures there. One of the seams outcropping here, the Bulli Seam produces the best coking coal in New South Wales and is worked to the north at Helensburg, to the west at Appin and to the south at Mount Kembla.

The coal was discovered in this vicinity in 1796 by a shipwrecked sailor, William Clarke, whose ship the "Sydney Cove" was wrecked at Preservation Island in Tasmania. A rescue party of 17 men set off to travel the 740 kilometres to Port Jackson but bad luck pursued the survivors and their longboat was wrecked near Point Hicks in Victoria and they had to continue on foot. Only 3 of the rescue party made it back to Sydney and Clarke reported coal in the cliffs at Coalcliff - the second discovery of coal in Australia (The first coal discovery was made just south of the present Newcastle in 1791 by a party of escaping convicts, led by William and Mary Bryant). Soon after, George Bass offered to search for the coal outcrop and, with two of the survivors, he left Port Jackson on 5 August 1797 in Governor Hunter's whale-boat. He was back in eight days with specimens of the coal and a report of its abundance around Coalcliff. The lack of a suitable harbour prevented mining for many years.

The importance of geology in infrastructure construction is demonstrated by the cliffs at Coalcliff. The old cliff hugging road was built on relatively soft Wombarra Claystone, which readily erodes away from under the Scarborough Sandstone and in the past created huge problems with rock falls. The Sea Cliff Bridge was built to solve this problem. When construction began, the RTA estimated a 1 in 50 chance of a fatality due to a rock fall. At completion of the bridge the chance of a fatality from a rock fall had been reduced to 1 in 1,000,000.

Continue south along Lawrence Hargrave Drive. At Wombarra turn off to the ocean pool. Here at the top of the headland there is a coal seam outcropping. Also note the undercutting of the cliff face at the level of the rock platform.

Note the coal seam in the cliff at Wombarra Pool. The eroded zone at the base of the cliff is Wombarra Claystone

Look across the platform - north to south to see a basalt dyke about 40cm wide crossing the entire width of the platform.

Back at Lawrence Hargrave Drive note the recent landslide of the Hawkesbury Sandstone at the top of the escarpment.

Landslide of the Hawkesbury Sandstone

Large blocks of Hawkesbury Sandstone occur near Coledale, these fell and rolled from the cliff faces to the west many years (probably hundreds of years) ago. At Coledale there was heavy flooding and destruction of houses by a large mudslide in 1988.

At Austinmer, stop at the parking lot next to the beach. Walk to the northern headland where the banded Tongarra seam is exposed. It can be traced north around Bells Point. There are white clay bands present, and below the seam there is evidence of an "underclay", a possible soil horizon, often called a "seat earth". Plant fossils occur in many of the beds. The Tongarra Seam is overlain by the Austinmer Sandstone Member.

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