Long Reef - a photo on Flickriver

Long Reef

It's best to photograph this interesting area late or early in the day, when the colours fully come out. Remember to go at low tide.

Long Reef is unique in the Sydney region, as this headland is primarily made of Bald Hill Claystone. Mostly, it's a soft reddish rock, formed in the early Triassic period. The maximum thickness of this rock type is 20 metres.

An interesting variety of sedimentary rocks may be viewed at Long Reef. There's much iron influence here, most evident in the haematite. Much of the rocks here are of the Narrabeen Group of Sedimentary Rocks. There's also volcanic elements, such as a dyke of Jurassic dolerite. It was two metres tall, but it's since been partially removed for industry.

An abandoned copper mine is at Long Reef. A tunnel was dug into the purple claystone to explore for copper. It was situated along the claystone, between the red-brown oxidised rocks and grey-green reduced siltstone.

There are masses of fossils in the grey coloured claystone, however, they are mostly strands of vegetation and are not particularly impressive.

The commonest of the fossils being a primitive plant, known as the horsetail, "Phyllotheca". It's in the form of a stem with a whorl of leaves. These plants grew like reeds, which indicates they were swamp dwellers.

Less often, fossils of a shrub-like forked leaf "seed fern" (Dicroidium) may be seen. One more interesting fossil is of a large amphibian. The animal would have been around a metre long. Named "Bulgosuchus gargantua."

The commonest rock types are shales, sandstone and claystones. The sandstones are described as "lithic" meaning they have plenty of other rock fragments within.

The sands of the nearby beaches are orange in colour. Black coloured influences in the sand may be seen along the nearby beaches. Prominent of these dark minerals is rutile. Others include ilmenite and monazite. Geologists suggest these are derived from ancient rocks from the Broken Hill region.

Ages ago, I first visited this area in a school excursion. The school teacher was impressive intellectually. However, he mis-read the tide listings. And we went at high tide. He also said that so many of the fossils have been removed that there's hardly any left. This latter remark is barely true, as the rock keeps crumbling away and more fossils are revealed.

Taken in: Australia / New South Wales / Sydney / Long Reef (show map)

Taken on: September 12, 2011

Tags:

Long Reef

triassic

NSW

narabeen group of sedimentary rocks

Bald Hill Claystone

sydney basin « less

Groups appears in: • Australian Images • Australian Natural more » • Flickr Australia « less

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