Monday, 19 January 2009

Sydney Sandstone Tour: The coda and a geology lesson

Dark Beach, Murramarang National Park.

This beach, about 275 kilometres south of Sydney, and near where we go for our summer holidays, is significant for its geology.

It is here that the lip of the sandstone Sydney Basin reaches the surface at its southern most end.

The strata of the Sydney Basin, seen at the northen end of the beach, were laid down in the Permian (300-250 million years ago) and Triassic (250 - 205 million years ago) eras. They formed a saucer shape and lay in shallow water. They were lifted up out of the sea bed midway through the Triassic.The sandstone at this beach is the oldest part of the Sydney Basin, where the base rocks curve up and emerge. This is exposed in the magnificent cliff at the northern edge of the beach. To get to the sandy beach you have to climb over the sharp dark rock formation, which we didn't do.

On the southern end of the beach are rocks of the much older Wagonga formation (Ordovician - 500 to 450 million years ago). This junction is known as an Unconformity, where adjoining rocks are separated in age by 200 million years.

The beach derives its name from the dark pebbles on the southern end of the beach.

For the rest of my Sydney Sandstone Tour photos click here.

For more pictures of this beach and its rocks and vegetation, click here.


  1. Terrific post. Interesting and great pictures. Thanks.

  2. I did not know all that, Sally. I thought the Sydney basin ended somewhere relatively closer to Wollongong, like about the St Georges Basin. Good to know better. Fascinating photographs ...

  3. My other half was actually a geologist before he got the art bug, so I get all this about the island. Really well put together and gorgeous images.