Monday, 19 January 2009

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.

Below: Looking south

Below: Looking north towards the sandstone cliff and beach

Below: Layers of sandstone at the northern end.

Below: The sandstone cliff and white sandy beach

Below: G'day!

Below: Conglomerates at the southern end of the beach

Below: Pebble beaches are great for rock throwing Below: The southern end

Below: Walking south

Below: trees on the headland above the beach

Photos taken 11 January 2009

1 comment:

Helen said...

Hi Sally, It's a while since I've visited your blogs, as it's been pretty busy around here over the past month or so. I can't help thinking how lucky your son is to have such an informed mother to pass on her amazing knowledge and love of everything to him. I hope he appreciates you. It makes me feel quite inadequate. In the meantime, I'll keep looking and learning from you as well - thank you!!

The channel at Moruya

The exit from the Moruya River to the sea