Members of the Nature Coast Marine Group and some Durras locals met at Wasp Head car park recently to learn more about the geology of the Durras area. We moved to the beach where Paul May, using the damp sand as a blackboard, spoke about the formation of the Sydney Basin. The Sydney Basin, which has Sydney above the deepest part, and which extends to the Newcastle area, is an average of 100 kilometres wide and extends offshore to the edge of the continental shelf.

The southern end of the Basin is here at South Durras and we followed the shoreline to the extremity of the Basin, viewing mostly sedimentary rock which was created over a period of about 50 million years. During this time coal was also laid down.

In the Sydney Basin are three major cities. As Newcastle and Wollongong are situated above the sides of the basin, the coal beneath their environs is accessible, but the coal around Sydney, being at the deepest part of the basin, is inaccessible.

With this and more background, we commenced the exciting part of the day following the beaches south and marvelling at the beauty of the weathering of the rocks. We noted the very long lines of jointing or splitting of the rocks from east to west, and less often, shorter splitting or fractures running north-south. Where pressure was released from above for some reason, causing expansion of the sandstone and cracking to the surface, some wonderful geometrical patterns were found. Everyone enjoyed the contrasting rich red colours where sandstone had been stained by iron salts, the honey comb weathering, and the wave patterns left from so long ago.

As we walked and tried to absorb all the above, and why a drop stone was angular or smooth, and how the conglomerates came to be there, Jenny Edwards helped the younger members of the party to identify shell and marine animals at the waters edge.

 

 

The views above Myrtle Beach were spectacular as we looked north but it was on to look at the spot which is the very southern end of the basin. Here at Myrtle Beach is where the sedimentary rock of the basin ends and the formation known as Wagonga shale begins.

The photo shows Paul showing us the sedimentary rock above his hand and the Wagonga shale below.

Thank you Paul, and thanks also to John Perkins, for a very informative and interesting day. On these walks there are always many people sharing their knowledge of the marine life, the bird life, the botany of the foreshore plants and in this case, the geology of the area and that’s what makes the walks, along with the socializing, very worthwhile.