Posted by barbara on October 12, 2011
South of Narooma the outcropping rocks are a pronounced orange colour
Anyone familiar with the NSW coastline between Newcastle and Nowra can picture the typical headland and rock platform coastal landforms carved out of layers of sedimentary sandstone.
In contrast, a string of South Coast beaches south of Narooma feature another type of sedimentary rock in the form of brightly coloured cherts. Like sandstone, cherts are predominantly composed of quartz in the form of silicon dioxide. Unlike sandstones, the sediments that accumulated to form cherts are more likely to have been countless fossils of micro organisms.
Following the accumulation of such sediments in an ancient sea or lake, in a secondary process, these beds were later impregnated with silica during the solidification process.
So where do the sedimentary chert's intense colours come from? The answer lies in trace elements in the sediments around the time of compaction (including oxides of limonite or hematite).
The 'unnatural' red colours of exposed cliffs on the southern 'fold' of Twofold Bay
The aqua seas of the Sapphire Coast of southern NSW meet the rouge rocks of Twofold Bay
Last updated 4 April 2017.