This post is for Rosemary whose research skills and interest turned a vague intention into something concrete.
Today we are not visiting a beach: we are visiting the Narooma Accretionary Complex, although it is also called Narooma Beach, or Glasshouse Rocks Beach, depending on who you ask.
The need to know more about the geology of my beaches has been simmering away for a while. Yesterday things began to come together. When, on advice from my research mentor, Rosemary, I googled “Eurobodalla geology”, instead of being precise about Potato Point, I struck it rich – a site with basic geological information, a map, and photos of a number of places close to home. One of my problems in the past has been converting diagrams and abstract information into a relationship with what I see in front of me.
J has a longstanding interest in geology (amongst longstanding interests in just about everything in the natural world), so on Sunday morning we set off to find the track from Narooma cemetery to the NAC, where we were promised chevrons, mylonite and chert. We found a track all right: steep, and slippery, and calculated to shoot your feet down faster than the rest of you. I was determined to reach the beach, so I bummed it down using my stick as a just-effectual brake, surprising J who was expecting me to be daunted.
And there they were, visible even to my inexpert eye, chevrons folded when the Pacific tectonic plate collided with land, creating the tremendous pressure which pushed the layered rock into this very clear zigzag pattern. We stood looking at them, J doing what he does so well: turning earth story into a once-upon-a-time narrative that I can understand.
The beach was stunning. How, I ask myself, could I never have been down here? The heavy seas have taken away sand so rocks once buried are now visible in all their patterned and coloured glory: I know this because of a conversation with another beach-walker. I can't explain the processes that created these beautiful patterns and designs, but one day I may be able to understand as well as admire.
Midway along this section of the beach, I spotted the formations called mylonites. Although I recognised them from the photograph, I can't make sense of any explanation I've yet found.
As I approached Glasshouse Rocks, poking up dark from the clear Narooma water, I saw a smaller companion rock, and beyond the headland, a cluster of spectacular even smaller rocks, some sharp-edged, some rounded. The mainfestation of chert was in deep shade which eradicated detail. I'll need to come back when low tide and afternoon light coincide, and when I'm wearing sandshoes rather than clodhoppery boots. Next time I'll be carrying a bit of knowledge in my head: chert is sedimentary rock material; when it breaks it has very sharp edges (and was therefore highly valued as tool-making material – it's also called flint); Narooma Chert was deposited on the ocean floor over a period of 50 million years (my imagination quails at the time scale) and carried west to its present location when the Pacific plate collided with Gondwana.
When it's time to go home, we don't have to belly our way up the steep, slippery track after all. There is a completely civilised, gently sloping sandy bush track, winding up the hill to the cemetery. I ramble up easily, admiring the view back to that wonderful beach, passing correa bushes, engulfed in the perfume of pittosporum.
Geological questions proliferate, and poring over geological helpmates at home raises more questions than answers. As I spend Monday morning trying to increase my geological knowledge, delighted that I had identified mylonite, chert, and chevrons, I find myself clicking on links every second word, and then links from links, and links from links from links, as I try to understand what I'm reading, and assess the reliability of sites. I tend to distrust any site I can even begin to understand without a savagely wrinkled brow and twenty five rereads.
I hereby certify that I understand at a very basic level anything I outline here, although the temptation of course was to pseudo-knowledgeably cut and paste! If I've got it wrong, please tell me.
Glossary of new words, in bold if I have an inkling of their meaning: chevron … subduction zone … tectonic plates … ductility … turbidite … orogenic belts … Lachlan fold belt … Bogolo formation … mylonites … chert