Rocks, ceremony and art

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“Restless Earth” exhibition, Camel Rock, Murunna Headland, Spiral Gallery

We’ve written for three or four hours – after all that is the designated purpose of our week together, me and a very special friend – before we set off to visit a geriatric who raises the bar of longevity and survival extraordinarily high. Camel Rock, so named by the whitefellas, has been around, one way and another, for 450 million years.

Baked, squeezed, buried, exhumed and eroded

It’s had a rough time of it and bears the marks of its history, as do all old things. It was birthed when an avalanche roared down over the continental shelf, carrying with it broken-down rock ranging from boulders to minute grains, which settled into layers on the bottom of the sea. Over the millennia they have been baked, squeezed, buried, exhumed and eroded to become today’s rockscape. Undulations in the fine layers at the top of each bed record the ripples as the flow comes to rest. Often turbidite beds are stacked on top of each other by many undersea avalanches covering vast periods of time. As you can imagine rocks now are often highly deformed by all this pressure.

Corroboree, ceremony, trade

More recently, the area around Camel Rock became a sacred Aboriginal site. People from up and down the coast and from the Monaro gathered on Murunna Headland above the Rock for corroboree, the last time as recently as the 1930s. Tools were traded and food from ocean, estuary, lake and river shared. A freshwater hole at the base of the southern side of Murunna was a sacred place for women. The head of a woman in the rock was seen as warning of a dangerous rip.

“Restless earth”

We were drawn to visit Camel Rock as a companion piece to an exhibition at the Spiral Gallery in Bega. The title of the exhibition is part of a quote from Professor Brian Cox: “Earth is our ancestor. The restless earth is your creator.” Joy Georgeson’s ceramic hollow hand-built sculptures, decorated with engobes, oxides and glazes, were inspired by the geology and biology of Camel Rock, and Ivana Gattegno‘s art, acrylic, and black and white charcoal, by the landscape around Gulaga and Mimosa Rocks. You may recognise a pile of stones and the offshore rock in the second image from a recent post.

Bogolo

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Bogola Headland, Bogolo Formation, braided essay, Natalie Stokes

I

You sit across the table from one another, you and Natalie. Her offering is a closely argued document called “Relationship of mafic rocks and surrounding rocks in the inferred subduction complex, Batemans Bay district, south-eastern NSW”. In front of you is a small black notebook, with the hopeful heading Geology 2017. You are here to negotiate understanding, you a novice geologist with serious limitations, her a university student offering her honours thesis. You feel blessed to have found her. She writes about a place you’ve visited, and she draws detailed  diagrams of different formations, which is the next best thing to her actually standing on a rock, pointing at it, and saying “This is the Bogolo formation. See here and here and here … these are the characteristics.”

But unfortunately for you, she uses words as well as diagrams, lots of them. Her lexicon is as dense as gabbro. One sentence might offer you “shear zone thickening”,  “olistrostomal flows” and “disrupted bedding”, leaving you with very little to hang understanding on. Simple pronouns lack meaning as you fail to understand their antecedents. Even a phrase like “migration of faults” where you know the meaning of the words in isolation raises questions about what exactly they mean here. However, she’s done her bit, so she leaves you to it.

You struggle on because you really want to know. You think about yourself as a learner: that urge to go and do something else – knit, cook, even housework – rather than battle on through the hard bit. “Geology for dummies” doesn’t always provide the desired definition.

It’s a long long time since you’ve done such intellectual battle. You mainly read history where the discourse and language is familiar. Even an occasional foray into the world of Nabokov’s butterflies or Gawande’s history of cancer doesn’t make this kind of stringent demand. There, if you don’t understand you can skim over the hard bit without missing too much. Rocks and their foundation stories make no such concessions. If you want to understand you have to persist and hope that eventually you’ll get it.

II

The Bogolo formation is more than 90% mudstone. Long, long, long ago very fine clay particles settled at the bottom of the ocean or a lake or a lagoon or a peaceful stretch of river. Slowly the resulting mud was buried and compressed by the weight of more sediment. The water squeezed out and the slurry became rock. But the Bogolo Formation isn’t just mudstone: it’s a mélange, including fragments and blocks of sandstone and basalt with a diameter somewhere between a centimetre and twenty metres in an unsorted mishmash. As a sedimentary rock it should be layered, but it isn’t, not systematically. It’s been knocked about in its formation. Geologists can’t agree on how. Caught up in a monstrous flow of debris? Crunched up in a fault system? A casualty of huge mud volcanoes? It hasn’t had an easy time of it, whichever explanation you go with.

III

It’s a glorious spring day as I walk down the spur to Bogola Headland, Gulaga looming a few paddocks away on my right and the sea sprawling and sparkling on my left. Surely this is where I’ll find laid out before me the Bogolo Formation Natalie has introduced me to and that I’ve read so much about. I round the corner and step onto a rock platform. It’s flat, unbroken by the fissures or the sharp edges that usually make rock hopping a business of intense concentration. I stroll over the surface, mostly level, no need to grapple with foot-eye coordination, except occasionally where a boot-sized hunk extrudes. The rock, grey-ochre, silver, purple, copper-streaked, with occasional constellations of white specks, has an almost talc-like smoothness and occasional stripes. I reach my hand down and stroke the silkiness and the slightly rougher streaks. Small nodules / excrescences in the vertical surface take the shape of coronet, braid, necklace. Near the ocean, lumps become pinnacular, sharp edged, huge. It’s easy to look and describe: I’m quite at home with rock patterns, the sun and the sea.

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Cemetery Beach gives again

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Cemetery Beach, chevrons, haiku, ontheroad, swirls

I walk down the familiar track to the pebble hillock and across the beach, camera holstered, thinking “Been here, seen it all, hohum.” This is emphatically not the case. The ocean has had a busy week, scouring out sand from the base of familiar rocks. Today a throne in a big beach rock requires climbing, whereas on previous visits it was within easy reach of an eager bottom. The base of the chevrons reveals a continuing line of folds. The tide is low as well and there are many more rocky outcrops, feet in the ocean, with shimmering rock pools, and the occasional chevron reclining amongst them.

We walk no further than Glasshouse Rocks, because we discover the ocean side of the rock where we first saw swirl circles and indeed I have not seen it all. We still have no idea what these swirls are, geologically, although J is mounting a search as I write. I do know what they are photographically: demanding!

By the end of our stroll J is convinced we’ve been led on a wild goose chase with mylonite, now struck off our register of Narooma rocks we recognise, despite its identification on a cartoscopic map site. His reasoning is beyond me, but no searches turn up mention of it around here. 

The haiku was inspired by this one featured in Suzanne’s ontheroad post.

 

In search of chert

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Australia Rock, BIM, Cemetery Beach, chert, chevrons, Glasshouse Rocks, mylonite

It’s a wild and windy Thursday, too wild for J to contemplate burning off, so we go in search of definitive recognition of Narooma chert.  We’ve decided to leave geological processes for now and concentrate on the naming of parts. Chert is a great choice, because there are a few large formations about 20 km from home and we know we’ll know what we’re looking at without any need for debate or any room for doubt.

First we visit Australia Rock near the Narooma breakwater. The blackish-grey rock looms above us out of an untidy rubble of huge squared granite lumps, presumably doing something breakwatery, but spoiling the majesty of the chert, which is  precisely where it ought to be. It was deposited on the Pacific Ocean floor over a period of 50 million years (from Late Cambrian to Ordovician period) and moved westward to its present location with the Pacific plate. When its carrier collided with Gondwana its journey ended and here it is. 

As we scrutinise the rock and mumble about its characteristics the gentle waves sussurrate the pebbles on patches of beach and the wind howls. The sun of course is behind the rocks, so photography is challenging, although far more familiarly so than geology.

After a half hour of scrutiny we drive to the headland cemetery and go down the track to a chert wonderland unfolding (not a word I should use in view of its geological meaning) as we stroll towards and beyond Glasshouse Rocks. The tide is low and the beach goes on, around headlands to yet another vista of islets and sand and bush-crowned cliffs, and we finally reach the pair of chert spires that has tantalised us ever since we began walking on this beach.

Maybe I have chert nailed, at least until I have to identify it somewhere else.

In our ramblings we encounter a recent acquaintance. Parading along the middle of the beach in an isolated formation, and lurking in the cliffs, is block in matrix mélange, which we now take the liberty of calling BIM.

Post-walk research – by J: I fell into a deep sun-filled sleep – suggests that we also saw mylonite. Wikipedia informs me that “as dislocations are added to subgrain boundaries, the misorientation across that subgrain boundary will increase until the boundary becomes a high-angle boundary and the subgrain effectively becomes a new grain.” Forget that, if you like, and just admire the outcome.

 Having identified chert, BIM and mylonite, we find we have a new mystery to solve. What is the origin of these swirls?

As we’re leaving the beach we encounter the chevrons we tracked down on our first geological foray, some years ago now,  glorious as the light moves and showcases their unmistakable detail. They are a comforting reminder that we have made some geological progress.

Looking for … goodness knows quite what

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BIM mélange, Smugglers Cove, uncertainty

And more particularly quite where. 

We think we’ve struck gold when we find “Field geology of NSW” by Branagan and Packham, and use it to shape a Sunday explore in search of aspects of Narooma Terrane (aka Narooma Accretionary Complex) that we haven’t been aware of before. Specifically, we’re hunting for BIM mélange. Wikipedia provides us with a photo (no scale) and some basic information. I’m most struck by the fact that this mélange probably rode the Pacific tectonic plate at least part of its 2500 km journey towards the east coast of Gondwana some considerable time ago. 

At this point we have a vague unformed idea of what we’re looking for. The next thing we need to know is where to find it. And that’s when local knowledge and the handbook come to the parting of the ways. We know exactly where pillow lava is, one of our few certainties in this geology game. But the headland nomenclature, always a bit shaky, doesn’t match. We follow written directions like good little students and although we find fascinating rockfaces that raise another lot of questions (Does that look like chert? Do you reckon this could be basalt? Is this side of this headland the same as the other side, only differently weathered?) we don’t find any sign of the imbricate stack. So we go a couple of beaches south to the patch of known pillow lava, and poke around muttering imprecations and mumbling interrogatively. We scurry around a headland between waves, and find what we’re looking for in Smugglers Cove.

Mind you, we were looking for a neat imbricate stack (don’t ask!), but we find BIM mélange that perfectly matches the Wikipedia photo (the first in the pairing below), the bottom layer of the imbricate stack sequence – if we’ve got it right. We give ourselves 50% for the morning’s work, and head home sun-soaked and weary.

What exactly is block in matrix mélange? As I search for an easy definition I’m back in the realm of every second word a mystery that needs to be solved. Breccia, tectonic accretionary prisms, olistostromal action, orogeny, boudinage, dilational veins, mylonite, imbricate stack. Talk about an accretionary zone in vocabularics! It’s a relief to meet a few old familiars, even if I’m not completely certain of their meaning: Lachlan Fold Belt, subduction, turbidites, chert. They’re like old friends spotted at a party filled with strangers.

Oh, and BIM mélange? A sedimentary deposit composed of a chaotic mass of mixed material turned to stone. I think.

Eurobodalla beaches: Mystery Bay kink zone

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kink zone, Mystery Bay

This post acknowledges my dentist who not only does pro bono dentistry in places like Nepal and East Timor, but is also on a mission to visit all the Eurobodalla beaches. We’re both on about 30, but her acquaintance includes unusual beach pastimes like swimming and snorkelling. Thank you Charmaine for making a visit to the dentist a pleasure (almost).

There are stories here at Mystery Bay: the mystery that gave it its name and the geological story behind its kinks.

The mystery story is easy to track down. In 1880, gold was discovered near Bermagui, just south of Mystery Bay. The Mines Department sent Lamont Young, one of its geologists, to report on the find. He travelled from Batemans Bay by rowing boat, a “green 8m vessel”, landed at Bermagui, and then left again, spotted by residents early in the morning as the boat moved slowly north. That afternoon a man riding along the coast found the boat on the rocks north of the goldfield, with no sign of the five men.

Police were puzzled. The boat had been steered through 70 metres of jagged rocks. There were four large holes in the hull but the planking had been stove out, not in. They found bait, a pocket knife, pipe and tobacco, food, a bag of potatoes, a bag of clothing, bedding, a sheath knife, an axe and shovel, three mother-of-pearl studs, a portion of a meal and three cigar butts. Large stones had been placed in the boat. None of the men were never heard of again despite searches, rewards, government inquiries and wide media coverage. That’s the mystery of Mystery Bay. The day I visit such sinister happenings seem impossible in the bright warm sun.

The geological story of the kink zone is a bit more difficult to research as google leads you to, amongst other things, sites dedicated to pansexual fetish lifestyles. The kinks I’m after are far more interesting and far older – like 500 million years old – cpressured into existence by the movement of tectonic plates. When I do find information it’s so technical that every third word eludes me. So understanding the mystery of the kink zone is a work in progress. 

What do I understand? That the rocks are sedimentary, which is obvious from the layering of patterns (maybe) and I’m told they’re chert, black mudstone and slate.  And that’s about where it ends for me. Once I encounter something like this – Differential shear stresses acting along or adjacent to a non-planar fault surface or shear zone may cause uneven acceleration during slip – my mind wants to doze off. Looking up each word and mastering its technicalities is life work I fear.

Then I stumble across an accessible definition: a kink is a tight curl, twist, or bend in a rock band. “Continued kink band growth can produce chevron folds.” That sentence is like meeting an old friend: I can recognise a chevron! Now all I need to do is to apply these definitions to the actual rock face – which means a return to Mystery Bay with J who has a better grip on such things than I do.

After this feeble excursion into geology I return to the more familiar aesthetics of the rock face, the rock pool, lichen and the leftovers from the tide.

 

It’s time to leave the kink zone and walk along to the sand and low rocks of the south end. As the sun warms me, I relax into another beautiful day, leaving the worries associated with ignorance behind me.

Eurobodalla beaches: Myrtle Beach, Dark Beach and Emily Miller headland

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Dark Beach, Emily Miller headland, Myrtle Beach

Please join me as I visit three contiguous and very different beaches on the same hot day.

 

Myrtle Beach

The walk in to Myrtle Beach is through twisty spotted gum bushland dense with burrawangs, including an ancient one with a tall, thick trunk. The drop to the beach is surprisingly steep, down wooden stairs.

 

 

What we are seeking here is unconformity, the place of rendezvous for the tilted / folded Wagonga Beds and the horizontal sedimentation of Sydney sandstone, where angles meet straight lines. We find it easily – even I can see the junction, although the camera has a bit of trouble. Things are complicated by chunky rubble in the rugged cliffs at the north end of the beach. Photography is difficult because the sun seems to be wherever I point the camera. But there are great fallen slabs, and slabbed is the best description of the sheer cliffs.

 

Can you see the unconformity?

 

 

 

 

Forget geology and admire beauty!

 

As we return up the staircase, I see “NUD …” scratched into the timber balustrade, and realise why the man who came down to the beach is fussing around settling his paraphernalia. He wants us gone, taking our unknown sensibilities with us. I'd forgotten this is a nudist beach.

On the way back to the car we follow side tracks looking for a way down to the next beach. The drop is always impossibly dauntingly steep.

 

 

 

 

Dark Beach

However, from the carpark there is a track we didn't notice when we arrived so we follow its gentle slope. Dark Beach is a surprise, unlike any other south coast beach I've encountered: fine dark gravel, ankle deep under our weight and puddling in the bottom of our footprints. The biggest surprise is the yellow sand of the next beach, just across a black Narooma chert barrier: how have the beaches remained so separate and distinctive?

Here again we find an unconformity, that magic junction between two totally different rock histories; breccia, a mash-up of angled rocks (or is it conglomerate since most of the jumble of rocks are rounded?); and one of our early geological acquaintances, hard black Narooma chert.

When we're ready to leave we have no problem finding the entrance to the track: a sinister dark glove rising out of the dark sand marks the way.

 

 

 

 

Conglomerate (rounded stones) or breccia ((angular edged stones)?

 

 

A comparison of two beaches

 

 

 

Emily Miller Headland

 

To get to the Emily Miller headland we walk along a fenceline protecting us from unstable cliffs and down a track that uses the sandstone as stairs at the bottom. The rock platform is cut by a trench which seems to be an old dike worn away. I was too timid to jump the abyss although it was an easy step across: next time when it's cooler and I haven't just had a lunch beer I'll be much more daring. While J explores the rock platform, I sit in the sun near a perfect curve containing a layer of gravel, basking in the beauty of pure sandstone country.

 

 

 

 

By lunchtime we are losing geological focus and drenched with sweat so we return home for a long afternoon doze and then a river-loll and wine by the rapids.

 

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Eurobodalla beaches: Wasp Head

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dropstone, fossils, sandstone, Wasp Head

Wasp Head is a beach unlike any other I’ve ever seen. At 280 million years old, it has all the apricot blush, lure and comeliness of geological youth. The landscape here is the result of sedimentation and the movement of glaciers and there isn’t only spectacular sandstone but shell fossils, ironstone box work, dropstones, and even, somewhere, fossil logs.

We begin our exploration admiring the colours and shapes of a sandstone cliff-face. Then we amble around honeycombed rocks until our way is stopped by the sea. At this point we do our usual find-a-path: a scramble up a slope slippery with casuarina needles and dry leaves, a stroll through a casuarina forest and a descent down a grassy hill to an expansive rock platform.

The rock platform is honeycombed, flat with the occasional standing rock. On one of these J spots a shell fossil, and the search is on. It wasn’t the only one.

There are also dropstones carried along and then discarded by glaciers, gravel flows embedded in rock, and strange holes for which I have no explanation.

As we move around the levels of the rock platform we look across to the island over a group of surfers, busy catching waves and breaking boards.

After a late picnic breakfast – potatoes, bread, hummus and leaf litter picked in a hurry from J’s garden (“We’ll just brush the dirt off!”), we head down the path to another platform, this time sloping in sandstone curves to the vivid sea. Here are patterns and curlicues; intricate ironstone boxes; and maybe even a leaf fossil.

The tide covers the beach below cutting us off from further adventures, so we head home, already planning to return to this astonishing landscape.

Maybe Jo’s Monday walkers would enjoy this taste of the NSW south coast.

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Discovery of the week: Fossilised ripples

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Cadgee, fossilised ripples

This won't become a weekly series, because there's no guarantee that each week will proffer a startling discovery. But last week did.

On Saturday afternoon we drove along the river road towards Nerrigundah, the road that I walked in twelve instalments last year with such pleasure. We wanted to examine the rock in the cuttings with new geological eyes, and see if it matched any rockage we'd seen on the ridge in the morning.

We scrutinised the rock face in a way that never occurred to me twelve months ago, noting the easy way pieces peeled or broke off and fell to the road.

Then, high up, a riveting sight. Our first local fossil. Not a shell or a leaf – these rocks are too old for that. What we were looking at was ripples, that most evanescent of motion, captured in stone.

 

Can you spot them?

 

How about now?

 

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Following the Kanawinka Geotrail: 2

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Budj Bim, Byaduk Caves, h, lava tubes, the "petrified forest", tumuli

After the watery interlude at Nelson, we continue our volcano safari east. I am eager to see the “petrified forest”, billed in the Kanawinka leaflet as a Moonah forest drowned by dunes that then hardened. So we head out towards the coast, passing an intriguing string of caves fenced off, a track leading up, but no signs to explain them. Later research told me they were the Tarragal Caves, undercuts in ancient dune limestone and important Aboriginal camping places: excavations in the 1970s revealed shell midden deposits and earth ovens over 11,000 years old.

 

 

Cape Bridgewater and the “petrified forest”

We arrive at the wild southern ocean to find a parade of wind turbines there before us, drowning the sound of the sea and intruding on the visual strangeness of the barren landscape: rock and saltbush and then the sea. We walk past what we interpret as hollows left by the dissolution of trees: circles on the ground and tubular shapes in the cliffs. Then we found an information panel that explains that the “forest” is not after all petrified trees, but a collection of hollow limestone tubes, eroded by millions of years of rainfall. This process begins when mineral-saturated water gathers in a shallow pan of sand and seeps downwards, dissolving the limestone and cementing the sand. However it was formed, it is an eerie desolate landscape. A flow of black basalt tumbles down to the sea, beginning grey like a wrinkled elephant hide before it turns typical basalt black.

 

 

Budj Bim

The approach to Budj Bim (Mt Eccles) is through flattish country towards an undistinguished horizon. The first time I drove out there years ago, drawn by a brown national parks sign, I didn't expect much. A mistake. Apart from koalas, it offers a crater lake, lava tubes and a lava cave.

Our first sight of Budj Bim itself is in cross-section. The whole side of the mountain has been sliced away by a extractinf scoria (igneous rock with bubble-like cavities) for road building.

 

 

 

After we pitch camp we head off to walk around the rim of the crater. Imagine yourself back in the time, 33000 years ago, when Budj Bim was formed. There is boiling lake and frothy lava jets up in a fountain. It cools rapidly to form scoria. There's a wind from the west and it blows the scoria from the crater to build the cone. Then liquid lava splashes onto the sides of the mountain. Some of it sticks and solidifies into basalt: some falls away before it turns solid and leaves gaping holes.

The lake is called Lake Surprise, named by a school child in the 1920s and is contained by three craters.

 

 

The next morning we begin the day with a stroll along the remains of a lava tube, the walls towering above us. Overflow from lava or splatter from a turbulent lava flow built up in thin layers to form levee banks. The banks grew inwards to overarch the flow, eventually joining to make a roof. There are signs of a collapsed roof along the lava canal. The deep cave, the natural arch, is one place where the roof hasn't collapsed.

 

 

Tumuli

The landscape not far from Budj Bim is scattered with roughly circular mounds of rock: tumuli or lava blisters, created by the buckling of brittle crust by the upward flow of underlying lava.

Beneath lowering clouds, we slither under an electric fence (there were no KEEP OUT signs) and dodging cow pats prowl around an area scattered with tumuli which are “rarely found in the volcanics of the world”: the only other sites are in Africa and Iceland. Sometimes drystone walls connect with the tumuli, a more orderly tumble of rocks.

 

 

Byaduk Caves

These caves are the result of action at Mt Napier (see below). The largest tunnels are up to 18 metres wide, 10 metres high, and extend to depths of 20 metres below the surface. The main features of Cave 1 are the ferns and mosses at the entrance and the large circular chamber at the far end with a complete domed lava floor. The western sinkhole is roughly elliptical, and at the western end this leads by various entrances to low-level passages. The western sinkhole is connected to the eastern one by a short tunnel.

The Caves support a sizeable Bent-winged Bat population and offer twenty species of ferns. Mammal bones including those of the Thylacine (Tasmanian Tiger) have been found in the caves.

And no. We entered none of them: the clambering looked too daunting.

 

 

Mt Napier and Harman Valley

 

Looking beyond the Harman Valley, in the distance, is the distinctive shape of Mt Napier. 8 000 years ago a spectacular lava fountain several hundred metres high roared up from a lava lake in Mt Napier's crater from a depth of thirty kilometres. Lava flows surged down several valleys including the Harman Valley, through lava tubes hidden under a solidified crust. Inside the tubes the rock stayed molten and travelled 27 kilometres.

Our last volcanic act in this ten-day volcano crawl is the ascent of Mt Napier, and a fitting end it is. The crater is a dry one and the rim gives a panoramic view out over country we'd been traversing, as far as the Grampians and the wind farms on the coast.

 

 

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