Greetings fellow Foxies,
Some years ago, a visiting Scot remarked that our granite rocks looked old and tired compared with the ones at his homeland. I had to agree. Unlike Scotland, our Yilgarn craton bedrock has been stable for millions of years. No geologically recent volcanism or mountain building events. And best of all no haggis!
 Granite forms when geological plates collide and one slips under the other (subduction, see this blog).
WA granites formed over 2 billion years ago
Over hundreds of millions of years, the top of our granite bedrock has been very slowly breaking down to soil that has been washed or blown away causing mountains to flatten.
About 300 million years ago the land was also ground down by glaciers. Overall, long term erosion has lowered the ground level by up to 5 km.
​It is over this time that our granites have cracked and weathered (become tired).
The bedrock has been fractured many times as the craton has been shunted around during supercontinent cycles. Intact solid rock outcrops like Yilliminning rock less frequent. Most granite outcrops have horizontal and vertical cracks (called joints) that weather to large boulder heaps and cracked rock outcrops.

The vertical joints are obvious on an aerial photo, as ridges and valleys that often trend east/west, northeast/ southwest, north/south or northwest/southeast, and make right angle turns. 
Locally, the most obvious area is southwest of Narrogin, where much of the old laterite cover has been removed and soil has formed on basement rock.
Newman Block is a great example. Lines of vegetation reflect changes in the granite ‘grain’ as well as faults and dykes. The image on the left of pallid zone clay on a ridge displays an amazing number of joints that are in the underlying bedrock.
Eager to learn why the joints follow particular directions I started reading on and on and on…… It is a long and fascinating story. 

​Our local bedrock has a northwest/southeast trend or ‘grain’ from the formation of the Yilgarn Craton as ‘islands’ of continental rock collided about 2.8 billion years ago. The red lines between the domaines/ and terranes show subduction zones where one slid under the other as they collided. These zones are called orogens.
The orogens on the north, northeast and southwest sides formed when the Yilgarn Craton collided with other land masses as the Australian continent was being built up. The Pinjarra orogen on the west side has had at least three collisions with other land masses including the Zimbabwe craton and India.

During this time, the craton has joined and separated from at least three supercontinents as it has drifted over the globe.
The images below show the position the WA in three supercontinents before they split apart. I have taken the liberty of rotating the supercontinents so that WA is in its present north/south orientation. 
The radiating multi-coloured lines on the Nuna supercontinent are joints caused by pressure from mantle hotspots that have filled with intrusive rock to form dykes (see this blog). These also affect the direction of joints in continental rocks.

When India and Antarctica separated from WA, reduction of weight from the combined continents on the underlying mantle created an upward pressure that caused the Darling Range to slowly rise on the west coast accompanied by parallel faults inland. On the south coast a line of uplift parallel to the coast (Jarrahwood Axis) caused east/west trending faults and formerly south flowing rivers to reverse flow and eventually join the Swan River. On the south side of this uplift the coast slumped forming a slope down to the ocean.
The Australian plate is inexorably drifting north and is subducting underneath the Eurasian Plate. In a couple of hundred million years Darwin could be a suburb underneath Bali, or possibly a ski resort!
This subduction is extremely slowly causing the Northern Australian coastline to sink, and the south coastline to rise (unfortunately not as fast a sea level rise from climate warming).
Stress from tilting of the Australian Plate is a cause of earthquakes like the Meckering quake.
 
It is no wonder that our granites look old and tired. Still they create interesting shapes and landscapes.

Greetings fellow Foxies,
I was blown away to find an outcrop of banded ironstone on a gravel ridge on the Banksia Walk. It is only a small outcrop but was a great surprise because banded ironstones are ancient deep-water sediments that are much older than the underlying granites in the district.
I consulted my geologist colleague Jefferson Harris who was equally blown away but offered the following amazing explanation. It is a long story that involves cataclysmic events over billions of years.
​The story starts somewhere around three billion (3000,000,000) years ago when there were ‘islands’ of continental rock in a world-wide ocean. At this time there was little oxygen in the atmosphere or the water that contained dissolved iron and other minerals coming from ocean vents.
In deep still-water basins around the islands, silica (an often-tinted type of quartz) was slowly deposited. Life at this time included early stromatolites (like those in Shark Bay) that gradually released oxygen.
When this oxygen reached a certain level, it combined with dissolved iron that settled out as a dark iron-rich layer on the sea floor. The oxygen depleted water then accumulated more dissolved iron.
As oxygen content of the water fluctuated, alternating quartz and iron-rich sediments accumulated as thick layers that became banded ironstone formations in areas like the Hammersley Ranges.

Now to explain how older banded ironstone came to overlay younger granite: -
As the islands and their associated deposits collided, the edge of one was forced under the other in a process called subduction. The sinking edge melted as it continued down into the very hot underlying mantle of the earth. This created huge molten blobs of granite that rose through the mantle until it met overlying cooler rock. (which in this case contained banded ironstone).
As the molten granite continued upwards its heat caused the overlying rock to crack and sink down into the lighter granite and be incorporated into it.
The island underlying Narrogin (the Boddington terrane) joined others to form by a huge stable slab of continental granite-type rock called the Yilgarn Craton that underlies most of the agricultural area and goldfields. This has remained relatively stable, and the exposed rocks slowly weathered to soil that was washed into the ocean. The land surface of the Narrogin area became lower until granite containing embedded banded ironstone was exposed on the surface
 A mere hundred million years ago the proteaceae family developed the ability to extract phosphorus from poor soils that led to the formation of lateritic soil from soils derived from weathered granite.
To simplify a long story, we now have banded ironstone embedded in laterite!

​Greetings fellow Foxies,
 I love climbing and understanding rocks (my wife thinks that there is mountain goat in my ancestry).
In the process of producing a Boyagin Rock brochure I climbed over and around it and compared it with our other great rock tourist destination, Yilliminning Rock. Both are inselbergs that outcrop from underlying granite basement rock that welled up when two older slabs of continental rock crashed into each other about two thousand seven hundred million (2,700,000,000) years ago. At the time volcanos erupted and a huge alpine mountain range similar to today’s Himalayas was formed. Over great time this bit of rock joined with others to form Australia and the supercontinent Gondwana, that joined more to form the global supercontinent Pangea, that then split up (greatly simplified). Very slowly the mountain range weathered and washed away.
Another mind-blowing statistic is that Yilliminning and Boyagin rocks were once part of magma chambers 5 to 7 kilometres below the ground surface. These have been exposed over eons as the overlying material was removed.
 
In the agricultural area, features like ridges, cracks and waterways tend to follow straight lines that may suddenly change from one direction to another. Our soils and the depth to crystalline bedrock are shallower than many other parts of the world. Surface features often reflect faults, intrusions and other changes in the mainly granite basement. Lines frequently trend northwest- south east, northeast -southwest, east-west, and north-south.
 
There are distinct differences between the two rocks.
Yilliminning Rock is more typical as a large granite dome arising from a gently undulating landscape.

​The Boyagin landscape is much hillier, and the rock itself is more variable. It is one of two adjoining large rocks project from the eastern side of a lateritic upland plain.
In the early morning, variations in the texture of Boyagin Rock granite can be seen in strange shapes where there has been uneven weathering of the rock. Look closely and you can see lines and mini ‘craters’ and lumpy spots on the otherwise smooth granite. 

​A look on a map shows that uplands and rivers in the Brookton area commonly trend north-south up to beyond the Avon Valley.

​An explanation goes back about 95 million years when India was once attached to, but slowly separating from WA. Brookton and surrounds were part of a plain with west-flowing rivers carrying sediment
into a rift valley that is now the Swan Coastal Plain (Perth – Bunbury etc.)
 
83 million years ago India finally separated from western WA and drifted north to crash into Asia.
With the weight of the Indian block removed, a line east of the Darling Fault from about Carnamah to the south coast bulged upwards to create the Darling Range. The land rose about 250 metres and was accompanied by other parallel downward and upward folds in the ground to its east.
 
These changes in slope completely blocked the old east-west flowing rivers and the blocked water ran down a new valley south from Dalwallinu (Mortlock North branch), and North from Pingelly (Avon South branch) into the Swan River.
The newly created Boyagin Creek then exposed Boyagin Rock.
​General north- south river systems and lines of ridges in the Darling Range can be seen on the before and after diagrams

​When I investigated the southwest base of Boyagin Rock I was surprised to see what looks like a quite recent north west-south east fault in the granite that had been exposed in a creek. 

As it turns out, generally east of Brookton is a localised earth movement hotspot in the southwest seismic zone (remember the Meckering earthquake?).
The Darling Range may also still be slowly rising so the old rocks may still be rocking. Of course the Wagyl also had a part to play.
 Click this link for a visual exploration of the rock.
Next time you climb Boyagin Rock take a good look around and be grateful for this true rock of ages.

​Greetings fellow Foxies,
Despite an exceptionally dry summer and autumn, we have had over 90mm of rain since mid June. If it all soaked in it would wet the soil to at least 2.5 metres. There has been relatively little runoff and I was gobsmacked, and very concerned to find dry soil within 5cm when digging side-drains on a range of soil types on walking trails to reduce erosion. These soils are massively water-repellent.

If the water largely didn’t run away, where did it go? Many of our native plants have excellent strategies for channelling water down their roots, and an experiment I did some years ago showed the importance of obstructing surface water flow to allow time for water to overcome the water repellence. The image below shows a section of water repellent soil where a racehorse goanna had been burrowing for insects in an old root channel. Note how moisture has wet the soil to depth around the root channel.

​I read this great article about the importance of woylies in the regeneration of sandalwood and native poisons. No doubt emus were also important.
​
Woylies and emus have gone from most of our reserves with the only burrowing animals being rabbits, reptiles and  echidnas. This is having a massive impact. Over time as plants die leaving bare ground and roots rot away there is less chance that new plants will replace them unless conditions change.

I commented on  irreversible changes in small reserves previously, and feel sad about the ongoing loss of nesting trees.
When entering Foxes Lair from opposite the caravan park, one can see poorer shrub and wildflower growth on the left side that hasn’t been burnt for over 50 years on the left, compared to vibrant growth on the right where an arsonist burnt about a third of the reserve.
That fire was a real revelation for me, as it triggered orchids I hadn’t previously seen and rejuvenated small bird life such as  quail that hide in dense undergrowth.
The arsonist had several goes in Foxes Lair After a small attempt I noticed a smouldering front moving through the soil under marri that burnt the water repellent organic surface layer to a depth of 3cm, and after the arsonist’s finale the fire continued to burn along underground tree roots for about 3 weeks (lesson here don’t walk through burnt country soon after a fire – your foot can plunge into underground burning root). The images below shows the difference burning made on the Valley Walk.

​What can be realistically done by volunteers and local government in small reserves?
 
Over time I have developed the following achievable strategies in Foxes Lair.

• Proper low intensity mosaic burns, with raking around big standing dead trees that are vital nesting spots. I developed a 10 plus year interval burning program for blocks in the reserve (no luck with implementation so far).
•  When pruning is required or trees fall across tracks etc. prunings are placed on bare areas to help trap water (amazing how quickly the leaves disappear).
• Dig small side drains at short intervals along trails and roads to return water to the bush more evenly.
• Spread soil from these side drains on to bare areas to introduce and retain seed and help water infiltration.
• Control weeds (so many).
• At the rate that large nesting trees are falling over, I reckon that nesting boxes will be needed one day.

I still remember being appalled at the lack of bird diversity when I travelled overland from India to Turkey a lifetime ago. Just sparrows,pigeons, crows and vultures!
​ I would hate Australia to go down that route.