My interest in ochre was rekindled recently, when I explored the Claypit Nature Reserve near Wickepin. Years ago as part of a mining lease there, the side of a mesa was excavated to get adjoining white and red ochre clays for brickmaking. The white section formed over granite, and red over a dolerite dyke.

​The importance of ochre for first nations people is summarised in this article on the ancient Weld Ranges Ochre mine.

An ochre pit at Dryandra National Park is one of over 440 recorded around Australia. For a nation this large, it is a small number, hence the value of ochre as an item of trade.

A good local example is the Uellelling Hill kaolinite mine east of Wickepin. The image below of a cutting in the exploration phase displays typical layers of an old laterite profile.

• ​The gravel layer contains most of the plant roots.
• The mottled zone layer is a transition to the pallid zone layer, which is stained by iron leaking down from the gravel layer.
• The pallid zone layer is decomposed bedrock, which has been weathered to clay and sand, and infilled with extra clay 

​The clay is a type of kaolinite called halloysite, which has many uses ranging from fine porcelain, paint additive, medicine and dentistry. Unlike other clays halloysite consists of microtubes rather than sheets.
​Electron microscope images of halloysite forming around bacteria lead on to a great story of soil development where plants lift minerals up from the depth in soil water, and microbes and fungi convert them to lateritic gravels, bauxite or clays.

​Pallid zone clay is also packed with salt, which was uplifted with soil water by native trees. When land was cleared, this salt washed down into rising groundwater and created our severe wheatbelt salinity problem.

White dams dotted around our landscape show the widely distributed pallid clay. If early Noongars had bulldozers, ochre would have been easy to get!
However, ochre only outcrops naturally on breakaway slopes. Granitic breakaways contain white ochre and less commonly yellow ochre (which contains an iron oxide called limonite). Red ochre contains an iron oxide called haematite which is mostly found on steep red-brown breakaways, which have formed off very iron-rich rocks such as dolerite.  Green ochre (containing a nickel oxide) is rare, only being found on ultramafic rock breakaway areas such as the Goldfields.
Good ochre contains very little sand.

​To see a jaw dropping breakaway, visit Buckley's Breakaway 70km east of Kulin

I found an easy way to make good ochre.

• Put the ochre sample in a bucket and add enough water to make liquid
• Swirl the liquid vigourously, then pour clay and water slurry off into another bucket leaving sand behind
• Leave the water and clay for a couple of days until the clay settles out leaving water above. Adding salt may help.
• Pour off the water leaving the clay slurry behind to evaporate to a creamy consistency

I take some samples in jars when I talk to visitors. The kids love it and as shown by the Foxyochrefoot image, even some adults indulge. it washes off easily. 

Further reading

• ​Ochre is of the Earth
• Exploring the biological dimension to pedogenesis with emphasis of the ecosoystems, soils and landscapes of southwestern Australia W. Verboom and J.F. Pate
• Why are plants and soils in the Narrogin area so diverse?

Greetings fellow foxies

Yesterday my wife Aileen and I were happily inspecting the effectiveness of erosion control and water spreading measures while rain was falling in in Foxes Lair. Aileen suggested that I should write down my reclamation tips for my successor (any offers?)
As in most small reserves, wildlife and plants in Foxes Lair have suffered greatly from European settlement. This blog showed that most of our soils are very water repellent but many native plants had exploited it to direct water to their roots. However water repellence greatly reduces seed germination. For regeneration, plants relied on periodic fires to reduce surface repellence, and the wealth of native burrowing animals such as bilbies, quendas and woylies to trap surface water. Early accounts mention that some areas of bush resembled ploughed paddocks. Alas most native animals have gone and water runs away. 

Access roads are another problem. They are too narrow for modern road graders to form roads up properly with two passes. Each time a road is graded, the road level is lowered,  and  water, which normally flows down a slope is diverted by the lowered road and the spoil bank. This starves slopes of water and causes excess stream flow. Narrogin shire has imported road making material to build up some eroded roads.
More sensitive road maintenance, burrowing animals and periodic burns are required. Feral pigs and rabbit cause great soil disturbance, but at great cost to agriculture and the environment.

​Narrogin's solution was to introduce a Dougosaurus. Considered by some to be a primitive tool-using hominid, he is an active digger and harmless unless provoked. He can even quite friendly if approached carefully! The digging is a cardio activity to increase lifespan, but he may forage for worms and witchetty grubs.

Can you spot him?

Here are some examples  of Dougosaurus activity, which can reduce the time between road grading.
​Frequent road drains reduce road erosion and return water to slopes

Where roads are too far below the road surface to use drains, rock barriers can be used to reduce water flow and trap silt.
Corrugations are best prevented by reducing traffic speed.
​Potholes tend to form on flat road sections. Without a compactor clay, sand or gravel fill is splashed out by tyres in wet weather. Experience has has shown that angular blue metal is the best material for drainage while staying in place.
Sand which accumulates in road side spur drains is not water repellent and often contain seeds. Seedling readily establish there, and the sand fast-racks seedling establishment when spread on bare areas.

Areas which have been bare for years are difficult to revegetate. Images below show how random Dougosaurus shovel scoops trap water, ground litter and seeds, which often enable new plants to establish. The process can take years.

Greetings fellow Foxies,

I have been reflecting on the recent fire, which severely burnt sections of North Yilliminning and Birdwhistle reserves.
Most plants in our bush are adapted to fire, but both reserves had been unburnt for about 50 years and were littered with dead material, which fuelled a very hot fire.
Annual plant seeds on the surface or seeds retained on plants were obliterated. Survival of seed in the soil varies with depth of burial.
Woody root plants which regrow from soil lignotubers (most eucalypts) and root suckers should survive well and resprout in the next few months.

Geophytes are fire tolerant perennial monocotyledons, which resprout from dormant underground storage organs each growing season - rhizomes, bulbs, corms and tubers.
The ability of geophytes to resprout at the break of the season enables them to outcompete annuals, and they survive hot and frequent fires. Unfortunately, many invasive weeds are geophytes, and some also have contractile roots, which draw them deeper into the soil. Introduced Guildford grass has spread through most loam and duplex soils at the expense of native annuals.
​Rhizomes are swollen underground stems, which are very common in sedges, rushes, Haemodoraceae (kangaroo paws), and  some native lilies. Depending on depth,  rhizomes provide fire resistance, however in the absence of fire, rhizomatous plants can take over from plants that depend on fire for seed germination. The image below shows the effect of a hot fire in Foxes Lair after a decade. The left side (unburnt for decades) has mainly mature rock sheoaks with a dense sedge understorey. To the right, fire has stimulated a range of shrubs to grow  from  buried seed, and has reduced sedge density.

Bulbs have a thickened stem base of modified leaves, which store nutrients. Examples include onions and introduced lilies such as daffodils, hyacinths, tulips, and Easter lily. Some Haemodorum species (bloodroots) are bulbaceous.

Corms are swollen stem bases filled with starch, which sit on the root base. These are very common in native and introduced geophytes. Natives include many lilies, sundews, and triggerplants. Some of our most aggressive introduced weeds (oxalis, freesias, watsonia) are cormous.

Tubers (swollen storage organs which form on roots and underground stems) are present on all our orchids and many native lilies, and many are bush tucker foods.
​Grass trees and zamias have above ground, fire resistant growing points called caudexes.

I will peg some spots in these reserves and see what comes up

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 is mostly created when geological plates collide and one slips under the other (subduction, see this blog).
WA granites formed over 2 billion years ago

The bedrock has fractured many times as the craton was compressed and cracked during supercontinent cycles. Intact solid rock outcrops like Yilliminning rock are less frequent in the district. Most granite outcrops have horizontal and vertical cracks (called joints), which 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.

After India 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. Antatrctica's separation caused a line of uplift parallel to the south coast (Jarrahwood Axis) and east/west trending faults. Formerly south-flowing rivers to reversed flow and now 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.

About 300 million years ago glaciers flattened the landscape. For 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. Overall, long term erosion has lowered the ground level by up to 5 km in this area.
​From about 100 million years ago, laterite has formed a layer over the landscape. Subsequent climate cycles and land movements have  created our present pattern of riges and waterways. More resistant laterites formed from mafic rock tend to coincide with uplands, and the very angular waterway patterns are following ancient cracks in the underlying bedrock.
This is shown on the relief map of the district below. Note the north/morthwest south/southwest cracks to the west, which formed with the Darling Range uplift.

It is no wonder that our granites look old and tired, but they create interesting landscape patterns.

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!