Sunday, 21 August 2016

Cutting Through Mysterious Granite on a Country Highway

Australia is known for its remoteness. There are some quite remote areas in the Northern Rivers too. Along the escarpment there are rugged areas and visitors are rare. This means that sometimes rocks even though mapped broadly have geological units that have not been researched enough to relate them to surrounding units. It is a rare thing though, and rarely have rock units not been named, and categorised, even rarer is when a rock is found by the side of one of the national highways!

un-categorized granite on the New England Highway, Glencoe

The picture shows a granite that is currently mapped as "unassigned Permian intrusive - felsic". There may have been some investigations here in the past. I just can't believe some place so obvious like this one has not been investigated in detail.

Monday, 25 July 2016

Blog Update #8

The Rocks of the Region page has been a big success and will continue to be expanded on. Unfortunately I've had very little time to do some actual blog posts recently. This is not for want of material (there is a huge range of topics and places just asking to be covered) but due to a change in my work commitments. I have taken up a new job with much longer days and therefore my free time is very limited. I have also relocated away from Lismore to Armidale and taken my family with me. We are still very much settling in.

Thank you to all the readers out there. I hope that I can continue to build a blog that is a good resource for the community to use. I guess there are people still reading this blog since there are more than 150 000 page views!

Coming up soon... what is going on with this rock?
Coming up

Wednesday, 6 July 2016

Geology of the Big Scrub Rainforest (Part 4)



Tasman Sea to the Alstonville Plateau

Following the Cretaceous during the Paleogene and possibly as a result of the action of the Tasman Sea formation, volcanic systems began to form throughout parts of eastern Australia. In the New England, the Hunter and Sydney areas swiftly flowing lavas erupted from long vents and covered large areas with basalt. The same thing happened in our region and until now it is one of the relatively unknown parts of our history. At  around 43Ma during the Eocene Epoch basalt lava flowed from vents somewhere in the area now known as the Alstonville Plateau (The area between Lismore to Lennox Head). The lava flow (called the Alstonville Basalt) tended to flow towards the North and West because the hills of the Blackhall Range formed a barrier to the South. The old Wilsons River seems to have been deflected from its southerly course and sent inland to join the Richmond River as lava flows dammed off the rivers original course. Small lakes were formed where the lava flows dammed streams and created little areas of sedimentary rock known as diatomite and even poor quality opal. It is interesting to note that during the 20th century diatomite was even been mined for use as a filter medium from layers between basalt at Tintenbar and Wyrallah.

Layers of diatomite were subsequently covered by new layers of lava and during the time between lava flows rich red soils developed and were subsequently covered by new lava. The rate of soil formation was high during this time because the world climate was the warmest (more than 10 degrees C hotter than the average today) it had been for 400 million years and be when combined with atmospheric moisture this time was known as the Mid-Eocene Climate Optimum. The lava covered soils (known as paleosols) are important today because they are conduits for groundwater (aquifers) which create long lasting springs resulting continually running streams and ecosystems dependent upon them. The aquifers are also drilled into for groundwater for some of the livestock, irrigation and town water supply on the Alstonville Plateau today. Eventually, the eruptions stopped and lovely fertile deep red soils developed and continue to develop today.

Thursday, 30 June 2016

Rocks of the Region Page

Sometimes pictures say more than words can. I have created a reference web page that has links to my Flickr pictures of most of the major stratigraphic units of the region. Here you can see pictures of rocks, minerals, landscapes and unusual features that within each of the rock units. Locations of each picture are provided in Flickr so that you can check these out for yourself if you are that eager!

In addition I've provided a link to the stratigraphic unit description in Geoscience Australia's Stratigraphic Name Database.

The whole exercise will never end. It is a work forever in progress. Let me know if you have a wish list of photographs. Click the photograph below to go to the reference page.

http://nrgeology.blogspot.com.au/p/rocks-of-region.html

http://nrgeology.blogspot.com.au/p/rocks-of-region.html

 

Monday, 30 May 2016

Geology of the Big Scrub Rainforest (Part 3)



Gondwana

The late Jurassic and Cretaceous marks a very important geological time. It is the time that the huge supercontinent of Pangea broke up. This when Gondwana became its own continent with present day Australia and Antarctica being a large part of a new smaller, but still impressive super-continent. Our region was actually quite close to the pole but, yet temperatures in our area were quite warm because the climate of whole of the earth was warmer and wetter than it is today. Life was abundant because summer days were nearly 24 hours long and the concentration of carbon dioxide in the atmosphere along with the warmth and moisture super-charged plant growth (in fact permanent ice did not exist anywhere on earth at this time). It was at this time that many of the plants synonymous with Australia and more specifically the ‘Bigscrub’ began their evolution (including the plant order Myrtales which includes eucalypts, bottlebrushes and lillypillys).

As the Jurassic gave way to the Cretaceous period big changes continued. India followed by Antarctica began to separate from Gondwana and finally at around 80Ma the Tasman Sea started to form. Prior to the Tasman Sea formation the landmass extended hundreds or even thousands of kilometers to the east before reaching the sea. The Tasman Sea caused major changes to the landscape. This area is known as Zealandia and as separation occurred it sank below the sea and is now known as the Lord Howe submarine rise. A bit like the mythical land of Atlantis, a huge land submerged under the ocean. The Australian continent now finishing only several of kilometres off the coast from the future Cape Byron. The detachment of Zealandia reduced the weight on the eastern side of Australia which then began to rise and form many of the inland ranges that now make up the Great Dividing Range. This continental crust “rebound” would progress over a long time and by the end of the Cretaceous the physical form of Eastern Australia was set for its last major changes through the actions of volcanoes.

Tuesday, 17 May 2016

Science, Philosophy and Politics


It is popular these days to start with a narrative and make the data fit in. Rarely do we think about alternative hypotheses other than our own already established professional narrative. Because researchers today rely on their reputation they must defend their theories or apparently loose credibility. Ironically, the most credible scientists are those willing to admit they may be incorrect.

Scientists today often delve into the areas of political intrigue. When this happens the scientists pet narrative becomes a fortress that must be protected. No one can criticize it because the scientist will see it as a personal affront since his whole credibility has been placed on the line. This in turn turns peers off from suggesting alternative hypotheses because they know if they make such a suggestion the whole thing will become a fight. Even suggesting an alternative that is not as popular as the politically expedient one can result in aggression, ostracism and public ridicule. No wonder scientists often find hiding in their laboratories the most rewarding experience!

When scientific concepts are backed by politics you know that you are onto ground that is not necessarily scientific. So with that in mind, here is a diagram that covers all the issues today that arise during scientific inquiry. This includes the moral, philosophical and political reasons for undertaking scientific research.
As a geological example that was publicized a couple of years ago in Nature on the problems with the mantle plume hypothesis. Even though the article recognizes many problems with the theory it demeans a group of scientists who have proposed alternatives that fit a wider range of data. It gently denegrates an alternative hypothesis by suggesting only a small number and therefore fringe group have advanced the hypothesis:
"No matter what the RĂ©union study finds, its results are unlikely to convince the few critics of the plume hypothesis."
Essentially, it is the anti-scientific idea of "consensus science" that is beginning to pervade all areas of inquiry. Some of these scientists responded  here is a link to a letter to the journal Nature. Unfortunately for the general public even to view this correspondence requires $18 just to read it (such is the nature of journals these days).

Saturday, 7 May 2016

Geology of the 'Big Scrub Rainforest' (Part 2)


The story of the 'Big Scrub' s preserved in the rock unit known as the Neranleigh-Fernvale Beds. The first post in this series is about this rock, the foundations of the region. This post deals with the period of big sedimentary basins which corresponds with the age of the dinosaurs. Some 50 or 60 million years elapse from the Neranleigh-Fernvale Beds until we come to our next period of rock formation.

The Big Basins

Walloon Coal Measures overlain by Orara Formation at Bexhill
This period begins in the age of the dinosaurs during the end of the Triassic Period. During this time tectonic forces became extensional, that is, the east coast of Australia was pulled and twisted apart, very little compression occurred. The crust became thinner as the once colliding continental plates began to relax and lowland basin-shaped regions formed. The thin crust allowed more volcanism to occur and the first geological units of the Ipswich and Clarence-Moreton Basin were formed. The Chillingham Volcanics consisting of lavas and volcanic ash was laid down in after 229Ma and this was subsequently overlain by units of lake and river deposits including the Evans Head Coal Measures, Laytons Range Conglomerate, Walloon Coal Measures and many other layers. By the height of the age of the dinosaurs, during the Jurassic great river valleys spread out from the mountains of the New England over our region. These rivers laid down great expanses of alluvial sand which were further overlain by other units. The great expanses of river sand are called the Orara Formation.

Today, like the Neranleigh-Fernvale Beds the sediments of the Clarence-Moreton Basin in the ‘Bigscrub’ area are mostly obscured by younger rocks. However, some of the Chillingham Volcanics seem to present in the Blackhall Range behind Wardell though this is difficult to identify. Rocks of the Orara Formation are present at the edge of Meerschumvale but are most obvious at Bexhill, indeed at Bexhill the Walloon Coal Measures are evident in the old brickpit. The Walloon Coal Measures are overlain by a sub-unit of the Orara Formation called the Kangaroo Creek Sandstone. This Sandstone forms nutrient very well-draining but poor soils. Lovely examples of the Kangaroo Creek Sandstone can be seen at Bexhill Open Air Cathedral or in the creeks near The Channon. This means that the vegetation on these areas consists of different plants to that of the rest of the ‘Bigscrub’. The soils in these areas cannot support the lowland subtropical rainforest that is the biggest component of the ‘Bigscrub’ unless they are well sheltered in a gorge.

Even though the units of the Ipswich and Clarence-Moreton Basins are dated from the age of the dinosaurs (the Triassic, Jurassic and Cretaceous Periods) no one has yet found fossils of dinosaurs preserved in any of these units in our ‘Bigscrub’ area. However, abundant fossils of plants and fish do exist in many units of the Clarence-Moreton Basin and dinosaur footprints have been seen in rocks of the Walloon Coal Measures in the Queensland part of the basin. Some fossil fish have been observed in the creeks near Nimbin. Along with the abundant coal during the Jurassic shows there was a very large quantity of organic matter and plants growing at the time. This was a time rich in life.