Sunday, 1 May 2016

Geology of the 'Big Scrub Rainforest' (Part 1)

Later this year it is intended that the Big Scrub Landcare group and many other contributors will release a book on people's connection with the 'Big Scrub'. It will be a multi-faceted book that introduces the emotional connection that people can have with a lovely part of the world. The book will even help picture the geological events that contributed to the formation of the amazing region. I understand that the book is intended to be launched in September at annual Big Scrub Rainforest Day. For those that would like some background information on the geology of the 'Big Scrub' I have provided a detailed outline of the rock types and events that went into building the foundations of this forest. There is a fair bit of information so I've broken this history into a series of blog posts. The book will have a different emphasis to this series of posts and will be a high quality visual feast. So I'll let everyone know more details about the book closer to the release date.

The oozy beginning

The history of the ‘Bigscrub’ starts a very long time in the past, yet it may be a surprise that by Australian standards the geology of our region is comparatively young. The oldest parts of Australia are 4400Ma (4400 million) years old but our little part of the Australian continent did not exist back then. It was not until 363-320Ma that the foundation rocks of our region were formed. These rocks are called the Neranleigh-Fernvale Beds

The Neranleigh-Fernvale Beds are derived from the deep sea. In the Devonian Period sediments settled to the bottom of the deep sea crust. The sediments were at first very fine and mainly consisted of the microscopic silica based skeletons of algae called pelagic ooze. The amount of sediment was only slowly deposited but over a long time a great thickness accumulated. Occasionally thicker layers of mud would be deposited from submarine landslides which occurred at the edge of the far away continental land masses, rarely submarine volcanoes laid down lava that was quickly solidified by the deep, cold ocean water.

The process of plate tectonics means that oceanic plates move slowly under continental plates. Gradually, as this process continued during the Carboniferous our area came closer to the continental landmass as the oceanic plate was subducted (is pushed under) under the Australian continent. Tall active volcanic mountain ranges existed along the edge of the continent much like the mountain ranges of the Andes Mountains in South America today. As our area approached the continent it meant that the size of particles increased. Erosion of the mountain ranges and continuing submarine landslides created layers in the sediments called turbidite sequences. These are sequences where the bottom is coarse grained (usually sandy) and the top is fine grained (mud). This is because fine sediments take longer to fall out of the water. Subsequent nearby landslides would start a new layer with coarse grained sands followed by finer grained mud and so on.

Eventually our part of the oceanic crust with its mass of deep sea muds and turbidite travelled to the zone of subduction where the collision with the Australian plate forced the oceanic plate under it. In this process the sediments that are on the oceanic plate are squashed and stuck onto the continent. Australia’s size grew as the process of accretion built up a thick wedge of submarine mud and turbidite. The pressure of the crustal plates sliding past each other squashed the sediments together and bent the layers into a complex arrangement of folds and faults. These are what we now know as the Neranleigh-Fernvale Beds.

As mentioned before, the Neranleigh-Fernvale Beds are the foundation rocks of our region. Today they form the ‘basement’ of the coastal Australian landmass from Gympie in Queensland to Broadwater on the Richmond River. However, in our region they are mostly obscured by younger rocks (discussed below) though it is possible to view outcrops of turbidite in several areas. These include on the Wilsons River at Laverty’s Gap, at Tintenbar and on the escarpment at Uralba between Ballina and Alstonville. Quartzite (from the silica rich sediment) is present on a hill near Nashua.

At the earlier stages of the carboniferous period the collision of the oceanic and crustal plates in our region stopped. The Neranleigh-Fernvale bed formation had been completed. The continent with its new additions ‘relaxed’ as compression eased and eventually stopped. Many more millions of years passed and what happened during that time is lost to history. No rocks are preserved in our region from the next time period known as the Permian. It is probable that the ‘bigscrub’ area remained stable for a long time with only erosion being the most significant geological process.

Wednesday, 27 April 2016

Geology dance moves

I'm moving on from my job hoping for more opportunities in the future. I was disappointed with many aspects of my position, not in the least the resistance from bureaucratic processes to fit in with geological reality! This was particularly disappointing with the search for groundwater resources which I felt seemed encumbered by the processes rather than where water could actually be found. I guess that is government, but it is sad when you feel that the public money your organization is entrusted with is poorly spent. I could have paid for my salary many times over if my advice was taken in the first place. After two years they discovered that exactly what I had said was the case! several hundreds of thousands of dollars later my top two recommendations were identified by expert consultants as the best two recommendations and we hadn't even drilled yet! A lesson for all those people that think they can understand what the environment without actually going out from behind their desk.

So it is with relief that I move on to other things. Time will tell what will happen but in the mean time I might learn some dance moves courtesy of the Amoeba People .

'The Alluvial Fan' is my first starting move:
"We think you'll agree that few things are more dance-inspiring than cone-shaped deposits of sand, gravel and silt."

Monday, 18 April 2016

History Snippet: Drake

I noticed that the Northern Star Newspaper has an interesting snippet about historical copper mineral exploration near Drake. I thought It would be worth directing readers to the article.

I've been meaning to do a detailed post on the geology outlined by Grace Cumming who in 2011 did a very detailed survey of the region and put together an interesting model which illustrates that the mines and prospects just north of Drake are actually the remnant of a very large 400 square kilometre volcanic caldera. I will get to that soon! There is always a million interesting things in our region that I seem to never get the chance to cover them all. In the mean time I can only point you to one post I've done about the 'Drake mines'.

If you are interested in the current explorer and operator of the mines just to the north of Drake here is the link to White Rock Minerals Mt Carrington project overview.

Monday, 11 April 2016

Most important movie of the year?!

An excellent song by the Ameoba People. I will be featuring some of their exceptional work all this month. Keep a look out for the Geology dance moves... and give them a go! 

Friday, 1 April 2016

A Brand New Month and a Brand New Eruption at Mount Warning

This morning started in a very interesting way. I wasn’t sure but there was some shaking of my house. I just thought it was a garbage truck going by so I thought little more of it. That was until I drove to work and looked out at Mount Warning. The clouds that hang around the peak in the morning (often to the dismay of tourists watching the sunrise from its peak) looked just a little odd shaped and darker. Again, I thought nothing of it.

What I didn’t know I had just experienced was one of the many small earthquakes that struck the region last night and continue today. You can see the latest seismic readings from geoscience Australia here. The clouds were actually not morning clouds but small amounts of ash and steam rising from the peak as a new vent opened up (the first in a very long time). Australia has not had a volcano erupt on the mainland since pre-colonial times and even those volcanoes erupted in Victoria and South Australia, no-where near our pretty part of the world.

The news websites are going very busy and I know that there are some interesting Instagram and facebook pictures going around already. I should have one of my own pictures up shortly. By all accounts there is little danger away from the mountain but people intending to visit the national park should be aware of the dangers present and not attempt to climb if they see any evidence of Holocene lava.

Saturday, 9 January 2016

A Rock of Gibraltar Range National Park - Part 2

Dandahra Creek Leucogranite
This post is a follow-on from an earlier post which can be read here.

The Dandahra Creek Leucogranite is mainly composed of granite which is depleted in dark (mafic) minerals. The crystals are of very similar size and medium to coarse grained. The crystals are mainly quartz with feldspars and occasional biotite mica. The term Leuco- simply refers to the light colour and lack of mafic minerals. There are also small amounts of other minerals that are disseminated through the rock these include the mineral zircon which is used for dating.

The dating of the Dandahra Creek Leucogranite was only conducted in the last couple of years. It is an example of using multiple techniques together to get an answer. The mineral Zircon is formed in magma chambers of granite and granite-like composition. This is a very stable mineral. Zircon locks up uranium in small amounts and this uranium undergoes radioactive decay to lead. By measuring the proportions of uranium to lead it is possible to determine how long ago the zircon had formed. In the past in some cases the whole zircon crystal have been used to determine the ratio. However, this method has some complications.

Not all of the zircon crystals in rocks show the same age. In the case of the Dandahra Creek Leucogranite some seemingly having much older ages. These crystals are actually inherited from the parent rock. The stability of the zircons means that they have not fully melted in the magma chamber. Often a good way to determine if a zircon is older than the magma chamber is to look at the shape and determine whether there has been any melting of the edges of the crystal. However, sometimes it is very hard to tell because the zircon often builds itself up again with an old core and a new crystal face.

To overcome the problem of age zoning in zircon crystals an alternative method was developed measure the ratio of lead and uranium. A high accuracy ion beam is aimed at the different portions of crystal. The ion beam vaporises the elements in that tiny area. The vapour is then measured for the abundance of each element and then the ratio of elements can be calculated. This is called the Sensitive High Resolution Ion Micro Probe or SHRIMP.

SHRIMP was a method developed right here in Australia. It is regarded as one of the most reliable ways to analyse microscopic crystals to determine when and how they formed. The need for the special machine came from dating the Rocks that make up the oldest parts of Western Australia which are the oldest in the world. It has no become a recognised tool around the world (Ireland et al 2008). There are 20 SHRIMP analysers around the world with four built in the last couple of years in Japan, China and Poland. Like Wi-Fi, the Hills-Hoist and Pavlova it is another example of Australian scientific ingenuity.

The age of the intrusion given for the Dandahra Creek Leucogranite using the SHRIMP method is 237.6 Ma (plus or minus 1.8Ma). This makes it the youngest example of the Stanthorpe Suite of Granites (Chisholm et al 2014) and nearly the youngest in the whole Standthorpe Supersuite (Thanks for the correction rockdoc!).


*Chisholm, E.I., Blevin, P.L. and Simpson, C.J. 2014. New SHRIMP U–Pb zircon ages from the New England Orogen, New South Wales: July 2012–June 2014. Record 2014/52. Geoscience Australia

*Clarke, Peter J. & Myerscough, Peter J. 2006. Introduction to the Biology and Ecology of Gibraltar Range National Park and Adjacent areas: Patterns, Processes and Prospects. Proceedings of the Linnean Society of New South Wales

*New South Wales National Parks and Wildlife Service 2005. Gibraltar Range Group of National Parks (Incorporating Barool, Capoompeta, Gibraltar Range, Nymboida and Washpool National Parks and Nymboida and Washpool State Conservation Areas) Plan of Management. February 2005. ISBN 0 7313 6861 4

*Ireland, T.R., Clement, S., Compston, W., Foster, J. J., Holden, P., Jenkins, B., Lanc, P., Schram, N. & Williams, I. S. (2008), "Development of SHRIMP", Australian Journal of Earth Sciences V55 p937–954

Thursday, 17 December 2015

ABC Radio Interview - The river that flows the wrong way!

I had the pleasure of being interviewed by Joanne Shoebridge of ABC North Coast Radio last week. The story was about the way the Clarence River flows backward!

This was my first ever live interview and boy did I um and err a lot! Hopefully the story is interesting though and the amazing story of our landscape comes out. Let me know what you think.

It was exciting to be interviewed but I also was excited to be offered a position on the National Parks and Wildlife Service Regional Advisory Committee for the Northern Rivers. Exciting to be part of a statutory board or Quango (quasi-autonomous non-governmental organisation) in Yes, Minister bureaucratic speak.