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 Supersuite of Granites in the New England area (Chisholm et al 2014).

References.Bibliography:

*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.
https://sites.google.com/site/nrgeologymediafiles/home/mp3/01%20Track%201.mp3?attredirects=0&d=1

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.


Sunday, 29 November 2015

Sediments of the Anthropocene

In my workplace I have recently had some fun improving my knowledge and application of erosion and sediment control methods. It reminds me that sometimes a little knowledge and the best intentions can actually lead to wasted time or even worse outcomes. I’d like to use this post to look at what erosion and sediment control means for sites that are to be disturbed. This is because of a construction site I visited in my town a couple of weeks ago that made me laugh (I had to see the funny side otherwise I’d always be crying!)

Is this working?
The first point to know is that erosion and sediment control is two things (erosion and… sediment control). They are not one and the same thing. In fact the most important part is the erosion control bit. If you have erosion control you don’t need sediment controls. This lack of distinction I think causes the biggest waste of resources.

Have a look at the picture here. This is a classic example of a waste of time. It is something that was never going to be the solution and inevitably failed and wasn’t even looked after anyway. In this example a small slope was disturbed. This small slope had water running on to it from a grass slope. The people responsible thought “hey, treatment: sediment fence!”… But thought nothing about fixing the problem in the first place. A better solution would have been to do one or a combination of erosion control measures. These could have included:

  • Diverting clean storm water around the exposed slope with a mulch bund or similar (many trees were chipped and removed from the area).
  • Spraying the surface with a synthetic soil stabiliser.
  • Spraying the surface with a hydro mulch or similar with grass seed.
  • Covering with a synthetic or biodegradable mesh framework which was then seeded

Is this working?
None of these things would cost much more in time or money than installing and re-installing failed silt fences. And they would have actually fixed the problem in the first place. Just to add a little icing to the cake here is another control measure that was located about 20 metres away. The good old sandbag near a stormwater inlet. At the best of times this can only be considered a supplementary technique that should never be used in isolation. In this case the sandbag has ruptured and the sand appears to have actually gone into the storm water system itself! The small amount of sediment retained seems to only be effective because of weeds growing in the gutter. No thought again, and no checking to make sure things work and no fixing of failed problems for an obviously long time.

Erosion control should always be the first focus and even when using sediment controls consideration needs to be given to whether they will even be effective. For example “silt fences” are actually not good at holding back silt. They only hold back sand! They should be called “sand fences”. Clays, silts and any dispersive soils will pass straight through a silt fence. It is important that people in the know to undertake erosion and sediment control works. This is important were ever significant disturbance is to occur or where sediment may easily enter waterways or other sensitive receptors.

Saturday, 21 November 2015

A rock of Gibraltar Range National Park - Part 1.

A lookout on the Gwydir Highway
I was going to write a very long post on the Dandahra Creek Leucogranite but I think it lends itself to two posts. This post will focus on the amazing Gibraltar Range National Park and the second will focus on Australian ingenuity and dating of the Dandahra Creek Leucogranite.

A few months ago I travelled from Glen Innes to Grafton via the Gwydir Highway. The landscape in this area is wonderfully diverse and surprisingly contradictory. For example usually Sandy soils on the plateau give rise to swamps with peat. It is a special area because the link between the geology, vegetation and even bush fire patterns is quite obvious. I'd like to focus on one rock unit that makes up the balance of the Gibraltar Range National Park area, the Dandahra Creek Leucogranite.

The Dandahra Creek Leucogranite was often referred to as the Danhahra Granite (and still regularly called this in botanical circles). It is part of the New England Batholith and has recently been dated at at 237.6 Ma (Chisholm et al 2014). It is the youngest member of the Stanthorpe supersuite of granites. Outcrops are very frequent in the Mulligans Hut area and the Gwydir highway transverses the unit.

The spectacular tors which are major features of the landscape of Gibraltar Range National Park arise from weathering from the Dandahra Creek Leucogranite. These tors form through onion peel weathering (technically called exfoliation or spheroidal weathering). This weathering process is where water enters cracks in the rocks and then freezes over night. As water turns to ice it expands and sheets off rock just like an onion skin. This is usually a fairly slow process except with the last sloughing off of the onion peel occurring quite rapidly.

Tall open forest is a major feature of the landscape of the Dandahra Creek Leucogranite. These eucalyptus dominated forests can have an open, grassy understorey featuring grass-trees and/or tree-ferns. These landscapes are quite fire prone. Indeed their structure is dependent on multi-decadal scale fires.

There are also some more unusual vegetation communities on rock outcrops because the tor outcrops lend themselves to protecting some vegetation from fires. They are also very thin soils with low nutrient content so even carnivorous plants can be found.

Heathlands and grasslands occur around the rock outcrops and are particularly important as they contain the greatest concentration of rare, threatened or geographically restricted species, or species found at the limits of their distribution (NPWS 2005). The grass and heath land burns very frequently often with bush fires only every several years.

The shallow wide valleys that are formed on the sandy granitic derived soils result in common large peat swamps. The shape of the valleys slows down water and the underlying massive granite means that the water does not infiltrate. The swamps contain sedges and other water loving plants.

If you are interested in the bush or interested in rock the Gibraltar Range National Park is for you. If you are in to camping, bush walking, amazing views of rugged valleys the Gibraltar Range National Park is for you. If you are in to spectacular flowers, rainforests, exploring a rocky creek the Gibraltar Range National Park is for you. If you are in to staying in a lodge, want to see some snow, or bathe in a rock pool on a summers day the Gibraltar Range National Park is for you.

References/Bibliography:

*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

Tuesday, 13 October 2015

Blog Update #7


Just a quick post as a bit of a gap-filler. I just wanted to mention that this blog has reached a huge milestone with over discrete 150,000 page views.

I’ve noticed that CSG related topics seem to be the most popular topics, still. I heard the local ABC radio station this morning report on the baseline CSG monitoring. For some more details I had previously posted exactly the information discussed. I like it when I’m 6-7 weeks ahead of the news cycle!

But there is a high degree of interest in many other stories too. I’m pleased to see that posts on ‘ordinary’ rocks are not unpopular. These are the very rocks that lead to the soils under our feet and the plants that grow. They are the basis for our landforms from our beaches to the rugged ranges. It is the ‘ordinary’ rocks that are the most extra-ordinary in my view. I hope that interest continues.

Thank you too for the help received for my daughter. We are about 1/3 of the way to getting to Adelaide for her treatment. Here is a link to a Today-Tonight Story that featured in Adelaide last week:

http://www.todaytonightadelaide.com.au/stories/eleanor-holland

Thursday, 1 October 2015

An appeal for help

Sometimes it is hard to ask for help. To reveal yourself as vulnerable and as being in need is hard. Being a man and the expectations that come with that to be a father, a husband, a protector and provider are not easy to do. But what happens when you realise that you can’t do one or some of those things. The only thing is to ask for help. That is what I am doing with this blog post. Forgive me for using this geology blog to ask for personal help but that is what my family is in need of.


I have a five year old daughter. She was recently blessed with a wheelchair and help with physiotherapy with the help of many people from Dick Smith to the congregation of the church we are part of. But we are now again in need. She has recently commenced a programme to get her eating again. She has not eaten food by mouth for over two years. The specialist therapists now think she should be able to with the help of more specialists and hospital support in Adelaide. The cost of this programme is immense.

My daughter, Eleanor has been thrust into the media while we ask for help. Even a Television crew are coming to our house from South Australia tomorrow morning. Eleanor has been on the Daily Mail, the Northern Star, the Northern Rivers Echo and National websites such as Mammamia. My wife blogs about her and Eleanor’s journey and there is probably the most detailed information available. But we do have a fund raising website which we are promoting and asking people to contribute. Please help us if you can.

Links to the stoes can be found here:

Northern Star

http://www.northernstar.com.au/news/shes-a-fighter/2784671/

Northern Rivers Echo

http://www.echonews.com.au/news/shes-a-fighter/2784671/

Daily Mail Australia

http://www.dailymail.co.uk/femail/article-3242690/The-little-girl-hasn-t-eaten-two-years-Five-year-old-born-devastating-health-problems-learn-eat-fed-tube.html

Mammamia

http://www.mamamia.com.au/parenting/raising-a-child-with-a-disability/


Faithfully,

Rodney Holland (Geology Rod)

Monday, 21 September 2015

Cooking the rocks at Emerald Beach

I have always been interested in the little things in life. The things that don’t get the attention that everything else seems to get. This even applies to rocks and rock outcrops. It applies to a little headland that I visited on a trip to Coffs Harbour earlier this year. The headland has no name but lies on the northern side of Emerald Beach and the village of the same name. It is made from a granite-like rock of a poorly understood suite of intrusions in north eastern NSW.

Boulder on Emerald Beach. Note the xenolith at the bottom
The rock is formally called the Emerald Beach Monzogranite. It is the eastern most granite on the Australian continent is also one of the youngest rocks in the New England area. The Emerald Beach Monzogranite has been dated at 228.5Ma and part of an informally super suite of granites called the Coastal Supersuite (Chisholm et al 2014). Originally the unit was formerly defined as the Emerald Beach Adamellite (Korsch 1978) but has been renamed to reflect the most up-to-date nomenclature. However, the name Monzonite (and hence Adamellite) is misleading. The composition of the rock is consistent with the definition of Granodiorite (Plagioclase Feldspar abundance greater than that of Potassium Feldspar (Korsch 1971, Chisholm et al 2014). No reference to Monzogranite (or Adamellite) have been made and the samples I’ve seen were plagioclase feldspar dominant so the present classification appears erroneous. Maybe the name Emerald Beach Granodiorite might be more correct.

The dating of the Emerald Beach Monzogranite 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. By this method Chisholm et al 2014 narrowed the age down to about 228.5 million years old. This is the Upper Triassic era which was the time of the best known dinosaurs.


Xenoliths of country rock are present in the rock (you can see an example in the picture above). These darker coloured xenoliths are inclusions of country rock which has been caught up in the magma chamber and have not quite been completely melted into the rest of the liquid rock. In the case of the Emerald Beach Monzonite the xenoliths are slightly elongated and display a preferred orientation. This orientation is probably caused by following the direction of intrusion of the molten rock (Korsch 1971).

The intrusion of the magma heated up the surrounding rock into which it had been emplaced. This heating up forms what is termed a contact metamorphic aureole (a metamorphic zone of effect). The Emerald Creek Monzonite had heated the muds in the surrounding deep sea Coramba Bed rocks to such an extent that new minerals were formed including very small but abundant crystals of biotite mica. Biotite mica forms at approximately 500 degrees Celsius (but varies by pressure) and disintegrates when hotter than about 800 degrees. Therefore the temperature of the molten rock was probably at least this. This type of contact metamorphic rock is referred to as hornfels.

It is an interesting example how little aspects again can tell a lot about how rock forms. Preferred orientation of xenolith inclusions and the formation of biotite in the surrounding rock show both the direction that the magma was moving and its temperature at the time. Have a look if you are in the area and see if you can spot some of the xenoliths. Those that are really in the know can say that the Emerald Creek Monzonite seems to have been incorrectly named.

References/Bibliography:

*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
*Korsch, R.J. 1971. Palaeozoic Sedimentology and Igneous Geology of the Woolgoolga District, North Coast, New South Wales. Journal and Proceedings of the Royal Society of New South Wales. Vol. 104.
*Korsch, R.J. 1978. Stratigraphic and Igneous Units in the Rockvale-Coffs Harbour Region, Northern New South Wales. Journal and Proceedings of the Royal Society of New South Wales. Vol. 111.