Saturday, 13 December 2014

What do people think I do

What do people think that geologists do? Well, here is one answer from the Geosphere Blog.

Sorry all for the delay in posting. Once I get my act together I will post again more regularly.

Sunday, 2 November 2014

Unconventional Gas - Gaps in Baseline Data

The NSW Office of Water has been busy compiling a series of videos on YouTube explaining various aspects of hydrogeology. This recent video is about data gaps in understanding baseline hydrogeological conditions in areas of 'unconventional' gas.

Monday, 20 October 2014

Blog Update #6

Over 100 000 page views for this blog, 3 years and over 130 blog posts. I honestly did not think that there would be so much interest in the geology of the Northern Rivers. This milestone was topped off by heaps of interest during a short presentation on the weekend at the Big Scrub Rainforest Day.

I was a little worried about my presentation since it directly followed Robyn Williams from the ABC Science Show. His whole professional life revolves around talking to an audience. I on the other hand am not used to public speaking. I wish my talk was more structured and I did not try and condense so much into it. But I think it was received surprisingly well all the same! The questions were excellent and I wish I had more time to answer them. There were still a lot of hands up when I had to hand over to A/Prof Isaac Santos from SCU for his talk.

Following the talk the 100 information sheets disappeared and many people were asking if there was more. So thanks everyone for your interest and sorry that I didn’t have more copies. The information sheets are the short articles I have recently done for a couple of the Big Scrub Rainforest Newsletter. The specific articles can be downloaded from the links below. The full newsletters can be obtained by contacting the Big Scrub Rainforest Landcare Group.

January 2013 – Mt Warning and Reading the Rocks

September 2014 – The Importance of Basalt in the Big Scrub and One CSG Related Anomaly

Regular visitors to my blog may have noticed the slightly declining number of posts over the months. This is nothing to do with a lack of subject matter. I am finding the time a little hard to find at the moment. As such, I am happy to open up this blog to guest bloggers from time to time. If you have a story about Earth Science that has even the slightest New England/Northern Rivers/ North Coast bent, please feel free to contribute to this blog. I can be contacted on the email address listed on the page “about this blog”.

Monday, 6 October 2014

Rocks in the Rocky River

Rocky River Monzogranite (Bungulla Suite).
The Monzogranite here contains large crystals of twinned pink K-feldspar.
The Rocky River Road is a very quiet, scenic and out of the way route to travel. It is slow and windy, but a pretty alternative to the Bruxner Highway route between Drake and Tenterfield. I had the pleasure of a trip along Long Gully Road and Rocky River Road just last week. I enjoyed it very much for the scenery and the clear water of the Rocky River (also known as the Timbarra River). The area is also very interesting in a geological sense. The rock that is found along Rocky River Road (the Rocky River Monzogranite) is actually remnants of outer part of a very large batholith that makes up Timbarra Tableland.

Previously, understanding of the inner rocks of the Timbarra Tableland were incorrectly thought to be Moonbi Supersuite, while the outer rocks were correctly part of the Stanthorpe Supersuite. Having two parts of an intrusion being apparently related to different Suites was all quite confused. Mustard (2004) suggested an informal renaming of the Bungulla Monzogranite in the area of Rocky River to the Rocky River Monzogranite. The Rocky River Monzogranite would in turn be part of the Bungulla Suite. The Bungulla Suite being rocks that are I-type (derived from melted igneous rocks) of the Stanthorpe Supersuite.  Although the nomenclature by Mustard (2004) was suggested as informal it is quite reasonable to adopt the name of Rocky Creek Monzogranite as formal. The previous identification of some rocks in the Timbarra Tableland as Moonbi Supersuite has since been shown to be incorrect - they are all Stanthorpe Supersuite.

The Rocky River Monzogranite is in the extensive eastern edge of the Timbarra Tablelands. It is comprised mainly of the rock monzogranite. This rock is comprised of abundant quartz and roughly equal proportions of plagioclase feldspar (sodium and calcium feldspar) and potassium feldspar. There are also smaller amounts of dark biotite mica and amphibole in the rock. The Rocky River Monzogranite is quite a course grained and the crystals are very, very large. The monzonite is notable as it has many 'inclusions' called xenoliths. These are blobs of rock are of a less granitic composition. They are very, very common in some areas as the rock comprises of about 10% or more xenoliths. The xenoliths indicate that mixing of different composition magmas was occurring when the intrusion formed.

A monzogranite tor in the sandy bed of the Rocky River.
Note different sized irregular shaped xenoliths.
Along the very margin of the intrusion (I didn't get to see this) the crystals are smaller in size and the feldspars are even more potassium rich forming the rock syenite. The central area of the Timbarra tablelands is comprised of granitic rocks that were high in fluids when the rock was crystallizing. These fluids (formed by residual enrichment of the original magma chamber), has resulted in the concentration of metals, most notably gold (Mustard 2004). The Timbarra gold mine targeted this inner zone of the tablelands as the outer granite (Rocky Creek Monzogranite) do not contain nearly as much gold. The erosion of the gold has led to alluvial gold deposits in the Rocky River and Clarence Rivers but the gold is very fine grained so fossickers panning can be tricky.

The many components of the Timbarra tablelands intrusion were emplaced in the Triassic period. They intruded the Drake Volcanics. The size of the granite plutons has caused significant contact metamorphism, creating a large metamorphic aureole around the intrusion.

There is much more to say about the zones in the Timbarra tablelands intrusion described by Mustard (2004). This includes the neatness of the tablelands cross section, the way that the slightly different granites tapped different parts of a deeper magma chamber and the way that differentiation of granite types occurred are all worthy of a discussion. Though, this needs more than just a few paragraphs and so I will have to cover these matters in future posts. In the mean time I hope this post gives a taste for some of the 'granite'.

*Mustard, R. 2004. Textural, mineralogical and geochemical variation in the zoned Timbarra Tablelands pluton, New South Wales. Australian Journal of Earth Sciences, 51.

Saturday, 27 September 2014

Big Scrub Day - October 2014

Every year the Big Scrub Landcare group and many other supporters put together a very interesting day. There are many exhibitors for those interested in natural resource management and restoration, tours of various kinds and workshops. This year is a particularly big year with the Big Scrub day occurring in conjunction with the Rous Water open day. There will be many formal presentations starting off with a key note address by Robyn Williams from ABC's science show. There will also be a lot of emphasis on what is below the ground this year with a presentations including:

  • 'geology of the big scrub';
  • 'the big scrub - a ground water dependent ecosystem'; 
  • 'future water strategy' (which involves groundwater as a key component); and
  • 'ground water and CSG'

I think this year will be very interesting so if you are in the area on Sunday the 12th of October come out to Rocky Creek Dam and have a look around. Maybe I'll see you there (I am actually presenting a short lecture). The schedule for the day is provided above.

Monday, 8 September 2014

Volcanic shockwave

A post a little off topic again today. This post is motivated by several related stories in the media. The first is a follow up from an earlier blog post where I criticised the Australian ABC for reporting an eruption in Iceland that was not even confirmed. A day or two later a large eruption occurred in our closest neighbour Papua New Guinea. The eruption was very large and was not even reported by the ABC – though it was picked up by ABC America! It occurred at Tavurvur Volcano near the mostly abandoned city of Rabaul.

On the 11th of September it will be the 100 year anniversary of Australia’s first military engagement in World War 1. Australian soldiers and sailors attacked German positions in the then German Colony of New Guinea. This first engagement, in which both Australian, German and ‘native’ soldiers were killed occurred near Rabaul. The occupation by Australian Soldiers led to Australian administration over Papua New Guinea until 1975. A short account of the battle can be read on the Australian War Memorial Website.

Finally, on the weekend a tourist recorded the moment when Tavurvur volcano erupted again. Though not as large an eruption as the initial one, the power of the volcano is clearly visible. The Youtube video shows massive lava bombs (probably bigger than cars) falling after the eruption and spectacularly a shockwave travelling through the air and hitting the camera. It is worth watching.

Too often we, in Australia forget that we have neighbours. Our news seems to be from the USA, UK a few European countries and ‘home’. But we always seem to forget our near neighbours, Papua New Guinea, Indonesia, East Timor and New Zealand. Let’s not forget the Solomon Islands and even France too (New Caledonia). I’ve previously posted on Indonesia and now I’ve mentioned in passing Papua New Guinea. These are important countries to know about and are so interesting in many ways, one of which is geology. It is beyond the scope of this blog to look in detail at these countries but we should as they affect us, even the geology of those places

Wednesday, 3 September 2014

Clarence-Moreton Basin Geology Video

The NSW Office of Water have posted an excellent video summary of the geology of the Clarence-Moreton Basin. It provides an excellent overview.