100,000 Geotourism Maps

Geoz had an article this week titled New South Wales holidays all mapped out. This article refers to a new map which has been developed which should help those that would like to know more about the physical features of the areas they are touring. The Geoz article is reproduced below:

The first state Geotourism Map in Australia has been released by Cartoscope Pty. Ltd. This NSW map features 96 sites and has an accompanying website so that users can get extensive geological detail in layman's terms and maps on each site. The map was supported by a TQUAL grant and sponsors helped lessen some of the costs. So far 15,000 of the 100,000 maps have been distributed mostly to visitor centres and many to secondary schools science departments. The map is receiving very favourable comments both from geoscientists and tourism information services. Accompanying website: http://bit.ly/XUsS9m

There are several areas which relate to our Northern Rivers:

• Mid North Coast
• New England
• Northern Rivers

I hope you find something for your area or something you’d like to look at while travelling through.

An excellent outcome from atmospheric atomic bomb testing

Human ingenuity surprises me again and again, especially the efficiency in which we can annihilate each other. During the 1940’s and 1950’s the superpowers were focused on increasing the efficiency in the way they could destroy everyone on the planet. It was a very worthy goal (yes that was a joke) and to achieve maximum efficiency they needed to conduct atmospheric tests of their bombs. Sometimes, unforeseen obvious benefits other than the benefits of death and destruction of humanity can arise.

I have recently been thinking about groundwater in the Richmond River area for which I have been consulting sections of a PhD thesis written by Leonard Drury in 1982 (Drury 1982). Drury's comprehensive thesis included qualitative identification on the age of groundwater in aquifers in the Richmond River by using an unstable isotope of hydrogen called tritium. Hydrogen is an atomic component of water (the H in H2O) but hydrogen actually comes in three natural forms based on the number of neutrons are in the nucleus of the hydrogen atom. These different forms are called isotopes. Hydrogen naturally has one neutron or less commonly two neutrons (called deuterium) and very rarely three neutrons (called tritium). In nuclear explosions the third isotope tritium, is created at concentrations much higher than the background. The reason why tritium is rare naturally is that it is only formed in the upper atmosphere but is unstable and loses the extra neutrons to become a smaller isotope over a period of time.

Half of the tritium in a given amount of water (or whatever) decays over a period of 12.5 years (this is called a half-life). Which means that over 25 years there is only a quarter of the original tritium left, 37.5 years one eighth, 50 years one sixteenth etc. Since tritium is not naturally occurring there is no practical use to measure for tritium unless you can introduce it into a system as a tracer and then measure its behaviour. This means that a large ‘slug’ of tritium was created during the 1940’s and 1950’s during atmospheric nuclear testing. Therefore if you can look for tritium in groundwater and if it is not present you can assume that that groundwater has been in existence for more than 50 years, i.e. it was present in the ground before any nuclear tests. If you detect tritium in several locations in an aquifer the relative abundance of the tritium will give an indication of the age of the water and whether mixing is occurring between old groundwater and new groundwater. It won’t give you an exact date but it will let you know a lot about behaviour of an aquifer.

The trouble is time is running out. The half-life of tritium means that as time goes on the ability for us to accurately measure the smaller amount of the isotope means that one day we won’t be able to use this as a technique. I was aware that time was running out on using tritium as an effective groundwater tracer but I was not aware how soon. I have had a few chats with an academic at Southern Cross University one of which was about using tritium, he said we actually only have about 5 or 10 years left to which I jokingly suggested to him that we should reset the tritium clock with some more atmospheric nuclear explosions! To which he informed me that actually there appears to be some more tracers that can be used following the Fukushima Nuclear Accident.

Bibliography/References:

*Drury, L.W. 1982. Hydrogeology and Quaternary Stratigraphy of the Richmond River Valley, New South Wales. University of New South Wales, PhD thesis.
*Moran, J.E. & Hudson, G.B. 2005. Using Groundwater Age and Other Isotopic Signatures to Delineate Groundwater Flow and Stratification. University of Illinois.
*U.S. Geological Survey (USGS), 2004, Stable Isotopes and Radiochemicals, in National Field Manual for the Collection of Water-Quality Data, Chapter A5 Processing of Water Samples. USGS Techniques of Water-Resources Investigation

More climate clues on the Northern Tablelands

In January last year I did a post called How Cold Was It? Glaciers in New England? that showed evidence of peri-glacial features in the Northern Tablelands of New England, specifically in the area just to the east of Guyra. Bob H, gave me a tip-off for these interesting features which went unnoticed for a long time – including by me. I’d even taken a photograph of a solifluction lobe and not identified its true nature! It is important to know that Solifluction lobes and other peri-glacial features such as cirques are not glacial features per se. However, Bob did mention a probable moraine elsewhere in the New England, specifically, near Ebor in the vicinity of Duttons Trout Hatchery. A moraine IS a glacial feature. Because of these interesting features and because that part of the country is wonderfully beautiful I have wanted to do a road trip into the area but as yet have not been able to. The best I’ve been able to do is look at Google Maps but at least even consulting Google you can find some little gems.

A Google Earth image of the area to the North of Wollomombi

While looking at Google Maps I recognised more evidence of peri-glacial features in the Wollomombi area, which is about 20km to the south east of where the above-mentioned features were identified near Guyra. Here too was evidence of solifluction (movement of soil due to the partial thawing of summer permafrost). I’ve not been able to identify with certainty any other evidence of solifluction or related features even in the higher (and therefore colder) parts such as Ebor. Maybe, it was the case that during the last glacial maximum (about ten to twelve thousand years ago) only isolated areas formed permafrost - seemingly small areas of south facing hills.

However, when noticing the places where periglacial features are present such as east of Guyra at Malpas Dam and those I just noticed north of Wollomombi, I thought that they seemed only to be present on hills that looked like they had soils derived from basalt rock. Indeed, upon inspection of the geological maps it became apparent that the only places where I can see these peri-glacial features are mapped as being on Cenozoic aged basalts. The map shows the south facing hills that are derived from other rock types such as granites and meta-sediments do not show the same evidence of being affected by permafrost or related processes. This is interesting because there are two possible reasons for this:

1. There was only isolated areas that were cold enough to maintain permafrost during the last glacial maximum; or
2. The soils derived from granites and meta-sediments did not preserve evidence of permafrost

Given that the solifluction lobes evident at both Wollomombi and Guyra are about 20km from each other I would suggest that it is unlikely that the effects would only occur in these two areas and not in the area in between, so option 2 is the most likely. This may have the following implications:

• Zones of permafrost (peri-glacial environments) and maybe small glacial environments probably existed in frequent patches on south facing slopes all the way between Guyra and Wollomombi and maybe even further to Ebor an area 60km long;
• The soils in this area are derived from three major types consisting of Carboniferous aged Meta-sediments of the Girrakool Beds and Sandon Beds, Permian and Triassic aged New England Batholith ‘granites’ of the Abroi Granodiorite, Rockvale Monzogranite and Round Mountain Leucomonzogranite and finally Cenozoic aged ‘basalts’ including the Doughboy Volcanics and others which are unnamed;
• Only the soils derived from the basalts have properties available to behave in a manner which produces and or preserve the evidence of permafrost in features such as cirques and solifluction lobes.

A Google Earth image of a spot next to Malpas Dam near Guyra.
Here the solifluction lobes are comparatively big

So, what does this mean? Well, it means that it was very cold over a large area in the New England. So much, that during the last glacial maximum, water was permanently frozen in the soil in south facing topographic areas over a widespread region extending at least from Guyra to Ebor. But, evidence for this was only preserved in the soils derived from basalts (I need to consult a pedologist (soil scientist) to figure out exactly why this might be the case).

So, if you are shivering and experiencing snow flurries in the area during winter, know that you would have been shivering harder had you been there about 20 000 years ago. It makes me wonder if the indigenous people of the region experienced that cold or whether the land was too cold and marginal for them to live there at that time.

A Volcanic Sedimentary Rock

My Wife and I have been in South Brisbane for a few weeks while my daughter has received treatment in a hospital there so I have not compiled any posts on the geology of the Northern Rivers during this time. However, I thought it might be worthwhile to tell you about an interesting rock I found in Brisbane that is of a type that can occasionally be found in the Northern Rivers especially in the New England Tablelands.

One morning while walking to the hospital, down the driveway of the apartment I was staying at I caught a glimpse of a rock fragment that was different to what I had previously seen in this area. The driveway was cut into weathered old Paleozoic aged rock called the Bunya Phyllite. But the rock fragment that I saw of interest because it was quite different from the phyllite as it had a large quartz cobble in it. Later when walking back to the apartment I had a closer glimpse. It appeared that this rock had fallen down the slope and there were other rocks inconsistent with the phyllite. I picked the piece up that first got my attention and washed it clean. It was a conglomerate, with large rounded clasts of quartzite and basalt and an angular clast of the aforementioned phyllite. The clasts were cemented together with a grey material with small angular crystal fragments. All of this was a surprise until I remembered that I was close to Kangaroo Point which is a cliff line made from a volcanic rock called the Brisbane Tuff part of a Triassic aged volcanic terrain.

It was apparent that what I had was conglomerate formed in the throws of the volcanic eruptions that created the Brisbane Tuff. The Roach (1997) and earlier authors interpreted the Brisbane Tuff as series of pyroclastic flows, surges and air falls that were deposited in pre-existing valleys formed during the Triassic. The valleys probably have had rocky streams evident from the rounded nature of the clasts in the conglomerate. After or during an eruption of the volcano combined with a lots of rain or the failure of a natural dam or lake a mud flow probably ran down the valley mixing all the rock, debris, mud and what ever got in its way stopping after the energy had been spent. The conglomerate would then have been covered and preserved by material from subsequent eruptions.

The sort of volcanic related mud flow described above is called a lahar. They are actually quite common in modern volcanic terrains but are often quickly eroded away so tend to be a little less common than would be expected in older volcanic terrains. Lahars are part of a larger group of volcanic-sedimentary rocks called volcaniclastic rocks. Volcaniclastic rocks are found in the Northern Rivers areas, particularly in the areas of the escarpment and tablelands where the Permian (pre-Brisbane Tuff) Wandsworth Vocanic Group is present (Barnes et at 1991), (The Wandsworth Volcanic Group includes such diverse units as the Annalee Pyroclasics near Armidale to the Drake Volcanics near Drake). The group is very extensive and deserves to be considered in several future posts. It is also worth noting that the Brisbane Tuff was deposited at the same time in a similar way as the Chillingham Volcanics which filled the bottom of the Ipswich Basin and now outcrops in the Tweed and lower Richmond River Valleys.

References/bibliography:

*Barnes, R., Brown, R.E., Brownlow, J.W. & Stroud, W.J. 1991. Late Permian Volcanics in the New England - The Wandsworth Volcanic Group. Quarterly Notes of the New South Wales Geological Survey.
NSW geosurvey quarterly notes, 84.
*Roach, A. 1997. Late Triassic Volcanism of the Ipswich Basin. Macquarie University, PhD Thesis.