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.

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.


*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:

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

Northern Rivers Echo

Daily Mail Australia



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.


*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.

Friday 4 September 2015

Baseline CSG methane in groundwater

A friend recently let me know that a paper that one of his students wrote for the Journal of Hydrology had been published. I had a very minor involvement in the formative stages of the paper which came about indirectly as a result of the protests of many local people about potential coal seam gas (CSG) and other natural gas types in the region. The paper (Atkins et al 2015) is essentially the results of a data collection exercise but has some interesting techniques and findings about the baseline concentrations of gas in groundwater bores in the Richmond Valley area.

Methane concentration for different geological environments
(after Atkins et al 2015)
91 water samples were collected from government and private bores in geological units overlying the target CSG geological formations in the Clarence-Moreton Basin (e.g. the Walloon Coal Measures). These units were quite diverse and ranged from sedimentary rocks of the Piora Member of Grafton Formation and the Kangaroo Creek Sandstone (recently reclassified as the Orara Formation), basalt lava flows of the Lismore, Astonville and Kyogle Basalts and Quaternary aged alluvium including coastal sands and riverine sedimentary environments.
Special glass water sample containers were used to collect the samples. These were then injected with a carbon dioxide and methane free gas to create a clean “air bubble”. The methane and carbon dioxide naturally dissolved in the water will then come into equilibrium with the “air bubble”. The resulting gas from the bubble can then be extracted and the concentration and isotopic composition of the carbon in the two compounds determined by an electronic analyser. The isotopic signature can then be assigned to recent biological formation (biogenic) or geologically derived (thermogenic) origin.
The end result was annoyingly quite not straight forward. The concentration of methane showed no obvious relationship to the chemistry of the groundwater. However there was a relationship between geological units. Methane concentration was very low in the basalt aquifers and relatively higher than the Clarence-Moreton basin sedimentary rocks and much higher in the Quaternary alluvium of the Richmond River valley floodplain and coastal sands systems. So there was more methane in some of the aquifers that were the less likely to be connected to any CSG formations! Quite counter-intuitive.
The isotopic signatures did not really help clear up this confusion very much. There appeared to be a large thermogenic component to the coastal sands and flood plain aquifer systems sometimes at concentrations greater than the formations that should be the thermogenic CSG source. Why? It was noted by some CSIRO scientists working in the Great Artesian Basin that sometimes biogenic gas can be oxidised and then be chemically reduced back to methane and this process favours the thermogenic isotopes (Day et al. 2015). So, It gives the impression of thermogenic gas.
This means that the methane gas concentration is related to the biological activity in and around the aquifer. The shallowest groundwater systems are the most connected with surface water and biological processes and therefore these have the highest concentrations of methane. The Clarence-Moreton Basin sediments are not connected with the CSG and natural gas rich formations.
This means that if companies like Metgasco do commence gas operations in the area there is a statistical background that can be used to compare if anyone becomes concerned about methane in their water bores. Interestingly, it also shows that methane in groundwater is probably not a good method to search for natural gas in the region. It might apply to other areas like the Great Artesian basin but apparently there are good barriers between CSG and non-aquifers in the Northern Rivers. This is good news since if something does go wrong it is now more easy to identify if it has impacted upon any groundwater.


Atkins, M.L., Santos, I.R. & Maher, D.T. 2015. Groundwater methane in a potential goal seam gas extraction region. Journal of Hydrology: Regional Studies. V4.
Day, S., Ong, C., et al. 2015. Characterisation of regional fluxes of methane in the Surat Basin, Queensland. CSIRO report EP15369

Sunday 23 August 2015

Hillgrove Monzogranite

Hillgrove is known for its mining history. The fortunes of the place have been directly related to gold and antimony mining for more than a hundred years. Armidale in comparison was tiny, a village in comparison with Hillgrove at its peak. Hillgrove still operates a mine for antimony and gold but is now quite a sleepy place with a handful of inhabitants. Most people working in the mine commute from Armidale. But the mine itself is not what I want to write about, it is about the attractive rock that is known as the Hillgrove Monzogranite. Despite its name the Hillgrove Monzogranite is not the extensive source of gold and antimony that is mined in the area. Most of the ore mineralisation is either directly or indirectly related to the nearby Bakers Creek Diorite or remobilisation of material from the adjacent marine sedimentary rocks.
Hillgrove Monzogranite on the Waterfall Way

According to the Australian Stratigraphic Names Database the Hillgrove Monzogranite was until recently known as the Hillgrove Adamellite (Adamellite being the outdated synonym for Monzogranite). It was previously classified as part of the Hillgrove suite which in turn is part of the Hillgrove Supersuite.  However, based on geochemical properties (and possibly just to confuse people) the Hillgrove Monzogranite is no longer considered part of the Hillgrove suite instead just being a member of the Hillgrove supersuite! However, it is clearly one of the S-type plutonic rocks collectively known as the New England Batholith (Bryant et al 2003).

Monzonite is unsurprisingly the dominant rock type of the Hillgrove Monzonite. It is an S-Type granite (derived from melted sedimentary rock). It is comprised mainly of quartz and feldspars (roughly equal potassium feldspar and sodium-calcium Feldspar), quartz, biotite mica and hornblende. The biotite often shows a foliation, which is a preferred alignment in the rock. The age of the Hillgrove monzogranite is estimated at between around 270 to 290 million years. To my knowledge, the age has not been directly measured but instead is based on its relationship to the surrounding rocks with their either calculate or approximate ages.

The landscape formed by the Hillgrove Monzogranite is one of my favourites. It forms a relatively large plateau which contains low rolling hills and lovely boulder outcrops. These outcrops often form lovely torrs (see pictures) formed by “onion-skin” weathering. Water enters cracks in the rock and during winter this freezes and expands gradually wedging the layers off the boulder. This is correctly termed frost wedging.

The Bakers Creek gorge has cut into some of the unit near the Hillgrove area but overall the appearance of the country is quite gentle. The rock unit extends a long distance from the location of Argyle in the west almost to Chandler Gorge in the east. The Waterfall Way (Armidale-Dorrigo Road) crosses in and out of the Hillgrove Monzogranite and Girrakool Beds into which it has intruded. Therefore it is an easy stop on the road when travelling this route.

The soils are sandy and not very fertile leading to an area used for cattle and sheep grazing on native and improved sown pastures. The forest is an open dry sclerophyll snow-gum type bush which is one of the typical environments of the New England high country. I love the appearance of this country. It is the quintessential high-lean New England landscape.
*Ashley, P.M. & Craw, D. 2004. Structural controls on hydrothermal alteration and gold-antimony mineralisation in the Hillgrove area, NSW, Australia. Mineralium Deposita v39.
*Bryant, C.J., Chappell, B.W. & Blevin, P.L. 2003. Granites of the Southern New England Orogen. Abstracts of the Ishihara Symposium: Granites and Associated Metallogenesis. GEMOC, Macquarie University

Friday 7 August 2015

Don't you hate it when...

Don't you just hate it when you have information to share but you are not permitted by contracts and commercial in confidence so share it? Our society is more and more being constrained by bureaucratic regulations set up by people who are career managers but have very little understanding of the real world. Little understanding that science and engineering knowledge benefit all people and that some perceived public image issue is more important than the wider good. This means that innovation can be stifled... at least in my personal opinion. The perceived public perception of scientific discoveries hinders the development of knowledge from Climate Change to Panadol!

By way of one a specific local example, I was helping an environmental centre have a ground water bore installed. The Department of Education which runs the environmental centre put absurd restrictions on access to the groundwater. One such limitation was that school children had to wear gloves when touching the groundwater in case it was contaminated. After running some tests it is apparent that the groundwater is actually better quality than the filtered tank water that they are currently drinking... but still the safety controls need to be in place! I'm happy to drink the water but the children must still wear gloves... go figure!

Another example is a cutting edge research project in the Woodburn-Evans area. The information gained from this research is very important for most coastal sand groundwater systems in eastern Australia. Alas, the words from a senior manager in a NSW government department are that no scientific information gained from the research is to be released to the public in the short term. What a shame. I understand that people are risk adverse today especially with regards to perceived public opinion but I don't think scientific knowledge should be hidden away.

On a slightly different note I have received a copy of an in-press paper on Coal Seam Gas monitoring in the Northern Rivers area. I provided some minor assistance in the paper and so an author kindly showed me before it was published. It is expected to be released in a few weeks and is likely to be in the newspapers too. Keep an eye out for those three letters C, S & G.
Sorry for the rant... just had to get that off my chest... hopefully a less opinionated post coming up shortly!

Tuesday 14 July 2015

Northern Rivers Geology Immortalized by the National Library of Australia!

People will have noticed that I have been very quiet of late. Unfortunately there are many family matters which are taking all my spare time and therefore this blog is suffering in the short term. The local newspaper ran a story about my family that may help to illustrate where my efforts are presently focused. A big thanks to Lismore City Lions Club, the congregation at Cross Roads Presbyterian Church and many anonymous donors who have helped our family recently.

However, even though I've been unable to post further stories on this blog I was chuffed to be contacted by the National Library of Australia seeking permission to be added to their web archive called PANDORA. The National Library describes PANDORA thusly:
The National Library's PANDORA web archive has been building a collection of Australian websites since 1996. Many of the significant sites preserved by PANDORA, such as the Sydney 2000 Olympic Games website are no longer available on the web.
So, wow! A big honour to be asked and one that I will accept. I was wondering what would happen to all my posts if blogger hit the wall. 

Thursday 14 May 2015

New England Geological Tour 2015

Just a quick note to let people know that the Australian Institute of Geoscientists (AIG) and the Geological Society of Australia (Queensland Branch) will be jointly running a field trip to the New England area of New South Wales and southern Queensland over the June long weekend 6th to 8th June). The field trip follows a one day seminar by the AIG. 

Geoz reports thusly:
6 - 8 June 2015 GSAQ–AIG Field Conference: New England District Regional and Economic Geology
A joint GSA–AIG field trip to the New England Orogen, with a preceding one-day seminar.
As a prelude to the Field Conference, GSAQ and Queensland Branch of the AIG
are proposing to run a one day seminar “New England Orogen, Regional and Economic Geology - an update” to showcase recent advances in the understanding of the New England Orogen.
 The main focus sessions of the pre-field trip seminar will include:
  • The New England Orogen – geology, granites and tectonic setting
  • Mineralisation styles of the northern and central New England Orogen
  • Geochemistry applications in the New England Orogen
  • Intrusive related mineralisation styles of the southern New England Orogen
The Field trip will start from Brisbane and and include tours and presentations in the Stanthorpe, Texas, Tenterfield and Drake areas.

Accomodation and some meals are included in the cost of the field trip. For more information on the field trip contact the GSA or AIG, for more information on the Brisbane pre-trip seminar contact the AIG.

Friday 3 April 2015

Jesus’ Easter: a geological tour

Limestone is not common in the Northern Rivers but there are several
small locations where it does occur (This picture is from near Tabulam).
Since this is the first day of Easter where Christians remember the death and resurrection of Jesus at Jerusalem, I thought I’d give some background by way of the geology of the city. Like all landscapes the landform that makes up the hills and valleys around the Holy City can be seen in the geology.

At the festival of Passover Jesus entered the city of Jerusalem from the western side from Bethany. Passing into the Kidron Valley and then up to the city. At Bethany the rock types are dominated by Cretaceous aged chert and chalk of the Mishash formation of the Mount Scopus Group. These rocks are typically marine deposited sediments made from the build-up of microscopic creatures called diatoms. Descending into the Kidron Valley the chert which caps the hills to the east of the city gives way to chalk and claystone which is much more erodible. This chalk and claystone is the Menusha Formation which is the earliest formation in the Mount Scopus Group.

Stratigraphy of the Jerusalem area
Image courtesy of  Dov Frimerman
Ascending into Jerusalem the geology changes to limestone of the Nezer and Shivta formations of the Judea Group. The limestones of the Judea Group dip at an angle of around 10-15 degrees. This means that any ground water travelling though the limestone flows to the west to the sacred springs along the top of the Kidron valley. The garden of Gethsemane where Jesus spent his last night praying is in the area of these springs.

The limestone is the rock that underlies all of the places where Jesus spent his last days. Jesus drove people from the Temple claiming that they were stopping people from reaching God. The foundations of the Temple are built on this limestone. Jesus was placed on trials for treason at the Roman governor Pontius Pilate’s palace and also at King Herod’s Palace around Mount Zion. Again, these places were built on the same Limestone.

The exact place of Jesus’ execution and burial is the subject of some debate. There appears to be a couple of alternative sites but all of which are in areas were limestone is dominant. This is particularly evident with the description of Jesus being crucified ‘near’ the city and the description of Jesus being buried in a cave. The old city of Jerusalem was built entirely on the Judea Group and limestone landscapes are very well known for having many cave systems. Caves are well known in the area around Jerusalem.

In the Northern Rivers of New South Wales there is a mountain called Mt Jerusalem which is part of the world heritage system of National Parks around the Tweed Valley. But the geology of Mount Jerusalem, NSW is a post for another day.

Want to see more? Here is the Israeli geological survey’s 1:25 000 scale maps of the country or here is a good website describing the geology of Israel in more detail. To find out more about Jesus during his last days the accounts of his apostles in the Bible is the most detailed description that remains. There are other references from other sources such as Josephus and Tacitus but nothing as comprehensive as the accounts of Matthew, Mark, Luke and John in the Bible.

Saturday 21 March 2015

Bedding with crossbedding through it

Cross-bedding in sandstone of the Evans Head Coal Measures
Shark Bay - Evans Head area
Cross-bedding is a common feature in many of the Mesozoic aged sedimentary rocks in our region particularly in the Clarence-Moreton Basin. Cross-bedding is a structure that can be confusing. However, is it is often very useful for understanding how a sedimentary rock is laid down. Because it is common in our region I thought it might be interesting to describe what this feature is.

Cross bedding forms in sedimentary rocks that have undergone transport. It is most easy to find cross bedding in sandier sediments that have been deposited in Aeolian (windy) and fluvial (riverine) environments. However, it is a feature that may be found less commonly in shallow marine, and estuarine environments but these processes are a tiny bit different and more complicated to describe, so I’ll deal with them some other time.

Sketch showing how cross-bedding is formed
The feature can be confusing especially because the cross-bedding can be mistaken as actual bedding layers. However, technically speaking, cross-beds are always laid down within the same bed. The cross-beds in a riverine environment form when the water in a stream loses energy and its ability transport sediment. The sediment then drops out of the water and is deposited along a point bar. Over time the river may dry up or migrate away and the point bar (now one big bed with cross-bedding) can then be preserved.

Cross-bed sets in sandstone of the Orara Formation (Kangaroo Creek Sandstone)
Eden Creek - Kyogle Area
Often sets of cross-bedding are present where the river will deposit another point bar over the top of the original. When this occurs the new bed usually erodes the upper part of the original bed. This is a useful bit of information because in some areas the rocks have been so deformed that it can be hard to tell whether they are upside down or not. If you are able to find cross-bedding in these rock looking for the erosion surface will tell you whether the rocks are right way up or have been turned over. It may be surprising to note that over turned bedding is actually common in the metamorphosed sediments in the New England and Tweed region. Since deformation of the Clarence-Moreton Basin has been relatively small it is unlikely that you will come across in-situ rocks that have been turned over in this basin.

The two pictures show examples from some of the oldest rocks of the Clarence-Moreton and Ipswich Basins and the one of the youngest. Despite being laid down up to 100 million years apart the manner of deposition of these two separate units was a very similar riverine environment. Nearly any outcrop of Orara Formation will show cross-bedding. So keep a look out at road cuttings or sandstone quarries.

Monday 2 March 2015

Do you trust a geological map? (Part 2)

In an earlier post I showed an example of how making the assumption that published geology maps are correct has some big problems. In that example it was the digging of test pits where coal was uncovered which clearly showed the mapping was wrong. Since that post I found another example and this one only needed a look out the car window to know that something was wrong!

My interpretation of the geology of the area in question
Note that the area is approximately 7km across
I had a 4WD day a few weeks ago in the Bungabee State Forest between Lismore and Kyogle. The state forest is located on the southern section of the Mackellar Rangers. It is a nice area but as usual for the Richmond River catchment is invaded by noxious and environmental weeds (In fact the worst variety of weeds I saw that day was at the National Parks managed Muckleewee Mountain Nature Reserve). But I digress... It was during this 4WD trip that I looked out of the window! Where there were cliffs or rocks exposed in streams I glanced out and saw that they were clearly Clarence-Moreton Basin sedimentary rock. I didn't think this was particularly unusual at the time but when a quick opportunity arose I had a closer look.

Present mapping (Brunker et al 1978)
Area is the same as my map above
At the base of the range (near Muckleewee Mountain Nature Reserve) I broke off a fresh bit of rock from a cliff face. The ‘fresh’ sedimentary rock was a rusty brown colour. It was composed of grains that were made from other rock fragments, from feldspar and from quartz. I'd call it a litharenite according to the classification of Pettijon et al (1987), however I might have underestimated the amount of clay particles in it. The appearance of the litharenite was quite dull. I consulted a geological map that night and noticed that the area was not even mapped as sedimentary rock. It was mapped as Lismore Basalt, old lava flows. There were however some areas on the map, a few kilometres away that did have some sedimentary rock (mapped as Kangaroo Creek Sandstone). However, the Kangaroo Creek Sandstone has a distinct saccaroidal texture, a sparkly sugar grained appearance. It was clearly quite different to the rock I was looking at. The only thing that looked consistent to me was larger scale features in the cliff faces showing cross-bedding. However, cross-bedding is a very common feature in most of the Clarence Moreton Basin.

So, with my field observations mind and while reviewing a new stratigraphic guide for the youngest members of the Clarenece-Moreton Basin, the rock I was looking at appeared to be consistent with the expected rock in the Bungawalbin Member of the Orara Formation as defined by Doig & Stanmore (2012). See this previous post for more details. When I found some spare time I did a quick remapping of the area based… As you can see from the pictures my mapping is quite different. This again just goes to show that a geological map might not give you an answer. It is best to look in the field and deeply consider what you find.

*Brunker R.L., Cameron R.G., Tweedale G. and Reiser R., 1972, Tweed Heads 1:250 000 Geological Sheet SH/56-03, 1st edition, Geological Survey of New South Wales, Sydney
*Doig, A., & Stanmore, P. 2012. The Clarence-Moreton Basin in New South Wales; geology, stratigraphy and coal seam gas characteristics. Eastern Australian Basins Symposium IV. Brisbane.
*Pettijohn, F.J., Potter, P.E., & Siever, R. 1987. Sand and Sandstone. Springer-Verlag, Berlin

Monday 16 February 2015

Eidsvold Earthquake 2015

I woke this morning to the news that a town to the west of Bundaberg had experienced a substantial earthquake. Well, substantial by Australian standards anyway. Geoscience Australia gives the intensity of 5.2 on the Richter scale. The quake occurred at about 2am local time (3am for those of us in the other eastern states coping with daylight saving).

The preliminary report from Geoscience Australia can be found here.
Seismograph from Eidsvold Station
It is in an interesting area because the area of the earthquake is in the northern part of the New England Orogen. This belt of squashed rocks extends from the Bundaberg area in a big arc all the way to Port Macquarie in the South. There are many faults in this area and some are still active, although they are generally small. An earthquake between Gunnedah and Tamworth in 2013 springs to mind.

The scale of the earthquake is quite large for Australia. Indeed the Newcastle earthquake was measured at 5.6. I've not done the maths but the new Eidsvold quake of 5.2 is about half the size of the Newcastle one (The Richter Scale is NOT linear).

Historically, the area is prone to small to medium sized earthquakes with Bundaberg being hit by a size 6.0 in 1918. This is nearly ten times more powerful than the most recent one though the 1918 quake occurred just off the coast.

Oh... and humour starts quickly:

Monday 12 January 2015

Guest Post - Dynamic beach sediments

Thank you to Dylan Gilliland for providing this guest post for us.

We all enjoy going to the beach but not every beach is the same. There are distinct differences between a north facing beach and a south facing one. An example of this is the Clarkes beach and Tallows Beach at Cape Byron. Most of the sand that makes up the beaches of the North Coast is derived from the granites of the Great Dividing Range. These granites are eroded and discharged into the coastal regime by flooding rivers. A smaller portion of the beach sediment is derived directly from the headlands and can sometimes form boulder beaches as seen at Lennox Head and Angourie near Yamba. This process has been in effect for at least 65 million years since the break-up of Gondwana and the opening of the Tasman Sea.

Once the sediment is incorporated onto the coastal fringe it is then subject to size sorting and further transportation. This is done through wind, wave and currents off the Tasman Sea which is predominantly from the south to the north and is due to anticlockwise flow of high pressure weather systems that dominate the Australian continent particularly during winter (Short and Woodroffe, 2009). This gives rise to the term that many earth scientists refer to as "the great river of sand". It has played an integral part in the formation of the Morton, Stradbroke and Fraser sand islands.

On a smaller scale, size sorting and northerly transportation affect a beaches shape and composition. This will ultimately dictate how we interact with it. An example would be to examine the location of where to launch a boat. This is usually done in southern beach corners as it is not only protected from waves but the beach has a very gentle slope and the sand is very compact allowing vehicle access without sinking in the sand. What causes this? Headlands form barriers to the dominant southerly swell and will deflect wave energy past the southern corners. This will leave the northern expanse of the beach exposed to the full force of generated wave energy. Therefore, many east coast beaches particularly long beaches develop a zeta-curve shape much like the curve inside a spiral shell.

The amount of energy to reach a beach has a profound effect on the mechanics of sand grains and where they are distributed. In the southern corners there is less energy directed toward the beach therefore smaller particles will be able to settle without being swept away. The smaller particles pack together tighter than large particles and this reduces the beach porosity. When waves wash up the beach it doesn’t soak into the sand dumping its load, instead any particles will recede with the wash resulting in a beach with a low incline and hard packed sand. The northern end of the beach will exhibit characteristics typical of a higher energy environment with coarser sand that has a higher permeability. This can result in a steeper, less compact beach. These can often have formations such as swales, berms and cusps. This is due to waves coming up the beach loaded with sand that gets dumped higher on the shore. The water percolates quickly into the beach and it doesn’t wash the sand back out into the surf zone. For these reasons, near-shore sand bars on the northern end of a beach can be hazardous to inexperienced swimmers due to steep drop-offs, currents and instability.

Beaches are highly dynamic systems that are constantly changing; they are constrained by local geology and dominated by regional weather systems. These dynamic systems give us the beaches that people enjoy so much and the coastal erosion many people fear.

This information is adapted from field notes taken from a coastal geomorphology course conducted by Dr Robert Baker at The University of New England.


*Short, A.D. and Woodroffe, C.D., 2009. The Coast of Australia. Cambridge University Press

Thursday 1 January 2015

The name of Paddy's Emu? At last a good answer

Paddy's flat is an area that many consider the middle of nowhere. It is not a well known area but it probably should be. There is a nearby place called Pretty Gully and this name gives a better indication of the Paddy's Flat area. It is some of the headwaters for the mighty Clarence River and includes major tributaries such as the Cataract River and Emu Creek. Researchers have returned to the Paddy's Flat area numerous times for more than a hundred years to try and resolve the tricky geology. But agreement on the geological relationships of the area has been mainly unreachable. However, one of the latest papers in the Australian Journal of Earth Sciences may have resolved many of those issues.

Gideon Rosenbaum and his team from the University of Queensland has been responsible for huge advances in geological knowledge in the Northern Rivers headwaters. The latest paper from Gideon Rosenbaum's team (Hoy et al. 2014) is another for which we should be thankful. The level of research by local universities is sadly very close to non-existent and one of the preeminent research universities has thankfully filled some of the gaps. But, I digress. What is so great about the Hoy et al (2014) paper?

The many ideas about the Stratigraphy of the Emu Creek Block.
from Hoy et al (2014)
There are many great things in Hoy et al (2014) but to me the biggest is something I've struggled with for a few years. It is how and when the area formed. It demonstrated that some of the rocks of the area probably formed in the same geological environment and time as those to the west of Tamworth. Hoy et al (2014) has resolved the three stratigraphic units of the Emu Creek Block. In doing so has demonstrated that the block was formed during the late Carboniferous period. This was when a great unit of subducting crust was sliding from the west under the New England region to the east. According to Hoy et al (2014) the rocks seem to have been deposited in a shallow ocean basin (a fore-arc basin) formed at the front edge of a chain of volcanoes (a volcanic arc). A modern day active fore-arc basin is the area between Sumatra Island and its offshore islands in Indonesia. This means it was the same processes that occurred in the Tamworth area. At the same time it showed just how big the continental collision zones were that created the New England region.

In proposing a new stratigraphy for the Paddy's Flat area, Hoy et al (2014) has now come close ending more than 100 years of head-scratching. There has been more than eight different relationships proposed for the units in the Emu Creek Block starting from the first in 1906. The best one until now was probably the Geological Survey of Queensland (Murray et al 1981).  Hoy et al (2014) proposes that the youngest unit in the block is the Emu Creek Formation which is overlain by the Paddy's Flat Formation which was deposited after a haitus. The Paddy's Flat Formation is then overlain by the Razorback Creek Mudstone. Hoy et al (2014) dated zircons in the rocks using the uranium and lead composition and compared this with the age of the fossils found in the area. The results were inconsistent with the Paddy's Flat fossils. This lead to the conclusion that in-situ fossils are present in the Emu Creek Formation but probably not in the Paddy's Flat Formation. Any fossils that were found within the Paddy's Flat Formation were probably eroded out of the Emu Creek Formation. Coming to this conclusion brings to an end to so much confusion that was present.

Once the Emu Creek Block were formed along with its related rocks from Coffs Harbour to Texas through to the Tamworth area, there was large scale bending of the New England area. So much so that the western facing fore-arc basin at Paddy's Flat was bent around so that it seems to be facing the north-east. This is what Rosenbaum (2012) terms the Coffs Harbour and Texas Oroclines and is the biggest but largely unknown tectonic features of our part of Australia. But more about that in a future post.


*Hoy, D., Rosenbaum, G.,Wormald, R. & Shaanan, U. (2014) Geology and geochronology of the Emu Creek Block (northern New South Wales, Australia) and implications for oroclinal bending in the New England Orogen. Australian Journal of Earth Sciences. Vol8.
*Murray C., McClung G., Whitaker W. & Degeling P. (1981) Geology of late Palaeozoic sequences at Mount Barney, Queensland and Paddys Flat, New South Wales. Queensland. Government Mining Journal V82.