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.

Softer sediments in the Wilsons River Valley

I’ve recently been observing an interesting environmental restoration programme on the Wilsons River upstream of Lismore. During this programme I started to think about the flood plain of the river and ‘recent’ geological history of the area. Cotter 1998 and in his earlier undergraduate work developed a concept of the geomorphology due to the lava flows associated with the Tweed Volcano and the earlier Alstonville Basalt. I did an earlier post on the flow direction of the Wilsons River as related to the volcanic history of the area but I’ve done just about nothing on the post volcanic sequences.

The best work done on the ‘recent’ sedimentary formations of the Wilsons River valley was a PhD thesis, Drury 1982. This was done as part of the then Water Resources Commission (now State Water) back when NSW government departments actually collected new information to guide future decision making (oops, there is a political comment in there). Drury 1982 was a huge thesis that provides a vast amount of information on the development of the Richmond Valley based mainly on the groundwater bores operating at the time supplemented by some (then) new drilling and geophysical techniques. To my knowledge no significant further published scientific assessment of the Quaternary sequences has occurred since Drury's thesis was written.

Cenozoic Stratigraphy of the Lismore area

It is probably hard to follow the stratigraphy very easily so hopefully my sketch to the left which is based on Drury’s work helps. Drury 1982 indicates that the upper most layer of sediment in the Wilsons River and Leycester Creek valleys upstream from Lismore was unsurprisingly, flood plain sands, silts and clays which continue to be deposited today following floods. Conformably underlying this flood plain sediment the material encountered is called the Green Ridge formation. This formation appears to be a delta system being built at the end of the Upper Pleistocene (~12,000 years ago). Often the top of the Green Ridge Formation is cut by the Wilsons River and its tributaries, for instance at Boat Harbour Nature Reserve the lower banks of the river seem to be quite deep maybe even cutting into the even older formations (e.g. the Gundurimba Clay). Drury (1982) demonstrated that the Green Ridge formation is both contemporary with and overlies the Gundurimba Clay, which is made from estuarine clays.

The Gundurimba Clay is a unit was formed during a period of relatively high sea level (higher than the present day) and warmer conditions. Shells were common but coral was found maybe indicating the idea that the area where the Gundarimba Clay was being deposited went through a warmer spell than we experience now.  Drury 1982 identified pollen spores indicating the surrounding area was dominated by rainforest with some eucalypt forest too, in my mind this creates a picture that it was possibly a proto-‘Big Scrub’ low-land rainforest with the ‘Big Scrub’ proper forming after the next cold period at the beginning of the Holocene. However worth noting that the Upper Pleistocene is recognised around the world as starting off in a warm period turning into a glacial period with the last glacial maximum occurring around 22,000 years ago.

Drury 1982 demonstrated that preceding the deposition of the Gundurimba Clay there was a period of erosion meaning that the Gundurimba Clay unconformably overlies the South Casino Gravel. The South Casino gravel in turn uncomformably overlies the Cenozoic volcanic rocks of the Lismore and/or Alstonville Basalt. The South Casino gravel is at least Middle Pleistocene in age and is derived from the erosion of the underlying volcanics. Given its coarse nature it is highly permeable and is considered a good source of groundwater in other parts of the Richmond Valley but to my knowledge is rarely used in the Wilsons River area.

I'm probably trying to combine a lot into this one post so I'll have to tease out the details a bit more in future posts, especially that relating to the Gundurimba Clay and palaeo-environmental conditions which I know at least some of my blog readers have a keen interest in. At least I hope that this provides a starting point.

References/bibliography:

*Drury, L.W. 1982. Hydrogeology and Quaternary Stratigraphy of the Richmond River Valley, New South Wales: In Two Volumes. PhD thesis, University of New South Wales.
*Cotter, S. 1997. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of north eastern New South Wales. MSc thesis, Southern Cross University.

How cold was it? Glaciers in New England?

I was very, very pleased to receive this comment by Bob (a physical geographer by ‘trade’) a bit more than a week ago. Bob posted the comment on my blog about Point Lookout and has been reproduced below:

"Rod,

You and your readers might be interested in a discovery made around Ebor and Guyra just last week, when I was working with a team of glacial buffs from UQ and UT. We found definite evidence of periglacial activity, presumably from the Last Glacial Maximum, ~20 000 years ago. The best examples were at Guyra on the slopes around Malpas Dam -- clear evidence of solifluction lobes, rock glaciers, snow hollows, and other freeze-thaw features, and what could only be described as incipient cirques -- ponds and bogs sapping back into the escarpment and probably still holding some snow in the frigid Guyra winters. The curious point is that they were between 1200 and 1300 metres, not at the highest points above 1500m where we were expecting them, but all on steep south facing escarpments.

One intriguing feature near Point Lookout, on the road up where it crosses the Little Styx River and at 1450m, was what looked very like a terminal moraine. This of course is a glacial, not a periglacial feature, so it is very hard to believe-but have a look at it, and see what you can make of it. There were at least 16 glacial cycles in the Pleistocene, so maybe one of them at least was really severe, and glaciated this far north. Otherwise, you have to go back to the Permian...

Bob H."


probable solifluction lobes and terraces on hill slope at Malpas Dam

This is exciting stuff to hear about because to my knowledge there is little or no evidence of cold climate landforms in the region. In fact I think the areas of the Tasmania are probably the only areas in Australia were these are frequent, though they have also been possibly identified in the Southern Alps and areas of Victoria. Certainly authors such as Petherick et al. (2011) and Hope (2005) did not identify such equivalent indicators of how far north such extreme cold could be detected. I understand that the cold climate landforms that Bob mentions have been found by researchers various universities such as from the University of Queensland, University of Technology, Sydney and the University of Tasmania. Acting on the tip off from Bob, I found an example of solifluction right on the northern side of Malpas Dam using Google Maps, this one is actually visible from the lookout on the southern side of the dam too (sorry about the quality of the photos, it was a long time since I took them and I didn’t realise what I was looking at that time). Get on Google maps and visit the dam yourself and have a look.


Same solifluction lobes visible south of the hill (same hill as picture above)

Solifluction is caused from the thawing of surface layers of permafrost during the summer leading to the thawed part of the soil profile slipping over the un-thawed permafrost and creating ‘lobes’ of soil. The cold climate structures that have been identified near Guyra are present on the southern side of the hill slopes where the sun was unable to melt much of the ice in the soil and therefore creates conditions of permafrost. Permafrost is not present anywhere on the Australian mainland today and demonstrates a significant change in climate has occurred (though those that know Guyra will still argue it is still uncomfortably cold there!).

What Bob appears to have found near point lookout is even more incredible, as a moraine is formed through the action of glaciers which are accumulations of ice on the surface that slowly moves through a landscape under the action of their own weight. Glaciers in Australia were thought to be limited to Tasmania and the Snowy Mountains. No doubt we will expect to see some published papers on the structure and context of these cold climate features in the region some time in the near future. I can't wait to read the published work that comes from this discovery. 

For further information on the individual cold climate features described above by Bob  visit the glossary, an online encyclopeadia or a good physical geography book such as Geosystems by Christopherson. If you are a little unclear about the locations of these sites and how they fit into a ‘Northern Rivers’ blog then it is worth mentioning this part of the New England, at Guyra and Malpas Dam are right at the head waters of the Gara River which is a tributary of the Macleay River that runs through Kempsey. The New England Highway in the Guyra area is pretty close to the actual crest of the catchments of the northern rivers, with the rivers to the west of it flowing into the Murray-Darling Basin and those to the east to the Pacific Ocean. Point Lookout is in the headwaters of the Bellinger River which runs trough Bellingen and is also part of the headwaters of the Macleay too.

References/Bibliography:

*Christopherson, R.W., 1997. Geosystems Wiley.
*Hope, P. 2005. The Weather and Climate of Australia During the Last Glacial Maximum. University of Melbourne, PhD Thesis, unpubl.
*Petherick, L.M., Moss, P.T & McGowan, H.A., 2011. Climatic and Environmental Variability During the Termination of the Last Glacial Stage in Coastal Eastern Australia: A Review. Australian Journal of Earth Science V.58.