Friday, 27 March 2015

Geology Field trip 3 Wee Jasper

An excellent day!

We had a very easy drive in to Deakin, despite the early start and set off on time.  It was a tad disquieting to find a couple of overweight cyclists taking up the whole road going down into Urriara Crossing.  There were quite a lot more of them just over the Crossing.
Apparently they were heading for Sydney, and had chosen a scenic route.  Some of them must have been from overseas as they didn't which side of the road to ride.
Others were on the right side of the road (just) but averse to the soft shoulder.
Stone the crows - at the end of Fairlight Rd (about 5km after the Crossing) they all seemed to be having another rest period.  Fortunately we were able to get past them all and head off to Taemas.

The business there was spotting the limestone outcrops, forming the eastern side of the anticline of which we were to see the Western side at Wee Jasper.
After Crossing Mountain Creek many more outcrops were visible  on the lower LHS of the road towards Wee Jasper.  I really like the interaction of the outcrops with the interlocking spurs here.
After a morning tea break at the Fitzpatrick trailhead we moved to the vicinity of Carey's Caves.  Here we could see red soil (and pebbles in a watercourse) in front of dark limestone outcrops going up the hillside.
The red coloured material is of a Silurian nature, while the limestone is the last marine deposits of the Devonian period.

Here is some more of the limestone decorated with Kurrajong trees.
The Kurrajongs seem capable of getting into small fractures in the limestone, despite the apparent lack of a sol substrate.
And then they might form interesting shapes ....
.. while dropping seed pods all over the place.
Many of the limestone outcrops showed this grooved, or pleated, weathering.  This is due to slightly acid rain carving small channels.  The white colour is lichen rather than as I suspected guano from raptors using the rock as a launch site.
Here are some joints in the rock.  They are probably future habitat for Kurrajongs!
We then moved on to Cooradigbee Station where fossils were on the menu.  As revealed on this piece of butchers paper the area was a shallow sea in the Devonian period (about 400 million years ago).
Sediment dropped into the sea but water remained above leading to the build up of about 1200m of sediment.  This took about 16 million years.    As well as what was in the sediment, it covered and preserved corals on the sea bed.
This is the imprint of an armoured fish's (Placoderm) eyeball.
The owner of Cooradigbee (Ian Cathles) provided us with a wealth of information about the nature of the fossils found on the property and how they are handled.
  • A key factor is that the fossils are mainly bone (calcium phosphate) whereas limestone is calcium carbonate.  This enables acetic acid (ie vinegar) to be used to dissolve the rock but not the fossil.  
  • The fossils can then be scanned using a CAT scanner.  The ones used at ANU take 200 scans per mm (while a human CAT scanner takes a shot every mm). 
  • This enables the development of 3D prints of the objects such as this resin form of a Placoderm eyeball.
Another real fossil of a nautiloid,
Out to the rocks.  The white lines represent cracks in the rocks into which water later with dissolve d minerals has run.  When the water evaporates the mineral material crystallises out.  This might form calcite (if the mineral is calcium based) or quartz if silicon.
Here is a coral fossil in situ.
And a nautiloid.
This is looking South down the Goodradigbee River.  It is the back end of Burrinjuck Dam which started to be built in 1907: well before the Snowy scheme.   When the dam is full the water reaches the tide mark visible on the RH bank.  In the most recent wet period it reached the top of the green patch on the left.  The trees were all dead when Ian's family arrived in 1948
Looking downstream the triangular outcrop is a hard sandstone layer, which is unusual in the area.
As we walked a number of pebbles like this were seen.  The stone is sourced from about 15km away and if peered at closely it could be seen that they had been worked by human efforts.  In other words they were Aboriginal tools: a hammer on the left and an axe head on the right.  They had almost certainly been carried there by a human.
There were a good number of Sulphur-crested Cockatoos at the homestead ...
... and surprisingly Australian Pelicans on, and above the River.
At the invertebrate level this wasp was running about in the paddocks, probably looking for a tasty spider.
Near the homestead there was evidence of elm leaf beetles.
They had basically defoliated some very large trees in a year.  Ian was investigating how to react to this, with banding the trees being a likely outcome.

1 comment:

Dolev Fabrikant said...

Great blog! But I see one major inaccuracy. The fossil that you claim to be a placoderm eyeball imprint, is actually a coral, to be more precise a rugose coral. It is an extinct order of coral that was very abundant during the paleozoic and perished in the permian-triassic mass extinction.