Thursday, 9 March 2017

Where you are: GDA2020 on the way

Australia's main datum for mapping and locating points on the australian continent is changing. You can occasionally find old maps using AGD66 in some shops, these are out of date. In 2000 GDA94 was adopted and now it too is changing. GDA2020 is here! Have no idea what I'm talking about?

Here is a good video that explains the change:

https://vimeo.com/191566518

While I'm on spatial data... why not increase the accuracy of your GPS? Many new GPS units have a WAAS option. Enable this and you will have greater accuracy in all three spatial dimensions. Of course it only works when certain satellites are visible to your GPS, in northern Australia it will detect the Indian and Japanese satellite systems but in Victoria and Tasmania you may find it harder to find a satellite that has WAAS type capabilities.

Want to know more about WAAS:

https://www.youtube.com/watch?v=CeIEs9l9aws

Saturday, 28 January 2017

Stunning in Red and White

A friend and colleague showed me his new lifestyle property on the edge of Armidale a couple of weeks ago. He is an observant soil scientist and noted that his land consisted of poor quality soils which grew only resilient grasses and some typical New England gum, stringy-bark and box woodland. He was curious about the rocks that were common on the surface of the dusty grey-brown soil. I was not surprised of the poor soils because the property is located on a geological unit called the Sandon Beds.

The Sandon Beds are common in the Armidale district, especially just to the north of the town. They were laid down sometime during the Devonian to Carboniferous periods. The rocks of the Sandon Beds are varied and include mudstones, conglomerates, volcanics and bio-chemical sedimentary rocks. The deposition of the unit was in the ocean debris flows from the continental shelf would form turbidites (coarse to fine grained repeating sequences), layers of fine mud would accumulate and occasional basalt volcanic rocks would occur. Sometimes, while a long distance from landmasses or spreading ridges very little would happen - only the gentle settling of dead primitive ocean organisms with silica skeletons.
Brecciated Jasper (chert) of the Sandon Beds

The settling of silica on the sea bed produces a rock called chert. It is common in the Sandon Beds with a red colour. The chert occurs in beds interspersed with dull mudstones, siltstones and the like. Possibly because of regional scale metamorphism or the effect of fluids in the rock the chert has been affected and displays its red colour. Because of the red colour it is often referred to as Jasper which is seen by some as a semi-precious stone.

Throughout my friend's property could be traced lines of chert running essentially north-south. This is because the beds have been tilted to a nearly vertical direction. There was nothing out of the ordinary with these beds but in one area some of the red chert caught my eye. I could not see the actual outcrop but scattered around one little area was red chert with bright white quartz veins. The chert had been broken apart and re-cemented together with the quartz rich fluid. The result was quite striking, a stunning red and white. In this one little area, at some time after the chert had formed and turned into hard rock it had been blasted apart apparently by hot fluids. A 'brecciated jasper' occurring in a little area that just happened to be on a friends new property just ready to be discovered.

Monday, 16 January 2017

Blog Update #11 - More rocks in our region

Not a lot to mention as far as the blog goes at this point, except that I've added photographs of three more stratigraphic units to the Rocks of the Region page. These are three of the many 'granites' in the Armidale district:

Gara Monzogranite --- Fickr Photos --- Stratigraphic Names Database
Glenburnie Leucomonzogranite --- Flickr Photos --- Stratigraphic Names Database; and
Rockvale Monzogranite --- Flickr Photos --- Stratigraphic Names Database
Typical landscape and outcrop characteristics of the Rockvale Monzogranite, Wollomombi area

On another note, while visiting a friends property near Armidale I observed a brecciated jasper in the Sandon Beds. I was aware of an abundance of jasper beds (red chert) in the region ever since my university days, however, I'd never seen a brecciated type and this was quite attractive. More to come in a week or so.