Intro: I recently got to take part in a neat project, called AusGeol, which provides a repository of digital geological teaching and learning resources that documents the diverse geology of Australia. A colleague and I were assigned the task of visiting the Northern Territory (N.T.) to document (through photography) some interesting and important geological sites. In this 2-part blog post I will be sharing some of the geology of the Northern Territory with regular photos and embed links to the 3-D examples.
The work was done using a regular DSLR camera and a UAV (drone) to basically take multiple photos from different angles of a rock outcrop or feature of interest. Then, as long as a GPS point was recorded and a scale with a north direction evident, we can turn these mosaics of images into a 3-D model (using a program called AgiSoft photoscan), or into full spherical panoramas (e.g., Google street-style stuff).
The program is part of the University of Tasmania, led by Dr. Michael Roach, with funding from the Australian Government Office for Learning and Teaching and partner institutions. Every captured geological outcrop is made freely available on the website http://www.ausgeol.org/, with an extensive virtual library that has a diverse selection of well-documented examples of important geological features to assist in the development of student geological field skills. For examples of my sites in the N.T. as well as others through Australia, check out the atlas http://www.ausgeol.org/atlas/.
Brief intro to Northern Territory
The N.T. comprises ~ 13% of the Australian continent. It is underlain by the North Australian Craton, and it is dominantly Palaeoproterozic in age (~ 1.8 billion years old), with some Archean basement ‘inliers’ (Ahmad and Scrimgeour, 2013). Along with the Palaeoproterozoic basins and orogens (i.e., North Australian Platform Cover and Orogenic Domains), there are large Neoproterozoic to Palaeozoic sedimentary basins (i.e., Central Australian Platform Cover and Younger basins). Geological regions of the N.T. are broken into “provinces” or “basins” which are areas with distinct geological characteristics and ages; they are separated from one another by major structures and/or unconformities (Ahmad and Scrimgeour, 2013).
The trip – part 1 (Darwin to Alice Springs)
The Northern Territory is a big place… in total we drove over 4,000 km in ~ 3 weeks! Thus I will only go through some places in these posts, with some of my favorite digital captures! This was largely done going down the Stuart Highway (known as “the track”) until just before Alice Springs, in which several detours were then taken to the west and east.
Starting from the north, not too far south from Darwin, is the Katherine Gorge, a popular destination for tourists as it is quite beautiful and offers lots of hiking, swimming, sightseeing, etc.! Though I didn’t do any of this though (haha), as we had to move fast to cover the N.T., we still managed to capture some of the stunning coarse-grained conglomerates of rounded boulders and cobbles that make up the gorge, as well as views of the banded sandstones along the riverside (~ Paleoproterozic 1.7 billion years old).
Continuing further south is the Davenport Range. This is best seen from the sky actually, and with geophysical goggles on! The range is part of the large Wauchope Fold Belt. It is composed of folded succession of shallow marine sedimentary rocks and volcanics that have gone under greenschist metamorphism. The mafic amphiboles units and very magnetic, which can be seen quite well in an air-magnetic photo!
Devil’s Marbles (Karlu Karlu)
Some odd, round boulders in the middle of the N.T. outback (along the “track”, i.e., Stuart Highway) are known as the Devil’s Marbles (Karlu Karlu), and are a popular stop. The Devil’s Marbles are a “nubbin”. That is, they are residual boulders and blocks from the top “layer” of a large granite body that has undergone exfoliation weathering.
Basically, molten magma solidified and formed granite beneath and within thick sandstone layers ~1.7 billion years ago. Joints and crack formed within the granite when it was uplifted closer to the surface and the sandstone was eroded away. Water penetrated the cracks and preferentially weathered them creating more prominent blocks. The curved, domal surface is a characteristic feature of granites called “onion skin” weathering (for more info on this features, check out my Freycinet, Tasmania or Rio, Brazil posts).
Alieron Station and Reynold’s Range
Nearby the Alieron Station is the Paleoproterozoic Reynold’s Range (part of the Aileron Province). Some pretty spectacular folds and structures are found here! Some examples included parasitic folds, mixed felsic-mafic orthogneiss, coarse-grained granitic augen gneiss and cordierite granulite!
Next we headed east, pass Mudtank (a famous gem fossicking area), into the Harts Range and Etna dome. Here some of the river-bed sands in the Harts Range are composed of gemstones! That is, they are full of garnet from eroded rocks of the Harts Range Metamorhpic Complex, which is full of garnet-biotite gneiss. Rocks here are part of the Irindina Province and are quite younger (i.e., Neoproterozoic in age) than surrounding provinces.
Ross River D’hala Gorge
Leaving the metamorphic Harts Range, we entered the extensive Amadeus Basin on an east to west transect towards Alice Spring. Rocks here are of a more sedimentary flavor, with the ~ 800 Ma Bitter Springs formations dominating the landscape with beautiful overturned folded mountain faces, and synformal layers of interbedded sandstone/siltstone and dolostone/limestone of the ~500 Ma Goyder Formation, near Ross River D’hala Gorge.