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My Geological Connection Between Minnesota and Western Australia The Compass: Earth Science Journal of Sigma Gamma Epsilon Volume 85 Issue 1 Article 1 7-30-2013 My Geological Connection between Minnesota and Western Australia Larry E. Davis College of St. Benedict / St. John's University, [email protected] Follow this and additional works at: https://digitalcommons.csbsju.edu/compass Part of the Earth Sciences Commons Recommended Citation Davis, Larry E. (2013) "My Geological Connection between Minnesota and Western Australia," The Compass: Earth Science Journal of Sigma Gamma Epsilon: Vol. 85: Iss. 1, Article 1. Available at: https://digitalcommons.csbsju.edu/compass/vol85/iss1/1 This Article is brought to you for free and open access by DigitalCommons@CSB/SJU. It has been accepted for inclusion in The Compass: Earth Science Journal of Sigma Gamma Epsilon by an authorized editor of DigitalCommons@CSB/SJU. For more information, please contact [email protected]. My Geological Connection between Minnesota and Western Australia Larry E. Davis1,2 1Department of Biology College of St. Benedict / St. John’s University Collegeville, MN 56321 USA [email protected] 2School of Arts and Sciences University of Notre Dame-Australia Fremantle, 6160 Western Australia AUSTRALIA [email protected] “I would rather have bowel surgery in the woods with a stick. If you are not stung or pronged to death in some unexpected manner, you may be fatally chomped by sharks or crocodiles, or carried helplessly out to sea by irresistible currents, or left to stagger to an unhappy death in the baking outback.” ― Bill Bryson, In a Sunburned Country Bill Bryson paints a rather scary occasions, “if you love Australia so much, picture of Australia, at least if you are why don’t you just move?” My response going to spend time in ‘the bush’. Much of is always, “it’s a great place to visit, but I Bryson’s description of the ‘sunburned certainly wouldn’t want to live there!” I country’ is done in his typical ‘tongue in have been fortunate in having had the cheek’ manner, but an Australian traveler opportunity to have seen a significant does need to be alert and aware. In truth, portion of the continent and according to Bryson’s description of Australia is not my Aussie friends, I have seen more of quite as bad as it seems, but I would Australia than most Australians, which is encourage any new visitor to Australia to an interesting compliment. So, here I am read In a Sunburned Country. If, during in Western Australia, 17,125 kilometres the reading, you don’t grin and giggle (10,641 miles) from home, surrounded by between some serious contemplation, then a flora and fauna dramatically different I would suggest you change your plans and from central Minnesota. However, as a visit Austria (P.S. If you do visit Austria, a geologist, I feel a certain geological country in central Europe, Austrians would connection to my home state of Minnesota prefer you don’t ask, “where are the when I look at Australian rocks. kangaroos?”). Australia is a great place to do field In terms of humans, Australia is the work, if for no other reason than the most urban country on Earth. The vast weather is nearly always ‘fine’. I’m serious! Evening news on the TV does the majority of Australians live in towns and weather for the entire continent in 5- cities, which means there is a great deal of minutes – it is fine in Perth, it’s hot and wide, open space to explore. This is my humid in Darwin, it’s fine in Brisbane, it’s 9th trip to Australia and I’m amazed with fine in Sydney, it’s fine in Adelaide, it’s each visit. I’ve been asked on numerous fine in Melbourne, and it’s raining in Hobart. Across the nation, the weather is The Compass: Earth Science Journal of Sigma Gamma Epsilon, v. 85, no. 1, 2013 Page 1 fine. Aussies can’t understand why intrusions, and meta-sedimentary rocks American’s are obsessed with the weather! and dated at 3.6 Ga. Immediately, readers Well, crickey the weather in America should balk at the above reference to the changes every 20-minutes and every 20- oldest dated rocks on Earth because the miles! When going into the field in Australia, do keep in mind you have to Isua Greenstone Belt in Greenland is dated drive on the left side of the road, you need at ~3.7, but zircons from the Jack Hills to have plenty of water, and always carry a Meta-conglomerate at Mt Narryer (Fig. 1) jar of vegemite. For the uninformed, are dated at 4,404 ± 8Ma (Wilde, et al., Vegemite is an axial-grease-like substance 2001). The conglomerate has been chock-a-block full of vitamins, which interpreted as being deposited in an Aussies smear on their morning toast. As alluvial fan-deltaic system. The zircons an American, having Vegemite as part of your ‘kit’ will endear you to your Aussie provide evidence that the Hadean Earth colleagues, even if you don’t actually eat might have been wetter than originally the stuff. thought and the existence of liquid water Apart from meteorites, Australian rocks 4.4 billion years ago could have important contain the oldest materials dated in the implications for the evolution of life Earth’s crust (at least to this point). The (Wilde, et al., 2001). Although not quite Narryer gneissic terrane in the Yilgarn as old, Minnesota does boast the Morton Craton of Western Australia is composed gneissic terrane (3.6 Ga) (Fig. 2). And, of highly deformed granites, mafic that is my first geological connection. Figure 1. Jack Hills Meta-conglomerate at Mt. Narryer in the Narryer gneissic terrane of Western Australia. Photo from: http://earthobservatory.nasa.gov/Features/Zircon/. The Compass: Earth Science Journal of Sigma Gamma Epsilon, v. 85, no. 1, 2013 Page 2 Figure 2. Outcrop of the Morton Gneiss in southeastern Minnesota, near Morton, MN. My next geological connection is pseudomorphic substitution of silica associated with the Brockman and Marra ‘tiger-eye’ following low-grade meta- Mamba Iron Formations in the Hamersley morphism that creates veins of crocidolite Range of the Pilbara region of Western asbestos. It should be noted that Heaney Australia (Fig. 3), which are equivalent in and Fisher (2003) disagree with the idea of age to the Biwabik Iron Formation of the pseudomorphic substitution but rather are Mesabi Iron Range in northern Minnesota in favour of synchronous mineral growth (Fig. 3). The banded iron formations of through a crack seal, vein-filling process. Western Australia are noted for their Since I am not a mineralogist, I’ll let occurrence of ‘tiger iron’, which is the others do the arguing. Figure 3. Polished slab of banded iron from the Brockman Iron Formation (left). Note the ‘tiger iron’ or tiger-eye in the sample. Biwabik Band Iron Formation (right) exposed in the Soudan Mine, Tower, MN. The Compass: Earth Science Journal of Sigma Gamma Epsilon, v. 85, no. 1, 2013 Page 3 My favourite geological connection domal stromatolites are well exposed in between Minnesota and Western Australia the Willow River Member of the Lower are the stromatolites. In northern Ordovician Shakopee Formation in Minnesota, beautiful stromatolites are southeastern Minnesota (Fig. 5) (May, et preserved in the 1.8 Ga Biwabik Iron al., 2012). Formation (Fig. 4), and large, puscular Figure 4. Digitate stromatolites in the Biwabik Iron Formation of the Mary Ellen Mine. Photo by Ms. Deborah Rausch, Duluth, MN. Figure 5. Stromatolites in the Willow River Member of the Lower Ordovician Shakopee Formation in southeastern Minnesota. Individual algal structures are outlined in green; overlapping algal growth is outlined in blue; and the entire stromatolitic structure is outlined in red. Photo from May et al., 2012. The Compass: Earth Science Journal of Sigma Gamma Epsilon, v. 85, no. 1, 2013 Page 4 Western Australia boasts some of very best examples of modern the oldest and youngest stromatolites on stromatolites – the famous Hamelin Pool Earth. Fine examples of ancient of Shark Bay (Fig. 8). Additionally, stromatolites can be found in the ~3.4 Ga Western Australia contains modern Strelley Pool Formation in the East Pilbara examples of thrombolites (Fig. 9), which Terrane (Fig. 6) (Wacey, 2010) and the are similar to stromatolites, but consist of ~3.49 Ga Dresser Formation in the ‘clotted’ algal structures formed by the Warrawoona Group of the Pilbara near precipitation of CaCO3, rather than North Pole, Western Australia (Fig. 7) layered accretions of trapped sediment by (Walter, et al., 1980). Of course, it is in cyanobacteria. Western Australia that one can find the Figure 6. Stromatolitic structures in the 3.49 Ga Dresser Formation of the Warrawoona Group in the North Pole Dome area of the East Pilbara of Western Australia. Figure 7. Stromatolitic structure in the 3.430 Ga Strelley Pool Chert of the Warrawoona Group in the East Pilbara of Western Australia. The Compass: Earth Science Journal of Sigma Gamma Epsilon, v. 85, no. 1, 2013 Page 5 Figure 8. Approximately 6,000 year old ‘living’ stromatolites in the Hamblin Pool, Shark Bay, Western Australia. Figure 9. ‘Living’ thrombolites along the shore of Lake Clifton approximately 100 km south of Perth, Western Australia. The Compass: Earth Science Journal of Sigma Gamma Epsilon, v. 85, no. 1, 2013 Page 6 Most recently, I visited the Boya and Low, 1978). The granites are Quarry (also called Government Quarry) associated with the accretion and assembly near Perth, Western Australia and was of Proterozoic proto-Australia. The immediately reminded of the granite Archean Yilgarn and Pilbara cratons were quarries only a few miles from my home in assembled into the West Australian Craton St.
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