Australia Fifteen: Preamble

A year proceeds quickly. My last entry was a series of reflections on Australia Fourteen. Suddenly it’s time for my fifteenth trip to what Bill Bryson calls “A Sunburned Land”. The upcoming trip follows a similar arc to last year. First, a week of poking around in new areas, i.e., vacation. “New areas” on this trip means the Kimberley Region of Western Australia, particularly the Bungle Bungles, and Kakadu National Park in the Northern Territory. Assuming I survive crocodile assaults in the Kakadu, this holiday will be followed by a few weeks of field research in the Pilbara.

Recap and Plans

In case you did not read my blog last year, check out this entry for explanation of how I’ve come to be a recidivist geologist/visitor in Australia. The short version is that I’m currently on a grant through my work with Oberlin College to study meteorite impact deposits. These strata are really old; the four layers we’ve recognized so far accumulated on the sea floor around 2.5 billion years or go, plus or minus 70 million years. The rocks we look at have been uplifted and very well preserved; they comprise the rocks of the Hamersley Basin. They outcrop in the Pilbara Region of Western Australia: the Outback with lots of iron mines. We’ve done a lot of work demonstrating that these layers formed after very large extraterrestrial impacts, and sorting out their environmental effects – massive tsunami and underwater landslides. On a personal level, in the twenty-five years I’ve been going down under, I’ve become extremely fond of the continent and its rocks, plants, animals and people. I always look forward to return and further exploration. I also relish the time away from the normal for reflection and restoration.

Australia Fifteen has two major scientific goals. The first is to finish up the main work of the grant project, which is to make detailed lateral measurements of the best exposed and preserved impact layer in the Hamersley Basin: the Bee Gorge Spherule Layer. I have a couple final sites to visit, including the mine property we were thwarted from reaching last year. We call the impact layers “spherule layers” because their most distinctive component is lots and lots of BB-sized spherical particles. These spherules formed from the cloud of vaporized rock blown out of the impact crater. They subsequently settled to the surface, forming a fairly unique sedimentary layer.

The second goal is more exploratory. The 2009 field season ended dramatically with discovery of a new Hamersley Basin spherule layer. We named this the Paraburdoo Spherule Layer, which I’ll call the PSL to save you all from trying to pronounce Par-a-bur-doo in your heads. By the way, Paraburdoo is one of the local mining towns, and its name comes from a presumably local Aboriginal dialect; “paraburdoo” means “meat feathers”. I can only hope this refers to emus or bustards, and not corellas or galahs, the local, nasty cockatoos. I’d describe them as gaudy crows, but that would be insulting crows. As I wrote last year, I literally stumbled upon the PSL, a 2 centimeter thick layer of impact debris, at my personal nadir point for Australia Fourteen. I was tired, cranky, sore and possibly flatulent (Louis – my field assistant - had cooked the night before). I climbed a rubbly hill, looked down, and there was the PSL.

This was particularly exciting because it was new. It’s the fourth spherule layer we’ve found in the Hamersley Basin. Based on looking at similar rocks in South Africa, I knew very roughly where it should be in the Hamersley rock sequence, but it was dead awesome to find it. However, since the PSL revealed itself almost at the end of last year’s field season, it remains a single point on a map. This is very unsatisfactory; we have no sense of the PSL’s distribution, or how its internal characteristics change from place to place. So I have put together a list of about a dozen exploratory sites that might have PSL outcrops. This will mean driving to the far reaches of the Hamersley Basin; seeing new areas and places I have not been for upwards of seventeen years. I expect this to be frustrating; the PSL interval is generally poorly exposed, the layer is damn thin, and it outcrops amidst nasty rubbly limestone. As some compensation for this, we’ll also spend a couple of days looking at drill core that might contain the PSL in the Geological Survey of Western Australia Core Library in Perth. Looking a core has its own challenges; rocks can look completely different when they are extracted from the ground than they do “normally” in a weathered outcrop.

Louis will again be my assistant and companion on this part of the journey. He’s an Oberlin student, a double major in geology and jazz trumpet. His help was outstanding last year. Not only is he bright and observant, but he can cook and put up with how inner-directed I get in the field. He’s one of the best student assistants we’ve had. I’m looking forward to more time with him. He’s going walkabout prior to meeting me in Perth, spending a couple weeks in New Zealand. I’m trusting that he’ll appear in Perth on the right day.