Prickles and Ripples

As I have been walking through the hills of Australia, I have had many different moments of dejavous.  Australia in my mind is a combination of many different places that I have traveled in the past.  

The vegetation reminds me of the deserts in the south west such as Joshua Tree and Death Valley.  The ground is hard packed sand and gravel that is sparsely covered with various scrubby plants that have stubbornly taken hold.   Many of them look innocent enough low to the ground with various hues of green and brown, but do not be fooled these plants are anything but innocent.  They wait for the chance bystander to step a bit too close and snag your sock with a thorn or barb of varying size.  Often times, the small poker remains elusive wedged somewhere between your sock and boot, but with every step you know it is there twisting itself into the perfect placement  to continually stab at your Achilles with a ridged prick.  Without fail, the hiker is forced to stop and contend with the unwanted prickle.  Catherine and her colleagues fondly nicknamed a particular hearty and plentiful strain of thorns the F***lettes.  There is no better name for this annoying plant although I am sure you will not find this genus next to the plant's picture in any identification book.    

As we traverse over rolling, barren hills, divided by ridges of rock outcrop it is reminiscent of Idaho.  I spent the summer after my junior year in high school building a barbed wire fence in Caters of the Moon National Monument.  It interesting because in the west fences are built with three strings of barbed wire while the top wire is smooth.  This is so the wild animals grazing can jump over the fence without becoming cut.  In Australia the bottom three wires are smooth and only the top wire is barbed.  While I have not seen it, apparently this design allows for the kangaroos and wallabies to jump through the fence unscathed.  Catherine says it is quite the sight to see a kangaroo cruise towards a fence, and then without changing its speed, it will torque its body sideways and slip between the wires. 

Australia is a vast country where it seems like yo can see forever.  There is no cover,  You can see herds of wild goats on distant ridges.  You can hear trucks motoring through side valleys, but never see them.  Distances are deceiving.  They are both close and unattainable at the same time.   Wind rips through the valley unhindered by any natural wind breaks.  Dave often complained about his distaste for wind after living in New Mexico.  I find it similar here.  I am excited on days where the air is still and my face and lips do not become chapped by the incessant wind.  

Because the vegetation is so minimal and the ground is so barren, this landscape is perfect for studying geology . . . and so we do.  The area that we have been working in has gone through major environmental changes throughout its lifetime and many of these variations are preserved in the rocks that we stand on.  The landscape is like Australia's family photo-album with moments in time preserved in the remaining rock layers.  It is our job to piece together this seemingly random collection of moments and interpret the story they create.   

Where we have focused our efforts for the last week or so is an hour drive from the town of Leigh Creek.  The area is dominated by three main types of rock: carbonate, siltstone and glacial diamictite.  The carbonate rocks form in a shallow warm sea where calcium carbonate creates solid rock. Often there are large fossilized structures created by algae mats called Stromatolites (more on these at a later time).  The red siltstones form in a deeper sea environment from the carbonates.  They are fine grained, sediments that dominate this particular area of Australia.  Diamictite is a rock consisting of two or more sediment sizes.  In the case of these particular rocks, the diamictite resulted from glacial ice gouging and ripping apart the bedrock it moved over millions of years ago.  The loose sediments are then transported miles and miles by the giant ice sheets - nature's greatest conveyor belt.  Once the ice sheet retreats, these clasts (chunks of transported rock) are deposited within a matrix of fine grained sediment.  We know that have traveled a long way because the clasts are made from rocks like granite which are not native to this area of Australia.

Diamictite - notice the larger clasts embedded in a fine-grained matrix

Looking at the patterns and positioning of carbonates versus silts versus diamictites, Catherine begins to write the story of Australia's past.  There is only one layer that has been dated at this time placing the rocks at roughly 635 m.y.a. (million years ago) - give or take you know a few million years.  

As I stand in the middle of the now desolate, barb encrusted, sunbaked, desert of the Outback, I try to imagine how this continental crust had once been covered by murky ocean water and then a shallow, warm, stromatolite rich reef, and then a massive sheet of ice and finally another warm water environment.  It is difficult to fathom what could have changed the landscape so drastically and so suddenly.

Ripple marks

Stromatolites