Dating an Ash

Students often want to know how "we" - the scientific community - know how old a particular rock formation is.  Its not like anyone was around during the Earth's early formation to document its "first steps".  There is no Wikipedia page outlining the year each layer was formed  Rather, we have to collect clues from the rocks themselves in order to constrain the age of the various bedding layers that we are studying.  There are two ways to consider how old a rock formation is: relative dating and absolute dating.  Relative dating is not asking your cousin out for coffee; rather, it is when we compare the age of one layer to the next.  Most of the time, the oldest layers will be on the bottom and younger layers will be on top.  It is the equivalent of saying: I am younger than my mother, but older than my sister.  Absolute dating is giving an actual number age to a particular rock.  I am 33 y.o. (years old), my mom is 62 y.o., and my sister is 29 y.o.  We know the ages of my family because of birth certificates and the fact that people have been around long enough to document each year of our lives.  

The best way to give an absolute age for a rock formation is to locate an igneous rock.   Molten rock that is ejected from a volcano will create igneous rocks.  The ash debris spit out from a volcano can cool and create an igneous (or ash) layer as well.  The benefit of the ash layers are that they can travel great distances by currents in our atmosphere far away from the original volcano.  Within the ash layers, there are small grains called zircons.  Zircon isotopes will decay at a certain rate (half life).  If we know the rate of decay, analysis of the amount of decay that has occurred will determine an age of the zircon; and therefore, the age of the ash layer it is found within.  As I mentioned in the previous entry, there is only one layer that has been positively dated in this area of Australia placing the rocks at approximately 635 mya.  Ideally, more ash layers will be located.  The more positively dated layers, the more accurately we can pinpoint the ages of the various formations.  For instance, if there are multiple ash layers with one located at the bottom and one at the top of the Trezona formation, we would be able to determine when and for how long this paleo-environment lasted.  Such a scenario of formations bookended with identified ashes is somewhat of a fairy tale in geology world.  Regardless, we are intrepid and ready to begin a search for the desireable ashes. 

Such was our quest!  Last field season four potential ash layers were located and sampled by the Princeton team.  Two of those previously sampled provided good dates, and two seemed less reliable.  Our goal this season is to relocate these ashes, collect more samples for analysis, follow them laterally, and hunt for additional layers in other locations.  We have GPS locations for the four previous ash layers and a written description for an additional one.  Not too bad, sounds doable.  Bring on the ash.

Ash hunting days are not always the most, shall we say, rewarding days.  I have been informed that ashes tend to be recessed layers.  Although, depending on the deposition of the ash, it can create a solid resistant layer.  The rock tends to be green (but one of the previous sampled ashes was red) that may or may not be sparkly.  Can we say needle in a hay stack!  Yesterday, Catherine and I worked our way through three separate locations of possible ash sightings.  The outcrops consisted of 20 plus feet of alternating red and green siltstone.  These siltstones maintain various levels of weathering resistance.  Some are crumbling debris layers.  Others are resistant ridges.  In the sun, many of them sparkle with secondary micas and other glittery minerals.  Standing on the side of one such cliff, armed with my rock hammer and hand-lens, I began to understand why there has only been one positively dated ash layer in the area - they are elusive and difficult to distinguish (at least for me).  In the end, we confidently resampled one of the three previously sampled ashes and the jury is still out on our success in locating the additional ashes.  Catherine has informed me that we can never do more than one ash hunting day in a row  as it is soul destroying, and I am considering the possible use of mood enhancers.  Stay posted on our future successes in Operation Ash Location! 

Three possible ash layers.
The oldest layer is about a meter below where Catherine is standing.  The second potential ash is the layer she is standing on and the youngest is where she is pointing.

Tea Time

When I came to Australia, I anticipated learning many new things about the geology of Australia.  And while I will return to my homeland saddled with a new recognition for field work, a greater understanding of the Trezona formation, and a budding ability to identify siltstone and carbonate; one of the greatest skills I have gained, revolves around a regular morning ritual.  Living six weeks with a Brit has instilled in me a new appreciation for the art of tea preparation.  Tea is not simply the watery drink that can substitute for coffee in a pinch.  It is a delectable drink that is only truly enjoyable when prepared under the correct conditions.  I have promised Catherine that as a liaison to the United States, I will do my best to educate my fellow Americans on the proper way to prepare, serve, and consume this often over looked beverage.  

Catherine and I enjoy Tea at the Copley Cafe

Step one: Boil water - this is the critical step that many Americans overlook.  This does not mean warm water, steaming water, or even water with the beginning boil bubbles collecting on the pan's surface.  This is a full on rolling boil *.  A convenient, affective way to achieve the necessary water temperature is to use an electric kettle**.

Step two: Pour boiling water over tea bag***.

Step three: Allow the bag to steep until rounded in flavor****.

Step four: Doctor tea as you see fit -  milk (2% or higher), sugar, etc.

Step five: Enjoy*****  I have to say that by following these simple guidelines I have experienced some of the best cups of tea.  All of a sudden, Lipton tea has been turned into a complete experience.

* Such a boil is impossible to achieve at higher elevations without the use of a pressure cooker.  To my Rocky Mountain friends, you may want to just skip the rest of this blog if such a cooker is not available to you at this time.

** When purchasing this boiling device, make sure that the box says electric kettle.  The hot pot is NOT an acceptable substitute as the 100 degrees centigrade will be impossible to achieve with the plastic bottomed basin.

*** Tea selection can be quite tricky in the United States as many of our teas are considerably weaker than the European counterpart and/or fruity in flavor.  (These directions are only good for black teas.  Disregard directions for green or fruit teas).  Apparently, Tazo loose leaf tea (which can only be purchased at Starbucks for an exorbitant price) comes even remotely close to achieving the correct potency. 

**** Apparently rounded flavor should occur in approximately one minute, but adjust to your personal preference.

***** As a contentious consumer, I often reused tea bags before permanently discarding.  This is a huge atrocity that sent Catherine into a substantial tirade revolving around the ignorance of a good cup of tea.

A rolling boil

Kangaroos

Christine is also maintaining a blog regarding her adventures in Australia.  At first glance, she is far more tech savvy then I am.  Her blog sports a nice image of Australia in the background and utilizes additional pages really well.  She also has two fun side bar features.  There is a count down clock that continually counts the seconds, minutes, hours, weeks that they have been in the field and she also has a Kangaroo count where she updates how many kangaroo sightings she has had while out and about.  I thought the roo counter was a great idea and debated hijacking her idea and adding it to my own blog.  When I mentioned it to Catherine, she laughed saying that it was going to be impossible to keep up with the roo counter as these pocketed mammals are EVERYWHERE.  I was dubious, especially after my first week in the field.  Our first field site location was at Oodnapanicken Bore.  This was a remote location over an hour in on a rough dirt track.  From there, we would hike over four hours away from any semblance of a track.  You would expect wild life to teem in such an isolated location, yet if I had had a roo counter it would have maybe topped out at 10 - 20 max.  All of these sightings were distant and fleeting.  I would whip out my camera and attempt to capture the exotic kangaroo only to have an image dominated by red earth and desert foliage.  Somewhere in the middle would be an indistinguishable, fuzzy blur that represents a fleeing wild roo that has recognized our presence from over a kilometer away and is making a fast break in the opposite direction.  Needless to say, the only kangaroos that I could get even remotely close to were in various stages of decomposition on the side of the road.  

Despite my slow start, Catherine's prediction was accurate.  This past week we spent in Flinders National Park.  The park is teaming with Winnebegoes, retired tourists, young kids on break, and crazy amounts of wildlife.  Kangaroos are so common place that I do not even get excited at a sighting.  It would be the equivalent of pulling out the camera to document every grey squirrel in Rutland.  After being in the park no more than fifteen minutes, we had seen dozens of kangaroos and multiple flocks of emus.  There were green parrots as well as colorful gallahs.  After setting up our tents, we made our way towards the information center.  Wedged between the shower house and manicured tent sites a mother kangaroo with a joey poking out of her pouch munched on some campground clover.  You will have to believe me that I was no more than ten feet away from the mother, since my camera was sitting in the car on the other side of the campround.  Grrr!!!!  

I measured that there mountain with this here yellow stick!

While this field season includes a variety of different projects, much of Catherine's work has revolved around detailed stratigraphic sections.  This work entails walking perpendicular to the beds and measuring the thickness of each layer.  This quickly becomes complicated as beds dip and tilt at odd angles to the direction that one is walking.  We attempt to correct for this change in the layers formation by tilting the measuring stick at an angle parallel to the beds and sighting a point on the ground.  Then you walk to that sighted location and repeat the previous steps.  Such is the process we followed in order to reach the top of the hill in the background of this picture.  Just a a side note, it was a damp, cold, super windy day when we did this work.  Two words . . . Hard Core!

Rock Formations

So there are a series of rock formations that Catherine and I are looking at.  Noted from the oldest to youngest.

Balcanoona (aka Etina) - Is a carbonate layer.  These are rocks made out of calcium carbonate, and therefore will bubble when in contact with acid.  In order for carbonate to form, there needs to be a relatively shallow, warm water sea that interacts with the atmosphere. 

Trezona - This is also a carbonate layer; however, often it is interbedded with siltstones which are formed in a deeper ocean environment.  This formation has a variety of exciting features.  There are ripples as well as stromatolites.  Stromatolites are a primitive life form that are believed to be one of Earth's earliest life forms.  Currently, stromatolites are only found in extreme locations such as Buzzard's Bay in Australia which has a very high salinity.  Stromatolites are formed by layers of algae mats and sediment.  The algae creates a sticky surface which sediment will adhere to.  As the layers of sediment and algae build on one another, mushroom like structures will form.  The stromatolites that I saw preserved in the Trezona varied in size from those smaller than my thumb to as large as a mini fridge.  As you walk over these seemingly insignificant rocks, it is fun to imagine what Earth must have been like at the time that these stromatolites dominated our seas.  

Stromatolite - note coin for scale

Note coin on right hand side of the stromatolite

Meditating on top of a massive stromatolite - meditator for scale

In between, the the stromatolite mounds, there are other interesting structures to be found.  Adam, Catherine, and the other Princeton colleagues noticed repeating shapes in the Trezona formation.  They found three repeating shape stuctures.  There were ones shaped like an H, a Y, and rectangles with either two or three spots in them.  After analyzing the different pieces of debris found in between the stromatolites, it has been proposed that these shapes represent different perspectives of a primitive sponge.  

I am pointing to the structure with two circles in it

Yaltipena - is a silt layer that has distinct feature specific to shallow water environments.  There are many layers of this red siltstone filled with ripple marks and mud cracks.  In some cases, the ripple marks will criss-cross one another creating a tic-tack-toe affect.  This shows that water currents changed directions in the particular area.  The mud-cracks formed in an environment where the sediments alternated with exposure to the air and covered by shallow water.  Think about areas influenced by tides. 

Cross-bedding - ripple marks preserved in profile

Ripple marks (top left hand) Mud cracks (lower right hand)

Modern mud cracks

Elatina - is the diamictite previously described in the last blog.  It is a formation created by glacial movements.  The rock matrix tends to be red in color and dominated by clasts of all different sizes and lithology (type).

Nuccaleena - is a dolomite (carbonate that has been chemically altered).  It is distinctive in its buttery color.

Snakes

When I first started telling people that I was traveling to Australia, many responded - Oh watch out for the snakes.  It is true that Australia is home to many of the world's most deadly reptiles, but Catherine assured me that the winter landscape is a benign land where all those things that bite, sting, and kill are tucked away deep in hibernation.  Catherine went on to assure me that in the four previous field seasons, she had never seen a snake.  In the last two days, her tally has now increased to two.  Apparently these serpents of the southern hemisphere do not always sleep for the entire winter.  

We were walking along, engrossed in the rocks and the fabulous clasts in the Elatina formation.  I noted an exceptionally large granite clast resting in the surrounding red rock.  "Catherine check out that clast."  Her response, "Oh my god!"  I thought that I may have found the clast of all clasts from the emotion imbedded in her response; however, OMG was quickly followed by "SNAKE!"  Without actually having my own visual of the beast, I screamed like a girl and tumbled backwards away from the clast and elusive snake.  

Once at a safe distance, we reassessed the situation.  The snake is an amazing animal easily disguised by the rock it sits upon.  It was over a meter long and coiled as it enjoyed the afternoon sun.  It was covered in brown spots that reminded me of a leopard's coat.  While I evaluated the snake and considered the possibility of other snakes emerging from the rock crevices, Catherine evaluated the granite clast and decided that in fact it was quite nice and would make an excellent photo.  Of all the Elatina in Australia, this clast was photo-worthy.  It was then a matter of positioning the rock hammer just under the snake's resting place in order for a scale oriented photo.  Couldn't the snake be used for scale?  Consistency - it must be the hammer.  The photo was taken and we moved much further down the creek for our lunch break.

Now, whenever I consider sitting down on an outcrop, I second guess how alone I in fact actually am and how difficult it is to awake a resting snake.

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