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.