Slippery Dip anyone .... EarthCache
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Difficulty:
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Terrain:
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Size: 
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The Brachina Formation is a red-brown and olive-green siltstone,
grading in places to shale and flaggy fine sandstone. In several
locations the Brachina Formation is highly fractured with regular
joints defining long rectangular prisms.
The rippled structure of the Brachina Formation (or 'slippery dip'
as it is affectionately known) is evidence of formation in a
shallow marine environment which saw frequent wave action.
The asymmetry of the ripples suggests a single-direction 'stream
flow.' Further downstream, there is a parasitic fold (anticline)
which demonstrates compressional forces.
Further downstream still, there is another major tectonic structure
- an unconformity. Essentially, the overlaying of the Ulupa
Siltstone on the Brachina Formation is a consequence of silt and
clay being deposited by a lake (which came into being when a river
was dammed by surrounding mountains some 100,000 years
later).
In itself, this means little but the endurance of the lake suggests
a cooler climate and/or higher rainfall rates than at
present.
At the location in front of you, a couple of questions:
Question 1.
How long is the break in time between the two distinct rock
units?
Question 2:
Looking at the size of the ripples and the direction they are
moving. Was it really wave action or stream movement that caused
these ripples? Or is this caused by folding and uplifting? Let me
know your theory and the reasons for your theory.
And of course the obligatory photo of your GPSr in front of the
formation. Enjoy.
Access to the Flinders Ranges National Park is subject to entry
fees. The Geological Trail is accessible to all types of vehicles;
however, the roads can be very rough in spots and at times there
may be some flooding, so it's a good idea to use a vehicle with
good ground clearance.
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