Today was the final mapping day of the Field School 2014!
Our participants were visibly upset and some even chose to stay out in the
field for longer than usual. A large team that included Taufeeq, Ngqondi, Sims,
Eve, Judy, Ndidi and Olma set out to answer some questions and recap the Gariep
Belt history. This team travelled the top of the basal thrust zone, exposed
within the Western region of the mapping area. This zone includes the tectonic
melange, recently mentioned and comprises of large (meter-thick) thrust faults
that have stacked diamictite and quartzite in a repetitive nature along at
least five noticeable thrust packages. Based on the steepness of these faults,
the team opted to spend some time practising their 4X4 skills before trying to quell
some lithostratigraphic issues.
4X4 training was done with the basal thrust packages as a
backdrop, literally. Participants engaged the low-range gear of our VW Amarok and attempted to crawl gently up the steep, rock slopes. All of this before having
to perform a three-point turn and crawl back down. This is vital skill needed
when driving in this kind of terrain and since we’re all alive now, everybody
passed this test with flying colours!
Slow and steady, keeps you alive! Low-range crawl down a slope
Now, problem number one: what is a diamictite; what is a
tillite:
A diamictite is essentially a sedimentary rock that has a
matrix (fine-medium grained) and at least two different kinds of clast. This is
as opposed to a conglomerate that mostly has one type of clast, commonly quartz
pebbles. Now, a tillite is a diamicitite (i.e. matrix with at least two
different kinds of clasts), but it has been deposited through glacial
processes. Moreover, how do we distinguish these two rock types in the field?!
Well, without the presence of proper drop stones (clasts that have “dropped”
into sediment and caused soft-sediment deformation) this is very difficult-
thus geology.com recommends diamictite as a safe name for “careful” geologists.
It will be interesting to see how our
team handles this based on what they've seen in the field and what the
literature elucidates to.
Spot the Diamicite/Tillite? Notice the dropstone!
Tomorrow further fears and questions will be quelled as we
slowly make our exit from the Richtersveld!
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