2014 Diary: Day 17 - Tillites are not a girl's best friend

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!

2014 Diary: Day 13 - Gannakouriep in 60 seconds

As we near the end of the first week of field work, it's becoming very clear that our teams are very well set in their mapping. The rock descriptions and structural measurements are of the highest quality and we'll be expecting great results at the end of this year's field school. Of course, slight complications do arise in the field. Today, we follow Penester, Shane and Eveline. This team traveled deep into the Richtersveld in an attempt to complete one of the more isolated sheets. This journey was long and arduous, and could have easily warranted a fly camp. In the end, the planned traverse was not possible, due to current soil rehabilitation programme in an exceptionally long drive.

Team putting the Amarok to the extremes of its capabilities

Subsequently, this team did some regional mapping. Firstly, looking at some of the Gannakouriep dykes and later extrusive felsic volcanic rocks. The Gannakouriep dykes were emplaced during the early stages of the Gariep Orogeny, ca. 717 Ma; and represents the maximum age of this orogenic event. In addition, these dykes show evidence of deformation in places, related to syntectonic emplacement; and displays a very strong foliation. In places, the Gannakouriep could be seen near bright felsic volcanics, together these bounded within the Vioolsdrift basement gneisses.

Despite the lack of intense geology, the team did manage to test a VW Amarok along some of the moderately challenging tracks within the Richtersveld National Park. With a low ground clearance (approximately 205 mm - with 265/70/16R BF Goodrich AT) and a 2.0 liter Bi-turbo engine, producing only 132 KW of torque (enough the carry passengers and rock samples), the Amarok does not necessarily convince relative to bigger Toyota's. However, it managed surprisingly well (just needing to be taken very slowly over the tricky sections, to avoid scratching the undercarriage). Dragging the towbar could not be avoided though - the approach angle is simply not sufficient (due to the bling-bling nudge bar). Off-roading gadgets are plentiful: hill assist, electronic differential lock and anti-slip regulation, all of which goes a long way to making the drive as comfortable as possible. 

Geology-wise, note that there are lots of steeply foliated carbonates and quartz-rich shears along most of these roads. These develop razor sharp edges that will slice through the relatively soft rubber compound of the BFG's. It's worth noting that this particular Amarok had BFG tyres fitted 3 months ago and are now horribly gutted and pitted. Luckily, the team hikes most of the time and are well prepared for any potential quagmire-situation.

Final assessment: 6/10.... Until you get stuck, of course.