2014 Diary: Day 10 - First Day at School

Today the team split into smaller groups and started mapping individual areas across the Gariep Belt. All teams began within the Richtersveld National Park following the southern route along the Hellshoogte Pass. This road provides some interesting scenery straddling tall quartzitic and dolomitic lithologies. The Field School of 2014 has split the final portion of the Gariep Belt into several smaller sheets (approximately 5 X 6 km). It is envisioned that everybody within the team will have their own sheet to complete, however with geological data being shared across all completed sheets. With this, team members will aim to ensure and motivate their partners to collect the data of the highest quality (not knowing who might be providing the bulk of their data).

Today we follow the progress of Tebogo, Belinda and Haajiera. This team aimed to complete a section across Zone 20. Preliminary remote sensing suggested that this would be a relatively simple sheet, however it was anything but. This team started in a strange clast-supported diamictite (previously not seen by this group). This is highly foliated and coarse-grained (ca. 1-2 cm), with clasts of quartzite, arenite and dolomite. Of further interest was the presence of basaltic dykes cutting across, and being entrained within this unit. The dyke had phenocrysts of plagioclase, showing a strong mineral elongation lineation and in some places amygdaloidal texture. This unit bares remarkable similarities to the volcanics within the Vredefontein, however provided this group with a few things to consider: 1. If this was older (Vredefontein being older than the Numees/Kaigas), why does this show no foliation/evidence for strong deformation; 2. If this was younger, why are there also rafts of dyke entrained in the foliated diamicitite?

Clockwise: Basaltic dyke entrained and cutting across a highly sheared, clast-supported diamictite; Kaigas-proper dimictite and Numees-proper varved carbonaceous shale with dropstone; our team hard at work

Thereafter, they proceeded to climb some mountains and encountered the Wallekraal, within the Hilda Subgroup. This unit, similar to what was seen during day 2 of the show-and-tell displays both a bedding plane and foliation plane. This is possible due to the bedding being preserved at the contact between the carbonate and phyllite layers. Deformation was concentrated due to strain partitioning in the phyllite, thus forming a prominent foliation in this rock while the carbonate would simply recrystallise in response.

Further along, the group encountered Vioolsdrift basement rocks of this area. This mostly comprised of metavolcanics and granite-gneisses. The metavolcanics in particular displayed strain markers highlighting a top-to-the-west sense of shearing. There were also several large thrust faults, forming tectonic contacts with the Rosyntjieberg quartzites; and shear zones forming a prominent crenulation cleavage in places.

In total this group consolidated their knowledge of identifying and measuring structural elements expressed in the various lithologies, in addition to completing thorough rock descriptions and producing detailed field sheets. They will now look forward to sharing/learning from others tomorrow as the groups will continue to vary and complete the respective sheets.

Click here to see the mapping route of the group: Mapping 1