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Trip report: Drilling in Orange Kloof Valley

11 Apr 2021 - 11:15

The poking day

The Orange Kloof Valley is a 30 minute drive south of UCT and is a water catchment area of the Western Cape. Because of this, the valley is highly protected and unique. To receive a coring permit for this valley is therefore a rare privilege.

In February 2021, a small group of palaeoecologists from the PCU Paleoecology Lab were excited to finally enter the valley, not only because of the coring permit, but also because it was the first field trip after the extended COVID-19 Lockdown. We arrived at the entrance equipped with a GPS device and maps that show possible coring sites in the Orange Kloof Valley and not to forget, the ‘poking stick’. The poking stick is a metal pole, approximately 2m long, which is used to search for suitable coring sites for the recovery of sediments by simply poking into the ground, seeing how far it goes and what sort of sediments (e.g. clay or sand) it probes. We were soon joined by a local resident, who helped in guiding us to the wetlands. Wetlands represent suitable palaeoarchives allowing the study of paleoecology by preserving pollen, spores, diatoms, and other useful proxies.

We started poking the valley floor, but the poking stick did not penetrate the wetland floor deep enough, what indicated that either a low sediments accumulation must have occurred, or the accumulated sediment eroded. The day went on by poking the valley basements for a suitable coring site and then, after a while, in the middle of a palmiet wetland the poking stick deeply penetrated the soil. To our surprise the poking stick did not touch the base of the wetland, which indicated that the possibility is quite high to recover a relatively old sediment core from this position within the wetland. Moreover, the sediment residues that adhered on the poking stick had a dark, moist, organic rich, silty, clay consistency with a low content of sand. These are exactly the characteristic hallmarks that palaeoecologists look for when searching for the perfect core to recover. These features are indicative for a fair proxy preservation. Delighted by these findings, we noted the GPS coordinates of the site.

 

The coring day

The next day we drove back to Orange Kloof Valley to recover the sediment. We decided to recover the core with a ‘vibracorer’, which is a piece of mechanical drilling equipment that facilitates the recovery of sediment cores. It operates with a motor and a vibrating device that helps to drive the coring apparatus into the ground. At the drilling site we started to arrange the drilling position by clearing some vegetation from the area and bringing the drilling equipment into place.

Janine Steytler and Adele Julier using the vibracorer to core the sediment at Orangekloof (photo: Sabine Prader)

For the recovery of the sediment core, we decided to use a 3m long aluminium pipe.The secure recovery of a core can be a tricky moment because the sediment could be lost for various reasons, such as high water content in the soil or the top of the pipe not being properly sealed before it is pulled out of the ground. However, this time the recovery was successful. We used our muscle power, assisted by farm jack (another useful piece of palaeoecological field equipment) to safely recover a core.