Kuruman Wind Energy Facility Grid Connection, Kathu & Kuruman, Northern Cape
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1 Palaeontological heritage: input for combined desktop and field-based Basic Assessment KURUMAN WIND ENERGY FACILITY GRID CONNECTION, KATHU & KURUMAN, NORTHERN CAPE John E. Almond (PhD, Cantab.) Natura Viva cc PO Box 12410 Mill Street CAPE TOWN 8010, RSA July 2018 CONCLUSIONS / EXECUTIVE SUMMARY Alternative corridors for the proposed Kuruman WEF overhead 132 kV grid connection – either to Segame Substation near Kuruman or to Ferrum Substation near Kathu - largely overlie Precambrian sedimentary bedrocks of low palaeosensitivity. These include basinal marine banded ironstones (BIF) of the Asbestos Hills Subgroup (Kuruman and Daniëlskuil Formations) and lavas of the Postmasburg Group (Ongeluk Formation) that underlie the Kurumanberge Range and the Lohatlha plains to the west. Direct or indirect impacts on small outcrop areas of fossiliferous Precambrian carbonate bedrocks (Campbell Rand Subgroup) along the eastern margin of the Kurumanberge are not anticipated. Late Caenozoic superficial deposits, such as BIF colluvial gravels, sandy and gravelly alluvium, calcrete and aeolian sands of the Kalahari Group, mantle most of the Precambrian bedrocks within the powerline corridors and are likewise fossil-poor. The only fossil remains recorded during a recent field assessment of the grid connection corridors comprise low exposures of stromatolitic carbonate of the Kogelbeen Formation (Campbell Rand Subgroup) near Segame Substation. The stromatolites see here are probably of widespread occurrence in the Ghaap Plateau region and are not considered especially conservation-worthy (Proposed Field rating IIIC Local Resource). No specialist palaeontological mitigation measures regarding these fossil assemblages are proposed here. It is concluded that, in terms of palaeontological heritage resources, the impact significance of the Kuruman WEF 132 kV grid connection is low (negative), both before and after mitigation. This assessment applies to both 132 kV grid connection options under consideration and is based on (1) the low overall low palaeosensitivity of the 132 kV grid connection study region (including both corridor alternatives) as well as (2) the small footprint of the individual electrical pylon footings and associated service roads (i.e. small volume of bedrock excavations or surface clearance entailed). There is no preference on palaeontological heritage grounds for either one of the grid connection route options. Significant impacts during the operational and de-commissioning phases of the 132 kV grid connection are not anticipated. Confidence levels for this assessment are medium, given the low levels of bedrock exposure. In the context of other alternative energy and associated powerline developments in the broader Kathu – Kuruman region, cumulative impacts posed by the Kuruman WEF 132 kV grid connection project are of low significance. Should substantial fossil remains be encountered at surface or exposed during construction of the 132 kV grid connection, the ECO should safeguard these, preferably in situ. They should then alert the South African Heritage Resources Agency as soon as possible (Contact details: SAHRA, 111 Harrington Street, Cape Town. PO Box 4637, Cape Town 8000, South Africa. Phone : +27 (0)21 John E. Almond (2018) Natura Viva cc, Cape Town 2 462 4502. Fax: +27 (0)21 462 4509. Web: www.sahra.org.za). This is to ensure that appropriate action (i.e. recording, sampling or collection of fossils, recording of relevant geological data) can be taken by a professional palaeontologist at the proponent’s expense. A procedure for Chance Fossil Finds is tabulated in Appendix 2. These recommendations must be incorporated in the Environmental Management Programme for the Kuruman WEF 132 kV grid connection project. There are no fatal flaws or objections on palaeontological grounds to authorisation of the Kuruman WEF 132 kV grid connection project, provided that the recommended mitigation measures - including the Chance Fossil Finds procedure - are fully implemented during the construction phase of the development. 1. GEOLOGICAL CONTEXT The combined study area for the 132 kV grid connection associated with the proposed Kuruman WEF stretches from Kathu in the southwest across the topographically subdued Lohatlha plains, through the hilly Kurumanberge Range and onto the western edge of the Ghaap Plateau near Kuruman, Northern Cape (Fig. 1). This area forms part of the semi-arid Southern Kalahari Physiographic Region of the Northern Cape (Partridge et al. 2010). The Kurumanberge comprise a NNW-SSE trending series of low, flat-crested hills which range in elevation from c. 1500-1770 m amsl. These are erosional relicts of an elongate, low, dome-shaped upland area that has become highly dissected by numerous small water courses draining towards the Ghaap Plateau and Kuruman River in the northeast and to the west into the Lohatlha Plains of the southern Kalahari. The geology of the Kathu – Kurumanberge - Kuruman region is shown on the 1: 250 000 sheet map 2722 Kuruman (Council for Geoscience, Pretoria), for which a full explanation has yet to be published (Fig. 2); this map is now outdated in several respects. Excellent simplified geological maps and sections of the region are provided in the Kalahari Manganese Field volume by Cairncross & Beukes (2013) (Figs. 3 & 4). The silicicastic and carbonate bedrocks here are assigned to the Precambrian (Late Archaean to Proterozoic) Transvaal Supergroup (Griqualand West Basin) on the western margins of the ancient Kaapvaal Craton (McCarthy & Rubidge 2005, Eriksson et al. 2006) (Fig. 5). They lie within the Ghaap Plateau Subbasin of the Transvaal succession, situated to the NE of the Griquatown Fault Zone. The Transvaal Supergroup bedrocks here have been folded into a major NNW-SSE trending mega-syncline, known as the Dimoten Syncline, and are cut by several broadly N-S trending faults. Within the 132 kV grid connection project area the bedrocks of the Ghaap Group – comprising shallow water carbonates of the Campbell Rand Subgroup overlain by deeper water banded iron formation (BIF) of the Asbestos Hills Subgroup - lie on both flank of the Dimoten Syncline. The youngest bedrocks in the core of the syncline, assigned to the Proterozoic Postmasberg Group, are glacial sediments of the Makganyene Formation and the overlying Ongeluk Formation lavas. These younger rocks, unconformably overlying the Ghaap Group, crop out in the core of the Dimoten Syncline to the west of the Kurumanberge Range. They are not mapped within the WEF project area (although they may in fact occur here as well due to faulting). Throughout the study area a large portion of the Precambrian outcrop area is mantled by various, mostly unconsolidated superficial deposits of Late Caenozoic age. These include Late Cretaceous to Recent aeolian sands, calcretes and older (deeply-buried) lacustrine to fluvial deposits of the Kalahari Group, BIF colluvial and surface gravels on hillslopes and hillcrests, as well as alluvial sediments along stream and river valley floors. John E. Almond (2018) Natura Viva cc, Cape Town 3 A brief summary of the main geological units traversed by the 132 kV grid connection alternatives from the Kuruman WEF to Segame Substation in the NE and Ferrum Substation in the SW is given here. More detailed accounts of the geology and stratigraply of these rock units is provided in the palaeontological assessment reports for the Kuruman WEF (Phase 1 and Phase 2) by the author (Almond 2018b, 2018c), to which the interested reader is referred. 1.1. 132 kV grid connection to Segame Substation, Kuruman: geology The 132 kV grid connection (red line in Fig. 1) runs from the proposed Kuruman Phase 1 WEF substation, located at c. 1530 m amsl in the central valley of the Kurumanberge, follows drainage lines across the eastern range of these BIF hills (Fig. 6) and then traverses gently sloping (c. 1430- 1330 m amsl) terrain on the western the margins of Ghaap Plateau to Segame Substation on the outskirts of Kuruman. For the majority of the powerline corridor the Precambrian bedrocks are mantled by Late Caenozoic superficial deposits while no major water courses are crossed. The superficial sediments include downwasted BIF (banded iron formation) gravels and scree on hillslopes of the Kurumanberge, sandy and gravelly alluvium along minor, mostly dry drainage lines within this range and on its margins, as well as Pleistocene to Recent aeolian sands (Gordonia Formation) and underlying calcretes in the Ghaap Plateau region (Fig. 8). Thick (several m.) orange-hued sandy deposits on valley floors within the Kurumanberge may represent reworked Gordonia dune sands, at least in part. Basal alluvial gravels here mainly comprise platy clasts of BIF with little to no rounding, implying a local provenance with little current reworking. Thick (several m.), eastward-thinning prisms of ferruginized BIF colluvial gravels with occasional carbonate clasts overlie the eastern margins of the Kurumanberge where they overlie Campbell Rand Subgroup bedrocks. Most of the potentially-fossiliferous carbonate bedrocks of the Ghaap Plateau between the Kurumanberge foot slopes and Kuruman are covered by thick Kalahari dune sands and surface calcrete (Fig. 8). In a small, flat-lying area to the south of the Segame Substation low, karstified exposures of greyish carbonate bedrocks of the Campbell Rand Subgroup (probably Kogelbeen Formation) crop out (Figs. 9 & 10). They are permeated by thin bands of ferruginous secondary chert that probably reflect