1 Palaeontological Heritage Impact assessment for N2 Upgrade between Grahamstown and Fish River. Prepared for: Coastal & Environmental Services 67 African Street Grahamstown Compiled by: Dr Robert Gess Rob Gess Consulting, Box 40, Bathurst, 6166 Research Associate of the Albany Museum, Somerset Street, Grahamstown [email protected] September 2013 2 Contents: page 1: Title page 2: Contents page 3: Background page 3: Geology page 9: Palaeontology page 10: Site Visit page 23: Conclusions and Recommendations. 3 Background Coastal and Environmental Services have been appointed to carry out a full Environmental Impact Assessment for upgrading of the N2 from north of Grahamstown to the east of the Fish River pass. Rob Gess Consulting was contracted to conduct a phase one Palaeontological Impact Assessment for this proposed development. Geology The area intended for development overlies strata of the upper portion of the Cape Supergroup and lowermost portion of the unconformably overlying Karoo Supergroup. In addition, portions of the Cape Supergroup rocks are capped by relict patches of Silcrete formed as a product of deep leaching during the Cretaceous. Cape Supergroup rocks represent sediments deposited in the Agulhas Sea, which had opened to the south of the current southern African landmass, in response to early rifting between Africa and South America during the Ordivician. The Witteberg Group is the uppermost of three subdivisions of the Cape Supergroup and was laid down during the Late Devonian and early Carboniferous. Within the study area the Lake Mentz subgroup of the Witteberg group is exposed. The Lake Menz Subgroup (Witteberg Group, Cape Supergroup) consists of four subunits (the Witpoort, Kweekvlei, Floriskraal and Waaipoort formations. The Witpoort Formation, the basal member, is characterised by thick light coloured quartzites, consolidated from mature quartz sand accumulated along a sandy shoreline, under linear barrier-island conditions. These form distinctive, resilient ridges that may be traced along the full length of the Cape Fold Belt. Thin black shale layers and lenses within this formation include deposits derived from muds carried by river systems into coastal estuarine lagoons. Much of the road is routed along the top of two great arched anticlinal folds of Witpoort Formation quartzite that have proved more resistant to weathering than the overlying mudstones. A sudden rise in relative sea level, corresponding to the Tournasion transgression at the end of the Devonian Period, terminated the sandy shoreline deposition of the Witpoort Formation, which is overlain by fine muddy sediments of the Lower Carboniferous Kweekvlei Formation. These shales generally weather to form lowered topography breaking away from the Witpoort Formation ridges. As the basin gradually shallowed, delta front and shoreline sands of the Floriskraal Formation encroached on the underlying silts and muds of the Kweekvlei Formation. Flouriskraal strata are in turn overlain by the Waaipoort mud and siltstone unit. This may represent a lagoonal environment behind and adjoining the prograding Floriskraal shoreline sands. It has been suggested that freshwater and lacustrine indicators, suggest that large lake- like environments may have developed on the continental margin. Localised glacially related 4 deposits including the Dirkskraal Formation, assigned to the Kommadagga Subgroup, are found overlying Lake Mentz subgroup in some parts of the Eastern Cape. The Witteberg is terminated by an unconformity, or gap in the geological record, of possibly 30 million years, after which the massive diamictites of the Dwyka Group (Karoo Supergroup) were deposited, indicating that an ice age had passed. This would be in keeping with palaeomagnetic interpretations which suggest that, at the time of deposition of the Witteberg Group, what is now South Africa was within the Antarctic circle. The strata of the Karoo Supergroup were deposited within the Karoo sedimentary Basin, which resulted from shortening and thickening of the southern margin of Africa, with coeval folding and uplift of the Cape Supergroup strata along its southern margin. Lowermost Karoo strata of the Dwyka and lower Ecca Groups were affected by folding in the vicinity of the Cape Fold Belt. The Dwyka Group (Karoo Supergroup), particularly here in the south of the basin consists almost exclusively of diamictite known as the Dwyka tillite. This is a distinctive rock type which, when freshly exposed, consists of a hard fine-grained blueish-black matrix in which abundant roughly shaped clasts are embedded. These vary greatly in both lithology and size. During the formation of the Dwyka, beginning in the late Carboniferous, southern Africa drifted over the south pole, whilst simultaneously, the world was experiencing a cold episode. Glaciers flowing into the flooded Karoo basin broke up, melted and discharged a mixture of finely ground rock flour and rough chunks of rock. These formed the matrix and clasts of the Dwyka tillite. Early in the Permian period the ice sheets retreated and fine muds were washed into the Karoo Basin, forming the Prince Alfred and Whitehill formations of the lower Ecca Group. These interfinger, at first, with the last tillites. Subsequent deposition of the Collingham, Ripon and Fort Brown and Waterford formations of the Ecca Group resulted from sediment carried into the Ecca Lake by rivers draining the recently upthrust Cape Mountains. These rivers formed deltas where they flowed into the Ecca Lake. Proximally the deltas tended to be sandy. Mud accumulating on the more distal front of the deltas periodically slumped and cascaded down into deep water, spreading out and depositing large layered fan shaped turbidite deposits. As the Ecca Lake silted up a subaerial (exposed) shoreline began to develop, initially in the south east of the basin. The lake steadily shrank towards the centre of the basin, leaving behind flat silty plains across which long rivers meandered from the Cape Mountains towards the much reduced lake. Sands were deposited along the river channels whereas periodic flooding deposited muds on the broad flood plains. These in time came to form the interbedded sandstones and mudstones of the Koonap, Middleton and Balfour formations of the Adelaide Subgroup, Beaufort Group. 5 During the Cretaceous and early Tertiary Periods much of Africa was weathered down to a number of level horizons collectively known as the African Surface. The area in the vicinity of Grahamstown was reduced to a flat plain close to sea level, remnants of which are referred to as the Grahamstown Peneplane. During the Tertiary, mudstones, shales and diamictites were leached to considerable depth, transforming them into soft white kaolin clay. Silica, iron and magnesium from these rocks was carried in solution by groundwater and deposited near the ground surface due to steady evaporation of mineral rich waters. This lead to the formation of a hard mineralised capping layer, often consisting of silicified soil. Resultant silcretes are referred to as the Grahamstown Formation. Though occasional occurrences of root and stem impressions have been recorded from the Grahamstown Formation it is generally considered unfossiliferous. With subsequent reduction of the relative sea level, deep valleys have carved back from the retreating coastline, cutting deep valleys and catchment areas into the African Surface. 6 Figure 1. Geological map of the study area based on geological survey data overlain on topography, with positions of the road route, borrow pits, quarries and info points overlain. 7 Figure 2: Stratigraphic column of the Cape Supergroup modified after Theron and Thamm (1990) following Cotter (2000). Red line indicates strata impacted by the development. 8 Figure 3: Karoo stratigraphy and biostratigraphy (after Smith et al., 2012). Red line indicates stratigraphic interval impacted by proposed development. 9 Palaeontology The stratigraphically lowest Witteberg Group strata present belong to the Late Devonian (Famennian) Witpoort Formation ( Lake Mentz Subgroup, Witteberg Group, Cape Supergroup) This largely quatzitic unit represents mature sandy strata deposited along a linear barrier island type coast. Particularly around Grahamstown black shale lenses, interpreted as estuarine deposits preserved during brief transgressive events, have proved remarkably fossiliferous. A series of lenses at Waterloo Farm, to the south of Grahamstown, have provided southern Africa’s most important Late Devonian locality, which has yielded at least 20 taxa of fossil fish (including jawless fish (Agnatha), armoured fish (Placodermi), spiny sharks (Acanthodii), sharks (Chondrichthyes), ray finned fish (Actinopterygii) and lobe finned fishes (Sarcopterygii) including Coelacanths (Actinistia), lungfish (Dipnoi) and Osteolepiformes. Dozens of plant and algal taxa have been collected, as well as remains of giant eurypterids and other arthropods such as scorpions. These latter fossils represent the oldest known terrestrial animal remains from Gondwana. Abundant trace fossils have also been collected. The top of the Witpoort Formation coincides with the end of the Devonian and is similar in age to the end-Devonian extinction event. Witpoort Formation quartzites have yielded a range of plant stem taxa and trace fossils. Lag deposits of bone have not, as yet, been discovered, but may be expected. The remainder of the Lake Mentz Subgroup, the Kweekvlei Formation, Floriskraal Formation and Waaipoort Formation