Fig 5 - available via license: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Content may be subject to copyright.
Thin section and photomicrographs for the ACC. A) Sample AV01 represents the basal flowstone from Pit 5 and Facies E B) Sample AV08 exhibits the vuggy nature of Facies B from Pit 14. C) Sample AV10 represented Facies F and shows a fining up sequence of laminated silt and sand.
Source publication
The region ∼40 km north-west of Johannesburg, South Africa, known locally as the Cradle of Humankind, is of global significance as the caves preserve Plio-Pleistocene faunal and early hominin fossils. Despite a long history of research, there is still a need to contextualise and date the remarkable collection of fossils. An important but understudi...
Contexts in source publication
Context 1
... sections were prepared to assist with lithofacies identification ( Fig. 5 ). An additional aim of the petrographic analysis was to determine mode of deposition and assess the viability of samples for palaeomagnetic analysis (AV01, AV08, AV10) and to define the calcite fabric of U-Pb dated layers (AV03, AV01; Fig. 6 ). ...
Context 2
... combined U-Pb magnetostratigraphy for the three sites is presented in Fig. 4 , with stratigraphic columns documenting the mode of deposition (externally derived clastic sediments vs flowstone). Facies for the site are presented in Table 1 . Thin section analyses were carried out to assist in lithofacies identification ( Table 2 ; Fig. 5 ) and to test the suitability of U-Pb samples (summarised in Table 3 ; Fig. 6 ) and palaeomagnetic samples ( Table 4 ). U-Pb dates were produced for the basal and capping flowstone with Terra-Wasserberg plot shown in Fig. 7 . Rock magnetic analysis shows that sample blocks preserve a stable magnetic record ( Fig. 8 ) and palaeomagnetic ...
Context 3
... section analysis was carried out to further characterise the facies, and to assess the suitability of samples for U-Pb and palaeomagnetic analysis ( Fig. 5 ; Fig. 6 ). AV01 is a flowstone sample which represents Facies E in Pit 5. The initiation of Facies B is observed in sample AV08 from Pit 14. AV10 from Pit 14 represents Facies F. Results for analysed thin sections are summarised in Table 2 . Fig. 5 A, shows flowstone sample AV01, the basal flowstone. This sample has five units of growth with ...
Context 4
... the facies, and to assess the suitability of samples for U-Pb and palaeomagnetic analysis ( Fig. 5 ; Fig. 6 ). AV01 is a flowstone sample which represents Facies E in Pit 5. The initiation of Facies B is observed in sample AV08 from Pit 14. AV10 from Pit 14 represents Facies F. Results for analysed thin sections are summarised in Table 2 . Fig. 5 A, shows flowstone sample AV01, the basal flowstone. This sample has five units of growth with the lower four being composed of precipitated CaCO 3 (calcium carbonate) and the top a clastic unit cemented with calcite. The basal unit is low porosity composed of large equant calcite crystals with a thin detrital layer ( Fig. 5 A1). Unit ...
Context 5
... capping unit has an irregular basal contact and is marked by an increase in clay content, and a dominance of large (200-300 μm) angular to sub rounded quartz grains in a calcite spar cement ( Fig. 5 A4) 4.1.2. Facies B: silty sandstone AV08 is a vuggy siltstone, with seven low porosity units defined by differences in calcite abundance and crystal form and the presence and abundance of lithic grains ( Fig. 5 B). The basal unit is a matrix supported silt with poorly sorted angular to sub rounded quartz and chert grains. ...
Context 6
... of alternating units of fine sand with high clay content and fine sands with high calcite content. This unit is low porosity, moderately sorted with angular to rounded quartz, 50% lithic grains 100-250 μm, 20% 30-100 μm. Rare bone is noted throughout unit along with degraded drusy calcite spar infilling voids. A thick sandy unit can be seen in Fig. 5 C3 which shows a short-lived change in feeding sediment, contrasting with the microlaminations seen in Fig. 5 ...
Context 7
... is low porosity, moderately sorted with angular to rounded quartz, 50% lithic grains 100-250 μm, 20% 30-100 μm. Rare bone is noted throughout unit along with degraded drusy calcite spar infilling voids. A thick sandy unit can be seen in Fig. 5 C3 which shows a short-lived change in feeding sediment, contrasting with the microlaminations seen in Fig. 5 ...
Citations
... These periods include the Pre-Pretoria Group period, the Pre-Waterberg Group period, and the Pre-Karoo and Cenozoic or Recent periods. While most of the ancient karst has eroded over time, there are still remnants of a fossil karst landscape, dating from arguably the oldest karst forms in the world (Martini and Kavalieris, 1976;Partridge and Maud, 1987;Partridge and Watt, 1991;Edwards et al., 2020). The karst landscapes found here include karst caves such as the Sudwala Caves. ...
Globally many valuable karst resources are under severe threat due to anthropogenic activities. This paper presents a review of the geomorphology of karst landforms including caves, sinkholes, etc. in southern Africa. It further presents the environmental threats and challenges faced by these karst landscapes, their genesis and controlling factors, as well as their possible mitigation and remedial measures. The karst landscapes in the region are most abundant in the interior of the sub-continent, whereas coastal karst is sparsely distributed and is mainly found in the Eastern and Western Cape and Kwa-Zulu Natal provinces of South Africa, as well as parts of Namibia. The karst of the interior is largely limited to the Proterozoic dolomitic limestone, while coastal karst is formed in the Tertiary coastal limestone and Quaternary calcareous sandstones. The human impacts threatening karst in southern Africa include mining and mineral extraction, construction and development, agricultural activities, climate change, and changes in the local hydrogeology. Anthropogenic impacts have particularly affected the karst landscape of the Gauteng and northern Free State Provinces of South Africa due to groundwater extraction associated with mining. Changes in land use and water management, consequential to development pressures and a variety of climate change scenarios, are the most significant threats currently facing southern African karst terrain. It is argued that sustainable engineering technologies, informed by sound geomorphological research, are necessary to ensure that future development, property, and life on karst terrain are safe from avoidable environmental problems.
... Allostratigraphic units (utilised in sequence stratigraphy) are deposits bounded by disconformities or unconformities at their upper and lower contacts (e.g. Edwards et al., 2020;Stanistreet et al., 2018). Soil stratigraphic units are deposits which can be identified as one or more horizons of a buried soil (e.g. ...
... Klasies is an undeniably complicated site compared to most MSA sites in southern Africa, with the varied depositional environments across the complex and the presence of both primary and secondary deposits making it perhaps more akin to the stratigraphic complexity of the karstic sites the Cradle of Humankind (e.g. Edwards et al., 2020;Stratford., 2020;Sutton et al., 2009), while the removal of deposits by erosion and excavation has made stratigraphic work even more difficult. However, this review highlights several issues of significance for research at other MSA cave and rock shelter sites, especially those which have undergone multiple phases of fieldwork. ...
Klasies River Main site, on South Africa’s southern Cape coast, has contributed significantly to understanding Late Pleistocene human evolution. Excavations across this complex of caves and rock shelters have uncovered important assemblages of human fossils, faunal remains and lithic artefacts which have allowed interpretations of human anatomy and behaviour, and the palaeoenvironmental context of human occupations. The stratigraphy of the site is complicated, and the deposits have been recorded and published at varying degrees of resolution and detail over three phases of fieldwork. This paper is the first detailed review of the stratigraphy of any part of the sequence, and considers the different stratigraphic approaches used at Klasies and the published data and interpretations for the basal deposits. These units have been assigned to the Light Brown Sand, Rubble Brown Sand and Shell and Sand Members, and have yielded MSA I and MSA II lithic assemblages and most of the human fossils. We argue that some of the published stratigraphic interpretations need to be reconsidered, that a purely lithostratigraphic approach to the deposits at Klasies is not currently viable and that further field description and micromorphological work is needed. More broadly, this review demonstrates potential complications for stratigraphic correlation during the reinvestigation of previously excavated sites. These include the importance of understanding site formation processes in a lithostratigraphic system, and the need to think about how, why and at what resolution we make correlations between different stratigraphic systems or different areas within a site or site complex.
... The technique has also been used, in conjunction with electron spin resonance (ESR) to date tooth enamel of fossil fauna in the Cradle, . However, most of the hominin-bearing sites in the Cradle have speleothems older than 500 ka and the uranium-lead ( 238 U-206 Pb, hereinafter U-Pb) isochron dating method has been used to date these (Walker et al., 2006;de Ruiter et al., 2009;2011a, b;Dirks et al., 2010;Hopley et al., 2019;Edwards et al., 2020). For Pliocene and younger samples, the U-Pb method requires a U content around 1 ppm or higher, and low contents of common Pb which must have a homogeneous initial isotope composition. ...
... In accord with this, Pickering and Edwards (2021) found that 'good', 'bad' and 'ugly' U-Pb ages (those with errors <5%, between 5 and 10% and >10%, respectively), can all be yielded by speleothems with fabrics ranging from primary to the most intense diagenetic mosaics with aragonite relics. Further the process has been argued to occur in early diagenesis in speleothems from the Cradle, taking place within 1000 years after formation (Edwards et al., 2020;Pickering and Edwards, 2021). Thus any accompanying He loss is not expected to affect apparent (U,Th)-He ages for old speleothems significantly. ...
The geochronology of cave deposits in the Cradle of Humankind UNESCO World Heritage Site in South Africa provides a timeframe essential for the interpretation of its fossils. The uranium-lead (U–Pb) and uranium-thorium disequilibrium (U/Th) dating of speleothems, mostly flowstones that underlie and blanket the fossil-bearing sediments, have been effective in this sense, but U–Pb is limited by the requirement of ∼1 ppm U concentrations and low common Pb contents, and U/Th has a c. 500 ka limit of applicability. Here we report age results for calcite-aragonite speleothems obtained using a new combined uranium-thorium-helium ((U,Th)–He) and U/Th dating routine. We reproduced within analytical uncertainty, the published U–Pb or U/Th ages for (a) flowstone in three drill core samples in the range 2000–3000 ka, (b) a flowstone hand sample taken at surface with an age of 1800 ka, and (c) five underground flowstone samples in the range 100–800 ka. Calcite retentivity for He under cave conditions is thus demonstrated. In the few cases where helium loss was observed in speleothems, only some of the subsamples were affected, and to varying degrees, suggesting loss by lattice damage not related to diagenetic processes, rather than volume diffusion. In the 100 to 800 ka range, the combined U/Th disequilibrium and (U,Th)–He method also yielded reliable values for initial (²³⁰Th/²³⁸U) and (²³⁴U/²³⁸U) activity ratios. Importantly, most subsamples had high initial (²³⁰Th/²³⁸U) values, ranging from 1.0 to 19.7, although having low Th/U ratios. This is probably due to incorporation of Fe–Mn oxides-hydroxides dust, on which ²³⁰Th was previously adsorbed. Such samples are mostly not dateable by U/Th without the additional input from the He analysis. If not detected and corrected for, such high initial (²³⁰Th/²³⁸U) values can lead to inaccurate U/Th and U–Pb ages. Our study shows that the incorporation of He analysis in U/Th dating has broad potential application, with four methods for calculating the ages, in carbonates from different environments where U-Pb or U/Th dating would not work.
Bolt’s Farm is the name given to a series of non-hominin bearing fossil sites that have often been suggested to be some of the oldest Pliocene sites in the Cradle of Humankind, South Africa. This article reports the results of the first combined Uranium-Series and Electron Spin Resonance (US-ESR) dating of bovid teeth at Milo’s Cave and Aves Cave at Bolt’s Farm. Both tooth enamel fragments and tooth enamel powder ages were presented for comparison. US-ESR, EU and LU models are calculated. Overall, the powder ages are consistent with previous uranium-lead and palaeomagnetic age estimates for the Aves Cave deposit, which suggest an age between ~3.15 and 2.61 Ma and provide the first ages for Milo’s Cave dates to between ~3.1 and 2.7 Ma. The final ages were not overly dependent on the models used (US-ESR, LU or EU), which all overlap within error. These ages are all consistent with the biochronological age estimate (<3.4–>2.6 Ma) based on the occurrence of Stage I Metridiochoerus andrewsi . Preliminary palaeomagnetic analysis from Milo’s Cave indicates a reversal takes place at the site with predominantly intermediate directions, suggesting the deposit may date to the period between ~3.03 and 3.11 Ma within error of the ESR ages. This further suggests that there are no definitive examples of palaeocave deposits at Bolt’s Farm older than 3.2 Ma. This research indicates that US-ESR dating has the potential to date fossil sites in the Cradle of Humankind to over 3 Ma. However, bulk sample analysis for US-ESR dating is recommended for sites over 3 Ma.
Waypoint 160 is a paleocave at Bolt's Farm in the 'Cradle of Humankind,' South Africa. It is known for the novel murid taxa Eurotomys bolti, argued to be morphologically intermediate between Eurotomys pelomyoides from Langebaanweg (∼5.1 Ma) and the earliest Otomyinae from Makapansgat Limeworks (∼3.0-2.6 Ma). Based on the presence of this specimen, an age of ∼4.5 Ma was inferred for Waypoint 160, making it far older than other Cradle sites. This biochronological age was used to argue that Parapapio and Cercopithecoides fossils from Waypoint 160 were the oldest in the region. Here, we provide a detailed sedimentological context for the in-situ deposits at Waypoint 160. We have identified interior cave deposits, in contrast to other sites at Bolt's Farm. Petrography confirms that one unit (facies D) contains in-situ microfaunal fossils, indicating the likely provenience of the E. bolti specimen. Palaeomagnetic analysis shows four periods of magnetic polarity in the sequence. Using U-Pb ages as chronological pins, we argue that the upper part of the sequence records a polarity change at the end of the Olduvai subChron (1.78 Ma). The lower part of the sequence records a polarity shift from normal to reversed that likely relates to the Feni subChron (2.16-2.12 Ma), based on a basal flowstone U-Pb age of 2.269 ± 0.075 Ma. Together this points to a depositional window of ∼500 ka, with the Parapapio and E. bolti tentatively attributed to the micromammal fossil-bearing layers dating to ∼2.27-2.07 Ma. This has significant implications for other biochronological dates in South Africa, as E. bolti is now less than ∼2.27 Ma, younger than the oldest Otomyinae at Makapansgat Limeworks and thus not ancestral to them. This chronology for Waypoint 160 challenges the presence of older, early to mid-Pliocene deposits >3.20 Ma in the Gauteng portion of the Cradle.
Caves in South Africa preserve a rich record of early hominin and early modern human development and have been the subject of much research. UPb dating of speleothems, particularly flowstones, has provided a much-needed chronology for cave sites in the Cradle of Humankind, the coastal cliff caves at Pinnacle Point and at the archaeological site of Wonderwerk Cave. The UPb ages range from ~3 Ma to just under 1 Ma and altogether represent a relatively large dataset of 35 U-Pb ages, from 34 flowstone samples, consisting of a total of 291 individual matched U and Pb isotope analyses. We look for patterns within these data and find that in general, the U concentration has little to no effect on age quality, while the lower Pb concentration, the better. Our data confirms the expected negative exponential relationship between UPb age and ²³⁴U/²³⁸U. There is no apparent relationship between U concentration and residual ²³⁴U/²³⁸U, suggesting U concentration patterns are controlled by ²³⁸U, not ²³⁴U. We divide the 35 U-Pb ages into three categories defined by the % error on the UPb age (the good, the bad and the ugly). We use the U and Pb isotope data, thin section petrography and laser ablation trace element transects through the flowstones to investigate the factors controlling the quality of the ages. The ‘good’ ages are produced by the coincidence of several features: a large number of points (10 or more) defining their isochrons, radiogenic ²⁰⁶Pb/²⁰⁴Pb ratios, with a few very radiogenic points defining the line of the isochron, U concentrations of ~1 ppm and well-preserved trace element signals. ‘Bad’ ages are caused by deficit in one of these factors but may be redeemed with additional analysis to better define the line of isochron and constrain initial ²³⁴U/²³⁸U. The ‘ugly’ ages are attributable to low levels of radiogenic Pb, a low spread of isochron and high Pb concentrations, possibly from detrital material. We show what a completely recrystallized flowstone looks like, where the original trace element signals are completely obliterated, and it is impossible to resolve a UPb age. The thin section petrography reveals all flowstones have undergone heavy diagenesis, with the dominant fabric observed consisting of mosaic calcite with relic aragonite. However, we argue that the preservation of trace element signals, in particular the abrupt, sympathetic step-like variation is Sr, U and in some cases Ba and Mg, indicate that this diagenesis is conservative. We identify a mixture of crystal and fluid dominated trace element patterns, both of which are ultimately related to flow dynamics, in turn related to changes in external hydroclimate. This hints at the potential to extract valuable palaeoclimate records out of these old, UPb dated flowstones, which would be very interesting given their association with important early human evolution sites in South Africa.
