Ph.D. Candidate, James Cook University
Providing geological and taphonomical context for the hominid Homo naledi fom the Rising Star Cave.
Cave system formation and the dynamic interplay between sedimentation events, sediment supply, erosion, and re-distribution of cave sediments (and their fossils) is a highly complex and poorly understood process. The hominin-bearing Rising Star Cave (Cradle of Humankind, South Africa) forms no exception and records a highly complex sedimentary history, resulting from a combination of regional tectonics, climate, and local geomorphology. This project aims to explain the depositional history of the Rising Star Cave with the goal to enhance our understanding of cave system sedimentary processes and their effective contribution to the presence, preservation, and taphonomical signatures of the Homo naledi fossils. Achieving this goal requires detailed stratigraphic mapping, description, and cross correlation (where possible) of the different sediments across key chambers in the Rising Star Cave, and quantifying a sedimentary budget to determine the volume of insoluble sedimentary components that are either autochthonous or allochthonous in origin. A significant portion of this sedimentary budget will be obtained via experimental approach, including dissolution methods to extract insoluble detritus from dolomite; determine the age and origin (provenance) of the externally derived sediments by means of SEM-CL and detrital zircon geochronology (U-Pb LA-IC-PMS) analyses; identify the lithological and geochemical makeup of the cave sediments, in addition to recognizing taphonomical signatures of the Homo naledi fossils by means of petrographical, XRD, and Raman analyses. Combining these results with aspects of southern African Plio-Pleistocene geomorphology and climate have the potential to further enhance the understanding of the depositional history of the Rising Star Cave. Subsequently, a detailed understanding of the depositional history of the Rising Star Cave has the potential to elucidate on the tempo and mode of burial of the Homo naledi fossils. More broadly, this study will also include a comprehensive review of the geological history of this portion of southern Africa and how this history relates to cave formation processes. Understanding the processes and links between southern African tectonics and subsequent cave formation in this region is critically important and has profound implications for understanding the link between tectonic regimes and their unique control on cave system formation.
Abstract: New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of (222)Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/-70 ka, whilst a minimum age scenario yields an average age of 200 +70/-61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.
Pub.: 10 May '17, Pinned: 30 Jul '17
Abstract: Gladysvale Cave is one of the few Plio-Pleistocene hominin-bearing cave sites in South Africa that contains a well-stratified cave fill with clastic sediments interspersed with flowstones. The clastic sediments can be divided into units based on the presence of intercalated flowstones, forming flowstone bounded units (FBU). Ten MC-ICP-MS uranium-series dates on several flowstone horizons in the Gladysvale Internal Deposit fan indicate deposition from the late mid-Pleistocene ( approximately 570 ka) to Holocene ( approximately 7 ka) during limited periods of higher effective moisture. Clastic sedimentation occurred during the interceding, presumably more arid, periods. This sequence is not consistent with earlier models for South African caves that simply assumed interglacial sedimentation and glacial erosion. (13)C/(12)C data suggest that flowstone tended to form during periods with higher proportions of C(3) plants in the local vegetation, while clastic sediments reflect higher proportions of C(4) grasses, although this is not always the case. We argue that flowstones are precipitated during periods of higher effective precipitation and restricted cave entrances, while clastic sediments accumulated during periods with more open vegetation. The sedimentary fill of the fossiliferous deposits are, therefore, highly episodic in nature, with large periods of time unlikely to be represented. This has serious implications for the other hominin-bearing caves close by, as these deposits are likely to be similarly episodic. This is especially pertinent when addressing extinction events and reconstructions of paleoenvironments, as large periods of time may be unrecorded. The Gladysvale Cave fill sediments may serve as a climatically forced chronostratigraphic model for these less well-stratified and well-dated Plio-Pleistocene sites.
Pub.: 09 Oct '07, Pinned: 30 Jul '17
Abstract: We describe the geological, geochronological, geomorphological, and faunal context of the Malapa site and the fossils of Australopithecus sediba. The hominins occur with a macrofauna assemblage that existed in Africa between 2.36 and 1.50 million years ago (Ma). The fossils are encased in water-laid, clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system, immediately above a flowstone layer with a U-Pb date of 2.026 +/- 0.021 Ma. The flowstone has a reversed paleomagnetic signature and the overlying hominin-bearing sediments are of normal polarity, indicating deposition during the 1.95- to 1.78-Ma Olduvai Subchron. The two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers.
Pub.: 10 Apr '10, Pinned: 30 Jul '17