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Uranium-Lead dating of hominid fossil sites in South Africa

By Joanne Walker

Abstract

Discoveries of hominid, or apeman, fossils in the twentieth century have brought human evolution into the scientific spotlight. It is important that ages are assigned to such hominids so that their place in human evolution can be established. South African hominids are found in cave sites that are complex in terms of their stratigraphy.\ud Dating methods previously applied at the caves include faunal, palaeomagnetic, electron-spin resonance and cosmogenic isotope methods. These have been unable to give conclusive ages to the fossils. South African hominids are therefore poorly dated in comparison to their East African counterparts, which lie in volcanic deposits that are more simply stratified and more simply dated.\ud \ud \ud U-Pb dating is a radiogenic method proven to be applicable to carbonate deposits. More recently it has been applied to young speleothem deposits with sufficiently high concentrations of U and low levels of common Pb. In this study U-Pb dating is applied to speleothern deposits in stratigraphic context with the South African hominid fossils.\ud \ud \ud Samples were taken from the Silberberg Grotto at Sterkfontein. The hominid fossil, StW 573, was found here in 1998. Three layers of flowstone were sampled, two\ud from above the skeleton and one from below. The combined results indicate an age for StW 573 of ≈\ud 2.2Ma. This is considerably younger than previous age estimates have inferred. Samples from three other caves were analysed - Kromdraai, Swartkrans and the Limeworks - but these did not produce reliable ages.\ud \ud \ud Within the samples both U and Pb were found to vary spatially over small scales in quantity, and Pb in composition too. Published studies in the area have revealed a major 234U excess in groundwater and speleothem. Where conventional age calculations are used this effect could result in an age much greater than the true age. After the sample analyses presented here, 234U excess analyses of some samples became available and these were used to calculate corrected ages. Variations in initial Pb composition introduced scatter on the age plots but this was\ud not investigated further here.\ud \ud \ud The results are presented firstly as maximum ages and following correction for 234U excess, as best estimates. The flowstone layers immediately above - layer 2C - and\ud below - layer 2B - StW 573 gave maximum abg es of 3.04 ± 0.08Ma (SK3 result) and 2.97 ± 0.13Ma respectively. Layer 2C was corrected for disequilibrium and gave a\ud best estimate age of 2.17 ± 0.17Ma using a weighted average of three results. The corrected age for Layer 2B was 2.24 + 0.09/ - 0.07.\ud \ud \ud There are important implications for the U-Pb age of StW 573. Firstly it provides evidence as to the age and formation of the Sterkfontein cave and therefore other hominid bearing caves with comparable faunal assemblages. The cave sediments exhibit complex stratigraphic relationships that render chronostratigraphy uncertain. More importantly it lends further information on how South African hominids fit into the family tree. At 2.2Ma StW 573 may come under the classification of Australopithecus africanus and be contemporaneous with the fossil Sts 5, also from Sterkfontein, which had previously been considered to postdate StW 573. It also confirms that the South African branch of this genus is probably not\ud as ancient as the East African and that these hominids were not widespread in Africa at 4Ma. With the first evidence for the genus Homo at 2.5Ma, StW 573 is unlikely to be a direct ancestor of modern humans.\ud \ud \ud Beyond their implications for human evolution, these results confirm the applicability of U-Pb dating to carbonates, and more specifically to young carbonates

Publisher: School of Earth and Environment (Leeds)
Year: 2005
OAI identifier: oai:etheses.whiterose.ac.uk:746

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Citations

  1. (1995). A highly sensitive HPLC method for the determination of Th and U concentrations in geological samples. doi
  2. (1994). A new explanation for extreme 234U/238 U disequilibria in a dolomitic aquifer. doi
  3. (1964). Anion Exchange Characteristics of Elements in Nitric Acid Medium. Analytical Chemistry 36,1157-1158. doi
  4. (1965). Anion Exchange Separations in Hydrobromic Acid-Organic Solvent Media. doi
  5. (2000). Ape-man: The story of human evolution.
  6. (2000). Appendix on Magnetostratigraphy of Makapansgat, Sterkfontein, Taung and Swartkrans. In doi
  7. (2003). Applications of Speleothems. In doi
  8. (1992). Archaeological Applications.
  9. (1982). Biostratigraphy and chronology, based particularly on Bovidae, of southern hominid-associated assemblages: Makapansgat, Sterkfontein, Taung, Kromdraai, Swartkrans; also Elandsfontein (Saldanha), Broken Hill (now Kabwe) and Cave of Hearths.
  10. (2002). Brief Communication: Revised Age Estimates of Australopithecus-Bearing Deposits at Sterkfontein, South Africa. doi
  11. (1992). Carbonate and Sulphate precipitates.
  12. (1988). Cathodoluminescence of Geological Mate7ials. Unwin Hyman. doi
  13. (1974). Chronological and ecological implications of the fossil Bovidae at the Sterkfontein Australopithecine site. doi
  14. (1978). Comparative UraniumThorium-Lead and Rubidium- Strontium study of the Saint Severin amphoterite: consequences for early solar system chronology. doi
  15. (1982). Crustal Evolution of Southern Africa: 3.8 Billion Years of Earth History. doi
  16. (2002). Dating of the depositional sequence and Australopithecine "Grey Breccia" of Makapansgat Limeworks using magnetostratigraphy.
  17. (1997). Dating of the time of sedimentation using U-Pb ages for paleosol calcite. doi
  18. (2003). Dating the Sterkfontein Fossils.
  19. (1993). Description and Preliminary Analysis of New Hominid Craniodental Fossils from the Swartkrans Formation. In doi
  20. (1982). Developpement de Vensemble Chronometrique U-Th-Pb. Contribution a la Chronologie Initiale du Systeme Solaire. These de doctorat d'etat, Universite de Paris VII.
  21. (2001). Direct ESR dating of a Pliocene hominin from Swartkrans. doi
  22. (1991). Direct radiometric age determination of carbonate diagenesis using U-Pb in secondary calcite. doi
  23. (1985). Early Hominids in Southern Africa: updated observations on chronological and ecological background. In
  24. (1977). Effect of initial radioactive-daughter disequilibrium on U-Pb isotope apparent ages of young minerals.
  25. (2000). Electron Spin Resonance dating of fault rocks. In doi
  26. (2002). Electron spin resonance dating of tooth enamel from Kromdraai B, South Africa.
  27. (1987). Electron Spin Resonance dating of tooth enamel. doi
  28. (1994). ESR dating studies of the australopithecine site of Sterkfontein, South Africa. doi
  29. (1987). First direct radiometric dating of Archean stromatolitic limestone. doi
  30. (1998). First ever discovery of a well-preserved skull and associated skeleton of Australopithecus.
  31. (1980). Further observations on the nature and provenance of the lithic artefacts from the Makapansgat Limeworks. Palaeontologia Afficana
  32. (1997). Further remains of carnivora (mammalia) from the Sterkfontein Hominid site. Palaeontologia Afficana 34,115-126.
  33. (1973). Geomorphological Dating of Cave Openings at Makapansgat, Sterkfontein, Swartkrans and Taung. doi
  34. (2003). Great Age suggested for South African Hominids. doi
  35. I (2002b). On the unrealistic 'Revised age estimates' for Sterkfontein.
  36. (1973). Implications of the New Age Estimates of the Early South African Hominids. doi
  37. (2003). ISOPLOT 3.00: A Geochronological Toolkit for Microsoft Excel.
  38. (1981). Isotopic Determination of Uranium in Picomole and Subpicomole Quantities. doi
  39. (1973). Isotopic Lead ages of Chondritic Meteorites. doi
  40. (2001). Isotopically heterogeneous initial Pb and continuous 222 Rn loss in fossils: The U-Pb systematics of Brachiosaurus brancai. doi
  41. (1989). Karst Geomorphology and Hydrology. Unwin Hyman. doi
  42. (2003). Lower Pliocene Hominid remains from Sterkfontein. doi
  43. (2002). Newly revealed information on the Sterkfontein Member 2 Australopithecus skeleton.
  44. (1970). Notes from members.
  45. (1994). On some new interpretations of Sterkfontein stratigraphy.
  46. (1991). Palaeo-ecology of the Sterkfontein Hominids: A review and synthesis.
  47. (1981). Palaeoecology of Aftica and the Surrounding Islands,
  48. (1986). Palaeoecology of the Pliocene and Lower Pleistocene hominids of Southern Africa: how good is the chronological and palaeoenvironmental evidence?
  49. (2004). Palaeoenvironmental reconstruction of South Affican hominin-bea7ing cave deposits using stable isotope geochemistry.
  50. (1981). Palaeomagnetic results from the Kromdraai and Sterkfontein hominid sites.
  51. (2002). Palaeornagnetic analyses of calcified deposits from the Plio- Pleistocene hominid site of Kromdraai,
  52. (1994). Pb-Pb and U-Pb geochronology of carbonate rocks: an assessment. doi
  53. (1996). Petrographic Evidences of Diagenesis in Speleothems: Some examples. Speleochronos 7,21-30.
  54. (2001). Pliocene- Pleistocene incision of the Green River, Kentucky, determined from radioactive decay of cosmogenic "Al and "Be in Mammoth Cave sediments. doi
  55. (1977). Preliminary palaeomagnetic results from Makapansgat and Swartkrans. doi
  56. (1986). PTinciples of Isotope Geology doi
  57. (1997). Quaternary downcutting rate of the New River, Virginia, measured from differential decay of cosmogenic "Al and "Be in cave-deposited alluvium. doi
  58. (1979). Re-appraisal of lithostratigraphy of Makapansgat Limeworks hominid site. doi
  59. (1978). Re-appraisal of lithostratigraphy of Sterkfontein hominid site. doi
  60. (1995). Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. doi
  61. (1957). Separation of Thorium and Uranium Nitrates by Anion Exchange. doi
  62. (1995). Serni-non-destructive, single aliquot ESR dating.
  63. (1910). Solution of a system of differential equations occurring in the theory of radio-active transformations.
  64. (1975). Some evidence of chronology and palaeoecology of Sterkfontein, Swartkrans and Kromdraai from the fossil Bovidae. doi
  65. (1982). Some preliminary observations on the stratigraphy and sedimentology of the Kromdraai B Horninid site. In
  66. (2004). Southern Africa: a cradle of evolution.
  67. (1973). Sterkfontein Cave System: Evolution of a Kaxst Form. MSc thesis,
  68. (1995). Sterkfontein Member 2 Foot Bones of the Oldest South African Hominid. doi
  69. (1993). Structure and Stratigraphy of the Swartkrans Cave in the Light of the New Excavations. In
  70. (1977). Subcommission on Geochronology: Convention on the use of decay constants in geo- and cosmochronology. doi
  71. (2003). The Behavior of U- and Th-series Nuclides in Groundwater. In doi
  72. (2004). The context of Stw 573, an early hominid skull and skeleton from Sterkrfontein Member 2: taphonomy and paleoenvironment. doi
  73. (2003). The formation and sedimentary infilling of the Limeworks Cave, Makapansgat, South Africa. Palaeontologia Afficana doi
  74. (2000). The Fossil Hominids. In doi
  75. (1995). The impact of diagenesis on high-precision U-Pb dating of ancient carbonates: An example from the Late Permian of New Mexico. doi
  76. (1995). The Influence of Climatic Changes on the Completeness of the Early Hominid Record in the Southern African Caves, with Particular Reference to Swartkrans. In
  77. (1999). The Makapansgat Australopithecine site from a speleological perspective. In doi
  78. (1981). The Making of Mankind. doi
  79. (1999). The new Hominid skeleton from Sterkfontein: Age and preliminary assessment. doi
  80. (1999). The Sequence stratigraphic concept and the Precambrian rock record: an example from the 2.7-2. lGa Transvaal Supergroup, Kaapvaal craton. doi
  81. (1991). The stratigraphy of the Sterkfontein Hominid Deposit and its relationship to the underground cave system.
  82. (2004). The stratigraphy, chronology and palaeoenvironment of the Pleistocene cave fill, Gladysvale Cave, South Africa,. MSc thesis,
  83. (2000). The transfer of uranium isotopes 234U and "'U to the waters interacting with carbonates from Mendip Hills area (England). Applied Radiation and Isotopes doi
  84. (1958). The Transvaal ape-man-bearing cave deposits. doi
  85. (1976). The Uranium-series methods of age determination. doi
  86. (2001). Thermal ionization mass spectrometry U-series dating of a homind site near Nanjing, China. Geology 29,27-30. 206 Appendices 207, doi
  87. (1995). U-Pb dating of a carbonate subaerial exposure event. doi
  88. (1991). U-Pb dating of a remagnetized paleozoic limestone. doi
  89. (1996). U-Pb dating of calcite concretions from Cambrian black shales and the Phanerozoic time scale. doi
  90. (1994). U-Pb systematics and alteration trends of Pennsylvanian-aged aragonite and calcite. doi
  91. (2003). U-series dating and Human Evolution. In doi
  92. (1992). U-Th chemistry and mass spectrometry at Lamont.
  93. (1985). U/Pb dating of discordant 0.1 Ma old secondary U minerals. doi
  94. (1975). U234/U23' Ratios in limestone cave seepage waters and speleothem from West Virginia. doi
  95. (1998). UPb Dating of a speleothem of Quaternary age. doi
  96. (1978). Uranium series dating and stable isotope studies of speleothems: Part 1. Theory and Techniques.
  97. (1975). Uranium series dating of stalagmites from Blanchard Springs Caverns, doi
  98. (2000). Uranium-series methods. In doi

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