Malapa Cave formed at a fracture in stromatolite-rich dolomite bedrock, some 2.64 to 2.5 billion years ago. The sediments which represent the subsequent filling-in of the cave are subdivided into five distinct sedimentary facies, named from base to top, A-E. The oldest facies (A and B) lie beneath a flowstone sheet. Facies D held the remains of Australopithecus sediba, and Facies E contained additional hominin remains.
Facies D overlies the central flowstone and is a massive, thick (up to 1.5 meters) layer of sandstone, containing the two Au. sediba, as well as the articulated remains of ancient horse. The fossil remains of the hominins are well-preserved and in close spatial location, separated vertically by no more than 40 centimeters.
Facies E is calcareous limestone and overlies Facies D. It contains abundant fossil bone, including additional hominins, but these materials are less well-preserved than those from Facies D.
A total of 209 non-hominin fossils were recovered from Facies D and E. Uranium-bearing elements of the facies, and examination of the polarity of the flowstones, placed the date of the sediments in which the hominins lie to 1.977 mya. Scholars believe the hominids were not living in the cave, but instead fell into the cave by accident.
Sources
Berger LR, De Ruiter DJ, Churchill SE, Schmid P, Carlson KJ, Dirks PHGM, and Kibii JM. 2010. Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa. Science 238:195-204.
Carlson KJ, Stout D, Jashashvili T, De Ruiter DJ, Tafforeau P, Carlson K, and Berger LR. 2011. The endocast of MH1, Australopithecus sediba. Science 333:1402-1406.
Dirks PHGM, Kibii JM, Kuhn BF, Steininger C, Churchill SE, Kramers JD, Pickering R, Farber DL, Meriaux A-S, Herries AIR et al. 2010. Geological Setting and Age of Australopithecus sediba from Southern Africa. Science 238 205-208.
Pickering R, Dirks PHGM, Jinnah Z, De Ruiter DJ, Churchil SE, Herries AIR, Woodhead JD, Hellstrom JC, and Berger LR. 2011. Australopithecus sediba at 1.977 Ma and Implications for the Origins of the Genus Homo. Science 333:1421-1423.
