Figure 8. | Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa

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Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa

Figure 8.

Affiliation details

James Cook University, Australia; University of the Witwatersrand, South Africa; University of Johannesburg, South Africa; University of Wisconsin-Madison, United States; Simon Fraser University, Canada; University of Colorado Denver, United States; Duke University, United States; Texas A&M University, United States; University of Zurich, Switzerland; American University, United States
Figure 8.
Download figureOpen in new tabFigure 8. Comparison of selected fragments and electron microprobe analytical data of Facies 2 (Unit 3, floor) sediment in the Dinaledi Chamber, and floor sediments in the Dragon's Back Chamber.

Analytical spot size is 5 μm diameter, which is generally larger than grain sizes. (A) Chert fragment impregnated with Mn oxi-hydroxide from the Dragon's Back Chamber. (B) Shale fragment from the Dragon's Back Chamber. (C) orange mud clast, typical of Facies 2 sediments from the Dinaledi Chamber, note much finer grain size than seen in (B). (DG) Plots of K2O vs Al2O3 for mud clast fragments in Facies 2 samples from both chambers show an important difference between them. M, muscovite compositional field. The samples from the Dinaledi Chamber (EG) yield some data close to the muscovite field, probably indicating sericite grains slightly smaller than the spot size, and all show a trend with K/Al ratios much lower than muscovite, up to a high Al2O3 content >30%, which indicates either illite, or mixtures of sericite and kaolinite or other K-free clay minerals. In (E) the analysis of the fragment shown in (C) is indicated. The sample from the Dragon's Back Chamber in (D) shows data in the muscovite field (data point corresponding to [B] is indicated in [D]), but otherwise only low K- and Al-concentrations, which are typical of Mn oxi-hydroxide impregnation (data point corresponding to [a] is indicated in [D]). No analytical data in d correspond to mudstone fragments such as shown in (C). (HK), plots of Fe as FeO vs Mn as MnO show similarity between the chambers with respect to Fe-Mn oxi-hydroxide impregnations and alterations within the fragments: in both cases, domains with high Fe rarely coincide with domains high in Mn. (LO), Plots of F vs Mn as MnO. Some elevated F concentrations at zero Mn values occur, but most data show a correlation for samples from both chambers: elevated Mn content is invariably associated with elevated F, with an atomic ratio F/Mn ≈ 0.14. No Mn oxi-hydroxide minerals with F have been described, but partial substitution of F for OH as in apatite might be suspected. The similarity of the F/Mn ratios in Mn oxi-hydroxide impregnated fragments from Facies 2 sediments in both chambers suggests a uniform geochemical environment during the Mn oxi-hydroxide alteration event.