Dating cave sediments
The age of the hominins in the Dinaledi Chamber has implications for our understanding of the mode and tempo of the morphological evolution of hominins (Hawks and Berger, 2016), raising questions about evolutionary stasis and the role of refugia. For the past 3 million years, hominin-bearing deposits in caves formed in broadly similar settings, involving debris cone accumulations near cave openings (Partridge, 1973; Wilkinson, 1985; Brain, 1993; Pickering et al., 2007; de Ruiter et al., 2009; Dirks and Berger, 2013; Herries and Adams, 2013; Dirks et al., 2010, 2016b; Bruxelles et al., 2014; Stratford et al., 2014), with deposits cemented by carbonate-rich waters dripping from cave ceilings (e.g., Wilkinson, 1985; Pickering et al., 2011b).The results challenge our ability to associate given hominin species to specific cultures and behaviours in the past. In contrast to all other hominin deposits in the Co H, the deposits that host H., an international team of scientists has recovered hominin genetic material from cave sediments ranging in age from 14,000 to 550,000 years ago.Nine samples, taken from four archaeological sites, produced enough mitochondrial DNA for analysis.Neanderthal DNA was found in eight of the samples, most of which came from archaeological layers where no Neanderthal remains had been recovered.
The team also looked for DNA of other mammals, and found it in layers dating to times when the animals were alive, but not in later layers dating to periods after the animals had gone extinct.
These issues are discussed in greater detail in an accompanying paper (Berger et al., 2017). naledi in Rising Star Cave are composed of largely unconsolidated, mud-clast breccia in a mud matrix with no evidence of coarse clastic sediment being carried in by water flow.
The caves in the Cradle of Humankind (Co H), South Africa have yielded rich fossil assemblages of late Pliocene to early Pleistocene age, which include a range of hominin species (A. This suggests a different depositional regime and timing for the sediments and the fossils (Dirks et al., 2015, Dirks et al., 2016a).
Rising Star Cave is situated in the Bloubank River valley, 2.2 km W of Sterkfontein Cave.
The cave system comprises several kilometres of mapped passageways (Figure 1a) that are stratigraphically bound to a 20–30 m-thick, chert-poor dolomite horizon capped by a 1–1.3 m-thick chert unit that forms the roof to the cave system (Dirks et al., 2015).