Multidimensional GIS modeling of magnetic mineralogy as a proxy for fire use and spatial patterning: Evidence from the Middle Stone Age bearing sea cave of Pinnacle Point 13B (Western Cape, South Africa)

Temporal changes in magnetic signal of burnt soils - A compelling three years pilot study

Wildfires strongly affect soils, including iron biogeochemical cycling and carbon storage. Thus, it is important to reveal the dynamics of iron oxide synthesis and transformations during and after a wildfire. This study investigates the temporal stability of strongly magnetic minerals appearing after a wildfire. Following a designed experimental fire, samples from vegetation ash and mineral soil were taken immediately after and at progressively longer time intervals. The magnetic susceptibility monitoring of samples during three years period demonstrates an initial increase in magnetic signal of ash-rich material taken immediately after the fire followed by a gradual decrease over time. The behavior of samples collected later after the fire showed only a moderate decrease. It is suggested that the magnetic susceptibility rise during the laboratory storage could be due to the increased availability of nutrients and microbial activity immediately after the fire and related intense redox reactions involving iron oxide particles. The decreasing trend in magnetic susceptibility is ascribed to the oxidation of ultrafine magnetite particles with time. All mineral soil samples from the deeper level showed an initial susceptibility increase, assigned to a similar process. Magnetic susceptibility monitoring was also carried out on samples gathered shortly after natural wildfires. The soil samples affected by strong and long wildfires show a decrease in magnetic susceptibility with time. This effect is more pronounced in the surface black-colored ash layer. The ash material from a site disturbed by a strong short wildfire demonstrates behavior similar to the ash from the experimental fire. It is supposed that the temporal evolution of magnetic susceptibility of the mineral alteration products of wildfires is influenced by the grain size of the produced iron oxide particles, their redox reactions mediated by the heterotrophic bacteria, as well as the amplifying role of pyrogenic carbon for intensification of the redox reactions.

Human remains from the Pleistocene-Holocene transition of southwest China suggest a complex evolutionary history for East Asians

BACKGROUND

Later Pleistocene human evolution in East Asia remains poorly understood owing to a scarcity of well described, reliably classified and accurately dated fossils. Southwest China has been identified from genetic research as a hotspot of human diversity, containing ancient mtDNA and Y-DNA lineages, and has yielded a number of human remains thought to derive from Pleistocene deposits. We have prepared, reconstructed, described and dated a new partial skull from a consolidated sediment block collected in 1979 from the site of Longlin Cave (Guangxi Province). We also undertook new excavations at Maludong (Yunnan Province) to clarify the stratigraphy and dating of a large sample of mostly undescribed human remains from the site.

METHODOLOGY/PRINCIPAL FINDINGS

We undertook a detailed comparison of cranial, including a virtual endocast for the Maludong calotte, mandibular and dental remains from these two localities. Both samples probably derive from the same population, exhibiting an unusual mixture of modern human traits, characters probably plesiomorphic for later Homo, and some unusual features. We dated charcoal with AMS radiocarbon dating and speleothem with the Uranium-series technique and the results show both samples to be from the Pleistocene-Holocene transition: ∼14.3-11.5 ka.

CONCLUSIONS/SIGNIFICANCE

Our analysis suggests two plausible explanations for the morphology sampled at Longlin Cave and Maludong. First, it may represent a late-surviving archaic population, perhaps paralleling the situation seen in North Africa as indicated by remains from Dar-es-Soltane and Temara, and maybe also in southern China at Zhirendong. Alternatively, East Asia may have been colonised during multiple waves during the Pleistocene, with the Longlin-Maludong morphology possibly reflecting deep population substructure in Africa prior to modern humans dispersing into Eurasia.

The stratigraphy of the Middle Stone Age sediments at Pinnacle Point Cave 13B (Mossel Bay, Western Cape Province, South Africa)

Pinnacle Point Cave 13B (PP13B) has provided the earliest archaeological evidence for the exploitation of marine shellfish, along with very early evidence for use and modification of pigments and the production of bladelets, all dated to approximately 164 ka (Marean et al., 2007). This makes PP13B a key site in studies of the origins of modern humans, one of a handful of sites in Africa dating to Marine Isotope Stage 6 (MIS 6), and the only site on the coast of South Africa with human occupation confidently dated to MIS 6. Along with this MIS 6 occupation there are rich archaeological sediments dated to MIS 5, and together these sediments are differentially preserved in three different areas of the cave. The sediments represent a complex palimpsest of geogenic, biogenic, and anthropogenic input and alteration that are described and interpreted through the use of a variety of macrostratigraphic, micromorphologic, and geochemical techniques. Three independent dating techniques allow us to constrain the age range of these sediments and together provide the stratigraphic context for the analyses of the material that follow in this special issue.