Abstract The Lower Son Valley is generally overlooked despite a lengthy history of archaeological and geological studies in the adjacent Middle Son Valley. However, recent explorations in the former have yielded a large number of Palaeolithic and microlithic sites. This paper provides an initial report on Doma, a newly discovered site with the first-known stratified bifaces in this part of the valley. The site preserves multi-period technologies in different contexts, including terminal Acheulean/early Middle Palaeolithic and Upper Palaeolithic (all tentatively assigned based on respective typologies). Preliminary field observations are presented on the sedimentary sequence, archaeological surveys, topographical mapping, raw material and the overall palaeoanthropological assessment of Doma. The raw material utilized at the site is primarily porcellanite, derived from exposures of the Semri Group of the Vindhyan Supergroup. The oldest Palaeolithic evidence at Doma broadly resembles Late Acheulean sites dated to c. 140–120 ka in the nearby Middle Son Valley. The Pleistocene sediments here also yielded mammalian fossil specimens, such as long bone fragments, dental specimens and antler fragments. Along with the lithics and fossils, the site also preserves datable sedimentary sequences with calcrete, all key proxies in developing a testable model of technological transitions within a palaeoenvironmental framework, in the future.

Abstract Colloid concentration is an important parameter in models of colloid-facilitated transport. The purpose of the present study is to characterize colloid concentrations and colloid stability in natural groundwater from the Horonobe Underground Research Laboratory (URL) in Hokkaido, Japan. The particle sizes of colloids in groundwaters from the Horonobe URL range from several nanometres to c . 500 nm, with a mode particle size of c . 120 nm. Evaluation of colloid stability by DLVO theory suggests that larger colloids (i.e. >100 nm in diameter) would be more stable than smaller colloids in some groundwaters. The estimated colloid particle concentrations when considering the results of DLVO calculations ranged from 2.33 × 10 6 to 1.12 × 10 8 particles/ml, and mass concentrations were estimated to range from 45 to 1540 µg l −1 for diameters greater than 100 nm. Colloids in Horonobe groundwaters appear to be less stable, with a moderate potential for transport, than colloids investigated in similar international studies. This reduced stability may be due to relatively higher ionic strengths and moderate dissolved organic concentrations in Horonobe groundwaters compared to their international counterparts.

Abstract New geochronological and geochemical data from bedded porcellanitic tuffs present within two sedimentary basins at the eastern fringe of the Archaean Bastar Craton, eastern India (the Ampani and Khariar basins) are presented and compared with data available from tuffaceous beds present within adjoining basins. U–Th–total Pb electron probe microanalysis data of monazite grains from the Ampani tuff revealed several age data clusters: c. 2400, c. 2130, c. 1600, c. 1450 and c. 1000 Ma. An age of 1446±21 Ma is proposed as the depositional/crystallization age for the Ampani tuff, considering its maximum probability. Comparable ages for the tuffaceous units from the Khariar (1455±47 Ma) and Singhora ( c. 1500 Ma) basins allow us to infer a major felsic volcanic event during c. 1450 Ma at the eastern margin of the Indian Craton. Detailed geochemical data suggest rhyolite to andesite character for the siliceous tuff units from three geographically separated basins and point towards the presence of an active volcanic arc in a subduction-related setting in the region. The geochronological and geochemical data prompted us to search for other contemporaneous events in the Indian continent and beyond, that is, within its erstwhile neighbours in the Precambrian supercontinent ‘Columbia’.

Abstract Pyrometamorphism of coal measures that overlie underground burnt-coal seams in the southern area of the Rotowaro coalfield, New Zealand, has produced porcellanites that enclose lenses of iron-rich magnetite and hematite-bearing slag-like rocks, which show various degrees of oxidation. Paralavas that are associated with the iron-rich lenses form stalactites around fissures and gas-escape vents and intrude the porcellanites. The slags are unusually rich in iron and contain magnetite, hematite, hercynite, titaniferous magnetite, and minor fayalite and silicate glass. Iron oxides in these rocks exhibit a variety of textures and morphologies, including dendritic, quench, exsolution, and oxidation. The paralavas contain abundant glass, which encloses feathery crystals of fayalite and orthoferrosilite, plagioclase, tridymite, cristobalite, and minor magnetite. Phase-equilibria data indicate that the paralavas and slags were formed at temperatures in the range of 1000–1600 °C. Composition plots of local coal measure sediments, a siderite nodule, and various porcellanites, slags, and paralavas with respect indicate that the porcellanites are iron-rich when compared to SiO 2 , Fe 2 O 3 , and Al 2 O 3 with the unmetamorphosed coal measures. The slags, irrespective of their oxidation state, plot on the iron-enrichment trend shown by the porcellanites. Although the siderite nodule lies within the iron-enrichment trend, most of the slags are more iron-rich than the siderite nodule. The paralavas diverge from the iron-enrichment trend, suggesting that they formed by partial melting of the porcellanites. The Rotowaro samples represent some of the most iron-rich natural slags collected from a combustion-metamorphic environment to date.