Clay minerals in chilled or brecciated margins (altered glass) and massive inner crystalline parts (mesostasis) of three basalt-hawaiite bodies from Mururoa Atoll (French Polynesia) have been studied in order to compare their chemical and mineralogical compositions. Polyphase assemblages comprise di- and trioctahedral phases, both of which consist of non-expandable layers (chlorite, celadonite) and two types of expandable layers (saponite and Fe-rich smectite or ‘nontronite-like’ material). The presence of the Fe-rich clays is supported by the presence of the X-ray diffraction 060 peak at 1.51–1.52 Å and of the infrared absorption bands at 875 and 822 cm−1 (Fe3+-Al-OH and Fe3+-Fe3+-OH groups, respectively). The chemical composition of the Fe-rich smectites does not fit with the theoretical nontronite field. The layer charge averages 1 per Si4O10 making these Fe-rich smectites close to ‘celadonite-type’ clays. This could explain the presence of mixed-layer celadonite-smectite. Plotted in an M+/4Si vs. Fe/sum octahedral cations diagram, the chemical compositions of clay minerals in the mesostasis form a continuous field limited by the celadonite-high-charge nontronite-like smectite and chlorite end-members. The clay assemblages are different from those formed in hydrothermal systems or low-grade metamorphic conditions which are characterized by the sequence: saponite → randomly ordered chlorite-smectite mixed-layered minerals (MLMs) → corrensite → chlorite. The systematic presence of Fe-rich clays either in the altered chilled margins or in the massive inner parts of the basalt-hawaiite bodies (high-charge nontronite-like smectite and mixed-layer nontronite-celadonite) makes the Mururoa sea-mount a potential terrestrial analogue for Mars surface exploration.

The clay minerals formed in chilled margins and massive crystallized inner parts of three basalt-hawaiite bodies of Mururoa Atoll (French Polynesia) exhibit contrasting textures. Glass alteration textures are observed around fractures crosscutting the quenched margins: Fe-rich clays grow inward into the glass (retreating surface) while Mg-rich clays grow outward (open space). The textures of clay deposits filling the diktytaxitic voids (mesostasis) in the massive inner parts of the three volcanic bodies are different: unoriented clay matrix with embedded euhedral apatite and pyroxene microcrysts (submarine flow); pallisadic clays coating the void walls and the crystal surfaces of apatite and K-feldspar microcrysts (subaerial flow); and clay muffs covering all the apatite needles, with the central part of the void remaining empty (dike). The unoriented texture could result from the alteration of a glass precursor concomitant with the olivine phenocrysts (clay pseudomorphs). However, such an alteration implies important chemical transfers which are not observed. The pallisadic and muff textures form through heterogeneous nucleation on the solid surfaces and crystal growth from a saline solution. No glass precursor existed. As the center of the diktytaxitic voids in the dike is empty, the residual liquid was probably boiling. The amounts of light rare earth elements (LREE), Sr, and the most incompatible elements are greater in clays from diktytaxitic voids relative to the amounts formed in the altered glass of the chilled margins. Thus, diktytaxitic clays formed from a residual liquid which gave either an evolved glass or a saline solution after cooling (fractionation process). The δ18O variation vs. loss on ignition (LOI) indicates that sea water was involved either in rock alteration or magma contamination. This is confirmed by the 87Rb/86Sr ratio of bulk rocks and clay fractions from the quenched and massive inner parts of the three volcanic bodies which do not fit with the 11.5 Ma isochron indicating that the Rb-Sr system was not closed at any stage during the magmatic history.

The earliest monumentality in Western Europe is associated with megalithic structures, but where did the builders of these monuments live? Here, the authors focus on west-central France, one of the earliest centres of megalithic building in Atlantic Europe, commencing in the mid fifth millennium BC. They report on an enclosure at Le Peu (Charente), dated to the Middle Neolithic (c. 4400 BC), and defined by a ditch with two ‘crab claw’ entrances and a double timber palisade flanked by two timber structures—possibly defensive bastions. Inside, timber buildings—currently the earliest known in the region—were possibly home to the builders of the nearby Tusson long mounds.

This paper describes a detailed petrographic and isotopic study of hypabyssal sheets of quartz-syenite that represent the ultimate differentiation product of the oceanite alkaline magmatic reservoir of the Piton des Neiges stratovolcano (Réunion Island). Clay minerals of the corrensite to chlorite series crystallized during the late-magmatic activity, with quartz, carbonates and accessory minerals from juvenile fluids filling the primary porosity of the quartz-syenite. It is proposed that a double chemical transfer occurred at the end of the crystallization process: degassing of the exsolved CO2-rich and SiO2-rich fluid from the magmatic chamber through the porous quartz-syenite and diffusion of Al, Fe and Mg from the intruded basalts affected by the juvenile fluids towards the primary porosity of the quartz-syenite, feeding the crystallization of late-magmatic clays in the residual primary pores after quartz and carbonate deposition. This process may be generalized to alkaline plutonism, as well as to the primitive crusts of terrestrial planets, and may be the first source of clays in early planets.

Chad is a key region for understanding early hominid geographic expansion in relation to late Miocene and Pliocene environmental changes, owing to its location 2500 km west from the Rift Valley and to the occurrence of sites ranging in age from about 6 to 3 Ma, some of which yield fossil hominids. To reconstruct changes in herbivore paleodiet and therefore changes in the paleoenvironment, we measured the carbon and oxygen isotope composition of 80 tooth-enamel samples from three time horizons for nine families of Perissodactyla, Proboscidea, and Artiodactyla. The absence of significant alteration of in vivo isotopic signatures can be determined for carbon, thus allowing paleodietary and paleoenvironmental interpretations to be made.

While the results generally confirm previous dietary hypotheses, mostly based on relative crown height, there are some notable surprises. The main discrepancies are found among low-crowned proboscideans (e.g., Anancus) and high-crowned rhinocerotids (Ceratotherium). Both species were more opportunistic feeders than it is usually believed. This result confirms that ancient feeding ecology cannot always be inferred from dental morphology or extant relatives.

There is an increase in the average carbon isotope composition of tooth enamel from the oldest unit to the youngest, suggesting that the environment became richer in C4 plants with time. In turn, more C4 plants indicate an opening of the plant cover during this period. This increase in carbon isotope composition is also recorded within genera such as Nyanzachoerus, Ceratotherium, and Hexaprotodon, indicating a change from a C3-dominated to a C4-dominated diet over time. It appears that, unlike other middle Pliocene hominid sites in eastern and southern Africa, this part of Chad was characterized by very open conditions and that savanna-like grasslands were already dominant when hominids were present in the area.