Revisiting Kalundu Mound,Zambia: Implications for the Timing of Social and Subsistence Transitions in Iron Age Southern Africa

African Archaeological Review - Novel trajectories of food production, urbanism, and inter-regional trade fueled the emergence of numerous complex Iron Age polities in central and southern Africa....     

Fluid inclusion and isotopic constraints on the origin of ore‐forming fluid of the Jinman–Liancheng vein Cu deposit in the Lanping Basin,western Yunnan,China

Extensive quartz–carbonate–Cu sulfide veins occur in clastic rocks and are spatially related to Paleocene granites in the western border of the Lanping Basin, western Yunnan, China. Abundant aqueous‐carbonic fluid inclusions occur in these veins but their origin is debated. In the Jinman–Liancheng deposit, individual primary inclusion groups contain either exclusively liquid‐rich inclusions (Gl), or coexisting liquid‐rich and vapor‐rich inclusions (Glv). Microthermometry and estimate of CO₂ content indicate that type Gl inclusions either have homogenization temperatures (Th) 238–263°C and contain c. 3.9–5.5 mole % CO₂, or have Th 178–222°C and contain c. 1.6–3.2 mole % CO₂. Type Glv inclusions are thought to represent samples of fluid unmixing that occurred at 183–218°C. At that time, the liquid phase in the unmixing fluid may contain c. 2.0–3.3 mole % CO₂. As such, the correlation of CO₂ content with Th for type Gl inclusions is thought to be caused by fluid unmixing with decreasing temperature and subsequent CO₂ escape. δ¹⁸O and δD values of the parent water mainly fall in the field below that of primary magmatic water, indicative of fluid derivation from degassed (in open system) magmatic water, with no contributions from basinal or meteoric water. Initial Sr isotopic compositions of hydrothermal carbonates suggest that the fluid was magmatic, probably derived from the Paleogene granites. δ¹³C_PDB values (?4‰ to ?7‰) of the hydrothermal carbonates and δ³⁴S_V‐CDT values of sulfides (mainly ?11‰ to +5‰) indicate that the carbon and sulfur can be derived from (degassed) magma and/or nonmagmatic sources. The CO₂‐rich and magmatic‐water‐derived fluid at Jinman–Liancheng differs from the CO₂‐poor and basinally derived fluid in sediment‐hosted stratiform Cu (SSC) deposits, which suggests that there are no genetic linkages between the vein Cu and SSC deposits in the Lanping Basin.     

Quantitative estimation of overpressure caused by gas generation and application to the Baiyun Depression in the Pearl River Mouth Basin,South China Sea

Hydrocarbon generation can yield high fluid pressures in sedimentary basins as the conversion of solid kerogen to hydrocarbons can result in an increase in fluid volume. To quantify the relationship between gas generation and overpressure in source rocks, a set of equations for computing the pressure change due to gas generation has been derived. Those equations can be used to quantitatively estimate overpressure generated by type III kerogen in source rocks by considering gas generation and leakage, gas dissolution in formation water and residual oil, thermal cracking of oil to gas, and hydrocarbon episodic expulsion from source rocks. The equations also take consideration of other factors including source rock porosity, transformation ratio, total organic carbon (TOC), hydrogen index, and compressibility of kerogen, oil, and water. As both oil and gas are taken into account in the equations, they can also be used to estimate the evolution of overpressure caused by hydrocarbon generation of type I and type II kerogen source rocks. Sensitivity analyses on the type III kerogen source rock indicate that hydrogen index is the most influential parameter for overpressure generation, while TOC and residual gas coefficient (β: ratio of residual gas over the total gas generated) have a moderate effect. Overpressure can be generated even if the gas leakage/loss in the source rock is up to 80% of the total gas generated. This suggests that the internal pressure seal of the source rock is not a critical factor on the pressure change as long as the source rocks are capable of sealing liquid oil. The equations were applied to evaluate the overpressure in the Eocene–Oligocene Enping Formation source rocks due to hydrocarbon generation in the Baiyun Depression, the Pearl River Mouth Basin by considering the source rock properties, hydrocarbon generation history, and hydrocarbon expulsion timing. Two episodes of overpressure development due to gas generation and release were modeled to have occurred in the Enping Formation source rock since 16 Ma. The overpressure release at 10.2–5.3 Ma via hydrocarbon expulsion was apparently related to the Dongsha phase of tectonic deformation, whereas the pressure release at 2–0 Ma was due to pressure generation that was exceeded the fracture‐sealing pressure in the source rocks.     

Bleached mudstone,iron concretions,and calcite veins: a natural analogue for the effects of reducing CO2‐bearing fluids on migration and mineralization of iron,sealing properties,and composition of mudstone cap rocks

This study investigates the Wangfu Depression of the Songliao Basin, China, as a natural analogue site for Fe migration (bleaching) and mineralization (formation of iron concretions) caused by reducing CO₂‐bearing fluids that leak along fractures after carbon capture, utilization, and storage. We also examined the origin of fracture‐filling calcite veins, the properties of self‐sealing fluids, the influence of fluids on the compositions of mudstone and established a bleaching model for the study area. Our results show that iron concretions are the oxidative products of precursor minerals (pyrite and siderite) during uplift and are linked to H₂S and CO₂ present in early stage fluids. The precipitation of calcite veins is the result of CO₂ degassing and is related to CO₂, CH₄, and minor heavy hydrocarbons in the main bleaching fluids. In our model, fluids preferentially enter high‐permeability fracture systems and result in the bleaching of surrounding rocks and precipitation of calcite veins. The infilling of calcite veins significantly decreases the permeability of fractures and forces the fluids to slowly enter and bleach the mudstone rocks. The Fe²⁺ released during bleaching migrates to elsewhere with the solutions or is reprecipitated in the calcite veins and iron concretions. The formation of calcite veins reduces the fracture space and effectively prevents fluid flow. The fluids have an insignificant effect on minerals within the mudstone. In terms of the chemistry of the mudstone, only the contents of Fe₂O₃, U, and Mo change significantly, with the content of U increasing in the mudstone and the contents of Fe₂O₃ and Mo decreasing during bleaching.     

Low‐temperature dunite hydration: evaluating CH4 and H2 production from H2O and CO2

Abiotic methane (CH₄) and hydrogen (H₂) produced after hydration of mafic/ultramafic rocks represent energy sources for microbes that may thrive in the deep subsurface regions of Earth and possibly on other planets. While H₂ is a direct product of serpentinization, CH₄ can form via Fischer–Tropsch Type (FTT) reactions (carbon reduction) that, due to potential H₂ migration, can be spatially and temporally detached from serpentinization. We tested an alternative process hypothesized by some scholars, in which CO₂ can be reduced through dunite hydration without initially added H₂, implying that CH₄ can form in the same serpentinized fluid–rock system. The experiment used natural dunite sand (Forsterite 92), CO₂ with δ¹³C ~ ?25‰ (VPDB), and a 1 mm dissolved SiO₂ solution mixed in 30 glass bottles (118 mL) stored for up to 8 months at low temperature (50°C) to simulate land‐based serpentinization systems. In addition, 30 control bottles without olivine were used as blanks. Trivial amounts of CH₄ (orders of 0.2–0.9 ppmv) were detected in both samples and blanks, likely representing analytical noise; essentially, no significant amount of CH₄ formed under the experimental conditions used in this work. Low amounts of H₂ (~2.55 ± 1.39 ppmv) were generated, with production yields that were one order of magnitude lower than in previously published experiments. Moderate concentrations of SiO₂ appeared to hinder low‐temperature H₂ production. Our experiment confirms that the low‐temperature reduction of CO₂ into CH₄ through direct olivine hydration, without initial H₂, is sluggish and not straightforward, which is consistent with previous studies. The presence of substantial amounts of H₂, as well as suitable metal catalysts, appears to be essential in the low‐temperature production of abiotic CH₄, as observed in published FTT experiments.     

Participant observation in obesity research with children: striated and smooth spaces

This article discusses the value of conducting participant observation in obesity research with children in an Australian community setting. Obesity is highly stigmatized, and the use of activity-based interviews exposed the intellectual and embodied consciousness that children negotiate when they take part in research about food and bodies. Instead of opening up possibilities, interview-based activities can lead to a moral correctness about healthy lifestyles. It was through participant observation, in engagement with what Deleuze and Guattari [1988 Deleuze, G., and F. Guattari. 1988. A Thousand Plateaus: Capitalism and Schizophrenia. London: Athlone Press. [Google Scholar]. A Thousand Plateaus: Capitalism and Schizophrenia. London: Athlone Press] call striated and smooth (or regulated and unregulated) spaces of children's everyday activities, that richer understandings of obesity and children's bodies became apparent. We argue that without participant observation, our understandings of what children say and draw about healthy lifestyles may be limited by the striated spaces in which we conduct our research and the constraints that accompany the cultural politics of childhood and obesity.