Rare earth and trace element geochemistry of termite mounds in central and northeastern Namibia: Mechanisms for micro-nutrient accumulation

Sako, Aboubakar; Mills, Anthony; Roychoudhury, Alakendra N.

doi:10.1016/j.geoderma.2009.08.011

Cited by 40 publications

(23 citation statements)

References 85 publications

(143 reference statements)

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“…Thompson et al / Geochimica et Cosmochimica Acta 119 (2013) 18-30et al, 1998;Minarik et al, 1998;Land et al, 1999). Attention to Y-Ho fractionation in soils is noticeably absent (Huang and Gong, 2001;Aide and Smith-Aide, 2003;Laveuf et al, 2008;Mourier et al, 2008;Zhang et al, 2008;Fernandez-Caliani et al, 2009;Laveuf and Cornu, 2009;Sako et al, 2009;Tematio et al, 2009;Laveuf et al, 2012). Perhaps this is because soils exhibit much higher solid-phase heterogeneity than marine systems (Tyler, 2004).…”

Section: Introductionmentioning

confidence: 99%

Fractionation of yttrium and holmium during basaltic soil weathering

Thompson

Amistadi

Chadwick

et al. 2013

Geochimica et Cosmochimica Acta

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Section: Introductionmentioning

confidence: 99%

Fractionation of yttrium and holmium during basaltic soil weathering

Thompson

Amistadi

Chadwick

et al. 2013

Geochimica et Cosmochimica Acta

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“…to Ce 4+ are useful indicators in analyzing pore water geochemistry (Sako et al, 2009). Under oxidizing and high pH conditions, Ce can coprecipitate with Fe-and Mn-oxyhydroxides as insoluble CeO 2 , producing a negative Ce anomaly in pore water.…”

Section: +mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…In addition, Ce and Eu have greater sensitivity to variations in redox conditions and their oxidation states will change from Eu 3+ and Ce 3+ to Eu 2+ and Ce 4+ , respectively (Dia et al, 2000;Johannesson et al, 2011;Willis and Johannesson, 2011). Thus, anomalies in these elements have important implications regarding the redox state of a system (Sako et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, changing the redox cycling of Fe and Mn appears to indirectly affect REE concentration and fraction patterns, owing to the different sorption ability and coprecipitation behavior of LREEs and HREEs (Augustsson et al, 2009;Biddau et al, 2009;Leybourne and Cameron, 2010 Johannesson et al, 2011;Willis and Johannesson, 2011). Thus, anomalies in these elements have important implications regarding the redox state of a system (Sako et al, 2009).The region of Caofeidian Harbor has relatively complex geological conditions and has experienced transgression many times since the late Pleistocene (Zhang et al, 1997). Due to the development of oil exploration and aquaculture and their associated surface-water contamination, extensive extraction of groundwater has resulted in seawater intrusion and subsidence in the area.…”

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confidence: 99%

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Geochemical signature of aquitard pore water and its paleo-environment implications in Caofeidian Harbor, China

Liang

Jin

et al. 2013

Geochem. J.

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Oxygen-18 (18 O), deuterium (D), and chemical patterns were determined in pore water samples extracted from 100-m depth in Caofeidian Harbor, China. The stable isotopic composition indicates that aquitard pore water was of meteoric origin and was basically not influenced by evaporation. Seawater diffusion was identified as the main influence on the isotope signature of pore water, according to the δ 18 O profile and positive correlation between δ 18 O and Cl -. The chemistry of aquitard pore water is characterized by high total dissolved solids (TDS) decreasing with depth, ranging from 26.89 to 7.26 g/L. The same trend was observed for Cl -, Na + , and Mg 2+ , as influenced by seawater. However, the typical ion ratios (i.e., Cl/Br, Sr/Ba) of pore water change significantly in different sedimentary facies along the study profile due to the long-term reaction between pore water and sediment, further supporting the finding that pore water was not replaced by modern water or seawater. Therefore, during long-term aquitard residence, the chemical composition of pore water would be influenced by other processes such as reduction of sulfates and cation exchange. The rare earth elements (REEs) of pore water are mainly affected by water-rock interaction. The shale-normalized REE fractionation patterns display enrichment of heavy REEs (HREE) relative to light REEs (LREE) and even greater fractionation degree in marine sediment pore waters (as larger La/Yb NASC ). The relative reduction environment in the aquitard and preferential mobilization of Eu 2+ in the water-rock interaction lead to the development of positive Eu anomalies (1.13 < (Eu/Eu*) NASC < 1.98) and slightly positive Ce anomalies (-0.13 < (Ce/Ce*) NASC < 0.35).Keywords: pore water, aquitard, origin, geochemistry, China of aquitard pore water flowing into adjacent aquifers (Lee and Byrne, 1992;Guo et al., 1995). Although aquitards play an important role in environment, geology, and hydrogeology, few studies have focused on the transport and geochemical reactions controlling solute concentrations in aquitards. Far less is presently known about aquitards than that of the behavior of solutes in aquifers (Hendry and Wassenaar, 2004;Timms and Hendry, 2008).Unlike transport of solutes in aquifers, which is dominated by advection, the transport of conservative tracers (e.g., δ18 O, δD, Cl -) in aquitards was shown to be dominated by molecular diffusion (Remenda et al., 1996;Guerrero et al., 1997;Hendry and Wassenaar, 1999). As pore water is retained for long periods within aquitards, its composition would be influenced by diagenetic processes (e.g., precipitation, adsorption, sulfide formation, remobilization, and biological degradation or uptake), causing the concentrations of chemical species in pore water to differ from free overlying water (Sacchi et al., 2001). Based on the weaker hydrodynamic condition and specific chemical composition, together with the stable isotope information (e.g., δ18 O, δD, and δ 13 C), aquitard pore water has been used in studies of gro...

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Calcium transfer and mass balance associated with soil carbonate in a semi‐arid silicate watershed (North Cameroon): An overlooked geochemical cascade?

Dietrich

Diaz

Deschamps

et al. 2021

The Depositional Record

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Calcium is a key element of the Earth system and closely coupled to the carbon cycle. Weathering of silicate releases Ca, which is exported and sequestered in oceans. However, pedogenic calcium carbonate constitutes a second Ca‐trapping pathway that has received less attention. Large accumulations of pedogenic calcium carbonate nodules, associated with palaeo‐Vertisols, are widespread in North Cameroon, despite a carbonate‐free watershed. A previous study suggested that a significant proportion of Ca released during weathering was trapped in palaeo‐Vertisols but the pathways involved in the transfer of Ca from sources (the granite and the Saharan dust) to a temporary sink (the carbonate nodules) remain unclear. This study aims to compare the distribution of elements in carbonate nodules and their associated past and present compartments for Ca in the landscape. These compartments are all characterised by a distinctive geochemical composition, resulting from specific processes. Three end members have been defined based on geochemical data: (a) the granite and its residual products, dominated by K2O and Na2O, Ti and Zr, HREE, and a positive Ce anomaly; (b) the soil parental material and the Saharan dust, dominated by Al2O3, Fe2O3 and MgO, V, HREE, and a positive Ce anomaly; and finally (c) the carbonate nodules, which are dominated by CaO, a depletion in V, Ti and Zr, and an enrichment in REE with a negative Ce anomaly. Mass balance calculations in soil profiles demonstrated that the accumulation of Ca in carbonate nodules exceeds the Ca released by chemical weathering of the parental material, because of a continuous accumulation and contribution from lateral transfers. Consequently, at the landscape scale, carbonate nodules associated with palaeo‐Vertisols constitute a temporary sink for Ca. Such a spatial relationship between sources and transient compartments opens an avenue to the new concept of ‘geochemical cascade’, similar in terms of geochemistry, to the concept of ‘sediment cascade’ developed by continental sedimentologists.

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Rare earth and trace element geochemistry of termite mounds in central and northeastern Namibia: Mechanisms for micro-nutrient accumulation

Cited by 40 publications

References 85 publications

Fractionation of yttrium and holmium during basaltic soil weathering

Fractionation of yttrium and holmium during basaltic soil weathering

Geochemical signature of aquitard pore water and its paleo-environment implications in Caofeidian Harbor, China

Calcium transfer and mass balance associated with soil carbonate in a semi‐arid silicate watershed (North Cameroon): An overlooked geochemical cascade?

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