Biogenically precipitated calcium carbonate such as coral skeleton, foraminifera shell, fish otolith, and bivalve shell are useful archives to reflect past ocean environment. I will present results of past environmental reconstruction using geochemistry of such biogenic calcium carbonate, focusing on boron isotope (δ¹¹B) measurement in particular. δ¹¹B measurement is one of the most difficult measurements in geochemistry because of 1) low concentration of boron in calcium carbonate; 2) susceptible to experimental contamination; and 3) strong isotope fractionation due to a large mass difference in isotopes (¹¹B and ¹⁰B). I will overview my recent marine carbon cycle studies using δ¹¹B measurements of coral skeleton by thermal ionization mass spectrometry (TIMS) and foraminifera shell by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS).

C3 and C4 Hydroxy amino acids (HAAs) are a new family of meteoritic amino acids recently identified in the Murchison meteorite. In this study, we investigated the distributions of structural isomers and enantiomers of C3 and C4 HAAs in CM and CR chondrites which have differing petrology and mineralogy using gas chromatography-mass spectrometry method. Although α-Methylserine in CR2 and CR3 chondrites is much more abundant than those in CM chondrite, β- and γ-isomers are less abundant than those of Yamato 791198 (CM2). Compared to other CM2 chondrites, Yamato 791198 have approximately 10 times abundant HAAs with the almost same relative abundance. Besides, HAA abundances decrease with increasing the degree of aqueous alteration. Based on these results, we considered that meteoritic C3 and C4 HAAs could be produced by two formation mechanisms and that their abundances and distributions reflect redox states in meteorite parent bodies.

Beryllium 10, which decays to boron 10 with a half-life of ~1.4 My, was produced mainly from spallation reactions with cosmic rays (solar or galactic), so that its abundance is a good indicator of irradiation conditions in the early solar system. Here we review recent observations about the distribution of Be-10 (and its decay product B-10) in CAIs and chondrules, and discuss irradiation conditions of (Solar) Cosmic Rays in the early Solar System.

Understanding the relationship between solidification from partially molten melt and the oxygen isotope composition of crystallized minerals is important to constrain the heating process and its environment in the CAI formation region. In this study, we have undertaken petrographic observation by SEM-EDS-EBSD and mineralogical investigation of the micro-mineral (JEOL JEM-2100F, Kobe University) by TEM for KU-N-02 compact type A CAI (CTA) in NWA 7865 CV3 chondrite. In addition, we have measured for minerals of several microns or more in size in situ oxygen isotope composition analysis by SIMS (CAMEC Ims-1280 HR, Hokkaido University).

Aluminium-26, which decays to Mg-26 with a half-life of ~0.7 My, has been used as an important chronometer to discuss, e.g., relative formation ages of CAIs and chondrules. However, the assumption that 26Al was homogeneously distributed in the early solar system is still under debate. In the present study, we have conducted basic experiments to improve precision and reproducibility of Mg isotopic analyses using ICP-MS. Using this method, we analyzed Mg isotopic ratios and Al/Mg ratios for chondrules in a primitive chondrite NWA 7936 (L 3.15). The results show 10-20 ppm lower 26Mg/24Mg ratios compared with terrestrial value for the chondrules with approximately solar Al/Mg ratios (~0.1). Based on the results, we will discuss possible constraints on the distribution of 26Al in the early solar system.

Terrestrial planets provide solar system insights into the evolution of accretion, core-mantle and mantle-crust differentiation, and surface processes. Our model composition for Mars (cf. Earth), constrained by Martian meteorites and satellite observations, finds that terrestrial planets accreted more high-temperature and less volatile materials than chondritic asteroids from the inner solar system. Mars’ depletion in moderately volatile element (but less so than the Earth’s) reflects a nebular chemical fractionation and restricts its core to having ~4 wt% (2 wt%) S. The core of Mars (Earth) is small (24% vs 33%), partially molten, and lacking a dynamo, making the planet inhospitable to uninhabitable. Mars’ (Earth) planetary Urey ratio of 0.81 (0.43) reflects limited remaining contributions from secular cooling. These attributes set compositional limits for habitable planets.

Most lunar meteorites are known to have complicated cosmic-ray exposure (CRE) records on the Moon and in space. Spallogenic products like ¹⁰Be, ²⁶Al, ³⁶Cl, and ⁴¹Ca, and neutron-captured products like ¹⁵⁰Sm and ¹⁵⁸Gd are useful for characterizing the CRE records of extraterrestrial materials. There are many reports on spallogenic short-lived radionuclides of lunar meteorites, while there are few on their neutron-captured products. A combination of short-lived radionuclides with stable isotopic shifts may provide the detailed estimation of the CRE records of lunar meteorites on the Moon and in space

One of the most plausible scenarios of the origin of life assumes the preceding prebiotic autotrophic metabolism in sulfide-rich hydrothermal vent environments. However, geochemical mechanisms to harness the reducing power provided by hydrothermal systems remain to be elucidated. Here, I introduce a geoelectrochemical route to overcome the difficulty that was likely to occur as a natural consequence of the active hydrotharmal processes on the Hadean Earth.

A chemosynthetic ecosystem supported by seafloor massive sulfide deposits as the energy source

The laterite as a promising Ni resource can make a greater contribution to Ni production with the worldwide increase of about 4 % per year [1]. Myanmar is perhaps one of the world's most prospective but least explored minerals jurisdictions because of a scarcity of available published geological literature and an unfavorable political climate [2]. The samples were collected from 1.6 m deep profile and outcrop bedrock in Mwe Taung of Myanmar, which lies at a crucial geologic juncture of flysch Eocene units, Cretaceous marine units, and Triassic limestone under tropical weathering conditions. Nickel concentrations in lateritic regolith developed on ultramafic rocks in the study area can reach up to 4.9wt% (often 1.0-1.6wt% Ni in lateritic units) due to Ni removal from upper layer (e.g., limonite layer) and subsequently accumulation in the lower layer, which produce a promisingly and importantly economic mineral resource of this territory. Quantitative XANES analyses at the K-edge spectra showed that Ni hosted in primary silicate minerals (17mol% of lizardite and 83mol% of olivine) in the bedrock is primarily incorporated in secondary garnierite (79mol% of lizardite, 3mol% of olivine, and 18mol% of hydrated Ni) and Fe-oxides (76mol% of biotite and 24mol% of goethite) in the saprolite unit and in 63mol% of goethite and 37mol% of hematite in the garnierite veins, supported by XRD results. The correlation of Ni and Mn of elemental mappings showed that the presence of garnierite within the vein or small crack. In addition, the occurrence of Mn4+ (MnO2) in garnierite indicates the weathering process is controlled by strongly oxidizing environment along a lateritic Ni-deposit profile. Finally, the ubiquitous occurrence of Ni-bearing goethite, biotite, and hematite emphasizes the major role of this phase in Ni speciation at the different weathering stages, which suggests that goethite and hematite represent the major host for Ni in the final tropical weathering stages under strongly oxidizing environment of Myanmar ultramafic rocks.

The distribution and speciation of scandium (Sc) in the limonite layer in laterite were examined by μ-XRF mapping and X-ray absorption fine structure (XAFS) spectroscopy in this study. In addition, similar information such as speciation was obtained also for other rare earth elements including yttrium (REY) to compare geochemical behaviors between Sc and REY.

Why Oklo was only once?

Simultaneous land-sea observations were conducted in southern area of Fukushima Prefecture for the sake of qualitative and quantitative evaluation of radio cesium transport processes from land to sea via rivers. Relatively high dissolved radio cesium was detected in the estuary, which is the boundary area between land and sea, compared to both two areas. This is probably due to the addition of desorbed radio cesium that had been sorbed on the particles along the salinity gradient. This is however thought to be one of the factors, so discussion will be also focused on other contributable factors.

Europium (Eu) is one of the rare earth elements (REEs) which provide valuable information for understanding evolution processes in earth and planetary system. Though most REEs exist in the trivalent state, Eu can also exist in the divalent state in reducing environment. Recently, Lee and Tanaka [1] developed a protocol for analyzing the Eu isotope ratio by MC-ICP-MS for studying Eu isotope fractionation in geological rocks with unprecedented accuracy and precision. The use of Sm isotopes for correction of instrumental mass fractionation of Eu isotopes was useful. First, in measurement of Eu isotope ratio, mass discrimination effect on two europium isotopes was externally corrected by the Sm isotopic composition added to the Eu samples (¹⁵⁰Sm/¹⁵⁴Sm ≡ 0.3244) on an exponential law. And then, we measured europium isotopic ratios (¹⁵¹Eu/¹⁵³Eu) precisely from six high-purity commercial Eu reagents including NIST 3117a. When compared with NIST 3117a used as the reference (δ^151/153Eu ≡ 0.0), other Eu reagents revealed that there are a little but significant of isotopic fractionations. Second, Eu isotope fractionation during the cation exchange column chemistry with a good separation technique of Eu fraction (more than 99.99% purity) was investigated. A known amount of REE standard solution was eluted from a column by using HIBA as a solute. The Eu isotope composition of the eluted fractions systematically changed from δ¹⁵¹/¹⁵³Eu= -1.80 in early stage of elution to δ^151/153Eu=2.56 during the late stage of elution. A numerically integrated value of the elutions agreed well with value of totally eluted solution. These results indicate that there exists Eu isotopic fractionation among the reagents. Particularly, Eu isotopic fractionation among the reagents suggests that it may be happened during the reagent production processes or inherited from the geological source materials. We also measured Eu isotopic variation among five different geochemical reference rocks (BCR2, BHVO2, BIR1a, GSP2, JG1a). The reference standards also showed slightly different ¹⁵¹Eu/¹⁵³Eu isotope ratios. These results suggest Eu isotopic fractionation in nature.[1] Lee and Tanaka (2019) Spectrochimica Acta Part B 156, 42-50.