Existing thermodynamic calculation programs use chemical formulas that have an integral number of oxygen atoms (e.g., Mg₂SiO₄). Such chemical formulas are defined in a Cartesian coordinate system compositional space (hereafter referred to as the “Cartesian formula”). However, geometric representations of phase equilibria require chemical formulas (e.g., 1/3・Mg₂SiO₄) defined in a barycentric coordinate system compositional space (hereafter referred to as the “barycentric formula”). This hinders the understanding of thermodynamics in petrology. To address this shortcoming, Cartesian formula-based calculations must be compared with barycentric formula-based calculations. This study demonstrates a method for converting the activity-composition models of THERMOCALC 3.33 software into barycentric type. However, care is needed in the conversion and calculations. In some phases, the conversion process includes modifications of calculation formulas for proportions of phase components. Furthermore, in barycentric formula-based calculations, projection from an excess phase may result in disappearance of the original phase component proportions. This study also shows that this care is not necessary if calculations in the barycentric compositional space are performed using the Cartesian formula. In other words, it is the coordinate system of the chemical formula that determines the processing method of the thermodynamic calculation.

To solve the aforementioned problem, a custom-made program for barycentric formula-based calculations is required. Therefore, this study presents a method for developing a program for such calculations using Excel 2010 and its Solver tool as well as thermodynamic data and activity-composition models from THERMOCALC 3.33. This method successfully calculates pseudosections based on the Gibbs free energy minimization method, demonstrating that the Excel Solver tool is useful for implementing these types of calculations.

Cold-seep-dependent molluscan assemblages occur in the outer-shelf facies of the middle Pleistocene Kakinokidai Formation of the Kazusa Group, a forearc basin-fill sequence on the Pacific side of central Japan, in strata corresponding to the interval 707.6-667.0 ka. The assemblages consist exclusively of chemosymbiotic bivalves (lucinids, thyasirids, and solemyids) and are associated with ¹³C-depleted authigenic carbonates (δ¹³C = −61.60‰ to −10.96‰ VPDB), which suggest that their main carbon source was anaerobic oxidation of methane (AOM). Authigenic carbonate precipitates are common on burrow walls (mainly acicular aragonite) and the surrounding sediments (mainly micritic high-Mg calcite and dolomite). The burrows are cylindrical, 1.5-3.0 cm in diameter, and >1 m long. Callianassid claws and the trace fossil Palaxius (probable callianassid fecal pellets) in the burrow carbonates suggest that the burrows were produced by sediment-dwelling callianassid decapods.

We propose the following formation mechanism of burrows and their related authigenic carbonates. Firstly, callianassids produced deep burrows, penetrating the AOM zone and reaching the methanogenic zone. Methane then seeped into the burrows and AOM occurred in its deeper parts, promoted by a supply of seawater via callianassid activity, resulting in an increase in the concentration of hydrogen sulfide ions. Thiobacteria flourished in the shallower parts of the burrows, which were enriched in dissolved oxygen, and provided a source of food for the callianassids. In the deeper parts of the burrows, acicular aragonite precipitated around suspended carbonate nuclei and sank to the bottoms of the burrows, forming geopetal-like carbonate structures. In the surrounding sediment, high-Mg calcite precipitated in response to an increase in the concentration of phosphate ions (due to the decomposition of organic matter), and dolomite precipitated in response to decreasing concentrations of sulfate ions (caused by active AOM).

Although the Hokutan Group is considered to provide evidence for the Miocene opening of the Japan Sea, the ages of the formations within the group are poorly constrained. We dated eight tuff beds from the Hokutan Group in the Tajima-Myokensan and Sobudake areas, where the type localities of the formations are located, using U-Pb and fission-track (FT) methods. Uranium contents were measured using laser ablation-inductively coupled plasma-mass spectrometry. A tuff bed in the upper Takayagani Formation and two in the basal part of the Yoka Formation yielded a mean U-Pb age of ~21.5 Ma, which is within the range of FT ages (26-19 Ma) of the samples. Accordingly, the boundary between these two formations is dated at ~21 Ma. U-Pb ages of ca. 16-15 Ma and FT ages of ca. 16-11 Ma were obtained from a tuff in the Toyooka Formation and from four tuffs in the Muraoka Formation, consistent with previously reported fossil ages. Considering the radiometric and fossil ages, the depositional age of the upper Toyooka Formation is taken as 17.0-16.5 Ma and that of the lower Muraoka Formation is taken as 16.5 Ma. The FT ages imply that the middle-upper Muraoka Formation is younger than 15-14 Ma.

This study investigated the usage of north symbols on maps in signboards, newspaper flyers, and textbooks of elementary, junior high, and high schools, and assessed the recognition of north symbols by university students as well as the effect of elementary, junior high, and high-school lessons on such recognition. Almost all students recognized symbols similar to the magnetic north symbol used by the Geological Survey of Japan as the appropriate sign for north, but very few students (around 5%) were aware that the iconic representations of true north and magnetic north were distinct from each other. North symbols used in signboards and newspaper flyers were varied. Students have not acquired accurate knowledge with regard to the differences in north symbols through lessons imparted to them in elementary, junior high, and high schools, suggesting that there is a need to improve instruction on the subject. Students specializing in geology should be taught the correct symbols denoting the notion of north.

The Akechi area in the western Mikawa-Tono region extends from Aichi to Gifu prefectures, central Japan. Here, four K-Ar biotite ages are reported from plutonic rocks in this area: (1) Inagawa Granite, Obara Mass (67.7±1.5 Ma); (2) Inagawa Granite, Gneissose facies (66.0±1.4 Ma); (3) Inagawa Granite, Massive facies in the Ryoke belt (67.0±1.5 Ma); and (4) Naegi-Agematsu-Toki Granite proximal to the Ryoke plutonic rocks (64.1±1.4 Ma). The first three ages are within error of K-Ar biotite ages from a corresponding lithology in the southern Asuke area. The age for (4) is a reliable estimate of the cooling age of the Naegi-Agematsu-Toki Granite in this region.