No abstract

One of the key areas and periods for dinosaur evolution is considered to be Early Cretaceous East Asia, of which paleoclimate, that affected dinosaur diversity, needs to be accurately estimated. This study reconstructed paleoenvironmental information from two paleosol sections of the Lower Cretaceous Tetori Group in Hokuriku province, Japan. Elemental and isotopic compositions indicate that the two sections (Sections K5 and T1) formed under similar mean annual temperature (MAT) and mean annual precipitation (MAP) but exhibit significantly different paleosol colors (red in the Section K5, and gray in the Section T1) and mineralogy of carbonate nodules (dolomite–siderite in the Section K5, and dolomite–calcite in the Section T1). In addition, the oxygen isotopic ratio of carbonate minerals in the Section K5 was significantly low. The differences in sedimentary features and isotopic composition were considered to reflect the differences of seasonal climatic factors (e.g., monsoon) and local settings (e.g., drainage condition) despite the two sections exhibiting similar MAT and MAP. The results of this study suggest that the northeastern margin of East Asia, where the Tetori Group was deposited, had temperate and humid climate with monsoonal contrast in humidity during Aptian to Albian.

The Suo Metamorphic Complex is characterized as subduction-related Triassic high P/T type metamorphic rocks occurring in southwest Japan. Recently, we have discovered tonalite mylonite ( Otabara tonalite ) from the Tsuno Group, Suo Metamorphic Complex in the western Chugoku province. LA-ICP-MS zircon U-Pb dating of the Otabara tonalite in its type locality yields the magmatic age of . . Ma (MSWD = . ) and . . Ma (MSWD = . ). Whole-rock chemical compositions from the Otabara tonalite show a volcanic arc signature. LA-ICP-MS detrital zircon U-Pb dating of psammitic schist from the Tsuno Group yields the approximated maximum depositional age of Ma with the single peak cluster at ca. Ma and the conspicuous lack of Precambrian zircons. The depositional age of psammitic schist is younger than the crystallization age of the Otabara tonalite. Possible origins of the Otabara tonalite are considered as ) an autochthonous body and a member of the Suo Metamorphic Complex, or ) an exotic block derived from another geotectonic unit. In the case of the possibility ), the arc-type granitoid in the Southern Maizuru Belt is the potential origin of the Otabara tonalite as they share similar ages and geochemical compositions.