The Nedamo and North Kitakami belts are composed of Paleozoic-Mesozoic accretionary complexes, forming part of the Kitakami Massif in Sotoyama district, east of Morioka City, Iwate Prefecture. These accretionary complexes are intruded by abundant dikes classified into nine rock-types. Mela-quartz diorite, porphyritic fine mela-quartz diorite, and hornblende andesite account for half of the dikes, with the remainder composed of quartz diorite, porphyritic fine quartz diorite, dacite, porphyritic fine tonalite, rhyolite, and mega-porphyritic rhyolite. The dikes are typically several meters thick, mostly high-angle, and trend roughly NNE-SSW. Hornblende andesite and fine quartz diorite dikes yield hornblende with K-Ar ages of 131±3 Ma and 122±6 Ma, respectively, and a rhyolite dike yields zircon with a U-Pb age of 120±1 Ma. Therefore, the dikes in the Sotoyama district are approximately 130-120 Ma (Barremian-early Aptian), and would have been intruded just prior to intrusion of the Early Cretaceous Kitakami Granitoids. Paleostress analysis of dike attitudes indicates that they formed in a WNW-ESE trending extensional stress field, marking a temporary change in the generally E-W compressional stress field within the Kitakami Massif during the Early Cretaceous.

Diatoms are one of the most important eukaryotic primary producers in the lower ecosystem; understanding their evolutionary history is therefore also important. Throughout most of the Cenozoic hydrosphere, diatoms have flourished. However, as a result of progressive diagenesis and dissolution of the opaline silica that forms their frustules, their early evolution during the Cretaceous is unclear, so the fossil record is incomplete. Largely because of this poor fossil record, little is known about the mid-Cretaceous interval (Cenomanian to Turonian). This study presents a new fossil record of Cenomanian opaline diatoms in carbonate concretions hosting ammonites from Hokkaido in the northwestern Pacific Ocean. Primitive floral assemblages composed of dominantly cylindrical or discoid forms are associated with a few hemiaulid diatoms, one of the predominant taxa since the Campanian age. The Cenomanian diatoms are similar to late Early Cretaceous (Albian) flora reported mainly from the Southern Hemisphere, but given their association with a few taxa typical of the Late Cretaceous, they are somewhat transitional.

The Hokusetsu Subgroup in the eastern Shidara basin, eastern Aichi Prefecture, central Japan, is the lower part of the Miocene Shidara Group. In ascending stratigraphic order, the subgroup consists of the Kawakado, Shimoda, Tsubosawa, and Kuroze formations, which formed during a continuous transgression. Re-examination of the lithostratigraphy of the Hokusetsu Subgroup in the eastern Shidara basin has revealed a thick sandstone formation in the upper part of the Shimoda Formation, which otherwise consists mainly of mudstone. The sandstone beds, which had previously been considered part of the Kawakado Formation, clearly extend to the north where they interfinger with the mudstone of the Shimoda Formation. The existence of these newly identified sandstone beds in the Shimoda Formation, named the Umedaira Sandstone Member, suggests that the Hokusetsu Subgroup formed not only by simple transgression, but also by the influence of tectonic movements. The Umedaira Sandstone Member may be the key to clarifying Miocene tectonics in the Shidara Basin.

Here we report on the operation of the JEOL JXA-8600SX wavelength-dispersive electron probe microanalyzer (EPMA) after replacing the outdated and damaged native computers with popular and up-to-date microcomputers (Arduino) and a desktop Windows PC. Stepper motors actuating the sample stage and spectrometers are driven by computerized numerical control (CNC) kits commercialized for hand-made 3D printers, open-source firmware GRBL installed on Arduino, and a common text-based command “G-code” sent from a PC. X-ray pulse signals from the single-channel pulse-height analyzer (SCA) and analog signals from the probe ammeter are also acquired by Arduino. Sending commands from the PC to Arduino and receiving signals from Arduino to the PC are routinized by a homemade program coded by Visual Basic.NET. Quantitative analyses of anhydrous silicates and oxides, applying the Bence-Albee correction, provide reasonable oxide concentrations that are generally within 99-101 wt.% in total and compatible with stoichiometry within a 1%-2% relative deviation. This alternative control system not only extends the use of EPMA hardware regardless of generational changes in computer technology, but also introduces optional analytical techniques not available in the built-in system.