The “Upper Miocene” Mitoku Formation in the south–central part of Tottori Prefecture, southwest Honshu, Japan, is a stratigraphic type of Mitoku-type flora, which is thought to represent the origins of the modern temperate forest vegetation on the islands of Japan. In this study, zircon U–Pb dating and palynostratigraphic analyses were undertaken to determine the age of the Mitoku Formation at the Naru site, north of the famous Mitoku-san historic site and place of scenic beauty, where Mitoku-type Misasa–Naru flora have been previously reported. The ages obtained for the pumice lapilli–tuff and tuff beds, which are intercalated with plant-fossil-bearing beds at the Naru site, are ca. 4.7 Ma (mid-Early Pliocene). The preliminary palynological results reveal that the flora comprise both cool and warm temperate elements, with the common and continuous occurrence of Cathaya pollen, which can be correlated with the NP-5 Neogene palynostratigraphic zonation (ca. 5.5–3.0 Ma). Warm elements in the Misasa–Naru flora were once considered to be remnants of mid-Miocene flora. However, our results show that the flora represent a warm temperate climate during the Early Pliocene, and might necessitate revision of the sequential changes in the Mitoku-type floras in this area, and even to the regional stratigraphy.

Despite the recent diversification of Tenthredinid sawflies in Japan, fossil records of this family are notably lacking. Here, we describe specimens belonging to this family from the Chibanian (Middle Pleistocene) lacustrine deposits of the Shiobara Group. These specimens are identified as Tenthredinidae gen. et sp. indet A and B and Nematinae gen. et sp. indet. This study represents the first report of fossil tenthredinids in the Shiobara Group and also an incontrovertible Cenozoic fossil record of this family from Japan.

Determining the depositional ages of the Early–Middle Miocene forearc basin deposits in southwestern Japan is essential for understanding the Neogene deformation and stress history of the forearc region. To constrain the depositional age of the Tanabe Group, an Early–Middle Miocene forearc basin sedimentary sequence, we analyzed the U–Pb ages of detrital zircon separated from eight sedimentary rock samples, and obtained 221 concordant ages from 330 zircon grains. The age of the youngest grain is 19.4 ± 0.6 Ma, which constrains an upper limit for the depositional age. However, the youngest grain is much older than a foraminiferal age (16.3–15.1 Ma) for the deposition of the group. The absence of zircon ages corresponding to the widespread mid-Miocene felsic volcanic activities on Kii Peninsula at ~15 Ma suggests that the deposition of the Tanabe Group ended before these volcanic events. The discrepancy between the youngest zircon age and depositional age can be attributed to volcanic quiescence in the provenance area during the deposition of the Tanabe Group. We also suggest that the E–W tensional stress recorded by synsedimentary clastic dikes was exerted before ca. 15 Ma in the southern part of Kii Peninsula.

The coastal lowlands of Japan are mostly covered by unconsolidated sediments deposited since the last glacial maximum (LGM). The sedimentary facies and physical properties of post-LGM deposits filling small incised valleys with catchments in upland areas are distinct from those of the major alluvial lowlands, due mainly to a low rate of sediment supply. We studied two borehole cores (GS-SUM-1 and GS-SMS-1) to investigate the depositional environments, facies, and physical properties of the post-LGM fills in a small incised valley in the Shibakawa Lowland, one of the largest valleys in the Ōmiya Upland in Saitama Prefecture, central Japan. Both cores consist of Pleistocene deposits, post-LGM deposits, and artificial fill in an ascending order. Post-LGM deposits in the two cores consist of fluvial, inner-bay to brackish–fresh water, and fresh-water swamp deposits. The inner-bay deposits are mainly mud with little to no sand and yield very low S-wave velocities (~100 m/s). We reconstructed the post-LGM depositional environments in the Shibakawa Lowland using the sedimentary facies and radiocarbon ages. After 9 ka, seawater entered the incised valley. The inner bay extended furthest upstream at ~6 ka, forming a ravinement surface. The valley floor transformed into a freshwater swamp by 4 ka. In addition to the low rate of sediment supply due to the small catchment area, the progradation of deltaic to fluvial deposits in the Arakawa Lowland downstream blocked the valley outlets at the time of the highstand, resulting in the deposition of very muddy soft sediments in the Shibakawa Lowland. On the margins of the uplands, similar soft post-LGM deposits filling the incised valleys are likely to be present beneath the alluvial plain; consequently, attention should be paid to the ground strength in such areas.

We propose the name ‘Obaneo Lava’ for Pliocene mafic volcanic rocks at Cape Haneobana, northeastern Tottori Prefecture. We undertook a geological survey of these rocks, measured their whole-rock major element compositions, and subjected them to plagioclase K‒Ar dating. The mafic volcanic rocks comprise at least three lava flows of clinopyroxene–olivine basalt and olivine basalt. Their chemical composition indicates they are alkali basalt. Their uniform compositions and the lack of evidence for dormancy indicate that they were derived from continuous volcanic activity. The plagioclase K‒Ar age of 4.28±0.11 Ma for the upper lava is older than the ages of surrounding Pliocene volcanic units (i.e., the Inabayama Basalt and rocks of Hamasaka Volcano). The Obaneo Lava is distinguished from these surrounding rocks on the basis of chemical composition and radiometric age.

To increase the number of radiometric dates of Jurassic accretionary complexes in Japan, we conducted zircon U–Pb dating of a sandstone sample from the Sawando Complex in the eastern Mino Terrane using a multi-collector inductively coupled plasma mass spectrometer coupled with a multi-spot femtosecond laser ablation system (msfsLA-MC-ICP-MS). Thirty two concordant dates from 72 analyzed grains are divided into seven groups: 1920–1850 Ma (Paleoproterozoic), 1110 Ma (Mesoproterozoic), 492 Ma (Cambrian), 442 Ma (Silurian), 262–260 Ma (Permian), 250–218 Ma (Triassic), and 186–168 Ma (Jurassic). The youngest single grain date (YSG) is 168.0±6.9 Ma (±2σ). The YSG is within uncertainty of radiolarian ages reported in previous studies (late Callovian to middle Oxfordian).

The depositional age and sedimentary environment of the Pleistocene succession beneath the Tokushima Plain in southwestern Japan remain poorly understood, even though it includes key marker beds and age constraints that are crucial for understanding the history of the basin. We identified brackish–marine beds and constructed the chronostratigraphy of the subsurface Pleistocene strata using analyses of tephra layers, the electric conductivity (EC) and pH of muddy sediments, and diatom and pollen fossils in borehole cores from the southeastern Tokushima Plain. We correlated four tephra layers to the G9L , Naruohama-IV (Nh-IV), Kakuto (Kkt), and Ata-Torihama (Ata-Th) tephra layers, based on major and trace element compositions and the refractive index values of glass shards. High EC, brackish–marine diatoms, and pollen assemblages highlighted five brackish–marine beds, which were deposited during highstands in marine isotope stages (MISs) 11 to 5e. The marine beds corresponding to MISs 11, 9, and 5e (or 7) occur in subsurface Pleistocene strata in the northern part of the plain, and thus provide age constraints on the evolution of the Tokushima Plain.

Sub-bottom profilers (SBPs) are essential tools for investigating geological structures beneath sea or lake floors. SBPs are widely deployed because they do not interfere with other onboard survey methods such as sediment sampling and seismic profiling. However, SBP data are underutilized because they are stored in multiple different proprietary formats and commercial software is expensive. To improve this situation, we initially targeted a SyQwest Bathy-2010 installed on the R/V Hakuho Maru (JAMSTEC) and developed a procedure for SBP data visualization. This note aims to be a practical manual, with step-by-step guidance and screenshots, allowing interested users to easily process SBP data. The procedure involves three key steps: onboard data conversion, running a Python script, and creation of an index map. To ensure accessibility, the workflow has been tailored for free platforms, including Google Colab, enabling users with limited technical resources or programming experience to process SBP data effectively. We hope this effort democratizes the use of SBP data and facilitates its broader application in marine geological research.