Detrital materials supplied from mantle-derived rocks have peculiar mechanical and chemical characteristics that make them excellent sedimentological and tectonic markers. Chromian spinels are well known and favored petrogenetic indicators because they contain several important cations, including Mg²⁺, Fe²⁺, Cr³⁺, Al³⁺, and Fe³⁺, as their main components. The Mg/(Mg + Fe²⁺) ratio (= Mg#), Cr/(Cr + Al) ratio (= Cr#), and Ti concentration are important parameters that are commonly analyzed to petrologically characterize chromian spinels. The main hosts in the chromian spinels of mantle peridotites (harzburgite and lherzolite) and their serpentinized equivalents are Mg# and Cr#, which are controlled by the equilibrium temperature (degree of subsolidus cooling) and degree of melt extraction, respectively. The chromian spinels in detritus materials are chemically stable during sedimentation processes, and can thus serve as powerful indicators of the tectonic and geologic history of the hinterland. The derivation of detrital chromian spinels, peridotites (serpentinites), chromitites, or volcanics can be partially identified by analyzing their Mg#, Cr#, and Ti concentrations in combination with their textures. The petrologic character of highly sheared serpentinite, such as the matrix of a serpentinite mélange complex, sometimes yields an inconclusive geodynamic history, but this can potentially be inferred from detrital chromian spinels in nearby sediments. Detrital chromian spinels from modern sediments are also useful for obtaining a general view of large peridotite bodies, such as the mantle section of the Oman ophiolite. When we compare the detrital spinels with those from in situ rocks, we should note that the host rocks containing the detritus material have already been eroded. If we analyze the serpentinite sandstones together with their closely associated peridotite bodies, we can possibly obtain information on the petrologic heterogeneity of the upper mantle. Our petrographic investigation of the Circum-Izu Massif Serpentinite Belt, central Japan, provides a good example of such a combined analysis of these peridotite-serpentinite sandstone pairs.

The stratigraphy of the Tetori Group in the Shiramine area of Ishikawa Prefecture and the Takinamigawa area of Fukui Prefecture has been reexamined, and the plant-bearing horizons stratigraphically compared. The Tetori Group in the study areas is divided into the Gomijima, Kuwajima, Akaiwa, and Kitadani Formations, in ascending stratigraphic order. Plant assemblages from the Akaiwa Formation around Mt. Oarashiyama in the Shiramine area comrise 23 species of 18 genera typified by the abundant occurrence of Tetori-type floral elements including ferns, ginkgoaleans, and conifers. The floral elements are associated with minor Zamites-like macrophyllous bennettitalean (or cycadalean) and microphyllous coniferous foliage represented by Brachyphyllum, indicating a climate with a dry season(s). Previously the occurrence of the Ryoseki-type floral elements was presumed to be consistent with floral change and a warming and drying climate during the deposition of the Kitadani Formation. However, this study suggests that such a trend started from the deposition of the Akaiwa Formation, earlier than previously thought.

Paleosol descriptions and sedimentary facies analysis were performed for the Miocene Seto Porcelain Clay Formation in Toyota City, Aichi Prefecture, to reveal the paleoweathering conditions after deposition. The sedimentary facies analysis suggests that deposition occurred mainly in a lacustrine, backswamp floodplain of a meandering river channel. Three paleosol horizons have been described and compared with modern soils. Histosol-like and inceptisol-like paleosols reflect the local topography and sedimentary features related to drainage conditions, vegetation cover, and sedimentation rate. Conversely, the vertic ultisol-like and ultisol-like paleosols were developed on a gently sloping terrace. The vertic ultisol-like paleosol is characterized by an illuviated clay-rich B horizon (Bt horizon, argillic horizon), pedogenic slickensides, hummock-and-swale microtopography showing gilgai microrelief, and festoon-shaped horizons showing mukkara subsurface structures. Vertic paleosol indicates the typical soil type, suggesting that the climatic conditions in this period were warm and humid with pronounced seasonality.

Paleocene diatoms are reported from a calcareous concretion in the Urahoro area, eastern Hokkaido, Japan. Although poorly preserved, the assemblage is predominantly composed of both Hemiaulus spp. and diverse resting spores, associated with Stephanopyxis spp. This study represents the first record of Paleocene diatoms in the Northwestern Pacific region and, therefore, is key to gaining a deeper insight into the regional chronology and global biogeography.