Fusuline biostratigraphy and faunal composition of the upper part the Ichinotani Formation and lower part of the Mizuyagadani Formation in the Fukuji area, central Japan are reexamined and compared to those of previous works. The upper part of the Upper Member of the Ichinotani Formation is composed mainly of the upper Kasimovian and lower Gzhelian strata, and is characterized by the partial reappearance of Moscovian strata dominant in the lower part of the Upper Member, suggesting a more complicated geological structure of the formation than previously assumed. Fusulines apparently correlatable to the middle part of the Kasimovian have not been found in the Fukuji area. The species Carbonoschwagerina morikawai is restricted to the lower part of the Mizuyagadani Formation. Faunal composition and correlation of age-diagnostic fusuline species are reviewed paleobiogeographically between the Fukuji and other areas especially of the Akiyoshi Limestone. Described herein are two species of non-fusuline foraminifers and nine species of fusulines including Montiparus japonicus sp. nov.

Salvinia pseudoformosa has been established as a Miocene species based mainly on specimens collected from the Sasakizawa River, Numata, Hokkaido, Japan. However, both Eocene and Miocene sediments are distributed within this area. In this study, we conducted geological surveys along the Sasakizawa River to identify the stratigraphic horizon bearing S. pseudoformosa and found that S. pseudoformosa occurs from the middle Eocene Itarakaomappu Formation of the Uryu Group. We also reexamined syntypes of this species and concluded that only those from the Sasakizawa River can be identified as S. pseudoformosa with certainty. Therefore, we designated a syntype from the Sasakizawa River as the lectotype. Although we could not specify the exact localities of the lectotype and remaining syntypes from the Sasakizawa River, lithological characters of the slabs containing these specimens indicate their occurrence from the Uryu Group. Salvinia pseudoformosa has been recorded from the middle Miocene in Japan and Korea, but the venation patterns of these specimens differ from those of S. pseudoformosa.

The discovery of the heteromorph ammonoid Amapondella amapondense (van Hoepen) in the lower middle Campanian in the Urakawa, Biratori and Hidaka areas of Hokkaido, northern Japan, represents the first report of this taxon in the Northwest Pacific region. Because the species flourished in other regions during Santonian to early Campanian time, its final geographic occurrence in Hokkaido suggests that global environmental changes likely had a significant influence on ammonoid biogeography during early middle Campanian time.

This study examined the functional morphology of the trace fossil Paleodictyon in terms of computational fluid dynamics. The modern specimens show a unique morphology that is composed of a hexagonal mesh structure, vertical shafts opening to the seafloor, and a shield-like mound on the seafloor. The traces of the vertical shafts were also preserved in some fossil examples. To explain their characteristic morphology, a “passive ventilation” hypothesis has been proposed suggesting that their function was to ventilate their burrows with bottom currents, which supply both oxygenated water and food. However, this hypothesis has not yet been verified. This study conducted numerical experiments to understand the functions of the structures created by this ichnofossil by using a model of computational fluid dynamics with the 3D geometry of Paleodictyon and estimating the efficiency of the ventilation in burrows. As a result, it was observed that seawater flowed in the vertical shafts in the marginal area of the mound, and flowed out from the shafts located on the top of the mound, flowing through the mesh structure. This ventilation was observed only in the case that Paleodictyon had a shield-like mound. The ventilation rate rapidly increased as the bottom current velocity increased. In contrast, the rate also increased with the height of the shield-like mounds, whereas it once dropped after the minor peak at 4 mm in height, which corresponds to the value measured in the modern specimens. This coincidence may imply that the height of the mound observed in modern specimens resulted from the optimization in balancing between the efficiency of ventilation and physical stability against erosion. Full exchange of water in the mesh structure by ventilation took less than a few minutes at this mound height, which is presumably sufficient for the ability of Paleodictyon producers.

Ocean acidification is now progressing, primarily due to the fact that the oceans have absorbed about 50% of the anthropogenic CO₂ emitted since the industrial revolution. Many marine calcifying organisms, such as foraminifers and coccoliths, are known to build their shells using carbonate ions present in the seawaters surrounding them. Carbonate saturation state has a crucial influence on foraminiferal calcification, and foraminiferal shell production is known to be sensitive to increase in ocean pCO₂. Moreover, ocean warming is also progressing along with acidification. Therefore, both environmental changes could affect foraminiferal shell formation. However, the relationship between foraminiferal shell parameters (i.e., size, weight, volume, and density) and ocean pCO₂ or sea surface temperature (SST), or both, remains unclear. In this study, we used fossil planktic foraminifer Globigerinoides ruber (white) in a late Quaternary sediment core (MD98-2196) from the East China Sea to investigate a relationship between the shell parameters and oceanographic properties estimated based on the proxies from the same core. The foraminiferal shells were scanned using high-resolution micro-X-ray computed tomography (MXCT) to determine shell volume and density. The results showed that the size-normalized weight and the size-normalized volume of the shell had a negative correlation with the SST and atmospheric pCO₂. The negative correlation between weight/volume and atmospheric pCO₂ agrees with the previous laboratory experiments and geological record during the Pliocene. However, the correlation between weight/volume and SST should be interpreted with caution because it might be an artifact due to the correlation between SST and atmospheric pCO₂. On the other hand, shell density is only weakly or insignificantly correlated with SST and pCO₂, suggesting that these environmental parameters do not exert any impact on shell density. Thus, future ocean acidification will negatively affect the carbonate productivity of planktic foraminifers, even if it will not affect shell density. The temperature effect on the shell formation of the planktic foraminifers might be much less than ocean acidification considering controversial results of the temperature sensitivity in previous studies.

A taxonomic revision of the ammonoid assemblage previously reported from the Osawa Formation at Akaushi in the Motoyoshi area, i.e., Columbites parisianus, Subcolumbites perrinismithi and Eophyllites cf. dieneri, leads to the conclusion that the fauna should be attributed to Hellenites tchernyschewiensis, H. inopinatus, Neocolumbites grammi, N. insignis, Procolumbites ussuriensis and P. subquadratus. In addition, this fauna also includes Deweveria kovalenkoi. Because these ammonoids are characteristic of the N. insignis Zone of South Primorye, Russian Far East, the lowest part of the Osawa Formation clearly correlates with the upper part of the lower Spathian (upper Olenekian, Lower Triassic), and the faunal similarity suggests that the South Kitakami Belt may have been located near South Primorye on the western side of the Panthalassa.

A bedded chert succession, intercalated with layers of coarse-grained sandstone and chert conglomerate, and a limestone block with a long axis of about 10 m are distributed in the Ban Rai area, southwestern Uthai Thani, central Thailand. The chert yielded early Carboniferous (Tournaisian to Visean) radiolarians composed of 10 species of five genera; the limestone yielded Middle Triassic (early Anisian) conodonts comprising five species (P1 element). The lower Carboniferous chert was presumably deposited on the upper continental rise of the Sibumasu Terrane in the Paleotethys Ocean, based on radiolarian faunal characteristics. The Middle Triassic limestone was probably deposited on the continental shelf of the eastern margin of the Sibumasu Terrane, judging from the inclusion of silt-sized quartz grains. Because the blocks of the lower Carboniferous chert and Middle Triassic limestone are currently located in a narrow area, these blocks are inferred to have been mixed with each other by submarine sliding after at least the Middle Triassic at the eastern margin of the Sibumasu Terrane.

Four sediment samples were collected from an outcrop of the Holocene-raised beach in Skarvsnes (Lützow-Holm Bay, East Antarctica) at an elevation of 0–10 m through a geomorphological survey conducted during the 46th Japanese Antarctic Research Expedition (JARE 46). These samples were used for grain size, CNS (carbon, nitrogen, and sulfur) elemental, and ostracod analyses. The ¹⁴C dating of an annelid tube collected from the same outcrop was also conducted using an accelerator mass spectrometry. The resultant age was estimated at approximately 5,800 cal. year BP. A total of 16 ostracod species belonging to 10 genera were identified for the first time from all study samples near Lake Suribachi-Ike, Lützow–Holm Bay, East Antarctica. The phytal species were found to be the most dominant, suggesting rich seagrass and/or seaweeds at that time. Autecological methods and modern analog technique of ostracod assemblages were used to estimate the paleoenvironment. The result from the modern analog technique suggested that the paleo-water depth of approximately 30 m at that time is the most probable estimation, implying the glacial-isostatic uplift of approximately 30–40 m (5.1–6.8 mm/year) until sample date.