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Foraminiferal faunas from the Upper Oligocene Minaminaganuma Formation recovered from boreholes of the Yufutsu Oil and Gas Field and MITI Umaoi located in southern Hokkaido are characterized exclusively by the large elphidiids Elphidium mabutii and Cribroelphidium ombetsuense. They indicate cold water temperatures and an inner to middle sublittoral paleobathymetry. The total organic carbon (TOC) content and hydrogen index (HI) values obtained by CHN Corder and Rock-Eval pyrolysis indicate the significant deposition of organic carbon of phytoplankton origin in the inner sublittoral condition. Elphidium mabutii and C. ombetsuense show ubiquitous distribution suggesting high tolerance of these two species against environmental stresses such as fluctuations in primary productivity (nutritional condition). This newly recognized shallow marine fauna is located between the Eocene-Oligocene Poronai-Momijiyama fauna (agglutinated foraminifera dominant) and the Miocene Takinoue fauna (Ammonia dominant). A comparison between the thickness of strata and the range of paleobathymetric changes in the study area suggests that an equilibrium between basin subsidence and sediment accumulation existed to keep this area under shallow marine conditions during a certain period in the Late Oligocene, which preceded the rifting of the Japan Sea during the Early Miocene.
Lower Triassic bivalve assemblages are recognized in the Yinkeng Formation, South China, and the Hong Ngai Formation, North Vietnam. Basinal mudstones and deep ramp carbonates contain the monospecific Claraia wangi assemblage. The Eumorphotis teilhardi-Towapteria scythica assemblage occurs in deep ramp deposits. The Claraia stachei-“Claraia” phobangensis assemblage is found in shallow ramp deposits. These bivalve assemblages are mainly composed of epifaunal species, and are characterized by low species diversity and parautochthonous elements. Most species of Claraia probably inhabited shallow to deep marine environments. Besides, Eumorphotis and Towapteria are useful indicators of Lower Triassic shallow marine environments above storm-wave base.
Well preserved fossil plants are newly collected from the Tochikubo Formation (Oxfordian) of the Somanakamaura Group exposed in the northeastern part of Fukushima Prefecture. A total of nine species including three unidentified ones are described herein, among which the following five species are recorded for the first time in this area: Lycopodites sp., Adiantopteris sp., Taeniatus elongatus sp. nov., Taeniopteris somaensis sp. nov., and Pelourdea nipponica sp. nov. In addition, a fragmentary specimen assignable to Neocalamites, the youngest representative of this genus, is obtained. A specimen of the reproductive organ of Williamsonia is newly collected from the Tomizawa Formation. Combined with the previously reported species lists, this study further clarifies the species composition of the Soma Jurassic flora in the Tochikubo and Tomizawa formations, lending considerable support to the representation of one of the important floras of the Ryoseki-type in the Outer Zone of the Japanese Islands.
The mode of occurrence of spatangoid spines in bottom sediments from the Japan Sea was examined in relation to temperature conditions. The remains of four species, Echinocardium cordatum, Spatangus luetkeni, Moira lachesinella, and Brisaster latifrons, were identified by comparing collected spines from bottom sediments with the morphological features of complete spines from living spatangoids. The spines were separated into four fragment types according to their preservational state: 1) the proximal part (with base, without tip), 2) the shaft (without both base and tip), 3) the distal part (without base, with tip), and 4) the intact spine. The spines were mostly fragmented, and the shaft and distal parts were found in almost all samples. The occurrence of the proximal part was strongly controlled by water temperature; the proximal part was dominant in warm water (9 to 25°C) but was seldom found in sediments in cold water (2 to 10°C). The decay process of Schizaster lacunosus in the laboratory in artificial seawater at three different temperatures (5°C, 20°C, and 30°C) was also studied. The disarticulation rate of the spines was strongly controlled by temperature, with low temperature drastically delaying the disarticulation process. The low occurrence of the proximal part in cold water can be explained by the long-term attachment of the spine base to its tubercle, preventing the echinoid carcass from supplying the proximal spine part to the sediment.
In the early 20th century, Tokunaga, followed by Naora, reported a Middle Pleistocene mammalian fauna from the Matsugae limestone cave deposits in northern Kyushu, West Japan. Within this fauna Naora (1968) described a new extinct species of otter (Lutra nipponica). Recently, we have identified new, well preserved dentitions of this mustelid in their original collection. We suggest that the definition of L. nipponica given by Naora should be emended, and that the specimens belong to a new genus of the tribe Galictini (Mustelidae, Carnivora), namely, Oriensictis gen. nov., according to the following characteristics: short muzzle; transversely expanded P4; and anteroposteriorly expanded M1. The extinct Chinese otter L. melina (Pei, 1934) from the Middle Pleistocene cave deposits of Choukoutien locality 1 is also included in Oriensictis based on the characteristics of M1 and a short mandible. These two occurrences of this genus are the first records of East Asian galictines, and this suggests that the Galictini might have been extensively distributed over areas in the Northern Hemisphere until the Middle Pleistocene.
A late Pliocene (1.8–1.9 Ma) wetland fossil forest community that was dominated by Metasequoia and Glyptostrobus was reconstructed based on the species composition of the stumps and other plant macrofossil assemblages. The plant fossils were recovered from a fossil forest preserved in deposits of the Kobiwako Group that are exposed in the Echi River, Shiga Prefecture, central Japan. Fossil wood of Metasequoia and Glyptostrobus was distinguished based on anatomical characteristics. Apportionment of the wood from different horizons in the fossil forest indicates Metasequoia grew over a long period of time in a stable environment, while Glyptostrobus and Alnus grew in unstable environments characterized by shortinterval floods. The fossil forest as a whole represents a fluvial back-marsh environment.
The upland forest was composed of mixed evergreen conifers and deciduous broad-leaved trees including Chamaecyparis pisifera, Tsuga, Magnolia, and Acer. Aquatic and wetland herbs such as Cyperus, Carex, Scirpus, Polygonum, and Menyanthes grew in and around the wetland forest. The assemblage of fossil plants recovered from the fossil forest consists of plants that are currently distributed in the cool temperate climate zone, such as Picea, Thuja, Betula maximowicziana, Pterocarya rhoifolia, and Menyanthes trifoliata. Glyptostrobus is distributed only in subtropical areas at present, but it also grew under a cool temperate climate zone in Japan during the latest Pliocene.
Early and Middle Ordovician conodonts are described and illustrated from the Thong Pha Phum and Kanchanaburi areas in western Thailand and the Li area in northern Thailand. The Thong Pha Phum fauna consists of 14 species representing ten genera and one unidentified species, and from the Kanchanaburi and Li sections two and five species, respectively, have been recovered. Two conodont zones, the Triangulodus larapintinensis and Aurilobodus leptosomatus zones, are established in the Thong Pha Phum section. The fauna from the T. larapintinensis Zone includes Panderodus nogamii, Triangulodus larapintinensis, and species of Juanognathus, and the A. leptosomatus Zone is characterized by A. leptosomatus, Histiodella holodentata, and Plectodina onychodonta. Two regression events are recorded in a lower part of the Thong Pha Phum section. The conodont biostratigraphy indicates that the regressions took place in latest Early Ordovician and earliest Middle Ordovician.
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