Geotectonic subdivision and areal extent of the Sangun belt, Inner Zone of Southwest Japan

The Sangun belt has long been considered to be a major coherent glaucophanitic terrane of Permian to Triassic age, and to be paired with the low-P/T Hida belt to the north. However, recent progress in geochronology, metamorphic geology, and tectonics has revealed that the belt is in fact comprised of two geologic units of different ages and with contrasting conditions of formation. The older unit is named the Renge belt and the younger the Suo belt. The Renge belt is the oldest of the high-P/T metamorphic belts in the Japanese Islands and extends from northern Kyushu, through the San-in coastal regions, to the Hida marginal belt. It is characterized by 330–280 Ma ages and the association of glaucophane–schist to epidote–amphibolite facies schists. The Renge belt is also typically associated with meta–ophiolite sequences (470–340 Ma) including serpentinite. The Suo belt is characterized by 230–160 Ma high-P/T schists closely related to weakly metamorphosed Permian accretionary rocks of the Akiyoshi belt. Metamorphic facies series is from the prehnite–pumpellyite facies through the pumpellyite–actinolite and glaucophane–schist facies to the epidote–amphibolite facies. The belt is widespread in west Kinki to north and central Kyushu via Chugoku, but also stretches further to the southwest and is present in the Ishigaki-Iriomote Islands of the southern Ryukyu Arc. Throughout this belt, there are scattered small blocks or lenses of meta–ophiolite, whose K–Ar ages of relict hornblendes are 590 to 220 Ma. Bounded by low-angle faults and thrusts, both belts define subhorizontal nappes dipping gently north. The geotectonic framework in the Inner Zone of Southwest Japan is made up of, from north to south, the Hida-Oki, Renge, Akiyoshi, Suo, Maizuru plus ultra-Tamba, Mino-Tamba, and Ryoke belts, with a tectonically downward-younging polarity. This has resulted from stepwise accretions during Palaeozoic to Mesozoic time.     

Middle Layer Intrusion as an Important Factor Supporting Phytoplankton Productivity at a Tidal Front in Iyo Nada, the Seto Inland Sea, Japan

Field observations were conducted to examine the processes governing the phytoplankton distribution and photosynthetic activity in and around a tidal front formed in Iyo Nada, the Seto Inland Sea, Japan. The existence of a middle layer intrusion, which, it has been suggested, moves from the mixed region to the stratified region of the tidal front, was ascertained by the phytoplankton distribution in addition to a T-S diagram. Skeletonema costatum, which originally inhabited the mixed region, was used as the indicator to reveal the intrusion. However, the tip of water containing the S. costatum population did not extend deeply into the stratified region. The velocity of the intrusion seemed to be slow enough to make biological processes, such as nutrient uptake by phytoplankton and subsequent growth, as well as the decrease in cell density due to zooplankton grazing, dominate during the transportation. The patchy distribution of copepod nauplii implied that grazing has an influence on the distribution pattern of phytoplankton. The location of high photosynthetic activity did not coincide spatially with the center of high phytoplankton biomass, suggesting the importance of these biological processes. Therefore, it is considered that the middle layer intrusion plays a role as an inducer of subsequent biological processes at the tidal front by not only supplying nutrients from the mixed region but also by increasing the vertical diffusivity.     

楼兰地区新发现斗检封及其指示意义

楼兰地区新发现一枚斗检封,该斗检封为红铜质,斗形,铸文释读为"官律所平"。对于丰富楼兰时期文字、书法、印玺艺术、文书程式等研究提供了珍贵的实物资料。斗检封所在周围的地理环境与周围散落的其他文物及楼兰周边遗址地理分布情况表明,楼兰先民的生产生活类活动可能主要集中在楼兰古城的东、南、西部区域,而大型的祭祀、宗教等活动主要集中在楼兰北部区域。斗检封所在位置应该是在楼兰通往外部的一条重要交通线上,"张千人丞印"附近可能是某一级官府所在地且周围环境利于人类生存。这对于认识楼兰时期古丝绸之路的位置以及楼兰古城周边生业环境状况能够提供重要参考。     

Contribution of benthic microalgae to the whole water algal biomass and primary production in Suo Nada,the Seto Inland Sea,Japan

Biomass and primary productivity of benthic microalgae (BMA) and planktonic algae in Suo Nada, the western part of the Seto Inland Sea, Japan were compared in terms of unit area with regard to their seasonal and spatial distribution in 2002. Judging from light compensation depth and water depth, the southwestern part of Suo Nada was considered to be a potential habitat for BMA. Whereas the contribution of sedimented planktonic algae was high in biomass at the sediment surface, BMA was obviously significant both in biomass and primary production in the shallow southwestern part. However, the contribution of BMA to the total biomass in the entire water column was 7% in winter and 2% in summer. The primary production of BMA varied between 4.0 and 74.0 mg C m⁻² d⁻¹ in the southwestern part, accounting for 2–12% of the whole water column primary production. The ecological roles of BMA in the Suo Nada ecosystem are discussed, such as reduction of benthic nutrient flux, oxidation of surface sediments and feed for higher animals.