Planktonic Foraminiferal Biostratigraphy of the Late Cenozoic Sedimentary Sequence, Central Honshu, Japan

Stratigraphic changes of planktonic foraminiferal assemblages in the Boso Peninsula, the Kakegawa area, and the Takasaki area situated along the Pacific side of central Honshu, Japan have been analyzed. These land-based sections provide a valuable record of planktonic foraminiferal events which took place during the Late Cenozoic in the middle latitude region of the North Pacific. Especially, the Boso section in which foraminifera are generally abundant and well preserved with prominent planktonic forms represents the most complete stratigraphic succession in the present study. The Boso section is also suitable for constructing the paleomagnetic stratigraphy as well as the biostratigraphy, because tuff beds frequently intercalated in the sequence serve as good keys for determining the stratigraphic position of samples from separate outcrops with considerable accuracy. Thirteen planktonic foraminiferal levels on the basis of first and last occurrences and three distinct levels defined by the coiling direction shift in the genus Pulleniatina are useful for stratigraphic correlation of the Middle Miocene to Pleistocene sequence distributed in the regions on the western Pacific side of Japan. They may not be applicable elsewhere, although some of these events seem to be important for a time-stratigraphic correlation of widely separate localities. The magnetic polarity sequence determined by measuring detrital remanent magnetization of samples from the same section of the Boso Peninsula of the present study is interpreted on the basis of six principal levels of the planktonic foraminifera, in comparison to a combined planktonic foraminiferal biostratigraphy and magnetostratigraphy established in deep-sea cores in the equatorial Pacific covering the time span from the Magnetic Epoch 5 to the Brunhes Normal Epoch. Climatic fluctuation within the Pleistocene on the basis of the vertical changes of the planktonic foraminiferal assemblages in the Boso sequence which were dated in terms of the paleomagnetic scale shows a warming trend across the Olduvai Event. A cooling trend, denoted by the upward decrease in the abundance of warm-water fauna associated with an increased abundance of cold-water fauna and influx of sinistral coiling Globigerina pachyderma in varying frequency, occurs shortly before the Jaramillo Event prior to the onset of the severe cooling in the earlier part of the Brunhes Normal Epoch. This may mark the initiation of mid-latitude glaciation

Geographical Distributions of Planktic Forminifera in Japan Sea Sueface Sediments

金沢大学大学院自然科学研究科東北大学Promoting Environmental Pesearch in Pan-Japan Sea Area : Young Researchers\u27 Network, Schedule: March 8-10,2006,Kanazawa Excel Hotel Tokyu, Japan, Organized by: Kanazawa University 21st-Century COE Program, Environmental Monitoring and Prediction of Long- & Short- Term Dynamics of Pan-Japan Sea Area ; IICRC(Ishikawa International Cooperation Research Centre), Sponsors : Japan Sea Research ; UNU-IAS(United Nations University Institute of Advanced Studies)+Ishikawa Prefecture Government ; City of Kanazaw

Late Cenozoic Micropaleontologic Events in the Equatorial Pacific Sediments

A microbiostratigraphical investigation of five deep-sea sediment cores from the equatorial Pacific was carried out by utilizing planktonic foraminifers, radiolarians and calcareous nannoplankton. Several micropaleontologic events characterized by the first occurrence of taxa were found to provide reliable datum planes for stratigraphic correlation of post-Miocene sediments. These datum planes are : The Buccinosphaera invaginata Datum, Collosphaera tuberosa Datum, Globoquadrina conglomerata Datum, Pulleniatina obliquil-oculata Datum, Gephyrocapsa oceanica Datum, Gephyrocapsa caribbeanica Datum, Anthocyrtidium angulare Datum and Globorotalia (G.) truncatulinoides Datum, in downward sequence. These datum planes are related to the biostratigraphic zonations based on various microfossils, and further to the previously determined paleomagnetic stratigraphy. One new radiolarian species, Amphiropalum praeypsilon, is described

Planktic foraminiferal assemblages and stable isotope records of the southern Japan Sea during the last 27,000 years

Abstrac

日本脳炎伝搬蚊,特にコガタアカイエカの生態5.コガタアカイエカとシナハマダラカの越冬

The time of awakening from winter diapause in Culex tritaeniorhynchus summorosus and Anopheles sinensis was examined from the data of mosquito catches in winter and early spring from 1965 to 1971 in the Nagasaki area. The results indicated that at least until the end of February most females of G. t. summorosus are still in a diapausing state, i. e., they do not feed on animals even on a warm day, while many of An. sinensis females are in such a physiological state already in January that they can feed on animals if the temperature is high enough for their flight activity. From the observations in the field and the experiments in the laboratory, it was implied that the main overwintering place of C. t. summorosus, and probably An. sinensis too, is the underground small space of stone walls, banks and the likes which are common in the terraced rice field area.コガタアカイエカとシナハマダラカの雌成虫が冬期の休眠から覚醒する時期を,長崎地方で1965-1971年の冬及び早春に採集した蚊の資料を用いて吟味して,次の結果を得た.コガタアカイエカの大多数の雌成虫は少なくとも2月の末までは休眠状態にあり,暖い日であっても吸血に来ることは殆んどない.これに反してシナハマダラカの雌成虫の多くは1月には既に休眠から覚醒していて,気温が飛翔活動に充分なほど高くさえあれば,多数の吸血蚊が観察される.野外及び実験室での観察から,コガタアカイエカが(そしておそらくシナハマダラカも)越冬するのは,階段状の水田が多くある地方の石垣や土手などの中の小さなすき間であるように思われる

Mid-Quaternary Paleoceanographic Trend in Near-shore Waters of the Northwest Pacific : A Case Study Based on an Offshore Well

An exploratory oil and gas well was drilled on the continental shelf in water 38 m deep at lat. 36°9′33.8″N., long. 140°43′49.3″E., 13 km off the coast of Kashima, Ibaraki Prefecture, Kanto District, Japan. This well sank to the total subbottom depth of 2100 m penetrated sediments ranging back to Late Cretaceous in age. The upper 500 m of well sequence which comprises largely Quaternary sediments was subjected to paleoenvironmental analyses by jointly analyzing microfossils (calcareous nannoplankton and benthic and planktonic foraminifera), mineral content, and oxygen and carbon isotope stratigraphies. Three dated horizons, 0.128, 0.27 and 0.46 Ma, were established by recognizing one marked excursion to negative values in the oxygen isotope record and two calcareous nannoplankton datum levels in the well sequence. A possible hiatus at about 465 m depth terminates this mid-Quaternary sequence which is underlain by late Pliocene strata of about 1.9 Ma and older. Mid-Quaternary paleobathymetric trends were reconstructed for the well site area mainly on the basis of Q-mode cluster analysis of benthic foraminiferal faunas. Deposition of the mid-Quaternary sequence began in the upper bathyal zone and a steady shallowing followed through outer shelf environments to the present-day inner neritic zone. Other paleo-depth indicators such as abundance variations of nannoplankton Florisphaera profuuda and planktonic versus total foraminifera ratios, and variations of ^C isotope record are all supportive of this benthic foraminifera-based depth-trend. Paleotemperature fluctuations were estimated by analyzing oxygen isotope compositions of benthic and planktonic foraminifera and by calculating with the aid of paleoecological transfer functions quantitative estimates of past winter temperatures. The paleotemperature fluctuations estimated for the well site area by these two methods agree well for the lower part of the well sequence, but begin to diverge from the mid-sequence and upwards, probably reflecting increasing effects of local water masses to the oxygen isotope variation. In the Quaternary isotope record of Kashima SK-1 well, no definite interval correlatable with the even-numbered isotope stages was observed. In view of the fact that distinct hiatuses occur in the onshore Quaternary record of Kanto District located to the west of the well site, the lack of even-numbered isotope stages is interpreted to signify periods of greatly reduced sedimentation or possibly non-deposition in a broad coastal region encompassing also the continental shelf around the well site. Mid-Quaternary paleoceanography around the well site prior to about 0.35 Ma was under the general influence of cold Oyashio Current with its strength varying greatly from time to time, whereas the latter time period responding to the diminishing Oyashio Current saw a seesaw game of two warm currents, Kuroshio and Tsugaru, expanding and retreating alternatively over a broad region of the sea off Northeast Honshu, Japan

日本脳炎伝搬蚊,特にコガタアカイエカの生態 : 3.コガタアカイエカがドライアイスに誘引される時刻の季節的変化

The time of being attracted to dry ice of Culex tritaeniorhynchus females in the evening roughly depends on the sunset time. Strictly speaking, however, the former time much fluctuates seasonally than the latter time. In spring, the starting time of being attracted to dry ice is usually over half an hour earlier than the sunset time, and the peak time appears around the sunset time. With the progress in season, the time in relation to the sunset time becomes later gradually and in summer and autumn the starting time, and consequently the peak time, becomes in most cases, later than the sunset time. In other words, the illumination in Lux at the time of being attracted to dry ice is much higher in spring than in the other seasons.コガタアカイエカ雌成虫が,夕方,ドライアイスに誘引される時刻は,季節的に,おおよそ日没時刻の変化に平行的であるが,厳密に言うと日没時刻よりも早い季節と遅い季節がある.春には,通常,日没の30分以上も前から誘引され始めて,日没頃に最も多く誘引されるが,季節が進むにつれておくれ,夏や秋には日没後に初めて誘引され始めるようになる.すなわち誘引される時刻の照度は,春の方が夏,秋に比分べて,一般に,はるかに高い

New Planktic foraminiferal transfer functions for the Kuroshio-Oyashio current region off Japan

Volume: 1Start Page: 291End Page: 31