The discovery of a gigantic crater, of which buried circular structure is located at Chicxulub, on the north coast of Yucatan, Mexico, has gained wide acceptance that the crater is probably the long-sought K-T boundary impact site. Its size and shape were disclosed by Bouguer gravity anomalies, showing a 180-km-diameter circle associated with a central high and two internal concentric lows (Hildebrand et al., 1991). Shocked quartz grains and spherules from core samples, together with the anomalous concentration of iridium (Ir), are the best evidence to show that all these are the impact products. Moreover, 40Ar/39Ar ages obtained from glassy melt rocks of cores are 65.2±0.4 Ma (Sharpton et al., 1992) and 64.98±0.05 Ma (Swisher et al., 1992) respectively, irrefutably displaying the time of K-T boundary. Some unusual sedimentary structures at the K-T boundary sections around the Gulf of Mexico are compatible with the theory of nearby (Chicxulub) impact. The cause of the dramatic extinction event at the K-T boundary has been ascribed either to the impact of a large extraterrestrial material or to the extensive volcanism. However, characteristics of lamellar deformation in shocked quartz are clearly distinguishable from those in quartz of volcanic (eruptive) origin (Alexopoulos et al., 1988). Critics who prefer the world-wide volcanism to the bolide impact have been unable to explain reasons why the eruptive-type deformed quartz grains do not exist at the boundary sections. Although mass extinctions have occurred many times during the Phanerozoic time, some workers now believe that the K-T boundary extinction might have been the only probable case by the bolide impact (e.g., Hallam, 1989). Other mass extinctions, like P-Tr (Permian-Triassic) extinction, might have been caused by the substantial sea-level change, variable sea water temperature and CO2 content in atmosphere. These factors are essentially controlled by plate tectonics, but not by the bolide impact.
Volcanic ash soils occur widely on South Kanto district. The surface soil has black color and high humus content. The parent material is derived from Holocene volcanic ash. There are some buried humic horizons resulted from a succession of volcanic ash accumulation and plant residue supply leading to the accumulation of soil organic matter or humus. It has commonly been considered that Mt. Fuji supplied parent material of those soils. A huge amount of Holocene volcanic ejecta (tephra) with a large particle size accumulates at the eastern foot of Mt. Fuji, Tephrochronological studies enabled us to identify each scoria layers. However, little information of the tephrochronological study is available for soils formed in the region away from Mt. Fuji, such as on Musashino Plateau. A small amount of volcanic ash accumulation with a small particle size, compared with those in the eastern piedmont region close to Mt. Fuji promoted soil formation in this region, it is difficult to identify the characteristic tephra on Musashino Plateau on the contrary to the tephra of piedmont region which can easily be identified. Furthermore, it is assumed that more than one volcano in addition to Mt. Fuji such as Mt. Asama and Mt. Haruna supplied volcanic ash with a different rock type from that of Mt. Fuji in Musashino Plateau region. It is important to claryfy to what extent other volcanoes contributed in south Kanto district as a source volcano of the parent material of soils. In this paper, we compared morphological features, primary mineral composition, and element composition of three profiles which were locatd in Fujisawa City, Kanagawa, Fuchu City, Tokyo, Hidaka Town, Saitama respectivery. They are located almost in the same ditsance but the different direction from Mt. Fuji. At first, we directed our attention to buried humic horizon which was often identified as a horizon where it covered the archaeological site and remnants of the Nara-Heian period in Fuchu City, Tokyo. The horizon has some morphological and mineralogical characteristics; most blackish color in the solum, fine granular structure, and high olivine content. We gave the horizon tentative name as H-1BB (Holocene 1st Black Band). The results are summarized as follows:(1) On the basis of primary mineral composition, following were concluded: The dominance of heavy minerals and high content of olivine indicated that, parent material of Fujisawa pedon was supplied from Mt. Fuji. The dominance of light minerals, high content of non-colored volcanic glass and clinopyroxene, parent material of Hidaka pedon was supplied from Mt. Asama, Fuchu pedon indicated the transitional character between Fujisawa and Hidaka.(2) H-1BB is identified morphologically in all profiles based on relatively strong blackish color and structure. There was high content of transparent olivine in this horizon in every pedon. Because Fujisawa pedon indicated the highest olivine content, We assumed that H-1BB in three pedons were derived from more or less the same parent material erupted from Mt. Fuji.(3) From the viewpoint of chemical classification of volcanic rock, Si contents themselves, didn't directly reflect primary mineral composition of these soils. However, the profile which abounded in the parent material from Mt. Fuji had high Ca and Sr content. H-1BB in three profiles had high Ca and low K proportion in base element.
According to the growing recognition of the importance of global environmental research, many global datasets are being produced. The common shortcoming of the existing global datasets is the lack of accuracy data and other auxiliary data. This paper describes accuracies in three types of information, i. e. space, time, and attribute, of the global land surface data, and shows what auxiliary data including accuracies need to be recorded. Moreover, some examples are given to show how accuracy data are used in data processing.
Since the Tokai district was designated as an“ntensified Observation Area” in 1974, many kinds of observation for the purpose of earthquake prediction have been done by various institutes. Among them, automatic data collection and real time monitoring of the changes in groundwater level and radon concentration were started in 1976 by Geological Survey of Japan (GSJ). These data are automatically transmitted through the telephone line, and received by an engineering work station at GSJ, in Tsukuba. During these observation period, we have detected some ground water anomalies caused by earthquakes. This system is constructed with taking the following points into account. 1) Water level is observed in pressured ground water. The ground water, that is sensitive to barometric pressure and earth tide, is expected fairly sensitive to an earthquake. 2) Radon is observed in self-flowing ground water, because it is difficult to control pumping power for non-self-flowing ground water and distinguish radon anomalies from pumping rate fluctuations. 3) Aiming low operation cost and flexibility of the system, data transmitting path has been changed from simple conventional telemetering equipment to computer communication. These computers on the observation sites are sampling data every 2 minutes, and transmitting data every hour. 4) The computer at data collecting center has been substituted from mini-computer system to engineering work station with LAN system. So, high quality data processing can be performed on specified independent computer system.
A synthesis of geological, geomorphological, and petrological data was made to reconstruct the tectonic evolution of the collision zone between the Honshu and Izu-Bonin Arcs during the middle to late Miocene time. The collision zone is composed of four allochthonous terranes, which are overlaid by syn-collisional trough-filling deposits. The four terranes, Izu, Tanzawa, Misaka, and Koma Terranes, were originated in the Izu-Bonin volcanic arc and have in turn collided with and accreted into the Honshu Arc at about 1, 5-3, 11, and 15 Ma, respectively. The geomorphology of the northern part of the Izu-Bonin Arc is characterized by two N-S trending ridges, Shichito-Iwojima and Nishi-Shichito Ridges, and Nishinoshima Trough between the two ridges. We interpret the Nishi-Shichito Ridge as a remnant volcanic arc of early Miocene age. The Nishi-Shichito Ridge was left by backarc rifting, which occurred between the Nishi-Shichito and Shichito-Iwojima Ridges during 15-10 Ma. The backarc rifting resulted in the increase of downdip angle of the Pacific plate slab and the eastward migration of the Izu-Bonin volcanic front. The rifting also generated along-arc compressional strain, which caused the intraarc deformation of the Shichito-Iwojima Ridge at about 10 Ma. This interpretation well explains the geologic history of each allochthonous terrane in the collision zone between the Honshu and Izu-Bonin Arcs as well as the present distribution of the allochthonous terranes.
This paper discusses the relationships between relief energy and types and intensity of erosional processes in an active folding zone in the northeastern margin of the Niigata plain. It is recognized that there is a positive correlation among relief energy, magnitude of erosional processes and intensity of denudation in areas that have relief energy less than 150 m and are underlain by the upper Miocene mudstones. This relationship suggests that the intense areal denudation in the higher relief zone provides an upper limit of relief energy in the areas of less resistant rocks. In the study area, where denudation is not yet in the equilibrium with uplifting, the relief energy will reflect the amount of uplift. Large amount of uplift is expected to produce large relief energy, and mountainous landscape characterized by large-scale landslide and lack of crest-flats in the southern part of the surveyed area. In contrast with the southern part, in the northern part of the surveyed area, where the amount of uplift is smaller than the southern part, the hilly landscape characterized by the broad crest-flats and numerous gullies are formed in the low relief area.
The fracture strength of the earth crust is estimated from the published strength data of granite in laboratory, considering confining pressure dependence, temperature dependence and strain rate dependence on the fracture strength. The strength of granite increases non-linealy with increased confining pressure, decreases about 7 per cent for 100°C increase in temperature, and decreases about 2 per cent for tenhold decrease in strain rate. Assuming three dependences are mutually independent, the estimated fracture strength of the crust has a maximum strength of 920MPa at a depth of 15 km for a temperature gradient of 15°C/km and a strain rate of 10-14/sec. The fracture strength of the crust becomes equal to the frictional strength at a depth of 12 km. This result suggests that the fracture at a depth of more than 12 km is a high-pressure type fracture.
There are few complete and high-resolution pollen records in the last interglacial-glacial cycle in Japan. We made clear in the recent paper (1990) that the paleoclimate from the Last Interglacial to the Lastglacial maximum in Hokkaido coincided closely with oxygen-isotope records from deep-sea cores by a pollen analytical study on the peat or peaty layers intercalated in the terrace deposits of the Hidaka district, southern Hokkaido, adding the terrestrial paleoclimatic evidence of paleo-glacial, paleo-periglacial, paleo-dunes, and so on. The Hidaka district is one of the best successively developed areas of marine and fluvial terraces in Japan. We continued the survey in the same district and collected many samples for pollen analysis from the terrace deposits of different places and different ages. The stratigraphical sequence of the samples was mainly determined by the tephra layers which were inter-calated in the terrace deposits and were dated by various methods. The aim of this paper is to show the more detailed paleoclimatic features of the last interglacial-glacial cycle by syn-thesizing the former pollen records and newly obtained ones. Five climatic types, glacial maximum (GM), glacial sub-maximum (GM′), glacial (G), lateglacial (LG), and postglacial (PG), were classified as a criterion for the zoning of pollen assemblages based on the pollen records of Kuromatsunai, southwestern Hokkaido and also Sakhalin which were obtained by the senior author. The synthesized results are shown in Fig. 8. The paleoclimatic diagram obtained is closely coincident with the normalized oxygen-isotope curve which is proposed by Martinson et at.(1987). The pollen of Sciadopitys varticillata which is separately distributed in central and western Japan south of 37°C37'N and is not existent in Hokkaido (Fig. 6), is recognized around 140 ka BP, 90-100 ka BP, and 40-45 ka BP in the Hidaka district and is co-existent with boreal -type pollen. The occurrence of Sciadopitys pollen is also recognized in some locations in southern Hokkaido. The main occurrence periods of Sciadopitys pollen during the late Pleistocen e are well coincident through over Japan. These periods are considered to have been mo re humid.
In this paper, major agricultural changes in the Ile-de-France region, i. e. the Paris metropolitan area, are described through the examination of the results of four agricultural censuses effectuated in post-war France (in 1955, 1970, 1979 and 1988). The rural landscape and agricultural system of the region have been greatly transformed by those changes summarized as follows. Very striking is the retreat of market gardening (agriculture spécialisée) in favor of the urban growth of Paris agglomeration. In particular, the decrease of fruit gardening is most conspicuous. Accordingly, the agriculture of this region becomes more and more characterized by large-scale cereal farming. But the nature of this type of farming has also greatly changed during post-war period. The raising of livestock (mainly cattle and horses), which was generally combined with cereal farming in 1955, is almost disappearing. The former type of mixed farming has been replaced by specialized cereal farming whose farm-size becomes increasingly enlarged. The retreat of livestock raising, the collateral decline of oats, and the enlargement of farm-size are notable reflections of the structural transformation of agriculture in this region. On the contrary, changes in land-use, which influence rural landscape to a major degree, are determined in many cases by temporary factors, such as the variation of crop price or the changes of agricultural policy. Both the increase of wheat in the 1970's and the rapid expan-sion of sunflower in the 1980's are closely connected with the Common Agricultural Policy of the European Community. At the same time, the rapid increase of maize and sunflower can be realized through the improvement of plant breeding. In this way, the agricultural changes which caracterized each decade in post-war period, are related with concomitant changes in political, economic and technical circumstances.