著者

鈴木 和恵 丸山 茂徳 山本 伸次 大森 聡一

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.6, pp.1173-1196, 2010-12-25 (Released:2011-03-17)

参考文献数

48

被引用文献数

20 35

---

The Japanese Islands have long been considered to be the most evolved of all the island arcs in the oceans. A simple scenario has been implicitly accepted for the growth of the Japanese Islands: since subduction started sometime around 520 Ma, the TTG crust has increased over time in association with the steady-state growth of the accretionary prism in front. Here, we show very different dynamic growths of TTG crusts over time than previously thought, i.e., four times more TTG crusts than at present must have gone into the deep mantle due to tectonic erosion, which occurred six times since subduction was initiated at 520 Ma. Tectonic erosion is a major process that has controlled the development history of the Japanese islands. It can be traced as a serpentinite mélange belt, which indicates the upper boundary of past extensive tectonic erosion.

著者

山上 萬次郎

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.26, no.11, pp.851-862, 1914-11-15 (Released:2010-10-13)

著者

都司 嘉宣

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.106, no.4, pp.486-502, 1997-08-25 (Released:2009-11-12)

参考文献数

12

被引用文献数

2 7

---

A field survey of the damage of the Amami-Oshima-Kinkai earthquake (Mw 7.1) and its tsunami of October 18, 1995 was conducted for four days from the next day of the main shock. A large aftershock (Mw 6.8) occurred in the next day and was also accompanied with a small tsunami. We conducted interviews of the inhabitants, and measured heights of the both tsunamis. The maximum height of the tsunami of the main shock was 3.0 m at Urahara Port on the south coast of Kikai-jima. Earthquake damage mainly occurred on Kikai-jima, where stone walls were fallen down at 91 places, the water supply facility of the island was disordered, and several concrete slabs slid down at Wan Port. Several fishing boats were wrecked due to the both tsunamis at ports on Kikai-jima and Amami-Oshima. Imamura-Hatori's magnitudes of the main shock and the large aftershock are m=1.0 and m=0.0, respectively. Abe's magnitude of the tsunamis the main shock is estimated to be Mt=7.6 and is large for the earthquake magnitude. A gigantic earthquake (M8.0) with a larger tsunami occurred on June 15, 1911 in the sea region close to the present event, and its folktale is handed down by the inhabitants of Kikai-jima.

著者

大倉 敬宏 安藤 雅孝

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.103, no.5, pp.464-470, 1994-10-25 (Released:2009-11-12)

参考文献数

15

被引用文献数

2

---

The relation between the Pinatubo eruption of 1991 and the Philippine earthquake of 1990 is studied on the basis of strain changes calculated from a fault model of the Philippine earthquake. At Pinatubo volcano, which is located 100 km away from the earthquake fault, the volumetric strain change induced by the earthquake is about 10-6. This caused gradual squeeze up of magma to the surface and the Pinatubo volcano erupted eleven months after the earthquake. The volumetric change calculated by a fault model of the 1990 earthquake is, however, several orders of magnitude smaller than the total volume observed during the eruptions. The magma squeezing model alone cannot explain the whole volume of ejected magma. A possible interpretation is that the volumetric strain change could have squeezed up magma in the magma reservoir, resulting in lowering the density of magma and enhanced the magma to rise further more. Such a positive feedback process could have occurred after the Philippine earthquake of 1990. It is possible that the Philippine earthquake triggered the activity of Pinatubo volcano.

著者

宮本 真二 安田 喜憲 北川 浩之

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.104, no.6, pp.865-873, 1995-12-10 (Released:2009-11-12)

参考文献数

13

被引用文献数

1 2

---

A continuous long core of peaty sediments bored from the Naka-Ikemi Moor Central Japan (lat. 35°39' N., long. 136°5' E.), contains records of paleoenvironmental changes during the Last Glacial and Holocene periods. The Naka-Ikemi Moor stretches about 1.3 km from the west to east. This peculiar shapes and crustal movements had been pointed out by purely from a topographical point of view. And this moor is regarded as a waste-filled valley created by sort of tectonic depression at the eastern part of the Tsuruga Plain. From the stratigraphical examination, some volcanic ashes were detected as follows : Kikai-Akahoya Tephra (K-Ah : 6.3 ka), Aira-Tn Tephra (AT : 24 ka), Daisen Kurayoshi Tephra (DKP : ca. 50 ka). Values of bulk density measurements and radiocarbon dates of core samples indicate that the Naka-Ikemi core samples contain continuous records for the past 50 ka. The average sedimentation rate of Naka-Ikemi Moor was increased after the fall of AT volcanic ash had occurred. The sedimen tation process of Naka-Ikemi Moor has also been clarified by sedimentary facies and value of loss on ignition of core samples. Value of loss on ignition began to increase since the end of Last Glacial, suggesting the increase of organic material caused by environmental changes.

著者

安藤 寿男 勢司 理生 大島 光春 松丸 哲也

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.104, no.2, pp.284-303, 1995-04-25 (Released:2009-11-12)

参考文献数

38

被引用文献数

14 22

---

The Futaba Group is the Lower Coniacian to Lower Santonian, fluvial to shallow-marine sedimentary succession distributed in the southern Abukuma Belt in north Honshu. Fifteen depositional facies were discriminated. They include alluvial fan, meandering river, braided river, transgressive lag and upper shoreface to inner shelf sediments. It is divided into three formations, the Ashizawa (the Asamigawa and Obisagawa Members), Kasamatsu and Tamayama Formations in upward sequence. Each formation consists of a third-order depositional sequence (DS).The first depositional sequence (DS 1) has a lowstand systems tract (LST) as the lower main part of the Asamigawa Member distributed in the northern half of the area. It is lithologically characterized by upper alluvial fan conglomerate and mid to lower fan sandstone and siltstone nonconformably overlying lower Cretaceous granite (sequence boundary 1 : SB 1). In the southern periphery of the distributed area the member contains talus or upper fan angular conglomerate. The upper part of the member distributed over the area is interpreted to be transgressive conglomerate with a sharp base called a ravinement surface (RS 1) which was formed by transgressive shoreface erosion. It may represent transgressive systems tract (TST). The following highstand systems tract (HST) is represented by the upper shoreface to inner shelf, medium to fine sandstone of the Obisagawa Member.The Kasamatsu Formation (DS 2) unconformably (SB 2) overlying the preceding depositional sequence (DS 1), is substantially characterized by fluvial upward-fining successions composed of channel sandstone and flood plain siltstone. The third sequence (DS 3) is characterized by thick fluvial (braided river) sandstone of the lower to middle part of the Tamayama Formation interpreted as LST and the upper shoreface to inner shelf sandstone of the upper Tamayama interpreted as HST. The sudden lithofacies change between the Kasamatsu and Tamayama Formations implies some large-scale changes in fluvial depositional systems by sea-level fall (SB 3). The transgressive conglomerate just above RS 2 in the basal part of the upper Tamayama Formation represents a thin TST. The upper sequence boundary (SB 4) of DS 3 shows the conspicuous clinounconformity between the Futaba Group and the Paleogene Shiramizu Group.

著者

松倉 公憲

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.126, no.3, pp.271-296, 2017-06-25 (Released:2017-08-03)

参考文献数

131

被引用文献数

3 6

---

A brief review of our weathering studies is presented, specifically from a geomorphic perspective. The review suggests that experimental work and microscale investigations using new analytical methods have advanced studies on weathering processes, while steady advances have been made in research on changes in properties and rates of weathering. Assignments and priorities are presented arising from our studies, including the need to: (1) accumulate data on rates of change of rock properties due to weathering (especially strength reduction); and, (2) construct a geomorphological equation of weathering rates based on the relationship between weathering processes and rock properties.

著者

阿部 隆 磯田 弦 山科 絢香

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.130, no.2, pp.213-238, 2021-04-25 (Released:2021-05-19)

参考文献数

18

被引用文献数

7

---

In this study, evacuees' rosters and other relevant disaster records are used to geographically clarify the relationship between people's evacuation behavior following the Great East Japan Earthquake, social and demographic characteristics of evacuees, and housing damage caused by tsunami following the earthquake in Yamada Town, Iwate Prefecture. The trend of shelter entry and exit is analyzed on the basis of three scales. The first scale is the municipality unit; trends in the numbers of people entering shelters in Yamada Town are compared to those in other affected municipalities on the coast in Iwate Prefecture and regional differences in these trends are clarified. The second scale is the district or small area unit; regional differences in rates of entry to shelters in Yamada Town and factors affecting these differences are explained geographically. The third scale is the shelter level; regional differences in rates of entry to school shelters in small areas are analyzed in relation to evacuees at two elementary schools. Furthermore, regarding evacuees in a school shelter where a daily list is available, a logistic regression analysis is performed to explain evacuees' decisions on whether or not to stay in the shelter on the basis of variables such as gender, age, and family situation. The regression analysis for the first scale reveals that the decreasing trend in the number of evacuees in shelters in Yamada Town has been slow compared to those in other affected coastal municipalities. The study reveals that progress in the construction of emergency temporary housing is the factor with the greatest impact on an evacuee's decision to leave a shelter. Regarding the second scale, the geographical distribution of the number of shelter residents in Yamada Town is analyzed on the basis of the scale of a district and a small area. The analysis reveals that regional differences in shelter entry rate reflect social network, topographical features, and developmental process of the settlement. Regarding the third scale, the relationship between distance from the shelter and entry rate of affected households is analyzed by small area using the rosters of Yamada Minami Elementary School and Orikasa Elementary School evacuation shelters. A significant correlation is found between average road distance from Yamada Minami Elementary School and affected household entry rate, and it is observed that many residents were from areas located within 1 km from the school. On the other hand, no significant correlation is found between average road distance from Orikasa Elementary school and affected household entry rate. Regarding the Orikasa Elementary School shelter, almost daily entry and exit records could be obtained for the period from April 9, 2011 to August 3, 2011. Using this record, age and family composition of withdrawers during this period could be identified. A logistic regression analysis was performed with gender, age group, marital status, and family type as explanatory variables. With respect to the influence of a resident's age and family structure on his or her exit time, it is found that the withdrawal rate of residents aged 75 years or more was high until the beginning of May. Households that stayed in the shelter with 0 to 18-year-old juveniles tended to find it better to stay in the shelter until their children's schools reopened. After resumption of schools, at the beginning of April; however, they tended to leave in higher numbers. The study concludes that, although schools should support evacuees during the earlier period of an evacuation as large-scale evacuation shelters, various types of shelter should be developed and reorganized to suit the evacuees' needs in case the evacuation is extended for a long period.

著者

遠藤 毅

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.113, no.4, pp.534-538, 2004-08-25 (Released:2009-11-12)

参考文献数

10

被引用文献数

3

著者

丸山 茂徳 戎崎 俊一 黒川 顕

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.128, no.4, pp.513-548, 2019-08-25 (Released:2019-09-20)

参考文献数

103

被引用文献数

3 4

---

Several models of the birthplace of life have long been proposed and discussed. However, those discussions are chaotic. To test the birthplace models, we introduce nine requirements that must be met for the emergence of life. These requirements are: (1) energy source (ionizing radiation and thermal energy), (2) supplies of nutrients such as phosphorus and potassium, (3) supplies of main life constituent elements (C, H, O, and N), (4) condensed reducing gas, (5) dry wet cycle, (6) Na poor water, (7) clean lacustrine environment, (8) diversified surface environment, and (9) cyclic nature. Based on these nine requirements, most proposed birthplaces, such as the mid-oceanic ridge hydrothermal system, do not meet the requirements for life to emerge. The only possible site is a nuclear geyser system. Under the Hadean surface environment, sites satisfying the nine requirements are extremely limited because it is significantly difficult to meet the nine requirements, including extrinsic conditions. This difficulty to fulfill all the requirements indicates that only one site is the birthplace of life on Hadean Earth.

著者

松原 聰

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.131, no.2, pp.147-161, 2022-04-25 (Released:2022-05-13)

参考文献数

28

被引用文献数

2

---

I here outline to the definition of a mineral, solid solutions in mineral nomenclature, rules of naming of minerals, and procedure for establishing of a new mineral by the Commission on New Minerals, Nomenclature and Classification, the International Mineralogical Association. Also discussed are the implications of new minerals and minerals found first in Japan. Detailed accounts are given of new minerals from Japan.

著者

山本 純之 磯﨑 行雄

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.122, no.5, pp.791-806, 2013-10-25 (Released:2013-10-31)

参考文献数

86

---

Ever since the term stromatolith was first coined by Kalkowsky in 1908, research studies on stromatolites have continued for more than a century. This article reviews the study history of living and fossil stromatotelites. The history is divided into two parts by the discovery in 1961 by Logan of living stromatolites in Shark Bay, Western Australia, because this determined the subsequent main trend of studies on both living and fossil stromatolites. Major contributions during the last three decades include documentation of (1) a worldwide bloom of stromatolites in Proterozoic low-middle lateral shallow seas, and (2) oxygen-producing cyanobacterial activity related to stromatolites from the 1990s, resulting in various new aspects being clarified, which include in-vitro cultivation gradually revealing cyanobacterial calcification and dome-formation. Future studies will be directed towards reconciling morphological disparities and formation mechanisms among fossil, living, and cultured stromatolites.

著者

平田 大二 山下 浩之 鈴木 和恵 平田 岳史 李 毅兵 昆 慶明

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.119, no.6, pp.1125-1160, 2010-12-25 (Released:2011-03-17)

参考文献数

142

被引用文献数

8 10 5

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This paper reviews the geology, petrology, and tectonics of the Proto-Izu-Mariana arc against the Honshu arc, Japan, since 15 Ma, to formulate current topics related to the Pacific-type orogeny. Since the first pioneering work by Sugimura (1972), which placed the plate boundary on-land Japan north of the Izu peninsula collision-accretion tectonics of the Proto-Izu-Mariana arc against the Honshu arc started to be extensively investigated through multi-disciplinary methods. Aoike (1999) proposed a comprehensive scenario of five successive accretions of Proto-Izu to the present, with all bounded by top- and bottom-faults since 15 Ma. Oroclinal bending of the Honshu arc began simultaneously with the collision and indentation of the Proto-Izu arc, as is well documented by the Neogene paleomagnetic declination of sedimentary rocks in the Kanto district (Niitsuma et al., see summary, 1989). The entire Izu-Mariana arc is subducting without any accretion now under Honshu, as is well documented by seismic tomography imaging by Hasegawa et al. (see Hasegawa et al., 2010). Tanzawa Tonalite–Trondhjemite–Granodiolite (TTG) pluton intruded into the already-accreted Tanzawa Group at 4 Ma (Tani et al., 2010), resulting in a contact metamorphic aureole ranging from amphibolite through greenschist to zeolite facies at a depth of ca. 10 km, and tectonically denudated along the Kan-nawa fault to be exposed on the surface by 1.0 Ma. The Proto-Izu-Mariana arc was built on the Pre-Paleogene, presumably Cretaceous MORB crust on which boninitic and fractionated silicic lava flows accumulated since 48 Ma, which is older than the bending of the Hawaii–Emperor seamount chain at 43 Ma. Hence, we need another plate off Proto-Ogasawara arc, called North New Guinea plate (Seno, 1985), and ridge subduction underneath Ogasawara arc to initiate subduction magmatism. Both calk-alkali rock series (CA) and coeval blueschist–eclogite rocks are exposed along the inner wall of the Izu–Mariana trench. This strongly suggests that extensive tectonic erosion occurred, resulting in the coexistence of two rock units that were formed 100-150 km from each other horizontally, i.e., rocks on the volcanic front and rocks on the descending oceanic slab. Petrogenesis of juvenile crust and TTG rocks are being debate with two models: basaltic arc magma fractionation (Kawate and Arima, 1998) and delaminated mafic lower crust (Nakajima and Arima, 1998). In the latter model, a difficulty is derived from density at the Moho depth and small size of delaminated residue. Instead, extensive tectonic erosion that transports not only the upper crust but also the lower mafic crust together with parts of the descending slab could be more plausible than these two models in order to present a thinner mafic lower crust.

著者

尾方 隆幸

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.5, pp.846-852, 2011-10-25 (Released:2012-01-17)

参考文献数

13

被引用文献数

4 5

---

The Ryukyu Islands strongly promote the geodiversity of Japan. A sub-tropic natural environment forms coral reefs and various landscapes linked to surface processes, active tectonics, and Quaternary environmental changes. Field excursions permit geoscientific observations of such landscapes, which reveal geodiversity and a framework for geotourism. Fieldwork was undertaken to arrange an educational program for conserving geodiversity and for geotourism. This program demonstrates the geodiversity and geotourism of the Ryukyu Islands, in terms of geomorphology and related disciplines. Basic geotours observe landforms and sediments, and consider geomorphic processes: weathering, erosion, transport, sedimentation, uplift, and sea level change. Applied geotours observe landscapes indicating global environmental problems, such as global warming, climate change, sea level rise, acid rain, and ecosystem based on geomorphology and related geosciences. For instance, acid rain accelerates the chemical weathering (decomposition) of limestone and erosion of karst landforms that are distributed widely on raised coral reefs. Such geotours require both scientific and attractive geostories managed by geoscientists. Japanese geoscientists should propose models for geotours derived from field excursions for landscape observations that will contribute to education, conservation, and geotourism.

著者

新井 智一

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.4, pp.676-691, 2011-08-25 (Released:2011-11-10)

参考文献数

22

被引用文献数

3 2

---

This paper discusses locational conflicts surrounding a new waste disposal facility in Koganei City from the viewpoint of “the politics of scale”. Since 1957, Koganei, Chofu, and Fuchu cities have disposed of their waste at Nimaibashi Waste Disposal Facility. In 2007, Koganei City officials proposed the construction of a new facility by 2017 at the site of the Nimaibashi Waste Disposal Facility, which was located at the periphery of Koganei City, or at the site of a former Janome sewing machine factory, which was located at the center of the city. Although people residing near both sites protested against the construction of the new facility, the Koganei City officials decided to construct the new facility at the site of the Nimaibashi Waste Disposal Facility. The reason for this decision is summarized as follows: (1) Most of the citizens of Koganei City appeared to be indifferent to this locational conflict; (2) The Koganei City officials were adamant about constructing an incineration facility; (3) The actions of the people residing near the former Janome sewing factory, unlike those of the people residing near Nimaibashi Waste Disposal Facility, were successful in protesting given the scale of Koganei City.

著者

渡辺 武男

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.73, no.2, pp.125-128, 1964-04-30 (Released:2009-11-12)

著者

野口 里奈 栗田 敬

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.125, no.1, pp.35-48, 2016-02-25 (Released:2016-03-22)

参考文献数

71

被引用文献数

3 6

---

Cone morphologies with a variety of origins and sizes have been widely identified on Mars using remote sensing data such as ultra-high resolution visible images. Currently, small cones of less than 100 m in bottom diameter can be identified. These Martian cones are located in young surface regions, suggesting they were produced in an environment that existed in recent geological history. They had volcanic, periglacial, and other origins. This paper first introduces a classification of terrestrial cone morphology: volcanic (spatter cones, scoria/pumice cones, maars, tuff rings, tuff cones, and rootless cones), periglacial (pingos), and others (mud volcanoes). Then, it reviews the characteristics of cone morphology on Mars focusing on morphology, morphometry, and distribution. Previous cone studies show the existence of explosive basaltic eruptions on recent Mars, while young lava flows were pervasive. The prevalence of rootless cones suggests the presence of water/ice during their formation at many places on Mars. These discoveries contribute to clarifying the recent surface environment and thermal state of Mars. To further apply terrestrial knowledge to Martian cones, it is necessary to understand the relationship between the morphology and the formation process of cone morphologies on Earth from a wide perspective.

著者

松田 博貴

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.2, pp.297-308, 2009-04-25 (Released:2010-04-01)

参考文献数

34

被引用文献数

3 4

---

Dolomite (dolostone) is a common carbonate rock in the geological records and is also a very important carbonate reservoir rock, which stock about 40% of global oil reserves. Most of the dolomites in the geological record are considered to be of replacement origin, although some were precipitated directly from pore-fluids. A variety of dolomitization models in different diagenetic environments are currently proposed for interpreting ancient dolomites: (1) evaporative dolomitization including sabkha and seepage-reflux models, (2) mixed-water dolomitization, (3) marine dolomitization, (4) burial dolomitization, (5) hydrothermal dolomitization. The dolomites formed by each dolomitization model have different geological, petrographical, mineralogical and geochemical features. Based on these features, we can, therefore, identify dolomitization models and diagenetic environments of ancient dolomites. A dolomite reservoir is often of as good quality as a limestone reservoir. Dolomitization affects carbonate reservoir characteristics, such as porosity and permeability, and, as a result, reservoir characteristics are significantly changed from those of primary carbonate rocks. The important factors associated with dolomitization and controlling the characteristics of carbonate reservoir rocks are: (1) increasing crystal size (2) decreasing porosity due to a net addition of dolomite, (3) developing moldic pores, (4) increasing resistance to compaction, and (5) increasing fractures. Dolomitization and diagenetic history of individual carbonate reservoirs differ from each other and result in the complexity of reservoir characteristics. It is, therefore, indispensable to understand the processes that formed each dolomite reservoir.

著者

鳴海 一成 丸山 茂徳

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.128, no.4, pp.649-665, 2019-08-25 (Released:2019-09-20)

参考文献数

104

被引用文献数

2 3

---

Natural ionizing radiation, which potentially affects biota inhabiting the Earth, can be broadly divided into two types according to origin: cosmic radiation and subsurface radiation. Cosmic radiation contains galactic cosmic rays and solar energetic particles. Subsurface radiation is derived from radionuclides such as uranium, thorium, and radon. The levels of these forms of natural radiation were not constant temporally and spatially, and underwent a lot of changes in the early Earth environment. However, the ground level radiation dose rate of secondary muons derived from a supernova event that causes the most severe biological effects among forms of cosmic radiation is estimated to be 1 sievert (Sv) per year at most, which is too low to have lethal and mutagenic effects on terrestrial microbes. On the other hand, a nuclear fission chain reaction occurred in Oklo uranium ore deposit in Gabon about 2 billion years ago and continued intermittently for 105-106 years. The average total radiation dose rate of a typical natural fission reactor in Oklo is estimated to be 47.4 Sv per hour. This value is high enough to serve as a physical mutagen for subsurface microbes inhabiting areas near the reactor, and a million years is long enough to generate a new species of microbes. The observed growth-inhibitory critical dose rate for Escherichia coli is estimated to be 36 to 67 Gy per hour. On the other hand, the radioresistant bacterium Deinococcus radiodurans is shown to be cultivated without any growth delay at up to 126 to 180 Gy per hour of gamma rays. Recent EXAFS and isotopic analyses indicate that biogenic processes are more important for uranium ore genesis than previously understood. D. radiodurans and its closely related species Thermus thermophilus are shown to have the ability to reduce U(VI) to U(IV) under anaerobic conditions. These lines of evidence suggest that a common ancestor of Deinococcus and Thermus might be involved in the formation process of Oklo uranium ore deposit. Therefore, the radiation dose rate at Oklo-type natural nuclear reactors would be suitable for affecting the growth of microbes and generating genome evolution through accumulated mutations.

著者

柏木 洋彦

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.126, no.4, pp.513-531, 2017-08-20 (Released:2017-09-27)

参考文献数

86

被引用文献数

2 2

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Weathering is deeply related to global climate change. In the carbon cycle, silicate weathering, especially volcanic rock weathering, transfers carbon in the atmosphere (as CO2) to the lithosphere, and oxidative weathering of organic matter releases carbon (as CO2) from the biosphere to the atmosphere. Moreover, as an indirect effect of weathering on climate change, negative feedback in the climate system, which results from the dependence of weathering rate on temperature and evolution of terrestrial plants, is crucial. It has stabilized the long-term global climate throughout the Phanerozoic. Weathering rate is controlled by several geochemical external factors: tectonic forces such as lithology, continental uplift, and continental drift (paleogeography); climate forces such as temperature, runoff, and glaciations; and, biological forces such as terrestrial plant evolution. Regarding biological forces, accelerated weathering assisted by ectomycorrhizal fungi (EM fungi) and arbuscular mycorrhizal fungi (AM fungi), as well as vascular plants of gymnosperms and angiosperm, are emphasized. Variations of global weathering in the geological past are estimated using experimental approaches, such as isotope analysis (e.g., 87Sr/86Sr, 187Os/186Os, δ7Li), and theoretical approaches, such as numerical simulations (e.g., carbon cycle model). Each is used differently according the purpose of a study. Based on these estimates, geological past climate changes in the Phanerozoic are found to be closely related to weathering. For example, on the order of magnitude of 107 years, changes in weathering patterns due to continental drift (paleogeography) have resulted in variations of atmospheric CO2, hence climate change. On the order of magnitude of 106 years, it is suggested that a decrease in atmospheric CO2 from the mid- to late Cretaceous was caused by enhanced weathering according to terrestrial plant evolution and that variations of atmospheric CO2 in the late Cenozoic were regulated by weathering directly or indirectly influenced by continental uplift. Additionally, contributions of weathering to global climate change involved in oceanic anoxic events in the Mesozoic have been investigated.