Mineralogy of phyllosilicate-rich micrometeorites and comparison with Tagish Lake and Sayama meteorites     

Takaaki Noguchi  Tomoki NakamuraWataru Nozaki 《Earth and Planetary Science Letters》2002,202(2):229-246

Four phyllosilicate-rich micrometeorites (MMs) were investigated by a synchrotron radiation X-ray diffraction technique and transmission electron microscopy. Three are saponite-rich MMs and one is a serpentine-rich one. In the saponite-rich MMs, we could not find serpentine, and vice versa in the serpentine-rich MM. In the saponite-rich MMs, major constituent minerals are saponite, Fe- and Ni-bearing sulfides, and magnetite. Two saponite-rich MMs contain fine-grained magnesiowüstite-rich aggregates. The aggregates consist of <50 nm polygonal magnesiowüstite coexisting with minor Fe sulfide grains. Their texture, chemical composition, and the result of heating experiments on matrix fragments of the Tagish Lake carbonaceous chondrite strongly suggest that these aggregates were formed by the breakdown of Mg- and Fe-rich carbonate grains when the MMs entered the Earth’s atmosphere. The estimated major mineral assemblage of the saponite-rich MMs before entering the Earth’s atmosphere is very similar to that of the Tagish Lake carbonate-rich lithology, and we suggest that the MMs and the meteorite were derived from similar asteroids. The major mineral assemblage and texture of the matrix of serpentine-rich MM are similar to the matrix of the Sayama CM2 chondrite that experienced heavy aqueous alteration. Chemical compositions of serpentine in the MM suggest that the degree of aqueous alteration of the MM is weaker than that of Sayama. In the MM, cronstedtite does not coexist with tochilinite, which is different from CM2 chondrites that experienced weak to moderate aqueous alteration. However, the possibility that the serpentine-rich MM was derived from the CM chondrite asteroid cannot be ruled out, because tochilinite can be preferentially decomposed during atmospheric entry heating due to its lower decomposition temperature than that of cronstedtite.  相似文献   

Early diagenesis of fatty acids in lacustrine sediments—III. Changes in fatty acid composition in the sediments from a brackish water lake     

Hiromi Matsuda 《Geochimica et cosmochimica acta》1978,42(7):1027-1034

A 3-m sediment core taken from Lake Suigetsu, in which a shift from fresh to brackish water occurred about three hundred years ago, has been examined for variation with depth of organic carbon and fatty acids. From the difference in total amounts of sulphur between sediments under fresh and brackish water environments, the surface sediments above approximately 35 cm depth were deduced to be accumulated under a brackish water environment. The total contents of organic carbon and fatty acids, and percentage composition of fatty acids gave discontinuous profiles above and below the 35–40 cm sediment layer. At a depth of 12.5 cm, the distribution in chain length of the fatty acids changed from a unimodal (the predominance of C₁₂-C₁₈ over C₂₀-C₃₄) to a bimodal pattern, which was mirrored by the composition diversity index (CDI).Although the fatty acids in the surface sediments (0–40 cm) from Lake Suigetsu seemed to suffer milder degradation through microbial activity than those in a core (0–150 cm) from Lake Suwa, a freshwater eutrophic lake, both lacustrine sediments showed similar trends in the alteration of fatty acid composition with depth.  相似文献   

Recent formations and their basal topography in and around Tokyo Bay,central Japan     

Sohei Kaizuka  Yo Naruse  Iware Matsuda 《Quaternary Research》1977,8(1):32-50

This paper summarizes the subsurface geology of the recent (both $\text{Holocene}$ and latest $\text{Pleistocene}$ formations and the buried topography beneath them in and around Tokyo Bay, the type area of the late Quaternary in Japan. Buried abrasion platforms in the buried topography are classified into upper (ca. 0 to ?10 m high) and lower (ca. ?20 to ?40 m) platforms; upper and lower buried river terraces are also distinguished, and are correlated to the subaerial late Pleistocene terraces of Tc₁ and Tc₂, respectively. A buried valley system is elucidated, of which the trunk valley floor reaches ?70 m in Tokyo and emerges into a flat surface at the shelf edge in the entrance to Tokyo Bay. Approximate dates for these geomorphic surfaces are given. The height of sea level contemporaneous with the buried valley floor (ca. 20,000–15,000 yr BP) is estimated at about ?135 m. The recent formations are divided into two members, upper and lower, by a middle sand bed, in addition to the lowest buried valley floor gravel. The lower member, which is composed of brackish to marine deposits of complicated lithofacies, was accumulated in narrow drowned valleys during the early stage of the Yurakucho (Flandrian) transgression. The middle sand bed is the foreset bed of deltas, which was formed during a slight regression between ca. 11,000 and 10,000 yr BP. The upper member, which consists mainly of widespread homogeneous marine clay and deltaic sand, was accumulated in a wide bay and its embayments during the late stage of the Yurakucho transgression and the following stage of a relatively stable sea level.  相似文献   

The structure of cool accretion disks in semidetached binaries     

D. V. Bisikalo  A. A. Boyarchuk  P. V. Kaigorodov  O. A. Kuznetsov  T. Matsuda 《Astronomy Reports》2004,48(6):449-456

We present a qualitative analysis of possible changes in the structure of accretion disks that occur in the transition from hot to cool disks. We suggest that an additional spiral-density wave can exist in the inner parts of the disk, where gas-dynamical perturbations are negligible. We consider the formation of this wave and its parameters. The results of a three-dimensional gas-dynamical simulation of a cool accretion disk are presented; these results confirm the possibility of the formation of a new, “precessional,” spiral wave in the inner regions of a cool accretion disk. Possible observational manifestations of such a wave are discussed.  相似文献   

Evaluation of Interpolation Accuracy of Neural Kriging with Application to Temperature-Distribution Analysis   总被引：8，自引：0，他引：8  

Katsuaki Koike  Setsuro Matsuda  Bin Gu 《Mathematical Geology》2001,33(4):421-448

An interpolation method based on a multilayer neural network (MNN), has been examined and tested for the data of irregular sample locations. The main advantage of MNN is in that it can deal with geoscience data with nonlinear behavior and extract characteristics from complex and noisy images. The training of MNN is used to modify connection weights between nodes located in different layers by a simulated annealing algorithm (one of the optimization algorithms of the network). In this process, three types of errors are considered: differences in values, semivariograms, and gradients between sample data and outputs from the trained network. The training is continued until the summation of these errors converges to an acceptably small value. Because the MNN trained by this learning criterion can estimate a value at an arbitrary location, this method is a form of kriging and termed Neural Kriging (NK). In order to evaluate the effectiveness of NK, a problem on restoration ability of a defined reference surface from randomly chosen discrete data was prepared. Two types of surfaces, whose semivariograms are expressed by isotropic spherical and geometric anisotropic gaussian models, were examined in this problem. Though the interpolation accuracy depended on the arrangement pattern of the sample locations for the same number of data, the interpolation errors of NK were shown to be smaller than both those of ordinary MNN and ordinal kriging. NK can also produce a contour map in consideration of gradient constraints. Furthermore, NK was applied to distribution analysis of subsurface temperatures using geothermal investigation loggings of the Hohi area in southwest Japan. In spite of the restricted quantity of sample data, the interpolation results revealed high temperature zones and convection patterns of hydrothermal fluids. NK is regarded as an interpolation method with high accuracy that can be used for regionalized variables with any structure of spatial correlation.  相似文献   

Late cretaceous to early paleogene paleomagnetic results from Sikhote Alin, far eastern Russia: implications for deformation of East Asia   总被引：1，自引：0，他引：1  

Yo-ichiro Otofuji  Takaaki Matsuda  Tetsumaru Itaya  Takeshi Shibata  Michiko Matsumoto  Takahiro Yamamoto  Chiyo Morimoto  Ruslan G. Kulinich  Petr S. Zimin  Anatoly P. Matunin  Vladimir G. Sakhno  Katsuhiro Kimura 《Earth and Planetary Science Letters》1995,130(1-4):95-108

Welded tuffs in the Bogopol and Sijanov groups were sampled at 27 sites from 12 caldera formations in the Sikhote Alin mountain range around Kavalerovo (44.3°N, 135.0°E) for chronological and paleomagnetic studies. KAr age dates show that the welded tuffs erupted between 66 Ma and 46 Ma. All sites yield reliable paleomagnetic directions, with unblocking temperatures higher than 560°C. The high-temperature component at 12 sites and the medium-temperature component at 3 sites in the Bogopol Group show reversed polarity (D = 193.7°, I = −57.6°,₉₅ = 8.1°). The high-temperature component at 11 sites in the Sijanov Group showed both reversed and normal polarities and its mean direction reveals no detectable deflection from north (D = −2.9°, I = 59.6°,₉₅ = 11.2°). The combined paleomagnetic direction of the two groups yields a paleomagnetic pole of 250.5°E, 84.1°N (A₉₅ = 8.8°), which falls near Cretaceous paleomagnetic poles from Outer Mongolia, Inner Mongolia, the North China Block and the South China Block. The Sikhote Alin area appears not to have been subjected to detectable motion with respect to East Asia since about 50 Ma. This implies that the Sikhote Alin area behaved as an integral part of East Asia during the opening of the Japan Sea at about 15 Ma. However, significant separation between the paleomagnetic poles of East Asia and Europe during the Jurassic-Paleogene implies a major relative movement between these two blocks since the Paleogene.  相似文献   

Geochemical implications from Sr isotopes and K-Ar age determinations for the cook-austral islands chain     

Jun-Ichi Matsuda  Kenji Notsu  Jun Okano  Katsumi Yaskawa  Leonard Chungue 《Tectonophysics》1984,104(1-2)

Sr isotopes and K-Ar ages were determined for volcanic rocks from three islands, Samoa, Rarotonga and Rurutu in the Austral-Gilbert-Marshall chain. We have established that Rurutu originated from the same “hot spot” as Tubuai and Raivavae in the Cook-Austral chain as indicated by its 11 m.y. K-Ar age and ( ) ratios. The ( ) ratios for Rurutu, Tubuai and Raivavae lie in the restricted range 0.7026–0.7035. K-Ar ages of all volcanic rocks from Samoa and Rarotonga are all less than 4 m.y. and their ( ) ratios are much higher than those in Rurutu, Tubuai and Raivavae. These findings suggest that Samoa and Rarotonga did not originate in a single hot spot for the Cook-Austral islands.  相似文献   

SHRIMP U-Pb Zircon Age of the Inishi Migmatite around the Kamioka Mining Area, Hida Metamorphic Complex, Central Japan     

Masatoshi Sakoda    Takashi Kano  C. Mark Fanning  Takaaki Sakaguchi 《Resource Geology》2006,56(1):17-26

Abstract. SHRIMP U-Pb ages were determined on single zircons separated from the Inishi migmatite in the Kamioka mining area, Hida metamorphic complex, central Japan. Twenty one determinations were distributed within the age of 234.2±1.8 Ma, excluding one inner core of a grain. As the analyzed crystals were mostly euhedral igneous zircons, the age indicates the crystallization of zircons from granitic melt during the formation of Inishi migmatite. The age of ca. 234 Ma corresponded to the later stage of the major regional metamorphic event in the Hida complex, while the age of ca. 265 Ma determined in a grain suggested the inherited age of the earlier phase of the metamorphism.  相似文献   

Development of microbial carbonates in the Lower Cretaceous Codó Formation (north‐east Brazil): Implications for interpretation of microbialite facies associations and palaeoenvironmental conditions          下载免费PDF全文

Anelize M. Bahniuk  Sylvia Anjos  Almério B. França  Nilo Matsuda  John Eiler  Judith A. Mckenzie  Crisogono Vasconcelos 《Sedimentology》2015,62(1):155-181

The study of microbial carbonates has acquired new significance with the recognition that they retain valuable information related to biomineralization processes associated with microbial activity throughout geological time. Additionally, microbialites have a demonstrated economic potential to serve as excellent hydrocarbon reservoirs. The Lower Cretaceous Codó Formation, located in the Parnaiba Basin of north‐east Brazil, comprises a unique stratigraphic sequence of up to 20 m thick, well‐preserved carbonate microbialites. Deposited in a continental basin during the initial break up and separation of South America from Africa in the Early Cretaceous, this lacustrine carbonate sequence provides an excellent example to investigate the palaeoenvironmental conditions controlling microbialite facies development. Based on macroscopic and microscopic observations of outcrop and drill core samples, four microbialite facies (stromatolite, lamina, massive and spherulite) were defined and distinguished by textures and microbial fossil content. Changes in facies type are related to alternating palaeo‐water depths, as reflected by ⁸⁷Sr/⁸⁶Sr cycles resulting from fluctuations in the sources of meteoric water. Clumped isotope measurements of stromatolitic fabrics yield precipitation palaeo‐temperatures with an average value of 35°C. The δ¹⁸O values of bulk carbonate (?6·8 to ?1·5‰ Vienna Pee Dee Belemnite) imply precipitation from water with calculated δ¹⁸O values between ?1·6‰ and 1·8‰ Vienna Standard Mean Ocean Water, reflecting precipitation from variably modified meteoric waters. The δ¹³C values of bulk carbonate (?15·5 to ?7·2‰ Vienna Pee Dee Belemnite) indicate a significant input of carbon derived from aerobic or anaerobic respiration of organic matter. Combined, the data indicate that the evolution of the Codó Formation occurred in a closed lacustrine palaeoenvironment with alternating episodes of contracting and expanding lake levels, which led to the development of specific microbialite facies associations. The results provide new insights into palaeoenvironmental settings, biogenicity and early diagenetic processes involved in the formation of ancient carbonate microbialites and, by extension, improve the knowledge of the reservoir geology of correlative units in deep waters offshore Brazil.  相似文献   

Three-dimensional gas-dynamical modeling of changes in the flow structure during the transition from the quiescent to the active state in symbiotic stars     

M. Mitsumoto  B. Jahanara  T. Matsuda  K. Oka  D. V. Bisikalo  E. Yu. Kilpio  H. M. J. Boffin  A. A. Boyarchuk  O. A. Kuznetsov 《Astronomy Reports》2005,49(11):884-891

The results of three-dimensional modeling of the flow structure in the classical symbiotic system Z Andromedae are presented. Outbursts in systems of this type occur when the accretion rate exceeds the upper limit of the steady-burning range. Therefore, in order to realize the transition from a quiescent to an active state, it is necessary to find a mechanism capable of sufficiently increasing the accretion rate on the time scales typical for outburst development. Our calculations provide support for a mechanism for the transition from quiescence to outburst in classical symbiotic systems suggested earlier based on two-dimensional calculations (Bisikalo et al., 2002). Our results show that an accretion disk forms in the system for a wind velocity of 20 km s^?1. The accretion rate for the solution with the disk is ～22.5–25% of the mass-loss rate of the donor, which is ～4.5?5 × 10^?8M_⊙ yr^?1 for Z And. This value is in agreement with the steady-burning range for the white-dwarf masses usually accepted for this system. When the wind velocity increases from 20 to 30 km s^?1, the accretion disk is destroyed and the disk material falls onto the accretor surface. This process is followed by an approximately twofold jump in the accretion rate. The resulting growth in the accretion rate is sufficient so as to exceed the upper limit of the steady-burning range, thus bringing the system into an active state. The time during which the accretion rate is above the steady-burning value is in very good agreement with observations. Our analysis leads us to conclude that small variations in the donor wind velocity can lead to the transition from disk accretion to wind accretion and, as a consequence, to the transition from a quiescent to an active state in classical symbiotic stars.  相似文献