Noble gases in individual chondrules of the Allende CV3 chondrite

We analyzed noble gases in nine individual chondrules, an assemblage of small chondrules, and four whole‐rock samples of the Allende CV3 chondrite. Major elements were also determined for five chondrules. The cosmic ray exposure ages are calculated from cosmogenic ³He to be 5.17 ± 0.38 and 5.15 ± 0.25 Myr for the averages of the chondrules and whole rocks, respectively, showing no significant pre‐exposure evidence for the studied chondrules. Large amounts of ³⁶Ar, ^80,82Kr, and ¹²⁸Xe produced by neutron capture are observed in most samples; the abundances of these nuclides are correlated among the samples. The epithermal neutron flux and neutron slowing down density are calculated based on [⁸⁰Kr]_n, from which a sample depth of about 30 cm can be calculated. The measured chondrules contain variable amounts of radiogenic ¹²⁹Xe. The abundance ratios of radiogenic ¹²⁹Xe to neutron capture–produced ¹²⁸Xe are rather constant among the studied chondrules; four chondrules give more precise ratios at the high‐temperature fractions, ranging from 1920 ± 80 to 2280 ± 140, which corresponds to a time difference of 3.9 ± 2.4 Myr. It is noticeable that most chondrules also contain ²⁴⁴Pu‐derived fission Xe. The average ²⁴⁴Pu/²³⁸U ratio for nine chondrules is 0.0069 ± 0.0018, which agrees well with the preferred ratio reported for chondrites.     

A survey of emission-line stars in the perseus dark cloud

The results of an objective prism survey of H_α emission-line stars in a 5° × 5° region around NGC 1333 are presented. We have identified 25 stars as having H_α -line in emission, of which 11 have been discovered in the Lick H_α-survey. The limiting magnitude of the present survey is about 16.7 mag. in blue. These are suspected to be mainly T Tauri stars. Based on the UGR(Kiso) multiexposure plates, we have found that, on the [(G - U), (R - G)]-diagram, the domain of H_α emission line stars is fairly well delineated and separate from other stars. Some interesting features in their space distribution are also discussed briefly.     

Geochemistry of late Cenozoic lavas on Kunashir Island, Kurile Arc

Middle Miocene to Quaternary lavas on Kunashir Island in the southern zone of the Kurile Arc were examined for major, trace, and Sr–Nd–Pb isotope compositions. The lavas range from basalt through to rhyolite and the mafic lavas show typical oceanic island arc signatures without significant crustal or sub-continental lithosphere contamination. The lavas exhibit across-arc variation, with increasingly greater fluid-immobile incompatible element contents from the volcanic front to the rear-arc; this pattern, however, does not apply to some other incompatible elements such as B, Sb, and halogens. All Sr–Nd–Pb isotope compositions reflect a depleted source with Indian Ocean mantle domain characteristics. The Nd and Pb isotope ratios are radiogenic in the volcanic front, whereas Sr isotope ratios are less radiogenic. These Nd isotope ratios covary with incompatible element ratios such as Th/Nd and Nb/Zr, indicating involvement of a slab-derived sediment component by addition of melt or supercritical fluid capable of mobilizing these high field-strength elements and rare earth elements from the slab. Fluid mobile elements, such as Ba, are also elevated in all basalt suites, suggesting involvement of slab fluid derived from altered oceanic crust. The Kurile Arc lavas are thus affected both by slab sediment and altered basaltic crust components. This magma plumbing system has been continuously active from the Middle Miocene to the present.     

A review of kentriodontine dolphins (Cetacea; Deiphinoidea; Kentriodontidae): Systematics and biogeography

Abstract Fossil dolphins belonging to the extinct family Kentriodontidae are small to medium-sized toothed cetaceans, which probably include the ancestors of some living species. Kentriodontids are known from rocks of Late Oligocene to Late Miocene age in various parts of the world. Among kentriodontids, species in the subfamily Kentriodontinae (e.g. species of Kentriodon Kellogg, 1927) are the most ubiquitous and generalized; these are now known from latest Oligocene to earliest Miocene strata in New Zealand and Patagonia, and Middle Miocene deposits in Maryland, Virginia, California and Japan. The diversity, morphologies and distributions of Miocene species of Kentriodontinae seem to parallel those of the living species of mostly pelagic delphinids in the subfamily Delphininae, and the fossil group may have been an ecological or behavioral/functional counterpart of the latter. Kentriodontines are inferred to have been wide-ranging neritic to pelagic animals that ate small fish and other nectonic organisms; they were probably active echolocators, and might have formed large schools. They are relatively common as fossils and, therefore, are potentially useful for intercontinental correlations of marine deposits.     

Seasonal differences in catches of leptocephali in the East China Sea and Suruga Bay, Japan

The species composition, distribution, and size of eel larvae, or leptocephali, caught near the continental shelf in subtropical and temperate regions of East Asia were compared between two seasons (May–Jun and Oct–Dec) to learn about the seasonality of reproduction of marine eels. There was greater species richness and evidence of spawning by more species of marine eels during the late autumn surveys in both the East China Sea (ECS) and in Suruga Bay along the east coast of Japan. Small leptocephali <10 mm TL and a wide range of sizes of various taxa were collected during both seasons along the outer edge of the continental shelf in the ECS, indicating that some marine eels may spawn there all year. The lack of small leptocephali during the spring survey in Suruga Bay suggested that most eels have a clear seasonal cycle of summer or autumn spawning at the higher latitudes of coastal Japan where there is much greater fluctuation of water temperature throughout the year than in the ECS. At lower latitudes such as in the ECS, and in tropical areas where water temperatures are higher and more constant, some marine eels may spawn all year round.     

Meander of the Kuroshio front and current variability in the East China Sea

To investigate the fluctuation of the Kuroshio front, moored current meters were deployed near the shelf break and on the continental slope in the East China Sea, northwest of Okinawa Island, during a period from 25 June to 22 July 1984. Two mooring arrays were deployed on the slope of about 800 m water depth (under the Kuroshio), about 30 km apart along the path of the Kuroshio. Another two arrays were set near the shelf break of about 300 m water depth. The fluctuation of current on the slope is found to have a predominant period of 11–14 days and a were length of 300–350 km, propagating toward the downstream direction of the Kuroshio with a phase velocity of about 30 cm sec^?1. When the Kuroshio front approaches the shelf break and the crest of the meander covers the mooring site, the current direction moves toward the downstream direction of the Kuroshio and the water temperature increases. On the other hand, when the trough of the meander covers the mooring site, the current direction changes off-shoreward across the Kuroshio or in the upstream direction of the Kuroshio, and the water temperature decreases. Three-dimensional distributions of water temperature and salinity around the mooring site were observed with a CTD twice at 5.5 days intervals, which indicate the meanders of the front is about 180° out of phase. This coincides with a period of 11–14 days obtained with the moored current meters. Wave lengths of the dominant meander of the front in the satellite thermal images were about 350 km and 100–200 km, which also coincides with results obtained with the moored current meters.     

Magma plumbing system beneath Ontake Volcano, central Japan

Ontake Volcano in central Japan was last active from ~ 100–35 Ka. The eruptions contained rhyodacite pumice and lavas in the first stage (stage O1, > 33 km³), followed by eruptions of andesite lavas and pyroclastics (stages O2 and O3, > 16 km³). Modeling of major and incompatible elements with Sr isotope ratios suggests that the primary magma was a high-alumina basalt. One andesite magma type appears to have evolved from the basalt in a closed system magma chamber, in part by fractional crystallization, and its generation included crustal assimilation. The other andesite magma type is considered to have evolved in an open system magma chamber in which repeated input of primary magma occurred together with wall-rock assimilation and fractional crystallization. The rhyodacite is inferred to have evolved in a closed system magma chamber by fractional crystallization of the second type of andesite. These genetic relationships require that the magma chamber functioned alternately as an open and a closed system. Geobarometry indicates that there may have been multiple magma chambers, located in the upper crust for the rhyodacite, near the upper–lower crust interface for the andesite and in the mid-lower crust for the basalt. These chambers were stacked to form the magma plumbing system of Ontake. Incompatible element compositions of the basalt are considered to have changed during the eruptions, suggesting that two different plumbing systems for stage O1 magma and for stages O2, O3 magmas existed during the 65 Ka of activity. Evolutionary history of the systems implies that the primary magma was introduced into the magma plumbing system each for ~ 17 500 years and that the life span of a magma plumbing system was shorter than 40 Ka.     

Advances in computational morphodynamics using the International River Interface Cooperative (iRIC) software

Results from computational morphodynamics modeling of coupled flow–bed–sediment systems are described for 10 applications as a review of recent advances in the field. Each of these applications is drawn from solvers included in the public-domain International River Interface Cooperative (iRIC) software package. For mesoscale river features such as bars, predictions of alternate and higher mode river bars are shown for flows with equilibrium sediment supply and for a single case of oversupplied sediment. For microscale bed features such as bedforms, computational results are shown for the development and evolution of two-dimensional bedforms using a simple closure-based two-dimensional model, for two- and three-dimensional ripples and dunes using a three-dimensional large-eddy simulation flow model coupled to a physics-based particle transport model, and for the development of bed streaks using a three-dimensional unsteady Reynolds-averaged Navier–Stokes solver with a simple sediment-transport treatment. Finally, macroscale or channel evolution treatments are used to examine the temporal development of meandering channels, a failure model for cantilevered banks, the effect of bank vegetation on channel width, the development of channel networks in tidal systems, and the evolution of bedrock channels. In all examples, computational morphodynamics results from iRIC solvers compare well to observations of natural bed morphology. For each of the three scales investigated here, brief suggestions for future work and potential research directions are offered. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd