Nuées ardentes of 22 November 1994 at Merapi volcano, Java, Indonesia

Nuées ardentes associated with dome collapse on 22 November 1994, at Merapi volcano traveled to the south–southwest as far as 6.5 km, and collectively accumulated roughly 2.5–3 million cubic meters of deposits. The damaged area comprises 9.5 km² and is covered by two nuée ardente facies, a conventional “Merapi-type”, valley-fill block-and-ash flow facies and a pyroclastic surge facies. The proximal deposits reflect the accumulation of dozens of nuées ardentes, with many subsidiary flow units. The distal deposits are more simply organized, as only a few individual events reached to distances >3.5 km. The stratigraphic relationships north of Turgo hill indicate that the surge deposits are a facies of particularly mobile nuées ardentes that also deposited channeled block-and-ash flow facies. They further suggest that the surge facies beyond the channel margins correlate laterally with a finer-grained sublayer locally developed at the base of the block-and-ash flow facies. Eyewitness reports suggest that the emplacement of the block-and-ash flow facies in the distal part of the Boyong river may have followed, by a short time interval, the destruction and deposition of the surge facies at Turgo village. The stratigraphy is in accord with the eyewitness reports. The surge facies was emplaced by a dilute surge current, detached from the same dome-collapse nuée ardente that, as a separate flow unit, subsequently emplaced the distal block-and-ash deposit in the Boyong valley. The detachment occurred at higher elevations, likely at or above the slope break at about 2000 m elevation. This flow separation enabled the surge current to shortcut over the landscape and to emplace its deposit even as the block-and-ash flow continued its tortuous southward movement in the Boyong channel. Dome-collapse nuée ardente activity formed the bulk of the eruption, which was accompanied by virtually no significant vertical summit explosive activity.     

Early biodégradation of ligneous organic materials and its relation to ore deposition in the tréves zn-pb ore body (gard, france)

Previous petrographical and geochemical studies on the organic content of mineralized and non-mineralized carbonate series in the Trèves Zn-Pb stratiform deposit led to the conclusion that ore deposition occurred during the diagenetic history of the sediments, in a mixed fresh/hydrothermal system (Gauthier and Disnar, 1984; Gauthier et al., 1985a). These circulations of fluids are probably responsible for the dolomitization of the original limestones and for the deposition of the ore through microbial activity (Gauthier, 1984; Gauthier el al., 1985b).The occurrence of this activity is supported by the formation of two kinds of organic components which are attributable to this uncommon bio-alteration process: alphatic-rich bitumen-like products and aromatic polyethers. The chemical composition of these two types of compounds suggests that they were produced from ligneous debris by (sulfate-reducing?) bacteria.Other indications of the occurrence of a biological activity have been found in the nature and relative abundance of microbial amino compounds. However, these constituents are thought to have been introduced only recently into the sediments whereas other evidence supports the idea that ore deposition occurred before diagenesis.     

Debris flow during intense rainfall in Snowdonia,North Wales: A preliminary survey

Intense rainfall after the abnormally dry and warm summer of 1983 triggered debris flows in mountainous terrain in North Wales. This preliminary investigation concentrates on a flow which blocked the A5, requiring £56,000 of remedial work. An estimated 118·4 mm of rain fell over steep, rocky catchments in 5 hrs (peak intensity 39·9 mm hr^?1) and water emerging from a rock chute mobilized colluvium on lower slopes, in which pore water pressure was probably already rising fast and bulk properties and other geotechnical conditions, including low shearing resistance, were favourable. Debris flowed in a narrow concave track 585 m long, x slope 27·8°, descending 282 m. The scoured channel, levées and debris lobes typical of documented flows elsewhere suggest that flow was rapid, turbulent, and pulsing.     

Natural occurrence of 4-methyl-phenanthrene in petroleums and recent marine sediments: A new sensitive method to identify and quantify isomers in a series of alkyl—PAH: High resolution spectrofluorimetry at 15 K in n-alkane (Shpolskii effect)

HPLC extracts of crude petroleums and of marine recent sediments, containing the monomethyl-phenanthrene series, are examined by high resolution spectrofluorimetry in n-hexane at 15 K (Shpolskii effect). Identification and relative quantification of each of the five isomers is obtained on six natural samples. The distribution of the monomethyl-phenanthrenes and the relative absence of 4-methyl-phenanthrene in petroleums compared to marine sediments may reflect steric inhibitions.     

An Early Paleozoic Tectonic Mélange at the Western Margin of West Cathaysia: Constraints from Organic-walled Microfossils

The Jiangshan-Shaoxing-Pingxiang Fault(JSP Fault) is traditionally considered as the boundary between the Yangtze and Cathaysia blocks in South China. Whether the previously defined Shenshan and Kuli formations located along the JSP fault and near the Xinyu City, Jiangxi Province, are continuous strata or parts of a tectonic mélange is important for understanding the geological history of South China. A carbonaceous phyllite from the area, previously considered as part of the Neoproterozoic Shenshan and Kuli formations, is analyzed palynologically in this study. The AsteridiumComasphaeridium acritarch assemblage found in the slate can be correlated with the basal Cambrian AsteridiumHeliosphaeridium-Comasphaeridium(AHC) acritarch assemblage in Tarim and the Yangtze Block. The early Cambrian biostratigraphical age assignment for the carbonaceous phyllite indicates the presence of both Neoproterozoic and Cambrian rocks in the sedimentary package, and supports that the package is a part of tectonic mélange rather than a continuous Neoproterozoic strata. The Cambrian slate is the youngest known lithology in the mélange at present.     

Comparison of the Climate during Marine Isotope Stage 9 and 11 Inferred from a Speleothem Isotope Record from Northern Norway

A stalagmite from northern Norway is dated with 12 thermal ionization mass spectrometry U-Th dates, and at least four separate growth periods are identified that correspond with marine isotope stages 9, 11, 13, and probably 15. The calcite is tested for isotopic equilibrium with the Hendy test. Oxygen isotope measurements on 231 subsamples on a vertical transect are used as a paleotemperature proxy. The detailed isotopic record from MIS 9 show apparent similarities to a Holocene record from the same cave, both in the climatic evolution and the overall temperatures: both show temperature oscillations changing from high-frequency, low-amplitude cycles in the beginning of the interglacial period to lower frequency, higher amplitude cycles in the later part of the interglacial period. The isotope record from MIS 11 shows a distinct isotopic event toward heavier values. The isotopic record together with the porous, humus-rich calcite are interpreted as indicating a warmer than present interglacial period with several episodes of heavy rainfall.     

Beryllium geochemistry in soils: evaluation of Be/Be ratios in authigenic minerals as a basis for age models

Soils contain a diverse and complex set of chemicals and minerals. Being an ‘open system’, both in the chemical and nuclear sense, soils have defied quantitative nuclear dating. However, based on the published studies of the cosmogenic atmospheric ¹⁰Be in soils, its relatively long half-life (1.5 Ma), and the fact that ¹⁰Be gets quickly incorporated in most soil minerals, this radionuclide appears to be potentially the most useful for soil dating. We therefore studied the natural variations in the specific activities of ¹⁰Be with respect to the isotope ⁹Be in mineral phases in eight profiles of diverse soils from temperate to tropical climatic regimes and evaluated the implications of the data for determining the time of formation of soil minerals, following an earlier suggestion [Lal et al., 1991. Development of cosmogenic nuclear methods for the study of soil erosion and formation rates. Current Sci. 61, 636–639.]. We find that the ¹⁰Be/⁹Be ratios in both bulk soils and in the authigenic mineral phases are confined within a narrower range than in ¹⁰Be concentrations. Also, the highest ¹⁰Be/⁹Be ratios in authigenic minerals are observed at the soil-rock interface as predicted by the model. We present model ¹⁰Be/⁹Be ages of the B-horizon and the corresponding soil formation rates for several soil profiles. The present study demonstrates that the ¹⁰Be/⁹Be ratios in the authigenic phases, e.g. clay and Fe-hydroxides, can indeed be used for obtaining useful model ages for soils younger than 10–15 Ma. However, the present work has to be pushed considerably further, to take into account more realistic age models in which, for instance, downward transport ¹⁰Be and clays, and in-situ dissolution of clay minerals at depths, altering the ¹⁰Be/⁹Be ratios of the acidic solutions, are included. We show that in the case of younger soils (< 1 Ma) studied here, their ¹⁰Be inventories and ¹⁰Be/⁹Be ratios have been significantly disturbed possibly by mixing with transported soils.     

以大洋钻探开展冲绳海槽热液活动研究的建议

关于沟弧盆构造体系下的海底热液活动,因涉及的问题繁多,一直是海洋地质学界十分注目的重要研究课题。相比之下,西太平洋沟弧盆体系的马里亚纳海槽和西南太平洋的汤加－斐济海盆中的劳海盆都有ＤＳＤＰ／ＯＤＰ的支撑,有关海底热液活动及其构造属性、地壳类型、形成时代等已有了十分明确的结论,唯冲绳海槽至今尚未有此机会。为了迎接１９９８年大洋钻探船来西太平洋海域,特建议在冲绳海槽设站钻探,可在地理座标２７°１５′～２７°３５′Ｎ,１２６°５６′～１２７°１０′Ｅ的范围、水深１３００～１５５０ｍ水域内海底热液活动活跃区选站,连续钻探４～５孔,其目的拟解决以下４个问题：１．冲绳海槽现代海底热液活动通道在岩层中的最大透过深度及其岩石学性质;２．冲绳海槽的热液类型和成岩成矿作用;３．热液活动与地壳性质;４．热液活动在沟弧盆体系演化中的意义。     

Picoplankton: Contribution to Phytoplankton Production in the Strait of Messina*

Abstract. Biomass and primary production rates derived from photosynthesis-light curves on picoplankton (< 1 um fraction) and total phytoplankton were compared for the Strait of Messina. Picoplankton biomass ranged between 0.063 and 0.094 mg Chi a m^-5 and accounted for 56–63 % of the total. Total primary production rates were between 0.22 and 1.56 mg C-m^-2-h^-1 of which the picoplankton contribution ranged from 24 to 43%. In this turbulent nearshore environment, the contribution of picoplankton to total phytoplankton production is considerably less than in calmer open-ocean waters. Carbon assimilation numbers (Pm^b), the initial slope (a), adaptation parameter (I_k), optimal irradiance (I_m) and compensation intensity (L_m,) for the picoplankton were lower than for the > 1 μm fraction. Fitted respiration (Rm^B) for the picoplankton was, however, on the average higher (10.3 % of Pm^B) than for the > 1 μrn fraction (6.6 %). Assimilation numbers for the > 1 μm fraction in the southern stations were of higher magnitude (8.5–12.0 mg C mg Chi a^-1 h^-1) than in the northern station, possibly due to the impact of upwelled water flowing southward along the Sicilian coast.     

Timing of granite emplacement and cooling in the Songpan–Garzê Fold Belt (eastern Tibetan Plateau) with tectonic implications

New U–Pb and Rb–Sr geochronology on syn- and post-orogenic granites provide constraints on the timing of major tectonic events in the Songpan–Garzê fold belt, west Sichuan, China. The Ma Nai granite was probably syn-kinematic with the main deformation and yields an age of 197±6 Ma that is interpreted as an upper age limit of the Indosinian event. Zircons and apatites from the post-kinematic Rilonguan granite also yield Jurassic ages (195±6 and 181±4 Ma). The post-orogenic Markam massif gives two ages of 188±1 and 153±3 Ma. Both granites are undeformed and cut structures in the Triassic sedimentary rocks. These results demonstrate that the major deformation and décollement tectonics in the Songpan–Garzê fold belt occurred prior to the Early Jurassic. The wide range of ages obtained for post-kinematic granites (from Early Jurassic to Late Jurassic) suggests that, locally, magmatic activity persisted for a long time (at least 50 Ma) after the Indosinian compressional tectonism. No Tertiary ages have been obtained, suggesting that these granites were not affected strongly by the India–Asia collision.