A COMPARISON OF EASTERN AND WESTERN HONG KONG PHYTOPLANKTON FROM WEEKLY SAMPLES (1997-1999)

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｍａｉｎｐｕｒｐｏｓｅｏｆｔｈｉｓｓｔｕｄｙｗａｓｔｏｄｅｔｅｒｍｉｎｅｔｈｅｍａｇｎｉｔｕｄｅａｎｄｆｒｅｑｕｅｎｃｙｏｆｈａｒｍｆｕｌｄｉａｔｏｍａｎｄｄｉｎｏｆｌａｇｅｌｌａｔｅｏｕｔｂｒｅａｋｓｉｎＨｏｎｇＫｏｎｇ’ｓｗｅｓｔｅｒｎａｎｄｅａｓｔｅｒｎｗａｔｅｒｓ (ｅ .ｇ.ＬａｍｍａＳｔｒａｉｔｓａｎｄＰｏｒｔＳｈｅｌｔｅｒｒｅｓｐｅｃｔｉｖｅｌｙ)ｆｏｒｔｈｅｐｅｒｉｏｄＪａｎｕａｒｙ 1 997ｔｏＤｅｃｅｍｂｅｒ1 999.Ｔｈｉｓｗａｓｄｏｎｅｉｎｏｒｄｅｒｔｏｄ…     

Interpretation of aeromagnetic data across the central crystalline shield area of Nigeria

Summary. A residual map of the total magnetic field (above 25 000 nT base) is presented for a portion of the central crystalline shield area of Nigeria and overlapping small portions of the Chad basin and the Benue rift (8°30'−12° 00'lat, and 7°−10°30' long). The map (based on a dataset digitized from recently released aeromagnetic sheets of Nigeria) leads to four results. (1) A magnetic boundary, evident on the map, separates the Younger Granite complexes into two groups. The groups are petrologically different, and the boundary may be a fault line with uplift to the south. (2) South of the boundary the map is dominated by a system of sub-parallel anomalies striking NE–SW, possibly representing major tectonic trends, and a set of fractures through which the Younger Granite complexes were intruded. The trend of the system parallels the Benue rift and lineaments in the oceanic crust off West Africa. (3) Negative magnetic anomalies lie over most of the known ring complexes, and over some suspected buried ring complexes and other intrusions. (4) 2½-and 3-D modelling shows that the larger complexes extend to 12 km depth, and the smaller ones to 6 km. They have nearly vertical sides, and magnetization contrasts range from 0.3 to 0.5 A m⁻¹.     

The host galaxies of active galactic nuclei

We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with  0.02 < z < 0.3  selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O  iii ]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L [O  iii ]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O  iii ] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O  iii ] luminosities.     

Denudation,vertical crustal movements and sedimentary basin infill

Denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass. Recent empirical results from a wide range of sources are presented on the rates of these processes. Denudation alone can cause non-tectonic (isostatic) surface uplift of the right magnitude predicted by theory. A case is made, following Ahnert, for a single linear relationship (although with much scatter) between denudation rate and mean drainage basin relief for large basins. Some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation. Application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one-dimensionality and neglect of suspended and washload contributions. Basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland, but problems arise in the apportionment of the various hinterland fluxes that occur in »real-world« three dimensional basins. Sediment yields in smaller half-graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields. Examples are given from extensional basins in the Western USA and Greece. The »length« of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed (through the fractal form of Hack's Law) and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands.

---

Zusammenfassung Denudation und vertikale Krustenbewegungen sind verbunden durch das isostatische Gesetz über den Erhalt der lithosphärischen Masse. Neuerliche empirische Ergebnisse aus einem weiten Quellenbereich werden im Verhältnis zu diesen Prozessen präsentiert. Denudation allein, kann nicht tektonisch bedingte (isostatische) Oberflächenhebungen hervorrufen, die in der richtigen Größenordnung liegen, wie sie auch theoretisch ermittelt wurden. Es wird in Anlehnung an Ahnert ein Fall geschaffen, in der eine einfach lineare Beziehung (obgleich mit vielen Streuungen) zwischen der Denudationsrate und dem durchschnittlichen Abflußbeckenrelief für große Becken vorliegt. Einige neue Ermittlungen der Denudationszeitkonstanten wurden vernachlässigt, um tektonische und isostatische Begriffe einzufügen, welche sich der Verringerung des Reliefs durch Denudation widersetzen. Die Anwendung des Verbreitungstransportmodells zum Bestimmen der Sedimentationsrate sind streng begrenzt durch die ihm innewohnende Eindimensionalität, und der Vernachlässigung der Schwebe- und Schwämmfrachtbeteiligung. Bekkenfüllungssequenzen können benutzt werden um vergangene Sedimenttransferkoeffizienten aus dem Hinterland festzulegen; aber es treten auch Probleme bei der Verteilung der verschiedenen Hinterlandeinträge auf, die bei einem realen dreidimensionalen Becken vorhanden sind. Sedimenteinträge in kleineren Halbgräben und Growth-fold Becken müssen die Größe des Abflußbeckens widerspiegeln, sowie die komplexen lokalen Steuerungen auf die Sedimenteinträge. Beispiele von Dehnungsbecken aus dem Westen der USA und Griechenlands werden angesprochen. Die Länge des tektonischen Reliefs in verkippten Blöcken und Growth-Folds wird die Fläche des entwickelten Abflußbeckens kontrollieren (durch die fraktale Form des Gesetzes von Hack), und daher die Ablagerungsmenge von Sedimentbecken in der Nähe von tektonischen Hochlagen.

---

Résumé L'érosion et les mouvements crustaux verticaux sont liés par l'équation isostatique de conservation de la masse lithosphérique. Des résultats empiriques récents provenant d'un large éventail de sources sont présentés en relation avec ces processus. L'érosion seule peut être la cause d'une montée non tectonique (isostatique) dont l'ampleur est prévue exactement par la théorie. Un cas est présenté, d'après Ahnert, qui montre, pour de grands bassins, une relation linéaire simple (mais avec une forte dispersion des points) entre le taux de dénudation et le relief moyen de l'aire de drainage. Certaines déterminations récentes des constantes de temps de dénudation ont omis de tenir compte des termes tectonique et isostatique qui s'opposent à la destruction du relief par érosion. L'utilisation de modèles de transport diffus en vue de déterminer le taux d'accumulation des sédiments est sévèrement limitée par le caractère unidimensionnel de tels modèles et par le fait qu'il ne tiennent pas compte de la fraction en suspension. Les séquences de comblement d'un bassin sédimentaire peuvent être utilisées pour déterminer les anciens cfficients de transfert à partir de l'hinterland; mais des difficultés surgissent à propos de la répartition des différents flux en provenance de l'hinterland dans le cas réel d'un bassin à 3 dimensions. Les apports sédimentaires dans les bassins de demi-graben et de »growth-fold« doivent traduire la grandeur des aires de drainage et les facteurs locaux complexes qui régissent ces apports. Des exemples sont présentés, relatifs à des bassins d'extension de l'ouest des USA et de Grèce. La »longueur« des reliefs tectoniques en relation avec les blocs basculés et les »growth-folds« déterminent, par la forme fractale de la loi de Hack, la surface des aires de drainage ainsi engendrées et, en conséquence, l'importance des dépôts dans les bassins sédimentaires voisins des reliefs tectoniques.

---

. , . () , . , ( ) . , , , . , . , , ; , . « » (GrowthFolds) . . — « » Hack'a , , .

     

V792 Her=HD 155638: A totally eclipsing RS CVn binary

Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27^d.07±0^d.07, which is slightly different from the 27^d.5384±0^d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R _h=2.58R ,R _c=12.28R ,M _h=1.40M ,M _c=1.46M ,i=80^o.61 and velocity semi-amplitudesK _c=48.36 km s^–1±0.79 km s^–1, andK _h=50.50 km s^–1±0.33 km s^–1. The apparent magnitudes areV _h=9 ^m .73 andV _c=8 ^m .48. The distance to HD 155638 was estimated to be 310 parsecs.     

Archean high-Mg monzodiorite–syenite,epidote skarn,and biotite–sericite gold lodes in the Granny Smith–Wallaby district,Australia: U–Pb and Re–Os chronometry of two intrusion-related hydrothermal systems

The Granny Smith (37 t Au production) and Wallaby deposits (38 t out of a 180 t Au resource) are located northeast of Kalgoorlie, in 2.7 Ga greenstones of the Eastern Goldfields Province, the youngest orogenic belt of the Yilgarn craton, Western Australia. At Granny Smith, a zoned monzodiorite–granodiorite stock, dated by a concordant titanite–zircon U–Pb age of 2,665 ± 3 Ma, cuts across east-dipping thrust faults. The stock is fractured but not displaced and sets a minimum age for large-scale (1 km) thrust faulting (D2), regional folding (D1), and dynamothermal metamorphism in the mining district. The local gold–pyrite mineralization, controlled by fractured fault zones, is younger than 2,665 ± 3 Ma. In augite–hornblende monzodiorite, alteration progressed from a hematite-stained alkali feldspar–quartz–calcite assemblage and quartz–molybdenite–pyrite veins to a late reduced sericite–dolomite–albite assemblage. Gold-related monazite and xenotime define a U–Pb age of 2,660 ± 5 Ma, and molybdenite from veins a Re–Os isochron age of 2,661 ± 6 Ma, indicating that mineralization took place shortly after the emplacement of the main stock, perhaps coincident with the intrusion of late alkali granite dikes. At Wallaby, a NE-trending swarm of porphyry dikes comprising augite monzonite, monzodiorite, and minor kersantite intrudes folded and thrust-faulted molasse. The conglomerate and the dikes are overprinted by barren (<0.01 g/t Au) anhydrite-bearing epidote–actinolite–calcite skarn, forming a 600-m-wide and >1,600-m-long replacement pipe, which is intruded by a younger ring dike of syenite porphyry pervasively altered to muscovite + calcite + pyrite. Skarn and syenite are cut by pink biotite–calcite veins, containing magnetite + pyrite and subeconomic gold–silver mineralization (Au/Ag = 0.2). The veins are associated with red biotite–sericite–calcite–albite alteration in adjacent monzonite dikes. Structural relations and the concordant titanite U–Pb age of the skarn constrain intrusion-related mineralization to 2,662 ± 3 Ma. The main-stage gold–pyrite ore (Au/Ag >10) forms hematite-stained sericite–dolomite–albite lodes in stacked D2 reverse faults, which offset skarn, syenite, and the biotite–calcite veins by up to 25 m. The molybdenite Re–Os age (2,661 ± 10 Ma) of the ore suggests a genetic link to intrusive activity but is in apparent conflict with a monazite–xenotime U–Pb age (2,651 ± 6 Ma), which differs from that of the skarn at the 95% confidence level. The time relationships at both gold deposits are inconsistent with orogenic models invoking a principal role for metamorphic fluids released during the main phase of compression in the fold belt. Instead, mineralization is related in space and time to late-orogenic, magnetite-series, high-Mg monzodiorite–syenite intrusions of mantle origin, characterized by Mg/(Mg + Fe_TOTAL) = 0.31–0.57, high Cr (34–96 ppm), Ni (22–63 ppm), Ba (1,056–2,321 ppm), Sr (1,268–2,457 ppm), Th (15–36 ppm), and rare earth elements (total REE: 343–523 ppm). At Wallaby, shared Ca–K–CO₂ metasomatism and Th-REE enrichment (in allanite) link Au–Ag mineralization in biotite–calcite veins to the formation of the giant epidote skarn, implicating a Th + REE-rich syenite pluton at depth as the source of the oxidized hydrothermal fluid. At Granny Smith, lead isotope data and the Rb–Th–U signature of early hematite-bearing wall-rock alteration point to fluid released by the source pluton of the differentiated alkali granite dikes.     

Brine-pool deposition for the Zn–Pb–Cu massive sulphide deposits of the Bathurst mining camp, New Brunswick, Canada. II. Ocean anoxia during mineralisation

Current models of massive sulphide ore genesis in the Bathurst mining camp, New Brunswick, involve settling of sulphide particles from a stagnating, low-salinity hydrothermal plume spreading laterally in an anoxic ocean layer with minimal sulphate content. There is fragmentary evidence of ocean anoxia in the form of local fine lamination in the shales that host some of the deposits but the total organic carbon, S, Fe, U/Th, Ni/Co, V/Ni and V/Cr relationships indicate deposition under oxic or dysoxic conditions. Vanadium and Mn values range from oxic to anoxic and sulphate-reducing to non-sulphate reducing but Mn may be anomalously low due to derivation by erosion of acidic volcanic rocks. The somewhat equivocal physical and chemical data, combined with the likely disturbing effects of penecontemporaneous volcanism, considerably weaken the case for an anoxic bottom layer in a static ocean. The presence of barite with ambient seawater ³⁴S values in Brunswick no. 12 ore, and the abundance of sulphate in modern euxinic basin waters, make a sulphate-free layer unlikely, even if anoxic. Sulphate-bearing, low-salinity fluids mixing with seawater would lead to growth of barite-bearing chimneys and baritic rubble mounds, which are not observed. A model involving brine-pool deposition better explains the major features of the Bathurst ores.     

Comparison of oscillatory and stationary flow through porous media

Experiments were conducted in an oscillatory water tunnel to investigate what effects temporal inertia has on the resistance of a granular medium. The flow law governing stationary porous media flow is reasonably well accepted and understood but the effects of unsteady flow have commonly been neglected. The present research was designed to assess the magnitude of the acceleration effects on media of uniformly packed spheres of equal diameter and on one sample of randomly placed stone.Oscillatory flow tests were made in a large oscillatory flume tunnel with periods varying from 3 to 12 seconds. The influence of properties of the medium (grain size and porosity) were tested by using spheres with two different diameters and packing each size sphere in different geometric arrangements. Tests made on a stone sample provided a qualitative assessment of the effects of more random material properties.For the experiments described in this paper, the Forchheimer unsteady-stationary flow law described the oscillatory measurements well when velocities and energy losses were maximum. Empirical coefficients determined from steady-stationary flow were generally found to apply to the unsteady flow, however some evidence of dependency on the period of oscillation was noted.     

On the sulphur chemistry of a super-anoxic fjord, Framvaren, South Norway

The concentrations of total carbonate (C_t), sulphate, sulphide, thiols and oxygen, the ratio between the stable sulphur isotopes ³⁴S and ³²S in sulphate and sulphide, and the density (used to calculate salinity) were determined on samples from the water column of Framvaren, a superanoxic fjord in southern Norway. From a depth of 18m (the oxic-anoxic boundary) the initial sulphate concentration, ([SO₄]_init), as calculated from salinity, is significantly higher than the sum of the measured sulphur species. This is attributed to a loss of sulphur from the water column. The amount of total carbonate produced, corrected for the initial concentration (C_t - 2.4 Sal/35) is found to be proportional to the amount of sulphate consumed, ([SO₄]_init - [SO₄]), according to the following relation C_t- 2.4 Sal/35 = 1.84 ([SO₄]_init - [SO₄]). Isotopic fractionation caused by bacterial sulphate reduction in the anoxic part of the water column produces sulphide with a δ³⁴S 40‰ lower than the δ³⁴S for sulphate at corresponding depths. The isotopic fractionation also results in δ³⁴S value for the remaining sulphate at depths below 80 m being considerably higher than the mean value for ocean water, which is close to + 20‰. The δ³⁴S values for sulphate at depths between 10 and 50 m were lower than + 20‰ which indicates oxidation of sulphide, which follows upon diffusion of sulphide from deeper parts of the water column and inflow of oxygenated seawater over the sill into the anoxic water of the fjord. A conclusive scenario of the Framvaren sulphur chemistry is presented.     

一次模拟的非外力大洋—大气突发气候事件

格陵兰东南部和相邻大洋表层气温时序中记录了一个急剧的事件。这一事件大约出现在３１００ａ（模拟年） ,持续约４０ａ ,以温度降低３°Ｃ为特征。由于其峰值比平均值高６个标准偏差（σ）以上 ,可以认为降温是急剧的。如果该区域年平均表层气温时序正常排布 ,那么这种异常可能每数亿年出现一次，如此大幅度降温持续那么久的概率极小。如果将不足４０ａ的变化从时序中去掉 ,那么事件高峰期表层气温低于平均值１０～１１σ。大气层较低层位的这种急剧降温源于海面温度急剧下降。大约３０８６ａ开始 ,格陵兰东海岸中部滨外发育了约０．５°Ｃ…