保持几何形状的矢量地图水印算法应用分析

不同类型的矢量地图水印嵌入算法对矢量地图几何特征的影响程度不同,导致含水印矢量地图的可用性遭到不同程度的破坏.针对这一问题,实现了一种现有的保持几何形状的矢量地图水印算法,将其应用于某居民地面矢量数据,并提出了几何形状和坐标精度评价方法,对该水印嵌入算法的普适性和有效性进行分析与评价.     

The role of bathymetry and directional wave conditions on observed crescentic bar dynamics

Nearshore sandbars are important features in the surf zone of many beaches because they strongly influence the mean circulation and evolving morphology. Due to variations in wave conditions, sandbars can experience cross-shore migration and vary in shape from alongshore uniform (shore-parallel) to alongshore rhythmic (crescentic). Sandbar dynamics have been studied extensively, but existing observational studies usually do not quantify the processes leading to crescentic bar formation and straightening. This study analyses the dynamics of crescentic bar events at the fetch-limited beach of Castelldefels (northwestern Mediterranean Sea, Spain) using 7.5 years of hourly time-exposure video images and detailed wave conditions. The results show that, despite the generally calm wave conditions, the sandbars were very dynamic in the cross-shore and longshore directions. They often migrated rapidly offshore during storms (up to 70 m in one day) and more slowly onshore during post-storm conditions. Crescentic bars were often present at the study site (48% of the time), but only when the sandbar was at least 10 m from the shoreline. They displayed a large variability in wavelengths (100–700 m), alongshore migration speeds (0–50 m/day) and cross-shore amplitudes (5–20 m). Wavelengths increased for larger bar–shoreline distances and the alongshore migration speeds were strongly correlated with the alongshore component of the radiation stresses. Crescentic patterns typically developed during low–medium energetic waves with limited obliquity ( $\theta \lesssim 20$° at 10 m depth), while bar straightening occurred during medium–high energetic waves with strong oblique angles of incidence ( $\theta \gtrsim 15$°). Overall, this study provides further proof for the important role of wave direction in crescentic bar dynamics and highlights the strong dependence of crescentic bar development on the initial bathymetric configuration.     

Carbonatites from Eastern Paraguay and genetic relationships with potassic magmatism: C, O, Sr and Nd Isotopes

Summary Geochemical characteristics were systematically determined for Early Cretaceous samples of carbonatitic rocks from Eastern Paraguay (Rio Apa, Amambay and Central Provinces). The data show that all the occurrences have an enriched isotopic signature and that the carbonatites have negligible or absent crustal signature. A petrogenetic model (parent liquids, fractional crystallization, hydrothermal interactions and weathering) is proposed as a function of incompatible trace element, stable (O-C) and radiogenic (Sr-Nd) isotope variations with the aim to test the significance of carbonatitic complexes as a marker of the metasomatized subcontinental lithospheric mantle. The results indicate that the carbonatites and primary carbonates from eastern Paraguay, and those from the north eastern Paraná Basin (SE Brazil), were affected by metasomatic events distinct in time and composition.

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Karbonatite aus Ost-Paraguay und ihre genetische Beziehung zu Kalium-Magmatismus: C O, Sr und Nd isotope

Zusammenfassung Die geochemischen Charakteristika von frühkretazischen Karbonatitproben aus Ostparaguay (Rio Alpa, Amambay und Zentrale Provinzen) wurden untersucht. Die Daten belegen, daß alle Vorkommen eine isotopische Anreicherungssignatur zeigen und daß ihnen eine entsprechende Krustensignatur fehlt. Ein Petrologisches Modell (Ausgangsschmelze, fraktionierte Kristallisation, hydrothermale Interaktion und Verwitterung) wird auf Grund der Verteilung der inkompatiblen Spurenelemente, der stabilen (C-O) und radiogenen (Sr-Nd) Isotope vorgeschlagen. Es versucht die Bedeutung der Karbonatitkomplexe als Markerhorizonte des metasomatischen subkontinentalen Mantels zu überprüfen. Die Ergebnisse zeigen, daß die Karbonatite und die primären Karbonate in Ostparaguay, und jene aus dem Paraná Becken SüdostBrasiliens durch zeitlich und zusammensetzungsmäßig unterschiedliche metasomatische Prozesse erfaßt wurden.

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With 10 Figures     

Textures exhibited by feldspars in the Giant Mottled Anorthosite (GMA) of the bastard unit in the Upper Critical Zone,Western Bushveld Complex

Summary The Bastard Unit, overlying the Merensky Unit, is the uppermost and most complete of the cyclic units in the Upper Critical Zone and its upper contact is taken as the boundary between the Critical and Main Zones (as recommended by SACS, 1980). The Unit is different from underlying units for three reasons: it does not have a well-defined top contact (with an overlying unit); it is much thicker than the Merensky and Footwall Units; and it has an unusually thick sequence of mottled anorthosite at its top. This distinctive composite anorthositic sequence is termed the Giant Mottled Anorthosite (GMA) which is predominantly made up of poikilitic anorthosite. The GMA can broadly be subdivided into three distinct parts; the Lower Giant Mottled Anorthosite (LGMA), Giant Mottled Middling (GMM) and the Upper Giant Mottled Anorthosite (UGMA).Petrographic examination of 82 samples taken in the GMA from 11 borehole profiles around the western limb of the Complex revealed that the LGMA and GMM are essentially adcumulates while the UGMA is orthocumulate in character. By its very nature the dominant phase throughout the GMA is cumulus plagioclase feldspar ( 85%) with the balance being made up of intercumulus orthopyroxene and clinopyroxene and minor biofite — all of which constitute the darker mottles. Intercumulus inverted pigeonite occurs in the upper part of the GMM, throughout the UGMA and for c. 30 m into the Main Zone. K-feldspar also joins the paragenesis within the UGMA and occurs both as intercumulus orthoclase and antiperthite. Cumulus plagioclase grains, showing varying degrees of complex oscillatory-zonal growth are common in the upper part of the GMA. These grains are interpreted as records of growth episodes during earlier influxes of magma which were responsible for the development of the underlying cyclic units, but escaped incorporation into the cumulate pile.

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Feldspat-Texturen im Giant Mottled Anorthosite der Bastard-Einheit in der oberen kritischen Zone des westlichen Bushveld-Komplexes

Zusammenfassung Die Bastard-Einheit, die die Merensky-Einheit überlagert, ist die oberste und am besten entwickelte der zyklischen Einheiten in der oberen kritischen Zone; ihr oberer Kontakt gilt als die Grenze zwischen der Kritischen und der Main-Zone (entsprechend den Empfehlungen von SACS, 1980). Die Einheit unterscheidet sich aus drei Gründen von den Einheiten im liegenden: sie hat keinen gut definierten oberen Kontakt (mit einer darüberliegenden Einheit), sie ist wesentlich mächtiger als die Merensky und die Footwall-Einheiten, und sie hat eine ungewöhnliche mächtige Abfolge von Mottled Anorthosite als obersten Teil der Abfolge. Diese wohldefinierte anorthositische Abfolge wird als Giant Mottled Anorthosite (GMA) bezeichnet, und besteht hauptsächlich aus poikilitischem Anorthosit. Die GMA kann in 3 Teile, den unteren (LGMA), den mittleren (GMM) un den oberen (UGMA) unterteilt werden.Die petrographische Untersuchung von 82 Proben in der GMA aus 11 Bohrlöchern im Westteil des Bushveld-Komplexes zeigt, daß LGMA und GMM im wesentlichen Adkumulate sind, während die UGMA ein Orthokumulat darstellt. Die Hauptphase in der gesamten GMA ist Kumulus-Plagioklas ( 85 %); der Rest besteht aus Intercumulus-Orthopyroxen, Klinopyroxen, und geringen Mengen von Biotit. Diese sind die Komponenten der dunkleren mottles. Intercumulus invertierter Pigeonit kommt im oberen Teil der GMM, in der gesamten UGMA und in den unteren 30 Metern der Main-Zone vor. Innerhalb der UGMA tritt K-Feldspat hinzu, dieser kommt als Intercumulus Orthoklas und Antiperthit vor. Körner von Cumulusplagioklas mit verschiedenen Intensitäten komplexer Zonierung sind im oberen Teil der GMA verbreitet. Diese Körner werden als Hinweise auf Wachstumsepisoden während früherer Magmenzufuhr-Phasen interpretiert, die für die Entwicklung der zyklischen Einheiten im Liegenden verantwortlich waren, aber selbst nicht Teil der Cumulatabfolge wurden.

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With 5 Figures     

冀西北长城纪宣龙式铁矿层中微体植物化石的发现及其意义

本文研究的是笔者等在冀西北长城系串岭沟组宣龙式铁矿层中发现的微体植物化石,这些化石都保存在铁质叠层石(肾状赤铁矿)和铁质核形石(鲕状赤铁矿)的基本层中。微化石以丝状体为主,部分为球状体。归属于原核生物蓝藻门颤藻科的两个属和色球藻科的一个属。化石层同位素年龄约在1800—1757Ma。这些化石与北美冈弗林特组微化石比较,既有些相似,又有些区别。该化石的发现为研究铁矿的成因,指示沉积环境及层位对比都很有意义。     

The chemistry of orthophosphate uptake from seawater on to calcite and aragonite

The chemistry of orthophosphate uptake from synthetic seawater onto the surfaces of synthetic calcite, aragonite and low-magnesium biogenic calcite has been studied, in order to elucidate the kinetics of the process (generally believed to be the major control of dissolved reactive phosphate in carbonate-rich marine sediments). Our results differ from those obtained by others, who have studied orthophosphate uptake in low ionic strength solutions and at much higher supersaturations relative to apatite.In both ‘free drift’ and chemostat experiments, Mg and F have only a minor effect on the reaction rate. Even at constant solution composition the rate of orthophosphate uptake was found to decrease by 10⁶ over a two week period. The data from the ‘free drift’ experiments can be fitted to the Elovich equation. This indicates that the kinetics observed for this reaction can be explained by an exponential decrease in available surface reaction sites and/or a linear increase in the activation energy associated with chemisorption as the reaction proceeds.     

The appearance of Mars from 1907 to 1971: Graphic synthesis of photographs from the I.A.U. center at Meudon

Using selected high quality plates collected at the I.A.U. Planetary Data Center in Meudon (Paris), the author has drawn 32 Mercator charts of the planet Mars for every opposition from 1907 to 1971. This graphic synthesis of albedo distribution may be used in the study of major surface changes over the years.     

Elucidation of different forms of organic carbon in marine sediments from the Atlantic coast of Spain using thermal analysis coupled to isotope ratio and quadrupole mass spectrometry

Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO₂) and m/z 18 (H₂O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ¹³C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.     

Are the South and North Liaohe Groups of North China Craton different exotic terranes? Nd isotope constraints

The Liaohe Group is an important Paleoproterozoic stratigraphic unit in the northeastern part of the North China Craton and is traditionally subdivided into the North and South Liaohe Groups. Associated with both the North and South Liaohe Groups are voluminous Paleoproterozoic granitoid rocks, named the Liaoji granitoids. Different tectonic models, including terrane amalgamation, continent–arc collision and rift closure, have been proposed to interpret the tectonic setting and evolution of the North and South Liaohe Groups and associated Liaoji granitoids. At the centre of the controversy between these models is whether or not the North and South Liaohe Groups developed on the same Archean basement. Nd isotopic geochemistry of the Liaoji granitoids provides important constraints on this controversial issue. The Liaoji granitoids associated with the North and South Liaohe Groups display similar ε_Nd values, restricted to a narrow range from 0 to 2, implying that these granitoid rocks were derived from the same or a similar magma source. Moreover, the Liaoji granitoids associated with the North and South Liaohe Groups have similar Nd model ages (T_DM), ranging from 2.4 to 2.6 Ga, suggesting that the protoliths of the Liaoji granitoids associated with both groups may have formed simultaneously, and that the basement rocks underneath the Liaoji granitoids and associated North and South Liaohe Groups belong to the same continental block rather than two different blocks. Combining lithological, structural and geochronological considerations, we interpret the North and South Liaohe Groups as having developed on a single late Archean basement that underwent Paleoproterozoic rifting associated with the intrusion of the Liaoji granitoids and the formation of the Liaohe Group, and closed upon itself in the Paleoproterozoic.