Fruit polymorphism in ephemeral species of Namaqualand: IV. Growth analyses of plants cultivated from the dimorphic diaspores     

Karen Beneke  Margaretha W. Van Rooyen  G. K. Theron 《Journal of Arid Environments》1993,24(4)

Growth analyses were conducted on two polymorphic annual species, Dimorphotheca sinuata and Arctotis fastuosa of Namaqualand, Republic of South Africa. Plants cultivated from disc diaspores of D. sinuata produced significantly more inflorescences, produced bigger mature plants and allocated more biomass to reproduction than plants cultivated from ray diaspores. Plants of both D. sinuata and A. fastuosa growing on less disturbed sites in the field allocated more biomass to reproduction than plants growing on more disturbed sites. Reproductive allocation of A. fastuosa increased with a decrease in plant size, whereas reproductive allocation was not affected by plant size in the case of D. sinuata.  相似文献   

Sandstone diagenesis and porosity modification during basin evolution     

Knut Bjørlykke  Mogens Ramm  Girish C. Saigal 《International Journal of Earth Sciences》1989,78(1):243-268

The properties of sandstones as potential reservoirs and shales as source rocks depend on primary facies relationships and diagenesis. Porostiy loss due to mechanical compation and pressure solution is essentially a function of grain parameters (sorting, packing and composition) and net overburden stress. The porosity loss can be predicted to a certain extent. The importance of secondary porosity caused by dissolution of framework grains and cements has been fully recognized. The discussion has focused on the processes causing such dissolution and to what extent it can cause net increase in porosity.The most critical factor in clastic diagenesis is the nature of porewater flow and the degree of mass transfer taking place as a result of this. In the North Sea reservoir rocks, petrographic and geochemical evidence suggest that most of the leaching of feldspar and mica resulting in the formation of kaolinite occurred early during fresh wather flushing. Recent calculations indicate that »acids« derived from source rocks are inadequate to explain the secondary porosity observed in reservoir rocks. Mathematical modelling suggests that thermal convection is of limited importance in sedimentary basins, except where there are high lateral changes in geothermal gradients. Evidence from porewater geochemistry suggests that porewaters in sedimentary basins are often stratified or compartmentalized in a way which is inconsistent with large scale convection or compactional flow, making it necessary to assume that diagenetic reactions are relatively isochemical during deeper burial.A better understanding of the diagenetic reactions will help us to improve our predictions about porosity/depth relations, pore size, and pore geometry distribution in reservoir rocks.Porosity depth trends from offshore Norway and published data from other basins are discussed. Empirical linear best fit lines are found to illustrate the relationship quite well for depths between one and five km. Within a specific region, the linear porosity gradient is a function of mineral composition and of temperature and pressure gradients. Primary porosity tends to be best preserved in sandstones with high proportions of stable grains (e. g. in quartz arenites) down to about 3 or 4 km. At greater depth, porosity loss is accelerated due to increased pressure solution. Secondary and primary porosity adjacent to feldspar grains then tends to be selectively preserved relative to primary pores between quartz grains.

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Zusammenfassung Die bestimmenden Faktoren von Sandsteinen als mögliche Speichergesteine und von Schiefern als Bildungsort von Kohlenwasserstoffen liegen in den Verhältnissen der primären Fazieausbildungen der Gesteine und deren Diagenesegeschichte. Korn-Parameter (Sortierung, Pakkungsdichte und Zusammensetzung) und Netto-Auflast steuern mechanische Kompaktion und Drucklösung. Diese sind für Porositätsreduzierungen verantwortlich, die bis zu einem bestimmten Grad abgeschätzt werden können. Der Einfluß von Lösungserscheinungen für die Bildung sekundären Porenraums, der hier definiert werden konnte und die Vorgänge, die Lösungsphasen iniziieren, bilden den zentralen Punkt der Diskussion.Größte Bedeutung in der Diagenese klastischer Sedimente kommt dem Charakter der Grundwasserbewegungen und deren Eigenschaft im Bereich des Stofftransportes zu. Daten der Petrographie und der Geochemie ergeben für die Speichergesteine der Nordsee, daß der Hauptanteil der Lösung von Feldspat und Muskovit, ein Vorgang, der zur Bildung von Kaolinit führte, frühdiadenetisch unter Einfluß von Süßwasser stattfand. Aufgrund neuerer Kalkulationen kann die Bedeutung saurer Lösungen, die man von dem Bildungsgestein hergeleitet, für die sekundäre Porosität der Speichergesteine ausgeschlossen werden. Mathematische Berechnungen räumen dem Einfluß thermaler Konvektion in sedimentären Becken meist geringe Bedeutung zu, es sei denn es gibt große laterale Unterschiede des geothermischen Gradienten. Die geochemische Analyse des Porenwassers ergibt vertikale und horizontale Zonierungen im Chemismus des Wassers. Diese Tatsache widerspricht der These einer großräumischen Konvektion, da in diesem Fall die Diagenese-Prozesse unter Bedeckung bei relativ einheitlicher chemischer Zusammensetzung ablaufen würden.Ein besseres Verständnis der diagenetischen Vorgänge wird die Abhängigkeit des Verhältnisses von Porosität zur Tiefe, der Verteilung des Hohlraumvolumens und der Hohlraumgeometrie in Speichergesteinen erleichtern.Diskutiert werden Zusammenhänge von Porosität und Tiefe, die Daten an Stellen vor der Küste Norwegens und anderen Becken entnommen wurden. Für Tiefen zwischen einem und fünf Kilometern scheinen empirische, lineare Geraden am besten die Verhältnisse zu verdeutlichen. Regional begrenzt kann der lineare Porositätsgradient als eine Funktion der Gradienten von Mineralzusammensetzung, Temperatur und Druck beschrieben werden. Primäre Porosität ist am besten in Sandsteinen mit einem hohen Anteil an stabilen Komponenten (z. B. Quatzarenite) bis zu einer Tiefe von drei oder vier Kilometern erhalten.Drucklösungserscheinungen sind für die zunehmende Abnahme der Porosität in größeren Tiefen verantwortlich. Dabei scheinen sekundäre und intergranulare Porenräume zwischen Feldspatkörnern relativ zu primären Porenräumen zwischen Quartzkörnern stabiler zu sein.

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Résumé Les facteurs qui caractérisent des grès en tant que réservoirs potentiels d'hydrocarbures et des shales en tant que roches-mères sont les relations facielles primaires et la diagenèse. La perte de porosité due à la compaction mécanique et aux impressionnements («pressure-solution») est fonction essentiellement des paramètres des grains (classement, ordonnance et composition) et des contraintes dues à la surcharge. La perte de porosité peut être prévue dans une certaine mesure. On connaît l'importance de la porosité secondaire provoquée par la dissolution des grains et des ciments. La discussion est centrée sur les processus responsables de cette dissolution et sur leur incidence dans l'accroissement net de la porosité.Le facteur le plus critique dans la diagenèse des élastiques est la nature du flux d'eau intersticielle et le degré de transfert de matière qui en résulte. Dans les roches-magasins de la Mer du Nord, les observations pétrographiques et géochimiques montrent que la plus grande partie de l'altération en kaolin du feldspath et du mica s'est produite lors du lessivage par de l'eau douce. Selon des calculs récents, les «acides» dérivés des roches-mères ne peuvent expliquer la porosité secondaire des roches-magasins. La modélisation mathématique suggère que la convection thermique ne joue qu'un rôle subordonné dans un bassin de sédimentation, sauf aux endroits de forte variation latérale du gradient géothermique. L'étude géochimique des eaux intersticielles montre que dans les bassins sédimentaires, elles sont souvent stratifiées ou compartimentées d'une manière qui est incompatible avec une convection à grande échelle car un tel phénomène impliquerait des réactions diagénétiques relativement isochimiques.Une meilleure compréhension des réactions diagénétiques doit nous aider à améliorer nos prévisions relatives à la relation porosité/profondeur, et à la répartition de la taille et de la forme des pores dans les roches-magasins.Une discussion est présentée à propos de la relation porosité/profondeur, à partir des données recueillies off-shore en Norvège et de données publiées provenant d'autres bassins. Il apparaît qu'entre 0 et 5 km de profondeur, des courbes empiriques linéaires rendent le mieux compte de ces relations. Dans une région donnée, le gradient linéaire de porosité est fonction de la composition minéralogique et des gradients de pression et de température. La porosité primaire tend à être bien préservée dans les grès riches en grains stables (p. ex. dans les arénites quartziques) jusqu'à une profondeur de 3 à 4 km. Plus bas, la perte de porosité s'accélère en raison des phénomènes d'impressionnement. Dans ces conditions profondes, les pores primaires et secondaires adjacents aux grains de feldspath semblent relativement plus stables que les pores primaires situés entre les grains de quartz.

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Population density and zoning of olivine phenocrysts in tholeiites from Kauai,Hawaii     

Sven Maaløe  Ole Tumyr  Dodie James 《Contributions to Mineralogy and Petrology》1989,101(2):176-186

The population density of olivine phenocrysts of the tholeiites display an exponential variation, which is typical of igneous as well as contact metamorphic rocks. The exponential variation is explained by a new growth probability model, which is consistent with experimental work. The forsterite content of the olivine phenocrysts decreases with decreasing size. Various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber, after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place.  相似文献   

Live standing crop and metabolism of the marsh grassSpartina patens as related to edaphic factors in a brackish,mixed marsh community in Louisiana     

David M. Burdick  Irving A. Mendelssohn  Karen L. McKee 《Estuaries and Coasts》1989,12(3):195-204

Effects of soil factors on physiological indicators ofSpartina patens and live standing crop of the macrophyte community were investigated in a brackish marsh. Three distinct physiognomic zones were studied along a transect perpendicular to a tidal creek: the marsh edge, which was directly adjacent to the creek; the levee berm, 6 to 8 m from the creek; and the inland zone, which extended through the marsh interior. Soil physicochemical factors (soil moisture, redox potential, interstitial pH, salinity, and ammonium and sulfide concentrations) were compared to physiological indicators ofSpartina patens (leaf adenine nucleotides, root alcohol dehydrogenase (ADH) activity, and levels of ethanol, lactate, alanine and malate in the roots). In correlation matrices of soil and plant factors, increases in soil moisture and decreases in redox potential were associated with depressed leaf adenylate energy charge ratios (AEC, an integrative measure of plant stress) and elevated ADH activities and metabolite levels in the roots. ADH activity was greatest in roots from the inland zone where soil waterlogging was greatest and exhibited seasonal increases that followed seasonal declines in soil redox potential. Leaf AEC was greatest in the berm and generally lowest in the inland plants. End of season live standing crop was also greatest on the berm, but did not closely follow any edaphic trends across the three zones. This suggests that several factors, (i.e., soil aeration, and sulfide and nitrogen levels) may be of greater importance to standing crop than any single factor, as is thought for salt marshes dominated byS. alterniflora.  相似文献   

Palaeomagnetism of late Precambrian dolerite dykes from Varanger peninsula,north Norway     

Johannes Kjøde 《Physics of the Earth and Planetary Interiors》1980,21(1):38-49

Palaeomagnetic investigations have been carried out on 12 dykes of Late Precambrian age from the Varanger peninsula, north Norway. The dykes are separated into two groups, the Kongsfjord dykes and the Båtsfjord dykes. In the Kongsfjord dykes, titanomagnetite is almost entirely erased, as a result of an extreme degree of alteration. Pyrrhotite is the dominating magnetic mineral, and only three stable specimen directions can be defined. In the Båtsfjord dykes, however, the most important magnetic constituent is nearly pure magnetite, and a two-axis magnetization structure is revealed. The directions of the major component conform to a Fisherian distribution, and are assumed to represent the relative Late Precambrian field. Superimposed on this magnetization is a minor component which is assumed to be of Caledonian origin, probably Ordovician. This latter remanence is in accordance with other Middle Palaeozoic results obtained in Western Europe. The upper age limit of the Late Precambrian field is discussed, and it is proposed that the polar shift from the Late Precambrian position to the main Palaeozoic group may have occurred as late as Middle Ordovician.  相似文献   

Multi-component carbon isotope evidence of early Holocene environmental change and carbon-flow pathways from a hard-water lake in northern Sweden   总被引：4，自引：2，他引：2  

Dan Hammarlund  Ramon Aravena  Lena Barnekow  Bjørn Buchardt  Göran Possnert 《Journal of Paleolimnology》1997,18(3):219-233

A 9000-year carbonate-rich sediment sequence from a small hard-water lake in northernmost Sweden was studied by means of multi-component stable carbon isotope analysis. Radiocarbon dating of different sediment fractions provides chronologic control and reveals a rather constant hard-water effect through time, suggesting that the lake has remained hydrologically open throughout the Holocene. Successive depletion of ¹³C in fine-grained calcite and carbonate shells during the early Holocene correlate with a change in catchment vegetation from pioneer herb communities to boreal forest. The vegetational change and associated soil development likely gave rise to an increased supply of ¹³C-depleted carbon dioxide in groundwater recharging the lake. This process is therefore believed to be the main cause of decreasing values of ¹³C in dissolved inorganic carbon of the lake and thereby in limnic carbonates. Strongly ¹³C-depleted sedimentary organic matter may be related to enhanced kinetic fractionation during photosynthetic assimilation by means of proton pumping in Characean algae. This interpretation is supported by a substantial offset between ¹³C of DIC as recorded by mollusc shells and ¹³C of fine-grained calcite.  相似文献   

Limits of solution of trace elements in minerals according to Henry's law: Review of experimental data     

Bjørn O. Mysen 《Geochimica et cosmochimica acta》1978,42(6):871-885

Results of a survey of experimental data on trace element partitioning between crystals and coexisting liquid and between crystals and coexisting aqueous fluid are reported. These studies involve combinations of elements such as Cs, Rb, K, Na, Li, Ba, Sr, Ni and Sm dissolved in minerals such as feldspars, micas, feldspathoids, garnets, pyroxenes, amphibole and olivine. It is shown that the concentration ranges of these elements in minerals with solution behavior according to Henry's law appear to extend to less than 1 wt.% and often to less than 100 ppm of the element in the crystalline phase.The available data indicate that the concentration ranges of solution in minerals according to Henry's law can be positively correlated with the difference of ionic radii between trace element and the host element for which the tracer is assumed to substitute. Furthermore, studies involving crystals and coexisting aqueous fluid have been used to determine whether Henry's law or Raoult's law adequately describes the solution. Based on the assumption that the aqueous fluid solution can be considered ideal, models have been proposed stating that if the difference between the ionic radii of the tracer and the host element in the crystalline phase is less than about 10% (relative to the host element), the solution is ideal (Raoult's law). With larger differences between the ionic radii, there is an excess free energy of mixing, although Henry's law is still obeyed in the concentration ranges where crystalliquid or crystal-fluid partition coefficients are independent of element concentration.  相似文献   

Impacts of vehicles on natural terrain at seven sites in the San Francisco Bay area   总被引：2，自引：0，他引：2  

H. G. Wilshire  J. K. Nakata  Susan Shipley  Karen Prestegaard 《Environmental Geology》1978,2(5):295-319

The impacts of off-road vehicles on vegetation and soil were investigated at seven representative sites in the San Francisco Bay area. Plant cover of grass and chaparral (with shrubs to 4 m tall) have been stripped by the two- and four-wheel vehicles in use. Impacts on loamy soils include increased surface strength (as much as 275 bars), increased bulk density (averaging 18%) to depths of 90 cm or more, reduction of soil moisture by an average 43% to 30 cm depths, greatly reduced infiltration, extension of the diurnal temperature range by as much as 12°C, and reduction of organic carbon by an average 33% in exposed soils. Very sandy soils respond similarly to vehicular use except that moisture is increased and surface strength of beach sand is decreased. These physical and chemical impacts reduce the land's capability of restoring its vegetative cover, which in turn adversely affects animal populations. Both the loss of plant cover and the physical changes caused by vehicles promote erosion. Measured soil and substrate losses from vehicular use zones range from 7 to 1180 kg/m². The estimated erosion rate of the Chabot Park site exceeds the rate of erosion considered a serious problem by a factor 30, it exceeds United States Soil Conservation Service tolerance values by a factor of 46, and it exceeds average San Francisco Bay area erosion rates by a factor of 17. The resulting soil losses are effectively permanent. Neither the increased sediment yield nor the increased runoff is accomodated on the sites of use, and both are causing adverse effects to neighboring properties.  相似文献   

Co-evolutionary dynamics and institutions: Innovation in a guild community in Norway     

Øystein Stavø Høvig 《Norsk geografisk tidsskrift. Norwegian journal of geography》2016,70(3):152-161

ABSTRACT

The video game industry is often portrayed as a ‘footloose industry’ in which electronic goods can be produced and distributed from any location without positive or negative effects from factors such as resources or proximity to market. Hence, a conventional assumption is that the role of place is greatly diminished in the case of such industries. The author tests this assumption by analysing firms’ practice in a game developer community in Bergen, Norway, and the spatiality of linkages between the community and the environment. He proposes an alternative analytical framework for understanding practice in the industry, one that recognizes that a firm's practice is either embedded within or related to networks and institutional structures. The question of how contextual conditions, embeddedness and networks are treated in the literature on innovation is discussed, and the concept of community as an analytical concept is introduced and applied. After showing how practice in the case community has evolved within the cultural, social and territorial context, the author concludes that a portrayal of the game industry as a ‘footloose industry’ disembedded from its surroundings should be avoided, and instead the dynamic relationship between actors, context and practice should be heeded.  相似文献   

Hydrochemical studies in coastal waters of the Spitsbergen Archipelago in 2014–2015     

E. V. Yakushev  P. N. Makkaveev  A. A. Polukhin  E. A. Protsenko  S. V. Stepanova  P. V. Khlebopashev  Sh. Kh. Yakubov  A. Staalstrøm  M. Norli 《Oceanology》2016,56(5):763-765

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