Berlin, Freie University, Diss., 2005. / Dateifortmat: zip, Dateien im PDF-Format.

Freie Universiẗat, Diss., 2005--Berlin. / Dateifortmat: zip, Dateien im PDF-Format.

The chief objective of the research was to establish the relative fertility of forest, scrub and grassland soils on chalk in SE England and to test hypotheses on the origin of fertility differences between the soils. A subsidiary objective was to relate the beech forests of the chalk in England to continental beech forests on calcareous parent materials and thus to utilize the results of continental studies on discussion of the nutrient status of the different forest types of Europe. Previous research by B.A. Key had concentrated on scrub and grassland, and my research concerned chiefly scrub and forest. The fertility of soils was assessed by bioassays with commonly occuring test species, i.e. <i>Galium aparine</i>, <i>Deschampsia caespitosa</i> and <i>Arctium minus</i>, by foliar analysis of component woody species and by soil incubation tests. The results of bioassays show that the scrub soils of the chalk in SE England are more fertile than either grassland or forest soils. Bioassay plants grown on forest soils showed considerable variation in yield and nutrient content indicating that there is much variation in the fertility of forest soils. Mercury beech forest soils as a class were more consistent and produced better growth of test species than grassland soils while beech forests without mercury, traditionally classed as sanicle beechwoods, were found to have soils of very wide ranging fertility. Beech foliar analysis did not distinguish between mercury and sanicle beech forests, although the trend was for higher N status in the beech leaves of mercury sites. No trend was observed in the P status of beech leaves. The potential for nitrogen mineralization was favourable in both scrub and forest soils but much lower in grassland soils. Soils underneath mercury beech forests were consistent in nitrification and yielded similar concentrations of nitrate during one-month incubation to soils beneath relict ash-hazel forests. No such consistency was found for the soils of beech forests without mercury, and contrary to expectation, their potential to supply nitrogen appeared to be higher than that of mercury beech forest soils. The fertility differences shown by bioassays were most probably due to phosphorus supply. Experiments with several species have shown that the primary limiting nutrient in chalk soils is phosphorus; especially when plants are grown in pots at low rooting density. Nitrogen limitation has been found but only after adding a phosphorus fertilizer solution or when plants are grown at high rooting density. In these experiments, except where the objective was to separate the effects of nitrogen from phosphorus, test plants were grown one per pot for a relatively short time. It was hypothesized that the differences in fertility level of soils supporting forest, scrub and grassland on chalk in SE England were chiefly the result of differences in the amounts of nutrients added each year in litter. Freshly fallen litter of several woody species of chalk beech forests was collected from nylon nets set out on the forest floor in autumn 1984 and 1985. In order to investigate the role of nutrient withdrawal, in autumn 1985 mesh bags were used to collect freshly fallen litter within the canopy of scrub and forest. In both types of experiments N and P content was analysed on a species-specific basis. In addition, fine litterfall in a typical mercury beech forest was estimated in 1984 and rates of litter decomposition of five key species were measured over a period of 1 1/2 yr. Beech litter has relatively low phosphorus concentrations and is slow to decompose. Phosphorus is retranslocated from falling leaves in greater amounts in beech than in <i>Crataegus</i>, and <i>Cornus</i>, the main constituents of scrub which would seem to explain the lower phosphorus status of beech forest soils than scrub soils.

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Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 370-386). Available also in a digital version from Dissertation Abstracts.

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Prompted by increased interest in understanding microporosity, recent efforts at describing and classifying pore types in mudstones have focused primarily on siliceous, gas producing unconventional reservoirs with little attention being paid to carbonate, mixed oil-and-gas producers. The Niobrara Formation in the Denver-Julesburg Basin is a self-sourced resource play producing oil and natural gas from low permeability chalks. Key reservoir lithologies consist of chalk, chalky marl and marl. These lithologies contain flattened chalk fecal pellets which play a significant role in providing porosity. Integration of depositional fabric with pore-type distribution emphasizes the unique textural and depositional nature of chalk and provides a starting point for evaluation of diagenetic porosity modification. Chalk depositional textures comprise two main subdivisions. The first, called rainstone, includes chalks that form largely from settling of planktonic skeletal remains and fecal pellets as marine snow. New terms related to pelagic chalk textures are pelagic mudstone, pelagic wackestone, and pelagic packstone. The second, called allochthonous chalk, consists of chalks formed from syndepositional tectonic disruption of the seafloor, resulting in mass-movement and redeposition of chalk as turbidites and slide sheets. New terms related to allochthonous chalk textures are allomudstone, allofloatstone, and allorudstone. A chalk porosity classification consisting of four major pore types is presented that can be used to quantify Niobrara chalk pores and relate them to depositional texture, porosity networks, diagenetic history, and pore distributions. Interparticle porosity occurs largely between coccoliths and coccolith fragments, and decreases with burial ranging from 27-38% to 5-17%. Intraparticle porosity occurs within chalk pellets, coccospheres, coccolith plates and foraminifera tests, and also decreases with burial. Organic matter pores are intraparticle pores located within organic matter and are related to hydrocarbon generation. Channel pores, where present, can have significant influence on hydrocarbon storage and permeability networks. In the Niobrara, burial diagenesis in the form of mechanical compaction, chemical compaction, and syntaxial cement overgrowths, modifies pore shape and abundance. Porosity distribution is controlled by the abundance of chalk pellets and the mineralogy of the matrix. Permeability is a function of matrix lithology (micrite-rich vs. silt- and clay-rich). Understanding chalk depositional and diagenetic processes, and how they relate to porosity formation and pore evolution provide a foundation for more accurately predicting the occurrence and distribution of hydrocarbon source and reservoir rocks within the Niobrara.