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The timing and duration of fluid flow through sedimentary basins is paramount to understanding basin evolution.  Episodes of fluid flow often deposit authigenic (low temperature) minerals around detrital grains and can result in the concentration of metalliferous deposits and hydrocarbons.  Although numerous studies have dated the growth of authigenic mineral phases in an attempt to date fluid flow, these studies have not been able to determine the properties of the fluids from which the minerals grew.  A new approach is therefore required which is capable of determining the temperature, salinity and composition of palaeo-fluids as well as resolving the timing and duration of fluid flow. Through analysis of authigenic K-feldspar cements using fluid inclusion petrography and microthermometry in conjunction with high-resolution UVLAMP Ar-Ar dating, this study has developed an integrated methodology capable of determining the parameters described above.  The methodology is outlined and through using core samples from the UK Atlantic Margin, the methodology was tested in a geologically complex area that has experienced several phases of rifting, basin-scale fluid flushing, magnetic intrusion and volcanic activity. The methodology was subsequently tested throughout the UK sector of the 480 Ma Laurentian Margin, a complex margin that has witnessed several phases of successive orogenesis. Although not intended as a definitive study of Ar-diffusion within authigenic K-feldspar, this research does provide a valuable data set from which discussion can begin.  Meaningful Ar-Ar ages were determined from authigenic K-feldspar which displays a subgrain microtexture.

In weak argillaceous rocks the unweathered strength may be barely sufficient to meet civil engineering reguirements and any reductjon due to weathering will be critical. This study investigates the weathering of the Lower Lias clays with particular reference to their petrography and engineering properties. Investigations revealed the Midland Basin of deposition to contain reasonable thicknesses of clay, relatively uniform in nature with a well developed weathered zone, From the available exposures, the weathering zone of the Blockley Clay pit was selected and sampled for laboratory investigations of; Structure, Mineralogy and Chemistry and Engineering Properties. The nature and orientation of the fissures in the unweathered clay were analysed. A close relationship was found to exist between the major joint set and the ground surface, with stress release due to excavation being almost negligible. Thin sections of the clay, examined for structural data, suggested that there exist layers or areas that have been disturbed as a result of density differences. Shear planes were found in both the unweathered and weathered clay, in the latter case often associated with remoulding of the material. A direct measure of remoulding was obtained from the birefringence ratio. The fabric was examined in closer detail using the scanning electron microscope. Mineralogy, as revealed by X-ray and optical techniques indicated illite as the dominant clay mineral, with kaolinite subsidiary; quartz, calcite, pyrite, chlorite/vermiculite are present as accessory minerals. Weathering changes this relationship, calcite and pyrite being removed early in the process, with illite being degraded. The cementing action of calcite and iron oxides was investigated however, this was shown to be negligible. Quantitative measurements of both fixed (with minerals) and free (oxide coatings) iron were obtained by atomic absorption, with the Fe 3+/ Fe2+ ratio obtained by Mossbauer spectroscopy, Evidence indicates that free iron oxide coatings only become important as a result of weathering with the maximum concentration in the very highly weathered material. Engineering index properties and shear strength values were taken throughout the profile, Relationships between moisture content and strength, liquid limit and iron (Fe) were obtained and a correlation between the weathering zomes and the shear strength/depth curve has been established.

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A palaeomagnetic study has been carried out on Vesuvian lava flows emplaced since 79 AD. This involved both palaeodirection and palaeointensity investigations of samples from sites on the W, S and SE slopes of the volcano. Thermal demagnetization of 3 component IRMs, susceptibility measurements and coercivity analyses have been carried out on one pilot specimen per site in order to identify the magnetic carriers and to estimate the magnetic grain size. The identificatìon of the primary direction of TRM was carried out following very stringent criteria (Incoronato, 1996). Palaeointensities were evaluated using both a modification of the Modified Thellier & Thellier method (McClelland et al., 1996) and the innovatìve microwave technique (Shaw et al., 1999). This study has shown that establishing whether or not different exposures or flows are contemporaneous can be established and, in most, but not all, cases can be undertaken successfully using magnetic information recorded by Vesuvian lavas to define the geomagnetic field direction and intensity at the time of their eruption. It is shown that numerous lava flows, outcropping on the W to S slopes of the volcano, must be associated to a large eruption in AD 1631, confirming some previous studies. A new age for a lava flow, ascribed in literature to the 1697 event, is suggested on the basis of both palaeodirection and palaeointensity investigations. Significantly different properties have been found between microwave and thermal experiments although they showed an exceptional level of agreement for the AD 1631 lava flow. In general the trend the palaeointensity variations was similar to that obtained by thermal processes for the last few centuries from other European, Mediterranean and Near East regions (Aitken et al., 1989).

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