This study utilised U-Pb geochronology, and 40Ar/39Ar and (U-Th)/He thermochro-nology to delineate arc magmatism, metamorphism, and exhumation of the pericratonic Yukon-Tanana terrane in the McQuesten map area of west-central Yukon, Canada. SHRIMP U-Pb ages delineate Mid to Late Paleozoic arc magmatism and fit key units into the regional lithotectonic framework of the terrane. The juxtaposition of unmetamorphosed and predomi-nantly undeformed Devono-Mississippian rocks in the northwest of the study area with polydeformed and up to amphibolite facies metamorphosed rocks in the southwest suggests a crustal-scale discontinuity, the Willow Lake fault, bounds the two domains. The asymmetric distribution of 40Ar/39Ar ages across the fault suggest it is extensional, and was active in the Early Jurassic. Zircon (U-Th)/He ages delineate erosion of rocks in the northwest through the upper crust during the Late Triassic and Late Jurassic to Early Cretaceous followed by Mid-dle Cretaceous erosion of the southwestern domain and possibly fault reactivation.

In contrast to early work establishing the importance of earthquake-induced liquefaction in producing soft-sediment deformation (SSD) of the Navajo Sandstone, this report advances the use of SSD analysis to: characterize wet climatic conditions and flood events during the depositional history of ancient eolianites; discriminate the signatures of multiple deformation events from those of complex deformation features formed in a single event; and to document the occurrence of liquefaction features unrepresented in modern Earth analogues. The diversity of deformation styles, presented here, is very unusual in a report from a single formation; yet the high resolution of interpreted time relationships between various processes of deposition, erosion, water table fluctuation, and deformation is even more notable. These exceptional features derive from the extraordinary outcrops of the Colorado Plateau, which expose many large-scale (tens of meters) features throughout their entire extent and reveal an extended history of episodic deformation through thick (hundreds of meters) sections of cross-bedded units, which frequently continue along several kilometers of cliff face. Prior studies of fluid escape from unconsolidated sand that support the present work are outlined in Chapter II. These include laboratory simulations of liquefaction and fluidization as well as analyses of analogous deposits, both ancient and modern. Chapter III provides an overview of outcrop evidence, gathered during the course of this study, for dramatic alterations in the topography and sedimentation patterns of the Navajo erg. Interpreted perturbations include: the foundering of active dunes; sediment eruptions; and the subsidence of interdune surfaces. Chapter IV constitutes an example of the detailed analyses that support the overview of Chapter III. Outcrop features from a site in West Canyon, Arizona provide the basis for interpreting the subsidence of a dry interdune surface to a position several meters below the contemporary water table, followed by the filling of this depression with a succession of mass flow, lacustrine, and eolian deposits. Chapter V outlines the implications of various outcrop features for the prevailing model of soft-sediment deformation in the Navajo Sandstone. Proposed modifications of this model accommodate a broader range of deformation dynamics and specifically incorporate the impact of wet climates.

In contrast to early work establishing the importance of earthquake-induced liquefaction in producing soft-sediment deformation (SSD) of the Navajo Sandstone, this report advances the use of SSD analysis to: characterize wet climatic conditions and flood events during the depositional history of ancient eolianites; discriminate the signatures of multiple deformation events from those of complex deformation features formed in a single event; and to document the occurrence of liquefaction features unrepresented in modern Earth analogues. The diversity of deformation styles, presented here, is very unusual in a report from a single formation; yet the high resolution of interpreted time relationships between various processes of deposition, erosion, water table fluctuation, and deformation is even more notable. These exceptional features derive from the extraordinary outcrops of the Colorado Plateau, which expose many large-scale (tens of meters) features throughout their entire extent and reveal an extended history of episodic deformation through thick (hundreds of meters) sections of cross-bedded units, which frequently continue along several kilometers of cliff face. Prior studies of fluid escape from unconsolidated sand that support the present work are outlined in Chapter II. These include laboratory simulations of liquefaction and fluidization as well as analyses of analogous deposits, both ancient and modern. Chapter III provides an overview of outcrop evidence, gathered during the course of this study, for dramatic alterations in the topography and sedimentation patterns of the Navajo erg. Interpreted perturbations include: the foundering of active dunes; sediment eruptions; and the subsidence of interdune surfaces. Chapter IV constitutes an example of the detailed analyses that support the overview of Chapter III. Outcrop features from a site in West Canyon, Arizona provide the basis for interpreting the subsidence of a dry interdune surface to a position several meters below the contemporary water table, followed by the filling of this depression with a succession of mass flow, lacustrine, and eolian deposits. Chapter V outlines the implications of various outcrop features for the prevailing model of soft-sediment deformation in the Navajo Sandstone. Proposed modifications of this model accommodate a broader range of deformation dynamics and specifically incorporate the impact of wet climates.

The Jurassic J-2 surface is one of the more extensive unconformities of the Western Interior (U.S.A.). Stratigraphic relationships show that this is an angular unconformity, which developed first in the north and progressively moved south. An examination of features associated with the J-2 surface reveals detrital and diagenetic chert grains, ventifacts, polygonal fracture patterns, oscillation ripples, and paleotopographic relief. Some of these features indicate that the J-2 unconformity was a hot, dry, deflationary surface, and that the level of deflation on this surface was controlled, at times, by the height of the water table. The ventifacts are a lag deposit of the overlying Gypsum Spring Formation. Three possible variables involved in the formation of the J-2 surface are fluctuations in water table, disruption of sediment supply, and tectonic activity. For the Early-Middle Jurassic, these variables can be associated with increased rifting rates in the Atlantic Ocean. The increase in rifting rate raised eustatic sea level, which resulted in a larger area for deposition of marine sediments and a rise in continental water table. A higher water table would have trapped sediment that was previously available for sand sea (erg) formation. Furthermore, a higher sea level might have changed sediment supply and transportation routes. As the increase in rifting continued, tectonic movement and tilting of the North American plate occurred. This tilting caused the uplift and erosion of some deposits, and influenced the sites available for sediment preservation. / text

An investigation of shale pore structure and compositional/geochemical heterogeneities has been undertaken to elucidate the controls upon gas capacities of potential shale gas reservoirs in northeastern British Columbia, western Canada. Methane sorption isotherms, pore structure and surface area data indicate a complex interrelationship of total organic carbon (TOC) content, mineral matter and thermal maturity affect gas sorption characteristics of Devonian-€”Mississippian (D-€”M) and Jurassic strata. Methane and carbon dioxide sorption capacities of D-€”M shales increase with TOC content, due to the microporous nature of the organic matter. Clay mineral phases arealso capable of sorbing gas to their internal structure; hence D-€”M shales which are both TOC- and clay-rich have the largest micropore volumes and sorption capacities on a dry basis. Jurassic shales, which are invariably less thermally mature than D-€”M shales, do not have micropore volumes which correlate with TOC. The covariance of methane sorption capacity with TOC, independent of micropore volume, indicates a solute gas contribution (within matrix bituminite) to the total gas capacity. On a wt% TOC basis, D-M shales sorb more gas than Jurassic shales: a result of thermal-maturation induced, structural transformation of the D-€”M organic fraction. Organic-rich D-€”M strata are considered to be excellent candidates for gas shales in Western Canada. These strata have TOC contents ranging between 1-5.7 wt%, thermal maturities into the dry-gas region, and thicknesses in places of over 1000 m. Total gas capacity estimates range between 60 and 600 bcf/section where a substantial percentage of the gas capacity is free gas, due to high reservoir temperatures and pressures. Inorganic material influences modal pore size, total porosity and sorption characteristics of D-M shales. Carbonate-rich samples often have lower organic carbon contents (oxic deposition) and porosity, hence potentially lower sorbed and free-gas capacities. Highly mature Devonian shales are both silica and TOC-rich (up to 85% quartz and 5 wt% TOC) and as such, deemed excellent potential shale gas reservoirs because they are both brittle (fracable), and gas-charged. However, quartz-rich Devonian shales display tight-rock characteristics, with poorly developed fabric, small median pore diameters and low permeabilities. Hence potential `frac-zones' will require an increased density of hydraulic fracture networks for optimum gas production.

The Lower Jurassic stratigraphy of seven contrasting areas in western Europe is compared in order to seek evidence for a pan-Western European stratigraphic forcing mechanism. Sequencestratigraphic models are discussed and emphasis is placed upon the differing response of sedimentary systems in "accommodation space-dominated" and "supply-dominated" settings. Spectral gamma-ray data from clastic successions in the Wessex and Cleveland basins (England) are used to elucidate vertical trends. A proximal-distal model for control of Th/K ratios is advanced. Stage-frequency regressive-transgressive cycles in the two areas are shown to be closely correlative. Sedimentolgical logs and spectral gamma-ray data are presented for the carbonate ramp into turbidite sequence of Peniche (Portugal) and for a new exposure of the Pliensbachian-Toarcian in southern Germany. Systematic variation in clay mineralogy across Europe is suggested. Cycles in the Lower Jurassic of the North Viking Graben (Norwegian North Sea) are examined using wireline log correlation and the stratigraphic evolution of the Tethyan Rift in the Western and Southern Alps is reviewed. X-ray diffraction studies of the Pliensbachian-Toarcian interval in the Southern Alps are presented in order to elucidate sediment supply to the pelagic realm. The cycles observed in the English sections appear to be manifest widely across western Europe in a variety of tectonic and sedimentary settings. Sharp basinward facies shifts (candidate sequence boundaries) do not appear to be synchronous between basins. ⁸⁷SR/⁸⁶SR analysis of belemnites from the Portuguese and German sections confirms the regional applicability of the results of Jones (1992) and the utility of this technique in long range correlation. Carbon and oxygen analysis of the same material supplements the data of other workers and a direct relationship is suggested between relative sea level and organic carbon burial in the Early Jurassic.

The collection and analysis of a large number of belemnites and oysters with excellent biostratigraphic and diagenetic control has resulted in a highly detailed determination of the seawater Sr-isotope curve through the Jurassic and Early Cretaceous. The new data confirm the broad trends established by previous work, but the much sharper resolution of the new data allows the application of Sr-isotope stratigraphy with an optimal stratigraphic resolution of ± 1 to 4 ammonite subzones (± 0.5 to 2 Ma). The data show a general decline from the Hettangian (Early Jurassic) to a minimum in the Callovian and Oxfordian (Middle/Late Jurassic). This is followed by an increase through the Kimmeridgian (Late Jurassic) to a plateau reached in the Barremian (Early Cretaceous). In addition, there are major negative excursions in the Pliensbachian/Toarcian (Early Jurassic) and Aptian/Albian (Early Cretaceous). Stable isotope data collected from belemnites and oysters have resulted in the most extensive Jurassic δ¹³C and δ¹⁸O database to date. While both the carbon and oxygen data appear to give reasonable marine signals, the scatter in the data suggests that future research must document possible biological fractionation effects and develop better indicators for the diagenetic alteration of 613C and 6i 8O. The final chapter documents an unexpected correlation between sudden shifts in the Sr-isotope curve, the occurrence of positive 513C excursions, and the eruption of flood basalts. In the Jurassic and Cretaceous there is a correlation in time between sudden downward shifts in the Sr-isotope curve (Pliensbachian, Aptian, Cenomanian/Turonian), the occurance of positive 613C excursions, and the eruption of flood basalts. Each of these major downward shifts in the Sr-isotope curve is followed by a sudden upward shift, which although associated with a positive 613C excursion is not associated with an episode of flood basalt volcanism. In the Cenozoic the Sr-isotope curve no longer displays downward shifts, but the correlation continues between the occurrence of flood basalts and positive 513C excursions. Several lines of evidence suggest that the eruption of flood basalts is associated with pulses of hydrothermal activity, and that this hydrothermal activity brings about the conditions necessary for the genesis of carbon-burial events.

The offshore facies of the basal Lias of S.Britain was studied as a typical example of an open-marine cyclic sequence. The sedimentology, geochemistry and power-spectral analysis were investigated in order to understand the cause of the interbedded rock types. Three sediment types were deposited on the sea-floor: light marl, dark marl and laminated carbonate-rich shale. Calcite microspar, the dominant carbonate component, appears to have been formed from the neomorphic aggradation of coccoliths supplied in zooplankton faecal pellets. During sulphate reduction, the most carbonate-rich horizons in the light marl and laminated shale beds were cemented by carbonate, producing early diagenetic limestone and laminated limestone beds and nodules. Walsh power-spectral analysis of several measured sections in the basal Lias indicate that two regular sedimentary cycles, with periods of tens of thousands of years, are present. The regularity, stability and periods of the cycles invokes the Milankovitch Theory of orbital forcing of sedimentation; the cycles thus probably represent periods of 41,000 and 21,000 years. The sedimentation appears to have been linked to climatic variation by the levels of runoff and the formation and destruction of wedges of brackish water. During dry periods relatively little runoff and low clay input allowed turbulent, oxygenated bottom-waters and the deposition of burrowed, organic-poor marl. During wet periods, brackish wedges caused widespread density stratification, bottom-water anoxia and high clay inputs that resulted in laminated shale beds. Walsh power spectra were generated for one Silurian, five Upper Lower Jurassic, one Kimmeridgian and one Oligocene formation. Unexpectedly the Early Jurassic appears to have been dominated by the Milankovitch cycles related to obliquity and precession rather than eccentricity. Of the thirteen spectra produced, including five from the basal Lias, ten (or about 80%) contain evidence for regular sedimentary cycles consistent with orbital forcing of sedimentation. Therefore the Milankovitch Theory should be considered whilst investigating open-marine 'cyclic' sequences.

An investigation of shale pore structure and compositional/geochemical heterogeneities has been undertaken to elucidate the controls upon gas capacities of potential shale gas reservoirs in northeastern British Columbia, western Canada. Methane sorption isotherms, pore structure and surface area data indicate a complex interrelationship of total organic carbon (TOC) content, mineral matter and thermal maturity affect gas sorption characteristics of Devonian-€”Mississippian (D-€”M) and Jurassic strata. Methane and carbon dioxide sorption capacities of D-€”M shales increase with TOC content, due to the microporous nature of the organic matter. Clay mineral phases arealso capable of sorbing gas to their internal structure; hence D-€”M shales which are both TOC- and clay-rich have the largest micropore volumes and sorption capacities on a dry basis. Jurassic shales, which are invariably less thermally mature than D-€”M shales, do not have micropore volumes which correlate with TOC. The covariance of methane sorption capacity with TOC, independent of micropore volume, indicates a solute gas contribution (within matrix bituminite) to the total gas capacity. On a wt% TOC basis, D-M shales sorb more gas than Jurassic shales: a result of thermal-maturation induced, structural transformation of the D-€”M organic fraction. Organic-rich D-€”M strata are considered to be excellent candidates for gas shales in Western Canada. These strata have TOC contents ranging between 1-5.7 wt%, thermal maturities into the dry-gas region, and thicknesses in places of over 1000 m. Total gas capacity estimates range between 60 and 600 bcf/section where a substantial percentage of the gas capacity is free gas, due to high reservoir temperatures and pressures. Inorganic material influences modal pore size, total porosity and sorption characteristics of D-M shales. Carbonate-rich samples often have lower organic carbon contents (oxic deposition) and porosity, hence potentially lower sorbed and free-gas capacities. Highly mature Devonian shales are both silica and TOC-rich (up to 85% quartz and 5 wt% TOC) and as such, deemed excellent potential shale gas reservoirs because they are both brittle (fracable), and gas-charged. However, quartz-rich Devonian shales display tight-rock characteristics, with poorly developed fabric, small median pore diameters and low permeabilities. Hence potential `frac-zones' will require an increased density of hydraulic fracture networks for optimum gas production.

The organic-rich mudrocks of the Jurassic Fernie Formation in British Columbia, Canada contain unusual silica concretions. The silica originated from dissolved volcanic ashes found in the Highwood Member. A lack of radial trends in d13C and internal zonation demonstrate that these concretions grew pervasively. Stable isotope data from calcite inter-grown within the silica matrix (d13C and d18O) indicate that the concretions formed during sulfate reduction and methanogenesis. The d34S revealed a suppressed sulfur fractionation and suggest that they formed in a system that became progressively closed. The Fernie concretions offer insight into the formation of siliceous concretions in marine environments.