No description available.

No description available.

No description available.

No description available.

Sedimentary cores from northern margin of the South China Sea have been studied to monitor the intensity of physical erosion and chemical weathering associated with the regional monsoonal climates during the Holocene. The tectonically quiescent Pearl River preserved an over 10-meter-thick continuous deposit in its delta, while ODP Site 1144 on the northern slope has captured sediment that has been dominantly discharged by mountainous rivers on the Taiwan island, which are situated in an active tectonic setting. Geochemical, mineralogical and isotopic analyses were performed on the cores at resolution equivalent to decadal years. Reconstructed weathering records in general show coherence with the speleothem rainfall records however with different variation patterns. Since the Early-Holocene climate optimum, chemical weathering remained strong until~5.5 ka in the Pearl River, while ODP Site 1144 only captured a short period of chemical weathering which predates 8 ka. Humidity indicator hematite/goethite, indicative of dry conditions at that time, suggests that the slope deposition was reworked, i.e. sediment that had been strongly weathered during glacial times on the Taiwan Strait was eroded to the slope by strong monsoon rains until the region was submerged by rising sea levels after ~8 ka which finally truncated the sediment supply. In the Pearl River delta, strongly weathered sediment from last glacial is also seen underlying the Holocene sediment. Data from the post-9.5 ka section of this site show a clear trend of more altered sediment correlating with a stronger monsoon. Again, enhanced reworking of fluvial terrace deposits is believed to be the cause of this chemical perturbation. After ~2500 years ago, sediment in Pearl River delta shows a marked rise of weathering intensity towards the highest level measured from modern river basin, despite a slightly strengthened monsoon. This change was most likely driven by human settlement and erosion of older weathered soils following the initiation of agriculture in the river basin.

Observations from modern day rivers are linked to the rock record and the implications for reservoir modelling of fluvial systems are investigated. In order to investigate the geomorphology of modern day fluvial systems, scale invariance and bar dimensions were evaluated. To provide a link between modern analogues and ancient deposits, an outcrop of the Kimmeridgian Salt Wash Member (Morrison Formation) in south-central Utah was described in detail, focusing on lithofacies distributions and dimensions of fluvial deposits in the rock record. The outcrop illustrates the difficulties in distinguishing between different planform geometries in the rock record. Collected data include detailed outcrop descriptions, sedimentary logs, GPS (Global Positioning System) measurements and a LiDAR (Light Detection And Ranging) survey. The interpretation of the different fluvial facies types was imported into the modelling software Paradigm GOCAD®. The resulting threedimensional digital outcrop model of the sedimentary facies was used as a training image to generate geologically realistic heterogeneities within three-dimensional models of fluvial systems, focusing on the small scale intra-channel and intra-bar heterogeneities. This study shows that bar dimensions are scale invariant and independent of planform geometry, climate, tectonic setting and gradient. Each river has the potential to create a range of planform geometries as well as facies assemblies. And without exposure in planview, it is not possible to confidently define a rock record fluvial deposit as braided or meandering. Irrespective of channel planfom, bars are the key architectural element that is primarily preserved in the rock record. Stacked bar complexes are bounded by accretion surfaces that are likely to represent the main barriers to fluid flow within fluvial channel deposits. Consequently, to increase the accuracy of fluvial reservoir models it is important to populate any channel element with accurate bar dimensions and associated bounding surfaces.

The Birimian rocks of southern Ghana host world-class gold deposits yet no equivalent-sized deposit has been found in the Birimian rocks in northwest Ghana. The reported gold occurrences in the area suggest a favourable environment for concealed mineralisation if the regolith and landscape evolution can be unravelled. A geochemical exploration model based on the evolution of the regolith-landform can help guide the choice of exploration methodology appropriate for the region. The developed regolith map classifies the landscape into ferruginous (F), relict (R), erosional (E) and depositional (D) domains. Depositional areas cover 72% whereas the remaining 28% represents residual environments. Discrimination, characterisation and identification of regolith materials were carried out by pit and outcrop mapping. Regolith geochemical data provided regolith profile information which helped to distinguish residual regolith from transported types. Binary plots of major and trace element geochemical data were used to determine the compositional variability and different regolith types. Superimposing geochemical data on the regolith map identified residual and transported anomalies, and thus prioritized the weak, subtle and discontinuous anomalies. Gold, Ag and As relations in the regolith were also useful in determining the anomaly type and presence of gold mineralisation. High Au-low Ag with smooth dispersal patterns represents residual anomalies whereas spiky dispersion patterns with high Au-high Ag characterize transported anomalies. The released As into the regolith appears counteracted by the precipitation of Fe-oxyhydroxides, which efficiently scavenge As3+ and As5+ at neutral pH in the regolith, resulting in the weak As concentrations in the analysed samples. Hence it may not be an appropriate pathfinder element for Au in the study area. The regolith mapping techniques devised for the study can be used to map complex regolith terrains. The landscape evolution model developed for the area will provide useful insight into the irregular distribution of the regolith and help in designing exploration techniques suitable for the Lawra belt and similar complex regolith terrains of the savannah regions.

This thesis describes two Carboniferous fluvio-deltaic sequences in which river channel fills are dominant, the Roaches Grit Group (Namurian R2b) in the south-west Pennines and Lower Pennant Measures (Westphalian C) in the Rhondda Valleys. In addition, sedimentation in non-meandering sandy rivers is reviewed and discussed. Non-meandering rivers can be classified into straight and two braided types. In the former, alternate bars attached to the channel sides give rise to solitary sets of cross-bedding which are eroded during falling stage. In braided rivers, channel fill characteristics vary with discharge regime. These range from regimes with pronounced short lived flood peaks with rapid rising and falling stages, probably producing relatively uniform cross-bedded fills, to those which show limited variation between high and low stage and where high stage sediments are mainly reworked. Multiple channel braided rivers should have channel abandonment sequences showing alternating periods of bedform movement and ponded water. Palaeocurrents vary with regime and some braided rivers may show a variance similar to that of meandering rivers.

No description available.

Detailed facies mapping and microfacies study were employed to improve upon sedimentological models for the margins of a carbonate platform of late Visean (Asbian - Brigantian) age in north Derbyshire, UK. The early Asbian upper slope was built of automicrite stiffened with early marine cements. The system also included marginal bioclastic sand shoals, situated c.500m from the platform break, which was in slightly deeper water, basinward from the shoals. Despite this bevelled configuration the upper slope received only low volumes of shallow water allochems until late in the early Asbian third order cycle. This early phase was characterised by nearly vertical aggradation of the margin. The later increase in basinward export resulted in a pulse of progradation and more mixed lithologies on the slope. In the late Asbian to Brigantian, the northern margin experienced an episode of local tectonic subsidence, resulting in back-stepping of c. 1km. However, high productivity by the benthic community enabled the margin to recover and build back to the previous platform break within three, fourth order, cycles. During this phase little automicrite was produced, or preserved, on the upper slope, production of automicrite moved to bioherms on the outer platform. Export of coarse bioclastic material to the mid and lower slope resulted in accumulation below a largely by-passed upper slope area. The southern margin also subsided in the Brigantian, but low productivity by a slightly stressed community meant the margin did not recover fully and remained as a low-angle slope, often dominated by the deposition of mud and silt exported from the platform interior. This, and the occurrence of ooids only on the southern margin, suggests the south to be a leeward margin. The facies architecture and the geometry of the margins were controlled by the interaction between eustatic sealevel changes and local tectonics.