A dynamic mathematical model has been constructed for the computer simulation of sedimentation in free meandering streams. The system is defined in terms of form and process, and component mathematical models (with mainly deterministic, but also probabilistic, characteristics) are formulated for the prediction of the following aspects of the system for a given physical situation and a single time increment; (l) The characteristics of the plan form of free meanders; (2) The movement of meanders in plan, and definition of cross sections across the meander in which erosion and deposition are considered in detail; (3) The hydraulic properties of the channel and the erosional and depositional activity within the channel as defined in specific cross sections; (4) Whether neck or chute cut off will occur; (5) A relative measure of the discharge during seasonal high water periods, which s is used in (3) and (4); (5) Aggradation. The limitations, qualifications and validity of the component mathematical models are discussed during their development, as is the input required. The overall model has been translated into a FORTRAN IV computer program and a set of experiments with selected input parameters has been performed. The results and their implications are fully documented and compared qualitatively with recent and ancient fluviatile sedimentation. The shape of simulated pointbar sediments, as controlled by channel migration over floodplains of variable sediment type, agrees broadly with the natural situation. Sheet deposits cannot be simulated because large-scale meander-belt movements are not accounted for; this also inhibits generation of thick sequences of alluvial sediments. When channel, migration is combined with a constant aggradation rate the model predicts a general slope (relative to the land surface) of facies boundaries and scoured basal surfaces upward in the direction of channel movement. If aggradation sufficiently increases the thickness of fine grained overbank material, there is a channel stabilisation effect. Epsilon cross-stratification, which represents the shape of a pointbar surface before falling-stage deposition (lateral and vertical), may be picked out in the simulated sediments. The epsilon unit thickness is that measured from bankfull stage down to the lowest channel position existing prior to deposition. The model records the characteristic fining upwards of grain sizes in the pointbar, and the systematic distribution of sedimentary structures. Channel migration combined with seasonal scouring and filling across the channel produces a characteristic relief in the basal scoured surfaces and the grain size and sedimentary structure boundaries. A related lensing and inter- fingering of grain size and sedimentary structure facies may also be present. The model also records large-scale lateral changes in grain size and sedimentary structure associated with changes in the shape of developing meanders. It is shown that a complete sequence of pointbar sediments capped by overbank sediments would rarely be preserved in the moving-phase situation. Such preservation only becomes likely when an aggrading section lies out of range of an eroding channel for a considerably longer time span than it takes a meander to move one half-wavelength downvalley. Deep channel-scours have a higher preservation potential than contemporary shallower ones. Where appropriate field data exist the model can be used in the more accurate recognition of ancient fluviatile sediments. Inferences may be made about the erosion-deposition processes operating in the ancient channel system, and the geometry and hydraulics of the system can be alluded to. A representative application of the model to the quantitative interpretation of an ancient pointbar deposit is illustrated. There is reasonable agreement between the natural and the simulated deposits, and a broad quantitative picture of the palace environment of sedimentation is obtained.

The aim of this research was to examine the depositional architecture of the Northern Mauritanian passive margin, West Africa, in order to infer the geological evolution from Mesozoic to Recent. The study is based on a seismic stratigraphic analysis of 2D and 3D seismic reflection data (18000 km2), well data, outcrops and published work. The results are summarised on fifteen paleogeographic maps and key points in the sedimentary and tectonic evolution of this study can be made. Important subsidence in the southern area occurred from the Jurassic to the Turonian, which caused the development of a fractured flexure zone. This was the main tectonic activity clearly seen in the study area. During the Early Cretaceous, the entire study area was located in a siliciclastic deep-water slope environment. From the Late Cretaceous to the Paleocene, the northern study area became progressively shallower and a carbonate platform developed, while deltas were supplying sediment to the deep-water slope in the southern study area. The Paleocene Thermal Maximum climatic event caused the demise of the carbonate platform in the northern area. From the Middle Eocene to the Recent, most of the area was in a siliciclatic deepwater slope environment. Rivers and deltas that drained the adjacent craton were supplying sediment to the area, which exhibits a complex architecture of gravity and bottom current deposits. Presently, numerous deep-water tributary channels incise the seabed of the study area. This study represents the first reconstruction of the paleoenvironmental evolution of the Mauritanian passive margin from Mesozoic to Recent.

Cone penetration tests (CPTs) have been developed for engineering investigations of sands and finer sediments. CPTs produce high resolution, repeatable and continuous records to depths of several tens of metres, and resemble wireline logs used in the petroleum industry. It is the objective of this dissertation to demonstrate that they can be used for facies analysis in a similar manner, by using these data to develop a facies model for the modern Fraser River delta, British Columbia, Canada. CPT data provide reliable estimates of sediment type and gram size, so that bed thicknesses, sharp and gradational contacts, coarsening and fining upward sequences, bed continuity and dips can be readily identified. The facies model of the Fraser delta is based on a database of over 800 CPTs and 20 continuously cored boreholes. These data demonstrate that the topset is dominated by a nearly continuous sharp-based sand unit that is 8 to 30 m thick, fines upward and is interpreted to represent a complex of distributary channel deposits. The widespread distribution of this sand unit is the result of distributary channel migration in a tidal flat setting and avulsion or channel switching in the upper delta plain. The sand unit is gradationally overlain by a thinner sequence of interbedded sands and silts deposited in tidal flat, abandoned channel and floodplain environments. Deposits of the upper foreset (<60 m) dip up to 7° seaward and are dominated by silts, interbedded and interlaminated with sands. Several intergradational facies, ranging from dominantly silt to dominantly sand, occur and represent increasing proximity to active distributary mouths. These sediments are organized into metre-scale sandy and silty coarsening-upward sequences that are interpreted to represent annual deposits, and sharp-based sand units that represent sedimentary gravity flow deposits. Deeper foreset deposits are dominated by bioturbated silts. The distribution of facies on both the topset and the foreset has been controlled by the interaction of tidal and fluvial processes. CPT data played a key role in developing this facies model of the Fraser River delta. Most facies have distinct CPT signatures. For example, the topset sand unit and overlying deposits have a CPT signature comparable to the “bell-shaped” gamma ray log signature typical of channel deposits. In the foreset, the seaward dips, the coarsening upward sequences and the sharp-based sands are readily observable on CPT data. Although cores were essential to confirm the facies significance of these signatures, the large volume of CPT data permitted recognition of facies distributions and relationships “at a glance” throughout the delta, rather than at the relatively few site where continuous cores were available. Furthermore, CPTs can be acquired for a fraction of the cost of continuous cores, so that CPT data are potentially an invaluable tool for stratigraphic investigations of other modern sedimentary environments dominated by sands and finer sediments. / Graduate

This study comprises an investigation of the source and supply of coarse sediment input to a semi-arid channel reach. Despite a growing body of lIterature documentIng research of various aspects of sediment response in semi-arId areas, few studies attempt to integrate processes active in specific source areas wIth sediment supply to the channel. Detailed In the present study is an account of the processes active in the study area, identifIcation of source environments, a discussion of some of the factors affecting supply, a comparison of the effectiveness of gravItatIonal and fluvIal supply processes and an estImatIon of the time sequence of sediment supply to and removal from a channel reach. The above aspects of sediment supply are embodied In the aims set for the study. The study is conceptualIsed withIn the framework of a coarse sedIment supply model. The model is formulated from supporting literature and tested in the light of the results obtained through an investigation of the above aspects of sediment supply in the specIfic study area. The model is prImarily a qualitative one and the data collected intended to strengthen the qualitative nature of the model, while at the same time add at least some measure of quantification. Several reasons for studyIng coarse sediment behavIour in semI-arid areas are identIfied and include the need to improve the present lack of understanding of the relatIonship between supply and removal of sediment, the temporal dIstributIon of sediment discharge and the relatIve contrIbutions of coarse sediment to the overall load of rivers. The study area is located within the semi-arid Ecca basin north-east of Grahamstown. A specifIc channel reach is chosen withIn a sub-catchment (catchment B) of the Ecca catchment area as it has a variety of channel bank environments, is accessible through the entire reach, and the proximity of a raingauge and flow measurIng weir provide the necessary hydrometeorological inputs. The methods of observing sediment response from five data collection sites Include the use of slope or bank base sediment traps, erosion pins, tracer particle monitoring. sequential photographic surveys, and channel bed surface profile surveys. Hydrometeorological data is provided by records drawn from the data bank at the Hydrological Research Unit. Rhodes University. All rainfall records as well as channel flow data are available in the form of continuous records. Rainfall amount and intensity for any period could be extracted from these records. Data collection is confined to a period of two years, during which time the study area was visited on an approximate monthly basis. The index of erosivity (EI₃₀) could also be calculated from the hydrometeorological records and has been used as an integrated measure of rainfall intensity over the monthly period between site visits. The results are presented on a sample day for sample day basis. The sediment response data together with hydrological data is represented graphically for each sample day, of which there were nineteen. Discussion and interpretation of the results is left to a separate chapter. The interpretation of the results are based largely upon graphical representation of data time series and of interrelationships between some of the variables measured. The limited number of sample days together with the assumed auto correlation present in much of the data precluded the use of simple statistical testing procedures. The use of more complex procedures is not considered worthwhile and is unlikely to add to the interpretation of the results. Bedrock weathering is found to be a fairly active producer of coarse sediment on exposed shale bedrock outcrops through which sections of the channel are cut. The transport of the weathered detritus to the channel is attributed to a combination of gravitational and fluvial transport processes, with each process dominating at different times, depending on the magnitude of the climatic input. A tentative comparison of the effectiveness of the two processes reveals that both are capable of transporting similar amounts of sediment but on different time scales. The trends of sediment supply from the various bank environments display remarkable similarity , suggesting a measure of consistency of response to climatic input through the entire reach. Source areas of coarse sediment identified were limited to a small percentage of the total valley area and consisted almost entirely of the immediate channel environment. A tributary gully appears to be an important source of coarse sediment during fluvially dominated supply episodes, while the channel banks supply sediment on a quasi-continuous basis. The total yields for each source environment were extrapolated from the sampled amounts, revealing that channel banks are the predominant source environments. An attempt is made to assess the role of various factors which might affect sediment supply. The factors include rainfall amount and intensity, channel flow, geology/lithology, dip of strata, aspect of channel banks and size of weathered material. The findings, though not conclusive, do give some indication of the role of the above factors. It is suggested though that this particular aspect of sediment supply receive further attention in future research. Discussion on the time sequence of supply to and removal from the channel draws attention to a pulse- like movement of sediment 'waves' through the channel, and two scales of removal-accumulation cycles are identified. Finally the validity of the model is assessed and with the exception of a tributary inflow process not envisaged in the original model, is found to be an accurate representation of sediment supply in semi-arid areas, in both its static and dynamic phases. The suggestion is offered that future research on the sediment supply system, in all climatic regimes, can be conceptualised within the context of the basic model proposed in the present study. Specific components of the model should be quantified by numerous individual research efforts, and in this way, serve to build up the model into a widely applicable tool with which to interpret sediment supply

Most of the Great Basin sediment-hosted gold deposits are located along well defined, northwest-striking trends. Trends coincide with faults, intrusive rocks and magnetic anomalies. Sedimentary host rocks are siltstone, sandstone, conglomerate, argillic, interbedded chert and shales. Silty bedded silty dolomites, limestone and carbonaceous shales are the most favourable hosts. High, and locally, low-angle faults are very important structural features related to the formation of the ore bodies. High-angle faults are conduits of hydrothermal fluids which react, shatter and prepare the favourable host rock. Decalcification, silicification, and argillization are the most common hydrothermal alteration types. Jasperoid (intense silica replacement) is a significant characteristic; not all of these deposits are gold-bearing. Most deposits contain both oxidized and unoxidized ore. Fine grained disseminated pyrite, arsenian pyrite, and carbonaceous material are the most common hosts for gold in many deposits. These deposits are also characterized by high Au/Ag ratios, notable absence of base metal and geochemical associations of Au, As, Sb, Hg, Ba and TI. Recently numerous sediment-hosted gold deposits have been recognized in different regions of the world. They vary in their size, grades, textwe, host rock lithology, degrees of structural control and chemical characteristics. However, they have many common features which are very similar to the general characteristics of sediment-hosted gold deposits in the Great Basin, U.S.A. Besides these similarities, several unusual features are recorded in some newly discovered deposits elsewhere, such as predominant fault controlled paleokarst related mineralization and the lack of two very common trace elements (Hg, TI) in Lobongan/Alason, Indonesia; and Early Proterozoic age metamorphosed host rocks and lack of Sb in Maoling, China. The discovery of the deep ores in the Post-Betze and Rabbit Canyon, Nevada, proposed sediment-hosted Au emplacement at deeper level (4 ± 2 km; Kuehn & Rose, 1995) combined with a lack of field evidence for paleowater table and paleosurface features has ruled out a shallow epithermal origin. Recent discoveries in other parts of the world throw important new light on the ongoing genetic problems. Intrusive rocks are present in nearly all sediment-hosted gold deposits. Numerous intrusion-centred districts worldwide are characterized by tWo or more different mineralization types and consequently by metal zoning. Sediment-hosted gold deposits are proposed as a distal part of intrusion-centred magmatic hydrothermal systems (Sillitoe &Bonham, 1990).

The pre-Jurassic tectonic events of the area controlled the nature of sedimentation. These tectonic events were the result of movements of the members of the tectonic framework. The nature of the tectonic framework was established during Beltian sedimentation and was inherited by the Paleozoic era. During the Paleozoic era, the movements of various members of the tectonic framework resulted in four sequences or cycles of sedimentation. Tectonism and its control upon sedimentation from Beltian to pre-Jurassic time is shown as Beltian sedimentation and the succeeding sedimentary cycles are discussed. Type localities are defined for the Beltian and Paleozoic strata of each sequence as they occur in the area. Problems of age determination for the stratigraphic units are discussed and the correlation of these units within and beyond the are presented. These correlations show the relationship of the stratigraphic nomenclature of Montana and Alberta. Since the thesis is mainly limited to published information, it indicates the present status of published geological thought in the area. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

One technique that is commonly used to replace the costly daily sampling of sedimentconcentration in assessing sediment discharge is the "rating curve" technique. This technique relies on the form of the relationship between sediment concentration and water discharge to estimate long-term sediment loads. In this study, a regression/time-series approach to modelling the relationship between sediment concentration and water discharge is developed. The model comprises of a linear regression of the natural logarithm of sediment concentration on the natural logarithm of water discharge and an autoregressive time-series of order one or two for the errors of the regression equation. The main inferences from the model are the estimation of annual sediment loads and the calculation of their standard errors. Bias correction factors for the bias resulted from the inverse transformation of the natural logarithm of sediment concentration are studied. The accuracy of the load estimates is checked by comparing them to figures published by Water Survey of Canada. / Science, Faculty of / Statistics, Department of / Graduate

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