No description available.

Alluvial fan construction within British Columbia was dependant upon temporary conditions resulting from deglaciation; there is no significant fan aggradation at present. Five study areas were selected from the semi-arid sections of the Fraser, Thompson, Bonaparte, South Thompson and Similkameen valleys. The Tertiary and Quaternary geo-morphic histories of these areas are similar in many respects--most significantly, one or more phases of Pleistocene glaciation were followed by fluvial and lacustrine aggradation--but vary regarding the amount of subsequent downcutting by major rivers. This ranges from several hundred feet in the Fraser and Thompson valleys to a few feet or none in the Similkameen and Bonaparte valleys. Stratigraphic evidence from the Fraser Valley indicates that fan building commenced soon after the valley floor became ice-free, probably whilst glacial conditions persisted in tributary basins. It continued during aggradation by major rivers and for sometime afterwards. In the Thompson and South Thompson valleys fans were most recently built upon degradational river terraces. The occurrence of Mazama volcanic ash within fans indicates that construction continued until after 6,600 years B.P. Fans were built during a phase of landscape readjustment from predominantly glacial to predominantly fluvial conditions. They resulted from the secondary deposition of glacial drift and locally weathered material by streams and mudflows. Fan composition was dependant upon the nature of the available material and upon the character of the parent basin. For example, the widespread occurrence of glacio-lacustrine silt in the Thompson Valley gave rise to fans composed of silty mudflow gravels. Generally, small, steep basins produced mudflows whereas larger basins had more constantly flowing streams which deposited fluvial gravels. Fan aggradation declined as the drift supply was exhausted; deposition of material derived by current weathering was insufficient to maintain the growth of the fans. After deposition ceased many fans were dissected as a result of local base-level lowering controlled by degradation of major rivers and/or fan-head trenching initiated as the debris supply declined. Fan-head trenching is best developed in the South Thompson Valley; base-level dissection predominates in the Fraser and Thompson Valleys. Where fan building persisted during degradation, multilevel fans were constructed. Statistical correlations among morphometric parameters describing fans and related basins indicate that basin characteristics exerted an influence upon fan geometry through the nature of the fan building stream. There relationships vary regionally, possibly reflecting lithologic, climatic and geomorphic contrasts. British Columbia fans are steeper and display a greater variation of morphometric relationships than fans of the arid American Southwest. Fans resulting from deglaciation are distinguished by use of the prefix "para-glacial". / Arts, Faculty of / Geography, Department of / Graduate

Pitt River, 30 km inland from. Vancouver, British Columbia at the southern margin of the Coast Mountains, links Fraser River estuary and Pitt Lake. Salt water seldom extends to within 10 km of Fraser - Pitt confluence; nevertheless, tides modulate Fraser flow and cause Pitt River to fluctuate 2 m and Pitt Lake as much as 1.2 m. There is an upstream movement of sediment in Pitt River from Fraser River, evidenced by identical mineralogy of Pitt River and Fraser River sediments, a decrease in grain size from the Fraser to Pitt Lake, and a predominance of flood-oriented bedforms in the river channel. A delta of 12 km2 area has accumulated at the lower (draining) end of the lake. The purposes of the study were to: (1) examine aspects of the hydrodynamics of Pitt River and Pitt Lake as a tidal system; (2) evaluate the effect of bidirectional flow on river and delta morphology; (3) determine processes of sediment movement in the river and of-sediment dispersal on the delta; and (4) estimate present sedimentation rate on the delta. Water Survey of Canada stage data from 3 locations in the system, used in conjunction with velocity measurements (profiles and tethered meter), revealed large seasonal and tidal variations in discharge. Calculations indicate that flood basal shear stress peaks early in the flow, whereas ebb currents have a lower basal, shear stress which peaks late in the flow. Thus, sediment moves farther forward on a flood flow than it moves back on the succeeding ebb. Studies of the river channel using hydrographic charts revealed regular meanders (^M = 6100. m) and evenly spaced riffles and pools which are scaled to the strongest flow (winter flood current, Qe). Meander point bars are accreting on the "upstream" side indicating deposition by the flood-oriented flow. The three dimensional geometry of the large-scale bedforms which cover the sandy thalweg of both river and delta channel was determined by echo sounding and side-scan sonar. Three distinct sizes (height/spacing = 0.8 m/10-15m; 1.5m/25-30 m; 3 m/50-60 m) of large-scale bedforms (sand waves) were found; their linear-relationship of height vs. spacing (XD) on log-log plot suggests a common genesis. The size appears to be related to channel geometry, not to depth of flow. Largest forms are found in reaches which shallow in the direction of water movement and smallest forms occur on relatively flat topography. The following tentative relationship is suggested for sandy meandering rivers: ^M/^B = Qe. Pitt delta morphology was studied with aerial photos and depth soundings. Its shape is considered an excellent example of sediment diffusion and deposition from a simple jet into a low energy lacustrine environment. Analysis of 190 sediment samples from river, delta, and lake bottom shows the sediment to be polymodal. Graphical partitioning of the cumulative probability plots reveals that sediments are composed of up to 4 log-normal distributions. Each distribution is interpreted as a population related to a process of sediment transport. Five subenvironments in the Pitt system are characterized by unique combinations . of these "process" populations. Cores in the delta topsets and lake bottom sediments reveal silt and clay rhythmites, interpreted as varves. The coarse layers are deposited during winter when discharge of Fraser River is low and tidally induced discharge in Pitt system is high. The fine layers are deposited during spring run-off when additional fines are added to the lake from the Pitt basin. 137Cs dating of sediments shows that as much as 1.8 cm/yr are accumulating in the active portions of the delta with an estimated 150 +/- 20 X 103 tonnes deposited annually. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

Sediments from the northern end of Juan de Fuca Ridge are Late Quaternary in age and contain widely correlatable cycles of turbidity current and hemipelagic sedimentation. Sediments from the Ridge were examined for their mineralogy, structure, components of the sand fraction, rates of sedimentation and grain size distribution to establish processes of sedimentation, stratigraphy, correlation and local hydrothermal relationships. Ten gravity and Phleger core sites along two profiles of the Ridge were examined in detail, one section was perpendicular to West Valley, the main spreading centre, and one section was within and parallel to West Valley. Sediment from Cascadia Basin was compared to the results of the Ridge study. Changes in sedimentation defined by core X-radiograph structure, components of the sand fraction and grain size distribution, indicated cycles of relatively coarse sediment overlain by finer bioturbated sediment with a repeated stratigraphic relationship in all but one Juan de Fuca Ridge core. Changes in sediment composition are attributed to brief, episodic, continent derived turbidity current deposition followed by lengthy periods of hemipelagic sedimentation for each cycle. Differences in composition exist between sediment of ridges and valleys, with a greater winnowed foraminiferal-hemipelagic and a lesser turbidity current influence in the former area. Radiocarbon dated foraminiferal-rich intervals from ridge sediments were exclusively Late Pleistocene with Middle Ridge sediment having an inferred 9000-9500 B.P. Late Pleistocene-Holocene boundary. Similar sedimentation cycles between Middle Ridge and valley localities enabled correlation of ridge and valley stratigraphy and the Late Pleistocene-Holocene boundary. A stratigraphic relationship based on the episodic deposition of continent derived turbidites exists between the northern end of Juan de Fuca Ridge and the continental Pacific Northwest. Pulses of turbidity current sedimentation coincide with initial interglacial warming trends during the Late Pleistocene. Holocene sedimentation for Juan de Fuca Ridge is of hemipelagic origin with rare local turbidity current deposition. Hydrothermal minerals were not detected. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

This study investigates the morphologic approach to sediment transport analysis and applies it to the Vedder River, British Columbia. The approach is based on the assumption that changes in channel morphology indicate sediment transport in the river. Despite the connection between these phenomena, only a few studies have examined this relation. The procedures, assumptions and limitations of the morphologic approach are discussed. It is more straightforward to construct a sediment budget for bed material than for wash material, as bed material travels relatively small distances. The Vedder River is a cobble gravel river with dyked banks. Therefore it is a good location for a study of the morphologic approach as bed material can be distinguished easily from wash material. The results of this study are important as aggradation in Vedder River has resulted in major flooding problems. Cross-section survey data were used to estimate volume changes along the Vedder River for incorporation into sediment budgets for several periods over the last decade. The construction of a sediment budget requires knowledge of at least one transport rate or transfer distance. Although the zero downstream transport assumption used in this study was found to be incorrect, it was retained as there are no transport rate measurements. Furthermore, the transport assumption is probably within the error ranges of the sediment budgets. Most of the errors in the sediment budgets were attributed to uncertainty in volume change estimates. When volume change estimates were calculated for different sets of cross-sections, the values varied significantly. This indicates that there is bias in the results. It is difficult to evaluate the degree of bias without a knowledge of actual channel changes. It. was found that the uncertainty in the transport estimates at Vedder Crossing ranged from ±8% to ±25%. These values compare favourably with error analysis results of direct measurements in the Fraser River (see McLean and Church, 1989). An analysis was performed to evaluate the cross-section density that is necessary to obtain a reasonable representation of actual channel changes. The average distance between cross-sections should be relatively smaller in reaches which have large variability in channel change patterns. It was suggested that cross-section spacing in the Vedder River should average between 250 and 300 m. The sediment budget results provide valuable information about the patterns of channel change and the magnitude of flows responsible for large amounts of deposition in the Vedder River. It was found that significant aggradation occurs during exceptional flood events. Most of the material is deposited in the several kilometers immedatiately upstream of the Vedder Canal. The morphologic approach provides a good method for evaluating the sediment transport regime of a river. The usual management time-scale ranges from several years to decades, which is coincident with the time-scale of this approach. Furthermore, the total field effort is less than that required for direct measurements. / Arts, Faculty of / Geography, Department of / Graduate

The Sustut Group within the study area is a nonmarine succession of fine to coarse grained elastics, deposited in an alluvial fan environment. Regionally, the Sustut Group is divisible into the Tango Creek and Brothers Peak Formations. In the study area, the two formations are entirely Late Cretaceous (Campanian to Maastrichtian) in age, based on palynological evidence. In the southern Sustut Basin, only the uppermost 400 m of the Tatlatui Member of the Tango Creek Formation is exposed. Sediments of the Tatlatui Member are divided into fine and coarse grained lithofacies. The fine grained lithofacies is composed of interbedded mudstone, siltstone and fine grained sandstone, which is interpreted as an alluvial plain deposit. Pebble conglomerate interbedded with coarse to medium grained sandstone comprise the coarse grained lithofacies which is considered to be a braided river deposit. The Brothers Peak Formation comprises 1 000 m of diverse elastics and tuffs, which are divisible into the lower and upper Laslui Member, and the overlying Spatsizi Member. The lower Laslui Member conformably overlies the Tatlatui Member of the Tango Creek Formation, and is characterized by several fining upwards sequences of cobble conglomerate to medium grained sandstone, attributed to deposition by high energy braided streams in the mid-fan region of an alluvial fan complex. Sediments of the upper Laslui Member are divided into a fine grained lithofacies consisting of mudstone, interbedded with lesser amounts of siltstone, fine grained sandstone and tuff beds, and a coarse grained lithofacies composed of orthoconglomerate, paracong1omerate and coarse grained sandstone. The fine grained lithofacies comprises the majority of the sequence and is interpreted as an alluvial plain deposit. Coarse grained sediments of the upper Laslui Member were likely deposited during stages of high water discharge, by major distributaries, sheetfloods and debris flows. The Spatsizi Member is gradational from the upper Laslui Member and is composed of sandstone/mudstone sequences interpreted as sandy braided stream deposits of an alluvial plain. Detrital components of the Tango Creek and Brothers Peak sandstones are mainly chert, quartz, plagioclase and volcanic rock fragments. Paleocurrent measurements and provenance considerations suggest source terranes were located to the east during Tango Creek deposition, and to the west during Brothers Peak deposition. In the southern Sustut Basin, the Tango Creek Formation documents uplift and erosion in the Omineca Belt and Paleozoic rock units, following accretion of the first composite terrane (terrane I) to the North American Margin. The Brothers Peak Formation is considered a result of local uplift and volcanic activity, accompanying the accretion of a second composite terrane (terrane II). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate