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This paper examines particle settling dynamics in a tidally‐influenced delta, including observations of convective settling, strongly modulated by seasonal discharge and tidal cycles. Long time series of Acoustic Doppler Current Profiler backscatter, a proxy for suspended sediment concentration in the water column, current and sediment accumulation measurements from the slope of the Fraser River delta show variability of sedimentary processes over timescales from semi‐diurnal to annual. Acoustic Doppler Current Profiler backscatter shows a lagged response to river discharge and strong diurnal/semi‐diurnal variability. Most of the tidal cycle is characterized by a buoyant effluent plume. During the ebbing phase of diurnal major tides, discrete settling events are observed extending through the entire water column. The pulse‐like nature of these events is the result of downward plunging fingers characteristic of convective settling, similar to those observed in laboratory flume experiments, and appear to be initiated at the interface between the surface buoyant plume and the underlying ambient water. Currents show strong variability in a three‐layer water column. The surface plume shows offshore and southward directed transport of sediments. The remaining water column is influenced by tidal flows, but near surface and intermediate water‐depth currents are out of phase by several hours, indicating a stratification of the basin water and decoupled propagation of surface and internal tides. This phase lag is unlikely to cause discernible facies changes, but may have implications for basin‐fill patterns in restricted basins with strong tidal range. The results of this work will help to better understand river mouth sedimentation processes and dispersal patterns in other modern deltas and in the geological record. [ABSTRACT FROM AUTHOR]

Sediment waves are commonly observed on the sea floor and often vary in morphology and geometry according to factors such as seabed slope, density and discharge of turbidity currents, and the presence of persistent contour currents. This paper documents the morphology, internal geometry and distribution of deep‐water (4000 to 5000 m) bedforms observed on the sea floor offshore eastern Canada using high‐resolution multibeam bathymetry data and seismic stratigraphy. The bedforms have wavelengths of >1 km but fundamentally vary in terms of morphology and internal stratigraphy, and are distinguished into three main types. The first type, characterized by their long‐wavelength crescentic shape, is interpreted as net‐erosional cyclic steps. These cyclic steps were formed by turbidity currents flowing through canyons and overtopping and breaching levées. The second type, characterized by their linear shape and presence on levées, is interpreted as net‐depositional cyclic steps. These upslope migrating bedforms are strongly aggradational, indicating high sediment deposition from turbidity currents. The third type, characterized by their obliqueness to canyons, is observed on an open slope and is interpreted as antidunes. These antidunes were formed by the deflection of the upper dilute, low‐density parts of turbidity currents by contour currents. The modelling of the behaviour of these different types of turbidity currents reveals that fast‐flowing flows form cyclic steps while their upper parts overspill and are entrained westward by contour currents. The interaction between turbidity currents and contour currents results in flow thickening and reduced sediment concentration, which leads to lower flow velocities. Lower velocities, in turn, allow the formation of antidunes instead of cyclic steps because the densiometric Froude number (Fr′) decreases. Therefore, this study shows that both net‐erosional and net‐depositional cyclic steps are distributed along channels where turbidity currents prevail whereas antidunes form on open slopes, in a mixed turbidite/contourite system. This study provides insights into the influence of turbidity currents versus contour currents on the morphology, geometry and distribution of bedforms in a mixed turbidite–contourite system. [ABSTRACT FROM AUTHOR]

Presents reply to the criticism of the research paper related to sediment intrusion and rheoplasis in Pennsylvanian fluvial strata of eastern Canada, prepared by the author, as of February 1989. Evaluation of the hypothesis of researchers H.W. van de Poll and I.M. Patel, regarding diapiric intrusion of siltstone into sandstone; Explanation regarding the visibility of two blocks of siltstones at Alma, Michigan; Reason for the absence of explanation of flutes and other structures in the research paper.

Discusses the research paper prepared by researcher A.G. Plint, regarding the concept of sediment intrusion and rheoplasis, in Pennsylvanian fluvial strata of eastern Canada, as of February 1989. Criticism of Plint's description of occurrences of slump blocks of Alma, Michigan, in the paper; Omission of the fluted mangled mass of twisted mudstone and sandstone in the paper; Demonstration regarding the formation of mudblocks and flute moulds in this area.

A thick late Pleistocene sequence comprising multiple beds of massive diamict facies resting on outwash gravels, occurs along the Bow River, near Banff, Alberta. Diamicts have a simple sheet-like geometry which dip downvalley at between 5° and 10°, with largely conformable bedding contacts. The sediments are strongly bimodal in texture, consisting of clasts supported by a silty sand matrix. Prolate clasts show a weak a-axis alignment parallel and transverse to the trend of the Bow Valley with a weak imbrication. Clasts of soft sediment are common. The diamict sequence has a maximum thickness of 30 m, infills the valley floor over an area of approximately 12 km[SUP2] and buries a channeled topography cut on the surface of underlying outwash gravels. Abandoned braided channels, veneered by windblown sand containing volcanic tephra dated at 6600 yr BP, occur on the infill surface. Diamict facies were emplaced as subaerial debris flows derived by the mixing and remobilization of large volumes of outwash and glaciolacustrine sediment. Orientation data from clasts and a few basal grooves indicate that debris was derived upvalley and from adjacent valleyside slopes. A major episode of debris flow sedimentation may have been triggered by the abrupt drainage of lakes in tributary valleys as the Bow Valley glacier retreated. Downslope resedimentation of large volumes of sediment resulted in braided river aggradation downstream along the Bow River and can be dated to between 12 000 and 10 000 yr BP. Similar conditions probably occurred during deglaciation throughout the Canadian Cordillera and many other alpine areas, where poorly-sorted late glacial debris-flow facies have been mistaken for tills deposited directly by glaciers. The late glacial setting identified in this paper provides a basis of comparison with ancient continental glacial facies preserved in area of active tectonism and high relief. [ABSTRACT FROM AUTHOR]

Facies relationships in Pleistocene braided outwash deposits in southern Ontario demonstrate the presence of a large braid bar with adjacent side channel. The core of the bar is up to 6 m high, and consists of crudely horizontally stratified gravels. Downstream from the core is the bar front facies, consisting of large gravelly foresets up to 4 m high, rounded off in many places by reactivation surfaces. Upstream from the core is the bar stoss side facies consisting of several sets (individually up to 35 cm thick) of tabular cross-bedding, arranged in coarsening-upward sequences. The stoss side-core-bar front relationships are continuously exposed in one 400 m long quarry face which is cut almost parallel to the palacoflow direction. A transverse quarry face shows the side channel facies, which consists if trough cross-bedded sands. Gravel layers can be seen to finger from the main gravelly bar into the sandy side channel, but they do not reach the base of the channel. This surprising relationship indicates that gravel moved only in the topographically higher parts of the system. After deposition in the side channel, and growth upstream and downstream from the bar core, the entire system aggraded. Crudely horizontally stratified, and imbricaled gravel sheets were laid down as a bar top facies. Grain size analyses indicate strongly bimodal distributions, implying that much of the sand in the spaces between pebbles and boulders filtered in after the gravel had been deposited. This interpretation is strengthened by velocity calculations—mean velocities in excess of 300 cm/s would be needed to roll the gravel as bed load, but at such a velocity, a large amount of sand would be transported entirely in suspension. In a final section of the paper, our results are combined with other work on braided systems in an attempt to formulate a more general facies model. [ABSTRACT FROM AUTHOR]

Deltas are at the transition between fluvial and marine sedimentary environments where sediment density flows are often triggered during high river discharge events, forming submarine channels and sediment waves. On wave‐influenced deltas, longshore currents are particularly efficient at transporting sediment alongshore, reducing the likelihood of sediment density flows from occurring at river mouths. This study describes four deltaic sedimentary systems at different stages of their evolution on a formerly glaciated continental inner shelf of eastern Canada in order to better understand the distribution of sediment density flows on wave‐influenced deltas. Three types of settings are recognized as being prone to sediment density flows: (i) in the early stages of wave‐influence and on large deltas, converging longshore currents can lead to offshelf sediment transport; (ii) on wave‐influenced to wave‐dominated deltas, a sandy spit can re‐route the river mouth and sediment density flows form where the spit intersects the delta lip; (iii) in advanced stages of wave‐dominated deltas and during their demise, rocky headlands are exposed and can intersect the slope, where off‐shelf sediment transport occurs. These types of sediment density flows were all characterized by debris flows or surge‐type turbidity currents which have limited offshore run‐out. More rarely, hyperpycnal flows form at the river mouths, especially where the river incises glaciomarine clays prone to landsliding in the river, which increases fine‐grained fluvial suspended sediment concentration. Overall, these results highlight the predominance of fluvial‐dominated deltas during a phase of relative sea‐level fall combined with high sediment supply. However, as soon as sediment supply diminishes, wave action remobilizes sediment alongshore modifying the distribution and types of sediment density flows occurring on wave‐influenced deltas. [ABSTRACT FROM AUTHOR]

Diagenetic models help explain reservoir quality of siliciclastic strata, which are globally important exploration targets for groundwater, petroleum and carbon sequestration. Siliciclastics occur in salt provinces worldwide but remain poorly studied despite documented deviation from basic eodiagenetic models. A new variation is explained based on evidence from Cumberland Basin strata (Grande Anse Formation, Pennsylvanian, Canada). These strata were deposited in a fluvial setting under semi‐humid to humid climates and represent an unconformable cover sequence over a salt wall. Optical microscopy and scanning electron microscopy, both employing cathodoluminescence, reveal that widespread early diagenetic phases are mostly deleterious to reservoir quality. These pre‐compactional eodiagenetic phases are: (i) variable dissolution/alteration of feldspars, micas and carbonate/evaporite clasts; clay and grain staining iron oxides; and pore‐filling kaolinite; (ii) microcrystalline calcite; quartz overgrowths, prismatic quartz, quartzine chalcedony and blocky quartz, the latter two pseudomorphous after gypsum; and barite; (iii) framboidal pyrite and locally extensive Mg, Fe and Mn‐bearing blocky calcite. The first phase is attributed to a seasonally wetted vadose zone under relatively low pH and positive Eh conditions characteristic of humid climates. In contrast, the second phase is usually associated with evaporitic conditions and arid climates, where authigenesis occurs in the capillary fringe to just below the water table, and where porewaters are much more saline. The third phase is related to authigenesis from shallow burial, anoxic, phreatic porewaters. How is the aforementioned humid/arid dichotomy deciphered? Important may be the distinction between vadose and circum‐water‐table phases. Beneath vadose deposits of the humid climate, the proximity of evaporite rock in the salt wall allows for its localized dissolution, providing abundant Ca, CO3 and SO4 ions to produce anomalously saline, shallow groundwater. Barite and transient gypsum precipitated, the latter subsequently replaced by chalcedony and pseudomorphous silica during sporadic events where flushing of meteoric water temporarily lowered pH. [ABSTRACT FROM AUTHOR]

Cyclic‐step bedforms typifying a Froude‐supercritical flow regime are a recurrent component of depositional/erosional turbiditic systems. Over modern delta slopes, cyclic steps have been inferred from observations of upslope‐migrating crescent‐shaped bedforms. However, the recognition in the sedimentary record of the resulting stratal pattern and depositional facies remains challenging. In this study, the depositional facies observed in exposed late Quaternary glaciofluvial upper delta‐slope sands (Portneuf‐Forestville, Québec) are compared to those cored from a modern analogue consisting of sediment waves interpreted as cyclic steps (Southwind Fjord, Baffin Island). The fossil and modern delta slopes share similar context, morphology and stratigraphic record. The clinoform foresets dip 2 to 6° and consist of prevailing sand‐sized material including subhorizontal to upslope‐dipping top‐cut‐out turbidites. Individually, the latter are 5 to 20 cm thick and massive to planar laminated (prevailing TA and TB subdivisions). In the fossil delta slope, related successions form relatively thick, well‐bedded suites, which are truncated downcurrent by, and onlap upstreamward on, inclined composite erosion surfaces here referred to as pseudo‐foresets. Pseudo‐foresets are regularly spaced (10 to 30 m) and have dips greater than the clinoform foresets (ca 20°). Large composite scours form pseudo‐channel structures filled in by structureless pebbly sand deformed by sheared flame structures, in association with coarse sand showing undulating lamination and rip‐up clasts. Similar depositional facies are observed on the modern delta slope. The stratal pattern is best compatible with upslope‐migrating bedforms and structureless sand indicates hydraulic jump deposits typical of cyclic steps. Cyclic‐step flow events, encompassing a succession of genetically linked erosional cyclic steps, depositional cyclic steps and subsequent waning‐flow conditions, were associated with the dense basal layer of high‐density (stratified) turbidity currents. They are specifically associated with pseudo‐channel incision and infill. The deposition of well‐bedded suites on the stoss side, occasionally also on the lee side, is interpreted to result from a different type of turbidity current, which decelerated over the bedform stoss and accelerated over the lee sides of pre‐existing cyclic‐step morphologies. Antidunal flow conditions in expanded (non‐stratified) turbidity currents are tentatively suggested, deposition being linked, in this case, to interactions between inherited bedform morphologies and a near‐bed tractive layer. In the resulting dual flow model, the bulk of delta‐slope sands was mainly deposited from turbidity currents not developing a cyclic‐step instability, yet cyclic steps were instrumental in shaping and/or re‐organizing the delta‐slope morphology, bedforms and resulting stratal patterns. In some delta systems, the upslope migration of supercritical crescentic bedforms may not only be due to repetitive cyclic steps but could also result from antidunal turbidity current conditions remobilizing an inherited cyclically‐stepped morphology. [ABSTRACT FROM AUTHOR]

Near Toronto, in Southern Ontario, Canada, glaciolacustrine muds and shoreface sands of Late Pleistocene age (Early Wisconsin glaciation; ≈45 ka) were deformed by icebergs ploughing the floor of an ancestral ice-dammed Lake Ontario. Outcrop mapping and a ground-penetrating radar survey identify ice scour structures up to 4 m deep, up to 10 m wide and at least several hundred metres long with high-standing lateral margins (berms). Ploughing of lake-floor sediment is also recorded by ice-keel turbated facies in which storm-deposited shoreface sands have been mechanically mixed with underlying muds. Palaeoenvironmental information for one prominent scour, such as water depths, estimates of the mass and draft of the ice mass and scouring forces, can be determined using a simple finite element numerical model. A mass of 0·04 million tonnes, a keel draft of between 10 and 30 m and a scouring force of 5 × 103 kN is consistent with scouring by a small iceberg (‘bergy bit’) or pressure-ridged lake ice; the former is preferred because of the considerable depth of the scour and the overall glacial depositional setting. Estimates of ice-mass dimensions agree with independent reconstructions of palaeobathymetry (no greater than 20 m) derived from storm-deposited hummocky and swaley cross-stratified facies that fill the scour. Data presented here aid the identification of ice-scour structures and turbated sediment in the ancient record; despite being a common process on modern high-latitude shelves, descriptions of ancient structures and facies are few. [ABSTRACT FROM AUTHOR]

Focuses on the flow and sediment transport over a subaqueous dunes in Fraser River, British Columbia. Applicability of bedform phase diagrams in deep flows; Relation of lee side flow separation to dune morphology; Control of dune morphology by fluid flow and sediment transport.

Near William Lake, in the central interior of British Columbia, the Fraser River exposes long section of late Pleistocene Glaciolacustrine sediments selectively preserved within a bedrock trough. The dominant facies types are thick, normally graded gravels and sands that occupy steeply dipping multistory channels up to 300 m wide and several tens of metres deep. Channels appear to have been simultaneously cut and filled by high density turbidity currents in a glacial lake floored by stagnant ice. Fining upward sediment gravity flow sequences up to 50 m thick may be the product of quasi-continuous 'surging' turbidity flows triggered by catastrophic meltwater4 discharges into the trough or retrogressive failure of ice-cored sediments. Large-scale post-depositional deformation structures, such as synclinal folds, normal faults, sedimentary dyke swarms and dewatering structures, record gravitational foundering of sediment and pore-water expulsion caused by the melt of underlying glacier ice. Melting of buried ice masses along the floor of the trough appears to have controlled the flow paths of turbidity currents by producing sub-basins within the overlying sediment pile. An idealized model of 'supraglacial' lacustrine sedimentation is developed that may be applicable to other glaciated areas with similar bedrock topography. [ABSTRACT FROM AUTHOR]

Two Pleistocene channel fills located in two different geological settings, on Guadeloupe in the jesser Antilles and along the Coppermine River in the Northwest Territories of Cananda, have different clast compositions, scale, and origin of fragmentation, but have similar depositional characteristics. Massive bedding or absence of structures caused by traction, sharp non-erosive contacts, reverse coarse-tail grading, matrix-supported clasts together indicate a debris-flow mechanisms in which mixtures of fine and coarse sediments moved downslope by laminar flow. Field evidence suggests sub aqueous deposition for both deposits. Both bed thickness (BTh)/maximum grain size (MGS) ratios and correlations appear characteristics of sub aqueous masses capable of flowing on slopes less than 1°. The two channel fills have random BTh and MGS variations, they do not thin and fine up-section. It is suggested that fills originating from laminar mass transport could normally have random BTh and MGS up-section variations. In flysch and volcaniclastic sequences, where coarse sediments interpreted as laminar flow deposits are common, up-section BTh and MGS variations may result from processes related to source, slope, and flow characteristics rather than from the environment in which the sediments accumulate (channel). [ABSTRACT FROM AUTHOR]

Presents the results of a comparative study of pockmark sediments and associated features appearing on both sides of the North Atlantic, on the Scotian Shelf off Nova Scotia and in the northern North Sea. Formation in seabed material consisting of soft silty clay; Seismic, sonar and lithologic characteristics of the sediments; Gas efflux through the seafloor.

Investigates the hydrology of the Isachsen rivers using Schumm's empirical relationships for modern rivers in Canadan. Variability in the moving average azimuth; Changes in stream competency with time; Sequences of bar deposits.

High‐frequency incised valley systems and subaerial exposure surfaces are prevalent in Aptian‐aged units, having been documented in numerous basins around the world. In light of a growing body of palynological, geochemical and sedimentological evidence, a glacio‐eustatic mechanism for their generation has been suggested, driven by the waxing and waning of polar ice caps. The densely‐penetrated McMurray Formation of north‐eastern Alberta, Canada, provides a unique opportunity to test for an Aptian glacio‐eustatic signal within the Western Canadian Foreland Basin. This study combines detailed drill core description with wireline log‐based stratigraphic analysis to map and evaluate a series of drainage networks located along the cratonic edge of the Western Canadian Foreland Basin. Four stratigraphically distinct composite channel‐form bodies are documented across an area >14 000 km2. Composite channel‐form bodies are up to 50 km wide and locally exceed 70 m thick, subtending from upward‐coarsening parasequence sets 2 to 12 m thick; bounding marine flooding surfaces are mappable over distances exceeding 280 km along the north–south trending basin. Detailed internal fill characterization of the four composite channel‐form bodies suggests that three represent tidal–fluvial incised valley networks, and one represents a deltaic distributary system. At least six cycles of transgression and regression are apparent within the McMurray Formation stratigraphy. Recent biostratigraphic assessment has constrained deposition of the McMurray Formation between ca 125 Ma and 118 Ma, and periods on the order of 0·7 to 1·7 Ma are estimated for the mapped transgressive–regressive cycles. The high frequency nature of these Aptian sequences suggests that the sea‐level oscillations recorded in McMurray Formation strata are consistent with a glacio‐eustatic driver. Linking the internal stratigraphic architecture of the McMurray Formation with interpreted global cooling events and sea‐level drops provides the first evidence of glacio‐eustasy within Early Cretaceous strata of western Canada. [ABSTRACT FROM AUTHOR]

Mud floccule ripples, small mud rip-up clasts, erosional scars and tool marks are reported for the first time from the macrotidal Petitcodiac River estuary, New Brunswick, Canada. The ripples occur on the intertidal flats and are ebb-oriented. Observations have been conducted during the spring low tide at high-river and low-river discharge. Floccule ripples forming during the high-river flow are characterized by increased silt fraction, low relief and sinuous to lunate form. The ripples forming during the low flow are clay-dominated, have very low relief and are characterized by narrow straight ridges and patchy distribution. The preserved mud floccule ripples manifest in interbedded silt-rich and clay-rich deposits with parallel, wavy, lenticular and current-ripple lamination. Presented floccule ripples are current-generated, non-episodic in nature and are sedimentologically characterized. The ripple origin is constrained by morphometric and grain-size analyses, and observed hydraulic processes. It is confirmed that mud floccule ripples originate under a similar range of hydraulic parameters as documented in previous flume studies. This study confirms application of work conducted in recent decades on mud-dominated marginal-marine environments and helps with understanding of properties and distribution of fine-grained sediments in tidally influenced settings. [ABSTRACT FROM AUTHOR]

Anastomosing rivers, systems of multiple interconnected channels that enclose floodbasins, constitute a major category of rivers for which various sedimentary facies models have been developed. While the sedimentary products of anastomosing rivers are relatively well-known, their genesis is still debated. A rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin, including important hydrocarbon reservoirs, urge the development of robust models for the genesis of anastomosis, to facilitate better interpretation of ancient depositional settings and controls. The upper Columbia River, British Columbia, Canada, is the most-studied anastomosing river and has played a key role in the development of an anastomosing river facies model. Two hypotheses for the origin of upper Columbia River anastomosis include the following: (i) downstream control by aggrading cross-valley alluvial fans; and (ii) upstream control by excessive bedload input from tributaries. Both upstream and downstream control may force aggradation and avulsions in the upper Columbia River. In order to test both hypotheses, long-term (millennia-scale) floodplain sedimentation rates and avulsion frequencies are calculated using 14C-dated deeply buried organic floodplain material from cross-valley borehole transects. The results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach, which is consistent with dominant upstream control by sediment overloading. The data here link recent avulsion activity to increased sediment supply during the Little Ice Age ( ca 1100 to 1950 ad). This link is supported by data showing that sediment supply to the upper Columbia study reach fluctuated in response to Holocene glacial advances and retreats in the hinterland. Upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems. The present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low-gradient floodplains, a situation commonly found in intermontane and foreland basins. [ABSTRACT FROM AUTHOR]

Differentiating between forced regressive deposits from deglacial periods in high latitude domains and forced regressive deposits from the onset of glacial periods in low latitude domains is fundamental for the accurate interpretation of glacial cycles within the geological record and then for the reconstruction of palaeogeography and palaeo-climate. A forced regressive deglacial sequence is documented from the Lake Saint-Jean basin (Québec, Canada). In this area, the Late Pleistocene to Holocene sediments have recorded the Laurentide ice sheet retreat accompanied by the invasion of marine waters (Laflamme Gulf) from ca 12·9 cal kyr bp. Subsequently, fluvio-deltaic and coastal prograding wedges were deposited; they followed the base-level fall due to glacio-isostatic rebound. This succession, representing a transition from glacial to post-glacial periods within a previously glaciated area, was investigated through recent mapping, preserved landforms, facies analysis, and new optical stimulated luminescence and radiocarbon dates. Three basin-scale geological sections share a common lower part made of isolated ice-contact fan deposits overlying bedrock. Throughout the entire basin, ice-contact fans are capped by glacimarine muds. Above, fluvial and coastal prograding systems were deposited and evolved through four steps: (i) deltaic systems progressively increased in width; (ii) coastal influence on sedimentation increased; (iii) hydrographic drainage systems became more organised; and (iv) deltas graded from steep (Gilbert delta) to low-angle foresets (mouth-bar delta). Deposited during the base-level fall from glacio-isostatic rebound, the complete succession has been designated as a single falling stage system tract referred to as a deglacial falling stage system tract. It is representative of a deglaciation sequence in areas previously covered by ice during glacial periods (i.e. medium to high latitude domains). Diagnostic criteria are provided to identify such a deglacial falling stage system tract in the geological record, which may aid identification of previously unknown glacial cycles. [ABSTRACT FROM AUTHOR]

The Timiskaming Graben is a 400 km long, 50 km wide north-west trending morphotectonic depression within the Canadian Shield of eastern North America and experiences frequent intraplate earthquakes. The graben extends along the border of Ontario and Quebec, connecting southward with the Nipissing and Ottawa-Bonnechere grabens and the St. Lawrence Rift System which includes a similar structure underlying the Hudson Valley of the eastern USA. Together they form a complex failed rift system related to regional extension of North American crust during the breakup of Rodinia and, later, Pangea. The Timiskaming Graben lies within a belt of heightened seismic activity (Western Quebec Seismic Zone) with frequent moderate magnitude (greater than magnitude 5) earthquakes including a magnitude 6.2 in 1935. These events threaten aging urban infrastructure built on soft glacial sediments; post-glacial landslides along the Ottawa Valley suggest earthquakes as large as magnitude 7. The inner part of the Timiskaming Graben is filled by Lake Timiskaming, a large 110 km long post-glacial successor to glacial Lake Barlow that was ponded by the Laurentide Ice Sheet 9500 years ago. The effects of frequent ground shaking on lake floor sediments was assessed by collecting more than 1000 line kilometres of high-resolution 'chirp' seismic profiles. Late glacial Lake Barlow glaciolacustrine and overlying post-glacial sediments are extensively deformed by extensional faults that define prominent horsts and grabens; multibeam bathymetry data suggest that faults influence the morphology of the modern lake floor, despite high sedimentation rates, and indicate recent neotectonic deformation. The Lake Timiskaming area provides evidence of post-glacial intracratonic faulting related to recurring earthquake activity along a weak spot within the North American plate. [ABSTRACT FROM AUTHOR]

A combined field and laboratory study in northern Lake Erie has provided new insights into the origin and dynamics of heavy mineral placer deposits on beaches consisting primarily of non-magnetic sediment. Work was conducted on the cross-shore and longshore transport of heavy magnetic minerals using magnetic susceptibility and fluorescent paints to trace the movement, in the field, of samples of magnetic (magnetite) and non-magnetic (quartz and calcite) grains, respectively. Laboratory experiments examined how the burial of small, dense magnetic minerals is affected by the grain size of the non-magnetic host material, and how grain burial affects magnetic susceptibility measurements at the surface. The field experiments demonstrated that the magnetic mineral tracers were buried rapidly beneath coarser, non-magnetic grains under low to moderate wave conditions, and subsequently were unable to move in the longshore or cross-shore directions. The laboratory experiments showed that the magnetic susceptibility rapidly decreased with the rate and depth of burial of the magnetic minerals, and that magnetic grain burial was most effective beneath coarser rather than finer non-magnetic sand and, for the latter sediments, under less rather than more energetic conditions. The results imply that magnetic mineral concentrations develop in this area through magnetic grain burial under fairly mild conditions, and subsequent settling, exposure and concentration in the upper swash zone during more energetic periods, when the non-magnetic grains are eroded. It is probably during these erosional periods, when the magnetic minerals are exposed in fairly homogeneous deposits, that longshore and cross-shore transport takes place. [ABSTRACT FROM AUTHOR]

The deeply dissected Southwest Grand Banks Slope offshore the Grand Banks of Newfoundland was investigated using multiple data sets in order to determine how canyons and intercanyon ridges developed and what sedimentary processes acted on glacially influenced slopes. The canyons are a product of Quaternary ice-related processes that operated along the margin, such as ice stream outwash and proglacial plume fallout. Three types of canyon are defined based on their dimensions, axial sedimentary processes and the location of the canyon head. There are canyons formed by glacial outwash with aggradational and erosional floors, and canyons formed on the slope by retrogressive failure. The steep, narrow intercanyon ridges that separate the canyons are composite morphological features formed by a complex history of sediment aggradation and degradation. Ridge aggradation occurred as a result of mid to late Quaternary background sedimentation (proglacial plume fallout and hemipelagic settling) and turbidite deposition. Intercanyon ridge degradation was caused mainly by sediment removal due to local slump failures and erosive sediment gravity flows. Levée-like deposits are present as little as 15 km from the shelf break. At 30 km from the shelf, turbidity currents spilled over a 400 m high ridge and reconfined in a canyon formed by retrogressive failure, where a thalweg channel was developed. These observations imply that turbidity currents evolved rapidly in this slope-proximal environment and attained flow depths of hundreds of metres over distances of a few tens of kilometres, suggesting turbulent subglacial outwash from tunnel valleys as the principal turbidity current-generating mechanism. [ABSTRACT FROM AUTHOR]

The textural variability of river bed gravels at bar scales is poorly understood, as are the relations between variability at this scale and at reach and river scales. Surface and subsurface grain-size distributions were therefore examined at reach, bar and bedform scales along lower Fraser River, British Columbia, Canada. Grain-size variations within compound bars are conditioned by longitudinal position, elevation and morphological setting. Surface and subsurface sediments tend to decrease in median size from bar head to bar tail by 33% and 17%, respectively. Sediment size is constrained at some upper limit that is inversely related to bar surface elevation and which is consistent with competence considerations. The surface sediments on unit bars are finer and better sorted than the bed materials in bar-top channels and along the main bar edges. Secondary unit bars tend to have a lower sand content than other features, a consequence of sediment resorting. Individual unit bars and gravel sheets exhibit streamwise grain-size fining and lee-side sand deposition. Over time, significant amounts of cut and fill do not ipso facto cause changes in surface grain sizes; yet, sediment characteristics can change without any significant morphological adjustment taking place. At the reach scale there is a clear downstream fining trend, but local variability is consistently high due to within-bar variations. The surface median grain-size range on individual bars is, on average, 25% of that along the entire 50 km reach but is 68% on one bar. While the overall fining trend yields a downstream change in surface median size of 0·76 mm km−1, the average value for ‘head-to-tail’ size reduction on individual bars is 6·3 mm km−1, an order of magnitude difference that highlights the effectiveness of bar-scale sorting processes in gravel-bed rivers. Possibilities for modelling bar-scale variability and the interaction of the different controls that are identified are discussed. [ABSTRACT FROM AUTHOR]

A hierarchical typology for the channels and bars within aggradational wandering gravel-bed rivers is developed from an examination of a 50 km reach of lower Fraser River, British Columbia, Canada. Unit bars, built by stacking of gravelly bedload sheets, are the key dynamic element of the sediment transfer system, linking sediment transport during individual freshets to the creation, development and remoulding of compound bar platforms that have either a lateral or medial style. Primary and secondary unit bars are identified, respectively, as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels. The record of bar accretion evident in ground-penetrating radar sequences is consistent with the long-term development of bar complexes derived from historical aerial photographs. For two compound bars, inter-annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer-term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys. Annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel, indicating that relatively little bed material bypasses the bars. Bar construction and change are accomplished mainly by lateral accretion as the river has limited capacity to raise bed load onto higher surfaces. Styles of accretion and erosion and, therefore, the major bar form morphologies on Fraser River are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features. For example, 65-year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers. [ABSTRACT FROM AUTHOR]

A relict mound of Holocene barite (BaSO4) tufa underlies the Flybye Springs, a small, barium-rich, cold sulphur spring system in the Northwest Territories of Canada. The tufa is composed of relatively pure barite with ≤0·34 wt% Ca2+ and ≤0·77 wt% Sr2+. The mound is made up of coated bubble, raft, undulatory sheet, stromatolitic, coated grain and detrital conglomerate barite tufa. Although previously unreported in barite, these lithotypes are akin to facies found in many carbonate spring deposits. Raft and ooid-coated grain tufa was formed via ‘inorganic’ barite precipitation in spring water ponds and tributaries where rapid oxidation of sulphide to sulphate established barite supersaturation. Undulatory sheet tufa may have formed by the reaction of dissolved barium with sulphate derived from the oxidation of extracellular polysaccharide-rich colloidal sulphur films floating in oxygenated, barite-saturated spring water ponds. Coated bubble, oncoid-coated grain and stromatolitic tufa with filamentous microfossils was formed in close association with sulphur-tolerant microbes inhabiting dysoxic and oxygenated spring water tributaries and ponds. Adsorption of dissolved barium to microbial extracellular polysaccharide probably facilitated the development of these ‘biogenic’ lithotypes. Detrital conglomerate tufa was formed by barite cementation of microdetrital tufa, allochthonous lithoclasts and organic detritus, including caribou hair. Biogenic textures, organic artefacts and microfossils in the Flybye barite tufa have survived diagenetic aggradational recrystallization and precipitation of secondary cements, indicating the potential for palaeoecological information to be preserved in barite in the geological record. Similarities between the Flybye barite tufa and carbonate spring deposits demonstrate that analogous textures can develop in chemical sedimentary systems with distinct mineralogy, biology and physiochemistry. [ABSTRACT FROM AUTHOR]

Ground penetrating radar (GPR) surveys of unit and compound braid bars in the sandy South Saskatchewan River, Canada, are used to test the influential facies model for sandy braided alluvium presented by Cant & Walker (1978) . Four main radar facies are identified: (1) high-angle (up to angle-of-repose) inclined reflections, interpreted as having formed at the margins of migrating bars; (2) discontinuous undular and/or trough-shaped reflections, interpreted as cross-strata associated with the migration of sinuous-crested dunes; (3) low-angle (< 6°) reflections, interpreted as formed by low-amplitude dunes or unit bars as they migrate onto bar surfaces; and (4) reflections of variable dip bounded by a concave reflection, interpreted as being formed by the filling of channel scours, cross-bar channels or depressions on the bar surface. The predominant vertical arrangement of facies is discontinuous trough-shaped reflections at the channel base overlain by discontinuous undular reflections, overlain by low-angle reflections that dominate the deposits near the bar surface. High-angle inclined reflections are only found near the surface of unit bars, and are of relatively small-scale (< 0·5 m), but can be found at a greater range of depths within compound bars. The GPR data show that a high spatial variability exists in the distribution of facies between different compound bars, with facies variability within a single bar being as pronounced as that between bars. Compound bars evolve as an amalgamation of unit bars and other compound bars, and comprise a facies distribution that is representative of the main bar types in the South Saskatchewan River. The GPR data are compared with the original model of Cant & Walker (1978) and reveal a much greater variability in the scale, proportion and distribution of facies than that presented by Cant & Walker (1978) . Most notably, high-angle inclined strata are over-represented in the model of Cant and Walker, with many bars being dominated by the deposits of low- and high-amplitude dunes. It is suggested that further GPR studies from a range of braided river types are required to properly quantify the full range of deposits. Only by moving away from traditional, highly generalized facies models can a greater understanding of braided river deposits and their controls be established. [ABSTRACT FROM AUTHOR]

Discordant zebra dolomite bodies occur locally in the Middle Cambrian Cathedral and Eldon Formations of the Main Ranges of the Canadian Rocky Mountains Fold and Thrust Belt. They are characterized by alternating dark grey ( a) and white ( b) bands, forming an ‘ abba’ diagenetic cyclicity. These bands developed parallel to both bedding and cleavage. Dark grey ( a) bands consist of fine (< 300 μm) non-planar crystalline impure dolomite. The white ( b) bands are composed of coarse (up to several millimetres) milky-white pure saddle dolomites ( b1) which are often covered by pore-lining zoned dolomite ( b2). The b phases often possess a saddle-shaped morphology. In contrast to the replacement origin of the a dolomite, the zoned b2 dolomite rims are interpreted as a cement formed in open cavities. The b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non-carbonate components. All the zebra dolomites studied are (nearly) stoichiometric and are characterized by enriched Na and depleted Sr concentrations. Fe and Mn concentrations in these dolomites differ depending on the sample locality. Fluid inclusion data indicate that the dolomites formed from relatively hot ( TH = 130–200 °C), saline (20–23 wt% CaCl2 eq.) fluids. A diagenetic high temperature origin is also supported by depleted δ18O values (−20 to −14‰ VPDB). A contribution of 87Sr-enriched fluids is reflected in the 87Sr/86Sr values (0·7091–0·7123). Zebra dolomite development is explained by focused fluid flow, which exploited areas of structural weaknesses (e.g. basin-platform, rim areas, faults, etc.). Expulsion of hot basinal brines in a tectonically active regime generated overpressures, which explains the development of secondary porosity during zebra dolomitization as well as the intra-zebra fracturing at decimetre to micrometre scale. [ABSTRACT FROM AUTHOR]

Vegetation-induced sedimentary structures (VISS) are primary structures formed by the interaction of detrital sediment with in situ plants. VISS provide physical evidence of vegetation's fundamental role in mediating sediment accumulation and erosion in clastic depositional systems. Despite the abundance of modern VISS, descriptions from the ancient record are surprisingly rare. Analysis of fossil forests in floodplain strata of the Pennsylvanian Joggins Formation has identified seven types of VISS. Five hydrodynamic types comprise simple forms developed around a single plant (centroclinal cross-strata, scratch circles, upturned beds) and complex forms where structures have amalgamated between several plants (coalesced scour fills, scour-and-mound beds). Two types (mudstone-filled hollows, downturned beds) form by the decay of an entombed plant and represent infilling of an empty hollow and/or soft-sediment deformation. Hydrodynamic types are present in both dryland and wetland settings, whereas decay-related types occur only in dryland settings where the water table was perennially or periodically low. VISS represent significant accumulations of sediment and are present in a high proportion of Joggins Formation strata. The paucity of descriptions from the ancient record suggests that these structures have been overlooked or misinterpreted as strictly hydrodynamic. Recognition of VISS in early to middle Palaeozoic strata may provide an important insight into the distribution of early land plants in oxidizing environments where organic material was not preserved. [ABSTRACT FROM AUTHOR]

Meteoric sphaerosiderite lines (MSLs), defined by invariant δ18 O and variable δ13 C values, are obtained from ancient wetland palaeosol sphaerosiderites (millimetre-scale FeCO3 nodules), and are a stable isotope proxy record of terrestrial meteoric isotopic compositions. The palaeoclimatic utility of sphaerosiderite has been well tested; however, diagenetically altered horizons that do not yield simple MSLs have been encountered. Well-preserved sphaerosiderites typically exhibit smooth exteriors, spherulitic crystalline microstructures and relatively pure (> 95 mol% FeCO3 ) compositions. Diagenetically altered sphaerosiderites typically exhibit corroded margins, replacement textures and increased crystal lattice substitution of Ca2+ , Mg2+ and Mn2+ for Fe2+ . Examples of diagenetically altered Cretaceous sphaerosiderite-bearing palaeosols from the Dakota Formation (Kansas), the Swan River Formation (Saskatchewan) and the Success S2 Formation (Saskatchewan) were examined in this study to determine the extent to which original, early diagenetic δ18 O and δ13 C values are preserved. All three units contain poikilotopic calcite cements with significantly different δ18 O and δ13 C values from the co-occurring sphaerosiderites. The complete isolation of all carbonate phases is necessary to ensure that inadvertent physical mixing does not affect the isotopic analyses. The Dakota and Swan River samples ultimately yield distinct MSLs for the sphaerosiderites, and MCLs (meteoric calcite lines) for the calcite cements. The Success S2 sample yields a covariant δ18 O vs. δ13 C trend resulting from precipitation in pore fluids that were mixtures between meteoric and modified marine phreatic waters. The calcite cements in the Success S2 Formation yield meteoric δ18 O and δ13 C values. A stable isotope mass balance model was used to produce hyperbolic fluid mixing trends between meteoric and modified marine end-member compositions. Modelled hyperbolic fluid mixing curves for the Success S2 Formation suggest precipitation from fluids that were < 25% sea water. [ABSTRACT FROM AUTHOR]

Abstract The Red River, Manitoba, is a mud-dominated, meandering stream that occupies a shallow valley eroded into a clay plain. The valley-bottom alluvium is the product of incision and lateral migration of river meanders. As revealed by a transect of five boreholes located across the floodplain at each of two successive river meanders, the alluvial deposits range from about 15 to 22 m thick and are composed primarily of silt. Sedimentary structures in the cores are weakly defined and consist mostly of beds of massive silt, thick (>0·4 m) massive silt and disturbed silt. Interlaminated sand and silt, and sand beds form relatively minor deposits, principally within the lower half of the alluvium, and thin beds of medium-coarse sand and pea gravel can be present locally within the lower metre of the alluvium. The alluvium is interpreted to consist of overbank deposits from 0 to 2–3 m depth, oblique accretion deposits from 2–3 to 8–12 m depth and oblique accretion and/or channel deposits from 8–12 m to the base of the sequence. The massive bedding within the oblique accretion deposits is interpreted to represent the remnants of couplet deposits that were initially composed of interbedded, muddy silt and sand-sized silt aggregates, as is consistent with the contemporary bank sedimentation. The post-depositional disintegration and/or compaction of the aggregates has caused the loss of the sand-sized texture. The disturbed silt beds are interpreted as slump structures caused by large-scale rotational failures along the convex banks. Overall, the Red River represents a portion of a continuum of muddy, fine-grained streams; where the alluvium lacks a distinct coarse unit, oblique accretion deposits form a majority of the floodplain, and large-scale slump features are present. [ABSTRACT FROM AUTHOR]

Abstract The Joggins Formation was deposited in the Cumberland Basin, which experienced rapid mid-Carboniferous subsidence on bounding faults. A 600 m measured section of coastal and alluvial plain strata comprises cycles tens to hundreds of metres thick. The cycles commence with coal and fossiliferous limestone/siltstone intervals, interpreted as widespread flooding events. These intervals are overlain by coarsening-upward successions capped by planar-based sandstone mounds, up to 100 m in width that represent the progradation of small, river-generated delta lobes into a standing body of open water developed during transgression. The overlying strata contain sand-rich heterolithic packages, 1–8 m thick, that are associated with channel bodies 2–3 m thick and 10–50 m wide. Drifted plant debris, Calamites groves and erect lycopsid trees are preserved within these predominantly green-grey heterolithic sediments, which were deposited on a coastal wetland or deltaic plain traversed by channel systems. The cycles conclude with red siltstones, containing calcareous nodules, that are interbedded with thin sandstones and associated with both single-storey channel bodies (1–1·5 m thick and 2–3 m wide) and larger, multistorey channels (3–6 m thick) with incised margins. Numerous channel bodies at the same level suggest that multiple-channel, anastomosed river systems were developed on a well-drained floodplain. Many minor flooding surfaces divide the strata into parasequences with dominantly progradational and aggradational stacking patterns. Multistorey channel bodies are relatively thin, fine grained and modestly incised, and palaeosols are immature and cumulative. The abundance and prominence of flooding surfaces suggests that base-level rise was enhanced, whereas the lack of evidence for abrupt basinward stepping of facies belts, coupled with the absence of strong fluvial incision and mature palaeosols, suggests that... [ABSTRACT FROM AUTHOR]

ABSTRACT In situ measurements of lakebed sediment erodibility were made on three sites in Hamilton Harbour, Lake Ontario, using the benthic flume Sea Carousel. Three methods of estimating the surface erosion threshold (τc (0)) from a Carousel time series were evaluated: the first method fits measures of bed strength to eroded depth (the failure envelope) and evaluates threshold as the surface intercept; the second method regresses mean erosion rate (E m ) with bed shear stress and solves for the floc erosion rate (E f ) to derive the threshold for E m = E f = 1 × 10-5 kg m-2 s-1 ; the third method extrapolates a regression of suspended sediment concentration (S ) and fluid transmitted bed shear stress (τ0 ) to ambient concentrations. The first field site was undisturbed (C) and acted as a control; the second (W) was disturbed through ploughing and water injection as part of lakebed treatment, whereas the third site (OIP) was disturbed and injected with an oxidant used for remediation of contaminated sediment. The main objectives of this study were: (1) to evaluate the three different methods of deriving erosion threshold; (2) to compare the physical behaviour of lacustrine sediments with their marine estuarine counterparts; and (3) to examine the effects of ploughing and chemical treatment of contaminated sediment on bed stability. Five deployments of Sea Carousel were carried out at the control site. Mean erosion thresholds for the three methods were: τc (0) = 0·5 (±0·06), 0·27 (±0·01) and 0·34 (±0·03) Pa respectively. Method 1 overpredicted bed strength as it was insensitive to effects in the surface 1–2 mm, and the fit of the failure envelope was also highly subjective. Method 2 exhibited a wide scatter in the data (low correlation coefficients), and definition of the baseline... [ABSTRACT FROM AUTHOR]

Abstract Ages of channels of the anastomosing upper Columbia River, south-eastern British Columbia, Canada, were investigated in a cross-valley transect by 14 C dating of subsurface floodplain organic material from beneath levees. The avulsion history within the transect was deduced from these data, and morphological stages in channel development were recognized. Additionally, floodplain sedimentation rates were established. The new data demonstrate that the upper Columbia River is a long-lived, dynamic anastomosing system. Results show that anastomosis at the study location has persisted since at least 2700 cal. years BP, with avulsions occurring frequently. At least nine channels have formed in the studied cross-valley transect within the past 3000 years. Channel lifetimes from formation to abandonment appear to be highly variable, ranging from approximately 800 to 3000 years. Log jams provoking avulsions and/or silting up of old channels are proposed as reasons for this variability. Long-term average floodplain sedimentation rates appear to be significantly lower than previously proposed by Smith (1983, Int. Assoc. Sedimentol. Spec. Publ., 6, 155–168). A long-term (4550 years) average of 1·75 mm year-1 (after compaction) was based on 14 C dates, while a short-term sedimentation rate of 0·8 mm was determined for a single, relatively small, seasonal flood in 1994 using sediment traps. However, short-term sedimentation rates vary considerably over the floodplain, with levees aggrading up to four times faster than floodbasins. Channels of the upper Columbia River anastomosed reach follow a consistent pattern in their development, with each stage being characterized by different morphology and processes. Channel evolution comprises the following succession: (1) avulsion stage, in which a crevasse splay channel deepens by scour and levee sedimentation; (2) widening and deepening stage, in which bank slumping and bed scouring dominates; (3) infilling stage, in which either channel narrowing (bank accretion) or channel shallowing (bed accretion) takes place; and (4) abandonment stage, in which the residual (remnant) channel is filled exclusively by silt, clay and organic material. Vertical stacking (super- imposition) of active channels on recent channel-fill sand bodies is a notable feature of the upper Columbia River, which suggests that reoccupation of residual channels is a common process. [ABSTRACT FROM AUTHOR]

In south-eastern Alberta, the Oxfordian Swift Formation comprises two unconformity-bounded sequences. Sequence 1 consists of the shale member. It unconformably overlies Bathonian calcareous shale of the Rierdon Formation and consists dominantly of shale with uncommon hum- mocky cross-stratified siltstone. The shale member comprises up to four parasequences that show a subtle upward-fining stacking pattern, suggesting overall deepening in a storm-dominated fully marine basin. Deposition of the shale member was terminated by a fall in relative sea-level, which in turn initiated sequence 2. During lowstand, a network of north-east- to south-west-trending meandering channels incised the top of sequence 1. Despite the preserved morphology of these channels, observations in core suggest that lowstand deposits are absent. These strata were most likely thoroughly reworked by ravinement processes associated with the ensuing transgression and are recorded only by a thin chert pebble lag. Also associated with transgression were significant changes in the physical and ecological conditions in the local Swift basin. These changes were related to modifications in basin configuration and the development of a low-energy strait, which probably formed as a result of uplift of the Sweetgrass Arch. Within this newly configured basin, brackish-water conditions prevailed, and sedimentation was dominated by suspension deposition of mud. Bed-load sediment, composed mostly of very fine and fine sand, made up only a small part of the total sediment flux into the area and was transported principally by low-energy combined flows with variable-speed microtidal currents and a low-energy oscillatory component related to storm waves. Sand was generally deposited in the form of small, discontinuous sand ridges that developed locally throughout the study area – it is these features that form the principal hydrocarbon reservoir bodies in the Swift Formation in the study area. After... [ABSTRACT FROM AUTHOR]

The partly dolomitized Swan Hills Formation (Middle-Upper Devonian) in the Simonette oil field of west-central Alberta underwent a complex diagenetic history, which occurred in environments ranging from near surface to deep (>2500 m) burial. Five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post-date stylolites in limestones (depths >500 m). These include early planar varieties and later saddle dolomites. Fluid inclusion data from saddle dolomite cements (Th=137–190 °C) suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data (Tpeak=160 °C). Thus, at least some dolomitizing fluids were ‘hydrothermal’. Fluorescence microscopy identified three populations of primary hydrocarbon-bearing fluid inclusions and confirms that saddle dolomitization overlapped with Upper Cretaceous oil migration. The source of early dolomitizing fluids probably was Devonian or Mississippian seawater that was mixed with a more 87Sr-rich fluid. Fabric-destructive and fabric-preserving dolostones are over 35 m thick in the Swan Hills buildup and basal platform adjacent to faults, thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults. This ‘plume-like’ geometry suggests that early and late dolomitization events were fault controlled. Late diagenetic fluids were, in part, derived from the crystalline basement or Palaeozoic siliciclastic aquifers, based on 87Sr/86Sr values up to 0·7370 from saddle dolomite, calcite and sphalerite cements, and 206Pb/204Pb of 22·86 from galena samples. Flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m, both vertically along reactivated faults and laterally in the buildup along units that retained primary and/or secondary porosity. [ABSTRACT FROM AUTHOR]

Sediment cores from six small lake basins in the Canadian high Arctic reveal a gravel-rich (≤30% by weight) to gravel-poor (≥2%) diamict facies underlying massive, post-glacial, clayey silt. Ten other lakes contain a second diamict facies within what are interpreted to be glaciolacustrine sedimentary assemblages. The sedimentology, clast fabrics and fossil remains (diatoms, ostracodes and chironomid head capsules) within both diamict facies suggest that these deposits are not tills. Clast fabrics yielded low S1 (0·41–0·57) and high S3 (0·09–0·22) eigenvalues, placing them within the range of ice-rafted diamictons and glacigenic sediment flows. The high percentage of clast dip angles >45° (15–61%), random clast azimuth and lower diamict contacts conformable to underlying current-bedded sediment favours an origin as a rain-out or settling deposit. Samples of the matrix and scrapings of clasts from the diamicts revealed a diatom assemblage dominated by littoral and planktonic forms, such as are found in the littoral regions of the lakes today. This contrasts sharply with the assemblages within the overlying clayey silt, in which benthic forms predominate. Clasts are thus interpreted to have been rafted from the littoral areas of the lake. The process proposed to explain this is rafting by the lake ice cover in a glacial-marginal environment. Early season meltwater, impounded along the lateral margin of retreating cold-based glaciers, would buoyantly lift the lake ice cover and any adfrozen lake sediment. Higher lake levels and increased areal extent of seasonal freeze-on between the lake ice cover and the lake bed would allow the redeposition of littoral sediments to the benthic regions through greater lateral shifting of the ice cover as it broke up. Incision by meltwater streams into the lateral glacial margins would later isolate the lake, allowing seasonal warming of lake water, enough to support the growth and maturation of the ostracode and chironomid species found as fossils within the diamicts. [ABSTRACT FROM AUTHOR]

Halite-impregnated carbonates in the Dawson Bay Formation of Saskatchewan lie between beds of halite and are buried to a depth of 1 km. They exhibit two different diagenetic styles – some resisted compaction and had high pre-salt porosities; others contain compaction-broken fossils and pressure-solution seams. The uncompacted rocks, together with the difficulty of explaining how halite cement could enter the Dawson Bay after overlying bedded halites were deposited, suggest that halite cementation occurred early with only a few tens of metres of overburden. Early diagenetic compaction is suggested by the presence of unbroken, displacive skeletal halite crystals, which cross-cut compaction structures, and by the difficulty of explaining how (1) later compaction could occur in halite-cemented rocks and (2) how pore-fluids could be expelled after surrounding rocks lost their permeability. The organic-rich nature of many carbonates may explain why compaction was both early and extensive, but this explanation fails to explain how similar compaction developed in horizons with lower organic contents. Chemical compaction may also have been enhanced by aragonite dissolution during seawater evaporation or brine dilution. Early chemical compaction in Dawson Bay carbonates indicates that compaction in other carbonates need not signify deep burial diagenesis; neither can compaction be used indiscriminately to identify other diagenetic events as being of deep burial origin. Early halite cementation, as in the Dawson Bay Formation, preserves carbonates at early diagenetic stages and may thus preserve geochemical information unmodified by later diagenesis. [ABSTRACT FROM AUTHOR]

Examines the anatomy and evolution of a Lower Cretaceous alluvial plain in the upper Blairmore Group in Alberta, Canada. Recognition of five types of palaeosols in the upper Blairmore Group based on lithology, the presence of pedogenic features and degree of horizonization; Regional distribution of various types of palaeosols.

The dynamic behaviour of sediment-laden underflows was examined in Peyto Lake, Alberta, Canada, which contains a midlake sill 7 m high. Sediment-laden underflows are driven by the downslope component of negative buoyant gravity multiplied by the current's thickness. Our measurements of wind, lake currents and water properties indicate that underflows pass over the sill due, to the active storage of turbid suspension near the bottom in the deepest proximal region. Sill overflows occurred only when a hydrological threshold of the inflowing river was exceeded, causing quasicontinuous underflow and associated sedimentation in the distal region of the lake basin. [ABSTRACT FROM AUTHOR]

Three stages of deposition are distinguished in thermokarst-lake-basin sequences in ice-rich permafrost of the Tuktoyaktuk Coastlands, western arctic Canada: (1) widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes forming a distinctive basal unit of impure sand and/or diamicton; (2) a reduction or cessation of slumping-because of the pinching out of adjacent ground ice, slump stabilization or climatic cooling, that reduces the input of clastic sediment, permitting reworking of sediment around lake margins and suspension settling, principally in basin centres; (3) lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand. Radiocarbon dating of detrital peat and wood from a progradational sequence (basal unit) defines a lateral younging trend in the direction of progradation. A progradation rate is calculated to be ∼4 cm yr[SUP-1], consistent with rapid deposition during stage (1) above. The nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents. In comparison with thermokarst-lake-basin sequences previously described in Alaska, Canada and Siberia the middle unit of those in the Tuktoyaktuk Coastlands is similar, whereas the basal unit is generally thicker and, by contrast often contains diamicton. These differences are attributed, respectively, to larger-scale resedimentation of upland sediments by retrogressive thaw slumping and debris-flow deposition in thermokarst lakes in the Tuktoyaktuk Coastlands. Compared with the sediments within supraglacial lakes in areas of moderate to high relief, the middle unit of thermokarst-lake-basin sequences in the Tuktoyaktuk Coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable. These differences are attributed to higher relief and larger volumes of meltwater and glacigenic... [ABSTRACT FROM AUTHOR]

Seven mud-filled incised valleys (MFIVs) in the paralic facies of the Dinosaur Park and Horseshoe Canyon formations (Upper Cretaceous) of southern Alberta were studied to better understand their morphology, geometry and depositional histories in an estuarine context. Two preservational geometries occur: simple, U-shaped forms; and internally complex forms. Both types of MFIV record deposition in the central zone of low energy (turbidity) in an estuarine setting. Simple, U-shaped MFIVs have sharp basal erosional surfaces and consist of mudstone-dominated heterolithic fills of channel-wide, concave-up laminae. Associated fossil assemblages are marine to brackish. Each simple MFIV records a cut-and-fill history associated with a cycle of relative sea-level drop and rise. Low-energy depositional settings, loss of channel form during infilling, and associated shoreface deposits, as well as the absence of clear tidal indicators suggest a coastal plain estuarine setting, along a wave-dominated, barred coastline. Complex MFIVs are rarer, and consist of imbricated, wedge-shaped sets of inclined-to-horizontal heterolithic strata. Tidal deposits and/or nonmarine-tomarine macrofossils occur locally. Complex MFIVs were infilled in meandering reachers of the central zone of low energy in tide-dominated estuaries. Their rarity compared to simple MFIVs and their freshwater palaeontological content suggest that they were contiguous landward with extensive fluvial channels. A complex MFIV near Onefonr comprises three in-channel depositional cycles. Each cycle consists of an erosional surface overlain by lateral accretion bedding and a conformable transition to vertically aggraded strata. Each cycle reflects a cut-and-fill event under the control of changes in relative sea-level that culminated in overbank All MFIVs formed in low-gradient settings (≤ 0.03%) where estnarine zones were stretched out over many tens of kilometres. Tide-dominated estuaries apparently exhibited... [ABSTRACT FROM AUTHOR]

The early Stephanian Bonar Cyclothem of the Sydney Basin. Nova Scotia, contains an erosional surface cut through coastal plain strata with economic coals and distributary channel bodies. The erosion surface is interpreted as a palaeovalley 20 m deep and at least 7 km wide that marks a sequence boundary formed during relative fall in sea level. The palaeovalley is filled with stacked alluvial channel bodies which become more isolated as the valley fill passes upward into red, alluvial plain deposits, probably laid down in an anastomosed river system. In an adjacent, interfluve, area, calcretes and red, vertic palaeosols cap coastal strat. Assemblage analysis of agglutinated foraminifera and the camoebians indicates that the palaeovaleey was filled with freshwater sediments before an initial marine transgression flooded the alluvial surface and adjacent interfluve. Valley incision probably reflects glacioeustatic sea level fall. However, the alluvial nature of the valley deposits suggests that valley filling reflects an abundant sediment supply during lowstand and/or transgressive stages and was not a direct consequence of sea level rise. During the subsequent transgression phase, aggradation was rapid as sediment supply apparently kept pace with rising sea level. Features of both channel and extra-channel facies suggest that seasonality intensified during the transition from coastal plain to palaeovalley and alluvial plan deposition. [ABSTRACT FROM AUTHOR]

Investigates Late Quaternary sediment, sediment mass flow processes and slope stability on the Scotian Slope in Canada. Evidence of erosion, rotational slumping and internal deformation at the near surface sediment; Observation that mass failure deposits form a part of the sedimentary column in this bathymetrically smooth region.

Ancient stream-dominated ('wet') alluvial fan deposits have received far less attention in the literature than their arid/semi-arid counterparts. The Cenozoic basin fills along the Denali fault system of the northwestern Canadian Cordillera provide excellent examples of stream-dominated alluvial fan deposits because they developed daring the Eocene-Oligocene temperate climatic regime in an active strike-slip orogen. The Amphitheatre Formation filled several strike-slip basins in Yukon Territory and consists of up to 1200 m of coarse siliciclastic rocks and coal. Detailed facies analysis, conglomerate :sandstone percentages (C:S), maximum particle size (MPS) distribution and palaeocurrent analysis of the Amphitheatre Formation in two of these strike-slip basins document the transition from proximal to middle, to distal and fringing environments within ancient stream-dominated alluvial-fan systems. Proximal fan deposits in the Bates Lake Basin are characterized by disorganized, clast-supported, boulder conglomerate and minor matrix(mud)-supported conglomerate. Proximal facies are located along the faulted basin margins in areas where C:S = 80 to 100 and where the average MPS ranges from 30 to 60 cm. Proxmal fan deposits grade into middle fan, channelized, well organized cobble conglomerates that form upward fining sequences, with an average thickness of 7 m. Middle fan deposits grade basinward into well-sorted. Laterally continuous beds of normally graded sandstone mterbedded with trough cross stratified sandstone. These distal fan deposits are characteristic of areas where C:S = 20 to 44 and where the average MPS ranges from 5 to 15 cm. Fun fringe deposits consist of lacustrine and axial fluvial facies. Palaeogeographic reconstruction of the Bates Lake Basin indicates that alluvial-fan sedimentation was concentrated in three parts of the basin. The largest alluvial-fan system abutted the strike-slip Duke River fault, and prograded westward across the axis of the... [ABSTRACT FROM AUTHOR]

Calcrete palaeosols have been found in the Upper Carboniferous Canyon Fiord Formation of south-western Ellsmere Island, Canadian Arctic. These calcretes were developed in fluvial and shallow marine sediments that accumulated within two adjacent subbasins, in which the tectono-sedimentary environment led to the deposition of five different sedimentary facies; (i) floodbasin sandstones; (ii) alluvial fan sandstones; (iii) alluvial fan conglomerates; (iv) braided fluvial sandstones; and (v) shallow marine limestones. Nodular/massive palaeosol profiles, consisting of cryptic, nodular, massive and laminar horizons, occur within the floodbasin sandstone and alluvial fan sandstone facies. Plugged palaeosol profiles, consisting of cryptic, plugged and laminar horizons, are restricted to the alluvial fan conglomerate facies. Massive/brecciated palaeosol profiles, consisting of cryptic, massive/brecciated and laminar horizons, occur essentially within the shallow marine limestone facies. The relationships between calcrete profiles and sedimentary facies suggest that profile types were controlled mainly by the texture and composition of the parent material: nodular/massive profiles are restricted to silicate-rich sandstone hosts, plugged profiles are restricted to carbonate-rich conglomerate hosts and massive/brecciated profiles are restricted to limestone hosts. Important relationships also exist between the maturity levels of nodular/massive profiles and sedimentary facies; profiles are generally amature in the flood basin sandstones, invariably immature in the alluvial fan sandstones and absent from the braided fluvial sandstones. These different maturity levels were probably controlled mainly by exposure time, vegetation and substrate composition. [ABSTRACT FROM AUTHOR]

Freefight Lake, Canada's deepest salt lake, is a meromictic, hypersaline lake located in the most arid part of the northern Great Plains The lake has a distinctive basin morphology, with a large expanse of seasonally flooded mud flats and sand flats adjacent to a deep, flat bottomed perennial waterbody. The mixolimnion, dominated by magnesium, sodium and sulphate ions, has an average salinity of 110 ppt and overlies a monimolimnion of 180 ppt total dissolved salts: the entire water mass is also saturated or supersaturated with respect to a number of very soluble sodium, magnesium and sodium + magnesium salts. The modern sedimentary processes operating in Freefight Lake give rise to six main sedimentary facies: (1) colluvium, (ii) mud flats and sand flats, (iii) algal flats, (iv) delta, (v) slope and debris apron, and (vi) deep basin. The colluvium, mud flats and sand flats, and delta facies are dominated by physical processes and consist mainly of detrital siliciclastic sediment. The algal flats, slope and debris apron, and deep basin facies are dominated by endogenic and authigenic sediments derived mainly by physicochemical and biologically mediated carbonate and evaporite mineral precipitation. AS one of very few deep water lakes in the world in which soluble evaporiate minerals are forming and being preserved, Freefight Lake occupies an important position within the realm of lacustrine sedimentology. Although many of the sedimentological and geochemical processes taking place in the basin today are unusual, the delineation and evaluation of these processes is essential in order to decipher properly the stratigraphic records of Quaternary lake sediments in this large area of North America, as well as lacustrine sequences from other arid and semiarid regions of the world. [ABSTRACT FROM AUTHOR]

The Taltheilei, Utsingi, McLeadn and Blanchet formations form a 175-390 m thick carbonate platform-to-basin succession in the lower part of the PaleoProterozoic Pethei Group, preserved in the eastern arm of Great Slave Lake. Carbonates accumulated along the south-east margin of the Slave Craton within a foredeep formed during the collision of the Slave and Churchill Cratons. The rocks include eight, predominantly microbial, carbonate facies that comprise five facies associations representing (1) shallow-water rimmed shelf, (2) shallow-water open shelf, (3) shallow-water ramp, (4) upper slope and deep ramp, and (5) lower slope and basin plain environments. Microbialite facies grew by organically mediated precipitation of spar and micritic cement and trapping and binding of lime mud. These wholly subtidal facies typically reflect progressive shallowing and changing geometry of the lower Pethei sea floor, from ramp, to open shelf, to shallow rimmed shelf, with associated slope and basin plain deposition. Repeated relative sea-level changes influenced platform growth. This resulted in five shallowing upward packages; each separated by an incipient drowning event of varying magnitude. Antecedent topography and the size of the preceding drowing event strongly influenced the initial growth of microbial carbonates to aggrade vertically, (b) changing sedimentation rates and (c) readjustments of relative base level. The lower Pethei succession is one of few PaleoProterozoic examples of carbonate platform growth within a foreland basin. It has (1) a low gradient profile, (2) extensive slope and basin plain carbonate production and sedimentation, (3) no ooids, (4) minor terrigenous clastic sediments, and (4) a mobile, submergent shelf rim lacking substantial carbonate sand shoals. [ABSTRACT FROM AUTHOR]

Stacked shallow marine cycles in the Lower Ordovic ian, Bell Island Group, of Bell Island, Newfoundland, show upward thickening and upward coarsening sequences, which were deposited on a storm-affected shelf. In the Beach Formation each cycle has a facies sequence compared, from base to a top, of dark grey mudstones, light grey mudstones, tabular sandstones and mudstones, lenticular sandstones and mudstones, and thick bedded lenticular sandstones, reflecting a progressive increase of wave orbital velocities at the sediment surface. The mudstones and tabular sandstones reflect an environment in which the sea floor lay in the lower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents. The lenticular sandstones in the succeeding facies are wave reworked sands, commonly lying in erosional hollows and having erosional tops and internal hummocky cross-stratification. Planar lamination is relatively uncommon and sole marks are mainly absent. In this facies oscillatory currents were dominant and accumulated sand in patches generally 10-30 m in diameter. The facis formed on the inner shelf where the oscilaltory currents generated by storm waves had powerful erosional effects and also determined the depositional bed forms. Mud partings and second-order set boundaries within sandstone beds are believed to separate the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds. This interpretation has important implications for attempts to estimate event frequency by counting sandstones beds within a sequence and for estimates of sand budgets during storm events. The thick bedded lenticular facies appears to have been formed by erosion of the mud beds between the lenticular sands, leading to nearly complete amalgamation of several lenticular sand bodies except for residual mud partings. In the overlying Redmans Formation the process of... [ABSTRACT FROM AUTHOR]

Middle to Late Ordovician subtidal carbonates in the Manitoulin Island area of Ontario are predominantly limestone in compositton, but non-ferroan and ferroan dolomite is a common cement as well as a selective or locally pervasive replacement phase. Integration of field, petrographic, geochemical {δ[sup 13]C, δ[sup 18]O) and fluid inclusion data indicates that lithification of these carbonates occurred during burial diagenesis, with much of the alteration controlled by regional fracturing and hydrothermal influences. Aqueous (type 1) fluid inclusion s in early calcite (pre-dolomite) and dolomite are saline (> 29 wt% NaCl eq.) solutions with Ca and/or Mg in excess of Na and display homogenization temperatures with modes of 95 and 101°C, respectively. These temperatures can be explained by significantly more burial than can be accounted for either by the available stratigraphic information or by an unusually high palaeogeothermal gradient, which also is not well supported The fluid inclusion temperatures are interpreted to have resulted from hydrothermal fluids which circulated during the burial diagenesis of these strata. Type 1 inclusions in late (post-dolomite) calcite are less saline (<19 wt% NaCl eq.) and have a biracial distribution of homogenization temperatures with a relatively well defined low temperature peak similar to those in early calcite and dolomite and a broad higher temperature grouping with a mode at 183°C. A small proportion of methane and light hydrocarbon-bearing fluid inclusions (type 2) are present in all stages of carbonate. Dolomitizing fluids were derived from burial compaction of argillaceous sediments in the more central earls of the Michigan Basin and the updip migration of these brines along fractures to the basin margin where the carbonates of the Manitoulin Island area were dolomitized. Alternatively, migration of dolomitizing brines downward from the overlying pervasively dolomitized Silurian sequence into... [ABSTRACT FROM AUTHOR]

A major palaeokarst erosion surface is developed within the middle Proterozoic Elu Basin, northwestern Canada. This palaeokarst is named the sub-Kanuyak unconformity and truncates the Parry Bay Formation, a sequence of shallow-marine dolostones that were deposited within a north-facing carbonate platform under a semi-arid climate. The sub-Kanuyak unconformity exhibits up to 90 m of local relief, and also formed under semi-arid conditions when Parry Bay dolostones were subaerially exposed during a relative sea-level drop of about 180 m. Caves and various karren developed within the meteoric vadose and phreatic zones. Their geometry, size and orientation were largely controlled by northwest- and northeast-trending antecedent joints, bedding, and lithology. Near-surface caves later collapsed forming valleys, and intervening towers or walls, and plains. Minor terra rossa formed on top of highs. Karstification was most pronounced in southern parts of Bathurst Inlet but decreased northward, probably reflecting varying lengths of exposure time along a north-dipping slope. The Kanuyak Formation is up to 65 m thick, and partially covers the underlying palaeokarst. It consists of six lithofacies: (i) breccia formed during collapse of caves, as reworked collapse breccia and regolith; (ii) conglomerate representing gravel-dominated braided-fluvial deposits; (iii) sandstone deposited as braided-fluvial and storm-dominated lacustrine deposits; (iv) interbedded sandstone, siltstone and mudstone of sheet flood origin; (v) dolostones formed from dolocretes and quiet-water lacustrine deposits; and (vi) red-beds representing intertidal marine mudflat deposits. Rivers flowed toward the northwest and northeast within karst valleys and caves; lakes were also situated within valleys; marine mudflat sediments completely cover the palaeokarst to the north. A regional correlation of the sub-Kanuyak unconformity with the intra-Greenhorn Lakes disconformity within the Coppermine homocline suggests that similar styles of karstification occurred over an extensive region. The Elu Basin palaeokarst, however, was developed more landward, and was exposed for a longer period of time than the Coppermine homocline palaeokarst. [ABSTRACT FROM AUTHOR]