Outwash Deposits Research Articles

Monte Carlo Simulations of Multiphase Flow Incorporating Spatial Variability of Hydraulic Properties

AbstractTo study the effect of spatial variability of sediment hydraulic properties on multiphase flow, oil infiltration into a hypothetical glacial outwash aquifer, followed by oil extraction, was simulated using a cross‐sectional multiphase flow model. The analysis was simplified by neglecting capillary hysteresis. The first simulation used a uniform mean permeability and mean retention curve. This was followed by 50 Monte Carlo simulations conducted using 50 spatially variable permeability realizations and corresponding spatially variable retention curves. For the type of correlation structure considered in this study, which is similar to that of glacial outwash deposits, use of mean hydraulic properties reproduces the ensemble average oil saturation distribution obtained from the Monte Carlo simulations. However, spatial variability causes the oil saturation distribution in an individual oil lens to differ significantly from that of the mean lens. Oil saturations at a given location may be considerably higher than would be predicted using uniform mean properties. During cleanup by oil extraction from a well, considerably more oil may remain behind in the heterogeneous case than in the spatially uniform case.

Quaternary sediments in central Edmonton, Alberta, Canada: Stratigraphy, distribution and geotechnical implications

Borehole logs were used to determine the stratigraphy and distribution of sedimentary units in central Edmonton. The Quaternary sediments overlying Upper Cretaceous sedimentary bedrock consist of preglacial fluvial sand and some gravel, glaciofluvial sand and gravel, a glacial diamicton complex composed of melt-out and flow diamictons, glaciofluvial sand and silt, glaciolacustrine silt and clay, and minor deposits of postglacial fluvial sand. The glacial sediments represent deposition during one major glaciation in the Late Wisconsinan. The diamicton complex has an intermediate stratigraphic position in the Quaternary sequence, is generally thick and laterally continuous, and serves as a satisfactory substrate for many deep foundations and tunnels, including part of the Light Rail Transit system. Seepage and block failures during tunnelling in the diamicton complex are mainly due to abundant saturated sand lenses in the upper part of the complex. The lateral continuity of the diamicton complex is interrupted by sand infilling a meltwater channel incised into bedrock. Tunnelling is difficult and costly within the sand, due to seepage and collapse. Mapping of the meltwater channel and associated outwash deposits allowed adjustment of the tunnel alignment to avoid intersection with the channel. Over the meltwater channel, deposits of outwash sediments and flow diamictons form a broad surface ridge.

Overlaying Soil and Timber Inventories to Assess Aspen Productivity in Northern Minnesota

AbstractForest soil productivity is a difficult quantity to measure, yet it is an integral component of forest management decisions and an important interpretation of soil inventories conducted in forested areas. Soil‐site studies are time consuming and expensive, and often cannot identify productivity differences between soil units. Merging timber‐inventory data with soil‐survey data may provide an efficient means for evaluating forest productivity. In this study, timber‐inventory data were overlaid with soil‐survey data for Beltrami County, Minnesota. Soil map units were grouped into 10 soil classes based on drainage and parent material. Productivity of aspen (Populus tremuloides Michx. and P. grandidentata Michx.) was compared between soil classes using the estimates of volume, site index, and basal area collected during the timber inventory. Analysis of the volume data indicated that the soils formed in outwash deposits were significantly less productive (mean volume of stands between 40 and 55 yr = 126 m3 ha‐1) than soils formed in calcareous glacial till or calcareous deposits of stratified fine sands and silts (mean volume of stands between 40 and 55 yr = 155 m3 ha‐1). Very poorly drained soils were also in the higher productivity group, though aspen was a relatively minor cover type on these soils. The site‐index data was of minimal value in separating soils into productivity groups. Basal area was highly correlated with volume estimates and may be a useful stand attribute for assessing forest productivity during land‐resource inventories.

New pollen-stratigraphic evidence for the deglaciation and lake drainage chronology of the Glen Roy-Glen Spean area

Synopsis Pollen-stratigraphic evidence is presented from a number of sites in Glen Roy and lower Glen Treig. The new data do not support the chronology of the Glen Roy-Loch Laggan proglacial lake drainage proposed by Macpherson (1978). The evidence also has a bearing on the controversy over the age of outwash fan deposits in upper Glen Roy, and this problem is re-examined here. Since no Late Devensian Lateglacial deposits are found anywhere in the region, whereas early Flandrian (Holocene) successions are found in several basins, the evidence as a whole is interpreted as indicating that the outwash deposits at the Roy–Turret confluence are of Loch Lomond Stadial age.

Surficial geology of the northwestern Canadian continental shelf

The northwestern Canadian continental shelf, including Dixon Entrance, Hecate Strait and Queen Charlotte Sound, can be divided into four surficial geological units all overlying Tertiary bedrock within the Queen Charlotte Basin. They include: (1) glacial till, deposited primarily in the troughs between banks and considered to be late Wisconsinan in age; (2) glaciomarine mud, deposited in the troughs as ice retreated from the shelf; (3) Queen Charlotte sands and gravels, outwash deposition in the north and sublittoral sand deposition in the south during sea level low stand and subsequent reworking during transgression; and (4) Queen Charlotte muds, deposited within the troughs of the region from late Wisconsinan times until present. These units are a result of a glaciation ending 15,000–13,000 years BP followed by relative sea level lowering by approximately 100 m, that persisted until 10,500 years ago, and a subsequent transgression that occurred over approximately 1500 years in a series of steps.

Locomotion and feeding traces in Champlain Sea subaqueous outwash deposits near Ottawa, Canada: Reply

Locomotion and feeding traces in Champlain Sea subaqueous outwash deposits near Ottawa, Canada: Reply

Locomotion and feeding traces in Champlain Sea subaqueous outwash deposits near Ottawa, Canada: Discussion

Locomotion and feeding traces in Champlain Sea subaqueous outwash deposits near Ottawa, Canada: Discussion

Lower Silurian-Upper Ordovician Subsurface Glacial Outwash Deposits, Northern Saudi Arabia

Recently acquired seismic data reinterpreted well information in northwest Saudi Arabia extends outcropping Lower Silurian to Upper Ordovician Zarqa/Sarah glacial and periglacial deposits into the subsurface. These deposits range from northeast-trending outwash-filled channels deeply incised into the underlying Ordovician Qasim and the Cambrian-Ordovician Saq Formation in the east. A southwest source for these sediments is implied by this new data. This supports previously interpreted source directions mapped from outcrop. It also correlates with the position of the Arabian plate relative to known Gonwanaland ice caps during the Early Silurian-Late Ordovician. The recognition of glacial outwash sediments in the subsurface provides new insight into the continuity and environments of deposition of the Qasim Formation members in northwest Saudi Arabia. The hydrocarbon-prone Lower Silurian Qusaiba Member of the Qalibah Formation overlies the Zarqa/Sarah Formations. The Qusaiba represents a rapid transgression of the Paleo-Tethys Sea during the final melting of the Gondwanaland ice caps. The seal-source characteristics of the Qusaiba Member, combined with the good porosity and permeability of the underlying outwash deposits, suggest a prospective hydrocarbon exploration play. Gas is produced from this reservoir in the Risha field of eastern Jordan.

The geophysical investigation of Quaternary geological environments

Abstract There is a considerable Variation in the lithology and thickness of glacial and fluvial Sediments in Western Europe. This wide range of materials is associated with significant engineering problems and considerable economic interest from the extractive industries. Geophysical techniques are widely applied to map and investigate areas with glacial deposits and fluvio-glacial sands and gravels. There are sheet-like outwash deposits, some with buried and therefore unpredictable Channels, and smaller fissure and pocket deposits in rock. An assessment of the geometry of a deposit can be accurately achieved with geophysical methods, and electrical techniques have been particularly successful. The nature of the deposit, layering within the deposit, lateral Variation of lithology, thickness and depth to bedrock may all be established quickly and with great cost effectiveness. Numerous other problems occur with Quaternary environments particularly alteration and contamination of rock masses. Electrical techniques are also a powerful investigative tool in these situations. The success of these techniques depends upon the geophysical properties of the material to be investigated and the geophysical properties of the underlying sediment or bedrock, the technique actually selected, professional field practice and interpretation. These factors will be discussed and illustrated with reference to a number of case studies.

Surface Expressions of Subsurface Structures in Parts of the Michigan and Illinois Basins

Study of glacial geology, stream drainage, bedrock topography, and subsurface structure maps in Isabella, Midland, Arenac, Gladwin, Clare, Ogemaw, Iosco, Mecosta, and Montcalm counties in Michigan revealed distinct correlations between patterns and types of glacial deposits and subsurface structures. Anticlinal structures associated with the Mt. Pleasant, North Buckeye, and South Buckeye, Hamilton, Deep River, Clayton, Logan, Six Lakes, and West Branch oil and gas fields occur along areas where northeast-trending glacial moraines and truncated, attenuated, or deviated. Furthermore, these anticlinal structures are associated with lacustrine sands and gravels and glacial outwash deposits nearly surrounded by glacial tills or lacustrine sands and clays. All of the anticlinal structures are associated with bedrock topography highs and alignment of streams parallel to the trends of the structures. Comparison of images of subsurface structure and surface elevation data covering the northern part of the illinois basin showed distinct correlations between glacial moraine patterns and subsurface structural trends. The Pesotum and Arcola end moraines bracket the major anticlinal structure at the Hayes oil field. The Westfield, Nevins, and Paris moraines are truncated or attenuated where they intersect the surface projections of the subsurface LaSalle anticlinal belt and the anticlinal structure associated with the Mattoon oilmore » field. These correlations among subsurface structure, bedrock topography, and surface glacial features indicate that the subsurface structural configuration influenced glacial depositional patterns in detectable and predictable ways, even in areas blanketed by over 100 ft of Wisconsin glacial drift.« less

EFFECTS OF HISTORICAL LAND CLEARING ON ORGANIC MATTER AND NITROGEN LEVELS IN SOILS OF THE FRASER LOWLAND OF BRITISH COLUMBIA, CANADA AND WASHINGTON, U.S.A.

Two soils derived from glacial deposits and one from alluvium were examined for changes in organic matter (OM) and nitrogen levels between 1943 and 1983 across the international boundary in the Fraser Lowland of western North America. Duplicate samples were collected from the upper 0.2 m from 60 randomly selected sites on the five land clearing periods (1943–1955, 1955–1966, 1966–1976, 1976–1983, uncleared) on each of three parent materials: glacial outwash, alluvium, and glacialmarine deposits in the United States and Canada. The land clearing periods were determined from medium scale aerial photographs taken in 1943, 1955, 1966, 1976, and 1983. Cultivation results in a 20% loss of OM after 35 yr on all soils. The largest loss is in the first 15 yr on all soils. Changes in N levels on the three parent materials is irregular. C:N narrows on all soils from about 15:1 to about 12:1. Key words: Organic matter, nitrogen, Fraser Lowland, land clearing, air photo interpretation, parent material

Locomotion and feeding traces in Champlain Sea subaqueous outwash deposits near Ottawa, Canada

Locomotion and feeding traces (repichnia and fodichnia) observed on bedding planes of rhythmically bedded subaqueous outwash deposits in the Brazeau sand pit, Nepean, Ontario, Canada, are the first bedding-plane traces described in detail from the western Champlain Sea. The Planolites–Palaeophycus-like and Taenidium-like traces are cylindrical with circular cross section, smooth sided, unlined, sinuous, sometimes branching, and sometimes meniscate. Organisms producing the traces are tentatively identified as errant polychaetes or nemerteans. The enclosing sediments are rhythmic couplets of alternating fine sand and silt layers overlain by silty clay and fine–medium silt layers. The occurrence of traces within the uppermost portion of the coarse unit, and within the coarser, upper portion of the overlying fine unit, and the rhythmic alternation of coarse and fine layers suggest these deposits may be varves. The traces formed during the more biologically suitable summer months but were preserved only during the latter portion of the summer. Traces are distributed on bedding planes in close association with bedforms and show a high correlation with the substrate and possibly the hydrodynamic regime. This is interpreted as indicating a strong preference in feeding behaviour. The presence of traces in the subaqueous outwash environment necessitates rethinking of the depositional environment to include the presence of errant polychaetes, nemerteans or similar organisms, and the lower life-forms such as epontic algae and bacteria on which they live.

Woody plant succession on earthquake-uplifted coastal wetlands of the Copper River Delta, Alaska

The delta formed by the Copper River stretches for more than 75 km along the south central coastline of the Gulf of Alaska. It is the terminus of the outwash deposits from a large part of the most heavily glaciated region of North America, and all major rivers that flow into the delta carry extremely high levels of suspended sediments. Coastal wetlands extend inland for as much as 20 km. In 1964, an earthquake of Richter magnitude 8.4 to 8.6 raised the entire delta from 1.8 to 3.4 m above the previous mean sea level. Subtidal areas became intertidal, and intertidal areas supertidal. Marshland advanced seaward as much as 1.5 km in the intertidal zone. Vegetation on many, but not all, newly supertidal levees began to change from herbland to shrubland. A change in frequency and duration of tidal inundation and water salinity has been thought to be the most obvious cause of this succession, but explanation is lacking. Freshwater dominates the estuarine circulation due to a bar-built estuary and the extremely high input of freshwater from glacier runoff and precipitation. Tides merely raise freshwater onto the wetlands. Halophytes are rare even at the seaward edge of vegetation. The characteristic species of the present intertidal marshes, Lyngbye sedge ( Carex lyngbyei), also is characteristic in inland freshwater marshes. Initial post-earthquake invasion of woody plants was confined to natural levees. More recently, shrubs have begun to move seaward into new inter-tidal marshland. Only three shrub species, sweetgale ( Myrica gale var. tomentosa). Barclay willow ( Salix barclayi), and Sitka alder ( Alnus viridis ssp. sinuata) are important in woody plant succession. Barclay willow was abundant before the uplift. Increased distribution and abundance of willow was the earliest indication of post-earthquake succession. Sweetgale is now the most aggressive species. It was present on tidally flooded levees before the uplift and has become a ubiquitous understory shrub in all willow stands and an invader on newly formed intertidal marshes. Sitka alder grows on supertidal levees where the substrate is wet, but aerated. Black cottonwood ( Populus balsamifera ssp. trichocarpa) and Sitka spruce ( Picea sitchensis) trees are present in many alder stands. Many Sitka alder stands have become black-cottonwood/Sitka-alder woodland. Sitka spruce forest may eventually develop on some supertidal levees. Shrubland, woodland and forest vegetation analogous to that developing on supertidal levees is present on older wetland habitats further inland. It is likely the same plant successions would have occurred without an uplift. The uplift appears to have altered locations and rates, but not the nature, of wetland plant succession on the Copper River Delta.

Effects of acidic deposition on North American lakes: palaeolimnological evidence from diatoms and chrysophytes

Analysis of sediment diatom and chrysophyte assemblages is the best technique currently available for inferring past lake water pH trends. Use of this approach for assessing the ecological effects of acidic deposition is increasing rapidly. As of August 1989, sediment core inferred pH data existed for at least 150 lakes in North America and cores from about 100 more lakes are being analysed. Equations for inferring past pH are based on at least 15-20 calibration data-sets involving about 700 lakes. Palaeolimnological studies indicate that recent acidification has been caused by acidic deposition in the Adirondack Mountains (New York), northern New England, Ontario, Quebec and the Canadian Atlantic provinces. Inferred pH decreases are commonly as much as 0.5-1.0 pH units. With the exception of one lake, no acidification trends were observed in regions currently receiving low deposition of strong acids (e.g. Rocky Mountains and Sierra Nevada in the western United States). Slight or no trends towards decreasing pH were observed in study lakes receiving moderately acidic deposition (upper Mid-west and northern Florida). The amount of inferred acidification (increase in H+concentration) correlates with the amount of S and N loading and the ability of watersheds and lakes to neutralize acid inputs, and is generally consistent with current lake-acidification theory. In most cases, the primary cause of recent acidification (post-1850) is acidic deposition, as opposed to land-use changes or natural processes, though these may be contributing factors. Acid loading has decreased in some regions since 1970 (e.g., northeastern United States). Some lakes have become less acidic in response, but others continue to lose acid neutralizing capacity. Many currently acidic lakes were naturally acidic (pH < 5.5) before the onset of anthropogenic acidification. These lakes are typically small (less than 10 ha) are located at moderately high elevations, have thin or peaty soils, or are located in outwash deposits. Many of these have acidified further recently.

Late pliocene and quaternary glaciations of New Zealand

Evidence of Late Pliocene glaciations is fragmentary. The Ross Glaciation in northwest South Island is correlated with the first marine faunal evidence of marked cooling in the Wanganui Basin in southern North Island; it is inferred to be in the 2.6-2.4 Ma age range. The Porika Glaciation, in a separate area of northwest South Island, is younger, judged by palynology, and is correlated with a cooling 2.2-2.1 Ma BP inferred from stratigraphic evidence of lowered sea level in the Wanganui Basin: A gap of >1.5 Ma in the record of glaciations is largely filled by Wanganui Basin marine sediments, although an unconformity cuts out the record between ca. 1.45 and 1.0 Ma BP; since then, the many sedimentary cycles caused by sea level changes are presumed to be glacio-eustatic in origin. Uplifted interglacial marine terraces, back to marine Oxygen Isotope Stage 17, and river terraces formed by cold-climate aggradation, are linked into the cyclic sequence through loess and tephra in their cover beds. East of the South Island, cores from the DSDP Site 594 in the southwest Pacific record the earliest glaciation and, higher in the core, nine periods of South Island glaciation in the last 0.7 Ma. Onshore, because of uplift and erosion, only the last four glaciations, assigned to Oxygen Isotope Stages 10, 8, 6, and 4+2, are identified, being named Nemona, Waimaunga, Waimea and Otira Glaciations. They are best known in north Westland (northwest South Island) where the relations of glacial outwash and interglacial shoreline deposits are displayed. The late Otira Glaciation (Stage 2) is radiocarbon dated as beginning somewhat before 22.3 ka BP, culminating ca. 18 ka BP, and ending at ca. 14 ka BP, when rapid deglaciation began. A relatively small advance at ca. 12 ka BP may have been followed by little change until after 8.6 ka BP. Recession was then followed by a period of advance from ca. 5 ka BP until recent centuries and a subsequent recession that still continues.

Comparison of soil groups in North and South Westland, and the implications for land use

Abstract The soils of North and South Westland have similar properties. The main soil groups present in both regions are gleyed recent soils, gley soils, organic soils, yellow-brown earths, podzols and gley podzols. However, the proportions and distribution of these soil groups within the landscape are not the same in the two regions. Differences in time for soil formation, landform variation and climate are chiefly responsible for the differences in proportions and distribution. The generally higher rainfall in the south compared with the north is a major influence. The parent materials and vegetation types in the two regions are broadly similar. In the north, more yellow-brown earths have formed on the widespread, low and intermediate glacial outwash terraces than on the low outwash surfaces in the south. In the south, soils of the outwash surfaces are mainly gley soils, organic soils and gley podzols. More podzols are found with yellow-brown earths in hill country associations in the north than in the south. In the south, organic soils are more widely distributed and are linked with wetter, cooler conditions. Relatively young piedmont till deposits separated by outwash surfaces, flood plains, and blocks of strongly dissected hill country dominate the South Westland landscape. In contrast, till deposits are localised in the north, with extensive outwash deposits in the form of flights of terraces located between blocks of dissected hill country. The areas and types of land that are capable of sustained use differ considerably between the two regions, because of the major differences in proportions of soil groups, landscape types and amounts of rainfall. As the soil-landscape-climate system is so dynamic in South Westland, extreme care must be exercised if the indigenous vegetation cover is to be changed. Proportions of soils with greater land use versatility are higher in the north, and this is reflected by current patterns of land use.

Stream Development in Glacier Bay National Park, Alaska, U.S.A.

The effects of hydraulics, sediment supply, channel condition, and riparian vegetation on stream development were examined in a chronosequence of five streams in Glacier Bay National Park where rapid retreat of glacial ice has exposed landscapes of different ages within a confined region. The youngest stream, Wolf Point Creek (deglaciated around 1955), is fed by a remnant glacier and had the highest suspended sediment concentrations of all streams (103-111 mg L-1 at baseflows). The main channel of Wolf Point Creek was relatively wide and stable because of the peak flow buffering effects of the remnant glacier and associated lake. However, the floodplain was periodically inundated and only sparsely vegetated and highly braided. The study reach at Nunatak Creek (deglaciated around 1950) was actively downcutting through fine glacial outwash deposits creating a deeper thalweg and redepositing some material near channel margins. About 100 yr after deglaciation (Ice Valley stream), woody riparian vegetation begins to stabilize streambanks and becomes established on gravel bars where it provides potential sites for incipient woody debris dams. The Ice Valley channel shows only minimal degradation. The increased accumulation of woody material and the subsequent colonization of gravel bars by alder and willow have begun to increase channel and bank stability and pool formation in Berg Bay South (deglaciated around 1830). Berg Bay South appears to be near equilibrium with respect to sediment supply and transport. Berg Bay North, a stream of similar age to Berg Bay South, stabilized more rapidly because of the buffered peak flows and greater sediment trapping efficiency attributed to the lakes and bogs in the north stream system. Fish habitat improves as postglacial streams develop: pools begin to form, riparian cover increases, and sediment transport decreases.

Paleomagnetic dating of postglacial sediments, Vancouver Island, Canada

Cores taken from lakes throughout Vancouver Island consist of a homogeneous sequence of postglacial sediments that is usually underlain by glacial varves or outwash deposits. The paleoinclination and the relative paleodeclination logs of the postglacial sequence for each core forms a fairly consistent pattern of oscillations that has been used for the correlation of the cores from lake to lake. This correlation method provides important information on the relative timing of the cessation of glacial outwash deposition as well as the rate of postglacial deposition from lake to lake. Unfortunately, 14C dates on discrete organic material and the presence of the Mazama tephra layer (6800 BP) in the postglacial sequence at Shawnigan Lake have not provided sufficient reliable information to date the paleomagnetic record or the postglacial-glacial boundary.

Late Quaternary stratigraphy, sedimentology, and history of the Jasper townsite area, Alberta, Canada

Geomorphic, stratigraphic, and sedimentologic evidence obtained from Quaternary sediments near Jasper, Alberta, is used to reconstruct depositional environments in the vicinity of two former confluent valley glaciers. Sedimentation occurred mainly in the valley centre in a pre-existing river channel. Lateral ice-marginal sedimentation along the inset valley walls was important during both the advance and the retreat stages. Prior to and during glacial advance, horizontally stratified gravels, sands, and silts were deposited in a braided stream. Near the valley bottom, diamictons containing trough-shaped sand lenses were deposited by subsequent proglacial debris flows and intermittent fluvial activity. At higher stratigraphic positions, outwash deposits confined to the valley wide are unconformably overlain by massive diamicton, interpreted as subglacial till, deposited as ice began to override the area. The diamicton grades towards the valley side into ice-contact debris deposited at the margins of the expanding glacier by water and sediment flows from the ice surface. Glaciers eventually overrode the entire area. During deglaciation, thick sequences of normally faulted, steeply dipping sand, gravel, and clast-rich diamicton were deposited in a kame terrace west of Jasper townsite. The orientation of bedding and faults and the nature of the sediments indicate they were derived from, and deposited in contact with, a linear belt of stagnating, debris-covered ice that extended along the valley centre east of Jasper. It is postulated that the stagnating ice originated from a well-developed medial moraine and debris septum that formed at the confluence of the large Athabasca and Miette valley glaciers. The knob-and-kettle topography, which eventually developed in the valley centre, was obscured by glaciofluvial and fluvial activity. A linear chain of kettle lakes remains as evidence of the possible existence of the moraine. Kettle chains and hummocky topography, formed in the positions of both medial and lateral moraines, may be relatively common geomorphic features in glaciated mountain valleys.

Sedimentology of the lower huronian supergroup (early proterozoic), Elliot lake area, Ontario, Canada

The Early Proterozoic Huronian Supergroup is a slightly metamorphosed sedimentary succession locally > 10 km thick, exposed to the north of Lake Huron, Ontario, Canada. The lower part of the supergroup, comprising the Matinenda, McKim, Ramsay Lake and Pecors formations, was studied in the Quirke Syncline area, Elliot Lake, and regions immediately to the west and south. Thirteen lithofacies are present: trough and planar cross-stratified sandstone, quartz pebble conglomerate, clay-rich sandstone, lenticular-bedded sandstone-siltstone-mudstone, laminated sandstone-siltstone-mudstone, massive sandstone- massive pebbly sandstone, massive diamictite, stratified matrix-supported diamictite, stratified clast-supported diamictite, graded diamictite, and massive siltstone. The lithofacies may be grouped into associations which correspond approximately to the mapped formations. The crossbedded sandstones and conglomerates comprise a fluvial association (Matinenda Formation), which was formed mainly in shallow braided channels. Clay-rich sandstone and the lenticular and laminated lithofacies, constituting portions of the McKim and Pecors Formations, were deposited on the strand and offshore areas of braid deltas, interfingering laterally and vertically with the Matinenda fluvial deposits. Four glacigenic subassociations are present in the Ramsay Lake Formation. An ice-proximal subassociation (I) consists of massive pebbly sandstone and diamictite which progressively truncates the Matinenda and McKim Formations to the north. The massive sandstone may be an ice-override deposit formed by erosion and reworking of the underlying Matinenda Formation, or a sub-ice shelf rain-out accumulation of locally eroded glacial debris. Subassociations II and III consist mainly of subaqueous sediment gravity flow and ice rain-out deposits. Subassociation IV is interpreted as an ice-proximal fluvial outwash deposit containing resedimented blocks of moraine material. Stratigraphic and paleocurrent data indicate a south-dipping paleoslope that tilted southeast during the deposition of the fluvial and deltaic units. A trough of relatively deep water extended NW-SE across the region, transverse to the E-W divergent continental margin hinge line that is assumed to have existed to the south of the project area. Analogies are suggested to Mesozoic-Recent basins on the Atlantic margin of Canada, where transverse paleogeographic trends reflect either landward extension of active oceanic fracture zones, or reactivation of earlier structural lineaments.