Columbia River Valley Research Articles

Trends in sedimentary Cladocera and metal(loid)s from Williams Lake (Washington, USA) track ∼125 years of trans-boundary contamination from smelter emissions in the upper Columbia River valley

The lead‑zinc smelter at Trail (British Columbia, Canada) has operated continuously for ∼125 years, with long-standing concerns that transboundary metal(loid) and sulphur emissions have contaminated water bodies in both western Canada and Washington (WA), USA. To assess aquatic ecosystems affected by over a century of industrial contamination requires an understanding of pre-smelting conditions. Here, we use a dated sediment core from Williams Lake (WA), downwind of both the Trail and the short-lived LeRoi (Northport, WA) smelters, to track regional contaminant history and other environmental stressors. Specifically, we examine a selection of chemical elements, cladoceran assemblages, visible range spectroscopy-inferred chlorophyll a (VRS-Chl a) and visible near-infrared spectroscopy-inferred lake-water total organic carbon (VNIRS-TOC). Sedimentary proxies recorded the onset of smelting in 1896 CE, peak periods of aerial emissions in the early to mid-20th century, and the history of emission controls. With a few exceptions, sedimentary metal(loid)s exceeded Canadian Interim Sediment Quality Guidelines during the height of the smelting era and have declined substantially since ca. 2000 CE. The loss of metal-sensitive Cladocera and declines in primary production (VRS-Chl a) at the onset of the regional smelting era indicate a strong biological response to airborne industrial contamination. The largest cladoceran change in the sediment record was concurrent with accelerated mitigation efforts at the Trail facilities following the 1960s; however, this compositional shift was between ecologically similar daphniid taxa. Steep declines in VNIRS-TOC concentrations during the period of peak emissions at Trail suggested an increase in sulphur deposition on the landscape that reduced terrestrial carbon supply. However, the persistence of calcium-sensitive daphniids throughout the record indicates that alkaline Williams Lake had not acidified. Current cladoceran assemblages remain substantially distinct from pre-industrial communities, demonstrating how paleoecotoxicological approaches can be used to track the effects of multiple stressors in a temporally appropriate context.

Multi-decadal floodplain classification and trend analysis in the Upper Columbia River valley, British Columbia

Abstract. Floodplain wetland ecosystems experience significant seasonal water fluctuation over the year, resulting in a dynamic hydroperiod, with a range of vegetation community responses. This paper assesses trends and changes in land cover and hydroclimatological variables, including air temperature, river discharge, and water level in the Upper Columbia River Wetlands (UCRW), British Columbia, Canada. A land cover classification time series from 1984 to 2022 was generated from the Landsat image archive using a random forest algorithm. Peak river flow timing, duration, and anomalies were examined to evaluate temporal coincidence with observed land cover trends. The land cover classifier used to segment changes in wetland area and open water performed well (kappa of 0.82). Over the last 4 decades, observed river discharge and air temperature have increased, precipitation has decreased, the timing of peak flow is earlier, and the flow duration has been reduced. The frequency of both high-discharge events and dry years have increased, indicating a shift towards more extreme floodplain flow behavior. These hydrometeorological changes are associated with a shift in the timing of snowmelt, from April to mid-May, and with seasonal changes in the vegetative communities over the 39-year period. Thus, woody shrubs (+6 % to +12 %) have expanded as they gradually replaced marsh and wet-meadow land covers with a reduction in open-water area. This suggests that increasing temperatures have already impacted the regional hydrology, wetland hydroperiod, and floodplain land cover in the Upper Columbia River valley. Overall, there is substantial variation in seasonal and annual land cover, reflecting the dynamic nature of floodplain wetlands, but the results show that the wetlands are drying out with increasing areas of woody/shrub habitat and loss of aquatic habitat. The results suggest that floodplain wetlands, particularly marsh and open-water habitats, are vulnerable to climatic and hydrological changes that could further reduce their areal extent in the future.

Tracking long-distance atmospheric deposition of trace metal emissions from smelters in the upper Columbia River valley using Pb isotope analysis of lake sediments.

Heavy metal discharge from mining and smelting operations into aquatic ecosystems can cause long-term biological and ecological impacts. The upper Columbia River is highly contaminated with heavy metal wastes from nearby smelting operations in Trail, British Columbia, Canada, and to a lesser extent, Northport (Le Roi smelter), Washington, USA. Airborne emissions from the Trail operations were historically and are currently transported by prevailing winds down the Columbia River canyon, where particulate metals can be deposited into lakes and watersheds. In lakes, sediment cores contain records of past environmental conditions, providing a timeline of fundamental chemical and biological relationships within aquatic ecosystems, including records of airborne metal depositions. We analyzed trace metal concentrations (Ni, Cd, Zn, As, Cu, Sb, Pb, Hg) and Pb isotope compositions of sediment cores from six remote eastern Washington lakes to assess potential sources of atmospheric heavy metal deposition. Sediment cores displayed evidence to support trace metal loading as a direct consequence of smelting operations in Trail. Smelter contamination was detected 144km downwind of the Trail Smelter. Cd, Sb, Pb (p < 0.001), and to a lesser extent As and Hg (p < 0.05) concentrations were correlated with Pb isotope compositions, suggesting that the Trail operations were likely the main source for these trace metals.

10Be dating of late Pleistocene megafloods and Cordilleran Ice Sheet retreat in the northwestern United States

During the late Pleistocene, multiple floods from drainage of glacial Lake Missoula further eroded a vast anastomosing network of bedrock channels, coulees, and cataracts, forming the Channeled Scabland of eastern Washington State (United States). However, the timing and exact pathways of these Missoula floods remain poorly constrained, thereby limiting our understanding of the evolution of this spectacular landscape. Here we report cosmogenic ^(10)Be ages that directly date flood and glacial features important to understanding the flood history, the evolution of the Channeled Scabland, and relationships to the Cordilleran Ice Sheet (CIS). One of the largest floods occurred at 18.2 ± 1.5 ka, flowing down the northwestern Columbia River valley prior to blockage of this route by advance of the Okanogan lobe of the CIS, which dammed glacial Lake Columbia and diverted later Missoula floods to more eastern routes through the Channeled Scabland. The Okanogan and Purcell Trench lobes of the CIS began to retreat from their maximum extent at ca. 15.5 ka, likely in response to onset of surface warming of the northeastern Pacific Ocean. Upper Grand Coulee fully opened as a flood route after 15.6 ± 1.3 ka, becoming the primary path for later Missoula floods until the last ones from glacial Lake Missoula at 14.7 ± 1.2 ka. The youngest dated flood(s) (14.0 ± 1.4 ka to 14.4 ± 1.3 ka) came down the northwestern Columbia River valley and were likely from glacial Lake Columbia, indicating that the lake persisted for a few centuries after the last Missoula flood.

River connectivity and road crossing effects on floodplain vegetation of the upper Columbia River, Canada

ABSTRACTFloodplain wetlands in the upper Columbia River valley are governed by the flood pulse. Water flows from the river into adjacent wetlands through channels incised through levees or over the top of the levees. This floodplain is relatively pristine with few road crossings restricting the flow of water in a 110 km length of the floodplain. We describe the floodplain vegetation at three points over 60 years to detect natural vegetation changes and contrast that with changes downstream of roads transecting the wetlands. We mapped eight landscape cover types within 40 floodbasins and four 2 km sections downstream of road crossings at three dates, over 60 years, using historical aerial photographs. Over 60 years the area of open water increased by 77% within the wetlands, and there was a decrease of 14.5% and 40% of marsh and shrub vegetation, respectively. During this time, floodbasins became more connected to the river. We observed greater change within the natural wetlands than in sections downstream of the road crossings. Since floodplain ecosystems are inherently complex due to their highly dynamic nature, isolating specific causes of trends is difficult. However, large-scale loss of vegetation and increase in open water has dramatically changed the wetlands.

Gone to the Spirits: A Transgender Prophet on the Columbia Plateau

This article examines the life of Kaúxuma núpika, an indigenous transgender prophet living on the Columbia Plateau in the early nineteenth century. As a Ktunaxa woman, she crossed cultural boundaries to marry a Euroamerican. When she left her husband, insisting on her independence and autonomy, she crossed another frontier. When Kaúxuma núpika declared herself no longer a woman, but a man, and secured himself a wife, he crossed further boundaries of gender and sexuality. As a warrior and a prophet, Kaúxuma núpika crossed the boundaries to the world of the spirit, returning with warnings, guidance, and hope for the tribal people of the Columbia River valley. In this project, I reflect upon the historical record in light of indigenous prophet traditions on the Columbia Plateau and current scholarship on gender and power among Native communities of the region, to consider notions of power, identity, and the religio-cultural dynamics of gender and sexual identity among indigenous communities on the Columbia Plateau.

Accommodation Space Controls on the Latest Pleistocene and Holocene (16–0 ka) Sediment Size and Bypassing in the Lower Columbia River Valley: A Large Fluvial–Tidal System in Oregon and Washington, USA

Peterson, C.D.; Gates, E.B.; Minor, R., and Baker, D.L., 2013. Accommodation space controls on the latest Pleistocene and Holocene (16–0 ka) sediment size and bypassing in the Lower Columbia River Valley: a large fluvial–tidal system in Oregon and Washington, USA.In this study, we establish the roles that increasing basin accommodation space have on sediment size and bypassing in the transgressive fill (16–0 ka) in the submerged Lower Columbia River Valley (LCRV). The antecedent forearc valley (225 km in length, 4–8 km in width, and 60–115 m in axial valley depth) is characterized by high sediment supply rates (10–15 million t y−1) but no delta at its mouth to the Pacific Ocean. Core sample sediment textures (N = 1600) are analyzed from 3000 m of borehole sections in 58 representative boreholes to characterize the ancestral valley fill: 57% sand, 17% muddy sand, 12% sandy mud, and 14% mud (total fill volume = 77 km3). Decreasing mud endmember texture from between 30 and 60% (early Holocene) to 18% (late Holocene) is directly related to (1) declining rates of increasing basin accommodation space and (2) increasing sediment bypassing through the LCRV. Both conditions result from decreasing rates of sea level rise (15.0–1.5 mm y−1) in Holocene time. The overall coarsening of sediments, both upvalley and upsection, is controlled by declining rates of increasing basin accommodation space (5.66 million–0.57 million m3 y−1) during middle to late Holocene time. Differences between middle and late Holocene sediment accumulation rates yield bedload bypassing rates of 5– 6 million m3 y−1, under assumed conditions of constant sediment supply rates in middle to late Holocene time.

Reactive nitrogen inputs to US lands and waterways: how certain are we about sources and fluxes?

An overabundance of reactive nitrogen (N) as a result of anthropogenic activities has led to multiple human health and environmental concerns. Efforts to address these concerns require an accurate accounting of N inputs. Here, we present a novel synthesis of data describing N inputs to the US, including the range of estimates, spatial patterns, and uncertainties. This analysis shows that human‐mediated N inputs are ubiquitous across the country but are spatially heterogeneous, ranging from &lt; 0.1 to 34.6 times the background N input for individual water‐resource units (8‐digit Hydrologic Unit Codes). The Midwest, Mid‐Atlantic, central California, and portions of the Columbia River valley currently receive the highest N loads. Major opportunities to advance our understanding of N sources can be achieved by: (1) enhancing the spatial and temporal resolution of agricultural N input data, (2) improving livestock and human waste monitoring, and (3) better quantifying biological N fixation in non‐cultivated ecosystems.

Pre-and post-Missoula flood geomorphology of the Pre-Holocene ancestral Columbia River Valley in the Portland forearc basin, Oregon and Washington, USA

Geomorphic landscape development in the pre-Holocene ancestral Columbia River Valley (1–5km width) in the Portland forearc basin (~50km length) is established from depositional sequences, which pre-date and post-date the glacial Lake Missoula floods. The sequences are observed from selected borehole logs (150 in number) and intact terrace soil profiles (56 in number) in backhoe trenches. Four sequences are widespread, including (1) a vertically aggraded Pleistocene alluvial plain, (2) a steep sided valley that is incised (125–150m) into the Pleistocene gravel plain, (3) Missoula flood terraces (19–13ka) abandoned on the sides of the ancestral valley, and (4) Holocene flooding surfaces (11–8ka) buried at 70–30m depth in the axial Columbia River Valley. Weathering rims and cementation are used for relative dating of incised Pleistocene gravel units. Soil development on the abandoned Missoula flood terraces is directly related to terrace deposit lithology, including thin Bw horizons in gravel, irregular podzols in sand, and multiple Bw horizons in thicker loess-capping layers. Radiocarbon dating of sand and mud alluvium in the submerged axial valley ties Holocene flooding surfaces to a local sea level curve and establishes Holocene sedimentation rates of 1.5cmyear−1 during 11–9ka and 0.3cmyear−1 during 9–0ka. The sequences of Pleistocene gravel aggradation, river valley incision, cataclysmic Missoula flooding, and Holocene submergence yield complex geomorphic landscapes in the ancestral lower Columbia River Valley.

Latest Pleistocene and Holocene (2–16 ka) sedimentation in the Columbia River Estuary, Oregon, USA

A deep borehole drilled at Warrenton, Oregon in the ancestral valley of the Columbia River represents a geologic record that extends from 2 ka to 16 ka. Prior to the onset of the Holocene marine transgression at 16 ka, the incised Columbia River valley was cut to 112 m below present sea level at this location. The onset of estuarine circulation in the Columbia River estuary occurred at 11.5 ka as determined by the first appearance of brackish water diatoms in sediments from borehole cores at a depth of 70 m. Grain size and heavy mineral analyses indicate that the Columbia River tidal basin served initially (16–11 ka) as a bedload-bypassing conduit to the continental shelf, and/or the Astoria Canyon. With the ongoing Holocene transgression, the Columbia River tidal basin became more efficient as a river sediment sink between 11.5 and 9.0 ka. After 9.0 ka, the filling tidal basin again served as a sediment-bypassing conduit (source) of sand to the coastline and continental shelf. Heavy mineral analyses indicate that between 16 and 11 ka the Columbia River tidal basin was dominated by sediment from the metamorphic interior basins of the Columbia drainage basin. The dominant sediment source changed from the metamorphic interior basins of the Columbia drainage basin to the Cascade volcanic arc between 11.5 and 9.0 ka. After 9.0 ka, the tidal basin was dominated by Cascade volcanic arc derived sediments. The total volume of Holocene sediment, primarily bedload, which has accumulated in the lower Columbia River valley, is 73 km 3. This compares to only 13-km 3 accumulation during the last 5 ka. The tidal basin accumulation rate gradually increased from 0.6 million m 3/yr to slightly over 18 million m 3/yr between the depths of 112 m and 30 m (16 to 9 ka). Above the 30 m depth (corresponding to 8.2 ka), the rate of basin volume fill dramatically decreased to just over 4 million m 3/yr. Such a large decrease in sediment accumulation rate suggests that after 9 ka sediments were bypassing the nearly full tidal basin to the beaches and inner shelf. The rates of bedload bypassing the lower Columbia River valley, substantially greater than 2.4 million m 3/yr, supported the shoreface progradation in the littoral cell during the late Holocene.

In-Cloud Icing in the Columbia Basin

Abstract On 24 November 2005, 11 lattice steel towers of a high-voltage electrical transmission line running along the edge of an escarpment were damaged by an accumulation of rime on overhead ground wires. Cold air pooling in the Columbia basin of eastern Washington several days before the failure led to the formation of low-level fog and low clouds with temperatures below freezing at the elevation of the transmission line. The liquid water content profile of the cloud formed by air rising over Badger Mountain north of Wenatchee, Washington, is estimated using the air temperature, dewpoint temperature, and air pressure as measured at Wenatchee in the Columbia River valley below the line. Cloud median volume droplet diameters are estimated using typical droplet concentrations. The validity of the computed liquid water content is determined by comparing the measured cloud-base heights at Wenatchee with the calculated cloud-base heights. The mass and density of ice accreted on the ground wires and conductors of the transmission line are modeled using assumed wind speeds at the top of the escarpment with the estimated cloud properties. Results are compared with the density and mass of an ice sample retrieved from the field. This event is compared with other modeled in-cloud icing events from 1973 to 2007 using the period of record of Wenatchee weather data. This paper illustrates an approach for estimating the severity of in-cloud icing on the wires of transmission lines subject to cloud liquid water contents that have been enhanced by the local terrain.

A review of the moss-monitoring survey around the Trail smelter,British Columbia

The distribution of aerially deposited metals, As, Cd, Cu, Hg, Pb and Zn, was studied using passive collection moss monitoring in the vicinity of the smelter in Trail, British Columbia, Canada. The concentrations of metals/metalloids were measured in moss bags exposed to atmospheric deposition for periods of three months. The results show the greatest deposition of metals proximal to the smelter, and a decrease in deposition with increasing distance from the smelter. The pattern of deposition varies with the season, the element under study, and the location of the monitoring station. The depositional pattern around the Trail smelter is controlled mainly by the physiography of the region as related to shape and orientation of the Columbia river valley and direction of the prevailing wind. The results show that the annual aerial deposition of metals is directly related to the quantity of stack-emitted metals and Pb–Zn production levels. The distribution of Pb, Zn and Cd in surface soils around the Trail smelter shows a similar pattern to their deposition at moss-monitoring stations. These soils are characterized by an elevated concentration of metals in the proximity of the smelter, indicating the effect of airborne materials on the geochemistry of the soils in the study area. Such similarity was not found for Hg, Cu and As, indicating that the variation of these elements in soil samples is more likely related to soil chemistry rather than to atmospheric deposition.

Number and size of last-glacial Missoula floods in the Columbia River valley between the Pasco Basin, Washington, and Portland, Oregon

Field evidence and radiocarbon age dating, combined with hydraulic flow modeling, provide new information on the magnitude, frequency, and chronology of late Pleistocene Missoula floods in the Columbia River valley between the Pasco Basin, Washington, and Portland, Oregon. More than 25 floods had discharges of 1.0 106 m3/s. At least 15 floods had discharges of 3.0 106 m3/s. At least six or seven had peak discharges of 6.5 106 m3/s, and at least one flood had a peak discharge of 10 106 m3/s, a value consistent with earlier results from near Wallula Gap, but better defined because of the strong hydraulic controls imposed by critical flow at constrictions near Crown and Mitchell Points in the Columbia River Gorge. Stratigraphy and geomorphic position, combined with 25 radiocarbon ages and the widespread occurrence of the ca. 13 ka (radiocarbon years) Mount St. Helens set-S tephra, show that most if not all the Missoula flood deposits exposed in the study area were emplaced after 19 ka (radiocarbon years), and many were emplaced after 15 ka. More than 13 floods perhaps postdate ca. 13 ka, including at least two with discharges of 6 106 m3/s. From discharge and stratigraphic relationships upstream, we hypothesize that the largest flood in the study reach resulted from a Missoula flood that predated blockage of the Columbia River valley by the Cordilleran ice sheet. Multiple later floods, probably including the majority of floods recorded by fine- and coarse-grained deposits in the study area, resulted from multiple releases of glacial Lake Missoula that spilled into a blocked and inundated Columbia River valley upstream of the Okanogan lobe and were shunted south across the Channeled Scabland.

Stratigraphic and geochemical controls on naturally occurring arsenic in groundwater, eastern Wisconsin, USA

The diversity of microbial populations and microbial communities within the earth's subsurface is summarized in this review. Scientists are currently exploring the subsurface and addressing questions of microbial diversity, the interactions among microorganisms, and mechanisms for maintenance of subsurface microbial communities. Heterotrophic anaerobic microbial communities exist in relatively permeable sandstone or sandy sediments, located adjacent to organic-rich deposits. These microorganisms appear to be maintained by the consumption of organic compounds derived from adjacent deposits. Sources of organic material serving as electron donors include lignite-rich Eocene sediments beneath the Texas coastal plain, organic-rich Cretaceous shales from the southwestern US, as well as Cretaceous clays containing organic materials and fermentative bacteria from the Atlantic Coastal Plain. Additionally, highly diverse microbial communities occur in regions where a source of organic matter is not apparent but where igneous rock is present. Examples include the basalt-rich subsurface of the Columbia River valley and the granitic subsurface regions of Sweden and Canada. These subsurface microbial communities appear to be maintained by the action of lithotrophic bacteria growing on H2 that is chemically generated within the subsurface. Other deep-dwelling microbial communities exist within the deep sediments of oceans. These systems often rely on anaerobic metabolism and sulfate reduction. Microbial colonization extends to the depths below which high temperatures limit the ability of microbes to survive. Energy sources for the organisms living in the oceanic subsurface may originate as oceanic sedimentary deposits. In this review, each of these microbial communities is discussed in detail with specific reference to their energy sources, their observed growth patterns, and their diverse composition. This information is critical to develop further understanding of subsurface geochemical processes and to develop new approaches to subsurface remediation.

Geology and paleoecology of early Holocene lacustrine deposits in the Columbia River valley near Fauquier, southern British Columbia

Early Holocene lake sediments are exposed near Fauquier, on the east side of the Arrow lakes in the Columbia River valley of British Columbia. A glacial lake occupied the valley at the time of deglaciation, but by 10 ka BP this had been replaced by a nonglacial lake that was at least 250 km long and as much as 5 km wide.Comparison of pollen and macroscopic plant remains in these nearshore and littoral deposits with modern vegetation indicates that many of the plants present between 9 and 10 ka BP are found in the area today, either along the valley floor or at higher elevations in the subalpine zone nearby. Some of the organic material may be allochthonous; this complicates paleoecological and paleoclimatological interpretations. It appears that the climate in the Columbia River valley between 9 and 10 ka BP was as wet or wetter than at present. The presence of many of these species in the southern Columbia River valley of British Columbia during early Holocene time suggests that elements of the modern vegetation had migrated rapidly northward from southern refugia, probably within 1500 years of the end of the last glacial episode.

Status of Glacial Lake Columbia during the Last Floods from Glacial Lake Missoula

AbstractThe last floods from glacial Lake Missoula, Montana, probably ran into glacial Lake Columbia, in northeastern Washington. In or near Lake Columbia's Sanpoil arm, Lake Missoula floods dating from late in the Fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves. The highest three interflood intervals each contain only one or two varves, and about 200–400 successive varves conformably overlie the highest flood bed. This sequence suggests that jökulhlaup frequency progressively increased until Lake Missoula ended, and that Lake Columbia outlasted Lake Missoula. The upper Grand Coulee, Lake Columbia's late Fraser-age outlet, contains a section of 13 graded beds, most of them sandy and separated by varves, that may correlate with the highest Missoula-flood beds of the Sanpoil River valley. The upper Grand Coulee also contains probable correlatives of many of the approximately 200–400 succeeding varves, as do nearby parts of the Columbia River valley. This collective evidence casts doubt on a prevailing hypothesis according to which one or more late Fraser-age floods from Lake Missoula descended the Columbia River valley with little or no interference from Lake Columbia's Okanogan-lobe dam.

Anastomosed River Deposits--Modern and Ancient Examples in Western Canada: ABSTRACT

Depositional facies of two Canadian modern anastomosed river systems, the upper Columbia River and lower Saskatchewan River, occur in intermontane and plains settings, respectively. Both systems contain low-gradient, multiple, interconnected, laterally stable sand-bed channels, with adjacent splay, levee, and shallow wetland deposits, all aggrading in accordance with channel sedimentation. While aggrading cross-valley alluvial fans or subsidence tend to control sedimentation rates in intermontane valleys, basin subsidence and/or regional tilting controls deposition rates in plains settings. Deposits in the upper Columbia River valley (120 × 1.5 km) consist of low-sinuosity multistoried stringers (textural cycles) with planar tabular cross-bed sets of channel sands and numerous sandy crevasse-splay deposits. Channel deposits are laterally contained by deposits of levee silt and lacustrine mud, and when buried are vertically mud encased. Aggrading at an average rate of 60 cm/100 years over the past 2,500 years, the anastomosed system is very dynamic, exhibiting many avulsions and channel End_Page 631------------------------------ fills. Deposits in the lower Saskatchewan River valley (120 × 80 km), a much wider basin with much slower aggradation rates (± 15 cm/100 years), occur as channel sands flanked by laterally extensive (1 km) sheets of overbank levee deposits of fine sandy silt, which grade into even more laterally extensive thick deposits of mud or peat. With time, dominant channels become sinuous, thus causing increased flow resistance, major avulsions upriver, and eventual channel filling and abandonment. Many channel sand-fill deposits form cross-section geometries, ranging up to 15 cm thick by 120 m wide. Facies differences of the two anastomosed river systems are believed to be caused by both the rate of sedimentation and width of the sedimentary basin. Other than size differences of similar sedimentary environments, Columbia River channels are less sinuous, avulse more frequently, and contain coarser grained sand. In the Saskatchewan, some crevasse-splay (sheet sands) and associated avulsions are laterally extensive (10 × 30 km) and very complex. Wetlands in the Columbia are dominated by marsh (organic-rich mud) and lacustrine silt, whereas thick (up to 3 m) laterally extensive peat bogs dominate in the Saskatchewan system. Within the upper Mannville Group of the Lloydminster area there exists a large-scale mappable complex of fluvial channel-fill sandstones that exhibit an anastomosed pattern. The complex has areal dimensions of 250 km (width) by 700 km (length). Channel sandstones are thick (up to 35 km), narrow (300 m), can be traced for several kilometers, and are stratigraphically variable. The channel fills are multistoried, with the predominant sedimentary structures consisting of plane beds, cross-beds, and climbing current ripples. Interchannel sediments consist of interbedded sheet sandstones, siltstones, mudstones, and coals. The predominant sedimentary structures of the interchannel sandstones are the same as those found within channel sandstones. From a compare-and-contrast approach, it is concluded that meandering, sandy braided, valley-fill, deltaic, or tidal origins cannot account for the observed sand-body geometries and facies distribution. The modern model that best explains the sediment and facies distributions within the upper Mannville is the anastomosed fluvial model in which narrow, vertically accreting channels are bordered by extensive aggrading interchannel wetland deposits with interbedded crevasse-splay sands. Hydrocarbon distributions within the upper Mannville are stratigraphically controlled and oil quality can be directly related to depositional facies. Common trapping mechanisms consist of updip shale-filled channels, structural closure formed by differential compaction, and lateral sandstone pinchouts. End_of_Article - Last_Page 632------------

Geometry of Modern Anastomosed Channel Deposits and Potential Hydrocarbon Traps: ABSTRACT

The anastomosed fluvial model, interpreted from modern deposits in the upper Columbia River valley between Radium and Golden, British Columbia, consists of aggrading, multiple, low-gradient, low-sinuosity, thick, sand-filled channels laterally contained by levees, crevasse splays, and various wetland deposits. While active aggrading cross-valley alluvial fans controlled sedimentation in the upper Columbia valley, basin subsidence and/or regional tilting were controls for probable ancient anastomosed fluvial rocks, such as in the Cretaceous Western Interior molasse basin. The uniqueness of anastomosed fluvial style compared to that of meandering rivers is attributed to regional rapid aggradation, which subsequently favors anastomosed deposits for deep burial and preservati n. In the Columbia valley, the cross-valley profile of anastomosed channel deposits consists of vertically and laterally multiple stringers of channel sand, longitudinally interconnected at different stratigraphic levels. Individual channel cross sections consist of mud-contained, thick channel fills with multistoried textural cycles dominated by planar, tabular cross-bed structures. The upper ¼ to 1/3 of each channel fill consists of either mud or sandy point bar, contained laterally by mud resulting from waning river discharge. Several different trapping processes may account for hydrocarbon accumulations in ancient anastomosed fluvial sandstones, based on core observations from modern deposits in the Columbia valley. The most common trap occurs in upper channel fill point-bar sands contained laterally and above by mud. A less common trap is a sand-filled channel segment plugged at both ends with a mud-filled master channel and capped with lacustrine mud. Two other traps result from differential of mud versus sand: (1) deep scour holes at the downstream confluence of two channels allow the thicker sand-filled scour to form a domelike compaction high when capped with mud; and (2) a cross overlap of two stratigraphically different channels results in an anticline of the upper channel where it cros es over the lower channel. End_of_Article - Last_Page 631------------

Structural and stratigraphic setting of the Downie slide, Columbia River valley, British Columbia

The Downie slide is a late to postglacial rockslide situated on the western slope of the Columbia River valley about 70 km north of Revelstoke, British Columbia. It attains a maximum thickness of 270 m and is estimated to involve 1.5 × 109 m3 of rock and debris. The head of the slide is bounded by a nearly vertical escarpment reaching heights of more than 125 m; its lateral boundaries are defined by a prominent east–west trending scarp on the south and a more subdued linear northeast trending ridge on the north. The toe forms the west bank of the Columbia River in this area.The slide occurs within a compositionally anisotropic formation of high-grade pelitic and semipelitic schists and psammites. The main shear zone at the base of the slide is located in pelitic schists. Minerals in the rock of the shear zone have been mechanically crushed and locally reduced to a fine-grained gouge.Three distinct phases of deformation are recognized in the Downie slide region. The location and attitude of the second and third fold phases and their associated fabrics controlled the external geometry of the slide.Along the western slopes of this part of the Columbia River valley the second phase of deformation has been dominant. Within the formation that contains the slide, bedding is extensively deformed by tight to isoclinal second phase minor folds that exhibit a penetrative axial plane foliation. At Downie slide this foliation dips approximately 20° eastward towards the Columbia River, and nearly parallels the slope of the hillside; the basal shear zone of the slide developed parallel to the axial plane foliation.West of the slide, third phase major and minor folds have been superimposed on the second phase geometry, but they die out eastward, and are of only minor significance within the main body of the slide. The eastern limit of major superposition coincides with the head scarp of the slide. The slide mass broke away along the hinge zone of the first major monoclinal flexure fold associated with this front of phase 3 folding.Late fracturing probably influenced the position of the northern and southern lateral boundaries of the slide.

Age of the last major scabland flood of the Columbia Plateau in eastern Washington

Pumice layers of set S from Mount St. Helens can be correlated with certain ash beds associated with young flood deposits of the channeled scabland. The correlation points to an age of about 13,000 14C yr B.P. for the last major flood to have crossed the scabland. Until recently, the last major episode of flooding was thought to be closer to 20,000 yr B.P., an age inferred chiefly from the relation of the flood to glacial events of the northern Rocky Mountains. Several investigations within the last few years have suggested that the last major flood occurred well after 20,000 yr B.P. Tentative correlations of ash beds of the scabland with set S pumice layers, the relations of flood and glacial events along the northwestern margin of the Columbia Plateau, and a radiocarbon date from the Snake River drainage southeast of the plateau all indicate an age much younger than 20,000 yr. The postulated age of about 13,000 yr B.P. is further supported by a radiocarbon date in the Columbia River valley downstream from the scabland tract. Basal peat from a bog on the Portland delta of Bretz, which is a downvalley deposit of the last major scabland flood, has been dated as 13,080 ± 300 yr B.P. (W-3404).