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In regions formerly covered by continental ice, till sheets may contain distinctive clastic particles derived from local bedrock sources such as ore bodies. Such particles, especially in thicker tills, may be distributed in three-dimensional dispersal trains or plumes. Developments in our understanding of glacial erosion, entrainment, and deposition over the past two or three decades help clarify formation of these plumes. Much of the debris in the basal ice of ice sheets is likely incorporated at places where water is freezing onto the base of the ice sheet. This water, largely a product of melting of basal ice further upglacier, has migrated downglacier under the influence of a gradient in the hydraulic potential controlled primarily by the ice surface slope and secondarily by basal topography and thermal regime. Refreezing occurs over a substantial distance along flow, so as the ice moves away from an ore body, material eroded from the body is later elevated above the bed by refreezing of more meltwater, incorporating additional material derived from the country rock. Broadening and mixing of the plume, both vertically and horizontally, can occur by shear in the ice, by shifting ice flow directions, by collisions between particles, and by folding of basal ice layers. Further downflow, where net basal melting resumes, the debris is deposited by meltout or lodgement. Many idiosyncrasies of dispersal plumes are likely caused by non-steady-state changes in basal thermal regime. Dans des regions anciennement recouvertes de glace continentale, les couches de till peuvent contenir des particules clastiques distinctives provenant du socle rocheux local, p. ex des amas mineralises. De telles particules, surtout dans les tills a grande epaisseur, peuvent etre distribuees dans des trains ou des panaches de dispersion a trois dimensions. Au cours des deux a trois dernieres decennies, une meilleure comprehension de l'erosion glaciaire, du transport et de la deposition a aide a expliquer la formation de ces panaches. Une grande partie des debris dans la couche de glace basale est sans doute incorporee a des endroits ou l'eau gele a la base de la nappe glaciaire. Cette eau, provenant en grande partie de la fusion de la couche de glace basale plus en amont du glacier, a migre vers l'aval sous l'influence d'un gradient du potentiel hydraulique, lequel est surtout controle par la pente de la surface glaciaire et puis par la topographie a la base du glacier et le regime thermique. Le regel a lieu sur une grande distance le long de l'ecoulement; donc, a mesure que la glace s'eloigne d'un amas mineralise, le materiel erode de l'amas est par la suite eleve au-dessus du lit par le regel d'autre eau de fonte, incorporant du materiel additionnel provenant de la roche encaissante. L'elargissement du panache et le melange a l'interieur de celui-ci, horizontalement et verticalement, peuvent se produire par le cisaillement de la glace, le changement de direction d'ecoulement de la glace, des collisions entre les particules et le plissement de couches basales. Plus encore vers l'aval, lorsque recommence la fonte basale nette, les debris sont deposes dans un till de fusion ou de fond. Plusieurs particularites des panaches de dispersion proviennent probablement de changements d'etats non stationnaires au regime thermique de base. [Traduit par la Redaction], Introduction For over two centuries, it has been recognized that ore bodies could be located by tracing clasts in glacial till back to their origin in the bedrock. The process [...]

We review over 100 years of literature on Prairie buried valleys to provide a platform for future research and policy development. Prairie buried-valley fills commonly function as aquifers that yield abundant groundwater. They have distinct geologies and a distinct stratigraphic setting, which imparts them with distinct hydrogeological properties and gives clues as to how they formed and filled. Prairie buried-valley aquifers are commonly encased in low-permeability strata: Cretaceous shale commonly underlies them, and thick (10-300 m) low-permeability Quaternary till tends to overlie them. This reduces recharge, in rare cases nearly completely, while protecting groundwater resources from contamination and drought. It also tends to lead to highly mineralized groundwater chemistries. The stratigraphic position of Prairie buried valleys also speaks to their origin: those that subtend ('hang') from the bedrock unconformity were likely eroded by preglacial fluvial systems during late Tertiary uplift of the Rocky Mountains, whereas those that subtend from surfaces within the till package are likely glaciofluvial valleys eroded in proglacial spillway or tunnel-valley settings. Another key trait of Prairie buried valleys is that their fills tend to be heterogeneous and architecturally complex. Sand, gravel, mud, and diamicton are common; any one can dominate the fill at a given location. This heterogeneity, in conjunction with irregularity common to buried-valley bedrock floors, commonly causes aquifer compartmentalization and makes prediction of aquifer potential difficult prior to drilling. It also suggests that most Prairie buried valleys filled over time, and likely over multiple glaciations, in multiple depositional environments. Nous passons en revue 100 ans de litterature sur les vallees enfouies des Prairies afin de fournir une plate-forme pour la recherche future et le developpement de politiques. Le materiau de remplissage des vallees enfouies sert souvent d'aquiferes fournissant beaucoup d'eau souterraine. Ces vallees enfouies ont des geologies distinctes et un environnement stratigraphique distinct ce qui leur confere des proprietes hydrogeologiques distinctes et fournit des indices quant a leur mode de formation et de remplissage. Les aquiferes de vallees enfouies sont frequemment encaisses dans des strates de faible permeabilite : ils reposent souvent sur des shales datant du Cretace et sous d'epais (10 a 300 m) tills du Quaternaire a faible permeabilite. Cela reduit la recharge, dans certains cas presque completement, tout en protegeant les ressources d'eau souterraines de la contamination et de l'assechement. Cela tend aussi a donner des eaux souterraines hautement mineralisees. La position stratigraphique des vallees enfouies des Prairies temoigne aussi de leur origine : celles qui sont a la base (qui << pendent >>) de la discordance du socle rocheux ont probablement ete erodees par des systemes fluviaux durant le soulevement des montagnes Rocheuses au Tertiaire tardif, alors que ceux qui sont a la base de surfaces dans le till sont probablement des vallees fluvioglaciaires erodees dans un environnement de deversoir proglaciaire ou de vallee-tunnel. Un autre trait caracteristique des vallees enfouies des Prairies est que leur remplissage tend a etre heterogene et a avoir une architecture complexe. Le sable, le gravier, les boues et les diamictons sont frequents; n'importe lequel pouvant dominer la composition du remplissage a un endroit donne. Cette heterogeneite, de concert avec l'irregularite frequente des surfaces du socle dans les vallees enfouies, engendre une compartimentation de l'aquifere et rend difficile la prevision du potentiel de l'aquifere avant les forages. Cela suggere aussi que la plupart des vallees enfouies des Prairies se soient remplies avec le temps, et probablement durant de multiples glaciations, dans plusieurs environnements de deposition. [Traduit par la Redaction], Introduction Buried valleys eroded into bedrock and covered by till were first identified in the Prairies over 100 years ago along river cuts in Alberta and Montana (Fig. 1; Bell [...]

Based on its anomalous thickness (~150 m) and stratigraphic position above continental-slope mudstone, an upward-coarsening succession consisting in part of tidal rhythmites in the Glenelg Field, offshore Nova Scotia, Canada, is interpreted to be a strongly tide-influenced shelf-margin-delta deposit. A large, funnel-shaped erosional shelf-edge invagination is observed where the paleoshelf edge is resolved in three-dimensional seismic data adjacent to Glenelg. We propose that the delta at Glenelg prograded into a similar shelf-edge invagination within which tidal currents were amplified and wave energy was attenuated. Given that funnel-shaped invaginations (e.g., slope canyon heads, slump scars, fluvially incised knickmarks) are relatively common along modern shelf edges, and that fluvio-deltaic systems should be focused into these topographic lows during regression across the shelf, it seems likely that shelf-edge invaginations play an important but underappreciated role in mediating terrigenous clastic sedimentation during sea-level Iowstands. Keywords: deltas, tides, shelf-slope break, sequence stratigraphy, facies.

In regions formerly covered by continental ice, till sheets may contain distinctive clastic particles derived from local bedrock sources such as ore bodies. Such particles, especially in thicker tills, may be distributed in three-dimensional dispersal trains or plumes. Developments in our understanding of glacial erosion, entrainment, and deposition over the past two or three decades help clarify formation of these plumes. Much of the debris in the basal ice of ice sheets is likely incorporated at places where water is freezing onto the base of the ice sheet. This water, largely a product of melting of basal ice further upglacier, has migrated downglacier under the influence of a gradient in the hydraulic potential controlled primarily by the ice surface slope and secondarily by basal topography and thermal regime. Refreezing occurs over a substantial distance along flow, so as the ice moves away from an ore body, material eroded from the body is later elevated above the bed by refreezing of more meltwater, incorporating additional material derived from the country rock. Broadening and mixing of the plume, both vertically and horizontally, can occur by shear in the ice, by shifting ice flow directions, by collisions between particles, and by folding of basal ice layers. Further downflow, where net basal melting resumes, the debris is deposited by meltout or lodgement. Many idiosyncrasies of dispersal plumes are likely caused by non-steady-state changes in basal thermal regime. [ABSTRACT FROM AUTHOR]

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The article discusses a study on the sequence stratigraphy of a glaciated basin fill using an integrated data set of cores, out-crop data, seismic transects from the Vars-Winchester esker in the Champlain Sea basin in Ottawa, Ontario. The researchers explained that the esker has been obtained from the underlying till by water that flowed through a subglacial conduit. They conclude that the geology of the esker shows gradual and catastrophic processes.