Search

Detailed studies of coastal cliff exposures through two end moraines form the basis for a model of ice-marginal sedimentation in large ice-contact glacier-fed lakes. The input to the ice-marginal environment directly from the glacier included subglacial till and subaquatic flow tills. The subaquatic flow till (thinly bedded diamicton) was deposited in an apron (up to 1 km wide) along the ice margin. An upward gradient of pore-water pressure immediately beyond the ice margin, causing heaving and dilation of the sediments, initiated debris flows of glacially derived debris (subaquatic flow tills). Most of the stratified sediments in the ice-marginal zone entered the lake by way of a large proglacial stream. Sedimentation was dominated by quasi- or near-continuous density underflows that resulted in the deposition of a sequence of thick rhythmites. The glacier in the Lake Erie basin most likely behaved like an ice stream, with its movement controlled predominantly by a deforming bed of glacial debris, separating the glacier sole from underlying predeposited sediments. The deforming bed is preserved as a massive diamicton layer, interpreted here as subglacially deposited till. Des études détaillées de coupes dans des falaises côtières à travers deux moraines terminales forment la base d'un modèle de sédimentation proglaciaire dans de grands lacs alimentés par des glaciers et en contact avec ces derniers. Les apports au milieu proglaciaire provenant directement du glacier comprennent du till infraglaciaire et des tills d'écoulement subaquatiques. Le till d'écoulement subaquatique (du diamicton finement lité) a été déposé dans une plaine d'épandage (de jusqu'à 1 km de large) le long de la marge glaciaire. Un gradient de pression d'eau interstitielle ascendant immédiatement au-delà de la marge glaciaire, à l'origine d'un gonflement et d'une dilatation des sédiments, a déclenché des coulées de débris d'origine glaciaire (tills d'écoulement subaquatiques). La plupart des sédiments stratifiés dans la zone proglaciaire sont entrés dans le lac par un grand cours d'eau proglaciaire. La sédimentation était dominée par des écoulements de fond par densité quasi continus qui se sont traduits par le dépôt d'une séquence de rhythmites épaisses. Le glacier dans le bassin du lac Érié se comportait vraisemblablement comme une coulée glaciaire dont le déplacement était principalement contrôlé par un lit mouvant de débris glaciaires séparant la semelle du glacier des sédiments sous-jacents déposés antérieurement. Le lit mouvant est préservé sous la forme d'une couche de diamicton massif interprétée comme étant un till déposé sous le glacier. [Traduit par la Rédaction], Introduction Studies at the margins of modern glaciers in ice-contact glacier-fed lakes are hampered by the inherent dangers of the environment, while studies on Pleistocene or older deposits in glaciated [...]

The Nipigon channels, located to the west and northwest of Lake Nipigon, Ontario, are thought to have enabled the eastward drainage of meltwater from glacial Lake Agassiz during the last deglaciation. Here we present the first direct ages of flood deposits in two of these channels using [sup.10]Be surface exposure dating. Five [sup.10]Be ages of a coarse- grained deposit near the Roaring River in the Kaiashk channel complex indicate deglaciation and cessation of water flow by ~11070 ± 430 years. To test for inherited nuclides in boulder samples, we also measured the [sup.10]Be concentrations of the undersides of two boulders at the Roaring River site. Five [sup.10]Be ages of boulders atop a large bed form near Mundell Lake in the Pillar channel complex indicate deglaciation and cessation of water flow by ~10 770 ± 240 years. Two [sup.10]Be ages of nearby bedrock are slightly younger (10 340 ± 260 and 9860 ± 270 years). The [sup.10]Be ages from the two sites are statistically indistinguishable and indicate that Laurentide Ice Sheet recession occurred rapidly in the region. We used clast diameters and channel dimensions at the Mundell Lake site to estimate paleodischarge and evaluate the possibility that meltwater drainage influenced climate conditions. We estimate a large maximum discharge of 119 000-159 000 [m.sup.3] x [s.sup.-1] at the site. However, the timing of meltwater discharge at both Roaring River and Mundell Lake is not contemporaneous with abrupt climate events. Les chenaux de Nipigon, situes a l'ouest et au nord-ouest du lac Nipigon (Ontario) auraient permis la vidange vers l'est de l'eau de fonte issue du lac glaciaire Agassiz durant la derniere deglaciation. Nous presentons les premiers ages directs de depots d'inondation dans deux de ces chenaux, obtenus par datation au [sup.10]Be de l'exposition en surface. Cinq ages [sup.10]Be d'un depot a grains grossiers situe pres de la riviere Roaring, dans le complexe de chenaux de Kaiashk, indiquent que la deglaciation et la cessation de l'ecoulement de l'eau avaient deja eu lieu vers 11070 ± 430 ans. Pour verifier la presence de nucleides herites dans des echantillons de bloc, nous avons egalement mesure les concentrations de [sup.10]Be des faces inferieures de deux blocs au site de la riviere Roaring. Cinq ages [sup.10]Be de blocs au sommet d'une grande forme de fond pres du lac Mundell dans le complexe de chenaux de Pillar indiquent que la deglaciation et la cessation de l'ecoulement de l'eau avaient deja eu lieu vers 10 770 ± 240 ans. Deux ages [sup.10]Be du substrat rocheux a proximite sont legerement plus jeunes (10 340 ± 260 et 9860 ± 270 ans). Les ages [sup.10]Be obtenus des deux sites sont statistiquement identiques et indiquent que le recul de la calotte glaciaire des Laurentides s'est effectue rapidement dans cette region. Nous avons utilise les diametres des clastes et les dimensions des chenaux au site du lac Mundell pour estimer les paleodebits et evaluer la possibilite que la vidange de l'eau de fonte ait influence les conditions climatiques. Nous estimons un important debit maximum au site, de l'ordre de 119 000 a 159 000 [m.sup.3] x [s.sup.-1]. Le moment de la vidange de l'eau de fonte tant a la riviere Roaring qu'au lac Mundell ne correspond toutefois pas a des evenements climatiques brusques. [Traduit par la Redaction], Introduction It has long been thought that channels in the areas located west of Thunder Bay and west and northwest of Lake Nipigon, Ontario (Fig. 1), served as eastern outlets [...]

The exposures at the St. Marys Cement Inc. quarry at St. Marys, Ontario, have been studied by geologists since the mid-1950s. This paper summarizes previous and new information collected in 2009, 2010, and 2012 and discusses the record of sediments resting on the bedrock surface that have been exposed during quarry operations. The exposed sediments illustrate the dynamic behavior of the Laurentide Ice Sheet in this area during the Late Wisconsin. Evidence for subglacial meltwater activity, shifting ice-flow directions during till deposition, a local or regional erosion event, possible subaerial exposure, and ice-marginal sedimentation is observed in the sequence of tills and stratified sediments exposed in the quarries. It also highlights how rapid lateral facies changes, complex contact relationships, and steep erosional contacts can prove to be challenging for correlation and extrapolation of subsurface units into three-dimensional stratigraphic models. Fourteen units were identified of which the lower six were deposited during the Nissouri age (Catfish Creek Drift). This included five layers of till deposited by a glacier that alternated from flowing out of the Lake Huron basin to that of a regional flow to the south-southwest. An angular unconformity cuts into these sediments and separates them from a finer-grained sediment sequence (primarily of Port Bruce age) consisting of glaciofluvial gravel, two fine-textured till layers, and rhythmically bedded glaciolacustrine sediments, all overlain by the uppermost till, the Rannoch Till, and Mitchell Moraine ice-marginal fan sediments. Les geologues etudient les affleurements a la carriere de la St. Marys Cement Inc., a St. Marys en Ontario, depuis le milieu des annees 1950. Le present article resume des donnees deja acquises et de nouvelles informations recueillies durant les annees 2009, 2010 et 2012; il traite du profil geologique des sediments qui reposent sur le socle et qui ont ete exposes durant l'exploitation de la carriere. Les sediments exposes illustrent le comportement dynamique de l'Inlandsis laurentidien dans ce secteur au Wisconsin tardif. Des evidences d'activite d'eau de fonte sous-glaciaire, la variation de la direction de l'ecoulement glaciaire, un evenement d'erosion local ou regional, une possible exposition subaerienne et une sedimentation en bordure de la glace sont observes dans les sequences de tills et de sediments stratifies qui affleurent dans les carrieres. Tous ces points soulignent aussi la maniere dont les changements lateraux rapides de facies, les relations complexes de contact et les contacts d'erosion abrupts peuvent poser des defis pour la correlation et l'extrapolation des unites sous la surface dans des modeles stratigraphiques tridimensionnels. Quatorze unites ont ete identifiees dont six unites inferieures qui ont ete deposees durant le stade glaciaire Nissouri (drift de Catfish Creek). Ces unites comprenaient cinq couches de till deposees par un glacier qui s'ecoulait alternativement entre le bassin Huron et de maniere regionale vers le sud-sud-ouest. Une discordance angulaire recoupe ces sediments et les separe d'une sequence a grains plus fins (surtout d'age Port Bruce) qui est composee de gravier fluvioglaciaire, de deux couches de till a texture fine et de sediments glacio-lacustres a stratification rythmique; le tout est recouvert par le till superieur, le till de Rannoch et des sediments de lobe proglaciaire en bordure de la moraine de Mitchell. [Traduit par la Redaction], Introduction With the onset of three-dimensional (3D) mapping of Quaternary sediments primarily for regional groundwater applications in areas surrounding the Great Lakes by State, Provincial, and Federal surveys, emphasis has [...]

Abstract: The Surficial Geochemistry Case Studies Project in the Lake Nipigon region involved detailed Quaternary mapping and multimedia geochemical sampling within five case study areas. Two of these areas, Lac [...]

Abstract: Many previously published studies of the behaviour of Pt and Pd in till and soils have been done in areas of complex stratigraphy or very thin overburden cover, making [...]

The paper by Phillip Larson and Howard Mooers (2005) is an interesting attempt to document the glacial dispersal of one heavy mineral and then try to relate the mineral's dispersal [...]

Detailed studies of coastal cliff exposures through two end moraines form the basis for a model of ice-marginal sedimentation in large ice-contact glacier-fed lakes. The input to the ice-marginal environment directly from the glacier included subglacial till and subaquatic flow tills. The subaquatic flow till (thinly bedded diamicton) was deposited in an apron (up to 1 km wide) along the ice margin. An upward gradient of pore-water pressure immediately beyond the ice margin, causing heaving and dilation of the sediments, initiated debris flows of glacially derived debris (subaquatic flow tills). Most of the stratified sediments in the ice-marginal zone entered the lake by way of a large proglacial stream. Sedimentation was dominated by quasi- or near-continuous density underflows that resulted in the deposition of a sequence of thick rhythmites. The glacier in the Lake Erie basin most likely behaved like an ice stream, with its movement controlled predominantly by a deforming bed of glacial debris, separating the glacier sole from underlying predeposited sediments. The deforming bed is preserved as a massive diamicton layer, interpreted here as subglacially deposited till. [ABSTRACT FROM AUTHOR]

We examine pollen, macrofossils and sedimentological proxies from the Ridge Site, an 18-m sequence of glacial and non-glacial sediments exposed along the bank of the Ridge River in the southern Hudson Bay Lowlands ( HBL), Canada. As the HBL is located in the previously glaciated region of North America, palaeorecords from this region have important implications for understanding ice-sheet palaeogeography and climate for the late Pleistocene. Two diamicton units were interpreted as subglacial till deposited by a glacier flowing toward the south-southwest (lower diamicton) and west-southwest (upper diamicton), respectively. Confined between these tills is a 6-m non-glacial unit, constrained to Marine Isotope Stage 3 ( MIS 3; c. 57 000 to c. 29 000 a BP) by three radiocarbon dates. Quantitative analyses of the pollen record (dominated by Sphagnum, Cyperaceae, Pinus, Picea, Salix, Alnus and Betula) suggest that average summer temperature (June, July, August) was 14.6±1.51 °C, which is similar to that of the present day at the site. Total annual precipitation was 527±170 mm as compared to 705 mm present-day. The macrofossil record confirmed the local presence of Betula, Salix and conifers. Our results, in combination with other records from the periphery of the Laurentide Ice Sheet, suggest that vast boreal forest-type vegetation, along with a drier interstadial climate, existed in the region during MIS 3. We also compare pollen-derived palaeoclimate reconstructions from the Ridge Site with reconstructions from a previously published site along the Nottaway River, HBL, which was dated to MIS 5a-d ( c. 109 000 to c. 82 000 a BP). This comparison suggests that, with additional data, it may be possible to differentiate MIS 3 and MIS 5 deposits in the HBL on the basis of relative continentality, with MIS 3 characterized by lower total annual precipitation, and MIS 5 by values similar or greater than present-day. [ABSTRACT FROM AUTHOR]

In-vitro drug release of triamcinolone acetonide from the I-vation implant can be controlled and tuned by varying its formulation ingredients. These release characteristics can be modeled using a parabolic partial differential equation to describe one dimensional Fickian drug diffusion in a durable polymer matrix.