Transport of Indicator Clasts by Ice Sheets and the Transport Half-Distance: A Contribution to Prospecting for ORE Deposits

Ströbel, Michael; Faure, Gunter

doi:10.1086/629164

Cited by 23 publications

(21 citation statements)

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“…The cumulative effect on glacial transport of two or more ice movements in the same general direction is rarely discussed in the literature, probably because of the difficulty of estimating it. Strobel and Faure (1987), tracing Precambrian Shield indicator clasts in till, from a source in southern Ontario, to large ice-marginal moraines in Ohio and Indiana, U.S.A., found a nearly constant 4% value for more than 800 km down-ice, in the tail part of the dispersal train. This value is higher than reported here at shorter distances, and may be due to contrasting lithology, i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Analytical methods used in this project are compared with those of two well-known long-distance transport studies (Salonen, 1986;Strobel and Faure, 1987), representative of most methods used in similar projects. Distances in transport studies are commonly measured along flow lines constructed from ice-flow directions derived from the orientation of icemarginal and streamlined landforms (Strobel and Faure, 1987).…”

Section: Field Methodsmentioning

confidence: 99%

“…Distances in transport studies are commonly measured along flow lines constructed from ice-flow directions derived from the orientation of icemarginal and streamlined landforms (Strobel and Faure, 1987). Flow lines are usually representative of the last regional ice flow (or flows) in a region.…”

Section: Field Methodsmentioning

confidence: 99%

“…Collecting large samples from shallow pits or sections distributed along ice flow lines, and brought back to the laboratory for petrographic analysis (Strobel and Faure, 1987), or clast counting performed in the field (Salonen, 1986), are the two most common methods to estimate glacial transport. This last method was preferred because, (1) large clasts facilitate petrographic identification in the field, (2) logistical considerations (transport by small boat) prevented systematic collection of large samples for further analysis, (3) large areas of clean, wave-washed, boulder pavements, allowed the detection of distinctive erratics and the counting of thousands of clasts in short periods of time.…”

Section: Field Methodsmentioning

confidence: 99%

“…Mapping the distribution of far-traveled erratics, from known source areas, has been fundamental to infer directions of movement and shifts of the ice mass through time (Prest and Nielsen, 1987;Kaszycki, 1989). The analysis of long-distance transport of Precambrian Shield indicator clasts in till, from a source in southern Ontario, Canada, to large ice-marginal moraines in Ohio and Indiana, U.S.A., led Strobel and Faure (1987) to conclude that the abundance of the clasts (100% at the source) decreases exponentially but then remains nearly constant (4%) for more than 800 km down-ice.…”

Section: Territoire Couvert Par Les Levés D'erratiques Dumentioning

confidence: 99%

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Ice-Flow Chronology and Palimpsest, Long-Distance Dispersal of Indicator Clasts, North of the St. Lawrence River Valley, Quebec

Veillette

2006

gpq

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An ice flow model, based on the distribution of distinctive Proterozoic erratics from the Lake Mistassini and Monts Otish sedimentary basins, and on the mapping of relict striations in a 230 000 km2 area located predominantly in Grenville Province, Québec, is presented to reconstruct the evolution of a large part of the Labrador Sector of the Laurentide Ice Sheet during the Wisconsinan. The results, were added to those of similar surveys carried out in the Abitibi region, and further north. Striated surfaces and indicator clasts from an early northwestward flow, overprinted by those from a widespread southeastward flow, and lastly by those from deglaciation flows toward the southwest, south, and southeast, revealed a complex sequence of events. The northwestward flow originated from a NE‑SW, early Wisconsinan, ice divide located in the Québec highlands, south of Lake Mistassini, that migrated to a position north of the lake, at the Last Glacial Maximum, to give rise to the widespread, southeastward ice flow, that left traces over a large part of Grenville Province. Deglaciation triggered a clockwise shift in ice-flow south of Lake Mistassini, and a counterclockwise shift, north of it. Inception of the northwestward flowing glacier probably results from the coalescence of ice caps formed at the highest elevations along a narrow fringe, north of and parallel to the St. Lawrence River Valley, and expansion toward the northwest suggests a similarity with the windward growth model of ice sheet expansion. The ice flow model has implications for mineral exploration methods based on the sampling of glacial sediments.Une séquence d’écoulements glaciaires est proposée pour expliquer l’évolution d’une grande partie du secteur du Labrador de la calotte laurentidienne au cours du Wisconsinien, à partir de la répartition d’erratiques distinctifs provenant des roches protérozoïques des bassins sédimentaires du lac Mistassini et des monts Otish, et de celle de stries glaciaires anciennes dans une région d’environ 230 000 km2, dont la majeure partie est située dans la province de Grenville, au Québec. Ces nouvelles données ont été ajoutées à celles provenant de levés semblables menés antérieurement en Abitibi, et plus loin au nord. Les surfaces striées et les indicateurs lithologiques de transport glaciaire, associés au premier écoulement vers le nord-ouest, recoupés par ceux d’un écoulement majeur vers le sud-est, et ensuite par ceux d’écoulements vers le sud-ouest, le sud et le sud-est, lors de la déglaciation du territoire, témoignent d’une suite complexe d’évènements glaciaires. Le mouvement initial, vers le nord-ouest, résulte d’une zone de partage des glaces d’orientation NE‑SO, située dans les hautes terres du Québec, au sud du lac Mistassini, laquelle se déplaça au nord du lac Mistassini au Pléniglaciaire, pour former l’écoulement vers le sud-est, dont les traces couvrent une grande partie de la province de Grenville. Lors de la dernière déglaciation des ajustements dans le sens d’écoulement des glaces ont engendré des ro...

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Section: Discussionmentioning

confidence: 99%

Section: Field Methodsmentioning

confidence: 99%

Section: Field Methodsmentioning

confidence: 99%

Section: Field Methodsmentioning

confidence: 99%

Section: Territoire Couvert Par Les Levés D'erratiques Dumentioning

confidence: 99%

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