Inferences on glacial flow from till clast dispersal, Waterford area, New Brunswick

Abstract

Dispersal patterns for till clasts from the Waterford area, New Brunswick, are compared to source outcrops and used to confirm dominant ice-flow directions in a region reported to show multiple and conflicting striae directions. The results demonstrate that the last glaciation produced elongated south and eastward trending dispersal patterns, indicative of the dominant ice-flow directions. Clasts have been derived locally. Train lengths generally vary from 4 km to about 10 km for material in basal till, but can achieve distances up to 26 km because of transport in englacial positions. Felsic and intermediate metavolcanic and intrusive clasts occur in till at locations north of outcropping plutons on the Central Plateau. The till overlies part of the Carboniferous Basin and has been derived in part, from underlying conglomerate bedrock. Since these conglomerate units contain fragments from the surrounding areas including the Central Plateau, they provided a secondary source for some lithologies during glaciation. Glacial erosion of underlying conglomerate units may account for occurrences of distinctive till clasts found at other areas of the New Brunswick lowlands, previously thought to imply northward glacial transport.Les patrons de dispersion des cailloux du till sont comparés aux affleurements d'origine afin de reconstituer les principales directions de l'écoulement glaciaire dans une région où les stries montrent des directions multiples et discordantes. Pour les tills de la dernière glaciation, les patrons de dispersion s'étirent vers le sud et l'est. Certains cailloux ont été remaniés localement. La longueur des traînées de dispersion varie généralement de 4 à 10 km en ce qui a trait au matériel du till de fond, mais peut s'allonger sur 26 km en cas de transport intraglaciaire. Des cailloux de roche intrusive ainsi que felsitique et métavolcanique intermédiaire se trouvent dans le till à certains sites situés au nord des plutons affleurant sur le plateau central. Le till recouvre une partie du bassin carbonifère et son matériel a été remanié, en partie, du conglomérat sous-jacent. Étant donné que ces unités de conglomérat renferment des fragments des régions avoisinantes, y compris du plateau central, elles sont devenues une source secondaire de certaines lithologies au cours de la glaciation. L'érosion glaciaire d'unités sous-jacentes de conglomérat peut expliquer la présence de cailloux particuliers dans le till trouvés dans d'autres régions des basses terres du Nouveau-Brunswick, qui témoignaient, croyait-on, d'un flux glaciaire vers le nord.Die Dispersions-Muster der Kiesel des Tills im Water- ford-Gebiet, Neu-Braunschweig, werden mit den ursprünglichen Ausstrichen verglichen, um Hauptrichtungen des Eisfließens in einem Gebiet zu bestätigen, wo mannigfaltige und diskordante Schrammen-Richtungen auftreten. Die Ergebnisse zeigen, daß die letzte Vereisung langgezogene süd- und ostwärts gerichtete Dispersionsmuster bewirkte, welche auf die Hauptrichtungen des Eisfließens weisen. Die Kiesel sind örtlich um...

Lithology and geochemical dispersal in till: Petitcodiac area, New Brunswick

“…In southeastern New Brunswick, the regional ice-fl ow direction during the Late Wisconsinan ranged between southsouthwest and southeast (Rampton et al 1984;Munn et al 1996;Broster et al 1997). Within the Petitcodiac map area, similar ice-fl ow directions have been documented (Chalmers 1890;Rampton et al 1984;Seaman 1987Seaman , 1991.…”

“…Also, rare north-northwest directed rat tails on the northern fl anks of the highlands, and distinctive felsic and mafi c till clasts found north of their original (Precambrian) source area, have been cited as evidence of northward fl owing glaciers during the Early Wisconsinan (Foisy and Prichonnet 1991). However, recent research south of the study area by Broster et al (1997) suggests that the Precambrian lithologies have undergone multiple (pre-Carboniferous) erosive and transport events and are present as clasts and boulders within the younger Carboniferous conglomerate units. These underlying conglomerate units were a second source of clast lithologies, originally from surrounding Precambrian bedrock units, and not considered defi nitive evidence of northward glacier transport .…”

Comparison of clast and matrix dispersal in till: Charlo-Atholville area, north-central New Brunswick

“…It is possible that there are unknown sources of rhyolite clasts to the southwest of some bulls-eye dispersal patterns. Broster et al (1997) demonstrate that conglomerate units in some areas can also serve as underlying sources for resistant clast lithologies, originally from much older units that were incorporated into younger conglomerates and subsequently eroded by a glacier. However, no local conglomerate sources have been reported here, or to the west of this area (Carroll 2003;Wilson 2003) These observations present a dilemma for identifying unknown sources of geochemical anomalies in the central part of the study area.…”

The pattern of glaciation on the Avalon Peninsula of Newfoundland

“…Clasts eroded by an initial glacial event may be transported by one or more subsequent glaciations, producing erratic clast distributions at variance with the orientation of other ice-flow indicators, such as striations (e.g. Schau, 1981;Broster et al, 1997). Clasts derived from pre-glacial weathering may also be incorporated into glacial deposits, complicating analysis of glacial transport processes and directions (e.g.…”

“…Although individual erratics may have undergone multiple episodes of transport, the presence of clasts which have been transported upslope indicates glacial redistribution (cf. Broster et al, 1997).…”