Skip to Main Content
Book Chapter

Glacial Dispersal of Rocks, Minerals, and Trace Elements in Wisconsinan Till, Southeastern Quebec, Canada

W. W. Shilts
W. W. Shilts
Search for other works by this author on:
January 01, 1973

Lennoxville Till of the Lac-Mégantic region is homogeneous with respect to fabric, texture, clay-mineral composition, and color. The homogeneity resulted from erosion and transportation by a glacier that moved southeastward over bedrock that had little petrologic variation. Lennox-ville Till is, however, also characterized by southeast-trending bands with high concentrations of certain rocks, minerals, and chemical components derived from scattered igneous bodies.

Chromium, nickel, and magnetite are dispersed in ribbonlike bands at least 50 km southeast of their principal source areas in the ultrabasic-basic rock complex at Thetford Mines. Concentrations of surface erratics derived from these same sources have dispersal patterns similar to those of Cr, Ni, and magnetite.

Plagioclase grains and granodioritic erratics are dispersed in bands southeast of the granodiorite stock of the Little Megantic Mountains. Granodioritic erratics that occur on the surface are thought to have been let down onto lodgment facies of Lennoxville Till during melting of the Lennoxville glacier, because they mantle the surface of its grano-diorite-poor clay-till facies. By extension, most of the boulder mantle that characteristically rests on Lennoxville lodgment facies may be an ablation deposit with dispersal characteristics locally reflecting glacier deflections and lobations that occurred during deglaciation.

Dispersal data strongly confirm ice-flow patterns inferred independently from striation, fabric, and geomorphic data. Most till components discussed show evidence of long-distance transport, except where topographic prominences have blocked or deflected ice-transported sediment.

No evidence was found to support the concept of glacier flow into Quebec from late-glacial highland centers of outflow located south or east of the area.

Texture of till has an important influence on observed concentrations of trace elements. Zr is concentrated preferentially in the silt fraction of silt + clay; Ti, Cu, V, Zn, Pb, Cr, and Ni are concentrated preferentially in the clay fraction. Concentrations of Cr, Ni, and Ti are thought to be texture-independent in samples located down-ice from igneous sources rich in these components.

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables


GSA Memoirs

The Wisconsinan Stage

Robert F. Black
Robert F. Black
Search for other works by this author on:
Richard P. Goldthwait
Richard P. Goldthwait
Search for other works by this author on:
H. B. Willman
H. B. Willman
Search for other works by this author on:
Geological Society of America
ISBN print:
Publication date:
January 01, 1973




A comprehensive resource of eBooks for researchers in the Earth Sciences

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

View Article Abstract & Purchase Options

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Subscribe Now