Magnetic and pebble fabrics of glaciomarine diamictons in the Champlain Sea, Ontario, Canada

Abstract

Glaciomarine diamicton(ite)s that contain articulated unbroken shell remains are usually assumed to have been deposited by the settling out of suspended mud with additions of coarse clasts derived from the melting of debris-laden floating ice. However, little is known about the magnetic and pebble fabrics of these composite sediments, and the purpose of this study is to describe and interpret the magnetic and pebble fabrics of fossiliferous glaciomarine diamictons found at three locations in the Champlain Sea, Ontario.At two of the three sites examined it is found that the long axes of the prolate and blade-shaped pebbles do not show well defined alignments, but they are not randomly distributed in either the horizontal or vertical planes. This observation and an analysis of the alignment of the magnetic particles in the matrix of the diamictons show that the diamictons have undergone syn- or post-depositional movement and fall into the category of glaciogenic subaquatic debris flows. At the third site the diamictons are stratified, and the magnetic fabric and field evidence show that post-depositional movement was caused by loading of sand layers into underlying muds.The results suggest that magnetic fabrics can be useful in interpreting pebble fabrics and that the dual approach may help to differentiate various types of glaciomarine diamicton(ite)s.