Sand intraclasts within a diamicton mélange,southern Niagara Peninsula,Ontario, Canada

Sand intraclasts found within diamicton units along the north shore of Lake Erie in the Mohawk Bay area of the Niagara Peninsula would appear to be part of a ‘block-in-matrix’ mélange. The intraclasts are undeformed and many exhibit primary bedding structures. Numerous intraclasts have been rotated and/or tilted and are, in general, subrounded in outline. Examination of the surrounding diamicton reveals that the diamicton clast fabrics exhibit a wide scatter and are not characteristic of any known till clast fabric. Around each intraclast exists an aureole of brecciated diamicton. Other evidence in the form of macro- and microshear structures, and banding within the diamicton indicate that the diamicton has been subject to high strain. Interpretation of the sand intraclasts seems to be intrinsically linked to the origin of the diamicton and together linked to the origin of the mélange. Various hypotheses are suggested separately for the sand intraclasts, diamicton and mélange. A subglacial deformable bed hypothesis is advanced as the most acceptable explanation for the complete sediment sequence in which diamicton and frozen sand intraclasts, the latter mobilised from the substrate, are moved as a mélange below an active fast-moving ice mass. Several implications from this study emerge with regard to glacial sedimentology and stratigraphic interpretations.