Brecciated diamictons from Mohawk Bay, S. Ontario, Canada

Abstract

Examination of sediments along the north shore of Lake Erie at Mohawk Bay reveals a relationship between the formation of intensely brecciated diamictons and the presence of sand‐block intraclasts. It is postulated that the sand blocks were subglacially deposited within a meltwater environment, and later frozen prior to being eroded and transported within a mobile subglacial debris layer. On immobilization the frozen sand blocks, encased within the diamicton, acted as a heat sink creating cryostatic stresses within the surrounding diamicton as a result of the advance of a frost front and related frozen ‘fringe’. The effect of these anisotropic stresses resulted in porewater migration to the frost front. Subsequent development of intense brecciation occurred as aureoles around the sand intraclasts due to localized high tensile stresses causing fracturing within the fine‐grained matrix of the diamicton.

Till—as a glacial “tectomict”, its internal architecture, and the development of a “typing” method for till differentiation

“…This area along the north shore of Lake Erie has been extensively investigated in the past where a lodgement till origin was ascribed to the red clay-rich till (Feenstra, 1981;Calkin and Feenstra, 1985), but more recently a more complex stratigraphy and till history has been suggested (cf. Menzies, 1990a). In Fig.…”

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

“…The sediments overlying bedrock can be subdivided into (Menzies, 1990). The intraclasts discussed in this paper are found only within unit A sediments.…”

“…sand intraclasts. Surrounding these intraclasts are aureoles of intensely brecciated circumjacent diamicton (Menzies, 1990).…”

“…Related to this is the contact zone around each sand intraclast where brecciated diamicton is usually found. This brecciated zone has been discussed elsewhere in some detail (Menzies, 1990). An origin for the breccia has been suggested associated with cryostatic stresses developed at the contact interface between the sand bodies and the diamicton subsequent to the incorporation of frozen sand units into a deforming diamicton melange within a polythermal subglacial environment.…”

“…These structures within the sand intraclasts tend to indicate that the sediments have not suffered secondary deformation in situ but have probably been moved by a process of erosive fragmentation, entrainment and emplacement within the diamicton melange. In the entrainment and/or early emplacement the intraclasts appear to have suffered considerable deformation but insufficient to disrupt the bodies completely, perhaps because of their confinement or frozen state (Menzies, 1990). Two possible explanations for this survivability seem likely.…”