ELSEVIER Sedimentary Geology 111 (1997) 161-175 Sedlme amO, Geology Evidence, fl:om microstructures, of deformable bed conditions within drumlins, Chimney Bluffs, New York State • a* John Menzles , , Kamil Zaniewski b,c, Derek Dreger d a Departments of Earth Sciences and Geography, Brock University, St. Catharines, Ontario, Canada b Department of Geography, Brock University, St. CathaHnes, Ontario, Canada c Fysisch Geographisch Bodemkundig Lab., University of Amsterdam, Amsterdam, The Netherlands d Geologisch-Palgiontologisches Institut, University ofKiel, Kiel, Germany Received 25 January 1996; accepted4 April 1996 Abstract Discussion on the process of drumlin formation has been ongoing for over a century. At present, two dominant schools of thought prevail, viz. formation by (a) subglacial hydraulic mechanisms, and (b) due to subglacial sediment deformation. The latter mechanism depends on the existence of a subglacial deformable bed. Evidence from part of the large central New York drumlin field reveals evidence of syn-depositional deformation during the emplacement of diamictons that constitute the major portion of drumlins exposed along shore bluffs in Chimney Bluffs State Park. These diamictons cannot be lodgement till facies members but appear to comprise facies indicative of mrlange-style deposition under subglacial deformable bed conditions. The evidence obtained from microstructures and plasma fabric within these diamictons supports the existence of a deformable bed during diamicton emplacement. It is likely that formation of the drumlins occurred under these same subglacial bed conditions. Keywords: micromorphology; diamicton; drumlin; deformable bed 1. Introduction In the past five years two dominant schools of thought as to the likely origin of drumlins have emerged, viz. (a) a subglacial hydraulic mechanism associated with major meltwater impact, and (b) a mechanism involving the attenuation and rheolog- ical variation of a subglacial deformable sediment layer. With the emergence of a greater understanding and appreciation of the possible role played by sub- glacial deformable beds (Boulton and Hindmarsh, *Corresponding author Fax: +1 905 688-6369. E-mail: jmenzies@ spartan.ac.brocku.ca 1987; Hart et al., 1990; Alley, 1991; van der Meer, 1993; Hart and Roberts, 1994; Hart, 1994, 1995; Murray, 1994; Menzies, 1995; Jenson et al., 1995; Menzies and Shilts, 1996), a related issue of the presence or absence of extensive deformable beds beneath Quaternary ice sheets has to be answered first before any resolution of the 'drumlin question' can be considered. Already an extensive literature on deformable beds has developed but only a few scattered papers exist concerning deformation beneath Quaternary ice sheets. The sole and critical reason for this defi- ciency is the need to seek convincing proof of such deforming subglacial sediment layers. Hart (1994, 0037-0738/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PH S0037-0738(97)00013-4