CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Aspden, S.T.; and Arnaud, E.
Date : 2005.
Title : Sedimentology and deformation styles of Upper Pleistocene deposits of the Oak Ridges Moraine, southwestern Ontario, Canada.
Publication : Joint Meeting of the Geological Association of Canada, the Mineralogical Association of Canada, the Canadian Society of Petroleum Geologists and the Canadian Society of Soil Sciences. May 15-18, 2005. Studley Campus of Dalhousie University, Halifax, Nova Scotia.
Issue :
Page(s) :
Abstract
The Oak Ridges Moraine (ORM) is the largest interlobate moraine in southern Ontario, extending approximately 160 km from the Niagara Escarpment east to Rice Lake, north of Toronto. This prominent physiographic landform is a major recharge zone for southwestern Ontario, and a key source of aggregate for industry. Detailed sedimentological studies have been conducted in several parts of the ORM by the government, industry, and academia. However, there is still much debate over the depositional history of this late Pleistocene deposit. Detailed studies of deformation structures and sediment architecture, along with traditional sedimentological analysis, can provide key information needed to help resolve some of these debates. The Dufferin Aggregates Mosport Pit (~80 km east of Toronto) was selected for a detailed sedimentological study due to its well exposed deformation structures and architectural elements. Three main units characterize the sedimentary succession. The lowermost exposed unit (~ 5 m thick) consists of interbedded fine sand, silt, and clay. The middle unit consists of clast- and matrix-supported cobble gravel units, which is the predominant lithology exposed in the pit. The gravels (~ 12 m thick) generally exhibit trough-cross bedding and low angle planar-cross bedding, with apparent paleocurrents directions ranging from NNW to NE. The uppermost unit (~ 3 m thick) consists of trough-cross bedded fine to medium sand and clast-supported pebble gravel layers. The lower sands and silts have been extensively deformed. Large flame structures, elliptical folds, and flow folds are found with hinge zones oriented upwards and hinge lines trending NE-SW. The cobble gravels show little evidence of plastic deformation. Upper sands exhibit a transition from undeformed trough-cross beds to increasingly deformed sands with extensive kink folding (down dip N-NE). Several normal faults with reject of 0.25-1.5 m affect the cobble gravel succession. The lower and upper sandy units are affected by small sets of normal and reverse faults with reject of 0.01-0.25 m. Paleocurrent directions within the cobbley gravel units parallel the direction of flow folds and hinge line trends of the underlying fine sediments. Rapid loading of the high-energy gravel deposits onto saturated fine sediments is most likely responsible for the extensive plastic deformation. Large-scale faulting of the gravel deposits was likely caused by the melting of buried ice blocks. Faulting of the gravel deposits could have mobilized the overlying sands, triggering slumping and debris flows. These sedimentary facies, deformation structures, and overall architecture suggest an ice-proximal depositional environment.
Bibliography of Canadian Geomorphology