Paper No. 5
Presentation Time: 2:35 PM
THE LIMESTONE PAVEMENTS OF CHAUMONT: THEIR ORIGIN AND RIDGES
This study addresses the question of the origin of limestone pavements including what mechanisms cause “grikes” (fractures), “runnels” (anastomosing, shallow cm-scale channels in the limestone), “clints” (limestone bridges within grikes), and popup ridges. Relationships between features and crosscutting in fractures were used to understand the sequence with which these features were created. Ground Penetrating Radar was also used to understand the depth of fracturing and the orientation of limestone bedding at depth. Based on average fracture width, the population of fractures trending 222 degrees are oldest, followed respectively by 44, 138, 202, and 312 degrees. Runnels are best developed in areas of high microrelief and terminate in fractures. Fracture widths vary along individual fractures with the widest fracture widths being associated with where runnels and other fractures intersect. The orientation of popup ridges are sub-parallel to the orientation of two anticlines in the study area which have been interpreted by a previous study to be caused by the movement of the glacier. Glacial movement during the recent Ice Age was to the southeast, while the pop up ridges trend to the southwest direction. The cyclicity of these pavements in space seems to suggest that they are not directly caused by glacial movement over the rock, because popup ridges are in some areas but not others. The Grike features are believed to also be caused by solution widening during post glacial times. We suggest that local microrelief may be related to the size and extent of Grikes. Greater microrelief and runnel density causes movement of surface water into localized areas which enhances weathering of the limestone. This leads to wider, deeper grikes. Shrubs and trees tend to root only in the larger grikes, except in places where sufficient soil overburden was present. Further work will evaluate the role that vegetation and local hydrology may have in the development of these features.