CGRG Bibliography of Canadian Geomorphology
Author : McCarthy, D.P.
Date : 1993
Title : Geobotanical dating in alpine-carbonate terrain: a chronology for Little Ice Age glacial activity in Peter Lougheed and Elk Lakes Provincial Parks, Alberta and British Columbia
Publication : Unpublished Ph.D. dissertation. University of Saskatchewan, Saskatoon
Page(s) : 238 p
This research attempts to improve the resolution and increase the variety of geobotanical dating techniques that are currently available for use in alpine-carbonate terrain. It evaluates and critically applies tree-ring dating, lichenometry and cushion-plant dating techniques to produce a chronology for recent glacial activity in the Kananaskis and Elk Lakes area of the Canadian Rockies. Measurements of plants growing on surfaces of known age or on surfaces dated by tree-ring and/or 14C dating methods were used to estimate long-term growth rates and growth curves for the lichens Xanthoria elegans and Aspicilia candida as well as the Silene acaulis cushion plant. The theory, potential errors and regional data base for each geobotanical dating technique used were carefully evaluated. Investigations into the resolution of the tree-ring dating technique found minor errors due to sampling height where sampling is done within a few centimetres of the root crown. Errors in estimating tree ecesis are potentially more significant because they arise from both methodological bias and from natural variability in historical tree regeneration. It is shown that methodological bias in ecesis estimation can be reduced, but not eliminated. Estimates of ecesis errors are difficult to predict and can only be assessed through the combined use of independent dating techniques. In evaluating lichenometric theory it is possible to conclude that the technique may be ecologically untenable because it assumes much about the growth habits and ecology of lichens. Methodologies tested in this work are tedious, but provide a basic description of lichen growth habits as well as measurements of thallus size. It is noted that X. elegans thalli in the study area commonly face east-south-east and are often found in concavities and cracks near the base of clasts that are embedded in moraines. The majority of thalli measured in this work have nearly circular outlines, are not in marginal contact with other individuals and exhibit little central fragmentation. The only clustering of X. elegans thalli that was observed occurred near rodent burrows. This suggests that closure of X. elegans communities and coalescence of thalli is an infrequent occurrence on sites that are not fertilized with animal dung. A consideration of the use of S. acaulis cushion plants as dating tools found that the technique has considerable potential for dating recently stabilized deposits. Further investigation is needed to define the ecology and relative growth rates of S. acaulis subspecies and test the sampling methodology and assumptions used to interpret cushion diameter and substrate age data. Geobotanical data collected in this study allow relative ages to be estimated for the stabilization of 19th and 20th century moraines above timberline. Data from moraines at eleven glaciers provide evidence for early-18th and 19th century Little Ice Age glacial expansion that coincided with periods of moraine stabilization documented elsewhere in the Canadian Cordillera.
Bibliography of Canadian Geomorphology