THE NATURE AND DISTRIBUTION OF POSTGLACIAL SEDIMENTATION IN SHALLOW, ORGANIC LAKES

In this study we examine the intrabasin stratigraphic variability of the post-glacial sediment infill in shallow, organic lakes through the examination of multiple cores and the application of a variety of geophysical techniques. Lithostratigraphic records were derived from seven percussion lake sediment cores obtained at various locations within Canoran Lake, Nova Scotia. The lack of a transgressive littoral zone indicates that upon deglaciation at 12.5 cal. kyr the basin filled quickly. Substantial variability was noted during post-glacial (Allerød) warming with shallow water sites exhibiting as many as six distinct clastic oscillations and deeper water sites showing little variability. The Younger Dryas oscillation is present in most cores but varies greatly in thickness and organic content;all cores exhibited a consistent fining upwards trend. The post-YD stratigraphy indicates the rapid establishment of an increasingly productive and stable landscape however the rate and magnitude of infill varies substantially throughout the basin. Sub-bottom profiling was used to assess the distribution of postglacial sediment within the lake and was accomplished with an inexpensive 50 khz sounder. The calibration of the sonar record and the interpretation of the nature of the sediment-water interface can be determined using an inexpensive, digital free fall penetrometer constructed from readily available components. This instrument is capable of determining the shear strength and hardness of modern sediment and was also useful for determining the optimum sites for gravity coring. Preliminary results indicate that intrabasin lithostratigraphy is highly variable and that basin hydrology, shape, topography, surface area to volume ratio, and fetch all influence the nature of post-glacial sedimentation. This study demonstrates that an understanding of intrabasin lithostratigraphic variability is important in the interpretation of paleoclimate records.