Historical variation of elements with respect to different geochemical fractions in recent sediments from Pigeon Lake, Alberta, Canada?

Geochemical analysis of elements and organic matter were conducted on verti cal profiles of the recent sediments from Pigeon Lake, Alberta, Canada, to determine historical variations in elemental content of the sediments as re lated to their geochemical fractions. The elements are grouped according to their affinity with different geochemical fractions, by using cluster anal ysis and sequential extraction experiments. As a result, four elemental fi actions were identified: elastic mineral detritus; carbonate; organic; and elements that show less similarity to the previous groups perhaps due to an thropogenic input or the influence of other fractions, such as oxyhydroxide s. Following the identification of geochemical fractions in the sediments, a three-step normalizing method was applied using parameters that represent each geochemical fraction. These normalizing techniques appear to be impor tant in verifying whether the variation of elements is indeed the result of anthropogenic and/or natural activities. The normalized data are correlate d with the recent history of human activity and natural events near Pigeon Lake. Given the age of the lake sediments, this correlation indicates that the depth profiles of elements after being normalized to the organic and ca rbonate fractions reflect the variation of detrital input into the lake. Ho wever, the former mainly corresponds to the coarse-grained elastic minerals originating from high-energy erosion as the result of natural events (e.g. , flooding), whereas the latter corresponds to the low-energy erosion of th e fine particles (enriched in lithophile elements) due to deforestation in the drainage basin. Normalizing to the elastic mineral detritus fraction re sults in the increase of heavy metals in the uppermost part of the sediment profiles, which coincides with industrial activities-during the past two d ecades in central Alberta. However, the concentration of these elements is negligible, as compared to the quantities released by geogenic processes (e rosion).