Abstract

The geochemistry of Recent sediments from Pigeon Lake, Alberta was studied using Rock-Eval-6 in conjunction with Instrumental Neutron Activation Analyses ¹³⁷Cs isotope. The results of this study indicate that the variations in Rock-Eval parameters within the sedimentary column are correlated with the concentration of lithophile elements. These variations appear to be controlled by a balance between a number of interrelated processes concerned with both the nature of the deposited biomass and the depositional conditions. Two marker horizons were identified showing an abrupt decrease in Rock-Eval parameters (TOC, S2, and HI) and an increase in concentration of lithophile elements, indicating the clastic nature of the sediments with low autochthonous organic contents. This is attributed to significant natural events such as a storm or flood, which result in a rapid increase in the rate of erosion and subsequently in a high clastic input to the lake. Two cycles showing high organic content were also identified. The first cycle (productivity cycle) corresponds to the increase in algal productivity of the lake due to agricultural activities in the lake’s catchment. In the second cycle (diagenetic cycle), the downward decrease of organic matter is interpreted as the result of selective degradation of organic matter during early diagenesis. The estimated sedimentation rates based on the established marker horizons and ¹³⁷Cs isotope indicate higher sedimentation in the deeper part of the lake prior to the productivity cycle. However, the sedimentation rates increased towards the littoral zone coinciding with an increase in productivity and subsequently the rise in growth of macrophytes in the near-shore area.