A POST-EMERGENCE RECORD OF LAMINATED ORGANO-CLASTIC SEDIMENTS IN A COASTAL FRESHWATER HIGH ARCTIC LAKE

This work describes a sediment core recovered from a coastal lake on the Colin Archer Peninsula, Devon Island, Nunavut, Canada. The core is inferred to represent a record of Holocene sedimentation in glaciomarine and lacustrine depositional environments. Faunal and sedimentary analyses support the hypothesis that the lower half of the core contains glaciomarine mud, potentially extending to ca. 8500 BP. Emergence as a result of postglacial isostatic rebound isolated the basin beginning ca. 5700 BP, and the sediment suggests this transition ended with the freshening of the basin and the establishment of a freshwater lacustrine environment. After freshening, the record is composed of 1.9 m of finely laminated sediment composed of alternating organic and clastic units. While the clastic units are relatively simple in structure, the organic units are composed of two distinct unit types: red, internally laminated units and yellow, featureless units. Based on sedimentary and compositional observations, it was hypothesized that these units are microbially induced sedimentary structures (MISS), the result of microbial mat formation and accretion on the lake bottom. Electron microscopy was used to identify the presence of filamentous bacteria and extracellular polymeric substances in the organic units. Microbial activity is known to occur in a wide range of Arctic environments, although the record described here represents the only known sequence of freshwater Arctic MISS extending through the latter part of the Holocene in the northern hemisphere. The record is physically similar to lacustrine microbial mat accumulations found in the Taylor Valley, Antarctica. Complications due to highly variable accumulation rates resulted in unreliable Pb-210 chronological constraint, although current work is examining the potential for identifying annual and/or seasonal patterns in the sediments.