LAMINATED SEDIMENT AND DEPOSITIONAL PROCESSES IN HIGH ARCTIC COASTAL ISOLATION BASINS, NUNAVUT CANADA

Coastal lacustrine and marine basins in the Canadian high arctic, isolated from open marine waters due to postglacial isostatic uplift, provide high resolution records of environmental change through the late Holocene. With progressive isostatic uplift the basins evolve through the following stages: (1) open marine inlets with prominent sill, (2) isolated marine inlet with restricted circulation and anoxic bottom water, (3) meromictic lake with saline anoxic bottom water, and (4) freshwater lake. Water column conditions were measured and sediment cores were collected from over a dozen basins in a transect that extends from Devon to Bathurst Islands in the archipelago. A composite sedimentary sequence from the basins is organized into litho- and biostratigraphic facies based on sediment textures, lamination type and biotic components: Facies 1: Massive mud interrupted by thin, disrupted biogenic/terrestrial laminae with dropstones, molluscs, and microfossils, representing deposition in an open marine inlet. Facies 2: Diffuse laminae grade up to finely laminated couplets indicating gradational onset of anoxia in the basin. Seasonal terrigenous sediment influx is coupled with biogenic productivity and preservation of organic matter. The laminated sediments are interbedded with massive beds (up to 10 cm thick) containing forams, diatoms and fecal pellets and reflects breaching of the emerged bedrock sill and re-oxygenation of the basin. Facies 3: Laminated sediments are variable in texture and composition and dominated by terrestrial sediments with increasing grain size. Diatoms and organic matter are rare. Facies 4: Turbidites within packages of laminated couplets. Facies 5: Laminae become thinner and finer until they become diffuse. Facies 6: The uppermost sediments are finely laminated, increasing in thickness and grain size and in presence of diatoms. The base of the composite sedimentary sequence in the basin reflects long-term conditions controlled by emergence and isolation of the basin in Facies 1,2, and 3. The recent sediment record likely reflects climatic changes of the last millenium with decreased terrestrial runoff and increased ice cover during the Little Ice Age (Facies 5) and increased runoff and decreased ice cover during the 20th Century warming.