THE BEHAVIOR OF MAJOR AND MINOR METALS USING A HIGH RESOLUTION XRF SCANNER ON LAMINATED HOLOCENE SEDIMENT IN SAANICH INLET, BRITISH COLUMBIA: MN AND CA SPIKES

New data at 100-µm resolution were obtained by X-Ray Fluorescence Spectroscopy, using an ITRAX core scanner, on a laminated sediment record from Saanich Inlet, a silled fjord on southeastern Vancouver Island. The data were from core MD02-2490, section XVIII (2548-2698 mm depth, ~5,000 yr BP), taken on part of IMAGES VIII (International Marine Past Global Changes Study) program. We discuss the behaviour and distribution of redox-sensitive elements in the laminated and non-laminated sediment.

The sediment sequence consists of 179 varves (average thickness: 4 mm) with 16 non-laminated layers (0.6 - 1.8 cm thickness), which may be caused by bioturbation or density flows. The ITRAX scanner has produced a high-resolution surface scans, an X-radiograph, and a measurement of major and minor elements. A 15,000 yr chronology based on C-14 dating, marker layers, and varve counting is available for nearby Ocean Drilling Program (ODP, core 1033B).

The data reveal a large Mn spike (1.6 mm thickness), associated with Ca spike (1 mm thickness) followed by numerous smaller spikes. These spikes occur in laminated terrigenous layers, and likely represent an abrupt and short period of decreased bottom water oxygen concentrations. Manganese is a redox-sensitive element, its solubility increases in a reduced environment and precipitates under oxic conditions. Post-depositional remobilization of Mn also occurs in reduced sediments. Calcium intensity varies with supply and dissolution of organic and in-organic calcium carbonate. Although no concurrent anomalies were found from X-radiograph gray-level and other trace elements including Fe, Ti, K, and Zn, an abrupt increase in varve thickness occurs 4 cm above the Mn and Ca spikes, which may be caused by increased productivity. While the results are inconclusive, subsequent organic carbon oxidation may have affected the local redox conditions in the previously oxic sediment column.