Quartz sand grain shape and other criteria used to distinguish glacial and non-glacial events in a marine core from Frobisher Bay, Baffin Island, N.W.T., Canada



Analyses of quartz sand grain shape, sediment influx rates and foraminifera define glacial and non-glacial episodes in a 9.69 m core from Frobisher Bay, Arctic Canada. Five radiocarbon dates on organic matter provide a preliminary core chronology, with a basal date of 11,910 yr BP. Quartz sand grain morphology is measured for samples at seven core levels using: (1) Fourier shape analysis; (2) percentage of grain surface conchoidally fractured. Samples at 2.0 and 7.5 m are most fractured and have Fourier roughness coefficients similar to particles sampled directly from glacier ice. These two samples probably represent glacial events in the core. Major intervals of non-carbonate sand influx occur at 9.0–4.5 m and 3.5–1.5 m, separated by several thousand years of slower sedimentation. Detrital carbonate influx rates are relatively high prior to 4.3 m, then decline rapidly indicating a shift in sediment provenance from limestones flooring Frobisher Bay to rafting from far-travelled icebergs. Bio- and lithostratigraphic analysis allows definition of five core units: (1) an environment similar to today below 8.5 m; (2) glacial conditions from 8.5–6.8 m, associated with ice proximal to the core site; (3) ameliorating conditions from 6.8 to 3.2 m; (4) cooler conditions from 3.2 to 0.5 m, probably related to increased iceberg flux rather than neoglacial advances of nearby ice caps; (5) an environment similar to today from 0.5 m. Sand grains sampled at 7.5 and 2.0 m, whose shapes indicate they are derived from glacier ice, lie within the cooler or glacial units defined from foraminiferal analysis. This indicates that quantitative measurement of particle surface morphology can provide useful environmental information in studies of marine cores.