TEMPERATE GLACIMARINE VARVES - AN EXAMPLE FROM DISENCHANTMENT BAY, SOUTHERN ALASKA

The sediment record of Disenchantment Bay, Southern Alaska, a large ma rine calving embayment, contains distinctive annual deposits, Each yea r a glacimarine couplet forms with a clast-rich stratified to massive diamicton deposited in winter by intense iceberg rafting and a summer, meltwater deposit of thinly laminated mud and turbidite sand beds, Al though iceberg rafting occurs throughout the year, coarse debris is de posited in high concentrations and forms diamicton only during the win ter because of minimal fine sediment from meltwater discharges and a l onger residence time of icebergs in the Bay due to winter fjord circul ation and meteorological factors, When meltwater discharge commences i n summer, laminated mud with drop-stones is deposited, Spring and fall conditions are recorded as transitional phases between winter and sum mer by clast-poor diamictons. Average sediment accumulation rates calc ulated from varve thicknesses range from 48 cm/yr, 3.4 km from Hubbard Glacier at the head of the Bay, to 14 cm/yr, 15 km away, Sediment acc umulation rates estimated from Pb-210 dating of core sediments are in the same range, Deposits from the 1986 Russell Fiord outburst flood ar e identified from anomalously high Pb-210 activities in sediments indi cating an alternative sediment source to Disenchantment Bay. Glacimari ne varves are a dating tool for the barren proximal sediments commonly deposited near calving glacier termini. They yield paleoclimatic info rmation because they are a product of both glacial ice in the sea and laminated sediments deposited from significant meltwater discharge fou nd in a temperate to subpolar climate.