Ea. Cowan et al., TEMPERATE GLACIMARINE VARVES - AN EXAMPLE FROM DISENCHANTMENT BAY, SOUTHERN ALASKA, Journal of sedimentary research, 67(3), 1997, pp. 536-549
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.