An origin for laminated glacimarine sediments through sea-ice build-up andsuppressed iceberg rafting

Laminated glacimarine sediments are observed in visual core logs and x-radi ographs from Scoresby Sund and Nansen Fjord, east Greenland. They are mostl y underlain and overlain by massive or stratified glacimarine diamicton (Dm m or Dms), which is a product of iceberg delivery of heterogeneous debris a nd, in Scoresby Sund, reworking by deep-drafted iceberg keels. The laminate d sediments are AMS radiocarbon dated to two cold periods since the last, L ate Weichselian deglaciation: the Younger Dryas stadial (Milne Land Stadial in east Greenland) and the Little Ice Age. During cold climatic events, mu ltiyear shorefast sea ice ('sikussak') formed in these fjords and trapped t he icebergs. Fine-grained, laminated muds (Fl) were deposited in Scoresby S und when the flux of icebergs was suppressed, but turbid meltwater continue d to provide some sediment flux to the fjord systems, varying through time to produce laminations. In Nansen Fjord, thinner and often massive mud laye rs (Fm) resulted from shorter intervals of sea-ice cover with no ice raftin g. Stratified diamicton layers (Dms), which alternate with mud deposition t o produce a laminated unit, probably represent intervening times of more op en conditions with iceberg rafting. In Scoresby Sund, foraminifera are eith er absent from the laminated unit or begin to appear towards the end of its deposition. The absence of both benthic and planktonic foraminifera also s uggests that multiyear sea ice was covering the core sites. There is no evi dence of macrofaunal activity, and bioturbation is absent from the laminate d sediments. Satellite data show that multiyear shorefast sea ice is presen t in several areas of the high Arctic today, and this traps icebergs calved from interior ice-cap drainage basins. Thus, the process of laminated glac imarine sediment formation is likely to be applicable to a number of areas of the modern and Quaternary Arctic.