| Abstrakt: |
Field relationships between a subglacial lake fill from the Enniskerry basin, eastern Ireland, provide evidence for dynamic links between the sedimentary fill, regional subglacial meltwater flow and regional ice dynamics. The basin fill (6–7 km2) forms an integral part of an extensive (30 km) subglacial meltwater system which developed parallel to north-south ice flow along the western marginal sector of the Late Pleistocene Irish Sea glacier. High-magnitude sediment fluxes were directed into the subglacial lake southwards across the northern basin rim from two Nye-type channels and westwards by a Röthlisberger-type channel. The resulting subaqueous fans typically consist of cones of coarse boulder gravels deposited by jet effluxes overlain by cross-bedded sands and foreset gravels. In places these are eroded and overlain by multistorey, dish-shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head. A variety of gravelly and sandy bedforms indicate that sediment migrated over efflux cores towards deeper parts of the basin. Facies variability within the ice-proximal fans and spreads record deposition from a wide range of high- and low-density turbulent flows, traction currents, density underflows, suspension and sediment gravity flows. A surficial drape of winnowed diamict is related to areal resedimentation as jet effluxes closed down. At one site the gravelly sequence shows a largely conformable transition upwards into glaciotectonised gravel and basal till in the lee of the basin rim. Elsewhere the upper part of the sediment pile is occasionally deformed by the drag of the ice roof. |
