26 research outputs found
Processes of ‘hummocky moraine’ formation in the Gaick, Scotland: insights into the ice-marginal dynamics of a Younger Dryas plateau icefield
Younger Dryas ice-marginal (‘hummocky’) moraines in Scotland represent valuable terrestrial archives that can be used to obtain important information on ice-marginal dynamics and glacier thermal regimes during a period of rapid climatic change. In this paper, we present detailed sedimentological studies of Younger Dryas ice-marginal moraines in the Gaick, central Scotland, the former site of a spatially restricted plateau icefield. Exposures demonstrate that moraines in the Gaick represent terrestrial ice-contact fans, with evidence of proglacial and subglacial glaciotectonization, as reported elsewhere in Scotland. The exposures also reveal the influence of local hydrogeological conditions, with pressurization of the groundwater system leading to the formation of hydrofracture fills within some moraines. Clast shape analysis shows that all the moraines contain debris consistent with transport in the subglacial traction zone. The sedimentological data, and the planform arrangement of the moraines as nested arcs or chevrons, indicate that retreat of the Younger Dryas Gaick Icefield outlets was incremental and oscillatory. This evidence strongly suggests a mainly temperate thermal regime and short glacier response times, but with narrow cold-ice zones near the margins facilitating the elevation of basal debris to the glacier surface. Analogous glaciodynamic regimes occur at modern ice-cap and plateau icefield outlets in Iceland and Norway, although there are significant differences in the nature of ice-marginal deposition. The glaciodynamic signature recorded by moraines in the Gaick has allowed us to shed new light on the ice-marginal dynamics and thermal regime of one of the most easterly Younger Dryas icefields in Scotland
Changes in the biota and sediments of glacial Lake Koźmin, Poland, during the late Saalian (Illinoian)
Famennian glaciation in the eastern side of Parnaíba Basin, Brazil: evidence of advance and retreat of glacier in Cabeças Formation
Soft-sediment deformations from glaciodeltaic, glaciolacustrine and fluviolacustrine sediments in the Kleszczów Graben (central Poland)
Thermal basal regime of the Elsterian ice‐sheet marginal zone in a hilly mountain foreland, Rychleby Mts., Eastern Sudetes
Complex kame belt morphology, stratigraphy and architecture
The development of glacier karst at the margins of melting ice sheets produces
complex glaciofluvial sediment-landform assemblages that provide information on ice
sheet downwasting processes. We present the first combined geomorphological,
sedimentological and geophysical investigation of the Brampton Kame Belt, an
important glaciofluvial depositional zone at the centre of the last British-Irish Ice Sheet.
Ground-penetrating radar (GPR) data allow the broad scale internal architecture of
ridges (eskers) and flat-topped hills (ice-walled lake plains) to be determined at four
sites. In combination with sediment exposures, these provide information on lateral
and vertical variations in accretion styles, depositional boundaries, and grain size
changes. Building on existing work on the subject, we propose a refined model for the
formation of ice-walled lake plains resulting from the evolution and collapse of major
drainage axes into lakes as stable glacier karst develops during deglaciation. The
internal structure of esker ridges demonstrates variations in sedimentation that can be
linked to differences in ridge morphologies across the kame belt. This includes low
energy flow conditions and multiple accretion phases identified within large S-N
oriented esker ridges; and fluctuating water pressures, hyperconcentrated flows, and
significant deformation within a fragmented SW-NE oriented esker ridge. In
combination with updated geomorphological mapping, this work allows us to identify
two main styles of drainage within the kame belt: (1) major drainage axes aligned
broadly S-N that extend through the entire kame belt and collapsed into a chain of icewalled lakes; and (2) a series of smaller, fragmented SW-NE aligned esker ridges that
represent ice-marginal drainage as the ice sheet receded south-eastwards up the Vale
of Eden. Our study demonstrates the importance of integrated geomorphological,
sedimentological and geophysical investigations in order to understand complex and
polyphase glaciofluvial sediment-landform assemblages