During the maximum advance of the Early Saalian Scandinavian Ice Sheet ice-dammed lakes developed within valleys of the Northwest German Mountain ranges. The blocking of the River Weser valley led to the formation of glacial Lake Rinteln where most of the sediment was deposited by meltwater. Two subaqueous fan complexes have been identified, which formed lakeward of retreating ice-lobes during an overall lake-level rise. The sediment transport on the fans has been dominated by sustained gravity-flows, mainly cohesionless debris flows or high-and low-density turbidity currents, reflecting discharge of semi-continuous meltwater flows. Intercalations of surge-type high-and lowdensity turbidites increase towards the mid-and lower-fan slopes, indicating more ice-distal and periodic deposition. Individual fan bodies commonly have a coarse-grained proximal core of steeply dipping gravel, overlain by gently to steeply dipping mid-to outer fan deposits. During glacier retreat commonly fine-grained sediments, rich in ice-rafted debris, were deposited on the ice-distal and ice-proximal slopes of the abandoned fans. Climbing-ripple cross-laminated sand may onlap coarse-grained upper fan gravel and in some cases overtop the older fan deposits. Phases of glacier still-stands are characterised by fan systems that display an upward flattening of fan clinoforms and minor vertical facies changes. The position of ice marginal fans was controlled by the combination of bedrock topography and water depth. At the eastern lake margin topographic highs served as pinning points for the retreating glacier and facilitated ice margin stabilisation. A strong lake-level fall probably triggered a major drainage event that tapped previously unconnected reservoirs of englacial and subglacial meltwater.
The Coppenbrügge subaqueous ice-contact fan complex of early Saalian age is about 10 km long and up to 10 km wide and is composed of offset-stacked fan clinothems that are transgressive-regressive sequences formed during an overall lake level rise. The individual fan bodies consist of coarse gravel in the ice-proximal part, passing distally into sandy facies and showing large-scale foreset bedding. The iceberg scour recognized in an open-pit outcrop is up to 1.5 m deep, up to 2 m wide and cut in undisturbed mid-fan deposits. The scour-fill can be traced laterally for about 15 m and consists of sheared sand and, in the frontal zone, of downbent overlying strata surrounded by a zone of deformed sediments. The deformed sediment produced by the iceberg keel's shearing of the trough walls is a sand mass containing angular soft-sediment clasts that show internal folds and fractures. The basal surface of the deformed sediment is a nearly horizontal shear plane, steepening up laterally as a discrete thrust and showing a flat-ramp-flat geometry. The scour was formed by the iceberg keel's ploughing the substrate and pushing the sediment sideways and frontally, forming a ridge of deformed sediments at the trough end. This ridge was concurrently eroded by an accompanying meltwater underflow which apparently developed a horseshoe system of scouring vortices around the grounded iceberg. The current's scour was filled with massive, nonstratified sand deposited rapidly from turbulent suspension. The iceberg eventually broke up and its keel part was buried. As these ice fragments gradually melted, the space was closed by normal faulting and downbending of overlying strata. The collapsing scour-fill became partly liquified, and the resulting water-escape structures cut the normal faults and the overlying deposits. Though produced chiefly by tangential shear strain, iceberg-ploughing features are readily distinguishable from other glaciotectonic deformations. They can serve as a diagnostic criterion for glaciolacustrine or glaciomarine environments and the distinguishing of ice-contact subaqueous fans from ice-contact deltas in the stratigraphic record.Glaciolacustrine ice-marginal deposits are important and well-studied palaeogeographic and palaeoclimatic archives recording the history and dynamics of glacier termini in lacustrine basins. Glaciolacustrine ice-contact systems are complex and there are major problems with the sedimentological recognition of such depositional settings (
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