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Subglacially-erupted volcanic sequences provide proxies for a unique range of palaeo-ice parameters and they are potentially highly useful archives of palaeoenvironmental information, particularly for pre-Quaternary periods. They can thus be incorporated by climate and ice sheet modellers in the same way as other environmental proxies, yet they remain largely under-utilised. Basaltic volcanic sequences erupted subglacially consist empirically of two major types, corresponding to eruptions under 'thick' and 'thin' ice, respectively. The latter are called subglacial sheet-like sequences and only one genetic type of sequence has been described so far. However, there is now evidence that there are at least two genetic types, with significantly different implications for interpretations of associated palaeo-ice sheet thicknesses. One type, which is relatively well described, is believed to be a diagnostic product of eruptions associated with a relatively thin glacial cover ( 1000 m). Eruptions that form the Dalsheidi-type of sequence commence with the injection and inflation of a sill along the ice: bedrock interface. Such 'interface sills' were predicted theoretically but had no known geological example, until now. Subsequent evolution commonly involves floating of the ice cover, catastrophic meltwater drainage and emplacement of widespread sheets of hyaloclastite, as cohesionless mass flows and hyperconcentrated flows. The water-saturated hyaloclastite is characteristically intruded by apophyses sourced in the underlying 'interface sill'. Eruptions are commonly not explosive until their later stages. Dalsheidi-type deposits are outflow sequences probably linked to subglacial pillow volcanoes, which in Iceland were erupted along fissures. They only provide an indication of minimum thicknesses of the associated overlying ice, although theoretical considerations suggest substantial ice thicknesses in excess of 1000 m. However, they are likely to be characteristic products of eruptions under the thick West Antarctic Ice Sheet, but are currently inaccessible. Such eruptions may be capable of destabilising that ice sheet. Keywords: subglacial eruptions; glaciovolcanic, basaltic; sheet-like; Dalsheidi; Pinafore; ice sheet; palaeoenvironments; West Antarctic Ice Sheet

We review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members. Processes of deformation, flow, sliding, lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members, ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton. The dominance of any one subglacial process varies both spatially and temporally, giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation/deposition at the ice-bed interface. We recommend that, while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes, genetic fingerprinting of subglacial tills should be less process-specific and till classification must reflect the range of products encompassed by the subglacial till production continuum. Glacial geologists can presently unequivocally identify: a) glacitectonite (rock or sediment that has been deformed by subglacial shearing/deformation but retains some of the structural characteristics of the parent material); b) subglacial traction till (sediment deposited by a glacier sole either sliding over and/or deforming its bed, the sediment having been released directly from the ice by pressure melting and/or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing); and support the theoretical case for c) melt-out till (sediment released by the melting of stagnant or slowly moving debris-rich glacier ice, and directly deposited without subsequent transport or deformation). Because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions, the patterns of which change temporally and spatially, it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone. Keywords: till; subglacial processes; subglacial deformation; glacitectonite; subglacial traction till

Loesses form wide belts in front of previously glaciated areas. Their thicknesses may be considerable, changing in Eurasia from maximally a few metres in the west to a hundred metres or more in the east. The Eastern (particularly Chinese) loesses are mostly unrelated to glaciations. The periglacial loesses from China and elsewhere predominantly date from the last Pleistocene glaciation: relatively few comparable occurrences are known from earlier Quaternary glaciations. As it is difficult to imagine that the conditions in front of the land-ice masses during the earlier glaciations differed fundamentally from those of the last one, considerable quantities of loess must have disappeared. This disappearance, which is commonly ascribed to fluvial and eolian erosion, is not easily explained as equivalent deposits that may have the older loesses as a source, are practically absent. A possible explanation might be that loess is recycled during successive glaciations. Some loess disappears during interglacials by erosion, but this quantity is more than compensated by the formation of new silt particles. The implication would be that the loess deposits increase in volume for each new glaciation. Keywords: silt; periglacial processes; sediment recycling; sorting; eolian abrasion; glacial grinding