Paraglacial Features Research Articles

The Mall Bay Formation (Ediacaran) and the protracted onset of the Gaskiers glaciation in Newfoundland, Canada

The Gaskiers is the oldest Ediacaran glaciation and thus represents Earth’s first icehouse since the end of the Snowball glaciations that characterized the Cryogenian world.Age bracketing of the 300-m-thick marine tillites of the Gaskiers Formation to 581–580 Ma has previously been taken as an indication that the Gaskiers glaciation was short-lived. New studies of the underlying ∼ 1000-m-thick Mall Bay Formation on islands offshore of Newfoundland, Canada, reveal a hitherto unrecognized protracted onset to the Gaskiers glaciation that nearly triples its known stratigraphic thickness and elucidates progressive stages in the development of an Ediacaran glaciation.The Mall Bay Formation consists predominantly of mudstone and fine-grained sandstone deposited in a deep-water, SW-NE trending, turbidite-dominated axial basin with abundant input of volcanic ash.No evidence of glacial activity was observed in the lower half of the Mall Bay Formation.Cold-climate proxies first appear approximately 550 m below the top of the formation in the form of glendonites (stellate pseudomorphs of the cold-water carbonate ikaite) that attest to cold bottom waters and hypothesized downwelling, while the preservation of outsized clasts, frozen aggregates (till pellets), and coarse sandstone lags near the same stratigraphic level imply the presence of icebergs floating above the depositional environment.Evidence for cold bottom waters and an influx of sediment from floating ice persists to the top of the Mall Bay Formation. There is a progressive stratigraphic increase in the abundance and size of iceberg-rafted debris in the formation that implies increasing proximity of glaciers to the study area.Pebbles showing dropstone features first appear 120 m below the top of the formation, and the lowest bed of pebble diamictite occurs 4 m below the top of the formation.The overlying cobble to boulder diamictite of the Gaskiers Formation likely represents the Gaskiers glacial maximum when glaciers reached the local shelf edge and glacially derived debris poured down the slope into the axial, turbidite-dominated Avalon Basin.The Ediacaran Gaskiers glaciation shows little similarity to the older panglacial Snowball glaciations of the Cryogenian but exhibits paraglacial features similar in many respects to the Paleozoic glaciations of Gondwana that followed it.

Rock glaciers and paraglacial features influence stream invertebrates in a deglaciating Alpine area

Abstract Climate change and progressive glacier loss are leading to rapid ecological shifts in alpine aquatic systems. Rock glaciers and paraglacial features such as proglacial lakes, moraines, and taluses can alter the gradients of glacial influence along alpine river networks, but the ecological responses are still understudied. We investigated benthic invertebrate communities of different stream types (upper kryal, lower kryal, glacio‐rhithral, krenal, and rock glacial) within a deglaciating area of the Italian Alps (Solda and Zay sub‐catchments). Alpha‐ (Shannon index and taxa richness) and β‐diversity (i.e. nestedness and turnover), production (abundance, biomass), average body mass of invertebrate taxa, and functional feeding groups were used to analyse the influence of habitat conditions on invertebrate communities in different microhabitats (mineral substrates, bryophytes, Hydrurus foetidus). We defined an index of habitat mildness based on water temperature, channel stability, turbidity, and organic detritus, to measure the difference in community metrics over a gradient of habitat amelioration, driven by the mixing of distinct stream types and their interactions with paraglacial features. While diversity proxies showed an asymptotic behaviour along the gradient, the quantitative metrics peaked at intermediate mildness. Peaks of invertebrate biomass/abundance were recorded at the glacio‐rhithral station below the talus. Highest average body mass occurred at Zay, specifically at the rock glacial stream, and at the lower kryal stations influenced by the lake/moraine and the rock glacier. The moraine outflow showed unexpected high biomass/abundance values of shredders and grazers, that were supported by a high epilithic production. Bryophytes acted as local scale multipliers of mildness as they stored more detritus, and hosted higher biomass/abundance of invertebrates and, in particular, of gatherer–collectors. Beta‐diversity, driven by the turnover component, was positively related to different habitat mildness of the sampling stations. Although influenced by distinct lentic/lotic conditions, rock glacial streams hosted several taxa typical of glacio‐rhithral and krenal stations, alongside large numbers of Diamesa (Chironomidae), a genus typical of kryal habitats. Under progressive deglaciation, rock glaciers and paraglacial features influence the invertebrate communities of alpine river networks. As they host a high number of taxa dwelling in non‐glacial locations, rock glacial streams may act as stepping stones facilitating invertebrate colonisation following glacier retreat. After glacier loss, rock glacial streams may represent climate refugia for cold adapted taxa and/or kryal specialists, because the slow thawing of their ice might sustain cold water conditions for a longer period of time.

Patterns of late Amazonian deglaciation from the distribution of martian paraglacial features

Mars has experienced widespread glaciation across the mid-latitudes during the Late Amazonian. Deglaciation has altered these mid-latitude regions, and the characteristics of deglaciation can be useful in determining the variability in environmental response to climate change. The paraglacial period describes the period over which deglaciation occurred, and is characterized by a suite of features that form due to ice loss. Glaciated craters in the martian mid-latitudes were documented for evidence of paraglacial activity to determine how local crater setting affects deglaciation. Five paraglacial features were identified: spatulate depressions, washboard terrain, gullies, polygons, and broad pits, and their occurrence in each glaciated crater was recorded. 71% of glaciated craters (~450 craters) contained some evidence of paraglacial activity. Relatively more southern hemisphere glaciated craters contained paraglacial features (89%) than northern hemisphere glaciated craters (42%). The spatial density of paraglacial features varies with location. Different combinations of paraglacial features were found in each crater, although some features were preferentially associated, including washboard terrain and gullies, and broad pits and polygons, suggesting dependent formation mechanisms. More types of paraglacial features (up to all five features) were found in small craters (~5–10 km) at a range of elevations, and at modest latitudes (~35–45°), which corresponds to a large region of the southern highlands. Few or no paraglacial features were found in craters containing glacial fill exceeding ~70% of their predicted depth. The thickness of crater fill appears to be the dominant control on paraglacial response, which is affected by crater diameter, and partly by latitude. The variation in thickness of crater fill is attributed to variable accumulation and ablation rates during peak glacial periods during the Late Amazonian. The similarity in paraglacial feature morphology across the mid-latitudes of both hemispheres suggests that deglaciation and paraglaciation operate via similar mechanisms, although climatic conditions and geologic setting at each crater will determine the specific pathway for paraglacial activity to occur. These observations can be used to predict where future paraglacial activity will occur, and where it may be inhibited.

Transient post-glacial processes on Mars: Geomorphologic evidence for a paraglacial period

On Earth a transitional phase between glacial and interglacial periods is referred to as the paraglacial period. This period immediately postdates glacial retreat and is characterized by ice removal, glacial unloading, and the exposure of steep slopes and large sediment stores. These responses led to the development of a suite of morphologic units (e.g., talus cones, gullies, sackungen, and polygons) which, when observed together, are indicative of the paraglacial period. A similar period of transitional climate and deglaciation is identified on Mars in the Late Amazonian, characterized by the association of features in a glaciated 10.6 km diameter mid-latitude crater. This crater contains concentric crater fill (CCF) formed by debris-covered glaciers, as well as a suite of stratigraphically younger geomorphic units (e.g., spatulate depressions, washboard terrain, gullies, and polygonal terrain) that are all indicative of the local environmental response to deglaciation. These features are interpreted to represent a geologically recent martian paraglacial period within this crater. The morphology and relative stratigraphic relationships among these paraglacial features are described in order to assess the processes operating during deglaciation and to document the recent history of glaciation on Mars: spatulate depressions formed by the differential sublimation of pure glacial ice near the base of the crater wall; subsequently, due to the loss of basal support and steepened slopes, remnant ice on the crater wall began to flow downhill, and formed transverse crevasses that created washboard terrain. Continuous thermal cycling of sediment-mantled ice on crater walls created fractures that formed polygonal terrain. During this time and after, gullies formed by the transport of sediment downslope from crater rim alcoves. Analyses of modeled obliquity variations suggest that the paraglacial period could have operated within the last ∼5 Myr and may still be ongoing, suggesting that the current martian paraglacial period is much longer in duration than typical paraglacial periods on Earth. Understanding the nature and sequence of paraglacial activity can help to identify variations in climate in recent Mars history.

Glacial geomorphology of the Tweedsmuir Hills, Central Southern Uplands, Scotland

The Quaternary glacial history of the Tweedsmuir Hills, Central Southern Uplands, Scotland, has received little attention since the 1980s, with earlier studies focussing on single lines of geomorphic evidence in isolated valleys. This study presents the first systematic glacial geomorphological assessment of the region, covering approximately 300 km2 with the map designed to be presented at A0. Mapping from remotely sensed imagery and field investigation reveal a large number of moraines and meltwater channels, both within valleys and occasionally extending to the plateau, alongside a range of peri- and para-glacial features, including solifluction lobes, alluvial fans, debris cones, river terraces and rock slope failures. Aspects of the mapped geomorphology are consistent with plateau icefield landsystems mapped elsewhere in Britain and this will hopefully form the basis for palaeoglaciological reconstructions which will improve our understanding of the extent and dynamics of former ice masses in the region.

Relict Talus‐Foot Rock Glaciers at Øyberget, Upper Ottadalen, Southern Norway: Schmidt Hammer Exposure Ages and Palaeoenvironmental Implications

ABSTRACTThree relict talus‐foot rock glaciers at Øyberget, upper Ottadalen, were dated using high‐precision Schmidt hammer exposure‐age dating (SHD). A SHD calibration curve was constructed for the local banded gneiss using two control points: (1) fresh bedrock in a road cutting; and (2) glacially scoured bedrock surfaces deglaciated c. 9.7 ka. Two alternative hypotheses are suggested to explain SHD ages (± 95% confidence intervals) of 10 340 ± 1280, 9920 ± 1385 and 8965 ± 1700 years obtained for the three rock glaciers located ~ 1000 m below the present lower limit of mountain permafrost, at a site covered by glacier ice throughout the Late Weichselian. First, the rock glaciers may be paraglacial features, which formed rapidly during deglaciation when enhanced debris supply may have buried residual ice bodies. If this was the case, the SHD ages are a true reflection of rock glacier age. Second, the rock glaciers may have formed during several thousand years of permafrost conditions in the Mid‐Weichselian (possibly during the Ålesund Interstadial, c. 34.5–38.2 ka) and then been preserved beneath a cold‐based ice sheet until renewed exposure during Holocene deglaciation. If the second hypothesis is true, then the true age of the rock glaciers is much older than their SHD ages, the latter failing to record the interval of burial when rock weathering would have been zero. Although evidence is currently insufficient to distinguish between these two interpretations, the paper demonstrates both the potential and limitations of high‐precision SHD in the context of rock glaciers. Copyright © 2013 John Wiley & Sons, Ltd.

Geomorphology and soils distribution under paraglacial conditions in an ice-free area of Admiralty Bay, King George Island, Antarctica

Abstract The main pedological, geomorphological and cryogenic features of Keller Peninsula, part of Admiralty Bay, King George Island, Maritime Antarctica, were mapped and quantified with emphasis on the relationship between the ice retreat process, melt-out, landform development and soil distribution. Moraines, protalus, scree slopes, inactive glacial cirques, uplift marine terraces, biogenic landforms, aretes and Felsenmeer were mapped. Scree slope is the main landform, covering approximately 25% of the peninsula, indicating prominent paraglacial features. Inherited, glacial landforms, such as lateral moraines, highland plateau and exhumed U shaped-valleys, are now being exposed in north Keller by ice shrinkage of former ice protecting cover. Landforms influenced soil formation and stability. Cryosols and Leptosols (WRB) roughly corresponding to Gelisols and Entisols (SSS), respectively, are the most common soil classes, with an overall tendency of absent permafrost in the coastal areas, changing to sporadic permafrost at mid-slope, and discontinuous permafrost with greater altitude and substrate stability.

Glacial geomorphological mapping of Coire Mhic Fhearchair, NW Scotland: The contribution of a high-resolution ground based LiDAR survey

Please click here to download the map associated with this article. Terrestrial Light Detection and Ranging (tLiDAR) surveys are valuable supplements to existing geomorphological mapping techniques, providing information which is of considerable interest to palaeoclimatologists and glaciologists. Fieldwork observations, and the interpretation of aerial photographs and digital elevation models, have been augmented by the study of 3D digital models produced from tLiDAR data, and have led to the production of a detailed geomorphological map at a scale of 1:10,000. A 2 km2 study was carried out in Coire Mhic Fhearchair (NW Scotland), a cirque landform which was covered by an ice-sheet at the Last Glacial Maximum, and experienced localised ice ow during subsequent deglaciation and readvances. The combined map includes glacial (moraines, striae, and depositional lineations) and paraglacial features (debris fans) which have been observed using some or all of the above methods. In addition to this, tLiDAR has been used in conjunction with colour photography to provide a ‘virtual reality’ observational tool at resolutions of up to 50 mm, with great potential for the detailed study of glacial geomorphology on the sub-km scale.