Glacigenic Diamicton Research Articles

The late Quaternary glacial depositional environment at Filey Bay, eastern England: Accretionary mechanisms for thick sequences of tills and stratified diamictons

Construction of the Holderness/Flamborough Head moraine belt on the East Yorkshire coast, England, records the oscillatory onshore flow of the North Sea Lobe of the British-Irish Ice Sheet from ~25.8 to ~19.7 ka BP, during which time a thick sequence of multiple diamictons and associated stratified sediments were emplaced. The sedimentology of a >40 m thick stratigraphy through the moraine belt at Filey Bay, in combination with local borehole records, is used here to reconstruct the depositional processes associated with glacier ice moving ca., 12 km onshore and damming the mouth of the Vale of Pickering, which resulted in the accumulation of an unusually thick and complex sequence of deposits traditionally classified as the “Filey till”. The base of the sedimentary sequence comprises stratified diamictons, which are interpreted as glacilacustrine deposits emplaced predominantly by sediment gravity flows in an ice-contact ‘mud apron’ on the distal slope of a subaqueous push ridge constructed in the earliest proglacial lake in Filey Bay; a vertical increase in coarse-grained lithofacies records increasing glacier proximity. Glacier overriding of the mud apron is recorded by a stacked sequence of tills that interdigitate with lake sediments inland. A zone of till-lake sediment interdigitation migrated first westward during North Sea Lobe advance and then eastward during its retreat, into and out of Glacial Lake Pickering, respectively. Multiple tills and intra-till stratified beds and lenses at the top of the sequence at Filey represent alternating deforming bed-sliding bed facies (subglacial traction tills and subglacial canal fills) associated with the construction of inset push moraines, constructed by sub-marginal incremental thickening or punctuated aggradation. This depositional scenario addresses the problems arising from genetic classifications of substantial accumulations of glacigenic diamictons as ‘till’ when modern analogues indicate only modest thicknesses of subglacial traction till beneath glaciers. Onshore thickening of glacigenic deposits through subaqueous push moraine construction and mud apron progradation is compatible with glacier surging behaviour, but not necessarily solely diagnostic of a surging North Sea Lobe during the last glaciation.

Postglacial sedimentary processes on the Storfjorden and Kveithola trough mouth fans: Significance of extreme glacimarine sedimentation

The depositional history of the Storfjorden and Kveithola trough-mouth fans (TMFs) in the northwestern Barents Sea has been investigated within two coordinated Spanish and Italian projects in the framework of the International Polar Year (IPY) Activity 367, NICE STREAMS. The investigation has been conducted using a multidisciplinary approach to the study of sediment cores positioned on high-resolution multibeam bathymetry and TOPAS/CHIRP sub-bottom profiles.Core correlation and the age model were based on 27 AMS 14C samples, rock magnetic parameters, lithofacies sequences, and the presence of marker beds including two oxidized layers marking the post Last Glacial Maximum (LGM) inception of deglaciation (OX-2) and the Younger Dryas cold climatic event (OX-1).Sediment facies analysis allowed the distinction of a number of depositional processes whose onset appears closely related to ice stream dynamics and oceanographic patterns in response to climate change. The glacigenic diamicton with low water content, high density, and high shear strength, deposited during glacial maxima, indicates ice streams grounded at the shelf edge. Massive release of IRD occurred at the inception of deglaciation in response to increased calving rates with possible outer ice streams lift off and collapse. The presence of a several-meter-thick sequence of interlaminated sediments deposited by subglacial outbursts of turbid meltwater (plumites) indicates rapid ice streams' melting and retreat. Crudely-layered and heavily-bioturbated sediments were deposited by contour currents under climatic/environmental conditions favorable to bioproductivity.The extreme sedimentation rate of 3.4cma−1 calculated for the plumites from the upper-slope area indicates a massive, nearly instantaneous (less than 150years), terrigenous input corresponding to an outstanding meltwater event. We propose these interlaminated sediments to represent the high-latitude marine record of MeltWater Pulse 1a (MWP-1a). Different bathymetric and oceanographic conditions controlled locally the mode of glacial retreat, resulting in different thickness of plumites on the upper continental slope of the Storfjorden and Kveithola TMFs. It is possible that the southern part of Storfjorden TMF received additional sediments from the deglaciation of the neighboring Kveithola ice stream.

The glacial sequence at Killiney, SE Ireland: terrestrial deglaciation and polyphase glacitectonic deformation

Depositional conditions of a complexly deformed glacigenic sequence at Killiney Bay, on the west-central margin of the Irish Sea are reconstructed. Deformation geometries provide conclusive evidence for polyphase glacitectonic deformation generated by terrestrial ice sheets. They are dominated by pure shear, simple shear and compressional deformation styles with abundant evidence for glacitectonic induced fracturing and hydrofracturing. There is no evidence of subaqueous sediment flow-induced deformation and impact deformation (iceberg scouring, rained out clasts). Glacigenic diamicton facies associations (FA's) are interpreted as glacitectonically stacked diachroneous units younging laterally away from palaeo-ice margins. Simultaneous deposition of proximal overconsolidated subglacial tills and distal low viscosity flowtills occurred, with the latter being deformed during re-advances. Structural chronology of deformation styles demonstrates polyphase deformation of tills, where glacial overriding produced overconsolidated and polyphase deformed subglacial tills from sediments initially deposited as low viscosity flowtills. It is proposed that relatively late during deglaciation, after retreat of a grounded Irish Sea Ice Sheet, Midland Ice invaded the area and deformed and reworked recessional Irish Sea Ice sequences. Deformation of these recessional sequences led to a heterogeneous stack of polyphase deformed glacigenic sediments with abundant hydrofracturing. The Killiney Bay sequence and other sequences in the Southern Irish Sea Basin demonstrate that MIS 2 deglaciation took place under terrestrial conditions with lower relative sea levels than present.

The eastern extent of the Barents–Kara ice sheet during the Last Glacial Maximum based on seismic-reflection data from the eastern Kara Sea

We present sub-bottom profiling (sparker and Parasound) results from the eastern Kara Sea, on the Eurasian Arctic margin, which enable the identification of the Last Glacial Maximum (LGM) ice extent. The analysed profiles show that glacigenic diamicton is ubiquitous at the seafloor, east of about 95°E and 78°N. The eastern margin of this diamicton is expressed in a conspicuous morainic ridge at the entrance to the Vilkitsky Strait, and to the south the diamicton projection aligns with the LGM limit mapped at the north-western Taymyr. The bottom of the Voronin Trough further north is also covered with diamicton and has numerous erosional bedforms, indicating a streamlined flow of grounded ice along the trough. Accurate dating of the diamicton is not attainable, but the correlation of pre-diamict sediments to well-dated sections in the Laptev Sea, and available 14C ages from sediments on top of the diamicton, indicate its LGM age. These results support the palaeogeographic reconstruction that assumes the extension of the LGM Barents–Kara ice sheet as far east as Taymyr. This configuration implies that LGM ice blocked the drainage of the Ob and Yenisey rivers on the Kara shelf. This inference is consistent with the presence of large (>100 km wide) lenses of basin infill adjacent to the southern margin of the diamicton. However, the limited distribution of the eastern Kara ice lobe, not extending on Severnaya Zemlya, suggests that the ice was fairly thin and short-lived: insufficient for the accumulation of the gigantic proglacial lakes that occurred during earlier glaciations.

The eastern extent of the Barents–Kara ice sheet during the Last Glacial Maximum based on seismic-reflection data from the eastern Kara Sea

We present sub-bottom profiling (sparker and Parasound) results from the eastern Kara Sea, on the Eurasian Arctic margin, which enable the identification of the Last Glacial Maximum (LGM) ice extent. The analysed profiles show that glacigenic diamicton is ubiquitous at the seafloor, east of about 95°E and 78°N. The eastern margin of this diamicton is expressed in a conspicuous morainic ridge at the entrance to the Vilkitsky Strait, and to the south the diamicton projection aligns with the LGM limit mapped at the north-western Taymyr. The bottom of the Voronin Trough further north is also covered with diamicton and has numerous erosional bedforms, indicating a streamlined flow of grounded ice along the trough. Accurate dating of the diamicton is not attainable, but the correlation of pre-diamict sediments to well-dated sections in the Laptev Sea, and available 14 C ages from sediments on top of the diamicton, indicate its LGM age. These results support the palaeogeographic reconstruction that assumes the extension of the LGM Barents‐Kara ice sheet as far east as Taymyr. This configuration implies that LGM ice blocked the drainage of the Ob and Yenisey rivers on the Kara shelf. This inference is consistent with the presence of large (>100 km wide) lenses of basin infill adjacent to the southern margin of the diamicton. However, the limited distribution of the eastern Kara ice lobe, not extending on Severnaya Zemlya, suggests that the ice was fairly thin and short-lived: insufficient for the accumulation of the gigantic proglacial lakes that occurred during earlier glaciations.

Pleistocene Stratigraphy of the Athabasca River Valley Region, Rocky Mountains, Alberta

The Pleistocene stratigraphy of the central Canadian Rocky Mountains is described from a region where few studies of Late Quaternary deposits have been conducted. Six informal lithostratigraphic units are recognized from newly mapped exposures in Jasper National Park. The oldest deposits are interpreted as paleofan deposits (Unit 1) and they are overlain by glaciofluvial gravels and sands (Unit 2), glaciolacustrine sediments (Unit 3) and by a glacigenic diamicton sequence (Unit 4) that includes basal till, supraglacial deposits and ice-marginal debris flow sediments. Proximal glaciofluvial gravels, debris flow deposits and minor glaciolacustrine sediments (Unit 5) and paragiacial fan deposits and loess (Unit 6) cap the stratigraphic sequence. Limited chronologic control suggests that nonglacial fluvial and alluvial fan sedimentation began prior to 48 ka and continued throughout the Middle Wisconsinan. Braided stream deposits were accumulating in the Athabasca River valley near Jasper townsite about 29 ka. In the Late Wisconsinan, Rocky Mountain and Cordilleran glaciers advanced through the area, initially damming lakes in a number of Front Range tributary valleys. During déglaciation, ice-marginal glaciofluvial activity and paragiacial debris flows dominated sedimentation. Glacial lakes were limited in extent. A radiocarbon date on shells from one small ice-marginal lake indicates that glaciers were well in retreat by about 12 ka. Alpine glaciers in the region were at or near their present limits by 10 ka.

Late Cenozoic prograding wedges on the NW European continental margin: their formation and relationship to tectonics and climate

During late Pliocene to Pleistocene times, prominent prograding wedges were deposited along the continental margin of NW Europe, resulting in seaward shelf break migration of up to 150 km. Much of the sediment accumulation occurred marginal to the former mid- to high-latitude ice sheets. The geographical distribution, and stratigraphical and chronological data may suggest that the instigation of the wedges was variously related to tectonic uplift as well as a response to the late Pliocene to Pleistocene climate deterioration and onset of major northern hemisphere glaciations. The onset of wedge growth on the NW UK and Irish margins was initiated at about 4 Ma in response to tectonic tilting of the margin in that region. However, glacially derived sediments here comprise a significant proportion of the wedges, especially since 0.44 Ma. For the Faroe margin, no detailed chronology is available; however, it may be inferred that onset of glacigenic wedge growth here did not post-date that observed on the NW UK and Irish margins. Offshore Norway, wedge growth has largely occurred since ca. 2.7 Ma in response to northern hemisphere glaciations, also recording a major change in sediments transport routes at 0.8–1.1 Ma (reflecting larger Fennoscandian Ice Sheets). Presently, it is uncertain whether the glacigenic wedge growth was preceded by a fluvial phase (in response to uplift) in this area. In the western Barents Sea, an early phase of wedge growth was (glacio) fluvial in character. Off western Spitsbergen, the development was similar to that of the Barents Sea although the glacigenic wedge-growth phase may have started somewhat earlier. The wedges commonly display gently inclined seaward prograding clinoforms, and transparent to chaotic internal acoustic facies. Sampling of their sediments reveals that they are mainly composed of glacigenic diamicton interbedded with marine and glaciomarine sediments that, to various extents, have been affected by bottom-current action. The clinoforms of these wedges vary in geometry from oblique to sigmoidal, and they also show varying degrees of aggradation throughout their development. The resulting stratal stacking pattern can be attributed to a combination of variations in sediment supply, sedimentary processes, and accommodation space, the latter being a function of tectonic movements and/or loading induced subsidence as well as eustatic sea-level fluctuations.

Organic Carbon, Texture, and Quantitative Color Measurement Relationships for Cultivated Soils in North Central Iowa

The quantification of soil organic C (SOC) concentrations is becoming increasingly more desirable because of environmental and economic concerns regarding the reactivity of SOC with pesticides, fertilizers, and waste materials. The objectives of this study were to quantify soil color organic C relationships and to quantify soil particle‐size organic C relationships for Ap horizons in north central Iowa. All of the 130 soils examined developed in glacigenic diamicton or local hillslope sediment derived from glacigenic diamicton. A Minolta CR‐310 chroma meter was used to quantify the percentage of reflectance, and Munsell value and chroma for both air‐dry and moist soils. Organic C concentration of the sample set ranged from 4.4 to 70.8 g kg−1 Significant relationships were observed between organic C concentration and percentage of reflectance (r2 = 0.77 moist, r2 = 0.74 air‐dry), Munsell value (r2 = 0.77 moist, r2 = 0.74 air‐dry), Munsell chroma (r2 = 0.68 moist, r2 = 0.77 air‐dry), the percentage of sand (r2 = 0.74), the percentage of clay (r2 = 0.71), and geometric mean particle diameter (GMPD) (r2 = 0.74). Logarithmic relationships existed for reflectance, Munsell value and chroma, and GMPD while linear relationships were observed for sand and clay contents. Chroma meter soil color measurements and particle‐size data are useful predictors of organic C concentrations for Ap horizons in north central Iowa. Evidence from this study and the literature suggest that unique relationships exist for different soil landscapes.

Organic matter deposition along the Kara and Laptev Seas continental margin (eastern Arctic Ocean) during last deglaciation and Holocene: evidence from organic–geochemical and petrographical data

Organic petrologic (maceral analysis) and bulk organic–geochemical studies were performed on five sediment cores from the Eurasian continental margin to reconstruct the environmental changes during the last ∼13 000 yr. The core stratigraphy is based on AMS- 14C dating, and correlation by magnetic susceptibility and lithostratigraphic characteristics. Variations in terrigenous, freshwater, and marine organic matter deposition document paleoceanographic and paleoclimatic changes during the transition from the last deglaciation to the Holocene. Glacigenic diamictons deposited in the St. Anna Trough (northern Kara Sea) during the Last Glacial Maximum (LGM) are characterized by reworked terrigenous organic matter. In contrast, the Laptev Sea shelf was not covered by an ice-sheet, but was exposed by the lowered sea level. Increased deposition of marine organic matter (MOM) during deglaciation indicates enhanced surface-water productivity, possibly related to influence of Atlantic waters. The occurrence of freshwater alginite gives evidence for river discharge to the Kara and Laptev Seas after the LGM. At the eastern Laptev Sea slope, the first influence of Atlantic water masses is indicated by an increase in the contents of MOM and dinoflagellate cysts, with Operculodinium centrocarpum prior to ∼10 000 yr BP. High sedimentation rates in the Kara and the Laptev Seas with the adjacent slope at the beginning of the Holocene are presumably related to increased freshwater and sediment discharge from the Siberian rivers. Evidence for elevated Holocene freshwater discharge to the Laptev Sea has been found between ∼9.8 and 9 kyr BP, at ∼5 kyr BP and at ∼2.5 kyr BP. In the Kara Sea, an increased freshwater signal is obvious at ∼8.5 kyr BP and at ∼5 kyr BP. Higher portions of MOM were accumulated in the St. Anna Trough and at the Eurasian continental margin at several intervals during the Holocene. Increased primary productivity during these intervals is explained by seasonally ice-free conditions possibly associated with increased inflow of Atlantic waters.

Seismic analyses of Cenozoic contourite drift development in the Northern Norwegian Sea

Four drift accumulations have been identified on the continental margin of northern Norway; the Lofoten Drift, the Vesteralen Drift, the Nyk Drift and the Sklinnadjupet Drift. Based on seismic character these drifts were found to belong to two main groups; (1) mounded, elongated, upslope accretion drifts (Lofoten Drift, Vesteralen Drift and Nyk Drift), and (2) infilling drifts (Sklinnadjupet Drift). The drifts are located on the continental slope. Mainly surface and intermediate water circulation, contrary to many North Atlantic and Antarctic drifts that are related to bottom water circulation, and sediment availability have controlled their growth. Sediments were derived both from winnowing of the shelf and upper slope and from ice sheets when present on the shelf. The main source area was the Voring margin. This explains the high maximum average sedimentation rate of the nearby Nyk (1.2 m/ka) and Sklinnadjupet (0.5 m/ka) Drifts compared with the distal Lofoten (0.036 m/ka) and Vesteralen (0.060 m/ka) Drifts. The high sedimentation rate of the Nyk Drift, deposited during the period between the late Saalian and the late Weichselian is of the same order of magnitude as previously reported for glacigenic slope sediments deposited during glacial maximum periods only. The Sklinnadjupet Drift is infilling a paleo-slide scar. The development of the infilling drift was possible due to the available accommodation space, a slide scar acting as a sediment trap. Based on the formation of diapirs originating from the Sklinnadjupet Drift sediments we infer these sediments to have a muddy composition with relatively high water content and low density, more easily liquefied and mobilised compared with the glacigenic diamictons.

Micromorphological evidence for polyphase deformation of glaciolacustrine sediments from Strathspey, Scotland

Abstract A combination of field investigation and micromorphological analysis has been applied to polydeformed Late Devensian rhythmites and glacigenic diamicton, exposed in Strathspey, Scotland. This provided information on the geometry, kinematics and relative ages of ductile and brittle structures, and records a complex subglacial deformation history. The deformation is interpreted as resulting from a single progressive event, associated with over-riding of proglacial lake sediments by wet-based ice. The earliest deformation (‘D 1 ’) resulted from compaction/loading (pure shear) and imposed a bedding-parallel (S 1 ) fabric throughout the rhythmites. S 1 was subsequently deformed by kink bands and minor ductile shearing during ‘D 2 ’. A later ‘D 3 ’ event, characterized by soft-sediment deformation and fluidization of matrix-poor sands, was accompanied by an increase in pore water pressure. This lead to hydrofracturing of the rhythmites. The most intense deformation (‘D 4 ’), which resulted from simple shear, was partitioned into the upper part of the sequence. It produced folding, thrusting and brittle microfaulting in response to NNW-directed ice-push. These findings indicate that, in general, subglacial deformation is not homogeneous and can extend to depths of >3 m below the presumed ice-sediment interface.

Glacigenic clast fabrics: genetic fingerprint or wishful thinking?

The interpretation of glacigenic diamictons is a subjective process, for which quantitative support is frequently sought from parameters such as clast shape and fabric. It has been widely suggested that different glacigenic diamicton facies possess distinct clast-fabric signatures. This paper examines this concept using a data set of 111 clast fabrics, and a synthesis of published results. Eigenvalues are calculated and compared for a variety sedimentary facies. It is concluded that clast fabric alone is not able to discriminate between different glacigenic facies, and it is argued that clast fabric offers little quantitative support in the interpretation of glacigenic sediments. It is suggested, therefore, that although clast fabric may continue to have a role as an indicator of relative strain at specific sites, its use in the discrimination of glacigenic facies is limited. Consequently, we should be much more selective in undertaking such analyses in the future. Copyright © 1999 John Wiley & Sons, Ltd.

Late glacial events in the central Russian Arctic

Investigation of glacigenic diamictons and landforms in the central Russian Arctic has established that continental glaciation was widespread during late glacial time. Diamictons in West-Central Siberia containing marine foraminifera and mollusca include glacitectonic deformation features, and are associated with glacial landforms. These sediments are interpreted as basal tills, formed by continental glaciation which expanded from the exposed Kara Sea shelf, southwards along the western flank of the Ural Mountains. Piedmont glaciers advancing westward from the Urals were obstructed by the southward-flowing ice and were areally restricted. Simultaneously, piedmont glaciers advancing eastward from the crests of the Urals were able to expand without restriction. Alpine glaciation within the Urals was areally restricted and culminated, simultaneously, with the maximum extent of the southward-flowing shelf-based ice. In West Siberia, rapid disintegration of an Early Weichselian ice sheet by marine calving was followed by slow stagnation of the dissected mass throughout the remainder of the Weichselian. In contrast, glaciation in the Pechora Basin reached its maximum during the Middle-Late Weichselian, at least 30,000 years after the glacial maximum in western Siberia. The transition to Holocene climatic conditions was influenced by the presence of remanent decaying glacial masses.

Late Weichselian submarine debris flow deposits on the Bear Island Trough Mouth Fan

Sedimentary processes on the Bear Island Trough Mouth Fan during the last glacial were studied using high resolution reflection seismics and gravity cores. The fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick. Debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km 2. The large debris flows were generated when the Barents Sea Ice Sheet reached the shelf break. Glacigenic sediments transported to the grounding-line were temporarily stored on the upper slope. Due to the high sedimentation rate, the sediments were unstable and earthquakes, oversteepening and/or build up of excess pore pressure triggered sediment release generating large debris flows. Sediments were also eroded and incorporated during the downslope flow. Debris flows were the most important sediment distributing process due to the relatively high shear strength, low flow mobility of the glacigenic diamicton, and the low fan gradient. The Weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the Early and Mid Weichselian. The Barents Sea Ice Sheet might have reached the shelf break twice during the Late Weichselian. On average one large debris flow, comprising 18 km 3 of sediments, was released between every 35 to 75 years during the last glacial maximum.

Iceberg scouring and sea bed morphology on the eastern Weddell Sea shelf, Antarctica

A detailed shallow seismic and side scan sonar study, combined with vibrocoring on the continental shelf off Riiser Larsenisen ice shelf, East Antarctica, has provided information on the different morphological patterns present in the area. Features related to the motion of grounded icebergs prevail, with relatively narrow iceberg plough marks being predominant. A‘washboard pattern’probably results from a wobbling motion of grounded, tabular icebergs under influence of direct push by the advancing ice shelf, and a hummocky disturbed sea bed morphology results from small scale sediment slumping, often triggered by iceberg action. Narrow, elongate depressions incise the sea floor sediments, which are composed of glacigenic diamictons. Formation of the depressions is not fully understood, but erosion by subglacial meltwater under an expanded East Antarctic ice sheet is a possibility, although this requires a different glacier thermal regime than that of the present-day. Although this study is restricted in area, the processes of the region are typical of the Antarctic continental shelf. The results may hence have a more regional significance.

Iceberg scouring and sea bed morphology on the eastern Weddell Sea shelf, Antarctica

A detailed shallow seismic and side scan sonar study, combined with vibrocoring on the continental shelf off Riiser Larsenisen ice shelf, East Antarctica, has provided information on the different morphological patterns present in the area. Features related to the motion of grounded icebergs prevail, with relatively narrow iceberg plough marks being predominant. A‘washboard pattern’probably results from a wobbling motion of grounded, tabular icebergs under influence of direct push by the advancing ice shelf, and a hummocky disturbed sea bed morphology results from small scale sediment slumping, often triggered by iceberg action. Narrow, elongate depressions incise the sea floor sediments, which are composed of glacigenic diamictons. Formation of the depressions is not fully understood, but erosion by subglacial meltwater under an expanded East Antarctic ice sheet is a possibility, although this requires a different glacier thermal regime than that of the present-day. Although this study is restricted in area, the processes of the region are typical of the Antarctic continental shelf. The results may hence have a more regional significance.

Pebble Fabric in an Ice-Rafted Diamicton

Pebble fabric studies on ice-rafted diamictons have been limited to general observations, with authors noting preferences toward vertical, random, or horizontal orientations. To clarify such observations, pebble fabric data were collected from a fossiliferous diamicton of late Pleistocene age located on Whidbey Island, Washington. The ice-rafted origin of this unit is supported by several independent characteristics including in situ macrofauna and microfauna, conformity with subaqueous lithofacies containing dropstones, lower bulk densities and higher void ratios than associated tills, soft sediment deformation structures suggestive of iceberg dumping, textural gradations, and facies relationships. Analysis using the eigenvalue method indicates that ice-rafted fabrics are nearly random with little consistency of vector orientations between sites and without any relationship to the probable direction of glacial flow. The weak fabric is mainly the product of settling through the water column and impact with, or penetration of, the bed. Samples that possess a weak preferred long axis orientation with a low angle of dip, including those from laminated muds, can best be explained by the intermittent effects of bottom currents, a resistant substrate at the time of deposition and post-depositional flowage. Comparisons of pebble fabrics from basal tills, recent sediment flow deposits, and basal, debris-laden ice of an active glacier demonstrate that the ice-rafted fabrics are distinct from those of basal ice and till but are quite similar to those of sediment flow diamictons. Ice-rafted diamictons appear, however, to contain a greater number of elongate stones with long axis plunge angles exceeding 45° than other glacigenic diamictons.