Glacial Diamictons Research Articles

Glacier dam evolution and knickpoint migration in the Yarlung Tsangpo Gorge, eastern Himalayas, since the last glacial period

The repeated cut-and-fill process induced by the late Quaternary glacial damming and catastrophic outburst events in the Yarlung Tsangpo Gorge (YTG) in the eastern Himalaya may reflect the interaction between rock uplift, climate change and river incision in the southeastern Tibetan Plateau. Here we provide the detailed reconstruction of the cut-and-fill history recorded at the entrance of the YTG, based on geomorphological, sedimentological and chronological analyses. The results reveal a catastrophic glacial-dam breach during the last deglaciation (∼18 ka), and the outburst flood eroded a ∼30–45 km long valley floor filled with glacial diamicton and glaciofluvial deposits, which was later further incised to form terrace T2 with a height of ∼350 m. The second dam failure occurred at ∼5 ka, producing a spillway, forming terrace T1 with a height of ∼100 m. The vertical incision and horizontal migration rate of the knickpoint at the glacier dams were estimated as 0.02 m/yr, and 2.5 m/yr since the last deglaciation, based on the age of the terraces and distance of the knickpoints. We consider the glacial dams to be effective in impeding headward river erosion during glacial periods. This, along with rapid river headward erosion during the last interglacial period, results in two knickpoints on the longitudinal profile due to the differences in erosion resistance. The fluvial reaches corresponding to the repeated cut-and-fill processes are confined to the center of the Namche Barwa massif, suggesting that rapid rock uplift counteracted fluvial headward erosion and maintained the stability of the bedrock knickpoint. Therefore, in comparison to glacial dams, tectonic uplift is the most important component in plateau margin stabilization.

Distinguishing glacial diamictons and landforms using till macrofabric and grain size analysis: Serra da Cabreira Mountains, NW Portugal

ABSTRACT Information on the nature of processes occurring in modern glaciers can be obtained through the study of diamictons and landforms that are the product of past glaciations. Macrofabric and grain size analysis of late Quaternary glacial diamictons and moraines present in several valleys of the Serra da Cabreira Mountains in northwest Portugal revealed the presence of two types of diamictons deposited in different stages and were used to re-construct the glacial paleo process history of this mountainous region. Supraglacial melt-out tills and paraglacially reworked tills by debris flows are dominant in this range. Supraglacial melt-out tills, representative of periods of glacial stability followed by recession, present girdle to transitional fabrics and coarser to medium, poorly sorted sediments. Paraglacially reworked tills by debris flows, representative of postglacial mass wasting activity, present girdle fabrics and coarser, poorly sorted sediments. These diamictons and landforms are of particular importance in the reconstruction of the glacial dynamics and history of the Serra da Cabreira Mountains due to a scarcity of chronological data based on absolute dating methods. These Atlantic mountains are also the lowest glaciated range in the Iberian Peninsula, which makes them a compelling area to investigate mountain glacial dynamics in low-elevation Atlantic ranges.

Where ice gave way to fire: deglacial volcanic activity at the edge of the Coast Mountains in Milbanke Sound, BC

Kitasu Hill and MacGregor Cone formed along the Principe Laredo Fault on British Columbia’s central coast as the Wisconsinan ice sheet withdrew from the Coast Mountains. These small-volume Milbanke Sound Volcanoes (MSV) provide remarkable evidence for the intimate relationship between volcanic and glacial facies. The lavas are within-plate, differentiated (low MgO < 7%) Ocean Island Basalts, hawaiites, and mugearites that formed from ∼1% decompression melting of asthenosphere with residual garnet. Kitasu Hill, on glaciated bedrock, formed between 18 and 15 cal ka BP. Dipping, poorly stratified, admixed hyaloclastite, and glacial diamicton with large plutonic clasts and pillow breccia comprise its basal tuya platform (0–43 masl). Subaerial nested cinder cones, with smaller capping lava flows, sit atop the tuya. New marine samples show McGregor Cone formed subaerially but now sits submerged at 43–200 mbsl on an eroded moraine at the mouth of Finlayson Channel. Seismic data and cores reveal glaciomarine sediments draping the cone’s lower slopes and show beach terraces. Cores contain glaciomarine diamictons, ice-rafted debris, delicate glassy air fall tephra, and shallow, sublittoral, and deeper benthic foraminifera. Dates of 14.1–11.2 cal ka BP show volcanism spanned ∼2000 years during floating ice shelf conditions. The MSV have similar proximal positions to the retreating ice sheet, display mixed volcano-glacial facies, and experienced similar unloading stresses during deglaciation. The MSV may represent deglacially triggered volcanism. The dates, geomorphic and geological evidence, constrain a local relative sea level curve for Milbanke Sound and show how ice gave way to fire.

Stream Recovery Post Channelization: A Case Study of Low-Gradient Streams in Central Illinois, USA

Stream channelization, which entails reducing the sinuosity of a stream, widening, and in some cases deepening the stream channel, is a widespread practice in agricultural regions. Channelization efforts in central Illinois have significant impacts on the geomorphology, flow regime, and sediment transport both in and adjacent to modified reaches. The goal of this study was to characterize the changes in stream channels by comparing three streams that are at various stages of recovery post channelization, 5 years (1900N), 7 years (Frog), and 35 years (Bray), to an unmodified stream reach (Crooked) and estimate a recovery rate. Measured channel slopes within the modified streams were one order of magnitude larger than the measured channelized streams in Crooked. The two streams most recently channelized exhibited little geomorphic change since their channelization, while the segment modified 35 years ago experienced bank failure and immature meander development. The lack of redevelopment resulted in sinuosity values lower than that of Crooked, and the reestablishment of meanders similar to Crooked would take an estimated 11,000 years. The distributions of the sediments within all the streams comprised poorly sorted sand and pebbles. The distribution of the sediment resembles the source, the glacial diamicton that serves as the surficial sediments. Mobilization of the sediment is frequent, with recorded scour greater than sedimentation. Overall, the channelized segments experienced limited recovery. The segments are still degrading (1900N and Frog) or are transitioning into a threshold stage (Bray).

Evidence for a “Little Ice Age” glacial advance within the Antarctic Peninsula – Examples from glacially-overrun raised beaches

Recognition of how dynamic the Antarctic ice sheets and glaciers were during the late Holocene has grown in recent years. Proxy data suggests the presence of Neoglacial advances but few moraines or glacial features from this time have been dated compared to glaciated landscapes of the Northern Hemisphere. Debate continues on whether parts of Antarctica experienced glacial advance at the same time as the “Little Ice Age” (LIA), which is well-documented in the Northern Hemisphere. We provide new evidence for late Holocene glacial fluctuations at three locations along the Antarctic Peninsula. A moraine or till sheet from a tidewater glacier cross cuts a series of dated raised beaches at Tay Head, Joinville Island along the northwestern Weddell Sea. At Spark Point, on Greenwich Island, a glacier has overrun Holocene raised beaches and a shell-bearing marine deposit is reworked into a glacial diamicton. A third site in Calmette Bay within the larger Marguerite Bay also contains a recent moraine that cuts across a series of dated raised beach ridges. The new ages constraining these glacial advances are in broad agreement with the handful of other existing ages on moraines and proxy records suggestive of cooler conditions within the Antarctic Peninsula. Combining available timing constraints into a Bayesian model yields an age of 400 to 90 cal BP (1550–1860 CE; 95%) for the LIA across the Antarctica Peninsula. Consideration of a two-phase glacial advance within our Bayesian framework does fit more of the data from across the Antarctic Peninsula and suggests advances from 575 to 330 cal BP (1375–1620 CE) and 400 to 50 cal BP (1550–1900 CE). However, more work is needed to determine if such a two-phase advance occurred. Regardless, its similar timing within the Antarctic Peninsula to that of the Northern Hemisphere supports recent assertions of a volcanic or solar forcing for the LIA. These recent readvances also provide a possible mechanism for changes in the rates of Holocene relative sea-level change recorded across the Antarctic Peninsula suggesting that the Antarctic ice sheets may have been more responsive to past climate changes than previously thought and glacial isostatic adjustment from the LIA and possibly other Holocene glacial oscillations is superimposed upon the longer relaxation from the Last Glacial Maximum.

Glacial landforms and sediments (landsystem) of the Smoking Hills area, Northwest Territories, Canada: Implications for regional Pliocene – Pleistocene Laurentide Ice Sheet dynamics

The Smoking Hills area in the western Canadian Arctic was purported to contain a regionally rare Quaternary stratigraphic section with multiple, local ice cap-derived tills and a long chronology constrained by palaeomagnetic markers. We present a fundamental revision of previous glacial and magnetostratigraphic interpretations based on detailed sedimentological and structural analyses of the main stratigraphic section and many new exposures, cosmogenic nuclide isochron burial dating, and a systematic reconstruction of the geomorphology and landscape evolution using a glacial landsystem approach. We demonstrate that the Smoking Hills area was fully glaciated during the last (Wisconsinan) glaciation. Previously reported tills ascribed to multiple glaciations represent instead a complex facies sequence of glacitectonic thrust stacking of Laurentide Ice Sheet (LIS) sourced diamictons, glacilacustrine and glacifluvial deposits, together with previously unidentified, poorly-consolidated Cretaceous bedrock rafts and deformed intraclasts. Much of this sedimentation and glacitectonic activity dates to the last (Wisconsinan) glaciation and can be reconciled with a polythermal ice sheet marginal landsystem signature, wherein ice-cored moraine belts are developed over subglacial bedforms (flutings) arranged in discrete flowsets. The flowsets record the complex interaction of ice streams nourished by ice flowing from three main sources: Great Bear Lake to the south, Amundsen Gulf (Franklin Bay) to the east and Liverpool Bay (Mackenzie Valley) to the southwest. Decoupling of the ice margins of these three ice sources gave rise to interlobate ice-dammed lake development over the lower Horton River area during final deglaciation. A cosmogenic 26Al/10Be isochron burial age of 2.9 ± 0.3 Ma (1σ, n = 4) from the lowermost glacial diamicton and glacitectonite sequence provides evidence of perhaps the earliest continental glaciation of this region. This deposit postdates, or is perhaps a later re-advance of the same initial glaciation that produced widespread glacitectonic disturbance of bedrock in preglacial valley networks and early glacifluvial and glacilacustrine deposits containing an ice wedge pseudomorph. Subsequent glaciations have largely removed or cannibalised pre-existing records to construct complex till and glacitectonite stacks that contain reworked organics with non-finite radiocarbon ages. One site preserves buried “old” glacier ice in which prominent ice wedges had formed during an interglacial permafrost phase and were then deformed down-flow by the LIS during the Wisconsinan glaciation.

Macrofabric and grain size analysis of moraines and other till deposits in the Serra da Estrela Mountains, central Portugal

ABSTRACT Till macrofabric and grain-size analysis of glacial diamictons and landforms present in several valleys of the Serra da Estrela Mountains in central Portugal were used to interpret till types and to reconstruct the glacial paleoprocess history of this mountainous region. Supraglacial melt-out and flow tills are dominant in this range. Supraglacial melt-out tills, representative of periods of glacial stability and stagnation followed by recession, present weaker fabric data and coarser, poorly sorted sediments. Flow tills, mainly representative of glacial stability followed by recession, present crude layering, and soft-sediment deformation structures with moderate fabric data and coarser to fine, poorly sorted sediments. Glacial diamictons affected by post-glacial paraglacial activity in the form of landslides were also observed in three valleys. These present weaker to moderate fabric data and coarser, poorly sorted sediments. These glacial diamictons and landforms are of particular importance in the reconstruction of the glacial dynamics and history of the Serra da Estrela Mountains due to a scarcity of chronological data based on absolute dating methods. These mountains also represent the southernmost Atlantic range in Europe where significant glaciation took place, which makes it an interesting area to investigate mountain glacial dynamics in low elevation humid Atlantic coastal ranges and compare it with other Atlantic ranges.

Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia

We present 14 new 10Be cosmogenic nuclide exposure ages quantifying asynchronous readvances during the Antarctic Cold Reversal from glaciers in the Baker Valley region of central Patagonia. We constrain glacier and ice-dammed palaeolake dynamics using a landsystems approach, concentrating on outlet glaciers from the eastern Northern Patagonian Icefield (NPI) and Monte San Lorenzo (MSL). Soler Glacier (NPI) produced lateral moraines above Lago Bertrand from 15.1 ± 0.7 to 14.0 ± 0.6 ka, when it dammed the drainage of Lago General Carrera/Buenos Aires through Río Baker at a bedrock pinning point. At this time, Soler Glacier terminated into the 400 m “Deseado” level of the ice-dammed palaeolake. Later, Calluqueo Glacier (MSL) deposited subaerial and subaqueous moraines in the Salto Valley near Cochrane at 13.0 ± 0.6 ka. These moraines were deposited in an ice-dammed palaeolake unified through the Baker Valley (Lago Chalenko; 350 m asl). The Salto Valley glaciolacustrine landsystem includes subaqueous morainal banks, ice-scoured bedrock, glacial diamicton plastered onto valley sides, perched delta terraces, kame terraces, ice-contact fans, palaeoshorelines and subaerial push and lateral moraines. Boulders from the subaqueous Salto Moraine became exposed at 12.1 ± 0.6 years, indicating palaeolake drainage. These data show an asynchronous advance of outlet glaciers from the Northern Patagonian Icefield and Monte San Lorenzo during the Antarctic Cold Reversal. These advances occurred during a period of regional climatic cooling, but differential moraine extent and timing of advance was controlled by topography and calving processes.

Middle Pleistocene marine deposits on the Kola Peninsula (NW Russia)

A unique Middle to Late Pleistocene site is situated in the southern part of the Kola Peninsula on the right bank of the lower Varzuga River, providing for the first time valuable evidence concerning Middle Pleistocene climate change and a marine transgression event during this period. The corresponding strata are exposed in a 2-km-long natural outcrop traceable along the abrupt slope of the river valley where the fluvial erosion and slumping have dissected a remnant elongated hill. Middle Pleistocene marine deposits compose here the basal part of the sedimentary succession. Lithological, sedimentological and structural field study accompanied by ESR dating of mollusc shells taken from marine sediments and a detailed palynological investigation have been carried out.The basal part of the Varzuga section is represented by superposition of consolidated clay, loam, sandy loam with subfossil mollusc shells, and small lenses of coarse-grained sand, and pebbles (Unit 1). Marine shells were ESR dated between 319.0 ± 38.5 ka and 316.0 ± 23.6 ka. Glacial diamicton and glacifluvial sands (Unit 2), probably also Middle Pleistocene in age, overlay the marine sediment with sharp contact. The uppermost part of the sequence consists of the Late Pleistocene marine sediments, glacial diamicton, glacifluvial sand, and presumably Late Glacial and early Holocene lacustrine deposits. One hundred samples of marine (Unit 1) and lowermost part of glacial (Unit 2) deposits were palynologically reinvestigated. On the basis of detailed palynostratigraphy, 19 pollen assemblage zones were identified. Recurring vegetative assemblages characterized by increasing quantity of Betula with occurrence of mesophilous and thermophilous components (Alnus, Quercus, Tilia, Ulmus, Carpinus, Corylus, Osmunda, Nuphar, Nymphaea) indicate five Middle Pleistocene warm events, mostly during Marine Isotope Stage (MIS) 9.

Basal Moraines: Communication 2. Identification and Some Concepts of Their Genetic Interpretation

Common basal moraines display diverse glaciodynamic structures inherited from the parental moraine-containing ice. Since these glacial diamictons are marked by instable structure and composition, they can resemble sediments of another origin and their identification is a difficult task. We cannot make substantiated genetic conclusions based on certain lithological properties typical of glacial diamictons. Only a set of specific features can provide sufficiently reliable determination of their glacial nature. Other methodical approaches applied in different regions, the Barents Sea included, for the identification of glacial diamictons based on the highly superficial analysis of some (usually secondary) features lead to a biased genetic interpretation of moraines.

Basal Moraines: Communication 1. Essential Lithological Features

The facies complex of basal moraines with glaciodynamic structures (common basal moraines) dominates among deposits of the given genetic type. These moraines represent glacial diamictons of diverse structure and lithology. Some of their features are also typical of sediments of other genetic types. Therefore, a comprehensive study of glacial diamictons and their occurrence mode on the glacial bed (unconsolidated or consolidated) within large outcrops is methodically correct. Only such studies can unravel the wide range of specific features typical of common basal moraines.

In Situ Temperature Measurements at the Svalbard Continental Margin: Implications for Gas Hydrate Dynamics

AbstractDuring expedition MARIA S. MERIAN MSM57/2 to the Svalbard margin offshore Prins Karls Forland, the seafloor drill rig MARUM‐MeBo70 was used to assess the landward termination of the gas hydrate system in water depths between 340 and 446 m. The study region shows abundant seafloor gas vents, clustered at a water depth of ∼400 m. The sedimentary environment within the upper 100 m below seafloor (mbsf) is dominated by ice‐berg scours and glacial unconformities. Sediments cored included glacial diamictons and sheet‐sands interbedded with mud. Seismic data show a bottom simulating reflector terminating ∼30 km seaward in ∼760 m water depth before it reaches the theoretical limit of the gas hydrate stability zone (GHSZ) at the drilling transect. We present results of the first in situ temperature measurements conducted with MeBo70 down to 28 mbsf. The data yield temperature gradients between ∼38°C km−1 at the deepest site (446 m) and ∼41°C km−1 at a shallower drill site (390 m). These data constrain combined with in situ pore‐fluid data, sediment porosities, and thermal conductivities the dynamic evolution of the GHSZ during the past 70 years for which bottom water temperature records exist. Gas hydrate is not stable in the sediments at sites shallower than 390 m water depth at the time of acquisition (August 2016). Only at the drill site in 446 m water depth, favorable gas hydrate stability conditions are met (maximum vertical extent of ∼60 mbsf); however, coring did not encounter any gas hydrates.

Sea ice, ice‐rafting, and ocean climate across Denmark Strait during rapid deglaciation (∼16–12 cal ka BP) of the Iceland and East Greenland shelves

ABSTRACTA suite of cores from the North‐West Iceland and East Greenland shelves sampled fossiliferous or unfossiliferous basal glacial diamictons. Radiocarbon dates above the diamictons are similar on both shelves, but the value of the ocean reservoir correction, ΔR, is unknown. Deglaciation occurred either ∼16 or 14 cal ka BP depending on the choice of ΔR. The ice sheets were behind the present coastline by 12.2 cal ka BP. We examine seven cores that record the glacial/deglacial transition and present new data on the sea‐ice biomarkers IP25 and C25:2 from four of the cores plus data on ice‐rafted debris counts, grain‐size spectra, δ18O on the near‐surface planktonic foraminifera Neogloboquadrina pachyderma (s), foraminifera assemblages, and quartz percentage. IP25 concentrations are markedly higher for the East Greenland sites, while they are frequently below the limit of quantification off Iceland, observations that parallel the wt% quartz in the sediments. The δ18O N. pachyderma (s) data show a strong gradient across Denmark Strait with lighter δ18O values towards the East Greenland shelf indicative of a large freshwater flux. The presence of the chilled Atlantic Water benthic foraminifera, Cassidulina neoteretis indicates that rapid ice sheet retreat was associated with ocean forcing, combined with other factors.

Re-assessment of the mid to late Quaternary glacial and environmental history of the Boco Plain, western Tasmania.

The glacial geomorphology and drill core-based stratigraphy of the Boco Plain, western Tasmania, reveal a complex sequence of Quaternary glacial and non-glacial episodes. The upper part of the southern Boco Plain stratigraphy was previously dated by 14C and U-series on interbedded organics of MIS 1 to MIS 5 affinity. U-series dating of ferricretes associated with glacial diamictons from Boco Plain cores suggested that there were glacial advances broadly correlative with MIS 6, 8 and ≥10. However, terrestrial cosmogenic nuclide (10Be and 26Al) exposure ages for the moraine sequence preserved on the wider Boco Plain area indicate that moraines previously attributed to MIS 6 and 8 advances were deposited during MIS 10 or earlier cold stages. There is no evidence for MIS 2, 4 or 6 affinity glacial advances onto the Boco Plain with ice of this age restricted to the West Coast Range. New palynological records from the Boco Plain core 6690 confirmed the late Quaternary ages of the upper part of the sequence, whilst extinct palynomorphs indicate a pre-Quaternary age for the glacial diamictons at the base of core Boco 4 and 10. Consequently, the mid-Pleistocene glacial sequence preserved in the Boco Plain is significantly older than previously envisaged, with the post MIS 10 to 12 geomorphology of the plain dominated by fluvial deltaic, swamp peat and lacustrine environments.

Multiple tropical Andean glaciations during a period of late Pliocene warmth

The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Here we expand the Pliocene glacial record to the tropics by reporting recurrent large-scale glaciation in the Bolivian Andes based on stratigraphic and paleomagnetic analysis of a 95-m sequence of glacial sediments underlying the 2.74-Ma Chijini Tuff. Paleosols and polarity reversals separate eight glacial diamictons, which we link to cold periods in the benthic oxygen isotope record. The glaciations appear to coincide with the earliest glacial activity at high northern latitudes and with events in Antarctica, including the strong M2 cold peak and terminal Pliocene climate deterioration. This concordance suggests inter-hemispheric climate linkages during the late Pliocene and requires that the Central Andes were at least as high in the late Pliocene as today. Our record fills a critical gap in knowledge of Earth systems during the globally warm mid-Piacenzian and suggests a possible driver of faunal migration preceding the large-scale biotic interchange in the Americas during the earliest Pleistocene.

Glacial deposits in the Serra do Gerês Mountains (NW Iberian Peninsula): till macrofabric analysis

Till macrofabric and grain-size analysis of glacial diamictons and sequences present in several valleys of the Serra do Gerês Mountains in the Northwestern Iberian Peninsula were used to interpret till types and to reconstruct the glacial paleoprocess history of this mountainous region. Subglacial lodgement, supraglacial melt-out, and deformation tills are dominant in this range. Subglacial lodgement tills, representative of periods of glacial advance followed by stability in several valleys, present cluster fabrics and generally poorly sorted and fine sediments. Supraglacial melt-out and deformation tills, representative of periods of glacial stability with some minor readvances followed by recession, present weaker fabric data and coarser, poorly sorted sediments. Glacial deposits affected by post-glacial paraglacial activity in the form of landslides were also observed in one valley. These present weaker to moderate fabric data and coarser, poorly sorted sediments. These glacial diamictons and sequences are of particular importance in the reconstruction of the glacial dynamics and history of the Serra do Gerês Mountains due to poor preservation of glacial landforms related to the Last Glacial Maximum in several glaciated valleys.

Rock avalanche scars in the geological record: an example from Little Loch Broom, NW Scotland

An embayment in the southern rock slopes of Little Loch Broom, NW Scotland, was surveyed using a combination of morphological mapping and engineering geology techniques. The evidence points to a large-scale rock slope failure (rock avalanche) mechanism of formation, occurring during glacial downwasting and retreat, perhaps initiated by debuttressing and stress release. Periglacial activity, such as macrogelivation or large-scale frost-wedging, may have exacerbated the internal joint network by expanding the aperture dimensions of pre-existing joints leading to an increase in stresses and a reduction in friction across joint surfaces. The rockwall cavity was completely evacuated by the rock debris, leaving the embayment with a mantle of sediments originating from the glacial diamicton that drapes the plateau above the backwall. The absence of any rock avalanche debris deposit has led to the conclusion that the debris run-out extended onto the surface of the glacier and was supraglacially transported and dispersed, which has implications for glacial dynamics and local glacial history for Little Loch Broom.

Till-Fabric analysis and origin of late Quaternary moraines in the Serra da Peneda Mountains, NW Portugal

The combined usage of till-fabric and grain-size analysis in the sedimentological interpretation of glacial diamictons allows the reconstruction of the processes responsible for the genesis of certain moraines. Till-fabric and grain-size data from several late Quaternary moraines present in three glacial valleys of the Serra da Peneda Mountains in northwestern Portugal revealed the presence of two types of till deposited during several stages. During the first stage, ice advanced into the lower Alto Vez and Branda da Junqueira valleys and deposited the lodgment tills present in the Alto Vez moraine 1 (unit 1) and Branda da Junqueira moraine; therefore, these features are interpreted to initially be lateral-terminal and lateral push moraines, respectively. Subsequent stages of glacial stability followed by recession in the Alto Vez and Rio Pomba lower valleys deposited the supraglacial melt-out tills (ablation tills) present in the Alto Vez moraines 1 (unit 2), 2, and 3 and the Rio Pomba moraine. These four landforms are interpreted to be lateral-terminal, lateral, lateral-recessional and recessional ablation moraines, respectively. The Alto Vez moraine 1 had two constructional events, starting most likely as a lateral-terminal push moraine and ending as a lateral-terminal ablation moraine.

Reconstruction of Wisconsinan-age ice dynamics and compositions of southern Ontario glacial diamictons, glaciofluvial/lacustrine, and deltaic sediment

Macrofabric analysis of till sections in south-central Ontario confirms that clast orientation yields information related to changing ice dynamics during the Wisconsinan glaciation. Test stations in six sections yield unimodal to multimodal macrofabrics that indicate ice flow direction, ranging from SE–NW vectors when ice was thin and flowing radially to variable NE–SW, NNE–SSW, and N–S vectors when ice thickened. Ice loci appear to range from the Lake Ontario basin and southern Quebec (thin ice), Labrador Ungava (thicker ice), and Hudson Bay (thickest ice). The north–south fabric may identify the intergrowth of Keewatin–Labrador ice, presumably the maximum ice thickness of the Last Glacial Maximum (LGM). The preliminary data support the theory that topography directed ice movement during preliminary and closing stages of glaciation in southern Ontario, while thick ice generated flow vectors largely unaffected by underlying topography; hence, leading to clast azimuthal variations reflecting changing ice loci with glacier growth. The fabrics analyzed suggest that inferring difference between ductile and brittle lodgement tills is possible as well as to identifying possible glacial tectonic action/overburden loading that disturbs the least friction-fit position of clasts in till. The changing dynamics within till sheets are supported, in part, by variations in glacial crushing seen in SEM imagery that depict a range of microtextures from full-scale fractures under brittle conditions to those indicating less viscous transport under ductile regimes. To some degree, changes in flow direction are further supported by geochemical variations that relate to bedrock/regolith up-glacier controlling Ca-dilution and variable concentrations of Rare Earth Elements (REEs).

Landscape evolution, valley excavation, and terrace development following abrupt postglacial base-level fall

Many high-latitude fluvial systems are adjusting to base-level changes since the last glaciation. Channels that experienced base-level fall may still be incising, often through glacial diamictons (tills). These tills can be quite competent, behaving more like weak bedrock than unconsolidated sediment, and erode at a fast pace, thus providing a unique opportunity to test models of channel incision and knickpoint migration in transient systems. Here, we integrate light detection and ranging (LiDAR) topography, strath terrace chronology, and numerical modeling to determine knickpoint migration and incision history of the Le Sueur River in central Minnesota, USA. Results indicate that the Le Sueur River is best modeled as a detachment-limited channel, with downstream coarsening related to lag clasts from tills playing a critical factor in longitudinal profile development. The Le Sueur River meanders as it incises, so we coupled the best-fit incision model to a meander model to determine valley excavation history. The excavation history was used to determine a natural background erosion rate, prior to land-use changes associated with settlement and agricultural expansion in the mid-1800s. We compared background fine sediment (silt and clay) erosion rates with historic decadal-average annual suspended loads. Results show that modern fine sediment contributions from sources associated with valley excavation are three times higher than modeled presettlement loads. Recent changes in hydrology associated with land use and climate change have increased flows in rivers, leading to higher sediment loads, not just from field erosion, but from increased bank and bluff erosion in the deeply incised valleys.