Search

Chronosequence studies of soil formation and ecosystem development provide important insights into the pathways and rates of change occurring on centennial and millennial time scales. In cool or temperate humid environments, Podzols are the predominant soil type formed under coniferous forests in coarse-textured parent material and have been a major focus of chronosequence studies. This study examined the rate and mechanisms of Podzol development and related forest productivity in a sand dune chronosequence in a hypermaritime climate in coastal British Columbia (BC). The sequence spans 10 760 ± 864 yr over eight sites and is the first documented chronosequence in coastal BC to span most of the Holocene Epoch. Soil samples from each genetic horizon were analyzed for bulk density, pH and concentrations of total carbon (C), pyrophosphate- and oxalate-extractable aluminum (Al) and iron (Fe), and total elements. Within ∼3500 yr, a mature Podzol had formed, with cemented horizons (ortstein and placic) present. Organo-metallic complexation appeared to be the dominant mechanism involved in podzolization. Despite a mild, moist climate conducive to chemical weathering, all soils had similarly low values for the chemical index of alteration, suggesting that congruent dissolution of primary minerals may be occurring. Ecosystem retrogression is apparent in the latter stages of the chronosequence — a phenomenon not previously documented in coastal BC. Further research is needed to examine the interactions of nutrient limitation, soil physical barriers, and other possible drivers of ecosystem retrogression.

Late Pleistocene and Early Holocene aeolian deposits in Tasmania are extensive in the present subhumid climate zone but also occur in areas receiving >1000 mm of rain annually. Thermoluminescence, optically stimulated luminescence, and radiocarbon ages indicate that most of the deposits formed during periods of cold climate. Some dunes are remnants of longitudinal desert dunes sourced from now-inundated continental shelves which were previously semi-arid. Others formed near source, often in the form of lunettes east of seasonally-dry lagoons in the previously semi-arid Midlands and southeast of Tasmania, or as accumulations close to floodplains of major rivers, or as sandsheets in exposed areas. Burning of vegetation by the Aboriginal population after 40 ka is likely to have influenced sediment supply. A key site for determining climate variability in southern Tasmania is Maynes Junction which records three periods of aeolian deposition (at ca. 90, 32 and 20 ka), interspersed with periods of hillslope instability. Whether wind speeds were higher than at present during the last glacial period is uncertain, but shells in the Mary Ann Bay sandsheet near Hobart and particle size analysis of the Ainslie dunes in northeast Tasmania suggest stronger winds during the last glacial period than at present.

The timing of Cordilleran Ice Sheet deglaciation along the central coast of British Columbia, Canada, informs climate forcing and early human migration. Thirty‐two 10Be exposure ages from glacial erratics and local bedrock on the western margin of the former ice sheet represent the earliest exposure ages for the Cordilleran Ice Sheet during the last deglaciation. These data show the western ice margin was retreating by 18.1 ± 0.2 ka, consistent with the global record of ice mass loss. In contrast, parts of the southern margin reached a maximum at ca. 17.6‐16.6 ka, and our data demonstrate a diachronous response of the Cordilleran Ice Sheet during deglaciation. We also show that a low altitude site was exposed by at least 17.7 ± 0.3 ka, implying that numerous ice‐free areas existed along the coastal margin by this time, providing a viable route for the first humans entering the Americas.

Contemporary sand wedges and sand veins are active in seasonally frozen ground within the extensive discontinuous permafrost zone in Northwest Territories, Canada. The region has a subarctic continental climate with 291 mm a−1 precipitation, −4.1 °C mean annual air temperature, warm summers (July mean 17.0 °C), and cold winters (January mean −26.6 °C). Five years of continuous observations indicate that interannual variation of the ground thermal regime is dominantly controlled by winter air temperature and snow cover conditions. At sandy sites, thin snow cover and high thermal conductivity promote rapid freezing, high rates of ground cooling, and low near-surface ground temperatures (−15 to −25 °C), resulting in thermal contraction cracking to depths of 1.2 m. Cracking potentials are high in sandy soils when air temperatures are

The Late Wisconsinan deglaciation period was a time of rapid climate adjustment that resulted in the widespread transition from proglacial/paraglacial conditions to non-glacial settings favourable for plant and animal colonization. Establishing the timing of this transitional period in northeastern British Columbia provides constraints on the rate in which the biomes adapted during this interval of rapid climate change. Preserved aeolian landforms (geomorphic) and macrofossil assemblages (biological) are complementary proxies for interpreting climate amelioration. Paraglacial aeolian dunes in the Kiskatinaw dune field developed following the retreat of glacial Lake Peace which formed after the separation of the Cordilleran and Laurentide ice sheets. These parabolic sand dunes are vegetation-anchored landforms that indicate plant colonization bio-morphologically influenced aeolian activity during stabilization. Optical dating established that stabilization occurred about 10.8 ± 0.3 ka ago (weighted mean of six ages), around the same time interval in which vegetation transitioned from herb and shrub tundra to forest tundra, then to a boreal parkland. Radiocarbon ages from macrofossil assemblages at the Flatbed River section infer paraglacial conditions likely persisted to around 12 000 cal yrs BP and the site had characteristics of a forest tundra. At that time, the Flatbed River was a dry floodplain that transitioned to a pond setting in a boreal parkland after 12 447–11 941 cal yrs BP and before 11 690–11 279 cal yrs BP. The site transitioned from pond to bog after 10 149–9771 cal yrs BP, coincident with the onset of boreal forest conditions that were established by 9901–9607 cal yrs BP. Biome succession recorded at the Flatbed River section and the stabilization of sand dunes indicates that the site transitioned from a paraglacial setting associated with tundra to a non-glacial setting characterized by a boreal forest environment over approximately 2 ka (ca. 12.0–9.7 ka ago). However, the change from tundra to parkland forest conditions took

The coalescence and subsequent divergence of glaciers near the McLeod Lake map area during the last (Fraser) glaciation are recorded by landforms, ice-flow indicators, and the distribution of sediments. Ice initially flowed into the study area from the northwest, with at least one fluctuation in the ice-front position. Ice flow during glacial maximum was generally to the northeast and transitioned to the east during deglaciation. The Quaternary stratigraphic record spans the Fraser Glaciation and is represented by a sequence of advance glaciolacustrine sediments, multiple till units, retreat glaciolacustrine and glaciofluvial sediments, and associated postglacial aeolian material. The surficial geology is dominated by thick, streamlined till that thins where relief is high. Glaciofluvial outwash occurs mostly in northeast- and southeast-trending meltwater channels, while ice-contact glaciofluvial deposits and ablation till occur in depressions throughout the region. Extensive glaciolacustrine deposits blanket low-lying regions in the southern parts of the study area. Meltwater and ice-flow features suggest that deglaciation in the region was dominantly frontal retreat and that ice was largely active as it retreated through the study area. Postglacial aeolian activity was brief; optical dating on K-feldspar from aeolian landforms indicates that the landforms had stabilized by between 8.71–10.71 and 12.3–14.3 ka, and provides minimum ages for ice retreat. The data from the study area are evaluated with similar data from adjacent regions to develop an ice-flow history, and refine the conceptual model of deglaciation for the northern Interior Plateau.

Descriptions of the Cordilleran Ice Sheet retreat after the last glacial maximum have included short-lived readvances occurring during the Older and Younger Dryas stadial periods and into the Holocene, but identification of these events has been largely limited to southwest and central British Columbia and northwest Washington State. We present evidence of a late Pleistocene readvance of Cordilleran ice occurring on the central coast of British Columbia on Calvert Island, between northern Vancouver Island and Haida Gwaii. Evidence is provided by sedimentological and paleoecological information contained in a sedimentary sequence combined with geomorphic mapping of glacial features in the region. Results indicate that a cold climate existed between 15.1 and 14.3 cal ka BP and that ice advanced to, and then retreated from, the western edge of the island between 14.2 and 13.8 cal ka BP. These data provide the first evidence of a major fluctuation in the retreating ice sheet margin in this region and suggest that a cold climate was a major factor in ice readvance. These data contribute to the understanding of past temperature, ice loading and crustal response, the nature of ice margin retreat, and the paleoenvironment of an understudied area of the Pacific Northwest.

This paper reports on the landform assemblages at the northern confluence of the Late Wisconsinan Laurentide and Cordilleran ice sheets with montane and piedmont glaciers in the northern Rockies and southern Mackenzie Mountains. Recent observations in northeastern British Columbia refine our knowledge of the pattern and style of ice sheet retreat, glacial lake formation, and meltwater drainage. At the onset of deglaciation, confluent Laurentide and Cordilleran terminal ice margins lay between 59°N, 124°30′W and 60°N, 125°15′W. From this terminal limit, ice sheets retreated into north-central British Columbia and Yukon Territory, with remnant Cordilleran ice and montane glaciers confined to mountain valleys and the Liard Plateau. Distinctive end moraines are not associated with the retreat of Cordilleran ice in these areas. Laurentide ice retreated northeastward from uplands and the plateaus; then separated into lobes occupying the Fort Nelson and Petitot river valleys. Ice-retreat landforms include recessional end moraines (sometimes overridden and drumlinized), hill–hole pairs, crevasse-fill deposits, De Geer-like ribbed till ridges, hummocky moraines, kames, meltwater features, and glacial lake deposits that fall within the elevation range of glacial Lake Liard and glacial Lake Fort Nelson (ca. 840–380 m). Meltwater and sediment transport into glacial lakes Fort Nelson, Liard, Nahanni, and Mackenzie was sustained by remnant ice in the Liard River and Fort Nelson River drainage basins until the end of glaciation. Optical dating of sand from stabilized parabolic dunes on the Liard Plateau indicates that proglacial conditions, lake formation, and drainage began before 13.0 ± 0.5 ka (calendar years). The Petitot, Fort Nelson, and Liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes Peace and Hay.

Glacier-fed river systems represent potentially significant sediment sources for aeolian processes owing to sediment production, flow seasonality, and winds within mountain settings. We investigate the timing and rates of Holocene loess and aeolian sand deposition in three major river valleys (Bow, North Saskatchewan and Athabasca) of the southeastern Canadian Cordillera through aeolian stratigraphy and dating of sedimentary materials. Source sediments are glacially-derived, seasonally-exposed alluvial deposits. Variation in river morphology promotes source-sediment deposition influenced by bedrock configuration, tributary stream deposition and alluvial fans. Two main settings for aeolian deposition are source-proximal valley-bottom sites and more distal lower-valley sites in sub-alpine and montane forest ecozones. Dating is well-constrained by radiocarbon ages and tephrochronology. Quartz optical dating is complicated, likely owing to minimal recycling of grains and quartz provenance. Mass accumulation rates (MARs) indicate that aeolian deposition was initiated soon after deglaciation and has occurred nearly continuously for at least 10000 years. Loess MARs ranged between 100 and 2500 g·m−2·a−1 during the Holocene. Rates in the last 3000 years are generally two to three times higher than those observed for earlier periods, and are highest in most recent times. We attribute Holocene accumulation at these sites in general to fluvial source sediment availability and the efficacy of forested valleys as sediment traps. The late Holocene increase in MARs is primarily attributed to increased glacial silt and alluvial sediment supply during neoglacial fluctuations including the Little Ice Age.

The Bigstick and Seward Sand Hills are possibly two of the oldest dune fields within the late Wisconsin glaciated regions of the Northern Great Plains. As with most Northern Great Plains dune fields, source sediments are former proglacial outwash sands. Thus, Holocene dune construction is primarily related to spatial–temporal variations in surface cover and transport capacity, rather than renewed sediment input. However, eolian landscape reconstructions on the Northern Great Plains have been temporally constrained to recent periods of activity, as older episodes of deposition are typically reworked by younger events. In this study, sediment cores from shallow lacustrine basins and interdune areas provide an improved record of Holocene eolian sand deposition. Eolian sand accumulation in the interdunes and basins occurred between 150 and 270 years ago, 1.9 and 3.0 ka, 5.4 and 8.6 ka, and prior to ca. 10.8 ka. These episodes of sand accumulation were bracketed by lacustrine deposition and soil formation, which represented wetter conditions. Other than mid-Holocene dune activity, which may be related to peak warmth and aridity, most periods of eolian sand accumulation coincided with cooler but drier climatic events such as the Younger Dryas, late-Holocene cooling prior to the Medieval Climatic Anomaly, and the ‘Little Ice Age’. These depositional episodes are also spatially represented by other dune fields in the region, providing a broad-scale view of the connections between past climatic events and eolian landscape evolution on the Northern Great Plains.

Geomorphic, stratigraphic and geochronological evidence from northeast British Columbia (Canada) indicates that, during the late Wisconsinan (approximately equivalent to marine oxygen isotope stage [MIS] 2), a major lobe of western-sourced ice coalesced with the northeastern-sourced Laurentide Ice Sheet (LIS). High-resolution digital elevation models reveal a continuous 75 km-long field of streamlined landforms that indicate the ice flow direction of a major northeast-flowing lobe of the Cordilleran Ice Sheet (CIS) or a montane glacier (>200 km wide) was deflected to a north-northwest trajectory as it coalesced with the retreating LIS. The streamlined landforms are composed of till containing clasts of eastern provenance that imply that the LIS reached its maximum extent before the western-sourced ice flow crossed the area. Since the LIS only reached this region in the late Wisconsinan, the CIS/montane ice responsible for the streamlined landforms must have occupied the area after the LIS withdrew. Stratigraphy from the Murray and Pine river valleys supports a late Wisconsinan age for the surface landforms and records two glacial events separated by a non-glacial interval that was dated to be of middle Wisconsinan (MIS 3) age.

Sea cliffs at Cape Ball on Graham Island, British Columbia, expose a thick sequence of Pleistocene sediments deposited during at least two glaciations. In sequence, from the base of the section, the units are (1) stony mud, (2) till, (3) silt, sand, and peat, (4) stony mud, (5) laminated sand and silt, (6) cross-bedded sand, and (7) till. Of special interest is unit 4, a massive to weakly stratified mud containing scattered stones that was deposited during the penultimate Pleistocene glaciation (marine isotope stage (MIS) 4). This unit contains wood and marine shell fragments that have yielded non-finite radiocarbon ages. Sand and silt with thin stringers of peat (unit 3) directly underlie this stony mud, and returned an optical age of 57.3 ± 5.7 ka. The stony mud is unconformably overlain by ponded sediments (unit 5) and advance outwash (unit 6) and till (unit 7) deposited during the Fraser Glaciation (MIS 2). The optically dated unit and a correlative peat and silty sand unit at a nearby exposure have pollen spectra with almost 100% non-arboreal pollen. Very low values of tree pollen, coupled with high frequencies of sedges, grasses, composites, Ericales, and the arctic−alpine indicator Koenigia islandica, indicate tundra vegetation and a cold climate. Abundant coprophilous Sporormiella (69%–91%) and Sordaria type (14%–47%) fungal spores in the peat samples indicate the former presence of grazing mammals at Cape Ball during MIS 4. During the MIS 3 interstade, subalpine forest existed at low elevations on Graham Island, providing environments suitable for the development of genetically distinct bird and mammal populations that survived in lowland refugia during the Fraser Glaciation.

The Quaternary geology of the central coast of British Columbia contains a rich and complex record of glacial activity, post-glacial sea level and landscape change, and early human occupation spanning the last ∼10,000 years. At present, however, this region remains a largely understudied portion of coastal North America. This study describes the luminescence characteristics of quartz and K-feldspar from coastal dune and beach sands on Calvert Island and develops a suitable optical dating protocol that will allow for a more rigorous chronology for post-glacial landscape evolution and human occupation on British Columbia's central coast. Luminescence signals from Calvert Island quartz are dim, and appear to lack the so-called “fast” component that is most desirable for optical dating. K-feldspar signals are sufficiently bright for optical dating. We test and refine a single-aliquot regenerative-dose (SAR) protocol for K-feldspar specific to Calvert Island samples through a series of dose recovery and preheat plateau tests. Two approaches for correcting a sample age for anomalous fading are compared and a correction for phototransfer is introduced and applied. Measured fading rates vary from sample to sample implying that, in this region, it is not sufficient to rely on two or three representative fading rates as has sometimes been done elsewhere. Refined age estimates show consistency with independent radiocarbon dating control and help identify radiocarbon-dated organic-rich sediments that have been reworked.

It is standard practice to measure particle fabrics in glacial studies to infer palaeo-ice flow directions and processes of till formation but few studies examine the relationships between particle fabrics at different (i.e. the macro- and micro-) scales. This knowledge is critical to inform the utility of the methods and limitations of the associated interpretations. Micro- (sand grain) and macro- (pebble) fabrics of pebble-rich, sandy subglacial till (Kamloops Lake till) deposited by the Cordilleran Ice Sheet, south-central British Columbia, were compared to assess their similarities and differences, and therefore their utility for understanding subglacial processes. Before comparisons were made, the data were tested for robustness by assessing various controls (e.g. sampling face orientation, number of particles measured, statistical variation resulting from sampling effects, particle shape, size and concentration) on particle fabrics. A new method of microfabric analysis was applied that involves the identification and delineation of distinct clusters of similarly orientated sand grains in order to compare them with macrofabrics and inferred ice-flow directions. The results show that microfabrics, on their own, are an unreliable indicator of ice-flow direction in Kamloops Lake till in the study area and should not be used as a substitute for macrofabric data, as they probably record late-stage microscale strain patterns and pore-water flow in addition to till deposition and deformation by overriding ice. We suspect that this would also be the case for coarse-grained till elsewhere. Our findings suggest that till microfabric interpretations should always be made after assessing corresponding macrofabric data alongside sedimentological and structural observations.

Recognition of positions of glacial lakes along the margin of continental ice sheets is critical in reconstructing ice configuration during deglaciation. Advances in remote sensing technology (e.g. LiDAR) have enabled the generation of accurate digital-elevation models (DEMs) that reveal unprecedented geomorphic detail. Combined with geographical information systems, these tools have considerably advanced the mapping and correlation of geomorphic features such as relict shorelines. Shorelines of glacial Lake Peace (GLP) developed between the Laurentide and Cordilleran ice sheets in northeastern British Columbia and northwestern Alberta. Shoreline mapping from high resolution DEMs produced more than 55 500 elevation data points from 3231 shorelines, enabling the identification of four major phases of GLP: Phase I (altitude 960–990 m a.s.l.); Phase II (890–915 m a.s.l.); Phase III (810–865 m a.s.l.); and Phase IV (724–733 m a.s.l.). The timing of Phase II of GLP is estimated by two optical ages of

Sea-level history since the Last Glacial Maximum on the Pacific margin of North America is complex and heterogeneous owing to regional differences in crustal deformation (neotectonics), changes in global ocean volumes (eustasy) and the depression and rebound of the Earth's crust in response to ice sheets on land (isostasy). At the Last Glacial Maximum, the Cordilleran Ice Sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore. This, combined with different tectonic settings along the coast, resulted in divergent relative sea-level responses during the Holocene. For example, sea level was up to 200 m higher than present in the lower Fraser Valley region of southwest British Columbia, due largely to isostatic depression. At the same time, sea level was 150 m lower than present in Haida Gwaii, on the northern coast of British Columbia, due to the combined effects of the forebulge raising the land and lower eustatic sea level. A forebulge also developed in parts of southeast Alaska resulting in post-glacial sea levels at least 122 m lower than present and possibly as low as 165 m. On the coasts of Washington and Oregon, as well as south-central Alaska, neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea-level changes.

Post-glacial sea level dynamics during the last 15,000 calendar years are highly variable along the Pacific coast of Canada. During the Last Glacial Maximum, the Earth's crust was depressed by ice loading along the mainland inner coast and relative sea levels were as much as 200 m higher than today. In contrast, some outer coastal areas experienced a glacial forebulge (uplift) effect that caused relative sea levels to drop to as much as 150 m below present levels. Between these inner and outer coasts, we hypothesize that there would have been an area where sea level remained relatively stable, despite regional and global trends in sea level change. To address this hypothesis, we use pond basin coring, diatom analysis, archaeological site testing, sedimentary exposure sampling, and radiocarbon dating to construct sea level histories for the Hakai Passage region. Our data include 106 newly reported radiocarbon ages from key coastal sites that together support the thesis that this area has experienced a relatively stable sea level over the last 15,000 calendar years. These findings are significant in that they indicate a relatively stable coastal environment amenable to long-term human occupation and settlement of the area. Our results will help inform future archaeological investigations in the region.

The luminescence characteristics and age estimates of nine samples of aeolian quartz are reported from the Southwood B section in the Arve Valley of southern Tasmania, Australia. New OSL and TT-OSL ages obtained from the deepest Tasmanian aeolian section found so far, the Southwood B section (>6 m deep), range from 20 ka (MIS 2) to 180 ka (MIS 6). Here we test two previously published TT-OSL protocols on our samples: the protocol of Brown and Forman (2012) and a protocol modified from Stevens et al. (2009). Congruencies between our TT-OSL chronology, OSL chronology and previously published TL ages suggest that the modified Stevens et al. (2009) protocol is the most robust for these samples. Furthermore, detailed comparisons of the laboratory data for TL, OSL, and TT-OSL samples provide information on their signal characteristics, their utility as chronometers, and give insight into the bleaching histories of the deposits. All OSL and TT-OSL ages obtained from the Southwood B section fall below the upper dating limits of these signals, which are reported to be as high as ∼280 ka and ∼570 ka, respectively. The TT-OSL signal saturates at doses that are two to three times those of the OSL signal, and may not only provide a chronology for sediments deposited during MIS 5, but also, according to the saturation limits, for any preserved sediments that accumulated during MIS 6 through to MIS 15. TT-OSL ages from older sediments in this region, combined with further stratigraphic studies have the potential to determine the climatic history of Tasmania over multiple glacial periods.

The Okanagan Centre section is the stratotype for marine oxygen isotope stage (MIS) 4 sediments (Okanagan Centre Drift) in the southern interior of British Columbia, Canada. Previous work suggested that these sediments record two glacial and two interglacial cycles. This study reports on detailed sedimentological and geochronological investigations of lithostratigraphic units comprising the Okanagan Centre sequence, revealing successive deposition of subaqueous and subaerial outwash, a subglacial till and glaciolacustrine sediments during MIS 4. A limiting optical age of 113 ± 8 ka defines the base of this sequence. Sedimentological, paleopedological, optical dating and tephrochronological data from sediments near the middle of the sequence reveal soil development (MIS 3) in eolian sediments deposited on a river terrace overlying a deglaciated surface. Within these sediments, identification of Mt. St. Helens set C tephra suggest sedimentation between 50 and 35k 14C a BP. Optical dating corroborates the tephrochronology and suggests that this surface formed after ∼52 ± 7 ka. The record of MIS 2 glaciation is restricted to deglaciation, and overlies MIS 3 sediments above an unconformity possibly related to regional subglacial meltwater erosion. Eolian sediments containing Mt Mazama set O tephra (∼7.62k cal a BP) cap the sequence.

Mega-scale glacial lineations (MSGLs) are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly-flowing ice streams. Knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets, but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses. This paper presents the results of a remote sensing survey of ∼46,000 bedforms on the Dubawnt Lake palaeo-ice stream bed, focussing on a central transect of 17,038 that includes highly elongate bedforms previously described as MSGLs. Within this transect, lineations exceed 10 km in length (max. >20 km) and 23% have elongation ratios >10:1 (max. 149:1). Highly elongate features are interspersed with much shorter drumlin-like features, but longer bedforms are typically narrower, suggesting that their length develops more quickly than, or at the expense of, their width. Bedforms are broadly symmetrical in plan-form and have a preferred lateral spacing of 50–250 m, which implies a regular, rather than random, pattern of corrugations. Comparison with drumlins reveals that the more attenuated MSGLs simply extend the ‘tail’ of the distribution of data, rather than plotting as a separate population. Taken together, this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity, but existing hypotheses of MSGL formation are either not supported, or are insufficiently developed to explain our observations. Rather, we conclude that, under conditions of rapid ice flow, MSGLs attain their great length relatively quickly (decades) through a probable combination of subglacial deformation, which attenuates ridges, and erosional processes that removes material from between them.

Mega-scale glacial lineations (MSGLs) are highly elongate, subglacial landforms produced beneath zones of fast-flowing ice. While qualitative data on their morphology have existed for several decades, studies of their composition and sedimentology are comparatively rare. Sediment exposures along the course of the Finnie River in Nunavut, northern Canada, provide a window into the internal stratigraphy and sedimentology of MSGLs formed by the Dubawnt Lake Palaeo-Ice Stream during regional deglaciation of the Laurentide Ice Sheet. Stratigraphic sections record evidence for an initial advance of ice into the study area followed by ice sheet recession and deposition of glacifluvial and glacilacustrine outwash. Subsequently, the Dubawnt Lake Palaeo-Ice Stream overrode and reworked this outwash subglacially forming an ‘MSGL till’. This till comprises a sandy, red diamicton facies, forming the core of the MSGL ridges and containing variably deformed lenses, stringers and rafts of outwash. The sedimentology of this diamicton is consistent with an origin as a glacitectonite and hybrid till formed by a combination of non-pervasive subglacial sediment deformation and lodgement. Facies variations from stratified to massive diamicton reflect, in turn, variations in strain and subglacial transport distance. The occurrence of stratified glacifluvial sediments within these ridges and the well-preserved nature of many of the sandy inclusions within the diamicton imply relatively short transport distances and incomplete mixing. MSGLs under the Dubawnt Lake Palaeo-Ice Stream formed through a combination of subglacial erosion and deposition. This included non-pervasive, subglacial sediment deformation and the reworking of pre-existing sediment depocentres during streaming flow. These results highlight the importance of sediment supply to MSGL formation with the presence of abundant pre-existing sediments which were subsequently overridden being critical to lineation formation.

Between 1857 and 1860 the British North American Expedition, led by Captain John Palliser, explored and surveyed the Canadian Prairies primarily to establish its suitability for agriculture and settlement. Historical and paleoclimate records indicate the Expedition coincided with below normal precipitation, leading to the perception of an arid or semi-arid region that would ‘forever be comparatively useless’ for agriculture. Today, this part of the Canadian Prairies is known as the Palliser Triangle, and is Canada’s productive dryland agricultural region. Here we present historic, geomorphologic, and chronometric evidence to reconstruct the landscape encountered by the Expedition. We contend that Palliser’s perception of the region was strongly influenced by his experience travelling through active sand dunes in the Middle Sand Hills of southeastern Alberta. At present, the dunes are entirely stabilized by vegetation, in contrast to Palliser’s report of ‘miles of burning sand’. Archival aerial photographs and optical ages of near-surface samples are used to reconstruct the landscape encountered by the Expedition in the Middle Sand Hills. Optical ages of presently stabilized sand dunes date primarily to between ad 1850 and 1934, peaking in c. ad 1925, and are indicative of a dune field undergoing reduction in activity, prior to the onset of 20th century droughts. Ages of interdune sand sheets further attest to regional dune activity occurring at least since ad 1750, concurrent with activity in other southern Canadian Prairie dune fields. Collectively, this evidence supports observations by Palliser of severe travelling due to bare sand conditions in 1857–1859. These conditions and Palliser’s inference of their extent influenced his perception of a ‘central desert’, thus delaying construction of the Canadian Pacific Railway along a southern route and postponing the westward colonization of Canada.

Glacial Lake Missoula formed when the Purcell Trench lobe of the Cordilleran ice sheet dammed Clark Fork River in Montana during the Fraser Glaciation (marine oxygen isotope stage 2). Over a period of several thousand years, the lake repeatedly filled and drained through its ice dam, and floodwaters coursed across the landscape in eastern Washington. In this paper, we describe the stratigraphy and sedimentology of a significant new section of fine-grained glacial Lake Missoula sediment and compare this section to a similar, previously described sequence of sediments at Ninemile Creek, 26 km to the northwest. The new exposure, which we informally term the rail line section, is located near Missoula, Montana, and exposes 29 units, each of which consists of many silt and clay couplets that we interpret to be varves. The deposits are similar to other fine-grained sediments attributed to glacial Lake Missoula. Similar varved sediments overlie gravelly flood deposits elsewhere in the glacial Lake Missoula basin. Each of the 29 units represents a period when the lake was deepening, and all units show evidence for substantial draining of glacial Lake Missoula that repeatedly exposed the lake floor. The evidence includes erosion and deformation of glaciolacustrine sediment that we interpret happened during draining of the lake, desiccation cracks that formed during exposure of the lake bottom, and fluvial sand deposited as the lake began to refill. The floods date to between approximately 21.4 and 13.4 cal ka ago based on regional chronological data. The total number of varves at the rail line and Ninemile sites are, respectively, 732 and 583. Depending on lake refilling times, each exposure probably records 1350–1500 years of time. We present three new optical ages from the rail line and Ninemile sites that further limit the age of the floods. These ages, in calendar years, are 15.1 ± 0.6 ka at the base of the Ninemile exposure, and 14.8 ± 0.7 and 12.6 ± 0.6 ka midway through the rail line exposure. The sediment at the two sections was deposited during later stages of glacial Lake Missoula, after the largest outburst events.

Lian, O. B. & Hicock, S. R. 2009: Insight into the character of palaeo-ice-flow in upland regions of mountain valleys during the last major advance (Vashon Stade) of the Cordilleran Ice Sheet, southwest British Columbia, Canada. Boreas, 10.1111/j.1502-3885.2009.00123.x. ISSN 0300-9483. A detailed glacial geological study was done on Vashon till, formed during the last (Fraser) glaciation, in upland areas of two relatively short and narrow mountain valleys which open onto the Fraser Lowland in southwest British Columbia. The orientation and association of glaciotectonic structures in till and bedrock, a-axis fabrics of stones in till and abrasion features, indicate that Vashon till formed initially by lodgement and that brittle deformation processes dominated at least during the latter stages of glaciation. The presence of local glacigenic bedrock quarrying suggests that ice flow experienced localized enhanced compressive flow along valley sides. These observations indicate that ice flow was relatively slow and they contrast with a previous study of bedrock geomorphology undertaken in some larger south Coast Mountains valleys and a model of ice-flow velocity in the Puget Lowland that suggest rapid ice flow. This indicates that either ice-flow conditions in the larger valleys were different from those in the valleys studied here, or that the observations from our study reflect subglacial conditions following the Last Glacial Maximum (LGM), but immediately prior to deglaciation when ice had thinned and slowed. If the latter scenario is correct, and if processes inferred from this study were also common along the upland parts of other southwest Coast Mountains valleys after the LGM, then the rate at which ice was supplied to lowland piedmont glaciers would have been reduced, and this may have accelerated decay of the southwest margin of the last Cordilleran Ice Sheet.

The sediments and landforms preserved on palaeo-ice-stream beds can provide important information about their subglacial conditions and flow mechanisms, and the processes accompanying their shutdown. In this paper, detailed observations of an intriguing subglacial landform assemblage of ribbed moraines superimposed on glacial lineations on the Dubawnt Lake Ice Stream bed (north-west Canadian Shield) are presented, including their morphometry, internal structure (from ground penetrating radar (GPR) surveys and from glaciogeological analysis) and sedimentological characteristics (from sediment architecture and lithofacies analysis). The observations suggest an abrupt change in ice dynamics that correlates with two phases of glacial landform development. This hypothesis is based on evidence from a deformed lodgement till, which subsequently underwent brittle deformation and developed prominent thrust (shear) structures and tension fractures. Tension fractures are observed in a sediment exposure and thrust structures are observed in GPR surveys, where they occur most prominently in the ribbed moraine ridge crests. The presence of the fractures, and their association with a population of clasts in the till that are orientated with their a-axes transverse to the inferred ice flow direction, suggests a compressional flow regime. It is therefore inferred that the glacial lineations were formed under an extensional flow regime during ice stream activity, but that at some point patches of till under the ice stream stiffened through dewatering. The subsequent increase in basal shear stress resulted in compressional flow and the development of subglacial thrusting and the building of ribbed moraines. We therefore suggest that ribbed moraines may form in areas of compressional flow under ice streams, i.e. sticky spots, and/or at the transition between slow and fast ice flow along parts of an ice stream. The general absence of ribbed moraines on most other palaeo-ice-stream beds suggests that either these ice streams continued operating during deglaciation or processes other than the development of localized compressional flow (sticky spots) led to their shutdown (e.g. ice depletion).

In lower Seymour Valley, much of the sediment derived from the erosion of valley-side drift (paraglacial sediments) remains in storage in the form of alluvial fans and aprons. Fluvial incision into these features has exposed sections for lithostratigraphic and chronological study. Radiocarbon dating of organic-rich beds within these deposits indicate that paraglacial sedimentation of lower Seymour Valley commenced before 11.4 ka, was periodic, and was essentially complete by about 9 ka; Seymour River had incised to its present vertical position by about 5 ka. Furthermore, our radiocarbon ages indicate that, although paraglacial sedimentation commenced shortly following deglaciation when the climate was cool and moist, a significant amount of sedimentation occurred during a transition from wet and moist climate to warm and dry (xerothermic) conditions (ca. 10 ka). Charcoal-rich beds indicate that some erosional events may have been a result of slope instability caused by fire., La plus grande partie des sédiments de la vallée résultant de l'érosion latérale des dépôts « paraglaciaires » demeurent accumulés sous forme de cône alluvial ou de plaine alluviale. L'encaissement fluviatile dans ces formes a mis au jour des coupes favorisant les études lithostratigraphiques et chronologiques. La datation au radiocarbone de lits riches en matière organique montre que la sédimentation « paraglaciaire » périodique a commencé avant 11,4 ka et s'est à toutes fins pratiques terminée vers 9 ka dans la vallée. L'encaissement de la Seymour River jusqu'à son niveau actuel était atteint vers 5 ka. De plus, les datations montrent que même si la sédimentation « paraglaciaire » a commencé peu après la déglaciation, alors que le climat était frais et humide, une bonne partie de la sédimentation s'est effectuée au cours d'une période de transition vers un climat chaud et sec (conditions xérothermiques) vers 10ka. Les lits riches en charbon indiquent qu'une certaine partie de l'érosion est attribuable à l'instabilité des pentes occasionnée par les feux.

An infilled backbarrier wetland located behind a stationary-type coastal bay barrier is used to reconstruct a 6000-year paleo-environmental record that incorporates gradual, catastrophic, and human-influenced sedimentation styles on the New Zealand coast. The record is assembled from a range of proxy indicators (grain size, magnetic susceptibility, organic content, diatoms, and pollen) and is temporally constrained by tephrochronology, radiocarbon dating, and optical dating. Postglacial sea-level rise, volcanism, tsunami, and catchment clearance are all evident in the sediment record, either as artifacts or indirect indicators. Results from optical dating also provide insights into the process of sediment reworking and mixing from multiple sources during tsunami transport. We argue that backbarrier wetlands formed behind stationary-type (aggraded) bay barriers are of greater value (more sensitive) for longer-term paleo-environmental reconstruction than wetlands associated with prograded-type and ...

Rapidly-flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance. Recent observations have revealed that ice stream flow exhibits considerable variability, with relatively rapid changes taking place in speed and direction. This spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction, known as ‘sticky spots’. In this paper, we provide a detailed review of sticky spot observations from both contemporary and palaeo-ice stream beds in order to better understand their nature and influence. Observations and theoretical considerations reveal four primary causes of ‘stickiness’: (i), bedrock bumps; (ii), till-free areas; (iii), areas of ‘strong’ (well drained) till; and (iv), freeze-on of subglacial meltwater. These may act together in one location, or in isolation; and a progressive increase in their distribution could lead to ice stream shut-down. Bedrock bumps are influential under active ice streams, where they provide form drag and can create thinner ice which increases the likelihood of basal freeze-on. Increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut-down because, over long time-scales, ice stream erosion might be expected to reduce their amplitude. The influence of till-free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas. They are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams. If an ice stream operates solely by till deformation, it is conceivable that a progressive increase in the exposure of till-free areas could lead to shut-down through a process of sediment exhaustion. Areas of strong, well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater. The collapse of an inefficient ‘cannalised’ system to a more efficient ‘channelised’ system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut-down in both contemporary and palaeo-settings. Basal freeze-on has also been observed and inferred from beneath modern and palaeo-ice streams, and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream. A paucity of data from ice stream sticky spots limits a better understanding of their nature, distribution and evolution beneath ice streams. Future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well-preserved palaeo-ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification. Such data will considerably enhance the basal boundary condition in ice stream models which will, ultimately, refine our predictions of the response of contemporary ice sheets to future changes in climate.

The West Mouth of the Great Cave of Niah is one of the major archaeological sites in Southeast Asia; the radiocarbon chronology of this site currently places the earliest presence of Homo sapiens (a Deep Skull find) in Southeast Asia at about 45 ka BP. An optical dating programme using sand-sized quartz was initiated in the West Mouth to complement the radiocarbon chronology. This paper reports on the progress in dating a key sample (sample 376r) that was taken from deposits containing the Deep Skull. A somewhat novel procedure was developed to separate and clean quartz grains from the unusual guano-rich deposits. From this, only a small quantity of quartz grains could be recovered and 36 aliquots (1 mm in diameter) were prepared, each consisting of ∼80 grains. This sample was dated by means of the single-aliquot regenerative-dose (SAR) method using the protocols of Murray and Wintle [2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73], and of Choi et al. [2003. Luminescence dating of well-sorted marine terrace sediments on the southeastern coast of Korea. Quaternary Science Reviews 22, 407–421]. The results showed a wide distribution of equivalent doses; this distribution is inferred to be due to bioturbation, variable bleaching at deposition, and to local variations in the dose rate within the sample site. Dose rates were measured using both field (in-situ γ-ray spectrometry, IGRS) and laboratory (inductively coupled plasma mass spectrometry/atomic emission spectrometry, ICP-MS/AES; and isotope dilution, ID) methods. There was significant disagreement between the concentrations of radioisotopes found using laboratory and field measurements, indicating sediment heterogeneity and also possible disequilibrium in the 238 U decay chain. Future work in the West Mouth should therefore concentrate on taking sediment samples of at least 500–600 cm 3 , improving the dose rate estimates (e.g. by high-resolution γ-ray spectrometry) and investigating other luminescence signals (e.g. red thermoluminescence) as potential geochronometers.

Luminescence dating comprises a collection of numerical-age techniques that are among the most significant chronological tools currently used in Quaternary research. This paper briefly reviews the key historical developments in luminescence dating, from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight-exposed sediments. We describe the principles and practicalities of the various techniques commonly used in luminescence dating, including multiple-aliquot, single-aliquot and single-grain procedures, and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation (e.g., by means of component analysis and dose distribution methods in optical dating). The overview also introduces the other papers in this special issue of Quaternary Science Reviews , which address a selection of important issues in basic research, technique development and application of luminescence dating to critical questions in the geological and archaeological sciences, illustrated with examples from around the world and the last million years of Earth history.

Anomalous fading in feldspars is now understood to be caused by the tunnelling of electrons from one defect site to another. Here we present some experimental observations concerning the phenomenon. The fading rates of a variety of feldspar crystals and K-feldspar separates from sediments are reported. It is found that (1) the fading rates of 77 K-feldspar extracts from sediments range from 1 to 10%/decade, with an average value of about 5%/decade, (2) the fading rates of K-feldspars extracted from sediments derived largely from volcanic bedrock are not higher than those from non-volcanic bedrock as is widely thought, (3) the fading rates of 31 individual feldspars range from 1 to 35%/decade, (4) in plagioclase feldspars the fading rate increases with increasing Ca and/or Fe content, (5) the fading rate increases with laboratory radiation dose at large doses, (6) for samples for which the time elapsed since burial is long enough for their luminescence to be in saturation, the fading rate is correlated with the ratio of the field saturation intensity to the laboratory saturation intensity; extrapolation to zero fading rate shows that trap emptying as a result of thermal eviction is not significant, and that the mean thermal lifetime in temperate environments of electrons in traps relevant to dating is ⩾4 Ma., and (7), different aliquots of a sample can have fading rates that differ by a factor as large as two even if the aliquots contain several thousands of grains, thus it is necessary to ensure when correcting ages for anomalous fading that the fading rate used is that applicable to the aliquots on which the equivalent dose is measured.

Past aeolian activity was reconstructed at four dunefields in the prairie parkland and boreal forest of central Saskatchewan to elucidate landscape response to environmental change. Optical ages from stabilized dunes in the boreal transition ecoregion indicate two episodes of activity. The first, at about 11 ka, corresponds to a period of early-Holocene parkland and grassland cover following deglaciation and drainage after about 13.0 ka, and brief establishment of boreal forest. The second, between about 7.5 and 5 ka, corresponds to a period of mid-Holocene parkland-grassland cover. Optical ages from dunefields in the prairie parkland primarily record mid-Holocene activity, between about 7.5 and 4.7 ka, corresponding to a period of grassland cover, with some reworking continuing into the late Holocene. Although this area was deglaciated by about 13.5 ka, there is no evidence of early-Holocene dune activity, suggesting that mid-Holocene activity may have reworked earlier deposits here. Consequently, much of the morphology and stratigraphy observed in these dunefields are associated with mid-Holocene activity, likely associated with increased aridity and reduced vegetation cover at that time. This study provides the most northerly evidence of mid-Holocene dune reactivation on the Great Plains, lending support to the assertion that aeolian activity was widespread at that time.

The chronology and stratigraphy of eolian deposits at two sites in south-central Saskatchewan were studied in order to extend the spatial and temporal record of dune activity on the Canadian prairies. Optical ages document the timing of valley-infilling by sand dunes in the Qu’Appelle River area, and of cliff-top eolian deposition along the South Saskatchewan River. These ages, along with published radiocarbon and optical ages, are used to develop a chronology of eolian activity for south-central Saskatchewan. Optical ages of eolian sands ranging from 5.7 to 0.14 ka (before AD 2000), with intervening paleosols, indicate alternating periods of eolian activity and dune stability during the late Holocene, supported by published radiocarbon ages. Other published radiocarbon ages ranging from 11.3 to 8.4 cal ka BP indicate early Holocene eolian activity. Mid-Holocene ages are predominantly absent from the chronology and this is interpreted as being due to extensive eolian reworking during at least the latter part of the mid-Holocene. The chronology in south-central Saskatchewan is similar to other parts of the southern Canadian prairies. It is likely that preserved mid-Holocene eolian deposits occur within depositional basins in the southern Canadian prairies, and at sites near the southern boreal forest boundary with the prairie ecozone., La chronologie et la stratigraphie des dépôts éoliens ont été étudiées dans deux sites situés au centre-sud de la Saskatchewan afin de reconstituer l’histoire spatiale et temporelle de l’activité dunaire. Les âges optiques fournissent des renseignements sur la chronologie du comblement de la vallée de la rivière Qu’Appelle par des dunes de sable et de la mise en place de dépôts éoliens au sommet des falaises le long de la rivière Saskatchewan du Sud. Combinés aux dates optiques et au radiocarbone déjà publiées, ces âges ont servi à établir une chronologie de l’activité éolienne dans le centre-sud de la Saskatchewan. Les âges optiques des sables éoliens, situés entre 5,7 et 0,14 ka (avant 2000), ainsi que les paléosols intercalés, montrent qu’il y a eu alternance entre périodes d’activité éolienne et périodes de stabilité dunaire à l’Holocène supérieur, alternance confirmée par les dates au radiocarbone déjà publiées. D’autres dates au radiocarbone échelonnées entre 11,3 à 8,4 cal ka BP montrent qu’il y a aussi eu activité éolienne à l’Holocène inférieur. Il n’y a pour ainsi dire pas de dates de l’Holocène moyen dans la chronologie, probablement en raison d’importants remaniements éoliens survenus, tout au moins, à la fin de la période. La chronologie du centre-sud de la Saskatchewan est semblable à celle d’autres régions du sud des Prairies. Il est probable que des dépôts éoliens de l’Holocène moyen aient été préservés dans les zones d’accumulation du sud des Prairies et dans les régions situées à l’interface de la forêt boréale et des Prairies., La cronología y la estratigrafía de los depósitos eólicos provenientes de dos sitios del centro-sur de Saskatchewan fueron estudiadas a fin de determinar la variación espacio-temporal de la actividad de las dunas en las praderas canadienses. La datación óptica puso en evidencia las variaciones temporales de invasión del valle por parte arenas de las dunas del Qu’Appelle River y por depósitos eólicos en la cima del acantilado a lo largo del Saskatchewan River en la zona sur. Estos datos unidos a la datación con radiocarbono y edades ópticas publicadas anteriormente fueron utilizadas para establecer la cronología de la actividad eólica de la zona centro-sur de Saskatchewan. La edad óptica de dunas de origen eólico situada dentro del rango de 5700 a 1400 años anteriores al presente así como los paleosuelos intercalados, indica periodos donde se alternan la actividad eólica y la estabilidad de las dunas que se sitúan en el Holoceno tardío, y que coinciden con la datación de radiocarbono publicada con anterioridad. Otras datos de radiocarbono situados entre los 11 300 y 8400 anteriores al presente indican una actividad eólica durante el Holoceno temprano. La datación correspondiente a edades situadas en el Holoceno medio se encuentran ausentes en la cronología, probablemente como una consecuencia de un trabajo eólico extensivo ocurrido a finales de dicho periodo. La cronología de la región centro-sur de Saskatchewan es similar a la de otras partes de las praderas australes canadienses. Es probable que algunos depósitos datando del Holoceno medio existan en los sedimentos de la cuenca al sur de las praderas y en la interfase entre los bosques boreales australes y las praderas.

Optical dating studies of samples of late-Holocene mud-dominated alluvium, and heated alluvium in features interpreted to be hearths, collected from the banks of the Red River, southern Manitoba, Canada, were undertaken to assess the viability of these deposits as chronometers for floodplain evolution. Optical dating was done by utilizing the violet luminescence emitted during infrared excitation of the potassium feldspar in the fine-silt polymineral fraction. The alluvial samples, dated by radiocarbon to be about 1 ka old, yielded maximum limiting optical ages between about 1 and 5 ka, indicating that optical dating of such samples may provide useful chronological information in cases where material suitable for radiocarbon dating is lacking, or in cases where a radiocarbon chronology needs support. Furthermore, the surprisingly low residual optical ages from sediments of this type indicate that there is a high proability that sediments representing similar mud-dominated alluvial environments in the Pleistocene record will yield ages with adequate precision and accuracy. Bulk sediment extracted from the centre of a buried hearth yielded an optical age (1.4 ± 0.2 ka) that was broadly consistent with its associated calibrated radiocarbon age (0.23-1.05 ka), but good agreement (0.79 ± 0.09 ka) was achieved when small fragments of hard-baked mud (ñ0.5 g) extracted from within the feature were optically dated separately; hard-baked fragments from two other hearths yielded similar results. Optical dating of sediments from hearths formed in mud-dominated alluvial sediments thus represents a viable method for obtaining a useful chronology in circumstances where organic material suitable for radiocarbon dating is absent.

Six luminescence age estimates have been obtained from raised beach sands and loess, and alluvial fan sediments in the outboard zone of the active Otago reverse fault province, coastal Otago, New Zealand. These age estimates constrain the timing of movement of the Akatore Fault and the Titri Fault System. Five of the samples were dated by optical dating of K‐feldspar in the polymineral fine silt fraction; the remaining sample was dated using thermoluminescence (TL) emitted from quartz (fine sand fraction). Raised beach sands from the lowest Pleistocene marine terrace on the upthrown side of the reverse faults (Taieri Beach) yielded ages of 117 ± 13 ka (optical dating, K‐feldspar) and 117 ± 12 ka (TL dating, quartz), indicating terrace formation during the peak sea‐level highstand of the last interglacial, marine oxygen isotope substage (MISS) 5e (c. 125 ka). The K‐feldspar optical age has not been corrected for anomalous fading, but its consistency with the quartz TL age indicates that anomalous ...

With the aid of three case studies we summarize sedimentological and structural evidence in Wisconsinan subglacial till and its substrate that can be used to infer the presence of former fast-moving ice. We compare sedimentological characteristics of till with its stone fabric, stone surface erosional features and orientations of fractures, faults and folds in till and substrate, in order to interpret the processes that formed the till. In the cases we studied, stones in tills that experienced ductile deformation (inferred to be associated with fast-moving ice) show variable alignment of latest surface striae. Moreover, striae are inconsistent with the orientations of lee ends and chattermarks on the same stones, and with the dip directions of shallow shear planes and (or) steeper tension fractures in the till matrix. These observations indicate that stones were rotating in a flowing till matrix prior to their final emplacement. Ductile shear of fine-textured, water-saturated till and Jeffrey-like rotation of stones are invoked where most of the following occur together: (i) delicate striae follow the curvature of stone surfaces; (ii) a-axis fabrics are multimodal to girdle-like; (iii) stone a axis eigenvectors, striae orientation and stone lee end alignments fall between the modes of stone fabrics; (iv) stone pavements are uneven with vertically oriented and inverted bullet-shaped stones; (v) soft sediment clasts and (or) fragile fossils are preserved.

A semi-continuous sheet of granule to cobble-size clasts forms a distinctive deposit on sand dunes located on a coastal barrier in Whangapoua Bay, Great Barrier Island, New Zealand. The gravel sheet extends from the toe of the foredune to 14.3 m above mean sea level and 200 m landward from the beach. Clasts are rounded to sub-rounded and comprise lithologies consistent with local bedrock. Terrestrial sources for the gravel are considered highly unlikely due to the isolation of the dunes from hillslopes and streams. The only source for the clasts is the nearshore to inner shelf of Whangapoua Bay, where gravel sediments have been previously documented. The mechanism for transport of the gravel is unlikely to be storm surge due to the elevation of the deposit; maximum-recorded storm surge on this coast is 0.8 m above mean high water spring tide. Aeolian processes are also discounted due to the size of clasts and the elevation at which they occur. Tsunami is therefore considered the most probable mechanism for gravel transport. Minimum run-up height of the tsunami was 14.3 m, based on maximum elevation of gravel deposits. Optical ages on dune sands beneath and covering the gravel allow age bracketing to 0–4.7 ka. Within this time frame, numerous documented regional seismic and volcanic events could have generated the tsunami, notably submarine volcanism along the southern Kermadec arc to the east-southeast of Great Barrier Island where large magnitude events are documented for the late Holocene. Radiocarbon ages on shell from Maori middens that appear to have been reworked by tsunami run-up constrain the age of this event to post ca. 1400 AD. Regardless of the precise age of this event, the well-preserved nature of the Whangapoua gravel deposit provides for an improved understanding of the high degree of spatial variability in tsunami run-up.

Optical dating of silt-sized potassium feldspar grains was found to be suitable for dating the formation of key loess units at two sites on the central east European Plain. Loess bracketing the Bryansk palaeosol yielded optical ages in agreement with the well-dated radiocarbon chronology when corrected for anomalous fading. Optical ages from loess bracketing a significant pedogenic unit below the Bryansk palaeosol support our lithostratigraphic interpretation that it is the Mezin palaeosol complex, and its formation during the Last Interglaciation, Oxygen Isotope Stage (OIS) 5. Optical ages from a stratigraphically older loess unit directly underlying a significant (∼10 m thick) till unit, in conjunction with its regional stratigraphic context, suggest that the loess, and the till were deposited during the Dnieper Glaciation, which probably occurred during OIS 6.