Stratigraphy of a Lateglacial lake basin sediment sequence at Turret Bank,upper Glen Roy,Lochaber: implications for the age of the Turret Fan

New lithostratigraphical, pollen-stratigraphical and tephrostratigraphical data are presented for a sediment sequence at Turret Bank, a site that lies close to the confluence of the River Turret with the River Roy in Lochaber, the western Scottish Highlands. The site is also adjacent to the inner margin of a major gravel fan, the Glen Turret Fan, the age of which has been debated and has a crucial bearing on the overall sequence of events in Glen Roy, especially concerning the maximum limit of Loch Lomond Readvance (Younger Dryas) ice. Several lines of evidence point to the sediment sequence at Turret Bank having been wholly deposited during the Loch Lomond Stadial-early Holocene transition: (i) the pollen sequence is typical for this transitional period; (ii) varved deposits preserved in the sequence bear a strong resemblance to mid-Stadial varves in a regional master varve scheme for Glen Roy and vicinity (the Lochaber Master Varve Chronology); and (iii) an early Holocene tephra – the Askja-S Tephra – is preserved within the sequence. Some limitations with the new data are considered, but it is concluded that the coherent integration of lithostratigraphic, geomorphological, pollen-stratigraphical and tephrostratigraphical data point to the likelihood that Loch Lomond Readvance ice extended to the inner margin of the Glen Turret Fan, and that the fan was probably constructed by glacial meltwaters at this time.     

A new early Holocene cryptotephra from northwest Scotland

Clarification of the temporal relationships amongst records of environmental change is dependent on accurate timescales. Event markers such as tephra layers are extremely important for constraining chronologies and providing tie points. In this report we present evidence of a previously unknown early Holocene Icelandic cryptotephra from a lake in northern Scotland—the ‘An Druim Tephra’. The calibrated radiocarbon age of 9560 cal. yr BP for this new cryptotephra makes it an important addition to the suite of cryptotephras now recorded from the last glacial termination and early Holocene in northwest Europe. In addition we report evidence in support of a ‘Younger Borrobol Tephra’ from Lateglacial sediments of Allerød age. Copyright © 2005 John Wiley & Sons, Ltd.     

The Late Quaternary sediment successions of Llangorse Lake,south Wales

The last British-Irish Ice Sheet (BIIS) created a landscape with many sedimentary basins that preserve archives of paleoenvironmental and paleoclimatic change during the Last Glacial-Interglacial Transition (LGIT; ~ 18-8 ka BP). The typical lithostratigraphic succession of these archives is composed of minerogenic/allogenic sediments formed during cold climatic conditions and organic-rich/authigenic sediments during warmer climates. This paper presents a multi-core lithostratigraphy compiled from the extant lake and surrounding basin at Llangorse Lake, south Wales, a basin lying within the southernmost limits of the last BIIS. This lake contains one of the longest continuous terrestrial sediment successions in the UK. Uncertainty previously existed concerning the presence and distribution of sediments at the site related to the Windermere Interstadial (~ 14.7 to ~ 12.9 ka BP) and Loch Lomond Stadial (~ 12.9 to 11.7 ka BP). A new borehole survey demonstrates that LGIT-age sediments are present at the site with nekron mud (gyttja), corresponding to the Lateglacial Interstadial, deposited in the deeper part of the lake waters and that these deposits are equivalent in age to marl deposits found at shallower depths at the margins of the basin. These deposits are associated with warmer conditions experienced during the Windermere Interstadial and Holocene, whilst minerogenic-rich sediments were deposited during the colder climatic conditions of the Dimlington Stadial and the Loch Lomond Stadial with rangefinder radiocarbon dates confirming this attribution. A model of lake level changes shows that drainage of the Dimlington Stadial glacial lake caused the largest fall, but there was also a further, smaller lake level fall at the end of the Windermere Interstadial and/or the start of the Loch Lomond Stadial, before the level rose in the early Holocene. The lithostratigraphic results presented here form the framework for further paleoenvironmental and paleoclimatic research at Llangorse Lake.     

The lateglacial lakes of Glens Roy,Spean and vicinity (Lochaber district,Scottish Highlands)

This paper summarises the evidence for glacial ice advance into lower Glen Spean during the Loch Lomond Stadial which involved the blockage of westward-flowing drainage to form a series of ice-dammed lakes, the former surfaces of which are marked by prominent shorelines. Detailed mapping of glacigenic landforms and instrumental levelling of the shorelines reveals a dynamic interplay between the glacier margins and lake formation. Subsequent deglaciation led to lowering of the lake levels, at times by catastrophic drainage beneath the ice (jökulhlaup). The abandoned shorelines have been warped and dislocated in numerous places as a result of glacio-isostatic deformation, faulting and landslip activity. The pattern of retreat of the ice can be deduced from the mapped distributions of retreat moraines and the levelled altitudes of numerous kame and fluvial terrace fragments. The sequence of events outlined in this paper provides important context for understanding the evolution of the landscape of the Glen Roy area during the Loch Lomond Stadial, and a prelude to more recent studies reported in other contributions to this thematic issue.     

Lateglacial to early Holocene multiproxy record from Loch Assynt,NW Scotland

A core, recovered from a water depth of 53 m in Loch Assynt, North-West Scotland, has yielded a 9 m sequence comprising two distinct units, an upper, organic-rich unit (Unit I, ca. 6 m) overlying a sequence of laminated clays, silts and sands (Unit II, ca. 3 m). The upper unit is essentially Holocene in age based upon three bulk AMS radiocarbon dates while a fourth radiocarbon date from Unit II confirms a late-glacial age for that interval and supports a broadly linear age–depth relationship. Distinct variations in the magnetic susceptibility record of the lower unit can be visually correlated to major changes in the Greenland ice core (GISP2), this together with pollen evidence supports the radiocarbon dating suggesting an age of approximately 11,000 to around 17,000 cal. BP for Unit II, with evidence for the Younger Dryas (Loch Lomond) stadial and the Bolling–Allerød climatic phases. Variations in the magnetic susceptibility record of the late-glacial sediments are thought to relate to climatically driven changes in soil cover and erosion rates. The multiproxy record from Loch Assynt indicates relatively continuous, sub-aqueous sedimentation during the last ～17,000 years, providing an approximate age for the initiation of modern Loch Assynt and supporting recent dates of moraine retreat lines in the Loanan Valley from about 14–15 ka BP. Pollen and chironomid sampling provides further insights to the history of this relatively deep water body and compliment existing high-resolution palaeo-precipitation records for the mid to late Holocene interval from speleothem archives within the loch catchment.     

The presence of Holocene cryptotephra in Wales and southern England

There have been few detailed studies into the tephrostratigraphy of southern Britain. We report the tephrostratigraphy of two sites, one in southern England (Rough Tor, Cornwall) and one in Wales (Cors Fochno, west Wales). Our study extends the known southernmost reach of Icelandic cryptotephra in northern Europe. Given the large distance between sites in southern England and eruptive sources (e.g. Iceland 1500–1700 km distant), most of the cryptotephra layers consist of sparse numbers of shards, even by the standards of distal tephrostratigraphy (as low as 3 shards cm⁻¹), each layer spanning only 1 or 2 cm in depth. We identify multiple cryptotephra layers in both sites, extending the known distribution of several tephra layers including the MOR‐T4 tephra (∼AD 1000) most probably of Icelandic origin, and the AD 860 B tephra correlated to an eruption of Mount Churchill, Alaska. The two sites record contrasting tephrostratigraphies, illustrating the need for the inclusion of multiple sites in the construction of a regional tephrostratigraphic framework. The tephra layers we describe may provide important isochrons for the dating and correlation of palaeoenvironmental sequences in the south of Britain. 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.

     

Late Devensian environments in the Vale of Mowbray, North Yorkshire, UK: evidence from palynology

Two radiocarbon-dated Lateglacial pollen diagrams from the Vale of Mowbray (northern Vale of York) are presented from sites in the lowlands between the washlands courses of the rivers Swale and Ure in North Yorkshire, an area with little previous palynological research despite its proximity to the Devensian glacial advance limits in eastern England. The profiles, from Snape Mires and Nosterfield, include the Loch Lomond Stadial (Younger Dryas) and the Holocene transition, while that from Snape Mires also includes the period from the early part of the Lateglacial Interstadial. This profile differs from most published Interstadial diagrams from the Yorkshire region in having a long-delayed expansion of tree and shrub taxa. Juniperus (juniper) remains important after vegetation development takes place and the pollen record includes evidence of two cold climate oscillations before the maximum development of Betula (birch) woodland near the end of the Lateglacial Interstadial. At both profiles Artemisia (mugwort) frequencies are lower during the Loch Lomond Stadial than at many regional sites, probably due to edaphic factors in these lowland locations. The two sites provide valuable environmental data that enable comparison between the more wooded Lateglacial vegetation to the south in the Vale of York and Humberside and the more open contemporaneous vegetation to the north in the Durham and Northumberland lowlands.     

The Late Holocene tephra record of the central Mediterranean Sea: Mapping occurrences and new potential isochrons for the 4.4–2.0 ka time interval

Five cores from the southern Tyrrhenian and Ionian seas were studied for their tephra and cryptotephra content in the 4.4–2.0 ka time interval. The chronological framework for each core was obtained by accelerator mass spectrometry ¹⁴C dating, the occurrence of distinct marker tephra and stratigraphic correlation with adjacent records. Tephrochronology allowed us to correlate the analyzed deposits with tephra markers associated with Somma-Vesuvius (79 ad ), Ischia Island (Cretaio), Mt Etna (FG, FL and FS) and Campi Flegrei (Astroni-Agnano Monte Spina) events. For the first time in the marine setting, a large single glass data set is provided for the Late Holocene Etnean marker beds including the FS tephra (ca. 4.3 ka). Moreover, unknown deposits from Lipari (ca. 2.2–2.0 ka) and Vulcano (3.6–3.3 ka) are also recognized at more distal sites than previously reported. These results contribute to improve the high-resolution tephrostratigraphic framework of the central Mediterranean Sea. They also provide new insights into the chemical composition and dispersal pattern of tephras that can be used as inter-archive tools for regional and ‘local’ stratigraphic correlations and for addressing paleoclimate research.     

Identification of the Askja-S Tephra in a rare turlough record from Pant-y-Llyn,south Wales

Tephrochronology and especially crypto-tephrochronology is an established chronological technique employed in a range of depositional environments in Europe and beyond. During the late Quaternary, Icelandic cryptotephra deposits are widely found in palaeorecords across northern latitudes of Europe e.g. Scotland, Ireland, Norway, Sweden and the Faroe Islands but are sporadic in southerly latitudes as distance from Iceland increases. As yet, very few Icelandic cryptotephras have been identified in Wales or southern England which may well reflect the geographical limit of Icelandic tephra distribution. Here, however, we report the discovery of an Icelandic cryptotephra deposit within a sediment sequence retrieved from the Pant-y-Llyn turlough (Carmarthenshire, south Wales), the only known turlough in Britain. Turloughs are groundwater-fed ephemeral lakes associated with limestone bedrock and can accumulate sediments that may yield records suitable for palaeoreconstructions. A discrete peak of glass shards originating from the Askja-S eruption is identified in the sediment record. This discovery extends the distribution of this early Holocene eruption giving new insight into its dispersal patterns and also indicates that sedimentary sequences from sites in these more southerly latitudes are valuable repositories for ash preservation. Furthermore, its discovery within a carbonate-rich sequence provides a minimum age constraint on the timing of sediment accumulation and provides an alternative tool for what is typically a problematic dating environment.     

A Lateglacial archaeological site in the far north‐west of Europe at Rubha Port an t‐Seilich,Isle of Islay,western Scotland: Ahrensburgian‐style artefacts,absolute dating and geoarchaeology

The exact pattern, process and timing of the human re‐colonization of northern Europe after the end of the last Ice Age remain controversial. Recent research has provided increasingly early dates for at least pioneer explorations of latitudes above 54°N in many regions, yet the far north‐west of the European landmass, Scotland, has remained an unexplained exception to this pattern. Although the recently described Hamburgian artefacts from Howburn and an assemblage belonging to the arch‐backed point complex from Kilmelfort Cave have established at least a sporadic human presence during earlier stages of the Lateglacial Interstadial, we currently lack evidence for Younger Dryas/Greenland Stadial 1 (GS‐1) activity other than rare stray finds that have been claimed to be of Ahrensburgian affiliation but are difficult to interpret in isolation. We here report the discovery of chipped stone artefacts with technological and typological characteristics similar to those of the continental Ahrensburgian at a locality in western Scotland. A preliminary analysis of associated tephra, pollen and phytoliths, along with microstratigraphic analysis, suggest the artefacts represent one or more episodes of human activity that fall within the second half of GS‐1 and the Preboreal period. © 2015 The Authors. Journal of Quaternary Science published by John Wiley & Sons, Ltd.     

First discovery of Holocene Alaskan and Icelandic tephra in Polish peatlands

Despite the discovery of cryptotephra layers in over 100 peatlands across northern Europe, Holocene cryptotephra layers have not previously been reported from Polish peatlands. Here we present the first Holocene tephra findings from two peatlands in northern Poland. At Bagno Kusowo peatland we identify the most easterly occurrence of the AD 860 B tephra, recently correlated to the White River Ash (WRAe) derived from Mount Churchill, Alaska. A shorter core from Linje peatland contains tephra from the Askja 1875 eruption, extending the spatial distribution and regional importance of this Icelandic tephra in Eastern Europe. Our research indicates the potential of cryptotephra layers to date and correlate the growing number of palaeoenvironmental studies being conducted on Polish peatlands and contributes towards the development of a regional Holocene tephrostratigraphy for Poland. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.

     

Dynamic landscape changes in Glen Roy and vicinity,west Highland Scotland,during the Younger Dryas and early Holocene: a synthesis

This paper introduces a special issue devoted to the sequence of events in and around Glen Roy during the Loch Lomond or Younger Dryas Stadial, the short but important cold period dated to between ∼12,900 and 11,700 years ago, during which glaciers last expanded to occupy the Scottish Highlands, and during the subsequent transition to warmer conditions at the start of the Holocene. The Glen Roy area is internationally famous for the ‘Parallel Roads’, pre-eminent examples of ice-dammed lake shorelines which were formed during the stadial. What makes these shorelines unique, however, is their role as distinctive time markers, allowing the order of formation of landforms and sediments to be construed with unprecedented detail. Varved lake sediments preserved within Glen Roy and nearby Loch Laggan provide a precise timescale – the Lochaber Master Varve Chronology (LMVC) – for establishing the rates and timing of some of the events. This introductory paper first sets the geological context for those new to this topic, with a digest of key advances in understanding made between the nineteenth century and the publication of the LMVC in 2010. It then summarises the evidence and ideas that have emerged from new research investigations reported in this special issue for the first time, and which shine new light on the subject. Two final sections synthesise the new data and consider future prospects for further refinement of the precise sequence and timing of events. A major conclusion to emerge from this new body of work is that the ice-dammed lakes, and the glaciers that impounded them, persisted in the area until around 11,700 to perhaps 11,600 years ago. This conflicts with recently promoted suggestions that the last glaciers in Scotland were already in a state of considerable decline by ∼12,500 years ago.     

Dawson tephra,a widespread 29-ka marker bed,in a marine core from Patton Seamount off the Alaska Peninsula and its potential marine–terrestrial correlation

A tephra layer with normal grading in the sub-bottom depth interval 119–122 cm in marine core SO202-27-6 was collected on Patton Seamount in the northeast North Pacific Ocean. Based on the geochemistry of volcanic glass shards determined by a wavelength dispersive electron probe micro-analyser and an X-ray fluorescence analyser, this layer is correlated to the Dawson tephra, a widespread late Pleistocene time marker tephra in Alaska and the Yukon. The age of the Dawson tephra in the core is 29.03 ± 0.178 ka (1 sigma) based on a published age model. The Dawson tephra is revealed to have been deposited in the transition from marine isotope stage 3 to 2, i.e. the last stage of Heinrich Stadial 3 derived from the ice-rafted debris signal. According to the correlation between Greenland (NGRIP ice core) and this core, the Dawson tephra occupies the record immediately before inter stadial 4 in the δ¹⁸O stratigraphy of NGRIP. The Dawson tephra on Patton Seamount includes lithic fragments, which suggests that it was deposited not only by fall-out but also in part via another mechanism, such as icebergs from the Cordilleran ice sheet or seasonal sea ice.     

Long-distance transported Pinus pollen as a possible chronostratigraphic marker in the Scottish early postglacial

Peaks of Pinus pollen inseveraldetailed early postglacial (Flandrian) pollen diagrams from western Scotland are interpreted as the result of a change in the prevailing wind direction and intensity during climatic amelioration following the Loch Lomond Stadial (Younger Dryas). This origin implies a degree of syn-chroneity in this palynological feature, which if proven would be valuable in the poorly dated early postglacial. The absence of this palynological feature at many sites may be the result of poor sampling or stratigraphic resolution.     

The Hekla 1947 tephra in the north of Ireland: regional distribution,concentration and geochemistry

A cryptotephra layer from the eruption of Hekla in 1947 has recently been discovered in Irish peatlands. This tephra layer represents the most recent deposition of volcanic ash in the UK prior to the eruption of Eyjafjallajökull in 2010. Here we examine the concentration and geochemistry of the Hekla 1947 tephra in 14 peat profiles from across Northern Ireland. Electron probe microanalysis of individual tephra shards (n = 91) reveals that the tephra is of dacitic–andesitic geochemistry and is highly similar to the Hekla 1510 tephra, although spheroidal carbonaceous particle profiles can be used for successful discrimination of the two layers. The highest concentrations of Hekla 1947 are found in western sites, probably reflecting the pathway of the ash fall event due to the prevailing wind direction. Comparable tephra concentrations from two cores (1 km apart) from a single bog and from nearby sites may suggest that tephra shard concentrations in peat profiles reflect ash fallout densities across a specific region, rather than site‐specific factors associated with peatlands. This paper firmly establishes Hekla 1947 as a useful chronostratigraphic marker for the twentieth century, although within a restricted zone. Copyright © 2012 John Wiley & Sons, Ltd.     

Small shards and long distances — three cryptotephra layers from the Nahe palaeolake including the first discovery of Laacher See Tephra in Schleswig-Holstein (Germany)

Investigations of Lateglacial to Early Holocene lake sediments from the Nahe palaeolake (northern Germany) provided a high-resolution palynological record. To increase the temporal resolution of the record a targeted search for cryptotephra was carried out on the basis of pollen stratigraphy. Three cryptotephra horizons were detected and geochemically identified as G10ka series tephra (a Saksunarvatn Ash), Vedde Ash and Laacher See Tephra. Here we present the first geochemically confirmed finding of the ash from the Laacher See Eruption in Schleswig-Holstein—extending the so far detected fallout fan of the eruption further to the north-west. These finds enable direct stratigraphical correlations and underline the potential of the site for further investigations.     

Evidence for restricted Loch Lomond Stadial plateau ice in Glen Turret and implications for the age of the Turret Fan

Despite a wealth of research on the patterns and timing of glaciation in Glen Roy over the last 150 years, glacial events within Glen Turret remain heavily debated. These debates centre on the extent and source of Loch Lomond Stadial (Younger Dryas) ice in Glen Turret, and the implications for the age and genesis of the Turret Fan. Here we present details of recent systematic geomorphological mapping of Glen Turret and the neighbouring valleys to the north and east. The geomorphological evidence recorded indicates a plateau icefield style of glaciation centred on the Carn Dearg plateau, of which the Turret Glacier was an outlet. A morphostratigraphical approach is used to identify a relative chronology of glacial events, and suggests that the Turret Fan may have formed prior to the Loch Lomond Stadial. A reconstruction of the Carn Dearg plateau icefield is presented, which was connected to the larger Monadhliath Icefield to the east. Equilibrium line altitudes for the outlet glaciers range from 560 ± 20 m to 646 ± 20 m and are comparable with those calculated for surrounding regions. This research suggests that the Turret Fan is predominantly an older feature that was deposited by a more extensive plateau ice-sourced Turret Glacier prior to the Loch Lomond Stadial, most likely during or immediately after deglaciation of the last ice sheet.     

Geophysical surveys of the sediments of Loch Ness,Scotland: implications for the deglaciation of the Moray Firth Ice Stream,British–Irish Ice Sheet

We present results from three geophysical campaigns using high‐resolution sub‐bottom profiling to image sediments deposited in Loch Ness, Scotland. Sonar profiles show distinct packages of sediment, providing insight into the loch's deglacial history. A recessional moraine complex in the north of the loch indicates initial punctuated retreat. Subsequent retreat was rapid before stabilisation at Foyers Rise formed a large stillstand moraine. Here, the calving margin produced significant volumes of laminated sediments in a proglacial fjord‐like environment. Subsequent to this, ice retreated rapidly to the southern end of the loch, where it again deposited a sequence of proglacial laminated sediments. Sediment sequences were then disturbed by the deposition of a thick gravel layer and a large turbidite deposit as a result of a jökulhlaup from the Spean/Roy ice‐dammed lake. These sediments are overlain by a Holocene sheet drape. Data indicate: (i) a former tributary of the Moray Firth Ice Stream migrated back into Loch Ness as a major outlet glacier with a calving margin in a fjord‐like setting; (ii) there was significant sediment supply to the terminus of this outlet glacier in Loch Ness; and (iii) that jökulhlaups are important for sediment supply into proglacial fjord/lake environments and may compose >20% of proglacial sedimentary sequences. Copyright © 2011 John Wiley & Sons, Ltd.     

Glacier Peak and mid-Lateglacial Katla cryptotephras in Scotland: potential new intercontinental and marine-terrestrial correlations

Using contiguous high resolution sampling methods, we report the detection of a Glacier Peak volcanic ash from North America in Lateglacial Interstadial lake sediments in western Scotland. It occurs in close proximity to the Icelandic Borrobol and Penifiler tephras, but is distinguishable by its rhyolitic major-element composition that is consistent with the earliest set G layer, one of a number of mid-Interstadial Glacier Peak eruptions dated between 13.71 and 13.41 cal ka bp. Another cryptotephra layer present in these same Interstadial sediments has a rhyolitic composition consistent with the Icelandic Katla source. However, it is in a stratigraphic position below the widespread mid-Lateglacial Stadial Vedde Ash from Katla, which is also present in these cores. The Katla layer is stratigraphically well defined, suggesting primary airfall, and is compositionally similar to a mid-Interstadial rhyolitic tephra reported from a North Atlantic marine sequence south of Iceland dated to ~13.6 ka. The detection of Glacier Peak G in the European tephrostratigraphy will permit direct high-precision correlation of mid-Interstadial palaeoenvironments between North American and European terrestrial sequences. Any correlation between the new Katla layer and similar marine layers remains provisional, though if verified would permit similar correlation between North Atlantic marine and European terrestrial records.     

Lateglacial and Holocene relative sea‐level changes and first evidence for the Storegga tsunami in Sutherland,Scotland

We reconstruct one of the longest relative sea‐level (RSL) records in north‐west Europe from the north coast of mainland Scotland, using data collected from three sites in Loch Eriboll (Sutherland) that we combine with other studies from the region. Following deglaciation, RSL fell from a Lateglacial highstand of +6?8 m OD (Ordnance Datum = ca. mean sea level) at ca. 15 k cal a BP to below present, then rose to an early Holocene highstand and remained at ca. +1 m OD between ca. 7 and 3 k cal a BP, before falling to present. We find no evidence for significant differential Holocene glacio‐isostatic adjustment between sites on the north‐west (Lochinver, Loch Laxford), north (Loch Eriboll) and north‐east (Wick) coast of mainland Scotland. This suggests that the region was rapidly deglaciated and there was little difference in ice loads across the region. From one site at the head of Loch Eriboll we report the most westerly sedimentary evidence for the early Holocene Storegga tsunami on the Scottish mainland. The presence of the Storegga tsunami in Loch Eriboll is predicted by a tsunami wave model, which suggests that the tsunami impacted the entire north coast of Scotland and probably also the Atlantic coastline of north‐west Scotland.