Late Quaternary glacial and environmental history of Kongsøya, Svalbard

On western Kongsøya, Svalbard, three coarsening-upwards sequences of marine to littoral sediments, separated by tills, are recognised in sections at ca 50-92 m above present sea level. These sequences show major glaciations in the northern Barents Sea, resulting in substantial glacioisostatic downpressing of Kongsøya. Till fabrics indicate ice movements controlled by the local topography, while glaciotectonic deformations suggest that ice moved from an ice divide northeast of Kongsøya. independent of the local topography. The stratigraphical evidences show two pre-Holocene ice-free periods, when the climate was similar to or slightly warmer than at present. The age of these periods is not clear. It is suggested that the elder ice free interval is older than isotope stage 5e. The younger ice free interval could be of Eemian or Early Weichselian age. The uppermost succession of sublittoral-littoral sediments is of early Holocene age. It relates to the high (≥100 m) postglacial marine limit, dated to approximately 10,000 bp.     

Early Holocene environment on Bjørnøya (Svalbard) inferred from multidisciplinary lake sediment studies

Bjørnøya, a small (178 km²) island situated between the mainland of Norway and southern Spitsbergen, provides the opportunity for the reconstruction of early Holocene terrestrial and limnic palaeoenvironments in the southwestern Barents Sea. The AMS ¹⁴C dating technique, geochemical, mineral magnetic, micro and macrofossil analyses were applied to sediments recovered from lake Stevatnet and the results are interpreted in terms of palaeoenvironmental conditions between 9800 and 8300 ¹⁴C bp. After the disappearance of local glaciers before ca 9800¹⁴C BP, the lake productivity increased rapidly at the same time as pioneer plant communities developed on soils which gradually became more stable. Insect data indicates that strong seasonal contrasts with mean July temperatures around 9°C and mean January temperatures around −12°C prevailed between 9500 and 8300 ¹⁴C BP. These high summer temperatures, possibly as much as 4-5°C higher than the present, favoured the development of a flora including Dryas and Angelica cf. archangelica . The enhanced freeze/thaw processes led to an increased erosion of minerogenic and organic material. After 8000 ¹⁴C BP the temperatures may have gradually declined. The environmental reconstruction derived from our data set supports the conceptual insolation model which proposes maximum Holocene seasonality for the Northern Hemisphere at ca 9000 ¹⁴C BP.     

Facies characteristics and architecture related to palaeodepth of Holocene fjord–delta sediments

Lithofacies characteristics and depositional geometry of a sandy, prograding delta deposited as part of the Holocene valley‐fill stratigraphy in the Målselv valley, northern Norway, were examined using morpho‐sedimentary mapping, facies analysis of sediments in exposed sections, auger drilling and ground penetrating radar survey. Various lithofacies types record a broad range of depositional processes within an overall coarsening‐upward succession comprising a lowermost prodelta/bottomset unit, an intermediate delta slope/foreset unit containing steeply dipping clinoforms and an uppermost delta plain/topset unit. Bottomset lithofacies typically comprise sand‐silt couplets (tidal rhythmites), bioturbated sands and silts, and flaser and lenticular bedding. These sediments were deposited from suspension fall‐out, partly controlled by tidal currents and fluvial effluent processes. Delta foreset lithofacies comprise massive, inverse graded and normal graded beds deposited by gravity‐driven processes (mainly cohesionless debris flows and turbidity currents) and suspension fall‐out. In places, delta foreset beds show tidal rhythmicity and individual beds can be followed downslope into bottomset beds. Delta plain facies show an upward‐fining succession with trough cross‐beds at the base, followed by planar, laminated and massive beds indicative of a bedload dominated river/distributary system. This study presents a model of deltaic development that can be described with reference to three styles within a continuum related primarily to water depth within a basin of variable geometry: (i) bypass; (ii) shoal‐water; and (iii) deep‐water deltas. Bypass and deep‐water deltas can be considered as end members, whereas shoal‐water deltas are an intermediate type. The bypass delta is characterized by rapid progradation and an absence of delta slope sediments and low basin floor aggradation due to low accommodation space. The shoal‐water delta is characterized by rapid progradation, a short delta slope dominated by gravity‐flow processes and a prodelta area characterized by rapid sea‐floor aggradation due to intense suspension fallout of sandy material. Using tidal rhythmites as time‐markers, a progradation rate of up to 11 m year^?1 has been recorded. The deep‐water delta is characterized by a relatively long delta slope dominated by gravity flows, moderate suspension fall‐out and slow sea‐floor aggradation in the prodelta area.     

A lacustrine record of late Pleistocene climatic change in the subtropical Andes

Significant changes in moisture have occurred in the subtropical Andes over the last 20,000 years as evidenced by shorelines of high lake stands and extensive glacial moraines. Lakes with sediment records that reflect these moisture changes are present in some valleys where headwalls are below the snowline elevation reached during the latest Pleistocene glacial culmination (14,000–12,000 BP). One such lake, Laguna Kollpa Kkota, which is located on the western slope of the eastern cordillera in Bolivia, has basal radiocarbon dates of about 20,000 BP. The snowline reconstruction for this site confirms earlier work in the region that suggests late Pleistocene snowline depression was less than 500 m, or half the amount generally considered for low-latitude regions during the last glacial maximum. The sediment stratigraphy from Laguna Kollpa Kkota indicates that sediment accumulation and organic carbon deposition increased significantly from 14,000 to 12,600 BP. This increase in sedimentation may have resulted from greater inwash to the lake and higher productivity In the lake itself as a result of higher lake levels. These changes could reflect the postulated late Pleistocene increase in precipitation that led to the formation of Lago Tauca on the Altiplano and to glacial advances in the surrounding cordillera.     

A marine seismic study of late Quaternary sedimentaion and inferred glacier fluctuations along western Inverness-shire, Scotland

A sparker survey was undertaken of the sea area inshore of the peninsula of sleat and the islands of Eigg and Muck in Western Scotland. This revealed major submarine moraines across the mouths of Loch Nevis and Loch Ailort, which help define the margin of a major glacier readvance phase, presumed to be equivalent to the late-glacial Loch Lomond Readvance. Formation names are suggested for the seismic para-stratigraphy. West of the moraines, there is a till (Minch Para-formation) resting on bedrock, overlain by a stratum (Muck para-formation) with well-defined internal layering parallel to the substratum. The till is presumed to have been deposited by an ice cap which at its maximum reached the western edge of the continental shelf at some time after 27,000 B.P. The Muck para-formation probably represents a glaciomarine unit deposited during the retreat of this ice cap, and has been deeply eroded. Above this erosion surface occur a series of sediments which infill local basins, and which appear to be of Flandrian age (Arisaig para-formation). East of the moraines in Loch Nevis and Loch Ailort the draped sediments are missing and the till is overlain by apparent equivalents (Nevis para-formation) of the marine sediments of Flandrian age to the west     

Late Vistulian insect assemblages from Zabinko, western Poland

Insect analysis was carried out in deposits from a Late Vistulian site at Zabinko, western Poland. Geomorphological, lithostratigraphical and palaeobotanical investigations have been carried out earlier at the same section and published elsewhere. The analysed samples are dated from c. 12,600 to 12,200 BP. A total of 54 insect taxa were determined, the majority being Coleoptera. No major change in the insect fauna during this 400 years period could be detected from the study. The presence of specific phytophagus beetles suggests the same local vegetational environment as reconstructed from the plant macrofossil record, namely a shallow pool with a well-developed reed vegetation. The pool was situated in an open landscape with scattered trees and herb vegetation. The climatic reconstruction from the insect assemblages suggests a cool temperate climate with an average July temperature of 14–15C, During the same time period arctic/ksubarctic conditionsd, with mean July temperatures of c. 10–12C, prevailed in southernmost Scandinavia. The climatic amelioration in western Poland seems to have started possibl 500 years earlier than in southern Sweden.     

Isolation basin stratigraphy and Holocene relative sea-level change at the Norwegian—Russian border north of Nikel, northwest Russia

The marine-lacustrine transition (isolation contact) in sediment cores from eight lake basins situated 13.5-72 m a.s.l., in the Norwegian-Russian border area north of Nikel, northwest Russia, was identified based on lithological and diatom analysis, radiocarbon dated, and used to construct a relative sea-level (RSL) curve for the Holocene. All the lakes except one (interpreted as having an unconformable slumped transition) show a regressive I-II-III (marine-transitional-lacustrine) facies succession, indicating a postglacial history of continuous emergence. The RSL curve shows rapid emergence between 10 000 and 8000 BP, very slow emergence between 7000 and 5000 BP, increased rate of emergence between 4500 and 4000 BP, and a moderate rate of emergence after 3500 BP. The low rate of emergence around 6000 BP correlates with the Tapes transgression of more coastal regions, but corresponding sea level, at 25-26 ma. present s.l., lies 5-10 m lower than the elevation predicted based on existing isobase maps for the region. The discrepancy suggests a need for further work in order to more rigorously define and map the Tapes transgression and associated shoreline complex in the northern Fennoscandian-Kola region.     

Environmental and climatic reconstructions during Marine Oxygen Isotope Stage 3 from Gossau, Swiss Midlands, based on coleopteran assemblages

The well-known lower lignite layer at Gossau (15 km SE of Zürich, Switzerland) has been radiocarbon-dated to between 30 000 and 54 000 yr BP. Though these dates may be considered to be beyond the acceptable limit of the technique, there can be little doubt on stratigraphical grounds that the deposits date from some early part of MOI Stage 3. The lower lignite has yielded 49 taxa of beetles from which a detailed palaeoenvironmental picture can be reconstructed. Quantified palaeotemperature estimates using the Mutual Climatic Range method, based on this fossil assemblage, indicate that the climate was cold and considerably more continental than it is today in the Swiss Midlands and close to the thermal limit for the growth of trees. The fauna bears similarities to others from the same general period in northern Europe.     

AMS dating Swedish varved clays of the last glacial/interglacial transition and the potential/difficulties of calibrating Late Weichselian 'absolute' chronologies

The increasing focus on the chronology of environmental and climatic changes of the last glacial-interglacial transition has led to several independent attempts to try to calibrate the ¹⁴C time-scale beyond the Holocene. The Late Weichselian Gotiglacial varved clays of the Swedish Time Scale could potentially be used for this purpose. The reliability of the Swedish Time Scale is discussed as well as different ways of using the Swedish varved clays for calibrating the ¹⁴C chronology. The strategy and initial results from an ongoing calibration project are presented. They show clearly that, if the right strategy is adopted, varved clay may be dated by accelerator mass spectrometry (AMS) ¹⁴C measurement of terrestrial macrofossils. A Late Weichselian 'event stratigraphy', including the Vedde Ash fall-out, is established for south Scandinavia using three dating categories: clay varve measurements, terrestrial macrofossil measurement, and lake sediment (including aquatic mosses) measurements. It suggests that a ¹⁴C chronology based on terrestrial organic remains is not consistent with the traditional Late Weichselian chronostratigraphy based on lake-sediment samples, and that 'clay varve years' exceed 'terrestrial ¹⁴C years' by c. 900 years at the end of, and by 1100–1200 years at the beginning of the Younger Dryas Chronozone. Further back in time, the time-scales appear to converge. These results are compared with other recently published calibration studies.