Beschreibung: Publication date: Available online 29 December 2014 Source: Quaternary Science Reviews Author(s): Zbyněk Engel , Grzegorz Skrzypek

Beschreibung: Publication date: Available online 26 December 2014 Source: Quaternary Science Reviews Author(s): Alberto Sáez , Santiago Giralt , Armand Hernández , Roberto Bao , Juan J. Pueyo , Ana Moreno , Blas L. Valero-Garcés

Beschreibung: Publication date: Available online 24 December 2014 Source: Quaternary Science Reviews Author(s): Ed Garrett , Natasha L.M. Barlow , Hannah Cool , Darrell S. Kaufman , Ian Shennan , Paul D. Zander New records of paleoenvironmental change from two lakes near Cordova, south central Alaska, combined with analysis of previously reported sediment sequences from the adjacent Copper River Delta, provide quantitative constraints on a range of Earth system processes through their expression in relative sea-level change. Basal sediment ages from Upper Whitshed Lake indicate ice-free conditions by at least 14,140–15,040 cal yr BP. While Upper and Lower Whitshed Lakes provide only upper limits to relative sea-level change, interbedded layers of freshwater peat and intertidal silt extending more than 11 m below present sea level in Copper River Delta indicate net submergence over the last 6000 years and multiple earthquake deformation cycles. In contrast, Lower Whitshed Lake, situated just above present high tide level, records only one episode of marine sedimentation, commencing AD 1120–1500, that we interpret as the result of isostatic subsidence due to Little Ice Age mass accumulation of the Chugach Mountain glaciers. Lower Whitshed Lake also records isostatic uplift at the end of the Little Ice Age before the end of marine sedimentation caused by ∼1.5 m coseismic uplift in the great Alaska earthquake of AD 1964. We successfully explain the records of relative sea-level change from both Copper River Delta and the Whitshed Lakes by integrating the effects of eustatic sea-level rise, glacial isostasy, earthquake deformation cycles, sediment loading, sediment compaction and Late Holocene changes in glacier mass into a single model. This approach provides initial quantitative constraints on the individual contributions of these processes. Taking reasonable estimates of eustasy, post-Last Glacial Maximum and Neoglacial glacial isostatic adjustment and a simple earthquake deformation cycle, we demonstrate that sediment loading and sediment compaction are both contributors to relative sea-level rise at Copper River Delta, together producing subsidence averaging approximately 1.2 mm yr −1 over the mid to Late Holocene. Further isolation basin studies have the potential to greatly improve our understanding of the individual contributions of these processes in this highly dynamic region.

Beschreibung: Publication date: 1 February 2015 Source: Quaternary Science Reviews, Volume 109 Author(s): Jonathan R. Lee , Oliver J.W. Wakefield , Emrys Phillips , Leanne Hughes Subglacial drainage systems exert a major control on basal-sliding rates and glacier dynamics. However, comparatively few studies have examined the sedimentary record of subglacial drainage. This is due to the paucity of modern analogues, the limited recognition and preservation of upper flow regime deposits within the geological record, and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments (e.g. glacier outburst flood deposits). Within this study, the sedimentological and structural evolution of a subglacial to subaerial (ice-marginal/proglacial) drainage system is examined. Particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context. Facies are attributed to subglacial meltwater activity and record sedimentation within a confined, but progressively enlargening, subglacial channel system produced under dune to upper flow regime conditions. Bedforms include rare large-scale sinusoidal bedding with syn-depositional deformation produced by current-induced traction and shearing within the channel margins. Subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel-abandonment or a seasonal drainage regime. Retreat of the ice margin, led to the establishment of subaerial drainage with phases of sheet-flow punctuated by channel incision and anastomosing channel development under diurnal, ablation-related, seasonal discharge. The presence of extensive hydrofracture networks demonstrate that proglacial groundwater-levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream.

Beschreibung: Publication date: 1 February 2015 Source: Quaternary Science Reviews, Volume 109 Author(s): Zhihai Tan , Yongming Han , Junji Cao , Chun Chang Huang , Zhisheng An High-resolution sedimentary charcoal and black carbon (BC, including char and soot) records from a loess–soil profile, combined with magnetic susceptibility, δ 13 C of soil organic matter of analyses, pollen counts and other paleoenvironmental proxies reveal past fire patterns and landscape evolution over the past 12,000 years. Results from the analyses of charcoal and BC influx show that regional fire activity was high in the early and late Holocene, whereas fire was less frequent and pervasive in the middle Holocene. Locally, fires were infrequent near the study site until the Late Holocene. Soot and char analyses do not parallel changes in charcoal variability, and thus appear to reflect either a different aspect of fire activity or else these data are registering aspects of particle transportation and deposition in addition to fire characteristics. The patterns in fire activity observed during the Holocene are consistent with variations in vegetation inferred from δ 13 C values in soil organic matter, pollen counts, and paleoclimate proxies. Drier and colder-than-present conditions on the Loess Plateau occurred during the Lateglacial and early Holocene (12,000–8500 years BP), which likely enhanced regional fire activity across the Artemisia and Gramineae -dominated steppe landscape in the south of the Loess Plateau. Wetter and warmer-than-present conditions during the mid-Holocene (8500–3100 years BP), reduced fire episodes and promoted the development of mixed forest and forest-steppe. The distribution of C 4 plants and woodland expanded at this time from 40% to 60% cover. The subsequent increase in fire-episode frequency during the past 3100 years is consistent with cooler and drier conditions in the late Holocene and also with changes in the spatial and temporal distributions of Neolithic burning practices, such as land reclamation and crop cultivation, during those periods (e.g., expansion of C 3 plants). The close association between millennial-scale variations in fire and monsoon activity on the Loess Plateau suggests that future shifts in monsoon-related climate variability could have important consequences for fire and human activities as both respond to regional climate change.

Beschreibung: Publication date: Available online 23 December 2014 Source: Quaternary Science Reviews Author(s): Christopher Bronk Ramsey , Rupert A. Housley , Christine S. Lane , Victoria C. Smith , A.Mark Pollard An open-access database has been set up to support the research project studying the ‘Response of Humans to Abrupt Environmental Transitions’ (RESET). The main methodology underlying this project was to use tephra layers to tie together and synchronise the chronologies of stratigraphic records at archaeological and environmental sites. The database has information on occurrences, and chemical compositions, of glass shards from tephra and cryptotephra deposits found across Europe. The data includes both information from the RESET project itself and from the published literature. With over 12,000 major element analyses and over 3000 trace element analyses on glass shards, relevant to 80 late Quaternary eruptions, the RESET project has generated an important archive of data. When added to the published information, the database described here has a total of more than 22,000 major element analyses and nearly 4000 trace element analyses on glass from over 240 eruptions. In addition to the database and its associated data, new methods of data analysis for assessing correlations have been developed as part of the project. In particular an approach using multi-dimensional kernel density estimates to evaluate the likelihood of tephra compositions matching is described here and tested on data generated as part of the RESET project.

Beschreibung: Publication date: Available online 23 December 2014 Source: Quaternary Science Reviews Author(s): Christopher Bronk Ramsey , Paul G. Albert , Simon P.E. Blockley , Mark Hardiman , Rupert A. Housley , Christine S. Lane , Sharen Lee , Ian P. Matthews , Victoria C. Smith , John Lowe The research project ‘Response of Humans to Abrupt Environmental Transitions’ (RESET) used tephra layers to tie together and synchronise the chronologies of stratigraphic records at archaeological and environmental sites. With the increasing importance of tephra as chronological markers in sedimentary sequences, both in this project and more generally, comes a requirement to have good estimates for the absolute age of these volcanic horizons. This paper summarises the chronology of the key tephra in the RESET tephra lattice in the time range 10–60 ka BP, from the existing literature, from papers produced as part of the RESET project, and reanalysis conducted for this paper. The paper outlines the chronological approach taken to the dating of tephra within the RESET project, and the basis for further work, as part of the INTIMATE (INTegrating Ice core MArine and TErrestrial records) initiative. For each of the tephra layers in the lattice, the existing literature is discussed and, where relevant date estimates updated using the latest radiocarbon calibration curves (IntCal13 and Marine13) and methods. Maps show the approximate extent of tephra finds, giving a visual indication of the coverage of the lattice in different time-periods.

Beschreibung: Publication date: 1 February 2015 Source: Quaternary Science Reviews, Volume 109 Author(s): Lee B. Corbett , Paul R. Bierman , G. Everett Lasher , Dylan H. Rood Constraining past responses of ice sheets to changes in climate enhances our ability to predict future changes in ice extent and sea level. Here, we employ surficial geologic mapping, stratigraphic analysis, radiocarbon dating of marine mollusks, and analysis of cosmogenic 10 Be in glacially-deposited boulders to make inferences about past ice extents in Thule, northwest Greenland. Our work shows the existence of two distinct diamict units in the Thule area; we infer that one diamict was deposited by the main Greenland Ice Sheet while the second was deposited by a subsequent outlet glacier re-advance. Boulders in the two diamicts ( n  = 13 and n  = 15, respectively) have similar bimodal distributions of cosmogenic 10 Be ages. Both diamicts have a group of younger 10 Be ages as well as a more diffuse group of considerably older 10 Be ages (∼20–30 ka). Many of the boulders likely contain nuclides inherited from previous periods of exposure, suggesting that glacial ice in the Thule region has been cold-based and non-erosive in the past. The landscape chronology we develop suggests that deglaciation after the Last Glacial Maximum occurred ∼10.8 ka and was later followed by a re-advance of outlet glaciers, possibly in concert with the 9.3 ka or 8.2 ka cold events.

Beschreibung: Publication date: 1 February 2015 Source: Quaternary Science Reviews, Volume 109 Author(s): D. Maddy , D. Schreve , T. Demir , A. Veldkamp , J.R. Wijbrans , W. van Gorp , D.J.J. van Hinsbergen , M.J. Dekkers , R. Scaife , J.M. Schoorl , C. Stemerdink , T. van der Schriek Anatolia lies at the gateway from Asia into Europe and has frequently been favoured as a route for Early Pleistocene hominin dispersal. Although early hominins are known to have occupied Turkey, with numerous finds of Lower Palaeolithic artefacts documented, the chronology of their dispersal has little reliable stratigraphical or geochronological constraint, sites are rare, and the region's hominin history remains poorly understood as a result. Here, we present a Palaeolithic artefact, a hard-hammer flake, from fluvial sediments associated with the Early Pleistocene Gediz River of Western Turkey. This previously documented buried river terrace sequence provides a clear stratigraphical context for the find and affords opportunities for independent age estimation using the numerous basaltic lava flows that emanated from nearby volcanic necks and aperiodically encroached onto the contemporary valley floors. New 40 Ar/ 39 Ar age estimates from these flows are reported here which, together with palaeomagnetic measurements, allow a tightly-constrained chronology for the artefact-bearing sediments to be established. These results suggest that hominin occupation of the valley occurred within a time period spanning ∼1.24 Ma to ∼1.17 Ma, making this the earliest, securely-dated, record of hominin occupation in Anatolia.

Beschreibung: Publication date: 1 February 2015 Source: Quaternary Science Reviews, Volume 109 Author(s): Francesco Muschitiello , Barbara Wohlfarth Until lately, it has commonly been assumed that the last major reorganization of the North Atlantic ocean–atmosphere system, the Younger Dryas climatic reversal, spread synchronously on continental to hemispheric scales. This assumption arose because reliable chronologies, which would allow capturing the complexity surrounding local responses to abrupt climate change, were lacking. To better understand the temporal structure at the inception of the Younger Dryas across the North Atlantic, we revised, updated and compared the chronological framework of four Northern European sediment sequences (Lake Kråkenes, Lake Madtjärn, Lake Gammelmose, Sluggan Bog) by applying classical Bayesian modelling. We found distinct and spatially consistent age differences between the inferred ages of the Allerød interstadial – Younger Dryas stadial pollen zone boundaries among the four sites. Our results suggest an earlier vegetation response at sites along latitude 56–54°N as compared to sites located at 60–58°N. We explain this time lag by a gradual regional cooling that started as early as c. 12,900–13,100 cal. BP. This phenomenon was probably linked to cooling around the Nordic Seas as a result of enhanced iceberg calving from the Fennoscandian Ice Sheet during the final stage of the Allerød interstadial. By contrast, vegetation shifts at sites located further north occurred significantly later and in concert with the establishment of full stadial climate conditions (c. 12,600–12,750 cal. BP). Our study emphasizes the need to develop solid regional 14 C chronologies and to employ the same age modelling approach to determine the temporal and spatial response to a climatic shift.