Seasonality of modern pollen and sediment deposition in an estuarine context: the Severn Estuary Levels,southwest England

Recent sedimentological and palynological research on subfossil Holocene banded sediments from the Severn Estuary Levels suggested seasonality of deposition, registered by variations in mineral grain‐size and pollen assemblages between different parts of the bands. Here we provide data that strengthen this interpretation from sampling of modern sediments and pollen deposition on an active mudflat and saltmarsh on the margin of the Severn Estuary, and comparison with a vegetation survey and contemporary records of climate, river and tidal regimes. The results of grain‐size analysis indicate deposition of comparatively coarse‐grained silts during the relatively cool and windy conditions of winter and comparatively fine‐grained sediments during relatively warm and calm summer months. Pollen analysis demonstrates the significance of long‐term storage of pollen grains and fern spores in the estuarine waterbody, superimposed on which seasonal variations in pollen inputs from local and regional vegetation remain detectable. Copyright © 2007 John Wiley & Sons, Ltd.     

河北白洋淀全新统沉积特征与地层划分

通过对河北白洋淀老河头剖面全新世沉积物岩性特征、地层层序、粒度组成及微体古生物组合等进行综合研究,重建了白洋淀全新世以来的环境演变过程。全新世以来白洋淀沉积特征所反映的气候环境特征表现为早期开始出现湖沼相沉积,气候寒冷偏湿;中期湖泊沉积发育,气候温暖湿润;晚期湖泊退缩,以河流-沼泽相沉积为主,气候向凉干转变。综合沉积特征、环境演变阶段与加速器质谱(AMS)14C测年资料对白洋淀全新统沉积序列进行系统分析,并将全新统划分为三段:下全新统(11000—8500 a)以灰黄色粉砂质粘土、粉砂为主,夹黑色粘土,冲积-湖沼相沉积发育;中全新统(8500—3200 a)为灰黑色粘土夹粘土质粉砂,湖沼相沉积发育;上全新统(3200 a~)以黄色、褐黄色粉细砂、粘土质粉砂为主,冲积-沼泽相沉积发育。白洋淀全新统中段含有黑色粘土沉积和大量微体与腹足、双壳类等古生物化石,为华北地区全新世地层的划分及区域对比提供了依据。     

A study of Holocene floodplain particle size characteristics with special reference to palaeochannel infills from the upper Severn basin,Wales, UK

Multiple sedimentary units from floodplain reaches at Welshpool on the upper River Severn and at the confluence of the Afon Tanat and Afon Vyrnwy (mid‐Wales, UK) were examined to ascertain if they have distinctive particle size characteristics. Changes in particle size characteristics and their possible relationship to known human and climatic impacts are also discussed. Ellipse plots of particle size characteristics from the River Severn floodplain at Welshpool show that coarse‐grained outwash deposits can be clearly discriminated from channel margin or palaeochannel sediments. In contrast, at the Afon Tanat–Vyrnwy study reach, this discrimination is not seen so clearly. The relationships between age and particle size characteristics from the most sampled sedimentary environment, palaeochannel infills, were also examined. The data from the River Severn floodplain at Welshpool show that palaeochannel sediments reveal a gradual but clear increase in particle size from the mid‐ to late Holocene towards the present day. Sediments deposited in the period 90–160 years BP are markedly coarser. It is suggested that these changes may be related to the combined effect of land‐use changes, metal mining impacts and changes in flood frequency and magnitude that occurred at this time within the upper Severn basin. In contrast, the particle size characteristics of post Late Devensian/Early Holocene units from Tanat–Vyrnwy palaeochannels were random with no discernible age–size patterns. It is suggested that the non‐systematic grain size distribution may be due to the steeper valley gradients of the Tanat–Vyrnwy system (and by inference higher stream powers) and its relatively narrow valley form enabling more effective coupling between coarser outwash deposits found on and at the edges of hillslopes and the valley floor. Although the two study reaches have undergone comparable environmental change during the Holocene and lie in the piedmont zone of their catchments, palaeochannel units of the same age possess distinctly different characteristics. Intrinsic reach‐scale geomorphic factors would appear to preclude the uniform application of particle size characteristics to determine alluvial response to environmental change. Consequently, care needs to be applied to the use of such data for environmental discrimination because the phenomenon of equifinality means that a specific set of sediment characteristics is not necessarily exclusive to specific fluvial environments in either space or time. Copyright © 2001 John Wiley & Sons, Ltd.     

全新世以来冲绳海槽北部S9孔粒度变化特征及其古气候响应

通过对冲绳海槽北部沉积物柱状样S9进行AMS 14C 测年和粒度分析,获取了全新世以来高分辨率的古环境演化记录.结果显示,千年尺度上,S9柱粒度组成呈现明显的两段式变化特征:10.5~8.0ka B.P.,平均粒径逐渐变粗并达到最高值,粉砂含量逐渐增加并达到最高值; 8.0~1.0ka B.P.,沉积物平均粒径呈现递减的趋势,粘土含量相对增加.S9柱粒度千年尺度上变化与区域海平面变化密切相关,显示了海平面对区域物质输运的控制作用.7.5ka B.P. 以来,海平面趋于稳定,粒度特征呈现出百年尺度上波动.S9柱粒度变化参数与源区指示季风降雨量石笋记录的 δ18O具有良好的相关性,7.5ka B.P. 以来持续减小的平均粒径对应持续减弱的区域夏季风降雨.此外,S9柱记录了约8.2ka B.P.,6.5ka B.P.,4.2ka B.P. 以及3.8ka B.P. 等多期粒度显著变细的百年尺度的气候事件,对应了区域季风降雨的减少时期.S9柱粒度组成信息揭示了全新世以来区域海平面变化及季风降雨的强弱对冲绳海槽沉积物组成的影响,同时也为利用海洋沉积物来重建区域季风降雨提供了有力的手段.     

近33ka以来辽河口沉积环境演变与生物硅记录

沉积物岩心记录着沉积环境的演变过程,其中生物硅(BSi)记录能反映硅质生物的生产力时间和空间变化,2012年5月在下辽河平原西南缘得到了ZK2钻孔柱状样,通过对其沉积物原位密度、生物硅、碳埋藏、粒度、AMS~(14)C和OSL测年、有孔虫鉴定、孢粉鉴定,将ZK2孔的沉积环境主要划分为上三角洲平原相沉积、海洋主导的沉积、湖相沉积、河道沉积4个沉积单元,其相应的生物硅(BSiO_2)浓度分布依次为(2.85±0.23)%、(1.55±0.10)%、(1.96±0.10)%、(0.92±0.05)%,并且生物硅的波动与颗粒有机碳浓度的波动同步。特别是在17~25 cal ka BP冰期形成的湖沼沉积出现较大的颗粒无机碳(PIC)浓度的波动,推测与当时干冷气候条件下CaCO_3过饱和从湖水中沉淀析出有关。钻孔沉积物生物硅浓度记录对格陵兰冰芯~(18)O同位素值的响应存在大约300 a的滞后现象。     

Carbonate dissolution revealed by silt grain-size distribution: comparison of Holocene and Last Glacial Maximum sediments from the pelagic South Atlantic

The current issue of global warming and the role of the ocean in global exchange of CO₂ increases the interest in solid budgets of marine carbonate production and dissolution. The present study utilizes grain‐size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the South Atlantic for the Holocene and Last Glacial Maximum (LGM, 19–23 cal kyr BP). A decrease in grain size (e.g. sand content, mean grain size of coarse carbonate silt) indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils. The spatial grain‐size pattern suggests a threshold water depth below which a gradual grain‐size decrease becomes increasingly rapid. This water depth is considered as the sedimentary lysocline. For the Holocene time slice, a constant, gradual decrease of foraminifer carbonate of about 5–10% per 1000 m water depth above the lysocline gives evidence for supra‐lysoclinal dissolution. The water depth of the lysocline for the Holocene is tied to the interface of North Atlantic Deep Water and Antarctic Bottom Water (AABW) (ca 4100 m). Submarine ridges which restrict intrusion of AABW into the Angola Basin cause an asymmetry in carbonate preservation across the Mid‐Atlantic Ridge. The lysocline was reconstructed at ca 3100 m for the LGM. These data suggest that the ca 1000 m rise of the lysocline eradicated the Holocene east–west asymmetry.     

Holocene transgression of the Rhine river mouth area,The Netherlands/Southern North Sea: palaeogeography and sequence stratigraphy

This study presents a detailed reconstruction of the palaeogeography of the Rhine valley (western Netherlands) during the Holocene transgression with systems tracts placed in a precise sea‐level context. This approach permits comparison of actual versus conceptual boundaries of the lowstand, transgressive and highstand systems tracts. The inland position of the highstand Rhine river mouth on a wide, low‐gradient continental shelf meant that base‐level changes were the dominant control on sedimentation for a relatively short period of the last glacial cycle. Systems in such inland positions predominantly record changes in the balance between river discharge and sediment load, and preserve excellent records of climatic changes or other catchment‐induced forcing. It is shown here that the transgressive systems tract‐part of the coastal prism formed in three stages: (i) the millennium before 8·45 ka bp , when the area was dominated by fluvial environments with extensive wetlands; (ii) the millennium after 8·45 ka, characterized by strong erosion, increasing tidal amplitudes and bay‐head delta development; and (iii) the period between 7·5 and 6·3 ka bp when the Rhine avulsed multiple times and the maximum flooding surface formed. The diachroneity of the transgressive surface is strongly suppressed because of a pulse of accelerated sea‐level rise at 8·45 ka bp . That event not only had a strong effect on preservation, but has circum‐oceanic stratigraphical relevance as it divides the early and middle Holocene parts of coastal successions worldwide. The palaeogeographical reconstruction offers a unique full spatial–temporal view on the coastal and fluvial dynamics of a major river mouth under brief rapid forced transgression. This reconstruction is of relevance for Holocene and ancient transgressive systems worldwide, and for next‐century natural coasts that are predicted to experience a 1 m sea‐level rise.     

The sedimentology,stratigraphy and 14C dating of a turf‐banked solifluction lobe: evidence for Holocene slope instability at Okstindan,northern Norway

The stratigraphy of a trench excavated through a solifluction lobe lying at an altitude of 860 m a.s.l. on the eastern flank of the Okstindan mountains is described. Sedimentological evidence suggests that the movement was probably dominated by a flow process, with silty sands episodically bursting‐out through a thinly vegetated lobe front in the spring and early summer thaw phases, when pore‐water pressures were likely to be increased. A continuous buried soil extends for some 14 m. Fourteen new radiocarbon age estimates from thin‐slice samples of this buried soil and organic fractions derived from laboratory pre‐treatment procedures are discussed. These data indicate that the solifluction probably commenced in the mid‐Holocene and continued throughout the Neoglacial. The slope instability may be correlated tentatively with the record of glacial variations, shifts in tree lines and archaeological evidence, supporting a link with regional climatic deterioration. Copyright © 1999 John Wiley & Sons, Ltd.     

Holocene Foraminifera as Indicators of Relative Estuarine–Lagoonal and Oceanic Influences in Estuarine Sediments of the River Murray, South Australia: Volume 53, Number 3 (2000), pages 378–391

In southeastern South Australia, the River Murray debouches through a coastal barrier separating euryhaline estuarine-lagoonal waters from the Southern Ocean. Depending upon the relative freshwater outflow of the river and ingress of the ocean, water salinity varies greatly within the lower estuary. Ammonia beccarii and Elphidium articulatum are euryhaline species of foraminifera that characterize the estuary and back-barrier Coorong Lagoon. The inner-shelf marine environment hosts an assemblage in which Discorbis dimidiatus, E. crispum, E. macelliforme, and various cibicidid species predominate. In cored sediments recovered from the shallow lower estuary, the relative abundance of A. beccarii + E. articulatum was compared with that of D. dimidiatus + E. crispum + E. macelliforme + other species. These data, and AMS radiocarbon ages determined for foraminifera and ostracods, provide evidence of a change from maximum oceanic influence (5255 ± 60 yr B.P.) to maximum estuarine influence (3605 ± 70 yr B.P.). Over this same time interval, sea level fell relatively by about 2 m. However, the event was also contemporaneous with falling water levels in several Victorian lakes, and it is thus attributed to onset of climatic aridity. Reduced precipitation in the River Murray catchment and reduced freshwater outflow enhanced development of the flood-tide delta and constriction of the mouth.     

Formal subdivision of the Holocene Series/Epoch: a Discussion Paper by a Working Group of INTIMATE (Integration of ice‐core,marine and terrestrial records) and the Subcommission on Quaternary Stratigraphy (International Commission on Stratigraphy)

This discussion paper, by a Working Group of INTIMATE (Integration of ice‐core, marine and terrestrial records) and the Subcommision on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS), considers the prospects for a formal subdivision of the Holocene Series/Epoch. Although previous attempts to subdivide the Holocene have proved inconclusive, recent developments in Quaternary stratigraphy, notably the definition of the Pleistocene–Holocene boundary and the emergence of formal subdivisions of the Pleistocene Series/Epoch, mean that it may be timely to revisit this matter. The Quaternary literature reveals a widespread but variable informal usage of a tripartite division of the Holocene (‘early’, ‘middle’ or ‘mid’, and ‘late’), and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology. We propose an Early–Middle Holocene Boundary at 8200 a BP and a Middle–Late Holocene Boundary at 4200 a BP, each of which is linked to a Global Stratotype Section and Point (GSSP). Should the proposal find a broad measure of support from the Quaternary community, a submission will be made to the International Union of Geological Sciences (IUGS), via the SQS and the ICS, for formal ratification of this subdivision of the Holocene Series/Epoch. Copyright © 2012 John Wiley & Sons, Ltd.     

Non-synchronous records of Holocene aeolian sand deposition and landscape stability at adjacent lake-side sites in the Falkland Islands,South Atlantic: a caution

Lithostratigraphical interpretation and ¹⁴C dating of adjacent lake-side sedimentary sequences at the Sulivan House lakes, West Falkland, indicate between-site non-synchronous records of Holocene aeolian sand deposition and landscape stability. It is inferred that the sands are associated with deflation of exposed sandy shorelines at times of lower lake levels, whereas stability phases are characterised by peat formation and/or organic matter incorporation into sand horizons at times of ‘normal’ lake levels. The data imply that a cautious approach to interpretation of lake-side sediments may be warranted if the purpose is to use lake-level changes and aeolian — non-aeolian interbeds as proxy indicators of regional climatic signals. © 1998 John Wiley & Sons, Ltd.     

The Holocene vegetation history of the Khibiny Mountains: implications for the post‐glacial expansion of spruce and alder on the Kola Peninsula,northwestern Russia

Pollen and peat botanical investigations of the Lutnermayok peat bog, Kola Peninsula, northwestern Russia, were carried out, and 21 surface pollen samples were studied. Combined with previous studies our data form the basis for the vegetation history over the last 7000 yr of the Khibiny Mountains. Pinus sylvestris was the dominant species between 7000 and 5000 yr BP and Picea obovata penetrated to the Khibiny Mountains ca. 5500/5300 yr BP. Since 4500 yr BP, Picea replaced Pinus in major parts of the area and dominated the forest cover. Picea immigrated to the Kola Peninsula after 7000 yr BP. There were two paths of spruce migration: from the southeast and the southwest. Grey alder, Alnusincana, immigrated to the Kola Peninsula from the southwest and northwest about ca. 8000 yr BP. Grey alder has been restricted to its modern range since 4000 yr BP. The range of vertical movement of the treeline in Khibiny Mountains during the last 700 yr was 240–260 m, which corresponds to an amplitude of summer temperature change of 2°C. Copyright © 1999 John Wiley & Sons, Ltd.     

The δ18O stratigraphy of the Hoxnian lacustrine sequence at Marks Tey,Essex, UK: implications for the climatic structure of MIS 11 in Britain

Marine Isotope Stage 11 (MIS 11) is considered one of the best analogues for the Holocene. In the UK the long lacustrine sequence at Marks Tey, Essex, spans the entirety of the Hoxnian interglacial, the British correlative of MIS 11c. We present multiproxy evidence from a new 18.5‐m core from this sequence. Lithostratigraphy, pollen stratigraphy and biomarker evidence indicate that these sediments span the pre‐, early and late temperate intervals of this interglacial as well as cold climate sediments that post‐date the Hoxnian. The δ¹⁸O signal of endogenic carbonate from this sequence produces several clear patterns that are interpreted as reflecting the climatic structure of the interglacial. As well as providing evidence for long‐term climate stability during the interglacial and a major post‐Hoxnian stadial/interstadial oscillation the δ¹⁸O signal provides strong evidence for abrupt cooling events during the interglacial itself. One of these isotopic events occurs in association with a short‐lived increase in non‐arboreal pollen (the NAP phase). The results presented here are discussed in the context of other MIS 11 records from Europe and the North Atlantic, particularly with respect to our understanding of the occurrence of abrupt climatic events in pre‐Holocene interglacials. Copyright © 2016 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.     

The stratigraphy and chronology of the fluvial sediments at Warsash,UK: implications for the Palaeolithic archaeology of the River Test

This paper reports new fieldwork at Warsash which clarifies the terrace stratigraphic framework of the Palaeolithic archaeology of the region. Sections were recorded in former gravel pits and at coastal locations, supplemented by the use of ground penetrating radar and luminescence dating techniques. The region’s extensive borehole archive was also analysed to produce a revised terrace stratigraphy at Warsash and for the Test valley as a whole. At Warsash, some of the sediments previously identified as the Mottisfont/Lower Warsash Terrace are reassigned to the Hamble, Belbin/Upper Warsash and Ganger Wood/Mallards Moor Terraces. A luminescence dating programme, using test procedures not utilised in earlier dating studies in the region, yielded age estimates for the Hamble and Mottisfont/Lower Warsash Terraces at Warsash and also highlighted the complicated nature of the fluvial sediments of the River Test, suggesting that published luminescence ages for these deposits should be treated with some caution. This study indicates that the data used to construct terrace stratigraphies also requires careful assessment. The use of bedrock height and sediment thickness data produces more coherent long profile correlations than those produced by terrace surface data alone. The revised terrace stratigraphy provides the framework for the Palaeolithic archaeology at Warsash and clarifies correlations within and between archaeologically important sediments of the Test Valley, enabling it to contribute to discussions on the Lower-Middle Pleistocene settlement history of southern Britain.     

The Pterosaur Collection at the Natural History Museum,London, UK: an Overview and List of Specimens,with Description of Recent Curatorial Developments

The pterosaur collection at the Natural History Museum is of great historical importance. Most of the material is figured or cited, and several specimens are types or casts of types. Pterosaurs from UK localities are well represented, but foreign material is also present as original specimens and as high quality casts. The entire collection has been recorded in a database and curatorial improvements have been made, which has improved physical and virtual access to the collection. Although many of the specimens were collected as long ago as the early 1800s, they are still useful today. A full list of Natural History Museum pterosaur specimens is published, for the first time since 1888.     

The role of tidal,wave and river currents in the evolution of mixed‐energy deltas: Example from the Lajas Formation (Argentina)

Many modern deltas show complex morphologies and architectures related to the interplay of river, wave and tidal currents. However, methods for extracting the signature of the individual processes from the stratigraphic architecture are poorly developed. Through an analysis of facies, palaeocurrents and stratigraphic stacking patterns in the Jurassic Lajas Formation, this paper: (i) separates the signals of wave, tide and river currents; (ii) illustrates the result of strong tidal reworking in the distal reaches of deltaic systems; and (iii) discusses the implications of this reworking for the evolution of mixed‐energy systems and their reservoir heterogeneities. The Lajas Formation, a sand‐rich, shallow‐marine, mixed‐energy deltaic system in the Neuquén Basin of Argentina, previously defined as a tide‐dominated system, presents an exceptional example of process variability at different scales. Tidal signals are predominantly located in the delta front, the subaqueous platform and the distributary channel deposits. Tidal currents vigorously reworked the delta front during transgressions, producing intensely cross‐stratified, sheet‐like, sandstone units. In the subaqueous platform, described for the first time in an ancient outcrop example, the tidal reworking was confined within subtidal channels. The intensive tidal reworking in the distal reaches of the regressive delta front could not have been predicted from knowledge of the coeval proximal reaches of the regressive delta front. The wave signals occur mainly in the shelf or shoreface deposits. The fluvial signals increase in abundance proximally but are always mixed with the other processes. The Lajas system is an unusual clean‐water (i.e. very little mud is present in the system), sand‐rich deltaic system, very different from the majority of mud‐rich, modern tide‐influenced examples. The sand‐rich character is a combination of source proximity, syndepositional tectonic activity and strong tidal‐current reworking, which produced amalgamated sandstone bodies in the delta‐front area, and a final stratigraphic record very different from the simple coarsening‐upward trends of river‐dominated and wave‐dominated delta fronts.