Environmental changes off North Iceland during the deglaciation and the Holocene: foraminifera, diatoms and stable isotopes

A combined study of foraminifera, diatoms and stable isotopes in marine sediments off North Iceland records major changes in sea surface conditions since about 15 800 cal years (yr) BP. Results are presented from two gravity cores obtained at about 400 m water depth from two separate sedimentary basins on each side of the submarine Kolbeinsey Ridge. The chronology of the sedimentary record is based partly on AMS ¹⁴C dates, partly on the Vedde and the Saksunarvatn tephra markers, as well as the historical Hekla AD 1104 tephra. During the regional deglaciation, the planktonic foraminiferal assemblages are characterised by consistently high percentages of sinistrally coiled Neogloboquadrina pachyderma. However, major environmental variability is reflected by changes in stable isotope values and diatom assemblages. Low δ¹⁸O values indicate a strong freshwater peak as well as possible brine formation by sea-ice freezing during a pre-Bølling interval (Greenland Stadial 2), corresponding to the Heinrich 1 event. The foraminifera suggest a strong concurrent influence of relatively warm and saline Atlantic water, and both the foraminifera and the diatoms suggest mixing of cold and warm water masses. Similar but weaker environmental signals are observed during the Younger Dryas (Greenland Stadial 1) around the level of the Vedde Ash. Each freshwater peak is succeeded by an interval of severe cooling both at the beginning of the Bølling–Allerød Interstadial Complex (Greenland Interstadial 1) and during the Preboreal, presumably associated with the onset of intense deep water formatiom in the Nordic Seas. The Holocene thermal optimum, between 10 200 and about 7000 cal years (yr) BP, is interrupted by a marked cooling of the surface waters around 8200 cal yr BP. This cold event is clearly expressed by a pronounced increase in the percentages of sinistrally coiled N. pachyderma, corresponding to a temperature decrease of about 3°C. A general cooling in the area is indicated after 7000–6000 cal yr BP, both by the diatom data and by the planktonic foraminiferal data. After a severe cooling around 6000 cal yr BP, the planktonic foraminiferal assemblages suggest a warmer interval between 5500 and 4500 cal yr BP. Minor temperature fluctuations are reflected both in the foraminiferal and in the diatom data in the upper part of the record, but the time resolution of the present data is not high enough to pick up details in environmental changes through the late Holocene.     

Benthic foraminiferal evidence of sediment supply changes and fluvial drainage reorganization in Holocene deposits of the Po Delta,Italy

Detailed benthic foraminiferal analyses performed on the Holocene subsurface deposits of modern Po Delta evidenced a complex palaeogeographic evolution. Hierarchical R- and Q-mode cluster analyses allowed to distinguish four assemblages indicative of different marine environments and sub-environments. Temporal and spatial distribution patterns of benthic foraminifers reflect changes in Po River discharge during delta evolution. The capability of foraminiferal assemblages to track nutrients and sediment supply oscillations permitted to recognize four main evolutionary phases (A–D), which took place after the maximum marine transgression (ca. 5500 cal yr BP).     

Holocene sedimentary history of some coastal plains in Hokkaido,Japan V. Sedimentary history of Kushu Lake and Akkeshi

Diatom assemblages of sediments obtained from Kushu Lake and Akkeshi were analyzed in order to clarify the local Holocene sedimentary history. The results revealed the following: 1) Sometime before about 9000 yr B.P., Kushu Lake was originally a freshwater environment. 2) The first marine diatom zone (MD₁ Zone) was deposited on the bottom of the paleo-Kushu Bay between 8500 and 6000 yr B.P. 3) This site changed to become the bottom of the paleo-Kushu Lagoon around 6000 yr B.P. owing to the formation of a bay-mouth bar across the paleo-Kushu Bay and the first Holocene regression resulted in a freshwater lake at about 4500 yr B.P. 4) At this time, the Akkeshi site changed from a sublittoral shore in a drowned valley to a peat moor. 5) The second Holocene transgression at about 3000 yr B.P. was detected at the Akkeshi site. 6) At Kushu Lake site the occurrence ofMastogloia elliptica between 7000 and 5000 yr B.P. suggested the influx of the Tsushima warm current into the Japan Sea.     

珠江三角洲晚第四纪环境演变的微体生物记录

珠江三角洲是主要由西江、北江和东江在珠江口湾内堆积而成的复合三角洲,自晚更新世开始形成。微体生物是珠江河口三角洲晚第四纪沉积记录中的重要组分,是重建第四纪环境变化极为有效的指标。本文样品取自PD孔岩心,钻孔位于珠江三角洲中部(113°28′35″E, 22°53′41″N),孔深16．7 m。代表约25 100年以来的沉积。PD孔中见有孔虫6属10种,其中以Ammonia beccani为优势种。根据地层分布特征,可识别3个有孔虫层位。介形类共7属9种,丰度较低,以Sinocytheridea impressa和Neomonoceratina delicata为代表,在5个层位相对富集。根据微体生物分布特征,并结合有机碳、氮以及磁化率数据,PD孔晚第四纪沉积可划分为6个沉积环境阶段。A．三角洲前缘阶段(-16．7～-13．5 m;25 100～24 000 aB．P．):岩性为粗砂、砂至砂质粉砂。主要含Ammonia属的4个种(A．beccarii、A．sp．、A．tepida、A．annectens),丰度均较低,其中Ammonia beccarii为优势种。不见适应于正常浅海的Elphidium属。介形类以滨岸类型Sinocytheridea impressa为主。出现少量双壳类。代表河口附近水深10 m以内软泥底质、受河流影响大、水体动荡的半咸水环境。有机碳含量和磁化率较低,同样指示低海平面时期的沉积。B．河口湾阶段(-13．5～-10．6 m;24 000～22 400 aB．P．):岩性为粘土质粉砂至粘土。前一阶段出现的Ammonia 4个种的丰度比较高,且出现浅海底栖分子Elphidium advenum和E．hispidulum,以及浮游有孔虫分子Globigerinoides sp．。介形类出现Bicornucythere leizhouensis、B．bisanensis、Alocopocythere goujoni、Pistocythereis bradyformis等适应水深较大的分子,而滨岸浅水分子较少。有机碳含量和磁化率相对升高。代表海平面相对较高时期的沉积。C．三角洲平原阶段(-10．6～-9．2 m;22 400～21 700 aB．P．):底部为一薄层花斑状风化粘土,表明曾短期露出水面。向上变为富含有机质的深灰色粉沙质粘土。不含微体生物和双壳类,反映不稳定的环境条件。由于海平面降低,磁化率表现为持续低值。有机碳和C/N比值很高,表明有丰富的陆源有机质输入,海洋影响较小。D．陆地风化阶段(-9．2～-7．4 m;21 700～3 700 aB．P．):岩性为1．6 m厚的杂色粘土,不含任何生物化石,有机碳含量极低,是长期强烈风化作用的产物,对应于末次冰盛期。E．潮坪沉积阶段(-7．4～-2．5 m;3 700～2 600 aB．P．):互层状深灰色粉沙质粘土、灰色粉沙和细沙,含广盐性有孔虫Ammonia beccarii和Arenoparrella asiatica,以及少量介形类,如Sinocytheridea impressa。典型的半咸水双壳类Potamocorbula amurensis较为丰富,另外还见藤壶和虫管碎片,指示盐度频繁波动的潮间带环境。F．上三角洲平原阶段(2 600 aB．P．以来):未见任何有孔虫和双壳类,顶部见少量陆相介形类Cypria yanchengensis,磁化率变化频繁,C/N比值较高,表明陆相影响不断增强,且环境条件不稳定。研究区晚第四纪古环境的演化是由海平面升降变化控制的。上述沉积环境变化序列表现出两次海进一海退旋回,分别对应阶段A至阶段D和阶段E至阶段F,相应于晚更新世和全新世的两次海平面上升事件。     

浙江钱塘江冰后期有孔虫化石记录及其古环境意义

本研究对浙江萧山SE2钻孔近50m沉积物岩心进行了详细的有孔虫定量统计分析,并结合测年资料重建了冰后期以来钱塘江沉积河谷的环境演化过程。有孔虫群落特征反映的古环境变化与沉积相分析结果一致。有孔虫资料显示:大约1万年以来该地区受到海水的影响、以胶结质壳Textularia-Reophax组合为特征,并在中全新世海水深度到达最大、以近岸浅水组合Ammonia beccarii-Elphidium magellanicum为代表,而晚全新世以来在全球海平面下降的影响下、该地区海水变浅的同时,却由于狭窄的特殊河口地形,水动力相对较强,显示强潮型河口地区特有的近岸分子Ammonia beccarii,Elphidium advenum和相对较深水分子Ammonia compressiuscula共存的底栖有孔虫群落特征。     

Palaeoenvironmental research on diatoms in early and middle Holocene deposits in central North Holland (The Netherlands)

In the geological research of the Holocene coastal deposits of The Netherlands, diatoms are used to reconstruct the sedimentary facies, palaeo-tide levels and salinity gradients during the deposition of the sediments. In this paper, the results of diatom research from 4 borings, taken from the early and middle Holocene deposits of central North Holland are presented. The oldest marine influenced sediments in the area are the deposits of the ‘Velsen layer’, a clay layer rich in organic matter and deposited about 8000–7000¹⁴C years before present (BP) at a depth of 20–12 m below present mean sea-level. This clay layer was formed in a shallow, permanently submerged environment with a limited tidal influence (lagoonal or pond-like conditions). The salinity changed from brackish/freshwater to marine/brackish. The younger sandy and clayey sediments, formed about 7000–4500 BP at a depth of 16–3 m below present mean sea-level, are classified as ‘tidal channel’ and ‘interchannel’ deposits. It is argued, on the base of both diatom and non-diatom criteria, that the lower and middle parts of the interchannel deposits in the central area of the palaeo-tidal basin of North Holland were formed in a subtidal environment. The upper part of the interchannel deposits and the deposits at the fringe of the North Holland tidal basin were formed in the intertidal zone or, at the fringe of the basin, even in the supratidal zone. The salinity in the North Holland tidal basin during the sedimentation of the tidal channel and interchannel deposits was marine/brackish to marine. This study indicates that diatoms, besides their palaeoecological applications, have chronostratigraphical significance (on a regional scale). The diatomsCymatosira belgica andActinoptychus splendens appear to be a useful (eco)stratigraphical marker in the Holocene coastal deposits of The Netherlands and Belgium.     

Holocene vegetational and coastal environmental changes from the Lago Crispim record in northeastern Pará State, eastern Amazonia

Vegetational and coastal environmental changes have been interpreted from a 600cm long and 764014C yr B.P. old sediment core from Lago Crispim located in the northeastern Pará State in northern Brazil. The radiocarbon dated sediment core was studied by multi-element geochemistry, pollen and charcoal analysis.Holocene Atlantic sea-level rise caused an elevation of local water table, which allowed the formation of organic deposits in a probably former inter-dune valley. Dense, diverse and tall Amazon rain forest, and some restinga (coastal vegetation) covered the study area at the beginning of the record at 764014C yr B.P. Mangrove vegetation developed along rivers close to the core site at that time. Subsequent decrease in less mangrove vegetation near the study site indicates a sea-level regression, beginning since around 700014C yr B.P. Lower sea-levels probably favoured the formation of a local Mauritia/Mauritiella palm swamp at 662014C yr B.P. Oscillations of higher and lower sea-level stands probably changed the size of the local palm swamp area several times between 6620 and 363014C yr B.P. Sea-level transgression at around 363014C yr B.P., caused marked coastal environmental changes: the development of mangroves near the site, the replacement of the local palm swamp by a Cyperaceae swamp, the substitution of the surrounding former Amazon rain forest and some restinga vegetation mainly by salt marshes. High amount carbonised particles suggest a strong human impact by burning on the coastal ecosystems during this late Holocene period.Highest concentrations of NaCl and also Ca, Mg and K in the upper sediment core indicate that the Atlantic was close during the late Holocene period. The core site, which is today 500m from the coastline and only 1-2m above modern sea-level, was apparently never reached by marine excursions during the Holocene.Less representation of mangrove since ca. 184014C yr B.P., may be related due to a slightly lower sea-level or to human impact in the study region. The modern shallow lake seems to be formed recently by road construction, forming an artificial dam.     

Holocene vegetation and water level history in two bogs of the Cordillera de Talamanca, Costa Rica

Pollen records of Holocene sediment cores from the Costa Rican Cordillera de Talamanca (La Chonta bog, 2310 m and La Trinidad bog, 2700 m) show the postglacial development of the montane oak forest zone from ca. 9500 to 1500 yr BP. During the early Holocene (ca. 9500–700 yr BP), alder vegetation covered the La Chonta and La Trinidad bogs and their adjacent hills. The upper forest line is inferred to be at 2800–3000 m elevation. A Podocarpus-Quercus forest characterised the middle Holocene (ca. 7000–4500 yr BP). The upper forest line is located at >3000 m reaching the present-day altitudinal distribution. A Quercus forest characterised the late Holocene (ca. 4500–1500 yr BP). Compared to modern conditions, the early Holocene has similar average temperatures, but the moisture level was probably higher. Pollen evidence for the late Holocene indicates drier environmental conditions than today. In order to improve the paleoecological interpretation, we described the local vegetation and used moss samples as pollen traps at both montane bogs along strong soil moisture gradients.The Netherlands Centre for Geo-ecological Research, ICG     

The Late Glacial–Holocene record from Central Adriatic Sea: Paleoenvironmental reconstruction based on benthic foraminiferal assemblages

New micropaleontological data coming from three cores collected on the meso-Adriatic continental shelf (Vasto area) are studied. Comparisons to foraminiferal assemblages and radiocarbon dates previously collected from cores in the San Benedetto del Tronto and Tremiti areas allow the correlation of patterns observed in shallow water areas with those in deeper parts of the basin. We focused on the response of benthic foraminifera during the Holocene high-stand, corresponding to the installation of the recent sedimentary and trophic system. An influence of anthropogenic impacts cannot be ruled out; its effects consist of a depletion of oxygen level with a consequent modification of the structure of benthic foraminiferal assemblages. During the glacial/post glacial cycle, three phases, characterized by a total of six foraminiferal biofacies including different species assemblages were recognized. The first phase, from 14 kyr BP to 11 kyr BP, corresponds to the Bölling/Alleröd and Younger Dryas cold event, before the Holocene sea-level rise. During this phase, the continental shelf was characterized by an infralittoral environment with productive waters owing to the proximity of the Po river delta at the edge of the Mid-Adriatic Deep. The second phase, from 11 kyr BP to 4 kyr BP, represents the Holocene sea-level rise and is characterized by a condensed sedimentation spread over the entire basin. The third phase corresponds to the Holocene high-stand, during which time the modern current system became established. During this phase, the eastern portion of the shelf underwent to the central part of the mud-belt, corresponding to the sub-recent conditions. Recent eutrophication resulting from human activities over the last few centuries is evidenced by frequency fluctuations of typically opportunistic taxa such as Nonionella turgida and Epistominella vitrea.     

The influence of climate and sea-level change on the Holocene evolution of a Mediterranean coastal lagoon: Evidence from ostracod palaeoecology and geochemistry

Coastal lagoons provide an excellent basis for the study of processes controlling the evolution of a coastal zone. We examine the relative importance of these processes during the middle to late Holocene through a study of an 8.5 meter-long sediment record from the Albufera de Valencia (Spain). We combine sedimentological analyses with investigations into the palaeoecology, taphonomy and geochemistry (Mg/Ca, Sr/Ca, δ¹⁸O and δ¹³C) of ostracod valves in order to assess the effects of sea-level changes, storm events and effective moisture on the evolution of a Western Mediterranean coastal wetland. The late Pleistocene sediments represent a subaerial environment, which was followed by a hiatus in deposition. The first Holocene unit (～8700–7500 calendar yr. BP) is composed of typical lagoon-barrier and backshore sediments, deposited when seawater intruded into the lake and the climate was arid. The upper part of the sequence (between 7500 and 3400 yr.) is characterized by two sedimentary units, which correspond to Holocene progradation phases and humid climate associated with an increased freshwater influx to the lake accompanied by several high-energy events (palaeostorms). Overall, the record shows that an arid climate prevailed in the western Mediterranean area between 8400 and 7600 yr. The main marine transgression and accompanying progradational phases occurred between 7000 and 3400 yr., which is confirmed by other studies of coastal evolution along the Mediterranean coast. The multiproxy reconstructions demonstrate that controls on sedimentation and palaeoecology in this Mediterranean coastal lagoon were complex.     

The Quaternary eolian sequence of Madeira: stratigraphy, chronology, and paleoenvironmental interpretation

A thick (ca. 40 m) sequence of coastal eolian sediments occurs on a narrow peninsula on the eastern end of the island of Madeira, located in the Eastern Atlantic at 33°N latitude. The sediments consist of black volcanic sands (with or without bioclasts) as well as clay units up to 2 m thick. A series of inceptisols (Eutrochrepts) and one alfisol (a Hapludalf) are developed in these sediments. Land snail shells and secondary carbonates, in the form of well-developed rhizoliths, calcretes, fissure-fills, and soil nodules, are present in abundance. The chronology of the sequence was determined by ¹⁴C and U---Th analyses of land snail shells and secondary carbonates and amino acid epimerization analysis of land snail shells. All sediments, including the clay units, are originally of eolian origin, derived from the beach to the south of the deposit, but some have been redeposited by colluviation. Temporal variation in the lithology of the sediments relates to variations in sea-level, with black sands being deposited during lower sea level stands and clays at the lowest. It is suggested that fine marine sediments, exposed during low sea-level stands, may also be the dominant source of silty or clayey units in other coastal eolian deposits in the subtropical Atlantic and Mediterranean.

The sequence spans from 200,000–300,000 years ago up to the 20th century. Sedimentation was discontinuous and often rapid; erosional hiatuses are present. During the Holocene, eolian sands started accumulating at 8200 yr B.P. during a transgressive phase and stopped at 4500 yr B.P. as sea level approached its present height. Colluviation increased dramatically following the first human settlement of the island in the 15th century and continued up to the 20th century, as dated by amino acid epimerization analysis of land snails. Earlier periods of colluviation were identified from the age distribution of land snail shells redeposited in younger colluvium.

Paleoenvironmental reconstruction was based mainly on soil and sediment features (including rhizolith morphology) and land snail faunas but also on stable isotope variations (¹³C, ¹⁸O) in land snails and secondary carbonates, pollen (generally not well preserved), and phytoliths. Most of the portion of the Middle Pleistocene represented in the sequence was characterized by moderately dry conditions, in comparison to the late Pleistocene and Holocene. During the last interglacial, relatively wet conditions occurred, wetter than during the Holocene interglacial. Moderately moist conditions were present during the accumulation of the thick unit dating to ca. 80,000 yr B.P. As sea level fell subsequent to this period, conditions appear to have become drier. Starting ca. 50,000–55,000 yr B.P., conditions were especially wet, but prior to the last glacial maximum, markedly arid conditions ensued. Toward the end of the last glacial, wet conditions returned and produced the best-developed soil preserved in the sequence. Moderately moist conditions occurred during the early to middle Holocene but apparently become slightly drier after 4500 yr B.P. The impact of human settlement can be seen in the loss of woody vegetation and enhanced gullying and colluviation during the last ca. 500 years.     

Foraminifera in a New Zealand salt marsh and their suitability as sea-level indicators

Vertical distributions of live and dead foraminiferal abundances are investigated in a salt marsh at Pounawea in southeastern New Zealand for potential use in Holocene sea-level reconstructions. Statistical analyses are conducted to determine whether dead foraminiferal abundances can be utilised as a proxy for elevation in southeastern New Zealand. It is concluded that dead salt-marsh foraminifera, which can predict elevations to within ± 5 cm or better, are precise sea-level proxies. Holocene sea-level reconstructions along the tectonically stable Catlins Coast based on fossil salt-marsh foraminifera can therefore serve as a potential baseline tool to estimate relative vertical tectonic displacement along tectonically active coasts in New Zealand.     

A multiproxy approach to inferring Holocene paleobotanical changes linked to sea-level variation,paleosalinity levels,and shallow lake alternative states in Negra Lagoon,SE Uruguay

A multiproxy analysis of diatoms, chrysophyte cysts, opal phytoliths, and palynomorphs was undertaken in Negra Lagoon, to decipher Holocene changes in paleobotanical proxies associated with sea-level changes and paleolimnological conditions. Before the Holocene transgression (7000 yr BP), a terrestrial system was inferred as no aquatic palynomorphs or biogenic silica remains were recorded. During the sea-level maximum (5200 yr BP), marine/brackish conditions were established as indicated by diatoms, Chenopodiaceae, and a high content of cysts of Peridinioideae. The catchment consisted of grasslands and wetlands as indicated by the opal phytolith data. The Holocene transgression was followed by a sea-level decrease, which led to the onset of brackish/freshwater conditions as inferred from the co-dominance of freshwater and marine/brackish diatoms. This is also supported not only by the concomitant increase in non-siliceous freshwater microalgae and emergent macrophytes, but also by the presence of Myriophyllum. As sea level continued to decrease during late Holocene, a freshwater system was observed because of the complete separation from the ocean. Chrysophyte cysts were consistently recorded and brackish diatoms exhibited reduced abundances. The observed limnological changes are consistent with the alternative states hypothesis of Scheffer’s model (1998). That is, the clear water phases were explained because of high macrophyte abundances, low phytoplankton frequencies, high cyst to diatom ratios, and increase in frequencies of benthic diatom species. Conversely, turbid phases were likely to occur when low cyst to diatom ratios together with increase in planktonic diatoms and decrease in macrophytes values were detected. This highlights the importance of this approach to detect long-term changes in shallow lake alternative states.     

Evolution of the sebkha Dreîaa (South-Eastern Tunisia,Gulf of Gabes) during the Late Holocene: Response of ostracod assemblages

The quantitative and qualitative study of the ostracod assemblages supported by the correspondence analysis (CA) allowed the reconstruction of the palaeoenvironnemental change during the Holocene in the sebkha Dreîaa of Skhira (Gulf of Gabes, SE Tunisia). Five phases were distinguished: the first phase (> cal. 6471–6874 yr BP) coincides with the first Holocene marine transgression following the deposition of the continental Holocene series. It induces the setting of an open lagoon where numerous Bivalvia, Gastropoda and marine ostracods lived. The second one (cal. 6471–6874 yr BP) is characterized by the development of brackish ostracods, high diversity index values and comparable percentages of the brackish, lagoonal and coastal assemblages. It corresponds to an open lagoon subjected to estuarine influences. During the third phase (cal. 3350–3752 yr BP), a marine environment, marked by the enrichment of marine ostracods, is evolving toward the closing. The settlement of the restricted lagoonal environments is linked to the building-up of sandy spit. At cal. 2839–3057 yr BP, the dominance of coastal ostracods, associated with coarse sands, show an open lagoon and probably a marine transgression evidenced by the progressive modification in the ostracods assemblages. After this transgression, the southern part of Sebkha of Dreîaa emerged and evolved towards the present state. The last phase, cal. 515–777 yr BP, is marked by a strong marine influence, in the northern part of the sebkha, with transport of marine Bivalvia, Gastropoda and ostracods towards the inner lagoon by means of storms. The rupture of sandy spits induced the introduction of marine macrofauna and microfauna which were accumulated and associated with charcoals and coarse sands.     

Palynofacies Analysis of Inner Continental Shelf and Middle Slope Sediments offshore Egypt, South-eastern Mediterranean

Marine palynological studies of Quaternary sediments usually focus on dinoflagellate and pollen assemblages for paleoceanographic and paleohydrographic interpretations of past events. This paper focuses on the use of palynofacies analysis for paleohydrological reconstructions of deltaic and deep sea environments to evaluate transport of organic matter to the ocean. These palynodebris data are used to interpret palaeoenvironmental and paleohydrographic changes in two marine cores from the continental shelf (core-1, 27 m water depth) and middle slope (core-2, 1030 m) offshore Egypt, south-eastern Mediterranean Sea, during the latest Pleistocene and the Holocene. The relative abundances of various types of sedimentary organic matter such as phytoclasts, zooclasts, amorphous organic matter and palynomorphs are related to paleohydrographic changes of the overlying water column. Based on the total palynodebris and organic carbon content, sediments of the inner continental shelf core are characteristic of a prodelta environment proximal to a fluvio-deltaic source and moderately distal oxic environments with enhanced structured organic matter preservation potential. In contrast, the palynodebris of the middle slope core show that the basal sediments (105-140 cm depth) indicate suboxic to dysoxic bottom water conditions, followed by anoxic-suboxic bottom water conditions for the interval from 30-85 cm, which represents the S1 Sapropel. The top sediments of core-2 (0-25 cm) were deposited under oxic bottom water conditions, suggesting good ventilation in the water column. A quantitative approach was also used for interpreting the Holocene sea-level changes, based on the correlation between phytoclast and organic matter abundances. Sedimentation rate in the continental shelf is varied, being relatively very low (6.7 cm/kyr) in the basal part and increased upward to be 20 cm/kyr (depth 115-120 cm). In the upper Gray clayey silt layer the sedimentation rate was high (about 40-45 cm/kyr) due to the high discharge from El Manzala Lagoon and Damietta Nile branch. In the middle slope depth the sedimentation rate was relatively low and uniform, around 14 cm/kyr.     

Changing distribution of late Quaternary terrestrial lacustrine and littoral environments in the Vestfold Hills,Antarctica

Relict marine terraces and associated boulder pavements allow the mapping of coastal environments in the Vestfold Hills and adjacent islands approximately 6000 a B.P. These structures are best developed in what were restricted tidal waters and are ascribed to sea-ice dynamics. The retreat of glacier ice, the subsequent flooding of many areas by sea water and the drainage of most of these as isostatic uplift raised the Vestfold Hills in the Holocene, have produced an immense variety of lacustrine environments as well as a diverse marine littoral. Glacial advance and retreat have occurred in the mid-late Holocene and is particularly evident adjacent to the Sørsdal Glacier.     

Palaeoenvironmental interpretation of microphytoplankton diversity trends in the Cambrian–Ordovician of the northern Sahara Platform

Analysis of vertical fluctuations in assemblage diversity and relative abundances of microphytoplankton morphological classes permits palaeoenvironmental reconstructions of the Cambrian–Ordovician stratal sequences in the Hassi-R'Mel area (north-central Algeria) and northern Rhadames Basin (southern Tunisia). Abundance fluctuations of acritarch morphological classes and assemblage diversity appear to be related to changes in depositional facies. The present palaeoenvironmental interpretation is primarily based on a comparison with microphytoplankton distributional trends in modern depositional environments. Where possible, the observations are tested against palaeoenvironmental information derived independently from previous lithostratigraphical, macropalaeontological, and petrographical studies of the formations investigated. The present data support the following palaeoenvironmental scenario: during Late Cambrian times, relatively shallow water, neritic conditions prevailed throughout the study area, with evidence for a more proximal environment in southern Tunisia. In the early Tremadoc, open marine, offshore conditions characterized the central Algerian region, but a shallower water setting is indicated for southern Tunisia. During the late Arenig–Llanvirn interval, an open marine, offshore setting is envisaged for the southern Tunisian region, with more proximal conditions prevailing in the Algerian Hassi-R'Mel area. During the entire Ashgill, an essentially restricted marine environment was established throughout the study area. Some stratigraphically important acritarch species (e.g. Acanthodiacrodium angustum) appear to be facies-sensitive; the recognition of palaeoecological control on microphytoplankton distribution has important consequences on the biostratigraphic application of these microfossils.     

Non-pollen palynomorphs in the Black Sea corridor

There have been few studies of non-pollen palynomorphs (NPP) in Holocene brackish water environments. The Black Sea is one of the world’s largest and deepest bodies of stable brackish water and a natural laboratory for study of marine carbon cycling to anoxic sediments. The main NPP in the modern sediments of this brackish water sea are dinoflagellate cysts (dinocysts), acritarchs (mainly the prasinophytes Cymatiosphaera, Micrhystridium, Sigmopollis and Pseudoschizaea) and diverse fungal remains. Other NPP include colonial algae, tintinnids, copepod and cladoceran egg covers, testate amoebae and microforaminiferal linings. These NPP assemblages are similar to those in the marginal marine environment of the Pliocene St. Erth Beds (England), but have more abundant NPP, and virtually lack scolecodonts. In the Black Sea corridor, modern assemblages from areas with salinity >22‰ have higher percentages of microforaminiferal linings and fewer prasinophytes, colonial algae and fungal spores. Prasinophytes dominate only in mid-Holocene sediments, during a 2000 years interval of sea level transgression and sapropel deposition. Early Holocene sediments have lower dinocyst diversity, increased fresh–brackish water colonial algae (Pediastrum spp. and Botryococcus braunii), zygnemataceous spores and desmids (including Zygnema, Cosmarium), ostracod linings and fewer foraminiferal linings. These assemblages are similar to those in the Baltic Sea where the annual salinity is about 6–8‰.     

The upper Quaternary sedimentary sequence at the Rieti Basin (central Italy): a record of sedimentation response to climatic changes

Lithostratigraphy, chronology and depositional environments of sixteen Holocene alluvial fill sediment cores from the southern part of the Conca of Rieti (central Italy) was established by sedimentological, palaeontological and ¹⁴C analyses. The study area experienced a lacustrine (or palustrine) conditions and the water level was effectively controlled by a natural damming of the valley due to intermitted travertine deposition at Le Marmore site. Apart from cores S10, S13, S14 and S8 which, at their bottom, cored sediments referable to ?Upper Pliocene and Middle Pleistocene which are not the object of this paper, as a rule the drilled sediments can be referred, bottom to top, to the following four episodes: interval a, corresponding to freshwater lacustrine/palustrine environment affected by alluvial fan progradations from the edges of the valley and active by ?Middle/?Late Pleistocene to early Holocene; in this interval, several hiatuses are supposed but are not evidenced by the bad state of preservation of the sediment cores; interval b, from 361 to 371–376 m a.s.l., recording a decrease of the water level, bracketed between the ¹⁴C ages of 6000 and 2700 yr B.P., which produced the formation of distinct shallow ponds/bogs, rich in aquatic vegetation; interval c, from 381 to 384 m a.s.l., indicating a further rise of the water level, recorded by sediments containing abundant molluscs and ostracods; interval d, the upper part of the cores, records an almost continuous drying up the area as shown by abundant hydrophilic land molluscs; and interval e, the top of all sediment cores, representing the present-day soil. It has been found that the water level fluctuations occurring in the ancient Conca are chronologically consistent with the postglacial climate pattern. It is further noticed that the episodes of water highstand correspond to the Boreal–Atlantic and Subatlantic climatic ameliorations, respectively, and that the water level dropped during the global cooling episodes recurred from ca. 6000 to 2100 yr B.P. The resulting palaeoenvironmental history agrees with that previously reported for the northern reach of the Conca of Rieti, thus suggesting a common setting for the whole area.     

Estudio paleoecológico de Foraminíferos de testigos del Holoceno de Golfo Nuevo (Patagonia, Argentina)

A micropaleontological study (Order Foraminiferida) was conducted on two Holocene cores from Golfo Nuevo (Patagonia, Argentina). The most abundant species are Buccellaperuviana f. campsi (Boltovskoy) and Bulimina patagonica (d’Orbigny), suggesting an inner-shelf environment. Qualitative and quantitative analyses indicate the paleoecological and paleoenvironmental variations along cores. A transition from normal marine conditions of the inner shelf during the Middle Holocene (ca. 8160-7700 years B.P.) to marginal marine conditions in the Late Holocene (ca. 1890 years B.P.) is inferred. This transition was accompanied by lower oxygen levels than the current values in Golfo Nuevo. These variations may have been due to an increase in precipitation near the study zone and a rise in sea level caused by an improvement in the climatic conditions related to the Climate Optimum (ca. 7000 years B.P.). These new conditions of higher temperature and lower salinity of the surface waters may have hindered deep-water renewal, producing a change in the circulation dynamics of the gulf and causing a reducing environment.