Holocene fossil Habrotrocha angusticollis (Bdelloidea: Rotifera) in North America

Holocene fossil shells of the rotifer, Habrotrocha angusticollus (Bdelloidea: Rotifera) is reported from two peatlands in northern Ontario, Canada. H. angusticollis is a common component of the microfauna in Sphagnum peatlands and other wet mossy habitats. Our knowledge of the distribution and ecology of H. angusticollis is limited and this paper is the first detailed report of the shells as fossils in North America. Fossil shells of H. angusticollis may prove to be a valuable paleoecological indicator in peat deposits once Quaternary paleoecologists learn to recognize them and neoecologists extend their surveys to peatlands.     

Late Quaternary deglaciation and climate history of the Larsemann Hills (East Antarctica)

The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice‐covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedimentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene climate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold conditions are inferred from high lake‐water salinities, and low water levels and an extended duration of nearshore sea‐ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stratified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea‐ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea‐ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice‐core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long‐term climate change on the terrestrial environment. Copyright © 2004 John Wiley & Sons, Ltd.     

Stratigraphic sequence, elemental concentrations and heavy metal pollution in Holocene sediments from the Tinto-Odiel Estuary, southwestern Spain

 The Holocene filling of the Tinto-Odiel Estuary comprises seven lithofacies over a Mio-Pliocene substrate. The sequence includes three system tracts: lowstand system (10 000 to 8700 years BP), transgressive system (8700 to 7000 years BP), and regressive system (7000 to Recent). Twenty sediment samples from the 50-m borehole were analyzed for their major components and minor element concentrations. Two multivariate analysis methods, principal component analysis and cluster analysis, were performed in the analytical data set to help visualize the sample clusters and the element associations. Samples corresponding to unpolluted, pre-mining sediments are clearly separated by cluster analysis, mainly as a result of the low content in sulphide-associated heavy metals such as Cu, Zn, As, Ag, and Pb. So, these sediments may be utilized as a background for geochemical analysis (bulk sample) in other adjacent estuaries, both in sandy and silty-clayey sediments. As a consequence of large-scale mining and smelting operations occurred since prehistoric times on the river banks, a rapid rise in the metal pollution was found in the upper 2.5 m of the natural filling, with values exceeding up to ten times the natural background levels. In addition, since the mid-1960s, large amounts of waste and pollutant effluents have been discharged from industries located around the estuary, increasing the heavy metal content in the last 0.3 m of the natural sedimentation. Received: 18 August 1997 · Accepted: 19 January 1998     

Holocene vegetation history of Bundjalung National Park and Bungawalbin Creek,north‐eastern New South Wales

Few studies have been conducted into the environmental history of the North Coast region of New South Wales (NSW). To address this, two sedimentary sequences located in the coastal Bundjalung National Park and at Bungawalbin Creek, just north of the Park (both near Evans Head, NSW) have been investigated. Palynological and geochemical analyses were used to reconstruct the history of the sites. Fossil pollen evidence representing much of the Holocene period — basal radiocarbon dates of 8700 ± 60 years BP and 6600 ± 60 years BP are available from the Bundjalung National Park and Bungawalbin Creek sites, respectively — indicates a dynamic past environment, with an overall tendency towards drier conditions. This evidence is supported, in part, by charcoal analyses indicating an increase in the occurrence of fire over time. Chemical analyses of the sediments indicate that the Bungawalbin site was strongly influenced by estuarine conditions, whereas the Bundjalung National Park site was only influenced indirectly by estuarine conditions.     

Geomorphology and late Holocene climatic change in Northeastern Spain

During the late Holocene, accumulation and downcutting stages affected the slopes and infilled valleys in the semiarid areas in NE Spain. The presence of archaeological remains, charcoal and ashes within slope deposits and valley fills makes it possible to carry out accurate datings. In the case of infilled valleys, the different accumulations may be diachronous at a regional level. These diachronisms among different infilled valleys may be caused by both human activity and complex responses of the system. On the slopes, one can distinguish between two accumulation periods separated by an incision period. The older accumulation stage has a widespread distribution and developed from the Bronze Age to the Iberian–Roman Epoch. The following accumulation period was formed in the Post-Medieval period and is spatially more restricted. Because of the widespread synchronism shown by these accumulations, a climatic cause is put forward as the possible triggering factor for the accumulation–incision stages in the slopes. The datings obtained indicate that the first accumulation corresponds to the Iron Age Cold Epoch (900–300 years B.C.) and the second to the Little Ice Age. Between both accumulation periods, a downcutting stage took place (approximately from 300 B.C. to 1450 A.D.). This downcutting interval can be related to the warm stages of the Subatlantic Period, during which there was a relatively lower percentage of vegetation cover. Finally, the last incision period, which is still taking place, has affected previous accumulations.     

The dune systems of the Konya Plain (Turkey): their relation to environmental changes in Central Anatolia during the Late Pleistocene and Holocene

Several sand flats located on the northern shores of the Late Pleistocene palaeolake of the Konya plain (inner Anatolia, Turkey), are related to changes in lake levels. In this paper, the two main dune systems are mapped according to their geomorphological, sedimentological and dynamic characteristics, and their significance is discussed with regard to the environmental changes since the Late Pleistocene, both at time of the former lake and during the drier periods of the Holocene. Cross-sections show the relationship of the dunes to the topography of the basement. Analyses of the sand fraction show distinct characteristics in size distribution, quartz and shell contents, wind erosion effects on the quartz grains and petrographic composition. Interpretation of the results, coupled with information provided by the geomorphology of the dune systems studied in the field and from aerial photographs and satellite images, highlights the importance and variations in time of local factors such as prevailing winds, sand sources, changes in lake levels and vegetation. A chronology of the main sand fields is proposed, based on the evidence of three main droughts during the Upper Pleistocene. The older one, much eroded (maximum height=3 m), covers a limestone surface at +50 m above the bottom of the dried lake. An Optical Scanning Luminescence (OSL) date shows a last period of accumulation at 14,328±3220 years. The younger one (maximum height=12 m) has moved over the emerged Late Pleistocene lacustrine marls. An OSL date gives an age of 5674±988 years for the last accumulation period. Evidence of very recent activation of this younger dune system is apparent as a result of overgrazing and excessive land reclamation. A third period of dominant wind action and dune construction is responsible for the installation of a younger and thin dune field over the Mid-Holocene lacustrine deposits of the Karapinar lake. The success of the stabilization programme of the dunes over the last 30 years shows that the last period of dune movement is not related to climate change but to overpressure on the land due to the needs and activities of an increasing population.     

A palaeolimnological study of Tugulnuit Lake, British Columbia, Canada, with special emphasis on river influence as recorded by chironomids in the lake's sediment

Sediments from Tugulnuit Lake in the Okanagan Valley of British Columbia, Canada, were examined for chironomid assemblages. The chironomid stratigraphy obtained encompasses the last 4000 to 5000 years and suggests a warm and fairly stable climate typical for a temperate lake at low- to mid-elevation. This is indicated by the even distribution of warm-water taxa, such as Cladopelma, Dicrotendipes, Polypedilum, Pentaneurini, Stempellina, Stempellinella/Zavrelia and Pseudochironomus throughout the core. Very few cold-water taxa occurred in the sediments. However, stream inputs have had a major impact on Tugulnuit Lake. Sandy sediments and the appearance of Simuliidae and stream-inhabiting chironomid taxa (e.g., Brillia/Euryhapsis, Eukiefferiella/Tvetenia, Rheocricotopus) indicate that a stream intruded into the current lake's basin ca. 3800 yr Before Present (BP). Sediments deposited prior to, and after, the stream's intrusion show a distinctly different chironomid assemblage exhibiting chironomid taxa more typical for lentic habitats. This result indicates that chironomids can serve to detect past stream influences on lake environments. Thus, rheophilic chironomids preserved in lake cores provide a new alternative for reconstructing stream palaeoenvironmental records.     

A high-resolution Holocene ostracod record from the Sahel zone of Northeastern Nigeria

The ostracod record from Kajemarum Oasis in the Sahel zone of Northeastern Nigeria covers the last c. 4000 cal. years of a 5500 cal. year lake-sediment sequence. The first appearance of ostracods, around 4000 cal. yr BP, reflects the switch from a very dilute lake during the mid-Holocene, to slightly oligosaline conditions that favoured the occurrence and preservation of ostracods. Between 3800 and 3100 cal. yr BP, the lake remained permanent and fresh or slightly oligosaline, with a Ca-Mg-HCO3 composition. A rise in salinity c. 3100 cal. yr BP, accompanied by a change to more variable conditions on a seasonal to interannual timescale, led to the influx of more-euryhaline taxa. Oligosaline conditions continued between 3100 and 1500 cal. yr BP. Around 1500 cal. yr BP, there was a sharp rise in salinity, probably accompanied by a shift to Na-CO3-type water, with marked seasonal and interannual variability. Salinity decreased after 900 cal. yr BP, although short-term variations were marked between 900 cal. yr BP and the top of the sequence, 95 cal. yr BP. Changes in the species assemblages and ostracod abundance were a response to climate-driven variations in the seasonal and interannual stability of the lake, together with changes in its salinity and solute composition, but there is no simple relationship between ostracod faunas and salinity. Within Kajemarum, there is no evidence of ostracod assemblages typical of deep, fresh water, nor of hypersaline Na-Cl waters. The sediments associated with the freshest waters at Kajemarum did not favour ostracod preservation, and the driest climatic conditions were associated with oligosaline to mesosaline water of Na-CO3-type. The species-poor assemblages reflect the short-term instability of the lake, coupled with the limited opportunities for the colonisation of this isolated basin.     

海滩岩在连云港的发现

作者在江苏连云港海滨首次发现的全新世海滩岩。经岩石样品及簿片、扫描电镜、＾１４Ｃ同位素等分析测定,海滩岩主要由陆源碎屑和生物碎屑组成,胶结物为文石和高镁方解石。该地海滩岩主要形成于全新世早期,当时气温高于现在８￣１０℃,据此对连云港市全新世早期古气候、水动力条件、海岸线的发展变化及古地理环境等作了初步探讨。     

内蒙古中西部地区全新世大暖期气候与环境初步研究

以大青山调角海子剖面的孢粉和地球化学分析资料为依据,结合邻区古土壤序列,湖泊演化及考古研究资料,阐明内蒙古中西部地区全新世气候最适宜期始于９２５０ａＢ．Ｐ．左右,结束于４０００ａ,Ｂ．Ｐ．前后,６３３０ａＢ．Ｐ．前后出现大暖期植被与气候变化的重要转折;