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Organic Sediment (organic + sediment)
Selected AbstractsDating methods for sediments of caves and rockshelters with examples from the Mediterranean RegionGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2001H. P. Schwarcz A wide range of potential dating methods may be applied to archaeological deposits found in caves and rockshelters, depending on the nature of the deposit and age range of the deposit. Organic sediments, including faunal and floral material, can be dated by radiocarbon (AMS and high-sensitivity beta-counting). Many karstic features contain speleothems which can be dated with high accuracy by U-series. Wind-blown detritus, where it is the dominant constituent of the cave deposits, can be dated by luminescence (TL, OSL, or IRSL), taking care to avoid material fallen into the deposits from the shelter/cave walls. Fireplaces contain burned rocks (including stone artifacts) which can be dated by TL. Enamel from the teeth of mammals is present in most sites, representing either animal residents of the shelter, or residues from food brought to the shelter by human residents. Electron spin resonance (ESR) dating of enamel is applicable over a wide time range, with high accuracy and reasonable precision where uranium accumulation in teeth is low, but with lower precision where uranium content in teeth is high. In general, multiple dating methods applied to a site may resolve ambiguities arising from uncertain model assumptions in some dating methods. © 2001 John Wiley & Sons, Inc. [source] Subantarctic flowering plants: pre-glacial survivors or post-glacial immigrants?JOURNAL OF BIOGEOGRAPHY, Issue 3 2010Nathalie Van der Putten Abstract Aim, The aim here was to assess whether the present-day assemblage of subantarctic flowering plants is the result of a rapid post-Last Glacial Maximum (LGM) colonization or whether subantarctic flowering plants survived on the islands in glacial refugia throughout the LGM. Location, The circumpolar subantarctic region, comprising six remote islands and island groups between latitudes 46° and 55° S, including South Georgia in the South Atlantic Ocean, the Prince Edward Islands, Īles Crozet, Īles Kerguelen, the Heard Island group in the South Indian Ocean and Macquarie Island in the South Pacific Ocean. Methods, Floristic affinities between the subantarctic islands were assessed by cluster analysis applied to an up-to-date dataset of the phanerogamic flora in order to test for the existence of provincialism within the subantarctic. A review of the primary literature on the palaeobotany, geology and glacial history of the subantarctic islands was carried out and supplemented with additional palaeobotanical data and new field observations from South Georgia, Īle de la Possession (Īles Crozet) and Īles Kerguelen. Results, First, a strong regionalism was observed, with different floras characterizing the islands in each of the ocean basins, and endemic species being present in the South Indian Ocean and South Pacific Ocean provinces. Second, the majority of the plant species were present at the onset of accumulation of post-glacial organic sediment and there is no evidence for the natural arrival of new immigrants during the subsequent period. Third, a review of geomorphological data suggested that the ice cover was incomplete during the LGM on the majority of the islands, and ice-free biological refugia were probably present even on the most glaciated islands. Main conclusions, Several independent lines of evidence favour the survival of a native subantarctic phanerogamic flora in local refugia during the LGM rather than a post-LGM colonization from more distant temperate landmasses in the Southern Hemisphere. [source] Recognition and palaeoclimatic implications of late Quaternary niche glaciation in eastern Lesotho,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2009Stephanie C. Mills Abstract Geomorphic evidence of former glaciation in the high Drakensberg of southern Africa has proven controversial, with conflicting glacial and non-glacial interpretations suggested for many landforms. This paper presents new geomorphological, sedimentological and micromorphological data, and glacier mass-balance modelling for a site in the Leqooa Valley, eastern Lesotho, preserving what are considered to be moraines of a former niche glacier that existed during the Last Glacial Maximum (LGM). The geomorphology and macro-sedimentology of the deposits display characteristics of both active and passive transport by glacial processes. However, micromorphological analyses indicate a more complex history of glacial deposition and subsequent reworking by mass movement processes. The application of a glacier reconstruction technique to determine whether this site could have supported a glacier indicates a reconstructed glacier equilibrium line altitude (ELA) of 3136,m a.s.l. and palaeoglacier mass balance characteristics comparable with modern analogues, reflecting viable, if marginal glaciation. Radiocarbon dates obtained from organic sediment within the moraines indicate that these are of LGM age. The reconstructed palaeoclimatic conditions during the LGM suggest that snow accumulation in the Drakensberg was significantly higher than considered by other studies, and has substantial relevance for tuning regional climate models for southern Africa during the last glacial cycle. Copyright © 2009 John Wiley & Sons, Ltd. [source] A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central FinlandBOREAS, Issue 4 2003MIA TILJANDER High-resolution physical analyses (varve thickness and relative X-ray density) were conducted on a 3000-year varved sediment sequence in Lake Korttajarvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajarvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980,1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30-year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580,1630 and AD 1650,1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c. 2800 years ago. [source] Fatty acid analyses reveal high degrees of omnivory and dietary plasticity in pond-dwelling tadpolesFRESHWATER BIOLOGY, Issue 7 2010MATT R. WHILES Summary 1.,Understanding the trophic relationships of consumers is central to ecology, but constructing meaningful food webs is often difficult because of a lack of detailed information on consumption versus assimilation and high degrees of omnivory. 2.,We used fatty acid analyses to examine the trophic relationships of three common larval anurans (Pseudacris crucifer, Lithobates catesbeianus and Lithobates clamitans) that are often classified as grazers or detritivores. Tadpoles and potential food sources were sampled in four ponds in southern Illinois and analysed for fatty acid composition. Single linkage cluster analysis was then used to compare fatty acid profiles among tadpole gut contents, tadpole muscle tissues and available food resources. 3.,Diets varied among species and within species among ponds, but organic sediments consistently contributed most to the fatty acid composition of the gut contents of all species. Fatty acid profiles also indicated that larval insects and phytoplankton were consumed by both L. catesbeianus and L. clamitans in one pond, while L. clamitans and P. crucifer consumed mainly periphyton along with sediments in another pond, and these diet differences appeared linked to physical differences among ponds, with periphyton and/or phytoplankton contributing more to tadpole diets in less shaded ponds. 4.,The fatty acid composition of muscle tissues of L. clamitans, the dominant tadpole in these systems, indicated that plant detritus and bacteria, which were the dominant components of organic sediments in the ponds, were common components of the assimilatory diet. 5.,Results demonstrate the utility of fatty acid analyses for assessing both consumption and assimilation. The tadpole assemblages we examined derive much of their energy from heterotrophic and allochthonous sources and exhibit high dietary plasticity. This information will allow for more accurate and comprehensive assessments of trophic interactions in freshwater habitats, as well as aid in amphibian conservation, management and captive propagation efforts. [source] Biostratigraphic and aminostratigraphic constraints on the age of the Middle Pleistocene glacial succession in north Norfolk, UK,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2009Richard C. Preece Abstract Considerable debate surrounds the age of the Middle Pleistocene glacial succession in East Anglia following some recent stratigraphical reinterpretations. Resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north-western Europe. The orthodox consensus that all the tills were emplaced during the Anglian (Marine Isotope Stage (MIS) 12) has recently been challenged by a view assigning each major till to a different glacial stage, before, during and after MIS 12. Between Trimingham and Sidestrand on the north Norfolk coast, datable organic sediments occur immediately below and above the glacial succession. The oldest glacial deposit (Happisburgh Till) directly overlies the ,Sidestrand Unio -bed', here defined as the Sidestrand Hall Member of the Cromer Forest-bed Formation. Dating of these sediments therefore has a bearing on the maximum age of the glacial sequence. This paper reviews the palaeobotany and describes the faunal assemblages recovered from the Sidestrand Unio -bed, which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland. There are indications from the ostracods for weakly brackish conditions. Significant differences are apparent between the Sidestrand assemblages and those from West Runton, the type site of the Cromerian Stage. These differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at Sidestrand and a much younger age. This conclusion is suggested by the higher proportion of thermophiles at Sidestrand and the occurrence of a water vole with unrooted molars (Arvicola) rather than its ancestor Mimomyssavini with rooted molars. Amino acid racemisation data also indicate that Sidestrand is significantly younger than West Runton. These data further highlight the stratigraphical complexity of the ,Cromerian Complex' and support the conventional view that the Happisburgh Till was emplaced during the Anglian rather than the recently advanced view that it dates from MIS 16. Moreover, new evidence from the Trimingham lake bed (Sidestrand Cliff Formation) above the youngest glacial outwash sediments (Briton's Lane Formation) indicates that they also accumulated during a Middle Pleistocene interglacial , probably MIS 11. All of this evidence is consistent with a short chronology placing the glacial deposits within MIS 12, rather than invoking multiple episodes of glaciation envisaged in the ,new glacial stratigraphy' during MIS 16, 12, 10 and 6. Copyright © 2009 John Wiley & Sons, Ltd. [source] Surface exposure dating of the Great Aletsch Glacier Egesen moraine system, western Swiss Alps, using the cosmogenic nuclide 10BeJOURNAL OF QUATERNARY SCIENCE, Issue 5 2004Meredith A. Kelly Abstract Egesen moraines throughout the Alps mark a glacial advance that has been correlated with the Younger Dryas cold period. Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide 10Be in rock surfaces, we attained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps. The 10Be dates range from 10,460±1100 to 9040±1020,yr ago. Three 10Be dates between 9630±810 and 9040±1020,yr ago are based upon samples from the surfaces of granite boulders. Two 10Be dates, 10,460±1100 and 9910±970,yr ago, are based upon a sample from a quartz vein at the surface of a schist boulder. In consideration of the numerous factors that can influence apparently young 10Be dates and the scatter within the data, we interpret the weighted mean of four boulder ages, 9640±430,yr (including the weighted mean of two 10Be dates of the quartz vein), as a minimum age of deposition of the moraine. All 10Be dates from the Great Aletsch Glacier Egesen moraine are consistent with radiocarbon dates of nearby bog-bottom organic sediments, which provide minimum ages of deglaciation from the moraine. The 10Be dates from boulders on the Great Aletsch Glacier Egesen moraine also are similar to 10Be dates from Egesen moraines of Vadret Lagrev Glacier on Julier Pass, in the eastern Swiss Alps. Both the morphology of the Great Aletsch Glacier Egesen moraine and the comparison with 10Be dates from the inner Vadret Lagrev Egesen moraine support the hypothesis that the climatic cooling that occurred during the Younger Dryas cold episode influenced the glacial advance that deposited the Great Aletsch Glacier Egesen moraine. Because of the large size and slow response time of Great Aletsch Glacier, we suggest that the Great Aletsch Glacier Egesen moraine was formed during the last glacial advance of the multiphased Egesen cold period, the Kromer stage, during the Preboreal chron. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||