Pleistocene deposits at Stoke Goldington, in the valley of the Great Ouse, UK
C. P. GreenG. Russell CoopeRobert L. JonesD. H. KeenD. Q. BowenA. P. CurrantDavid T. HolyoakΜ. IvanovichJ. E. M. RobinsonRobert RogersonRhea Young
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Abstract:
At Stoke Goldington in the valley of the Great Ouse in Buckinghamshire a river terrace at a height of about 7 m above the floodplain is underlain by fluvial sediments representing climatic fluctuations in the late Middle Pleistocene. Near the base of the succession, at a level only 1 m above the modern floodplain, a fossil assemblage, including pollen, plant macrofossils, molluscs, insects and ostracods, provides evidence for the local development of herb-rich grassland under temperate climatic conditions. The fossil record, amino-acid racemisation ratios and uranium disequilibrium dating all suggest deposition of this material during Oxygen Isotope Stage 7. The deposits containing the temperate assemblage are immediately overlain by typical cold-climate gravels of the Great Ouse. These have been subjected to a later cut-and-fill episode, with the fill accumulating in cool climatic conditions. The cut-and-fill episode was succeeded by aggradation, forming the overlying terrace surface. Amino-acid racemisation ratios indicate that the fill was emplaced, and the terrace surface created, during or after Oxygen Isotope Stage 5. © 1996 John Wiley & Sons, Ltd.Keywords:
Aggradation
Macrofossil
Terrace (agriculture)
Aggradation at bridges causes the bridge waterway opening to be reduced, possibly resulting in upstream flooding and increased contraction scour. Aggradation results when the sediment load supplied to a reach of river from upstream exceeds its capacity to transport sediment. Solutions to aggradational problems at bridges are often complex and expensive. Solutions include increasing sediment transport through the bridge by modifying the channel, constructing an upstream sediment trap, redesigning the bridge, dredging, and treating the cause of the aggradation. At many bridges, aggradation problems can be severe. As an example, aggradation at a bridge in northern Pennsylvania is described. The benefits, disadvantages, and costs for various possible solutions to the example problem are compared and the most cost-effective solution is presented.
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Bridge (graph theory)
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Alluvial fan
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Alluvion
Deposition
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Macrofossil
Taphonomy
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An analysis of plant macrofossils in a deposit from Gillis Lake is compared with the pollen analysis from the same deposit. The macrofossils belong to aquatic or lake-shore genera or to trees with wind-borne seeds. Zones containing a variety of macrofossils from aquatic plants and lacking those from lake-margin species in other zones are interpreted to reflect a drier climate. Of the 2 birch species represented, a larger number or exclusive presence of Betula lutea seeds suggests a milder climate, whereas a larger representation of B. papyrifera suggests cooler conditions. Using these criteria, the macrofossil record largely supports the conclusions made from the pollen analysis. The water milfoil Myriophyllum heterophyllum is identified from fossil seeds. This species is presumably extinct in the present flora of Nova Scotia.
Macrofossil
Myriophyllum
Nova scotia
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Plant macrofossils consist of reproductive and vegetative plant parts visible to the unaided eye. Lakes and peatlands are the most common repositories for the preservation of Quaternary plant macrofossils; however, natural tar seeps, calcareous nodules, spring deposits, packrat middens, and fossil dung are important sources of plant remains also. In Canada, the first plant macrofossils were collected in the mid-1800s, with a brief period of activity around 1900 before the beginning of modern Quaternary plant macrofossil analyses around 1960. Taphonomic studies indicate that plant macrofossils can be transported, sorted and redeposited long distances, which complicates paleoecological reconstructions. Plant macrofossils are valuable in geological studies of environmental history and climatic change; however, the use of plant macrofossils for biostratigraphic correlation must await further research. Four broad phytogeographic patterns are recognizable on the basis of Quaternary plant macrofossil records in Canada, and plant macrofossils can be used to trace the evolutionary origins of the modern flora.
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Taphonomy
Paleobotany
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