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J. R. L. Allen - One of the best experts on this subject based on the ideXlab platform.
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late Flandrian holocene tidal palaeochannels gwent levels severn estuary sw britain character evolution and relation to shore
Marine Geology, 2000Co-Authors: J. R. L. AllenAbstract:Abstract The exceptionally well-exposed Flandrian sediments on the Welsh shores of the Severn Estuary reveal tidal palaeochannel networks uniquely tied to vertically stacked peat–silt couplets. Field relationships show that channels multiplied and were enlarged as each peat (organogenic marsh) was rapidly transgressed, replaced by, and buried beneath silt (mineralogenic marsh). The networks infilled and shrank as the silt marsh later gave way regressively to the next peat marsh. Simulation and hydraulic models show that this cycle depended on an increase followed by a decrease in the tidal prism imposed on the marsh during a sea-level fluctuation. Coupled patterns of channel width, downstream orientation and coarseness of fill suggest that the many networks tied to the final Flandrian peat–silt couplet (Cycle III) ranged inland from a marsh-edge lying of the order of 2 km seaward from the modern coast.
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on the minimum amplitude of regional sea level fluctuations during the Flandrian
Journal of Quaternary Science, 1997Co-Authors: J. R. L. AllenAbstract:The mathematical form of a time–height sea-level curve representing intermediate-frequency fluctuations superimposed on an underlying upward trend yields a simple method for estimating the minimum amplitude of fluctuations from field measurements of the thickness of silt–peat couplets. Drawing on data from the Thames Estuary and the Fenland Basin, fluctuations of relative sea-level with minimum amplitudes between 0.08 m and 0.91 m seem to have occurred in the southeast British region during the mid-Flandrian. © 1997 John Wiley & Sons, Ltd.
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Subfossil mammalian tracks (Flandrian) in the Severn Estuary, S. W. Britain: mechanics of formation, preservation and distribution
Philosophical Transactions of the Royal Society B, 1997Co-Authors: J. R. L. AllenAbstract:Mammalian tracks and trackways are widely preserved at all stratigraphical levels in the Flandrian sediments of tidal mudflat and marsh origins which formed over the last 8000–9000 years on the marginal wetlands of the inner Bristol Channel and Severn Estuary. The fauna recorded in this way, however, is less diverse than that known from the few, small assemblages of skeletal remains, including some from archaeological sites, so far assessed. Missing or rarely represented in terms of tracks are the smaller of the large mammals. Humans are represented by tracks throughout the Flandrian deposits. In the earlier Flandrian, they were accompanied by deer and aurochs which gave way, in the later Flandrian, to domesticated cattle and sheep/goat; there are sporadic indications of the presence of horse. Wolf/dog, represented by just two records, is the only smaller large mammal so far recorded as a track. The tracks were made, modified, and eventually preserved under a wide variety of sedimentological conditions on the margins of the estuary. Those environmental conditions constrained the quality of the anatomical evidence preserved in the tracks but can be inferred from the character of the tracks. Field experiments suggest that the moisture content of the sediment at the time was crucial to the general nature of the tracks. The mudflat–marsh silts which received the tracks varied from semi–liquid to firm, depending on tidal and seasonal factors and on the elevation of the sedimentary surface relative to the tidal frame. Some tracks were made in marsh peats which offered little resistance. Deep tracks preserving little detail were produced in weak sediments of high moisture content; tracks formed in strong, firm muds retained full anatomical detail. Referring to mechanical theory, and to a series of laboratory experiments using plasticine, the act of making a track is shown to be similar in character and effect to the indentation of an ideal elastic–plastic material by a punch. The punch represents the descending limb of the animal, the face of the punch the sole of the animal's foot, and the elastic–plastic material the sediment which is pierced and deformed by the downward action of the limb. The character of the experimental tracks, and the range and relative size of the deformation structures they include, is qualitatively similar to what is recorded from the field. Many of the tracks recorded from the field were variously modified in a changeable and dynamic environment before final burial and preservation.
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the sequence of early land claims on the walland and romney marshes southern britain a preliminary hypothesis and some implications
Proceedings of the Geologists' Association, 1996Co-Authors: J. R. L. AllenAbstract:Altitudinal, stratigraphic and documentary evidence combines to suggest that the earliest artificial defence against marine flooding in the area is the structure herein called the Rumensea Wall, which strikes across the marshland from the rear of the coastal barrier (including the Dungeness foreland) apparently to the degraded cliff line at the Wealden scarp. The available evidence is interpreted to suggest that the Rumensea Wall could have been built in late pre-Conquest times, after the Lympne tidal inlet in the northeast had become closed. Approximately one-half of the marshland area was thereby at a stroke protected from marine flooding. Furthermore, the Rumensea Wall provided the springboard for a comparatively simple sequence of substantial land-claims on the salt marshes to the southwest that ranged in date into the early medieval period. The later Flandrian (Holocene) stratigraphy in this part of the marshland is variably abbreviated on account of these enclosures. For the same reason, the thick late mid-Flandrian peat which ranges beneath most of the area displays a significant, differential consolidation between enclosures, although remaining thickest near the margins of the wetland. The absolute thickness of the peat varies laterally with a number of sedimentological factors, including, in places, erosion of the top. but its degree of consolidation is largely controlled by the amount of overlying silt that could be accumulated prior to enclosure.
Honor C Prentice - One of the best experts on this subject based on the ideXlab platform.
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a late weichselian and early Flandrian pollen diagram from ostervatnet varanger peninsula ne norway
Boreas, 2008Co-Authors: Honor C PrenticeAbstract:A relative and absolute (pollen concentration) diagram is presented from Ostervatnet, southern Varanger peninsula, north of the Main sub-stage (Tromso-Lyngen) moraines. The pollen assemblage zones are correlated biostratigraphically with chronozones from Bolling to Middle Flandrian. Sediment analyses (loss on ignition and particle size) and implied sedimentation rates support this chronology. The three 14C-dates are considered too old by 1000–2000 years because of hard water error. Redeposited Tertiary palynomorphs were encountered in the lower, mineral sediments; their source is unknown. Pollen spectra and pollen deposition rates indicate tundra throughout the Late Weichselian, with Artemisia-grass steppe predominant during Older and Younger Dryas. Rapid vegetational changes began at around 10,000 B.P., followed by successive immigration and establishment of tree birch (with accompanying floristic change) and Juniperus. Ericales were conspicuously unimportant and the pollen diagram records a herb flora rich in basiphilous species
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Late Weichselian and early Flandrian vegetational history of Varanger peninsula, northeast Norway
Boreas, 2008Co-Authors: Honor C PrenticeAbstract:Relative a absolute (pollen concentration) diagrams are presented from Bergebyvatnet, Holmfjellvatnet and Stjernevatnet on Varanger peninsula. All three sites are outside the younger Dryas (Main substage) moraines and the pollen assemblage zones are correlated biostratigraphically with chronozones from Allerod to Middle Flandrian. Radiocarbon dates from Bergebyvatnet appear to have been affected by hard water error, but dates from the other two sites agree will with the inferred chronostratigraphy. Pollen diagrams from Varanger peninsula suggest broadly similar vegetational histories, the longest record beign that from Ostcrvatnet (H. C. Prentice 1981, Boreas, Vol. 10, pp. 53–70). Open tundra-like conditions prevailed throughout the Late Weichselian, with Salix dominance interrupted by unstable vegetation with abundant Artemisia during the Older and Younger Dryas zones. Major vegetational and floristic changes began just before 10,000 B.P., the rapid scquence from herb pollen flora was rich and varied, including a mixture of floristic clements similar to that found during the Late Weichselian in southern Scandinavia. Basiphilous herbs were particularly abundant at Ostervatnet and Bergebyvtnet. Betula nand and species of Ericales became locallydominant just before the full establishment of B. pubescens, which rapidly spread beyond its present limit. Later immigrants included Alnus incana; Juniperus communis; and Pinus sylvestris, which reached the south western part.
David D Kemp - One of the best experts on this subject based on the ideXlab platform.
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the late devensian and Flandrian history of the teith valley scotland
Boreas, 2008Co-Authors: D E Smith, Kenneth S R Thompson, David D KempAbstract:Two episodes of glaciation are identified in the Teith valley, central Scotland. During the earlier episode, the valley was wholly occupied by an ice sheet, but during the later episode, correlated with the Loch Lomond Readvance, ice only occupied the upper part of the valley. The deglaciation which followed each episode was marked in particular by sequences of kame and outwash terraces. A terrace related to the second episode grades into a large fan buried beneath a sequence of marine deposits in the nearby Forth valley. The latest of these, the carse clays, are related to Flandrian terraces in the Teith valley.
M P Waller - One of the best experts on this subject based on the ideXlab platform.
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Flandrian vegetational history of sout heastern england stratigraphy of the brede valley and pollen data from brede bridge
New Phytologist, 1994Co-Authors: M P Waller, A D MarlowAbstract:summary The results of palaeoecological analyses and lithostratigraphic investigations are used to reconstruct the Flandrian evolution of a valley in the East Sussex Weald, the Brede. Particular emphasis is placed upon mid-Flandrian vegetational history. Palynological data collected from one site, Brede Bridge, include detailed resolution of declines in Ulmus and Tilia pollen. Predominantly inorganic sediments were deposited in the valley during the early Flandrian. Marine conditions penetrated the lower valley under the general influence of sea level rise. After c, 6000 BP, peat formation became widespread and Alnus-dominated communities occupied the valley floor. Despite forest clearance on the adjacent slopes, relatively little sediment was deposited in the period c. 3700 to c. 1800 BP. The lower valley again came under a marine influence after c. 1800 BP. The dryland forests of the valley were, during the mid-Flandrian, dominated by Tilia. A general upward decline in Tilia pollen through the sequence is attributed to the valley floor widening and the Brede Bridge site becoming more distant from dryland areas. The first signs of human activity accompany the Ulmus decline, though major forest clearance is not evident until the Tilia decline c. 3700 BP. Comparison of the latter event with sires across south-eastern and southern England offers support for a phase of human expansion in the late Neolithic/early Bronze Age involving the preferential exploitation of areas of lime forest.
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Flandrian vegetational history of southeastern England. Pollen data from Pannel Bridge, East Sussex
New Phytologist, 1993Co-Authors: M P WallerAbstract:SUMMARY Pollen data, plant macrofossil remains and lithostratigraphy are used to reconstruct Flandrian vegetational history from a coastal site in south-eastern England. The record at this site, Pannel Bridge in East Sussex, extends back to c. 10000 BP and is the most complete so far obtained from this region. The thirteen pollen assemblages zones defined reflect, in part, the complex development of the site. Prior to c. 8500 BP, wetland in the Pannel valley was localized around the site. Between c. 8500 and c. 6000 BP, in response to changes in coastal configuration, such areas underwent expansion and the valley floor was occupied alternately by sedge fen and Alnus carr. A period of stability followed, with Alnus-dominated communities prevailing for c. 2000 yr. From c. 4000 to c. 2200 BP local conditions were more open with Cyperaceae and subsequently Myrica the dominant wetland types. Alnus carr became re-established c. 2200 BP. The vegetational history of adjacent dryland areas is obscured by the changing local conditions and nature of the deposits investigated. The problems of reconstructing past vegetation from coastal peats are explored. Amongst these are the determination of the pollen source area, establishing an environment of origin for many herb types, and distinguishing the processes controlling wetland vegetational change. The discussion focuses on the arrival and expansion of arboreal taxa in the early Flandrian and human activity. Unusually, Alnus is present in the pollen and macrofossil record from c. 10000 BP onwards. In dryland areas, after an initial Pinus, Betula phase, Corylus populations expanded c. 9500 BP, Quercus and Ulmus became woodland components from c. 9100 BP and c. 8400 BP onwards respectively. Pollen values for Tilia increased c. 7000 BP and Fraxinus c. 5900 BP though both of these taxa were probably locally present earlier. Openings in the forest canopy appear to have persisted after the arrival of the deciduous trees, possibly as a consequence of human activity during the mesolithic. There is some palynological evidence for human presence accompanying the elm decline, though substantial clearance did not occur until the decline in Tilia, c. 3700 BP. This, and a subsequent phase of disturbance c. 3200 BP, appear not to have been followed by periods of intense human activity. Woodland regeneration may have occurred c. 2000 BP.
Michael Walker - One of the best experts on this subject based on the ideXlab platform.
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holocene Flandrian vegetation change and human activity in the carneddau area of upland mid wales
1993Co-Authors: Michael WalkerAbstract:1. Five pollen diagrams from the Carneddau area of northern Powys provide evidence for vegetational change in the uplands of mid-Wales throughout the Holocene (Flandrian) and for possible human impact during the last four millennia. 2. The area formerly supported an extensive mixed woodland, but successive clearance episodes in the middle to Late Bronze Age (c. 3370 BP), at the Bronze Age/Iron Age transition (c. 2500 BP) and during the Romano-British period (1800–1900 BP) reduced this previously wooded landscape to open grassland and upland heath, with only isolated stands of birch, hazel, oak and alder. 3. Pastoralism appears to have been the principal farming type throughout both the historic and prehistoric periods. 4. These data from the Carneddau region are discussed in the context of other evidence from upland Wales for human activity during the mid and late Holocene.
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glacier response to climatic change during the loch lomond stadial and early Flandrian geomorphological and palynological evidence from the isle of skye scotland
Journal of Quaternary Science, 1992Co-Authors: Douglas I Benn, J J Lowe, Michael WalkerAbstract:The deglaciation of Skye at the close of the Loch Lomond Stadial is assessed on the basis of detailed geomorphological mapping and pollen-stratigraphic correlations. It is concluded that deglaciation proceeded in two distinct stages. The first was marked by numerous glacier stillstands and readvances, while uninterrupted retreat and local glacier stagnation occurred during the second and final stage. The pollen evidence indicates that the first stage was well advanced before the marked thermal improvement at the start of the Flandrian, and it is inferred that initial glacier retreat occurred in response to a decline in precipitation in the later part of the Loch Lomond Stadial. The first stage of glacier retreat continued into the early Flandrian, during which climatic amelioration was interrupted briefly. Final deglaciation appears to have occurred rapidly in response to sustained temperature increases. The collective evidence also indicates spatial variations in the timing of deglaciation, which appear to reflect differences in glacier morphology.