No description available.

No description available.

No description available.

No description available.

No description available.

The concern of the investigation described in this thesis has been to examine certain drift deposits in southern Wiltshire and to consider their distribution in relation to the accepted interpretation of the landscape. The area examined has been discussed by Wooldridge and Linton (1955) but lies on the periphery of the tract with which they deal, and their treatment is essentially theoretical and not circumstantial. In the course of the investigations which are described, samples were collected from over two hundred sites, surface indications of the geology were examined at a substantially larger number of sites and more than thirty sections were specially excavated in particularly interesting locations. The work is based not on the application of refined geological techniques but on the ability to distinguish, in hand specimens, common and distinctive rocks. In important sections, samples of gravel of from 6 lbs to 2O lbs weight were secured and broken down into three fractions (¹⁄₁₆"-⁵⁄₃₂"; ⁵⁄₃₂"-¹⁄₂"; ¹⁄₂" upwards); for correlative purposes exact counts of the component materials were carried out for the two coarser fractions. Although some of the individual examples encountered are problematic the conclusions have invariably been based on a significant volume of unmistakable material. The use of refined correlative techniques to confirm the results has not been attempted. This omission to some extent reflects the nature of the investigation, which is best regarded as a reconnaissance of a large area, describing evidence not only in Wiltshire but on the Chalk and Eocene outcrops elsewhere in We ss ex, for the most part on ground lying to the West of the Salisbury Avon. The results of the work are described in a comparative study of landscape features using, so far as possible, the whole geographical context of the ground examined: the dissection and weathering of the surface, the drifts and soils which rest upon it, and the relation of the ground to relief both above and below it. In Part One of the thesis an attempt is made to establish the nature of the sub-Eocene unconformity. A study of the Pleistocene river gravels about Salisbury suggests that Eocene formations may have been preserved on the western part of Salisbury Plain at the beginning of the Pleistocene period. This result is inconsistent with the views adopted by Wooldridge and Linton. The composition of the gravels examined suggests that the Eocene formations in question did not resemble formations now recognised in the main Eocene outcrops adjoining Salisbury Plain. A study of the Palaeogene outlier on Salisbury Plain, at Clay Pit Hill, shows the gravels in the outlier to be closely similar in terms of petrology to the distinctive gravels in the Bagshot Beds about Dorchester in Dorset, and a correlation with these beds is suggested. A distinctive gravel from another Palaeogene outlier, at Cley Hill, near Warrninster, is described. This gravel at a height of about 800' O.D. appears to be preserved at or near the level of its original deposition, and is tentatively referred to the Oligocene period. The evidence at Cley Hill and Clay Pit Hill is taken to show that the Chalk suffered extensive erosion during the Eocene and Oligocene periods. A study of sites on the ground intervening between the Palaeogene outliers on Salisbury Plain and the Bagshot outcrop in Dorset provides new evidence on the nature of the Reading Beds, which tends to confirm the results of the investigations on Salisbury Plain. In Part Two of the thesis drifts on the mid- Tertiary surface of Wooldridge and Linton (1955) are described. Drifts on the Upper Greensand outcrop in the Vales of Wardour and Warminster are believed to be of periglacial origin and Pleistocene age. Drift on the Portland outcrop in the Vale of Wardour appears to be the debris of Lower Cretaceous formations and probably rests on an intra-Cretaceous surface. On the Chalk a contrast is discerned between ground occupied by deep very flinty drifts of residual aspect and ground occupied by shallower flint drifts, also of residual aspect. The shallow drifts are shown to be associated with the relics of gravels incorporating Upper Greensand, Lower Cretaceous and Jurassic debris. The deep very flinty drifts are believed to confirm the views of Wooldridge and Linton concerning the mid-Tertiary surface, but the shallower drifts and associated gravels are thought to rest on a separate surface, and the Cretaceous and Jurassic debris is believed to imply the competence of transverse gradients during the dissection of the mid-Tertiary surface. The evidence described in Part Two of the thesis is difficult to reconcile with the concept of marine transgression across the Wiltshire Chalk. In Part Three of the thesis drifts on the supposed marine plain are described and the marine origin of the surface is rejected. Specific evidence of a 'Pliocene' transgression in Wessex is reviewed and a study of supposed 'Pliocene' material refers the material in question to the Eocene period. Problematic aspects of Pliocene stratigraphy and the concept of superimposition from a Pliocene surface are reviewed. Pinchemel's objections (1954) to a depositional surface are accepted but his views on fluvial aggradation are rejected in a study of gravel at Alderbury, near Salisbury, referred by him to this aggradation. Difficulties inherent in the concept of marine planation are recognised and ground referred by Wooldridge and Linton to the Pliocene marine plain is shown to be essentially indistinguishable from their mid-Tertiary surface and is therefore believed to be correlative with it. This view implies post-mid-Tertiary deformation of the Chalk. In Part Four of the thesis a theory of drainage evolution is developed to replace the hypothesis based on a concept of late Tertiary marine planation. Drifts, landforms and drainage morphology in the Vale of Wardour are shown to demonstrate a deformed, subaerial planation surface, bevelling the outcrop of the Chalk and earlier formations at a level below the mid-Tertiary surface of Wooldridge and Linton. The present drainage pattern is believed to have originated during the deformation of this surface, probably in the Plio-Pleistocene interval. This subaerial surface is also identified on Salisbury Plain and the origin of the drainage pattern there and in the Alderbury syncline is described. The available evidence suggests that the subaerial surface was elaborated during the Pliocene period following the deformation of the Oligo-Miocene (mid-Tertiary) surface. The character of the late Tertiary (Pliocene) surface suggests comparisons with the surfaces described by King (1962) and termed by him pediplains, although the nature of the process involved remains doubtful. In Part Five of the thesis some aspects of Pleistocene erosion are treated. Adjustments to the drainage pattern in the basin of the Avon above Salisbury during the Pleistocene period are discussed. This account is based on analyses of gravels of the Avon and its tributaries about Salisbury. The concept of successive stages of marine planation in the Hampshire Basin daring the Pleistocene period is rejected in a study of the composition and morphology of the Pleistocene gravels. An alternative scheme of subaerial planation is suggested and some morphological evidence of this planation on the Wiltshire Chalk and on the Eocene outcrop in the Hampshire Basin is described. The problems of scarp recession and the dessication of the dry valleys are reviewed and the concept of scarp recession is abandoned.

No description available.

No description available.

This thesis examines the extent to which geomorphological change in sub-arctic landscapes may be driven by rapid declines in population over timescales of decades to centuries. Demographic decline driven by disease in pastoral agricultural systems is expected to alter patterns of land use. Using a chronology with 20 visible dated tephra layers from AD 870 to present, 2625 tephra layers were identified in 200 sediment profiles. Rates of sediment accumulation dated by tephra provide a record of erosion in Skaftártunga, South Iceland. The scale of enquiry is that of individual landholdings (5–10 km2) over decades to centuries; in order to tackle questions of resilience and change within coupled socio-ecological systems larger and smaller spatial scales (regions of 400 km2 and individual sediment profiles) and longer and shorter temporal scales (2.6 ka and years to decades) are also considered. The novel application of photogrammetric techniques to recording stratigraphic sections increases the frequency of measurement from tens to hundreds per stratigraphic unit and the resolution from ±2.5 mm to ±1 mm. This technique improves the accuracy of representative measures of sediment accumulation and their use in measuring landscape change. Two little known 15th century AD Grímsvötn tephras are mapped and dated to AD 1432±5 and AD 1457± 5 using sediment accumulation rates. A period of landscape stability from AD 1389–1597 is consistent with reduced grazing pressure due to population declines of more than 30% after plague in AD 1402–1404 and AD 1494. Climatic deterioration from AD 1450-1500 does not increase erosion as much as expected; this may be due to decreased grazing pressure after population decline in the 15th century. Increased erosion from AD 935–1262 is related to woodland clearance and increases in sediment accumulation post AD 1625 are related to climatic cooling during the Little Ice age and the migration of erosion fronts into deep lowland sediments.

This thesis reports an investigation of soil erosion problems associated with maize cultivation in England. To place the investigation into a broader context, the study commences with a review of soil erosion problems more generally, before focusing on the specific on-site and off-site problems associated with maize cultivation. Agricultural statistics are used to quantify the recent expansion of maize cultivation in England and attention is directed to both the temporal trends and spatial patterns involved. A major expansion of maize cultivation occurred in England between 1990 and 2000. Particular attention is then directed to the expansion of maize cultivation in Southwest England, since this is a very important area for cultivation of forage maize. Against this general background, a more detailed investigation of soil erosion associated with maize fields and its impact on the local streams and rivers was undertaken. This focused on two river catchments, namely the River Culm above Cullompton, Devon, and the River Tone above Taunton, Somerset. These two basins were selected as having a high density of maize fields within their catchments. A detailed field survey was undertaken to identify all the fields used for maize cultivation in the two catchments during 2004 and the previous two years and to provide a map of their location. More detailed work, aimed at quantifying both gross and net rates of soil loss, was undertaken on six fields selected to be representative of maize fields in the two catchments. Beryllium-7 measurements were used to estimate the erosion associated with a period of heavy rainfall in late December 2004 and early January 2005, when the harvest fields were left in a bare compacted conditions, with little or no vegetation cover and field observations indicated that significant erosion occurred. The results obtained from the beryllium-7 measurements which related only to the short period in late 2004 and early 2005 were complemented by caesium-137 measurements in the same fields which were used to obtain an estimate of the longer-term (i.e. ca. 45 years) mean annual erosion rates associated with the more traditional land use that had characterized these fields prior to the introduction of forage maize cultivation. These results indicated that the introduction of maize cultivation increased gross and net rates of soil loss by ca. 4 and 8 times, respectively and significantly increased sediment delivery ratios, resulting in more efficient delivery of sediment from the eroding fields to the streams. An assessment of the likely impact of sediment mobilised from the maize fields within the catchments of the River Culm and River Tone during winter 2004-5 was made by establishing a sediment monitoring and sampling programme at the downstream gauging stations on these two rivers over the period November 2004 to March 2005. Estimates of the suspended sediment loads of both rivers were obtained for this period and these were compared with an estimate of the total amount of sediment delivered to the water courses in the two catchments from maize fields based on an upscaling of the results obtained from the beryllium-7 measurements undertaken on the six representative fields. Uncertainties regarding both field to channel and within channel and floodplain conveyance losses precluded definitive comparison of the estimates of the amounts of sediment delivered to the water courses from maize fields with the measured sediment loads. However, the results obtained demonstrated the likely importance of the contribution from eroding maize fields to the suspended sediment loads of the Rivers Culm and Tone during winter 2004-5. The geochemical properties of suspended sediment collected from the two rivers were also compared with the equivalent properties of soil collected from the surface of maize fields within the two study catchments, in order to provide further evidence of the impact of maize cultivation on their suspended loads. The available geochemical data confirmed that much of the sediment transported by the Rivers Culm and Tone could have been mobilized from maize fields, but the lack of detailed geochemical data, precluded a definitive conclusion regarding its source. The results obtained from the field-based component of the study have been combined with the information on the regional and national patterns of maize cultivation and synthesized to provide a general assessment of the likely environmental impact of maize cultivation in England. This information has in turn been used to consider the potential for developing improved land management practises to reduce the environmental impact of maize cultivation within the context of the EU Common Agricultural Policy (CAP) and the Water Framework Directive (WFD). Finally, recommendations for the further development and extension of the study are provided.