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M.Phil. dissertation abstracts 2001 - 2002

Copies of these dissertations are held in the University of Cambridge, Department of Geography Library.

Richard Betts

Dissertation "A palaeoenvironmental study of Tednambury, Essex" , supervised by Dr Charles Turner (Cambridge).

The palaeoenvironmental history has been reconstructed from Tednambury, Essex by using a multiproxy approach incorporating analyses of pollen, Mollusca, plant macrofossils, vertebrate remains and of the sediments themselves. Additional samples were also recovered from the High Cross storage area (University of Cambridge) and analysed. In BH6 the pollen stratigraphy displays a succession from an Early Temperate Interglacial zone with high levels of Betula, Poaceae and Hippophae. The presence of a sea buckthorn peak in the basal layer is reported excusively from Late Anglian zones before the initiation of the Hoxnian. A Hoxnian age for BH6 is supported by other phenomena in the pollen stratigraphy such as a late Carpinus entry and an early Quercus entry. Further, the Mollusca, by suggesting a lacustrine environment, closely resemble the faunal lists recovered from nearby Hoxnian sites such as Hatfield, Barton and Hoxne. Thus, the specifics of the pollen stratigraphy coupled with the palaeobotantical information derived from the other lines of evidence and the nature of basin formation suggest a Hoxnian age as opposed to Ipswichian or Holocene for this borehole. This conclusion confirms the beliefs of the British Geological Survey in 1978 and reveals a new East Anglian Hoxnian site. The age of the other boreholes (BH11 and BH17) does not appear to be as straightforward to resolve. The Hippophae peak found in BH6 is not encountered here. High percentages of local pollen taxa such as Alnus and Corylus suggest that these deposits were closer to the former lake.

Heather Cheshire

Dissertation "The Stage 6/Substage 5e transition in a core from Iberian margin", supervised by Professor Sir N.J.Shackleton (Cambridge).

At 37∞34’N 10∞1’W, marine core MD01-2444 is at the conjunction of the most southerly latitude to which the Polar Front migrates during extreme cold climate events and the point at which the River Tagus deposits its sediments. The Tagus drains a very large area of the Iberian Peninsula and lies at the climatically sensitive divide between Eurosiberian taxa to the north and Mediterranean taxa to the south. MD01-2444, therefore, is ideally situated for the purpose of obtaining a terrestrial climate signal from within a marine setting.
In this study the pollen record, together with planktonic oxygen and carbon stable isotope analysis , magnetic susceptibility, particle size and loss-on-ignition analysis, is used to investigate both the terrestrial and marine response to the Marine Isotope Stage 6/Substage 5e transition. An age model is constructed by comparison with planktonic oxygen isotope data from nearby core, MD95-2042 .
The vegetation response to ameliorating climate during the transition from glacial to interglacial is found to be within ~1000 years of the marine response. In the ocean, wind-driven, high-productivity upwelling declines as sea surface temperatures rise. On land, an open, arid landscape, with only a few hardy drought-tolerant trees, gives way to the gradual expansion of deciduous arboreal taxa. The latter, from their rapid exploitation of the improving climate, are seen to be expanding from glacial refugia. Mediterranean evergreen taxa appear ~128 ka BP, indicating the full inception of interglacial climate. This period is interrupted in the ocean by a period of intensified upwelling and high productivity, but there is no corresponding response by the land vegetation. Some time after climate has improved, a peak of the aquatic spore Isoetes, an indicator of high rainfall, is accompanied by very low pollen concentration and a peak in total organic carbon. A prolonged period of storminess is thought to have brought extraordinary amounts of vegetation debris in the ocean via the river. Although not the only source of organic carbon in these sediments, the river (and rising precipitation rate) is a significant contributor. A rise in total organic carbon is seen from the beginning of interglacial conditions, at a point when ocean productivity is falling, indicating the importance of terrestrial runoff. Mediterranean arboreal taxa are not affected by the ‘Isoetes’ event.

Anna Nelson

Dissertation  Soft-sediment deformation beneath a surge-type glacier in Iceland and the implications for fast-flow Quaternary ice sheets: a sedimentological approach supervised by Dr. Ian Willis (Cambridge).

The aim of this project was to understand the depositional processes that occur beneath and in front of Hagafellsjökull Eystri, a surge-type glacier in West-Central Iceland.  By gathering stratigraphic data from vertical sections of relic diamict units in the proglacial area of the marginal lobes and observing the present-day margin of the glacier, different depositional environments were identified.  A clast lithological approach was used to compare diamict units along the entire margin and identify any lateral correlations within sites.  The patterns displayed in the clast fabric and particle size and shape suggest facies provenance and degree of edge-rounding during transport, while preserved structures in the sections lead to glacio-tectonic interpretations.  There are three depositional environments identified:  glacigenic, glacio-fluvial, and glacio-lacustrine.  By studying these processes at Hagafellsjökull Eystri, the mechanisms operating on sediment deposition at the margins of surge-type glaciers may be better understood.

Hagafellsjökull Eystri is an outlet glacier of the Langjökull ice cap in West-Central Iceland (Figure 1.1).  This surge-type glacier is 7 km long from the terminus to the headwall and up to 6 km wide.  The front of the glacier feeds into Hagavatn (Figure 1.2), a proglacial lake with unknown bathymetry.  The lake has an elevation of 435m and an area of 5km2.  Currently Hagavatn drains through Nyifoss, a col in the volcanic rocks in the southeast corner of the lake.  In the past, this lake has drained through Leynifoss as well, 1.5 km west of Nyifoss (Bennett et al., 2000).  

John Trehearn

Dissertation "A palaeoenvironmental study of Thompson Common, Norfolk" , supervised by Dr Harriet Allen (Cambridge).

In western East Anglia belween the till and the levels, lie ground ice depressions. which are characterised by being shallow in relation to their breadth. These East Anglian depressions have been examined by Sparks et al. (1972) who argue that a non-committal term should be used rather than the name of any specific form of ground ice depression found elsewhere (i.e. pingo). They state that the more recent of these forms seem to date from 12.000-10,000 yr BP. AIthough Sparks et al. focus their study on Walton Common other sites sucl1 as Thompson Common contain similar depressions.

Previous investigations at Thompson Common have been conductecd by Bradshaw (1981) who exainined recent woodland history using a 1.12m1 core from a dry basin in the north-east corner of the common. 'l'his short core contains evidence of the recent woodland history from the Late Devensian to present.

This analysis of sediment and pollen from a core taken from a depression at 'I'hompson Common aims to ascertain the environmental history of the area during the Late Devensian and Holocene in more detail and with a higher resolution than previous studies. In order to obtain such a sample a core would have to be taken from one of the deepest pingo lakes and this would require a boat or platform.

T'he findings will increase the resolutionl and therefore the knowledge of the past environmental changes that took place at 'I'hompson Common. These results will be examined in the context of other studies i.e. Bennett (1981) lo examine hydrological system changes.

Thompson Common lies at 52"32*N 0"51'k, 14 km north of Thetford, Nolfolk. 'I'he site is situated on the north-eastern margin of the Breckland, lying 011 alluvial deposits at the head of a valley that drains into the River Wissey. 'I'o the north and east of the Common, till lies at the surface underlain by sandy soil and to the south. chalk underlies the light Breckland soils.