Quaternary environmental changes in the fluvial and faunal history of central Northamptonshire

This dissertation is an analysis of the Quaternary fluvial history of central Northamptonshire. It uses new freshwater ostracod data which are interpreted using information on Quaternary and present day habitats and examines in detail associated patterns of environmental change in coarse sediments from which the ostracods were extracted. Stratigraphic, lithological and sedimentological data, supported by a study of geological maps, borehole logs and papers, are employed to produce a new hypothesis to explain the Quatemary development of the Milton River and the River Nene. The alignment of the Milton Formation Valley is established to have proceeded to the east of, but parallel with, the Nene Valley between Northampton and Higham Ferrers, where it turned to the south-east. It comprises locally derived deposits which are shown to be pre-Anglian Glaciation and, at the time of the deposition of the ostracods studied here, an interglacial environment prevailed. However, during a ‘cooling phase”, Milton Formation sediments were incised and the channel became partially infilled with fossiliferous boreal sediments. Further sedimentation continued to produce a non-fossiliferous, periglacial sand, which is typical of the Milton Formation. It is argued that this period of deposition was followed by two glacial episodes, the latter relating to the Lowestoft Formation. Stratigraphic, sedimentological and lithological evidence from the Nene valley shows vestigial terrace gravels exist between Northampton and Wellingborough. The oldest gravels of these features pre-date the Anglian age, sub-glacial tunnel valley” at Northampton, implying the Nene Valley existed prior to glaciation. Before glaciation it is suggested that the Milton River became confluent with the Nene at Northampton and, concurrently, diverted to the north-east at Higham Ferrers. This is believed to be associated with the simultaneous abandonment of the Milton Valley to the south-east of Higham Ferrers and the upstream stretch at Northampton. Evidence presented of downcutting, lateral migration, gravel reworking and changes in the ostracod assemblages in the Nene Valley confirm a history of several climatic oscillations which took place in the pre-Devensian, Devensian and Holocene. These oscillations are tentatively correlated with stages of deposition in the Nene established downstream at Peterborough. This revised fluvial history elaborates the course and age of the Milton River and establishes a pre-Devensian age for much of the Nene Valley sediment. The significance of this new understanding of the upper Nene Valley has been compared with that of the lower Nene Valley at Peterborough, Cambridgeshire. The combined evidence is used to produce a pattern of river development within the Quaternary which may be used as a model when reconstructing the palaeogeography of other rivers and their floodplains by means of their sedimentary structures and related fossils. This idea is explored to a small extent in the thesis, but is more applicable to future work. The new ostracod data throws new light on previous studies from other sites in England. Ostracod species new to the Pleistocene record are to be added to a worldwide data base