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History of the major rivers of southern Britain during the Tertiary

A series of palaeogeographical maps illustrating
the evolution of the regional drainage system
of southern Britain over 50 million years

Compiled by Philip Gibbard 1 & John Lewin2

1. Godwin Institute of Quaternary Research, Department of Geography, University of Cambridge, Downing Street, CAMBRIDGE CB2 3EN, England, UK
2. Institute of Geography & Earth Sciences, University of Wales, ABERYSTWYTH SY23 2DB, Wales, UK
. Institute of Geography and Earth Sciencies, University of Wales, Aberystwyth SY23 2DB, Wales, U.K.

The maps


Palaeocene


Early Eocene


 Late Early Eocene
and Late Middle and Late Eocene

Oligocene

Miocene

Pliocene

The palaeogeographical maps are available for viewing from the individual pages listed here. They are accompanied by short explanations. For more detail, readers should consult the further reading list below. Maps like these are only as good as the evidence available to construct them. We welcome anyone who has evidence that can be used to update the courses to contact us without hesitation! Feel free to copy/paste images from these pages.

The original paper from which this information is taken is: Gibbard, P.L. & Lewin, J. 2003 The history of the major rivers of southern Britain during the Tertiary. Journal of the Geological Society 160, 829-845. ( download )
  1. Tectonic map
  2. Palaeocene
  3. Early Eocene
  4. Late Early Eocene
  5. Late Middle and Late Eocene
  6. Oligocene
  7. Neogene (Miocene and Pliocene)
  8. Synthesis
  9. Concluding points

The drainage maps represent a continuation of the work on the history of the NW European rivers of the last 3 million years , shown on other pages of this website.  The maps were drawn by Ian Agnew and Owen Tucker of the Cartography and Reprographics Unit of the Department of Geography, University of Cambridge.

Summary

The evolution of the drainage system of lowland Britain is discussed on the basis of available geological evidence, including that from both terrestrial sites and that from offshore.  Tertiary stratigraphy throws considerable light on landform and river development.  Palaeocene destruction of a chalk cover, was accompanied by basin sedimentation under a tropical climate.  The major elements, the Thames, Solent, Hampshire (?proto-Avon) river, Irish Sea river and possibly an early Trent river, existed almost throughout the Cenozoic.   The influence of Atlantic rifting and thermal doming in NW Britain appears to have been stronger and more temporally focused than the persistent flexuring that determined and maintained Tertiary drainage lines in the south-east.  Here also the folded Mesozoic terrains on the surface contrast with the more dominant block-faulted relief of the Palaeozoic ‘oldlands’.  The rivers of the south-east extended or reduced their lengths in response to relative sea-level change and gentle warping.  Drainage antecedence, the destruction of the Solent system and the breaching of the English Channel are also evident.  By contrast, the major river systems of the west are now entirely submerged.

Long-term drainage pattern stability reflects a persistent tectonic regime in the south, with a subdued low-relief landscape having a weathered regolith and dense vegetation cover.    Meandering river channels and alluvial styles predominated, although channel forms varied according to sediment load, slope and discharge variability.  Coarse gravel-dominated accumulations are rare and localised.   Chemically-stable lithologies dominate the clastic component throughout.

It appears that the deeply-incised river valleys seen today are related to high, predominantly coarse sediment yields, encouraged by substantial, rapid climate changes in the Pleistocene.  This emphasises the significance of mechanical compared to chemical weathering for the rate and nature of landscape dissection, and the modifications that have arisen as a result of glaciation, frost-climate weathering, rapidly-changing climates and sea-levels.

The stratigraphical evidence is at variance with older, largely geomorphologically-based landform evolution models (‘denudational chronology’), but gives considerable support to recent proposals that emphasise the significance of Palaeocene erosion, and enduring low-relief landscapes and drainage systems evolving alongside fold development during the Palaeogene.  Given the depobasin evidence now available, fluvially-active episodes can, and must, be linked to contemporaneous deposition.  Some at least of the many controversies involving the identity of erosion surfaces, the dating of them using only residual deposits and weathering mantles, and the selection of particular Tertiary episodes as ones of landscape development can now be resolved.

This work was originally published by Philip Gibbard & John Lewin in 2003. They are presented here, in downloadable format, for use by anyone interested in the longterm development of river systems.



Introduction

Long-term drainage and landscape evolution have been important research foci for over a century.  In southern Britain, investigations have centred on drainage evolution and its contribution to a 'denudational chronology' geomorphological school which reached its acme with the publication of Wooldridge & Linton’s work ‘Structure, surface and drainage in south-east England’ (published in 1939; 1955).  Despite criticisms their conclusions reigned supreme until the 1970s when a new generation of researchers began questioning the conclusions on the basis of evidence becoming available from increasingly sophisticated investigation of tectonic history, sedimentology  and pedology.  The results continue to provoke reassessments of the geomorphology of southern England and beyond.

The approaches of Wooldridge and Linton and their immediate followers were essentially underpinned by three concepts:
(i) Geomorphology could use deduction and inference to erect a history of landform development using evidence from landforms themselves to fill an apparent gap in earth history after the rock record ceased.  Only later on did the focus shift to a detailed reconstruction of processes and the stratigraphy of ‘superficial’ deposits.
(ii) The Davisian cycle of erosion was the persuasive theoretical basis available for interpretation.  In this, uplift was followed by progressive erosion and stream adjustment to geological ‘structure’ (including lithological outcrop) as relief reduced to an eventual peneplain.
(iii) Sea levels changed; this could include progressively falling base levels, and might involve marine onlap and offlap at particular periods.  Ideas concerning superimposition from a chalk cover and the development of marine shorelines came to Britain.

Thus the evidence which Wooldridge and Linton and their followers made use of was primarily geomorphological.  This included accordance of hill summits to identify former marine surfaces or peneplains, relationships between stream courses and structural elements in order to distinguish between surface types and to reconstruct drainage evolution over time, and field mapping of planation surfaces and related features.  In the three decades following initial publication of Wooldridge and Linton’s model, there followed a whole series of regional studies focusing on individual drainage basins or escarpment/backslope blocks and, generally speaking, upon episodic incision with a falling base level and on planation under hypothesised marine and fluvial conditions.  A similar effort was made to map and interpret surfaces in upland areas of western Britain, with recognition of marine or subaerial surfaces at higher levels, though with conflicting interpretations in the absence of related deposits.

Later research was able to involve a greater concentration on, and technical knowledge of, residual deposits and weathering products associated with particular surfaces.  In general these studies have thrown considerable doubt on the earlier Wooldridge and Linton model since weathering products, like the widespread Clay-with-flints on the Chalk, have not proved to be what they initially seemed.  Further north and west, residual deposits and Tertiary outliers have been carefully examined.  Again, conclusions from such studies conflict with earlier assumptions.   Finally, detailed mapping of surfaces and the interpretation of drainage patterns has suggested some convincing alternatives to the Wooldridge and Linton model.

Given also the new mobile tectonic framework made available through developments in plate tectonics, and new information derived from exploration of the shelf sea floor, evidence has been growing that the erosional landscape has inherited substantial elements from throughout the Cenozoic beginning in the Palaeocene and incorporating earlier elements in the west.  Thus any study of the evolution of the major drainage elements of the southern British Isles must begin at the latest with the Palaeogene or even earlier in the Palaeozoic ‘oldlands’ where a Chalk cover may not have been complete.

Futhermore, whilst the recent concentration on residuals and surfaces is fully understandable, it appears timely to reconsider the evidence provided by larger known bodies of Tertiary sediment.  Erosion and depositional systems are necessarily linked, with the latter able to provide key information on the timing, environment and extent of the former.  It appears that whilst the basal unconformities of Tertiary formations and epochs have been projected to indicate erosion levels (e.g. the variously-termed sub-Eocene, early Tertiary, sub-Palaeocene, sub-Oligocene surfaces recently incorporated into polygenetic models by Jones 1999), the diagnostic potential provided by the major bodies of Tertiary sediments has not been adequately developed.  There is now sufficient evidence to assess river development from the standpoint of fluvial sedimentology and provenance, rather than surface morphology alone.  Based on the location of deposits and their provenance, it is possible to indicate broad drainage lines (commonly called 'proto-' river systems) though not with very great detail.  In some instances, sediments allow former channel types and depositional styles to be suggested, whilst they may also be indicative of erosional energy and weathering regime in the catchments which supplied them.  A similar approach was successfully adopted for a synthesis of North-west European drainage history of the last 3 my .  The same approach is applied here, with the effects of supplementing or modifying earlier conclusions drawn largely from erosion surfaces and residual deposits.

The response of the British lowland drainage system to the external influences over the past 50 million years of the Tertiary Period has been complex being dependent on the scale and duration of the events. However, certain patterns emerge and indicate the impact of climatically- and tectonically-controlled variables on the system as a whole. These patterns are discussed on the individual pages below.



Further reading


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