Paleogeography of Denge Marsh

In 1991 Dr. Andrew Plater continued his geological study. of early environments at Dengemarsh, this time funded by ARC. In August he gave an impromptu field demonstration to a group of local members.

Stratigraphic investigations have been carried out on the area of Denge Marsh to the south-west of Lydd Airport, between the railway, Dengemdrsh Sewer and Dungeness Road. A grid was laid out with one axis parallel to the railway, and hand-drilled boreholes were dug at 25m intervals, so far covering approximately 75% of the area.

In this area the fine-grained marsh sediments inter-finger with course grained shingle ridges, which thin out towards the north-west from the apex of Dungeness.

The general sedimentary sequence is described below:

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Depth 0 .00 - 0. 30m 0.30 - 1.10m Description Rich brown topsoil with gravel and organic traces. Orange and browny-grey, sandy- clayey- silt with severe oxidation mottling. 1.10 - 1.60m 1. 60 - 4 .OOm

Laminated browny-grey sand and clayey-silt with infrequent organic horizons (thin peats, generally less than 0.10m). Coarsely-laminated blue-grey and black sand and silt with occasional gravel and shell horizons.

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This sequence becomes progressively finer-grained towards the top, which indicates that it was deposited in a low-energy tidal environment which was becoming increasingly remote from wave action as Dungeness grew outwards. The mott 1 i ng near the top of the sequence has resulted from severe oxydat ion which occurred as a result of drainage of the marsh by both natural and human agencies. and The sedimentary sequence becomes particularly interesting at the ends sides of the shingle "fingers", where thin bands of gravel are occasionally found between the lower and upper laminated facies.

It seems that the lower group of laminated sediments was deposited in sheltered, quiet-water conditions. It is probable that the succeeding shingle was deposited during a particularly stormy period, when bigger waves were able to move the shingle pebb 1 es. The upper group of laminated sands and clayey silts were then deposited when quieter conditions had been restored. In a few locations sufficient shelter and poor drainage led to the accumulation of vegetation, which formed thin peats. Unfortunately, none of these peats form a continuous horizon, although there is a high frequency of organ i c-ri eh sediments between + 1. 00 and +1.40m O.D.

A "type" core was taken in the field and returned to the laboratory at Liverpool. Selected sediment samples have been taken for particle size and microfossil analysis. Subsequent samples will also be used to investigate mi nera 1 magnetic properties and the presence of carbonaceous particles.

The next phase of the work will continue the stratigraphic investigations in the present area, and then continue on the other, south-west, side of the Dungeness Road. Particular attention will be paid to the organic horizons and the "feather edges" of the shingle ridges, because it is hoped that dating of these contacts will provide chronological information regarding the onset and cessation of the build up of shingle ridges in the Denge Marsh area.

Andrew J Plater
Department of Geography, University of Liverpool