3. Water level changes and sedimentation during the Flandrian Age in the Romney Marsh area

Michael Tooley and V. Roy Switsur with an Appendix by Dauid Huddart

Introduction: Sea-level changes and vertical movements in the UK The context for a consideration of the evolution and sedimentary record of the 25,000 or so hectares of unconsolidated sediments that constitute Dungeness and the two great marshes of Romney and Walland is provided by a brief description of relative sea-level changes and models ofvertical movements in the United Kingdom, both of which have been the subject of recent reviews (Tooley 1978a; Everard 1980; Greensmith and Tooley 1982; Shennan 1983a; Smith and Dawson 1983; Tooley and Shennan 1987). The separation of the two topics is unwarranted because the empirical data from both provide evidence of earlier intersections of the sea and the land from which can be derived information on the direction, scale and amount of sea- and land-level changes.

The pattern of uplift in north-west Britain and subsidence in south-east Britain, based in part on Wright's (1914) model ofisostatic rebound following de- glaciation, has been reinforced over the years by empirical studies, such as the analysis of tide gauge data by Jolly (1939) and Valentin (1953), the analysis of the displacement of deposits formed at sea-level 6,500 years ago by Churchill (1965), the analysis of the distribution of emerged or submerged shorelines of Late Pleistocene and Holocene Age by Stephens and Synge (1966), and the distribution of raised beaches and 'submerged forests' around the coasts of Britain by Dunham ( 1972). More recently, Flemming ( 1982), using a data set of 143 sea-level index points dated between 118f 48 BP and 9961 f 200 BP and all levelled to Ordnance Datum (Newlyn), showed a contour plot in metres/millennium with corrected and uncorrected values for which uplift in north-west Britain was confirmed, but a pattern of both uplift and subsidence was manifest in southern Britain. Flemming drew attention to the paucity and uneven distribution of data on the south-east coast which resulted in an uplift solution for this area. A recent analysis of tide gauge data for north-west Europe (Emery and Aubrey 1985) based on tidal data compiled by the Permanent Service for Mean Sea Level at Bidston, Birkenhead, purports to show subsidence in southern England of some 2 to 8 mm per year, which is several times greater than the + 1 mm per year global

sea level trend for the past century (Gornitz et al. 1982). Shennan ( 1987) compared relative sea-level curves from North Sea coasts with Morner's ( 1980) 'regional eustatic curve', and calculated uplift and subsidence values for thirteen coastal units. For the unit closest to the Romney Marsh area, the curves of relative sea-level change for the Thames estuary (Devoy 1979) were employed to calculate subsidence. Although there are significant, unexplained deviations from the linear trends prior to 5000 BP, from this time to the present a linear trend is evident, and for the uncalibrated 14-C data shows a subsidence rate of - 1.1 7 f 0.05 m/1000 yr (1.2 mm/yr). From 5500 BP to 8000 BP local uplift is manifest. Neither this nor the subsequent subsidence can be accounted for entirely by sediment consolidation or tidal changes.

The insufficiency and poor quality of data from the south-east coast of the UK, noted by Flemming (1982) and Shennan (1983a), militates against any corrobor- ation or refutation of the published models showing uplift and subsidence for this area. Caution must be exercised in the use of these models, but clearly, conclusions about the direction and rate of vertical movements along the south-east coast of England are crucial to an understanding of the mode of formation and the history of the coastal landforms and tidal flat, lagoonal, shingle and perimarine sedimentation in the Romney Marsh area, and the river valleys that debouch here.

More data are required, collected systematically and arising from the application of a common methodology. A methodology has evolved during the past fifteen years (Tooley 1978a, 1978b, 1982, 1985a), and Shennan (1983a) has provided an invaluable and explicit statement of sea-level research methods in an expanded and detailed model and applied it to data from the Fenland (Shennan 1986a, 1986b). Data accruing during the course of following the three routes provided for in this model will permit conclusions about local sea levels, regional sea-level tendencies and crustal movements. Shennan ( 1982, 1983a, 1983b) has also considered how representative a sea-level index point is as a basis for within- and between-area correlation. Hence, a site is considered to be a tract of ground over which a single sea-level index point is believed to be representative and between-site correlation yields an 'area', such as the

54 Michael Tooley and V. Roy Switsur

. . . . . . . . . . , . . . . . . . . . . . . . . . .

. , . . . . . . .

. . . . . . . . .

Old Marshland

New Marshland

. . . . . .

Direction of Creek Drainage

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0 km 5 1 1 1 1 ' 1

Fig. 3.1 Dungeness, Romney Marsh and Walland Marsh and adjacent areas showing new and old marshland according to Green (1968) and the location ofplaces mentioned in the text. Old marshland includes sand and shingle formations of Dungeness, Camber and

Hythe.

Fenland, the Thames estuary, the Somerset Levels, or Dungeness- Romney Marsh - Walland Marsh area and Romney Marsh. Between-area correlations constitute a the river valleys that feed it has been described by Lewis regional approach, such as the level of integration (1932), Lewis and Balchin (1940), Green (1968), achieved by Shennan (1987) for the North Sea. The site, Cunliffe (1980) Eddison, (1983a, 1983b) and Waller et area and regional scales are different levels of resolu tion al. ( 1 988). in a coherent and hierarchical model of sea-level research methods.

This model can be applied at present only to the site scale in the Romney Marsh area but provisional

Hor semar sh Sewer and Tishy's Sewer

between-site correlation, discussed later, indicates some Horsemarsh TQ982318 area1 homogeneity.

Two new sites - Horsemarsh Sewer, in the parishes of Kenardington and Warehorne, and Tishy's Sewer, Broomhill - are described: both lie in areas of decalcified or old marshland (Green 1968), one in the catchment of the Ham Street Arm of the Speringbrook Sewer and the other in the catchment of the Wainway Channel (Fig. 3.1). The Flandrian depositional history of the

Horsemarsh Sewer (Fig. 3.2) drains one of five small embayments along the north margin of Romney Marsh cut into Wealden Clay and the Hastings Beds. Each embayment is bounded by what Green (1968) described as an old, degraded sea cliff. The Horsemarsh Sewer has a small catchment area, and is fed by small streams from Faggs Wood to the north. The ground that lies adjacent to the sewer is low, with altitudes of + 1.0 to + 1.5 m

Water Level Changes and Sedimentation 55

OD, and is well below the altitude of mean high water of spring tides (+3.8 m OD) at Rye.

The Horsemarsh embayment lies to the north of the Royal Military Canal, and is adjacent to an area mapped by Green (1968) to the south as a silty clay or clay, with peat near the surface. The soils which have developed on the clastic deposits are all decalcified.

The stratigraphy was described (Fig. 3.3) a t eight sampling points across gently undulating ground south- west of the sewer. A metre-long gouge sampler was used for recording the stratigraphy and a power-assisted piston core sampler for taking 5 cm diameter samples for analysis from HM-4. The broken records in the strati graph^ indicate that the sampling undertaken at this site was not entirely successful. The signatures used in the stratigraphic columns show the composition and the physical properties of each layer, according to the scheme proposed by Troels-Smith ( 1955).

Unconsolidated sediments were proved to a depth of c. -4.3 m OD, and the maximum thickness of unconsolidated sediments of 570 cm recorded at HM-3. The floor of the buried valley is composed of a silty sand with some grit and gravel: at HM-4 (Fig. 3.3), stratum 1 is composed of 71 gravel and sand, 24% silt and 574, clay, by weight. This passes up into a grey, ashen, gravelly, sandy silt with some iron staining: a sample from within stratum 3 yielded 42% gravel and sand,

4g0b silt and 99,; clay, by weight. There is a fining- upwards sequence and an increasing organic content in stratum 4, and strata 5 and 7 are made up of silty clays, with an estimated organic content in excess of 27%, based on an organic Carbon content of 15%. The organic content is a limus with monocotyledonous rootlets and some herbaceous detritus. Stratum 7 is overlain by a battleship grey clayey silt with a slight organic content; stratum 8 comprised 50°/, by weight silt and 49% clay. Stratum 8 was rich in lagoonal, brackishwater diatoms, such as Diploneis interrupts, but the sediment was decalcified and contained no foraminifera. Above this is the main peat development in the valley (strata 9-16) and comprises a dark brown limus with marked woody and herbaceous detrital layers (strata 11 and 13) interrupted by waterlogged layers with massive trunks from which no samples could be recovered with the piston core sampler. The main peat lies at altitudes from c. - 3.3 to + 0.2 m OD, which is similar to the altitudes for the main peat development in the valleys of the Pannel Sewer and rivrrs Brede, Tillirlgham and Rother west of Walland Marsh and Pett Level, recorded by Waller et al. (1988). At HM-4, the main peat is overlain by silty clays with iron concretions, which form two creek ridges trending NW/SE at the mouth of the valley, rising 40 to 50 cm above the valley floor. These ridges (Fig. 3.2) are the landward, upvalley

Creek Drainage

Fig. 3.2 Location of sampling points in the valley of Horsemarsh Sewer, Kenardington and Warehorne. The pattern of creeks and creek ridges south o f the Royal Military Canal is based on the Soil Survey map of Romney Marsh and Figure 14 in Green (1968).

56 Michael Tooley and V . Roy Switsur

Fig. 3.3 A stratigraphic diagram from the entrance to the valley of'trlorsemarsh Sewer: the locatzon of the sampling points zs shown on Fig. 3.2. The stratigraphic gmbols and the vmbols for the physical properties of each stratum are according to the scheme of Troels-Smith (1955).

HORSEMARSH SEWER ~ ~ 9 8 2 3 3 1 8 5

depth %TREES +GROUP

m.00. c m iin-rrrrrm-rrrm11-rrrrrmi~i1171171mn1111111111111111111111m11111111111111111mn11m~m~

Fig. 3.4 A pollen diagram from Elorremarsh Sewer 4 ( H M - 4 ) , 405-469 cm. The percentage frequencies for each level counted were calculated on the basis of2 tree pollen for the tree pollengroup or for the other life forms or taxonornicgroups (shrubs, herbs, aquatics, pteridophytes and byophytes) on the basis of (2 tree pollen + group). The strata numbers showrl

refer to the sequence shore~n against the stratigraphic column H M - 4 on Fig. 3.3.

Water Level Changes and Sedimentation 59

extensions of the two creek ridges shown by Green (1968) on the south side of the Royal Military Canal, upon which soils of the Finn Series have developed. A sample from stratum 19 of HM-4 was decalcified and yielded no foraminifera.

Pollen diagrams from the lower part of the succession (strata 4-10; Fig. 3.4) and the upper part of the succession immediately subjacent to a creek ridge (strata 16 and 18; Fig. 3.5) assist in establishing both the age and the palaeoenvironmental conditions at the sampling site.

Stratum 4 is dominated by arboreal pollen and particularly the pollen of Tilia cordata and Quercus, indicating the presence of lime/oak forests in the pollen catchment area. If Andersen's (1973) correction factors are used to estimate the forest composition, then Tilia cordata accounts for more than 90% and pure stands of lime must have characterised the plateau soils, replacement slopes and perhaps even the clay soils of the marsh. Indeed, in Denmark, Iversen (1960) noted that Tilia is most frequent on rather moist clay soils and grows well on moist low-lying fertile soils where it is less resistant to water-level changes, especially when the water level fell, than Quercus or Alnus. Greig (1982) identified south-east England as the third main area in Britain where forests mainly of Tilia appear to have been characteristic during the Atlantic ( = Flandrian 11), and the data from the Horsemarsh Sewer valley, Kenarding- ton complement the high corrected percentage frequencies for lime from Lewes in Sussex and Hothfield Common in Kent, confirming Greig's conclusion. At 454 cm, at the top ofstratum 5, Tilia pollen frequencies drop markedly and those of Quercus rise, which may be a response to a change in the area occupied by oak, consequent upon a change in ground water conditions. It is noticeable that during the period oflime dominance followed by oak dominance, there is an increase in the frequency of the pollen of Chenopodiaceae and of other saltmarsh taxa, such as Aster, Artemisia, Glaux and Plantago maritima. Wetter ground conditions are indicated by low frequencies of the pollen of Typha angustzfolia, immediately following which organic sedimentation of stratum 7 gives way to the sedimentation of clayey silt of stratum 8. The proximity of marine conditions is testified by the presence in stratum 8 of DijAoneis interrupta, a diatom that occupies brackish water lagoons along the North Sea coast of Holland (van der Werff and Huls 1958-1974). The transgressive overlap at - 3.42 m O D has been dated to shortly after 5500 f 70 BP (Q. 2647). The regressive overlap at - 3.33 m O D has been dated to shortly before 5150 f 70 BP (Q. 2648) and a progressive plant succession is clearly evinced from the pollen assemblages from strata 9 and 10, following comparable successions described from Denmark (Iversen 1960) and England (Godwin 1956; Tooley 1978a, 1986; Shennan 1982). The pollen of saltmarsh taxa, such as Chenopodiaceae and Silene, is complemented by rising frequencies of the pollen of freshwater taxa, such as Typha angustifolia, Potamogeton and Lemna, and the pollen of herbaceous fen

and reedswamp taxa, such as Igthrum, Lysimachia, Galium-type, Thalictrum, Ranunculus and Calystegia. Fen oak woodland with reedswamp is replaced by alder carr through strata 9 and 10.

Both an elm and a lime decline occur a t 425 cm, placing strata 4 to 9 in late Flandrian Chronozone 11, and corroborating both radiocarbon dates. Elsewhere in southern England, Waton (1982) has dated the elm decline at Rimsmoor to 5 150 f 70 BP (HAR. 39 19), and Waller et al. (1988) have dated it a t Pannel Bridge to 5040 f 80 BP (SRR. 2888). The Tilia decline has also been dated by Waller et al. ( 1988) a t Brede Bridge, some 1400 radiocarbon years after the event in the Horsemarsh Sewer valley and at about the same time as the lime decline has been dated by Waton (1982) a t Rimsmoor, but the elm decline appears to be a better regional chronostratigraphic marker than the lime decline. The low frequencies ofAlnus pollen in strata 4-9 also point to considerable local variations in pollen catchments and recruitment at the sampling sites in this area, and only in stratum 10 do the frequencies of Alnus pollen rise to values expected in Flandrian Chronozone 11, unlike the situation in the Brede and Pannel valleys where Alnus pollen dominates the pollen assemblages during the period when the main peat formed (Waller et al., 1988).

A pollen diagram (Fig. 3.5) from limus immediately subjacent to the silty clay of a creek ridge at HM-4, yielded post-elm decline pollen assemblages with cereal pollen and the pollen of ruderals, such as Plantago lanceolata, Rumex and Taraxacum-type. Rising frequencies of the pollen of freshwater and aquatic taxa, such as Typha angustzyolia, T. latzfolia, Hydrocotyle and Myrio- phyllum altern$orum bear witness to rising ground water tables prior to the transgressive overlap at c. +0.3 m OD. Approaching marine conditions are indicated by the presence of the pollen of Chenopodiaceae, Artemisia, and Aster-type. It is probable that this transgressive overlap has been dated to 3020f 94 BP (NPL-23) on Appledore Dowels, where peat is overlain by estuarine alluvium (Callow et al. 1964, Shephard-Thorn 1975), and the altitude of the overlap has been measured here to between 0.0 and - 0.6 m O D (Field 1983). Further south, south-west of Old Cheyne Court, Everett (1985) has recorded the altitude of the overlap between + 0.9 and +2.2 m OD.

The evidence from the buried valley of Horsemarsh Sewer indicates that there were probably three transgressive overlaps and three regressive overlaps which directly affected the pattern of sedimentation in the valley. The sampling site a t HM-3 (Fig. 3.3) provides the most complete stratigraphic record in the valley: here, three clastic layers, interpreted as marine or brackish water facies, were recorded in strata 5, 11 and 16. The altitudes of the transgressive overlaps were - 3.7, - 2.9 and + 0.1 m OD, and the altitudes of the regressive overlaps were - 3.2, - 2.7 and + 1.5 m OD. At HM-4, from which sub-samples for micropalaeont- ological analyses and radiocarbon assays were taken, an incomplete series of piston core samples was recovered,

60 Michael Toolooley and V. Roy Switsur

and only two marine or brackish water facies were recorded with altitudes of - 3.4 and + 0.3 m O D for the transgressive overlaps and - 3.3 and + 1.1 m O D for the regressive overlaps, both falling within the altitudinal limits for the overlaps recorded at HM-3.

The ages of the overlaps are late Flandrian Chronozone I1 (5500-5150 BP) for the first pair, early Flandrian Chronozone 111 ( < 5000 BP) for the second and mid-Flandrian Chronozone 111 ( < 3000 BP) for the third.

The sediments from the buried valley of Horsemarsh Sewer provide therefore a range of types of sea-level index points from eight sampling points, comprising six transgressive and six regressive overlaps, two of which have been radiocarbon dated, and corroborated pollen analytically.

Tisishy's Sewer, Broomhill. TQ 995193 The coastal sedimentary environments in the Broomhill area provide a marked contrast to those in the valley of the Horsemarsh Sewer; but it was hoped that by applying the exploratory approach to sea-level investigations in these dissimilar areas where different processes were operating, the same overriding control affecting sedimentation in these areas could be identified. Additional attractions of the Broomhill area were that the most westerly surface exposures of the Dungeness shingle complex and the partly buried low- level barrier beaches described by Eddison (1983a, 1983b) could be found here, the records of buried peat (Green 1968) associated with sands and shingle further north-east allowed for the possibility of dating this early stage of the shingle formation, and rich historical records provided evidence of re-activation of the shingle during the storms of the Middle Ages (Eddison 1983c; Gardiner 1988).

The distribution of shingle banks, both buried and surface features in the Broomhill area, is shown on Fig. 3.6 as stippled areas, and is based on the soil map of Romney Marsh surveyed by R. D. Green, G. P. Askew and J. M. Hodgson (Green 1968). The area of shingle bisected by Tishy's Sewer extends further south-west, and has been proved beneath Broomhill Church (Gardiner 1988).

Opportunities were taken in 1985 and 1986 to record the stratigraphy and collect samples from a newly- cleaned and extended drainage dyke, which was named Tishy's Sewer, and which has drained into Pig's Creek Petty Sewer since the recent removal of the medieval sea wall known as Tore Wall. The new sewer (Fig. 3.6) cuts across the north-eastlsouth-west trending shingle ridges shown on the figure, but many more minor buried ridges were exposed in the new cutting at Tishy's Sewer, Broomhill-l. Between here and Pig's Creek Petty Sewer tidal flat and lagoonal palaeoenvironmental sediments were characteristic.

The characterisation of unconsolidated sediments, according to Troels-Smith's (1955) scheme, and the stages leading to the representation of sediment types in

a stratigraphic diagram have been described elsewhere (Tooley 1981). These stages have been applied to the sections in Tishy's Sewer. Figs. 3.7 and 3.8 show the stages in the recording of the strata and description of the components and physical properties of each stratum at the eight sampling points leading to the stratigraphic section displayed in Fig. 3.9 for that part of Tishy's Sewer where peat and silt-filled lows separate the crests of buried shingle banks trending north-eastlsouth-west.

In the section at Broomhill- l , the boundaries between the strata were recorded at eight sampling points, the altitudes ofwhich were related to Ordnance Datum. On Fig. 3.7 the boundaries are marked, and the stratigraphy recorded at the sampling points is shown on Fig. 3.8. The stratigraphic section (Fig. 3.9) cuts across the strike of two lows in the shingle a t - 120 cm and 0 m. Samples for analysis were taken from the basal strata in the deepest low at 0 m. Here (site B-l on Fig. 3.8), the basal stratum was a dark brown limus with herbaceous rootlets and flint cobbles about 2 cm diameter. This passed up into a dark brown limus (stratum 2) without flint cobbles but with a thin layer of sand at 104 cm, and thence (stratum 3) to a reddish-brown limus with iron mottling and some silt and fine sand. Stratum 4 is a brown, clayey limus from which several frustules of Diploneis interrupts were recovered and indicate brackish water lagoonal conditions. Stratum 5 is a battleship grey, plastic silty clay with monocotyledonous rootlets and some iron staining. From this stratum, a single test of Jadammina tnacrescens was recovered (see Appendix 1) and sponge spicules were also noted in the diatom preparations.

The pollen diagram (Fig. 3.10) provides evidence of palaeoenvironmental changes close to the sampling site. Throughout strata 1-4, non-arboreal pollen and spores characterise the assemblage. Of the tree pollen taxa Alnus and Quercus are characteristic, and the low frequencies or single grains of Ulmus point to a post-elm decline age for the oldest sediments infilling the low. Of the non-arboreal taxa, the pollen ofboth freshwater taxa

'

and saltmarsh taxa are conspicuous. Of the former, there is an increase in the frequency of the pollen of reedswamp taxa, such as Typha latgolia, T. angustfolia, Hydrocotyle, Galium-type, Lythrum, Caltha, Thalictrum and Filipendula, and of the pollen of obligate aquatics such as Nymphaea and Potamogeton. The pattern of frequencies of the pollen of saltmarsh taxa shows higher frequencies in strata l , 3 and 4 and a decline in stratum 2. In stratum l , Chenopodiacaeae frequencies reach 14% (Z tree pollen), whereas in stratum 2, Chenopodiaceae pollen frequencies have declined to 8%, rising to 20% and 17% in strata 3 and 4 respectively. In these strata, the pollen of saltmarsh taxa derives not only from this family, but also from genera such as Aster-type, Spergularia-type and Plantago maritima.

Chemical analyses point to an increase in salinity in the sedimentary environment from stratum 2-5. In stratum 2, the magnesium content is 1.69g per kg; in stratum 3, 1.8; in stratum 4, 2.0; and in stratum 5, 2.7. Ericsson (1973) concluded that magnesium is thought to be the best criterion ofpalaeosalinity, and the increase in

Water Level Changes and Sedimentation 6 1

Fig. 3.6 The Broomhill area showing the location of Tishy's Sewer and sampling points Broomhill-I and Broomhill-A. The distribution of shingle is based on the Soil Survey map of Romney Marsh (Green 1968). Mean High Water Mark intersects the coast at Rye and at Dungeness at + 3.8 m OD. The altitude of the shingle forming the coast lies everywhere higher than + 5.0 m O D and locally

rises to +8.0 m OD.

magnesium through the sediments, supported by other salinity indicators, clearly corroborates this conclusion.

The changes in sediment type and water quality and water depth inferred from the micropalaeontologica1, chemical and stratigraphic analyses provide two sea- level index points. The end of active shingle formation and the commencement of infilling of the inter-ridge lows with organic material can be interpreted either as a regressive overlap or as a consequence of continued shingle accretion to the east of Tishy's Sewer. The change in sedimentation from dominantly organic to dominantly inorganic (stratum 3 to stratum 4, Fig. 3.8), is interpreted as a transgressive overlap.

The ages of the regressive and transgressive overlaps are provided by two radiocarbon assays. A sample of lirnus from immediately above the flint cobble shingle on the floor of the low at an altitude of c. +0.8 m O D yielded a date of 3410 f 60 BP (Q. 265 1) and a sample of limus immediately subjacent to the brackish water lagoonal clay of stratum 4 at an altitude of c. + 0.9 m OD, yielded a date of 3 160 f 60 BP (Q. 2652).

Both these dates place the organic strata at the base of the low in the shingle in Flandrian Chronozone 111, and a post-elm decline date was inferred from the tree pollen assemblages.

Further north-west in Tishy's Sewer (Fig. 3.6), the

TISHY'S SEWER BROOMHILL- I

Fig. 3.7 The section at Tishy's Sewer, Broomhill-l shozeiing the boundaries at the seven samplingpoints. The boundaries were recorded from a clean, raked section along the north-east face of the sewer.

TISHY'S SEWER Fig. 3.8 The stratigrapb andphysical properties ofthe sediments for each stratum recorded at seven sampling points in Tishy's Sewer, Broomhill-l in January 1986. Monolith samples were collected from Broomhill-1 and the site levelled in April 1985, and

BROOMHILL - I the stratigraphy recorded from the monoliths in November 1985. The stratigraphic symbols and the symbols for the physical - E - - $D - I ~ ~ , t h - w e s t

Properties of each stratum are according to the scheme proposed by Troels-Smith (1955). south-east

p 0 f $ 2 8-1 -1800 -1600 -1400 -1200 -1000 -800 -600 -400 -200 0 +ZOO t 400 +600 +800 +IWO t1200cm

2 5 + I I I I I l I I l l I I I I I l

0 - 50'56' 16"N 00' 50' 31"E - TQ 9961 1931

J

I S + 100-

L P L 0 0

10%50:

860120 860120 860120 850402 860120 860120 851 115

Water Level Changes and Sedimentation 63

o subcrop of shingle banks has fallen away and a ; E 0 S P S P g I I I I I I I I I I I I I I I I stratigraphic succession more characteristic of tidal flat 5 E - O + and lagoonal palaeoenvironments is encountered. This "7

0 0 0 0 area lies within the zone defined by Green (1968) as old decalcified marshland, and the catchment of Tishy's

0 "I 0 -

Sewer was part of the catchment of Pig's Creek Petty F

' W U

Sewer which discharged into the tidal flats that later B became the new calcareous marshland drained by the F k

Wainway Channel. W f - The construction of the stratigraphic section for S

Broomhill-A follows the same stages as that for i? 3 Broomhill-l: on Fig. 3.1 1 the boundaries of the strata V

4 . recorded at four sampling points are shown; on Fig. 3.12 g 2 P - the stratigraphy at the four sampling points is shown; 2 2 and based on the data in Figs. 3.1 1 and 3.12, the 2 Cc; 3 stratigraphic section is shown in Fig. 3.13.

12 -W H - The stratigraphic section (Fig. 3.13) provides - h $ m evidence of two distinctive successions: from - 100 to hj g 'g + 500 cm south-east arr six strata with parallel to sub- , b parallel boundaries, which above the limus stratum are

0 8 - S markedly laminated and arch up in the the vicinity of 0 g h g = z +

-a .E g 1 cm; from - 100 to -300 cm north-west the beds are 2: 'W W U Q a 8 sharply truncated by a palaeo-creek, itself infilled with 2 g 8 p $ o -

I

five distinctive strata, all of which are unlaminated. E Samples for micropalaeontologica1 analyses and radio-

* 2 E carbon dating were taken in two monolith tins in 1985 : 2

o and the stratigraphy recorded in the field in 1986 (Fig. C9 2 R - 3.12). The differences in altitude of the strata arose 6 S 2 'a because the monolith samples were taken from a vertical

Y Y, face cut into the raked ditch bank, whereas the field Y

0 3 g record was taken on the raked ditch bank and projected * - I 2 g- onto a vertical plane.

At the pollen sampling site (0 cm on Fig. 3.12, and P S :

0

on Fig. 3.13), the following palaeoenvironmental % S

(D - .Ej .g I

changes were recorded. In the basal clayey silt, Cardzum shells in their living positions were recorded in April 3

S 5 1985, bearing witness to the low intertidal conditions * S B o under which this sediment accumulated. In January 2 % 0 -

I 1986 when the stratigraphy was recorded, the water .Y U e table was too high and the stratum with Cardium was not t Y

0 seen. Stratum 3 was a black crumbly limus dominated by

E $ - non-arboreal pollen (Fig. 3.14). At the base ofstratum 3, there were low frequencies or single grains of pollen of

? saltmarsh taxa, such as Silene-type, Artemiria and Aster-

$ o type, but these were succeeded by the pollen of

9 - I

reedswamp taxa, such as Typha angustzfolia, HydrocogLe, Galium-type and Mentha. The pollen assemblage in stratum 4 shows a reduction in the frequency of pollen of

o reedswamp taxa, and an increase in the pollen of P - saltmarsh taxa, such as Chenopodiaceae, Plantago

[r maritima, Glaux, Silene-type and Spergularia-type. The

5 0 0 0 0 0 0 0 presence of pollen and spores of pastoral indicators, as

g 'D - well as the pattern of changing frequencies of saltmarsh

W and reedswamp pollen taxa, points to a similar age for W T 2

? strata 3 and 4 at Broomhill-A and strata 1-4 at

- 4 5 Broomhill- l . e S ),I z m -

I I I I l 1 1 1 1 1 l l 1 1 1 l l Stratum 4 at Broomhill-A is overlain by a laminated,

X 5 I w ~ ) l l & d * a 0 S o o buff-coloured, sandy silt with iron concretions. This

S & a o i + + ; stratum is rich in both numbers and species diversity of m * P N - - Foraminifera (Appendix 1). TKe foraminiferal as-

TISHY'S SEWER BROOMHILL - A

South- east

Fig. 3.11 The section at Tishy's Sewer, Broomhill-A showing the boundaries at the four sampling points. The bolmdaries wen: recorded from a cleaned, raked section along the north-east face of the fewer.

P O . "

D , O l r n t Portli,. Ins Dlltrbvllon

Cnsmlcols LOS, 0" sn,t,sn

C-14

- O 3520 f60

Fig. 3.12 The stratigraphy andphysical properties of the sediments for each stratum recorded at four sampling points at Tishy's Sewer, Broomhill-A in January 1986. Monolith samples were collected from point 0 by Jill Eddison in January 1985and the site was leoelled in ,4pril 1985. The stratigraphic symbols and the symbols for the physical properties of each stratum are according to Troels-Smilh

(1955).

Fig. 3.13 The stratigraphic section from Tiishy's Sewer, Broomhill-A, based on Figs. 3.11 and 3.12, and employing the conventions for showing the components of each stratum according to Troels-Smith (1955).

Water Level Changrs and Sedimentation 67

semblage from 59-61 cm is a mixed death assemblage, dominated by Protelphidium anglicurn and Jadammina macrescens, both of which indicate a brackish water marsh. However, there is a higher percentage of species from the inner shelf than would be expected from such marsh environments. A similar situation obtains in the Severn estuary (Murray and Hawkins 1976) and it is probable that the transported Foraminifera indicate net transport directions. Hence, as in the Severn estuary, the origin ofthe silt in the Dungeness area will be not only from the land but also from the sea. Dr. Huddart (Appendix 1) explains the mixed death assemblage and the species diversity in terms of sedimentation in quiet water brackish lagoons protected by beach ridges, which are breached occasionally, allowing inner shelf forms to enter the lagoons. In the context of the beach ridges initiating the formation of the cuspate foreland of Dungeness, such a mechanism is quite appropriate, and further support is given by the proximity of buried shingle ridges at Broomhill- l .

The palaeocreek at - 100 to - 300 cm provides evidence of a period either of creek meandering and infilling or ofincision following a fall of sea level after the deposition of the sandy, silty clay (stratum 6 at 0 cm), and subsequently a period of infilling with a coarsening upward sequence (strata 1-3) followed by a fining upward sequence (strata 4 and 5). The presence of a clayey silt with laminations of clay and peaty detritus in stratum 1, of Nereis burrows filled with fine sand and indurated with iron in strata 1 and 3, and Scrobicularia plana in their living positions in stratum 4 and of clayey silt with diffuse iron staining in stratum 5, points to a more complex process of creek infilling than the well stratified, fining upwards sequence described by Evans (1965) from the creeks of the intertidal flats of the Wash.

The evidence from Broomhill-A provides several sea- level index points, two of which have been radiocarbon dated. In the pre-palaeocreek section, tidal flat sedimentation ended at an altitude of + 1.2 m O D and was replaced by biogenic sedimentation (strata 2 and 3), where a radiocarbon assay yielded a date of 3520f 60 BP (Q, 2649). Within the biogenic strata (3 and 4) the rise and fall of the pollen of aquatic taxa in stratum 3 and the rise of the pollen of saltmarsh taxa in stratum 4 presages the transgressive overlap. The overlap occurs a t an altitude of + 1.4 m O D and is dated to 3060 f 60 BP (Q. 2650). Immediately above the dated organic strata, laminated sandy silts with iron concretions and containing a high marsh assemblage of Foraminifera are recorded, and these pass up in a coarsening upwards sequence to a silty fine sand with occasional shell fragments of Cardium and no iron staining (stratum 4) to a fine sand conspicuously laminated and strongly iron stained (stratum 5) and thence back to a laminated silty fine sand, with some iron staining (stratum 6).

The cutting of a palaeocreek through this sequence with a floor altitude < + 0.6m OD, followed by infilling up to c. 2.4 m OD, provides evidence of complex water level changes post-dating 3060f 60 BP (Q. 2650), associated with the establishment of a creek system

draining into the Wainway Channel and with the continued progradation of the shingle barriers eastward.

Discussion The data from the sampling points in Horsemarsh valley and Broomhill have yielded six dated sea-level index points in the form of three transgressive overlaps and three regressive overlaps. Both stratigraphic and micropalaeontologica1 data have been employed to establish the nature of the overlaps and the sequences that precede and succeed them. Erosional and landform evidence can also be used. The eight sampling points in Horsemarsh valley and twelve sampling points a t Broomhill constitute sites, and the sea-level index points are representative of the points sampled in these two sites.

The second stage in the methodology is to determine the extent to which correlation of index points between sites is possible and to determine whether or not Romney Marsh and its catchment of lower river valleys with marine alluvium constitute an area within which a pattern of tendencies of sea-level movement can be established.

The sea-level index points from Horsemarsh valley and Broomhill can be enhanced with additional data from the marsh and its catchment (Shephard-Thorn et al. 1966; Smart et al. 1966; Green 1968; Shephard-Thorn 1975; Waller et al. 1988).

The temporal pattern of transgressive and regressive overlaps is shown on Fig. 3.15, which is based on the data displayed in Table 1.

The third stage is to enhance the overlap data with additional lithostratigraphic, biostratigraphic and landform data drawn from the area to demonstrate regional tendencies of sea-level movement (also shown on Fig. 3.15). Both negative and positive tendencies can be inferred: the former indicate an apparent decrease in the marine influence, whereas the latter indicate an apparent increase (Shennan 1983b).

The only index point on Fig. 3.15 that does not fit the partial chronology is the date from the transgressive overlap at the Blackwall Bridge, Wittersham Level, in the Rother valley (IGS/C14/13 3560f 100 BP). However, Waller et al. (1988, Fig. 1.8) have shown very clearly that the dated sample came from within the main peat bed of the valley and well below the level of the transgressive overlap. Hence, the date of the overlap is younger than the date of 3560f 100 BP, which would place this overlap within the group of sea-level index points from Walland Marsh, Appledore Dowels and Broomhill. Together these index points indicate a positive tendency of sea-level movement affecting an extensive area of the marsh and well up the main river valley. The index points come from quite different palaeoenvironments: Walland Marsh and Appledore Dowels are examples of tidal flat and lagoonal palaeoenvironments (sensu Hageman 1969 and Tooley 1978a, 1985b) whereas a t Broomhill low altitude shingle

68 Michael Tooley and V. R~JV Switsur

I I I I I I I I I

14 C years B.P.

2 Transgressive overlaps 9 A

Fig. 3.15 A graph to show the stages in the exploratory model of sea-level investigations.

I

A: distribution of sixteen radiocarbon dates on transgressive or regressioe overlaps in Dungeness - Romney Marsh - Walland iMarsh and in the adjacent lower river valleys shown in Table 3.1. B: distribution of twenty-four sea-level index points listed in Table 3.1 showing positive and negative sea-level tendencies from the same area. Solid lines are radiocarbon dates: dashed lines are estimated ages of tendencies based on lithostratigraphic and landform evidence. C: provisional partial chronolog~ of tendencies of sea-level movement in the the same area. L): a continuous chronology of tendencies of sea-level movement from the Fenland according to Shennan (19866). W ( W a s h ) indicates periods dominated by positive sea-level tendencies and Fe ( Fenland), periods dominated by negative sea-level tendencies.

I

ridges have been overlapped by tidal flat and lagoonal sediments. The transgressive overlap from Blackwall Bridge came from the lower part of the Rother valley, where perimarine sediments (sensu Hageman 1969) and tidal flat and lagoonal sediments are found. The temporal concurrence of these index points from different palaeoenvironments permits the identification of a positive tendency of sea-level movement and suggests that the conclusions of Jennings and Smyth ( 1982, 1985) from their investigations of coastal deposits further west in East Sussex that the lithostratigraphy can best be explained by local processes, especially the construction and breaching cycles of barriers, may require re-examination.

Another clustering of dates indicating a negative tendency of sea-level movement would be about 5000 BP, when index points from Horsemarsh valley, Wittersham Level and Pett Level record regressive overlap conditions.

Although the data base is, at present, small, and the periods of positive and negative tendency of sea-level movement are provisional and in part speculative, the results are sufficiently encouraging to conclude that, notwithstanding the diverse sedimentary environments, between-site correlation has pointed to the existence of an 'area'. The data base needs to be enlarged and considerably enhanced using results from further lithostratigraphic, biostratigraphic and chronostrati- graphic investigations on the marsh and its catchment. Further enhancement will derive from archaeological work on prehistoric and historic sites on the marsh. In this way, the provisional partial chronology of tendencies of sea-level movement can be converted into firstly a partial and secondly a continuous chronology, and between-area correlations made.

I t is premature to embark on a detailed consideration of between-area correlations, except to draw attention to

r, Regressive overlaps 7 z Positive tendencies 12

I 111111: , il I I B l I I I I

I I I

z Negative tendencies 12 I I 111 1 II :: : I

Positive tendencies of sea - level movement

I C

I I Negative tendencies of sea - level movement

Wash W.1 e- - -

W.II W.III / IV W.V W.VI D

Fenland Fe.1 Fe.ll Fe.lV Fe.V Fe.VI

L L

-

Water Level Changes and Sedimentation

Table 3.1 Data used for constructing Figure 3.15

Fig. 13.15A Radiocarbon dates on overlaps

Transgressive overlaps

Name Sources Lab. Code 14C date ( t t = 5570 f 30) Material

Wheelsgate, Old Romney Old Place, Icklesham Appledore Dowels Tishy's Sewer, Broomhill-A Tishy's Sewer, Broomhill-l Court Lodge, Old Romney Blackwell Bridge, Wittersham Horsemarsh Sewer Tilling Green, Rye

Regressive overlaps

(1) NPL.25 (2) SRR.2893 (1) NPL.23 (3) Q.2650 (3) Q.2652 (1) NPL.24 (4) IGS/C14/13 (St. 3068) (3) Q.2647 (5) IGS/C14/116 (St.3835)

Scrobicularia plana shells Peat Wood Silty Limus detrituosus Silty Limus detrituosus Wood Peat Silty Limus detrituosus ?

Name Sources

Scotney Farm, Lydd (6) Scotney Farm, Lydd (6) Tishy's Sewer, Broomhill-l (3) Tishy's Sewer, Broomhill-A (3) Blackwell Bridge, Wittersham (4) Horsemarsh Sewer (3) Brede Bridge (2)

14C date Lab. Code (t* = 5570 f 30) Material

NPL.91 2050 f 90 Peat NPL.92 2740 * 400 Roots Q.2651 3410f 60 Limus detrituosus with flints Q.2649 3520 f 60 Silty Limus detrituosus IGS/C14/14 (St.3069) 4845 f 100 Peat Q.2648 5150+70 Silty Limus detrituosus SRR.2646 5970f 150 Clayey peat

Fig. 3.15B Additional Data c. 6900 BP, positive tendency indicated by thelithostratigraphy at Old Place, Brede Valley (2). Age estimation by interpolation and altitude. IGS/C14/116 (St.3835) and SRR.2646.

c. 2600 BP, positive tendency indicated by the infilling of the palaeocreek at Tishy's Sewer, Broomhill-A.

c. 1900 BP, positive tendency indicated by the infilling of the palaeocreek at Wheelsgate near Old Romney and formation of creek ridge no. 2 (Green 1968, 28).

c. 1700 BP, negative tendency indicated by the lithostratigraphy at Old Place, Brede Valley (2). Age estimation by interpolation and altitude, IGS/C14/166 (St.3835) and SRR.2646.

5300 f 100 (1GS/C14/56.St.3405) and 5205 f 100 (lGS/C14/55.St.3400) two dates (7) on wood and peat from the 'submerged forest' at Pett interpreted as evidence for a negative tendency.

c. 2900 BP, negative tendency indicated by the cutting of the palaeocreek at Tishy's Sewer, Broomhill-A.

c. 2800 BP, negative tendency indicated by the abandonment oithe crrek ridges in the Horsemarsh valley with crest altitudes of + 1.1 and + 1.5 m OD.

c. 2800 BP, negative tendency indicated by the cutting of the palaeocreek at Scotney Court Farm, Lydd.

NB These interpretations are tentative and provisional: other interpretations are possible and revision is inevitablr as more data from the marsh becomes available. Figure 3.15C should not be used as a basis for correlation.

Sources: 1. Callow et al. 1964 2. Waller et al. 1988 3. Tooley and Switsur 1988 4. Welin et al. 1971 5. Welin et al. 1974 6. Callow et al. 1966 7. Welin et al. 1972

the fact that the provisional partial chronology of tendencies of sea-level movement for Romney Marsh and its catchment is out of phase with the continuous chronology for the Fenland (Fig. 3.15) (Shennan 1982, 1986a, 1986b; Shennan et al. 1983). An objective of future research would be to determine whether these differences are real or imaginary - an artefact of the methodology used - and to explain real differences in terms of differential subsidence or uplift, changes in palaeotidal regimes, sediment source and supply, and the r6le of the shingle barriers in affecting the nature, type and extent of sedimentation on the marsh.

Acknowledgements It is a great pleasure to thank Mrs. Jill Eddison for introducing one of us (M. J. T.) to 'the fifth quarter of the globe', and to the complex geography of Romney Marsh. In addition, she has been unstinting in helping in the field and in providing, often at very short notice, a base at Bethersden from which to work. We are grateful to Mrs. S. Block for drawing attention to the fresh exposures at Tishy's Sewer.

Many people helped at Durham in the collection of data both in the field and in the laboratory, and in

Michael Toolty and V. R~oy Switsur

preparing those data for publication: they are Mr. Frank grant from Durham University Staff Travel Fund to Bell, Mr. Arthur Corner, Mr. David Cowton, Mr. David undertake the field work upon which this chapter is Hume, Mr. Derek Hudspeth, Mrs. Joan Dorrill, Mrs. based. V. Roy Switsur gratefully acknowledges the help Vicki Innes and Mr. Jim Innes. Dr. Ian Shennan read of Mr. Alan Ward at the Godwin Laboratory, and commented on a draft of this paper. Cambridge.

Michael Tooley gratefully acknowledges the receipt of

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Appendix 3.1 The Forarninzfera from Broomhill-A (layer 5, 59-61 cm) - David Huddart.

Species JVo.

Protelphidium anglicum 68

Jadammina macrescens 57

Buccella frigida 20

Ammonia tepida 10

Elphidium earlandi 7

Elphidium umbilicatulum 6

Elphidium excavatum forma clavata 5

Bolivina pseudoplicata 5

Elphidium macellum 4

Elphidium incertum 4

Trochammina inflata 3 Ammonia aberdoveyensis 2

Triloculina trihedra 2

Oolina laevigata 2

Lagena clavata 1

Patellina corrugata 1

Elphidium excavatum forma selseyense 1

Rosalina williamsoni 1

Bulimina elongata 1

Bolivina ordinaria 1

Virgulina fusiformis I Total 202

Species Diversity 13 Total Number Of Species 21

This foraminiferal assemblage is a mixed death-assemblage from four well defined zones. These are :- a) High Marsh with 3. macrescens/T.inJlata b) Upper-Middle Low Marsh with Ammonia sp., P.anglicum,

E.excauatum c) Lower Low Marsh with P.anglicum, E.excauatum, E.umbilicatulurn d) Sublittoral, inner shelf with Elphidia spp. Lagena clavata, Patellina

corrugata, Oolina laeuigata, Triloculina trihedra, figulina fusiformzs, Rosalina williamsoni, Boliuina sp., Buccella frigida.

The brackish water marsh Formaminifera Protelphidium anglicum and Jadammina macrescens dominate the assemblage with 61.9% but there is also a relatively higher than normal percentage of inner shelf species present. Most ofthese shelfsperies are small and easily transported but there is a significant proportion of larger Elphidia. Possibly the environmental explanation is quiet-water brackish lagoons protected from the open shelf by beach ridges, which were broken periodically with the resulting transport and mixing of the foraminiferal assemblages. There is one ostracod present with both valves intact.