Barton-on-Sea and Highcliffe - Coast Erosion and Sea Defences

History of Coast Erosion and Sea Defences at Barton-on-Sea and Highcliffe

Barton and Highcliffe - Coast Erosion
History of Coast Erosion and Sea Defences at Barton-on-Sea and Highcliffe
Barton and Highcliffe - Bibliography
Hordle Cliff
Hurst Spit
Hengistbury Head and Mudeford Spit

LOCATION -

Barton-on-Sea, Hampshire

See Barton-on-Sea location on zoomable Bing aerial photographs and maps. See also Google Earth.

INTRODUCTION:

Safety

The main hazard at Highcliffe, Barton and Hordle Cliff is of sinking into soft mud, particularly on the clay terraces above the beach level. In wet conditions it is wise to stay on the beach and collect from the lowest part of the cliffs. On the few Highcliffe and Barton coast sections with steep cliffs there is a small risk of being struck by a falling rock, pebble or lump of mud. Safety helmets might be needed where such risk exists. Landslides are common in the area. Generally these do not move fast and are more of a hazard to property than to people. However, care should be taken. Adders live on these cliffs but bites are very rare. It is hazardous to stand on the cliff-top of gravel close to the edge. At some places there is a hazardous overhang.

INTRODUCTION:

Geology of Barton and Highcliffe - Maps and Locations

See also the Barton and Highcliffe Coast Erosion and Sea Defences webpage.

INTRODUCTION-STRATA:

Barton and Highcliffe Strata - General Introduction

The Barton Clay, the Barton Sand and the overlying Headon Hill Formation (of the Solent Group) form part of the well-known Hampshire Basin, and are exposed at Barton and Highcliffe in Christchurch Bay, and also at Alum Bay and Whitecliff Bay, in the Isle of Wight. The strata are of the Bartonian and Priabonian Stages of the Upper Eocene Series. In terms of age in years these strata were deposited between about 42.1 amd 35.4 million years (Harland et al., 1982). They correspond roughly in age with the famous Eocene gypsum deposits of Paris (from whence comes the name - Plaster of Paris).

The type-section of the Barton Clay and Barton Sand at Barton Cliffs on the mainland consists of sandy clays in the lower part , dark sandy clays and stiff drab clays in the middle part, and clayey sands and light-coloured sands in the upper part (29.26m). The total was given as 61.56m by Burton (1929) but Barton (1973) has more recently considered the Barton Clay to be thicker (46.4m) and given a total figure for the Barton Beds of 75.4m (note that Bristow, Freshney and Penn (1991) gave the range of the Barton Clay thickness in the Bournemouth area as 20 - 60m, less than this figure but probably based on Burton).

Most of the strata are very fossiliferous. The Barton Clay has yielded more than 500 species of fossil mollusc shells. These are quite robust and can easily be cleaned by simply washing them with a soft brush. They look much like modern subtropical shells but have lost their colour. The shell, though, is still of the original aragonite and only the organic matter has been lost. They range from minute corals (Turbinolia) and the little, prickly gastropod Typhis pungens to the robust and fairly common gastropod - Clavilithes macrospira to the rare fan-shell Hippochrenes amplus . The turreted gastropods Turritella imbricateria and Turritella sulcifera are very common, and sharks teeth and ray-fish teeth (see above) can be found from time to time. Both the sea-defences and the retreat of the coast away from the most fossiliferous strata has much reduced the fossil-collecting potential. Nevertheless good specimens can still be found in the Naish Farm area between Barton and Highcliffe, and the cliffs at the back of the beach here are well-worth a visit.

Not much of the Barton Clay can be seen from Barton eastward to the end of the Marine Drive East. The cliffs have large blocks of limestone at the base, some timber piles, much gravel spread above and some iron sheet-piling here and there. The engineering works also require roads or tracks for vehicles and machines. This central section is instructive with regard to the development of landslides, the use of and failure of sea-defences. It is also a good area to see the Pleistocene gravel at the top of the cliff and the yellow, oxidised Barton Sands or Becton Sand Formation. Apart from geologists it is of interest to geography students, environmental science students and civil engineering students. A visit is recommended.

East of Barton natural cliffs and good exposures start again near Becton Bunny. Longshore drift is from west to east because of the prevailing southwesterly winds. Much protective beach debris cannot get eastward past the Barton sea-defences, which are designed to hold it, so here there is terminal scour and enhanced coast erosion. This enables the Barton Sands or Becton Sand Formation to be seen in quite good exposures. There are some shells, of which the most robust is the white and conspicuous bivalve Chama squamosa of the Chama Bed. Above this horizon the bivalves and gastropods are thin-shelled, being of sheltered lagoonal or estuarine origin. The shells are not as strong or as abundant as in the Barton Clay.

STRATIGRAPHY

Succession of Strata

Pleistocene	Brickearth Plateau Gravel	0 - 2.1m 1.5 - 7.6m.
Eocene	Solent Group, Headon Hill Fm. (lower part only) Becton & Chama Sand Fms. (Barton Sand) Barton Clay Formation Bracklesham Group, Boscombe Sands ("Mudeford Sands" or "Highcliffe Sands" at Friars Cliff)	29m. 46.4m. >12m.

Thicknesses are from Barton (1973). The Plateau Gravel of Pleistocene age lies unconformably on the Barton Clay and Barton Sand (Chama Sand and Becton Sand). The Brickearth at the top of the gravel is a periglacial silt deposit, light brown in colour.

Above is the key diagram of the Eocene sequence here (click or double-click to enlarge!). To study the Highcliffe, Barton and Hordle Cliff sections successfully the field geologist should as far as possible commit this sequence to memory, keeping a paper copy at hand to remind him or her of the details. This is because parts of the section are obscured by sea defences and much is slumped in the cliffs or is overgrown with vegetation.

As is always the case when dealing with cliff sections look first for conspicuous markers and work from those. The basal pebble bed which lies above a sandstone cliff - Friars Cliff is obvious. The basal clay of the Barton Clay can be seen, with the approximate position of the Nummulites prestwichianus bed (although in poor condition now). A1 and A2 are not properly exposed now because of sea defences at Highcliffe. A3 might be seen at the western base of the Naish Farm section, depending on coast erosion and extent of slumping of the cliffs. Bed C, the Voluta suspensa is very obvious and occupies much of the lower cliff between Naish Farm and the first Barton sea defences. It cannot be missed because of the septarian nodules above and below, and also the pale, bored bed in the centre. D, E and F are now seen in limited slumped exposures in the cliff, often of difficult access (because of risk of sinking in). Exposures of G, the Stone Band (or Shell Bed) are not as common as in the past but might be seen here and there in the Barton landslides. The Chama Bed can often be seen at the foot of the cliff at the eastern end of the Barton Sea Defences, near Becton Bunny. Beyond the the Barton Sands or Becton Sand succession is quite clear and easily studied near Becton Bunny. The Lignite Beds, L, are two conspicuous black bands seen in Beacon Cliff. The Headon Hill Formation is fairly well exposed in Beacon Cliff and Hordle Cliff and for further information on this see the Hordle Cliff webpage.

STRATA

Clay Mineralogy

Introduction

Summary of Clay Mineral Abundances

The following notes are based on the excellent, detailed work of "Tunde" Bale (1984) which summarises the clay mineralogy of the Barton Formation. Much more detail is given and the interested reader should consult the original thesis (available for reference in the National Oceanography Library, the National Oceanography Centre, Southampton).

The clay mineralogy of the Upper Eocene succession of the Hampshire Basin essentially comprises illite which is greater or equal to smectite. In turn smectite is greater or equal to kaolinite (the coarser and non-expandible clay mineral). This is more abundant than the mixed-layer, illite-smectite. Chlorite is common but in quantitative terms is minor compared with the other clay minerals. This assemblage is similar to that observed by Gilkes (1966), who did the pioneering work on the Hampshire Basin clay mineralogy. A major advance of the Bale work is the recognition of the mixed-layered phases, which he identified and estimated semi-quantitatively.

Dioctahedral smectite and illite dominate. Together, these two phases generally account for about 70% of the clay fractions. Illite occurs in higher amounts than smectite in the non-marine 'Lower Headon Beds', whilst approximately equal amounts of illite and smectite occur in the marine Barton Clay and Barton Sand Formations. Some horizons however. possess considerable higher smectite contents. These notably include the marine sequence at Whitecliff Bay and the lower parts of the Barton Sand at Barton. Kaolinite and illite-smectite occur in lesser amounts of around 8-20%. Chlorite occurs only as a minor constituent in a limited number of the marine sediments, and the lignitic clays. In addition, some smectites with chlorite interlayers occur in some of the lignitic clays and limestones, with abundant carbonaceous matter. Deviations from the above occur in the succession at Alum Bay. At this locality the smectite, illite-smectite and chlorite are absent or occur in very low amounts in the clay fractions of the pebble bed and the Barton Sand. The depletions are of high significance in the palaeosol at the top of the Barton Sand and the succeeding lower parts of the Headon Hill Formation at Hatherwood Point, near Alum Bay, Isle of Wight. The depletion of these phases is accompanied by a substantial increase in the amounts of kaolinite and/or illite. This peculiar clay mineralogy at Alum Bay is thought to be due to localised differential derivation of detritus and/or the imprint of surficial (acid soil pedogenesis) processes. These are discussed elsewhere

Discussion of the Clay Mineralogy

The discussion of the clay mineralogy of the Upper Eocene sediments is centred on three factors that generally dictate the assemblage and relative abundance of clay minerals in sedimentary rocks. These are the nature of the source; contemporaneous neoformations and/or alterations; and sedimentological factors such as 'differential settling'. Diagenetic transformations are not considered important because of the shallow burial (~ 200m depth) history of the Upper Eocene succession under study. The clay assemblage of the sediments and those of other Palaeogene sediments in southern England were then employed for deducing the palaeo-environmental conditions and presenting a new view of the derivation of the clay assemblage.

Derivation of the Clay Assemblage

i) Constancy of Source

The general constancy of the illite-smectite-kaolinite-illite/ smectite assemblage in the Upper Eocene sediments suggests constancy of sources of detritus. A similar deduction of constancy of source was made by Blondeau and Pomerol (1968) from a study of heavy mineral assemblages in the sediments. With illite and smectite dominating in the clay fractions, the clays belong to the 'eastern province' assemblage of Gi1kes (1966, 1967). This, Gi1kes believed, was derived mainly from rocks exposed to the north and east of the Hampshire Basin. This hypothesis is broadly acceptable. However, recent advances in the geology of southern England necessitate re-assessing and updating views on the clay derivation.

(to be continued)

STRATA:

Lower Barton Clay - Introduction

At Friars Cliff, to the west of the main Barton Clay section and between Highcliffe and Mudeford there is a good exposure of the base of the Barton Clay with the Boscombe Sands beneath. The sands here have, in the past, been regarded as younger than the strata at Hengistbury Head and have received various names, including the Highcliffe Sands. They are now regarded as the equivalent of the Boscombe Sands at Hengistbury Head and have the same conspicuous pebble bed above and not far above that the prestwichianus Bed (with Nummulites prestwichianus). See Bristow, Freshney and Penn (1991), the Bournemouth Memoir, for further details.

STRATA:

Lower Barton Clay - Description

See also the Barton and Highcliffe Coast Erosion and Sea Defences webpage.

Rather less than half of the Barton Clay belongs to the "Lower Barton Beds". Various authors, following Prestwich (1849), have taken the base of a pebble bed to be the base of the Barton Clay. It seems sensible to take what is probably a transgressive pebble bed as the base and that method is used here. Note, however, that Keeping (1887) and Curry et al. (1978) used the bottom of the Nummulites prestwichianus Bed, a little higher, as the base. This nummulite bed consists of green, glauconitic sandy clay. Most of the Lower Barton Beds which follow are rather sandy and they include the so-called Highcliff Sands of Gardner, Keeping and Monckton (1888) (not to be confused with the conspicuous sands of Bracklesham age at Friars Cliff). White (1917) summarised these beds. He stated that they take in a set of loamy sands with Voluta athleta (Sol.) and Cassis ambigua (Sol.) (now known as Volutocorbis ambigua (Solander)), and ends with rusty sand containing abundant Pholadomya margaritacea J. Sowerby. Unfortunately, with degradation of the cliff and with the construction of sea-defences little can be seen of these fossil beds now. The Lower Barton succession was said to be the richest in species of molluscs, with a large proportion resembling living forms from Australia and Japan, and seeming to indicate a considerable depth of water (White, 1917). Small corals (Turbinoliae), echinoderms (Ohphiura wetherelli Forbes, etc), claws of crabs, teeth of fish (Arius, Myliobatis, etc.), turtle bones, a few worn freshwater shells, and drift wood, are among other fossil remains present in these beds. For a full list see Burton (1933).

STRATIGRAPHY:

Middle Barton Beds - Barton Clay

See also the Naish Farm Section, as described in the Barton and Highcliffe Coast Erosion and Sea Defences webpage.

The Middle Barton Beds includes the part of the Barton Clay still visible in the cliffs in spite of sea-defences. It is seen from Chewton Bunny at Highcliffe eastward to Barton-on-Sea, with the best section at Naish Farm just east of Highcliffe. The Barton Clay of the Middle Barton Beds is more truely argillaceous than the Lower Barton. The large, spectacular fossil shells of the Barton Beds have mostly come from these clays, although it is less easy now to find such specimens than in the past. Sharks teeth are present here (as in the Lower Barton). This sequence has septarian nodules of argillaceous limestone, usually with some sand and some glauconite. The lowest two layers are of rounded nodules, but only the one at the top of Bed C, the Voluta suspensa Bed, is well exposed at present. Two upper bands of nodules were originally visible, but now the upper part of the cliff is either badly slumped or covered with sea-defences, so that only one is easily found. Near the upper nodule horizons are exceptionally-rich fossil beds (Bed E - the Earthy Bed). The top of the Barton Clay is marked by the Stone Band or Shell Band, probably a storm accumulation of shells or some type of shell beach. This is brown and sideritic. It is not always firmly lithified, but often is, producing reddish, hardened slabs, which can be found on the beaches. These reddish slabs are full of Turritella and various bivalves. The Barton Clay of the Middle Barton has yielded remains of a rare cetacean - Basilosaurus , formerly referred to as Zeuglodon wanklyni Seeley, some bones of which together with a fine collection of Barton molluscs are in the building of the Bournemouth Natural Science Society (White, 1917).

LOCATION

Naish Farm, Highcliffe - Barton Clay Exposure

This photograph shows the base of the cliffs with fossiliferous Barton Clay, east of Highcliffe and below Naish Farm at about map reference SZ224931. The view is westward across the mouth of Chewton Bunny to a grassy hill at Highcliffe in the mist. On the top of the cliff here is a large car park which is reached by driving south at a sign "to the sea" from the centre of the main shopping street of Highcliffe. There are toilets at the car park.

A large groyne with blocks of Portland Stone (from the Isle of Purbeck) projects from the coast at Chewton Bunny. Longshore drift is from west to east because of the prevailing south-westerly winds. On much of the south coast of England groynes are able to bank up sand on the west side and cut off the supply of beach material to the east. This common phenomenon is known as "terminal scour" and where it happens local enhanced erosion and even the formation of embayments may take place. Here there is a retreating clay cliff and a sandy beach. Although much of the Barton and Highcliffe coast has lost its natural appearance and been turned into a defended embankment, this stretch remains relatively natural and is conserved as such largely for geological purposes. At one time the whole coastline here was like this and justifiably famous for fossil collecting. Good fossils can still be found in the clay and are occasionally washed out on the shore.

The lower cliff is eroded by the sea at high tide and particularly during storms. Part of it, like the projecting bulge here, consists of landslipped debris and part is of clay in situ. The best fossils tend to be found in the clay in place, although shells and occasionally vertebrate remains can also be found in the moved clay debris.

Here is a representative part of the cliff in the Naish Farm stretch (on 07.03.01). Most of the cliff consists of the dark grey Barton Clay, but at the top are a few metres of Plateau Gravel of Pleistocene age. This is the remains of a periglacial river terrace, that we will consider further later. The light brown gravel is to some extent slumping over the clay. You can see two terraces of Barton Clay with liquid mud flowing over the brink from the upper one. The mud is supplied with water that runs out from the porous and permeable gravel at the top. The combination of steepening of the cliff by the sea and the supply of water from above results in many small landslides. Incidently, the clay is "steaming" because the morning sun is just beginning to warm the wet, dark, heat-absorbing surface.

Coastal retreat of the Barton Clay cliffs has averaged about a metre per annum, but may be locally higher in the Naish Farm area, because of the effects of sea defences to the west. The low cliff formed by erosion of the lowest terrace is, just here, mostly of landslipped debris and is not good for fossil collecting. On the beach there are numerous septarian nodules washed out of the clay, as shown above. The sea floor offshore consists of numerous, residual septarian nodules of this type.

A little further east there is an undisturbed cliff and by comparision with the cliff diagram provided in this website the position can be fixed. Bed C is easily recognised because it between two septarian bands and with a thin, burrowed, light-grey marl in its central part.

The view is to the east, towards Barton on Sea, although it was not clearly visible because of mist when the photograph was taken. A terrace that was higher has descended to the beach now. Much of the clay here is in place, but there is some slumping, and some small channels of water and mud that descend to the beach. Notice the septarian nodules two-thirds way up the cliff in the left part of the photograph. These mark the top of bed C. This is a good place for collecting fossils, mostly because the clay is in situ . The tilted gun emplacement largely now buried under the beach sand. I knew this years ago when it was against the cliff, and still just about possible to get into. The gun emplacement was a cliff-top defence against invasion by Germany constructed in about 1940 in the Second World War. Accurate determination of the distance of this from the present cliff top would gove a measure of the extent of coastal retreat just here. See one at Abbotsbury on the Chesil Beach, and notice how the erosion there has been much less. The beach was photographed at low tide and consists largely of sand but much gravel. The sand has probably mostly come partly from sand within the Pleistocene gravel but also from much sand dispersed within the Barton Clay. Dark green glauconite grains in the beach sand demonstrate the Tertiary origin of much of it. The gravel is brown and subangular and has come from the Plateau Gravel. Only the clay is not accounted for. This is washed out to sea and in stormy conditions the muddy nature of the seawater is clearly seen.

STRATIGRAPHY continued:

Becton Sand Formation or Barton Sands

The Barton Sands or Becton Sand comprises about 27 to 30m of light-coloured, fine-grained sands, with some loamy and clayey beds, particularly at the base and near the top. These sands can be seen clearly in the photographs taken at the eastern end of the Barton sea defences. Because beach sediment can no longer easily reach here from the west (longshore drift is from west to east), being arrested by the sea-defences, erosion is intense and yielded excellent exposures of the Barton Sand or Becton Sand. The junction with the Barton Clay, marked by the Turritella-rich and iron-rich Shell Bed or Stone Band, is not exposed at present here, however, and it is the upper part of the Chama Bed which is first seen, unprotected, on the shore.

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STRATIGRAPHY continued:

The Chama Bed - Bed H

The Chama Bed, immediately above the Barton Clay, is a shelly, bluish-grey, sandy clay passing up into clayey sand. Chama incidently is pronounced "Kay-ma" because of the Greek origin of the name according to the late Professor Dennis Curry. The characteristic bivalve Chama squamosa Solander is abundant (squamous, incidently, means scaley, which well describes the appearance of this bivalve). It is sometimes found with paired valves, but, in general, as shown in the photographs, it is present in a death assemblage, a thanatocoenose. Probably there has been little distant transport of these shells, but movement by storms of the argillaceous shoal-sand in which they lived. Chama is a genus ranging from probably Upper Cretaceous to Recent. It is an epifaunal suspension feeder and usually attached. The modern Chama, larger and more spiny than these specimens, is known as a "Jewell Box" and occurs on reefs in Indo-Pacific tropical waters. I do not know whether the Barton Chama was attached, and if so, what to. The palaeolatitude was not tropical; it was about 37 degrees north, about the same as southern Spain, but a little wetter with no significant evaporites (not north of Paris). The temperature was higher than normal in the Eocene, though, so the presence of these tropical shells is not surprising. I wonder if they had some reddish or violet colour to them, like the modern ones.

A interesting aspect of the shells is the extent to which many have been bored by marine organisms. The shells are certainly thick enough to contain many borings, but it is not clear just why the borings are such features here because they are not particularly abundant elsewhere in the Barton strata.

The Chama Bed is now extensively covered by sea-defences of limestone blocks and gravel, further west but it is a notorious bed for quicksands, water running through the Barton Sands and emerging in this poorly lithified basal unit. Most of the quicksands in the cliff are now covered, but it is still a problem to horse riders in the New Forest, forming small but treacherous, yellow boggy springs on Yew Tree Heath and elsewhere in the eastern Forest. Oxidation of pyrite within it produces chalybeate (iron) springs both in the cliffs and in the New Forest. Notice the "rusting" along a crack in one photograph and the iron-cementation of some flint shingle from the beach on the face of the exposure in another. At Calshot, in the power station outfall tunnel, it is an oyster bed rather than a typical Chama Bed. The blue-green colour of the Chama bed is mostly the result of a content of much glauconite amongst the sand, but there is some variation in appearance according to the extent of oxidation and the proportion of clay present.

Burton (1929; 1933) has discussed the general characteristics and fauna of the Chama Bed. At Barton it is 5.5m (18 feet) thick. The lower part, 3m (10 feet), consists of bluish-grey sandy clay with numerous fossils. The upper part, 2.4m (8 feet), consists of greenish grey or bluish grey, clayey sand with fewer fossils, chiefly bivalves. It is this upper part which is shown here in the photographs, and has relatively few shells apart from Chama. If you look carefully, though, you will notice part of a Turritella. Of all the subdivisions of the Barton Beds, it is the lower part of the Chama Bed which has most foraminifera. Bryozoa are more numerous in this bed than in the Barton Clay beneath. An interesting feature of the Chama Bed, not normally seen now, is the presence of spheroidal concretions from 0.3m to almost a metre in diameter.

Burton (1933) pointed out that molluscs do not occur as thin seams of shells, as in the lower beds, but are distributed throughout the vertical extent of the bed. They can be lost through decalcification. This is seen in the top of the present exposure of the bed, where there are only moulds, and there has been decalcification where the bed is high in the cliff, west of Barton Court. The lower part is characterised by Chama squamosa and Lyria decora and the upper part by 'Meretrix' incurvata and Volutolithes pertusus. The fauna embodies a number of species not occurring in the lower subdivisions at Barton. Common Lower Barton species, absent in the Middle Barton, but reappearing in the Chama Bed are: Calliostoma nodulosum and Tornatellaea simulata . For more information on the fauna see Burton's (1933) faunal list for Bed H in his section VII. The bed is also exposed at Alum Bay and Whitecliff Bay; it is of broadly similar thickness and is very fossiliferous at both localities (White, 1921)

The Chama Bed can be regarded as a marker of a significant local change in enviroment about 40 million years ago. According to Murray and Wright (1974) the Barton Clay beneath is of shelf regime until the Chama Bed indicates marked shoaling. There was a silting-up of the sea, heralding the lagoonal and freshwater conditions of the Headon Hill Formation which were to follow in a while.

Above the Chama Bed come the Becton Bunny Beds; these are light-coloured unfossiliferous sands overlain by "earthy" sands. There follows dark sandy clay with the brackish water bivalve - Oliva branderi J. Sowerby. Next there is sandy loam with brackish water shells such as Cyrena, Dreissensia, Erodona etc. (White, 1917). Finally the white and yellow sands of the Long Mead End Beds contain Lucina gibbosula Lam., Batillaria pleurotomoides Lam. etc and are terminated by a thin band of greenish clay at the junction with the Headon Hill Formation ("Headon Beds" in the old literature). The Barton Sands shows evidence of shoaling water conditions and a progressive change towards the lagoonal and lacustrine environments of the Headon Hill Formation.

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STRATIGRAPHY continued:

Becton Sand Formation - Bed I

Next follows 7.9m (26 feet) of grey, yellow and white sand. It consists of greyish, micaceous sands in which the grains are held together by fine argillaceous natter. Below Barton Court parts of it are vivid yellow in colour, but it seems paler at a low level near the beach. It has been described as unfossiliferous, but moulds of shells occur in the upper part (Burton,1929;1933).

. STRATIGRAPHY continued

Becton Bunny Bed or the Oliva branderi Bed - Bed J

This shows the excellent exposure of the Becton Sands beyond the eastern end of the Barton sea-defences as seen from the cliff-top in September 2002. Becton Bunny is the vegetated valley or ravine on the left and has a small stream at the base. There has been some further erosion in this area by October 2003 but the cliff-face is similarly well-exposed.

Ian West, at the bottom of the cliff at the same locality. There is good access to the Becton Sands, with fallen material from the Becton Bunny Bed seen just here. It descends to the beach a short distance further east.

This grey argillaceous unit is well-seen in the photographs. It is 7.9m (26 feet) thick. Drab grey sandy clay forms the lowest 1.8m (6 feet), followed by 6m (20 feet) of greenish grey sandy clay, with much ferruginous matter near the surface. This causes it to weather to a pinkish drab colour. At about 3m (10 feet) from the base there are small spheroidal ferruginous concretions, averaging only about 10 cm (4 inches) in diameter (Burton,1929; 1933). Marine to brackish fossils are numerous but fragile and difficult to collect. The distinctive gastropod Olivella branderi is abundant, but also occurs in the bed above. Nautilus has been found but Turritella does not occur so high in the Barton sequence.

The cliffs near Highcliffe Castle were once subject to rapid erosion of the type that now takes place at the Naish Farm Section (in the Barton and Highcliffe Coast Erosion and Sea Defences webpage).

. Numerous small fossil and fish otoliths have been found in these cliffs in the beds A1 and A2 of the Lower Barton Clay. Now the beach has built up, just westward of the rock armour groynes of the Highcliffe sea defences. The sea rarely has much access to the cliffs now and the exposures are very poor. However, if you walk a few hundred metres further west to Friars Cliff then there is a good section of the Boscombe Sands overlain by the Lower Barton Clay. This is shown in the photographs which follow.

This section of coast between the main car park at Highcliffe and the end of the cliffs westward near Mudeford exposes the Upper Eocene, Lower Barton Beds underlain by the top of the Middle Eocene, Bracklesham strata. It is not as well exposed as previously. An interesting cliff of sand is visible in the western part but much of the eastern part of this stretch is now obscured by sea-defences and vegetation.

Barton Clay and Becton Sand Fossils

Barton Fossils of the Dent Collection

Bournemouth Natural Science Society of 39 Christchurch Road, Bournemouth, Dorset, BH1 3NS (telephone 01202-394534) has a large collection of fossils from the nearby coast of Barton and Highcliffe. The following notes are from Sir Daniel Morris in 1914:

Pleistocene Gravel

East of Barton Court, at the top of the cliffs there are good sections of Pleistocene, subangular, flint gravel lying unconformably on Eocene Barton Sand (Becton Sand Formation). At the location shown here, a few hundred metres east of Barton Court, a gravel terrace at about 30m height gives way eastward to a somewhat lower terrace. The periglacial river gravels contain much iron in ferric condition and this gives them their characteristic brown colour. Humic acids from decomposing vegetation in a podzol soil profile transports iron downwards in the relatively humid climate of southern England. The iron can be redeposited lower an iron-pan, and an example is shown here. These iron pans are not continuous for any great distance but in certain cases they are impervious enouth to hold up water. The Barton Sands beneath have been much oxidised and turned a more yellow colour than in the lower cliffs where eroded by the sea. Water goes through both the gravel and the underlying sand here and flows out at the base of the Barton Sands. This has been a major cause of landslipping in the past, and explains why landslides can sometimes be on a larger scale at Barton compared to Highcliffe.

Sedimentary structures in the gravels include shallow channels and some thin beds of sand. Cryoturbation structures from the freezing and thawing of the ground during periglacial conditions occur in places. Palaeolithic implements have been found here.

The brickearth above is a brown silt resembling loess. It has been claimed that in some places in southern England this is indeed of wind-blown origin. It may, however, in this area be largely river silt. Similar brickearth in the Hill Head area of Southampton Water has a clay mineral composition related to that of Chalk, but probably in that case there has been much solifluction from the Chalk of Portsdown Hill. The clay mineralogy of this brickearth in the Barton Cliffs has not been studied, but there is no nearby source of Chalk. Of course, the gravels beneath consist of the insoluble material, the flint, from the Chalk of the northern and western fringes of the Hampshire Basin, together with some Tertiary material. Exactly what was the origin of the brickearth is less obvious. Probably most has come ultimately from Tertiary clastic deposits with clay contributions from the Tertiary and Chalk and probably also with abraded flint debris (this is a suitable subject for a student project).

STRATIGRAPHY - PLEISTOCENE continued:

Brickearth

At the top of the cliff, over the gravel, is one to two metres of brickearth. This is a brown Pleistocene silt deposit, generally without visible stratification (there is one conspicuous parting in this area where the brickearth is very thick - 2 metres). It has been regarded by many as a loess deposit of wind-blown dust in cold conditions. Others have attributed it to solifluction. Near Salisbury a brickearth deposit has been found to contain the remains of lemmings which have been entombed in their burrows. It is of course possible that solifluction of a loess could occur.

Returning from the Cliffs

ADJACENT AREAS

For more on coast erosion and sea defences at Barton and Highcliffe see:

Barton and Highcliffe Coast Erosion Webpage.

Go west to:

Hengistbury Head and Mudeford Spit?

Go east to:

Hordle Cliff and Milford-on-Sea?

or

Hurst Spit?

ACKNOWLEDGEMENTS

I am very grateful to Paul Clasby for some very useful comments and corrections. Caroline Clasby and other students have assisted in the field. I thank Dr Ken Collins and Sarah Snowden for discussing septarian nodules in the field and the offshore distribution of Barton Clay horizons.

BIBLIOGRAPHY AND REFERENCES