The stratigraphy, sedimentology and palaeontology of the LowerWeald Clay (Hauterivian) at Keymer Tileworks, West Sussex,

southern England

Elizabeth Cook* and Andrew J. Ross"

COOK , E. & ROSS, A. 1. 1996. The stratigraphy, sedimentology and palaeontology of the Lower WealdClay (Hauterivian), at Keymer Tileworks, West Sussex, southern England. Proceedings of theGeologists' Association , 107, 231-239. The stratigraphy of the Weald Clay of Sussex in the region ofBurgess Hill is summarized. The Hauteri vianIBarremian boundary, using ostracod evidence in the Ripeborehole, appears to lie at the top of a red clay bed ju st below BGS Bed 3c2. Detailed sections of thesediments exposed in Keymer Tileworks clay pit are given. BGS Bed 3a is exposed at the top of the pit,indicating that the sediments below belong to the Lower Weald Clay and tire late Hauterivian in age. Thepit has yielded a divers e non-m arine fossil fauna and flora consisting of insects, dinosaurs, crocodil es,turtles, sharks, bony fish, crustaceans, molluscs, ferns, conifers and a new herbaceous, aquatic or marsh­dwelling plant. The insect s include the first Wealden records of the family Sciaridae (fungus gnats) andof the superfamily Coccoide a (scale insects). The sediments exposed and their fossil content indicatechanges from terrestrial condit ions through fluvial, culminating in a lacustrine environment.

• Department of Geology, University ofBristol, Wills Memorial Building, Queens Road, BristolBS81RJ.t Booth Museum ofNatu ral History. 194 Dyke Road, Brighron BN1 5AA; EESRU, University ofBrighton BN24GJ; Department ofPalaeontology, Natu ral History Museum, London SW7 5BD.

1. INTRODUCTION

The pit at Keymer Tileworlcs [National Grid Reference TQ323 193], Burgess Hill, West Sussex (Fig. I) exposes grey,green, purple and red clays with subordinate sandstones andsiltstones. The site has been worked since 1875 (Lobley,1882; Beswick, 1993), and has presumably produced fossilmaterials between then and now, although such finds seemrarely to have found their way into the literature. In 1927Mr. R. Kelsey of Keymer Tileworks donated an isolatedvertebra centrum (BMB 008263) to the Booth Museum,Brighton. It was identified by Sir Arthur Smith Woodwardas a sacral vertebra of an Iguanodon (J. Cooper, pers.comm.).

The Weald Clay was deposited in a non-marinelacustrine/lagoonal/mudplain environment in the subsidingWealden basin (Allen, 1981, 1990). The Keymer sedimentsillustrate a change in depositional environment fromoverbank to generally low-energy fluvio-Iacustrineconditions. They belong to the Lower Weald Clay, which isHauterivian in age (see below).

Many specimens of insects, plants and vertebrates havebeen found, the latter from a horizon of red clay located inthe northeastern corner of the pit. Most of the insects andplants were coIlected from sideritic mudstone and siltstonelenses higher up in the sequence. This paper describes thesedimentology of the clay pit, summarizes the floral andfaunal content and places the site stratigraphically withinthe Wealden succession.

Proceedings of the Geologists ' Association, 107,231-239.

2. STRATIGRAPHY

Very little has been published on the stratigraphy of theWeald Clay at the Keymer Tileworks clay pit. Reeves(1958) subdivided the Weald Clay into three groups. Heidentified the red clay at Keymer as his 'Oldest Red Clay'which marks the base of his Group II. Young & Lake (1988)gave a detailed section that was measured in 1977 andstated that the mudstones and sands lie 'at the level ofBed 3' in the terminology of the BGS.

Lithostratigraphy

Worssam (1978) recognized two major cyclic units in theWeald Clay which he referred to as lower and upperdivisions. He gave the boundary between the two units (nowgenerally regarded as the Lower and Upper Weald Clayformations) as the base of Topley's bed 5 and later indicatedthat this is equivalent to the base of British GeologicalSurvey (BGS) Bed 3a. The stratigraphy of the Weald Clayfor Sussex, east of the Burgess Hill fault, is shown in Fig. 2.

Keymer Tileworks pit is shown on British GeologicalSurvey Sheet 318/333 (Brighton and Worthing) to be justnorth of a sandstone bed. This bed crops out at the top of thepit and is the lowest of a group of four which are simplyreferred to as bed 3 in Young & Lake (1988). At the westernend of Sheet 318/333, four sandstone beds crop out that arereferred to as 3a, 3c1, 3c2 and 3e (GaIlois & Worssam,1993, p. 83). Bed 3a can be traced across the map area. It

00 16-7878/96 $07·00 © 1996 Geologists ' Associa tion

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232 E . COOK AND A . J. ROSS

10km

Fig. I. Outcrop area of the Weald Clay over southeastern England showing the location of the Keymer Tileworks and BGS map areas 318and 319.

forms the most northerly of the group of four, and is the onethat crops out at the top of the pit. The three overlying itmay be referred to as 3cl, 3c2 and 3e for convenience, butthere is uncertainty as to whether these correlate with thebeds outcropping at the western end of Sheet 318/333. Thebase of BOS Bed 3a is the boundary between the Lower andUpper Weald Clay. The sediments below Bed 3a at KeymerTileworks clay pit thus belong to the Lower Weald Clay.

Chronostratigraphy

Worssam (1978) indicated that the LowerlUpper WealdClay boundary roughly corresponds with theHauterivian/Barremian boundary. Anderson (1985)indicated that it corresponded with the boundary betweenhis Ewhurst (88) and Capel (89) ostracod faunicycles. TheEwhurstlCapel faunicycle boundary lies just below thebase of BOS Bed 3a in Clockhouse Brickworks, Capel,Surrey (Oallois & Worssam, 1993, p. 122). Anderson(1985) placed the EwhurstlCapel faunicycle boundary at adepth of 432.2 m in the Warlingham borehole, Surrey.Hughes & McDougall (1990), using palynomorphs, placedthe HauterivianIBarremian boundary between 1415-1423 ft(431.3-433.7 m) in the Warlingham borehole. Therefore, inSurrey, the Hauterivian/Barremian boundary correspondsclosely with the EwhurstlCapel faunicycle boundary, whichmay be taken as the base of BOS Bed 3a, that is theLowerlUpper Weald Clay boundary. (See also Horne, 1995and Ross & Cook, 1995).

Does the base of BOS Bed 3a also reflect theHauterivian/Barremian boundary in Sussex? UnfortunatelyCypridea has not been found at Keymer. However,Anderson (1985) placed the EwhurstlCapel faunicycleboundary at a depth of 143.2 m in the Ripe borehole, EastSussex. Lake & Young (1978) described a red mottledmudstone at 143.12-152.50m from this borehole andcorrelated it with one in the Laughton borehole, EastSussex, lying immediately below a sandstone. Westwards,just north of Barcombe Cross, East Sussex (8 0 S Sheet 319(Lewes» the lowest mapped red clay is shown to have asandstone bed immediately above it. This is probably thesame sandstone as the one in the Laughton borehole,and can be traced onto the eastern part of the Brightonsheet where it is identifiable as BOS Bed 3c2. Thereforein East Sussex the Hauterivian/Barremian boundary(= EwhurstlCapel faunicycle boundary) lies at the top of ared clay which apparently underlies BOS Bed 3c2. Thissuggests that beds 3a and 3c are diachronous and weredeposited earlier in the Burgess Hill area than in the Capelarea. As the sediments exposed at the Keymer Tileworks pitlie well below BOS Bed 3c2 they are probably lateHauterivian in age.

3. SEDIMENTOLOGY

The site exposes a variety of coloured clays, silts andsandstones. Three sedimentary logs (Fig. 3) covering mostof the site were measured in . 1994 and 1995. The field

LOWER WEALD CLAY, KEYMER TILEWORKS 233

Fig. 2. Stratigraphy of the Weald Clay, east of the Burgess Hillfault, Sussex, showing the position of the pit at Keymer Tile­works, the Lower/Upper Weald Clay boundary and theHauterivianIBarremian boundary. Thicknesses were calculatedfrom dip measurements on BGS map 318/333 (Brighton andWorthing).

observations were checked against borehole data madeavailable by the site managers. Figure 4 shows theapproximate size of the site and the positions of themeasured sections. Lateral variation across the pit is quitemarked, as is common in many of the Weald Clay pits.

The lowest section in the sedimentary sequence is seen inthe northern part of the site (Fig. 3, Log I). Here, clay formsmost of the section, with subordinate silt beds. The clays aregenerally reddish brown or purple in colour, often showingwell defined mottling. Towards the top of the sectionglaebuIes (iron-rich, concentrically layered concretionswith a maximum diameter of 10.0 mm) are common.

Section 2, measured in a gully (Fig. 3), is characterizedby a change from grey-brown and brown-red shaley clays to

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blue-grey silty clay with thin ironstones and fine-grainedmicaceous sandstones to interlaminated silt and flaggysandstones, dipping at go to the south. The uppermost iron­rich sandstone shows a well developed rippled uppersurface, internal ripple laminations, burrows anddesiccation cracks. The ripples on the upper surface gavestrike measurements of 110/290° and 176/356°. This bed islithologically similar to the Clockhouse Sandstone (Bed 3)that crops out below Bed 3a in Clockhouse Brickworks,Capel, Surrey. The unpublished borehole records indicatethat between sections I and 2 there is about 5 m ofgrey/green mottled clay, overlain by approximately 3 m ofgrey clay.

The lowest 7 m of section 3 (Fig. 3) are dominated bybrown and grey clays and shaley clay with thin siltstonehorizons. The uppermost part of this section consists of lightgrey silty clays with thin siltstone horizons capped by amassive yellow-buff fine to medium-grained sandstone(BGS Bed 3a). Section 3 contains fossiliferous sideriticmudstone and siltstone lenses at two horizons. Fossiliferousphosphatic mudstone lenses have also been found in the pit,but not in situ. The sideritic and phosphate lenses probablyformed during early diagenesis (Taylor, 1991).

The red and purple clays and associated terrestrialvertebrate fossils (Fig. 3, Log I) indicate sedimentdeposition on interfluves under predominantly oxidizingconditions. The coloration, absence of sedimentarystructures and the presence of glaebules suggest that thesesediments were subject to early-stage pedogenic processes(Retallack, 1990; Cook, I995a).

The sandy units at the top of section 2 display ripplelamination, indicating deposition by currents. This faciesassociation is interpreted as a background, low energysedimentary regime, probably under anoxic or poorlyoxidized conditions, indicated by the blue grey colour.Periodically, pulses of arenaceous sediments were depositedby rivers, probably during floods, and/or as small-scalecrevasse splays produced by avulsion. The uppermost iron­rich sandstone overlies desiccation cracks in the underlyingsilts which were subaerially exposed for a time, causingthem to dry out and contract. Fluvial deposition of themicaceous arenite followed, allowing burrowing organismsto colonize the unconsolidated sediment.

The topmost sediments record a return to dominantlylow-energy sedimentation, with minor phases of currentdeposition generating the laminated siltstones.

4. PALAEONTOLOGY

The pit has yielded a diverse fossil fauna (Table I), mainlyreptiles and insects. Two of the latter belong to taxa thathave not been recorded previously from the Wealden of theWeald. Crustaceans, molluscs and plants have also beenfound including well preserved specimens of a aquatic ormarsh-dwelling herbaceous plant (Hill, 1996).

The vertebrate, insect and plant materials described hereare held at the Booth Museum of Natural History (BMB),Brighton.

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medium brOwn/grey shaley Clay

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medium grey shaley clay. weathersbrown

medium brown blocky clay

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LOWER WEA L D CLAY. KEYMER TILEWORKS 235

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Fig. 4. Site map of Keymer lileworks showing the locations of thethree measured sec tions (1-3).

Invertebrates

Insects are abundant and can be found in sideritic and.rarel y, phosphatic mudstone and siltsto ne len ses.Unfortunately, most specimens were recovered from lensesthat were not in situ. A few came from in situ lenses whichcan be seen projecting from the weathered south-west face(Fig. 3, log 3). The lowest horizon is generally barren. Someof the loose insect-bearing lenses probably came from otherhorizons between the ripple-bedded micaceous sandstoneand BGS Bed 3a. A few insects, consisting of beetle wing­cases and cockroach forewings. have been found in the clayabove the ripple-bedded sandstone .

Most of the identifiable insect remains are beetle wing­cases (Coleoptera) which may be concentrated at the base ofthe lenses. Cockroach wings (Blattodea), a few dragonflywing fragments (Odonata), bug (Hemiptera),grasshopper/cricket (Orthoptera) and fly (Diptera) wingshave also been found. Wasps (Hymenoptera ), lace-wings(Neuroptera ), scorpionflies (Mecoptera) and caddisflies(Trichoptera) are very rare and only one or two specimensof each have been found. The Trichoptera are representedby a single larval case made of plant fragments. A graphshowing the total numbers of identified specimensbelonging to the different orders is shown in Fig. 5.

Table 1. Faunal and floral list for the Lower Weald Clay (Upper Hauteri vian) at Keymer Tileworks, Sussex

Invertebrates:Arthropoda:

Insecta:Odonata :

Aeschnidi idae?Blattodea:

MesoblattinidaeOrthoptera:

ElcanidaeHaglo idea

Hem iptera :CicadellidaeCoccoideaProgonocimicidae:

Ildavia incompletaValdiscytina picta

HeteropteraColeoptera

inc!. CupedidaeDiptera:

Mycetophilo idea (inc!. Sciaridae)Hymenoptera:

SphecidaeMecopteraNeuropteraTrichoptera

Cru stacea:Conchostraca :

Antronestheriid aeIsopteraOstracoda

Mollu sca:BivalviaGastropoda

Plan ts:Pterid ophyta:

Matoniaceae:Weichselia reticulata

Gymno spermophyta:Coniferales:

Brachyphy/lum sp.Anthophyta

Bevhalstea pebjaVertebrates:

Ostei chth yes:Actinopterygii:

Semionotidae:Lepidotes sp.

Amiid aeChondrichthyes:

Elasmobranchii:Hybodontidae:

Hybodus basanusReptil ia:

Testudin es:Plesiochelyidae:

Pleurostemon sp.Dermatemydidae:

Tretostemon sp.Crocod ylia:

Goniopholidae:Goniopholis sp.

Bernissartidae:Bemissartia sp.

Dinosauria:Ornithopoda:

Iguanodontidae:Iguanodon sp.

Theropod a

236 E. COOK AND A. J. ROSS

No. spec imens350 -

300

250

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150 ·

100

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Insect orders

Fig. S. Graph showing the total numbers of specimens belongingto the different insect orders that have been found at KeymerTileworks. The names of the orders are abbreviated. For thecomplete names see Table 1.

Two species of Keymer insects were wrongly describedas coming from near Capel (Surrey) by Klimasziewski &Popov (1993): Ildavia ineompleta Popov and Yaldiscytinapieta Popov (Fig. 6). These are representatives of an extinctfamily of bugs, the Progonocimicidae. Worthy of note is anisolated wing belonging to the Sciaridae (fungus gnats (Fig.7» ; the first undoubted record of this family from theWealden of England . Jarzembowski (1987) recordedsciarid-like mycetophiloids in the Wealden. The oldestsciarids are from Transbaikalia and are Berriasian­Valanginian in age (Blagoderov pers. comm.). The nextoldest sciarids are in Lebanese amber (Poinar, 1992) whichis believed to be Aptian in age (Rasnitsyn, 1994). Another

".

wing is the first representative of the superfamily Coccoidea(scale insects (Fig. 8» from the Wealden of England.

The total numbers of specimens for each order of insectfrom the Lower Weald Clay at Keymer Tileworks can becompared with those from the Upper Weald Clay at AuclayeBrickworks. Capel. Surrey (Jarzembowski, 1991, fig. 2).The same orders are present at both sites, and the totalnumber of beetles recovered are about the same, but otherorders are much rarer at Keymer than at Auclaye. Thissurely reflects differences in depositional environment. AtAuclaye the insects are preserved in very fine-grainedphosphate nodules and the wings of large insects, e.g.dragonflies, are usually complete ; even articulated insectshave been found (Jarzembowski , 1988). At Keymer thematrix is generally coarser and most of the insect remainsare very small. disarticulated and sometimes concentratedand fragmentary. The explanation must be that beetle wing­cases and cockroach forewings are tough, and have a muchbetter preservation potential than fragile insect wings.Dragonflies are represented only by small wing fragmentsat Keymer. The depositional environment at Keymer wasgenerally higher-energy than at Auclaye, and the insectswere subjected to more vigorous sorting and destructiveprocesses.

Crustaceans are represented by conchostracans, isopodsand ostracods. The conchostracans are abundant in thesideritic siltstone lenses and silty clay just below BGSsandstone Bed 3a at the top of the pit. Isopods and ostracodsare rare and have been found only in sideriticsiltstone/mudstone lenses that were not in situ. Theconchostracans and isopods belong to undescribed species,and the ostracods are generally poorly preserved, smoothforms that have not been identified.

Molluscs include poorly preserved bivalves from thebases of a few of the sideritic/mudstone lenses and rare

. ~

'.

-

Fig. 6. Valdiseytina picta Popov (Hemiptera: Progonocimicidae) showing original colour patterning. Lower Weald Clay (UpperHauterivian), Keymer Tileworks. BMB No. 0 18463 (Holotype), coil. A. J. Ross. Length of wing =4.15 mm.

LOWER WEALD C L A Y , KEYMER TILEWORKS 237

Fig. 7. The first fossil sciarid fungu s gnat (Diptera: Sciaridae)from the Wealden of southern England . Lower Weald Clay (UpperHauterivian), Keymer Tileworks. BMB No. 018954 , coli. A. 1.Ross. Length of wing = 1.45 mm.

impressions of gastropod operculae from within the lenses .No gastropod shells have been found, prob ably due todissolution of their calcareous shells . These lenses have notbeen found in situ.

Trace foss ils are present. Kennedy & MacDougall ( I969)recorded the shallow marine indicator Oph iomorphanodosa in the ripple-bedded micaceous sandstone at this sitethat currently crops out at the top of the gully (Fig . 3, log 2).However, the burrows attributed to Ophiomorpha in theWeald Clay have been shown recently to belong instead tothe ichnotaxon Beaconites, indicating fluvial environments(Goldring & Pollard, 1995).

Fig. 8. The first fossil scale insect (Hemiptera: Cocco idea) fromthe Wealden of southern England . Lower Weald Clay (UpperHauterivian), Keyme r Tilework s. BMB No. 018956, coil. A. 1.Ross. Length of wing =2.85 mm.

Plants

Only three plant taxa have been found. Piec es of thecommon Wealden fern Weichselia reticulata (Stokes erWebb) are fairly abund ant in a dark greylbrown blocky clayat the base of the southwest face, along with conifer twigsbelonging to the form genus Brachyph yllum. Both have alsobeen found in the insect-bea ring sider itic siltstone/mudstonelenses.

The sideritic siltstone lenses at the top of the southwes tface have yielded well preserved stems and leaves of a newaquatic or marsh-dwelling herbaceous plant belonging tothe group Anthophyta and named Bevhalstea pebja (Hill.1996).

Vertebrates

A major drawback to identifying the vertebrate remains isthe high degree of fragmentation. Over half of the fossilscan only be described as indeterminate bone or osteode rmalmateri al, due to poor preservation and/or small specim ensize. Identifiable materi al includes remains of bony fish ,sharks, crocodiles, turtle s and dinosaurs.

Lepidotes scales and an amiid vertebra (identified by C.Patterson ) were found weathering out of the brown and gre yclays above the medium brown-grey silty clay with siltlaminations in the southern comer of the pit. Teleost scalesand vertebrae, and Hybodus basanus teeth, have been foundscattered across the bases of the insect-bearing sideriticlenses.

The most common vertebrate remains are crocodileteeth , scutes and bone fragments (Fig. 9). Broadly conicalteeth (Fig. 9a) are thought to belong to one of the man yspec ies of Wealden goniopholid crocodile. The smallercru shing teeth (Fig. 9c) have been identified as Bernissartia(A. C. Milner, pers. comm.). Turtle remains are fairlycommon and two genera are present: Pleurostern on andTretosternon.

The remaining vertebrates comprise dinosaurs, ornitho­pods and rarer theropods. Ornithopods are known fromteeth, either in perfect condition (Fig. 9d), or with welldeveloped wear facets. Two theropod teeth (identified by S.Bazio and O. Rauhut) have been recovered. These are small(6.0 mm long), with serrated carinae running along theanterior and posterior edges of the teeth (Fig. 9f). Onephal ange attributable to a theropod «Fig. 9g) identified byD. B. Norman) is recorded (Cook, 1995b). A white quartzitegastrolith and many crocodile coprolites have been found inthe red clay, and an Iguanodon footprint probably from thesandstones of section 2.

All the vertebrate remains are fragmented to somedegree. The bone s are generally only slightly rounded,indicating that the material was probably not transportedover any great distance before final burial. The range ofabrasion clearly ind icates an attritional assemblage,produced by the gradu al accumulation of bones withvarying taphonomic histories. Most of the material isessentially unweathered, suggesting burial fairly soon afterdeposition (Cook, 1995a).

238 E. COOK AND A . J . R OSS

Fig, 9. Selected vertebrate material fromthe Keymer Tileworks ( ppcr Hauterivian):(a) Goniopholis sp. tooth (Bt-. IB No.020914): (b) Bemissurtiu sp. scutc (B t-.mj o. 01 423): (c) Bernissartia sp. tooth(Bt-.m No. 01 420): (d) iguanodon sp. tooth(B t-. IB i '0. 01 410): (e) Tretostemon sp.m r-.IB No. 01 407): rr & ~ ) theropodtooth (BMB 1 ' 0. 020915) and phalange(B r-. IB • '0. 01 406). cale bar =5.0 rnrn.

e

b

d

5. CONCLUSIONS

The pit at Keymer Tileworks comprises a sequence ofalluvial sediments dominated by clays and silty clays. Thered and purple mottled clay horizon s were probablydeposited on low-lying interfluves inhabited by dinosaurs,crocodiles and turtles. The resulting sediments were subjectto early soil-forming processes, followed by pulses ofhigher energy, presumably fluvial sedimentation and limitedsubaerial exposure of the sediments. Then followed achange to predominantly low-energy deposition of clay,with occasional influxes of silt, indicating a lacustrineenvironment. The local terrestrial environment supporteda rich insect fauna and terrestrial plant taxa, the remainsof which were washed into the lakes. The presence ofconchostracans towards the top of the pit indicatesshallowing prior to the deposition of sandstone Bed 3a.

ACKNOWLEDGEMENTS

Many thanks go to Tony Kindell and Fergus Cameron of theKeymer Tile Company for access to the site and for lettingus examine their unpublished borehole records. Thanks alsoto Peter York and Phil Crabb (NHM) for taking thephotographs of the insect fossils. The authors are grateful toProf. P. Allen, Dr M. J. Benton and Prof. R. Goldring forcomments on early drafts of the text; Prof. D. 1. Batten andan anonymous referee for comments an the submittedmanuscript. Elizabeth Cook acknowledges the financialsupport of the University of Bristol Alumni Association andvarious student Access Awards, and the NationalGeographic Society fieldwork grant number 4705-92.

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Received 27 November 1995; revised typescript accepted 17 April 1996