ZOBODAT - www.zobodat.at

Zoologisch-Botanische Datenbank/Zoological-Botanical Database

Digitale Literatur/Digital Literature

Zeitschrift/Journal: Zitteliana - Abhandlungen der Bayerischen Staatssammlung für Paläontologie und Histor. Geologie

Jahr/Year: 1982

Band/Volume: 10

Autor(en)/Author(s): Mortimore Rory N.

Artikel/Article: The stratigraphy and sedimentation of the Turonian-Campanian in the Southern Province of England 27-41 © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 27

Zitteliana 10 27-41 München, I. Juli 1983 ISSN 0373-9627

The stratigraphy and sedimentation of the Turonian-Campanian in the Southern Province of England

By RORY N. MORTIMORE*)

With 5 text figures and 2 tables

ABSTRACT

A new lithostratigraphic and revised biostratigraphic nian-Campanian Chalk was deposited in a complex basin scheme for the White Chalk of the Southern Province of Eng­ with an axial trough surrounded by shelves and containing land is proposed, introducing a Sussex White Chalk Forma­ many local periclinal shaped swells across which condensa­ tion with six Members, the Caburn, Lewes, Seaford, Newha­ tion occured. Consequently ideal type sections for stratigra­ ven, Whitecliff and Portsdown Chalks, based on stratotype phic purposes are limited. As far as possible the thickest and sections in East Sussex and the Isle of Wight. most complete sections have been chosen as stratotypes but Isopachyte and lithofacies data indicate that the Turo­ many anomalies occur; these are discussed.

KURZFASSUNG

Eine neue lithostratigraphische Gliederung und ein revi­ gen, daß die Turon-Campan-Kreide in einem differenzierten diertes biostratigraphisches Schema für den White Chalk der Becken mit einem axialen Trog abgelagert wurde, umgeben Süd-Provinz Englands wird vorgeschlagen. Es wird eine Sus­ von Schelfgebieten. Dieses Becken enthielt viele lokale kup- sex White Chalk Formation eingeführt mit 6 Unterteilungen: pige Schwellen, auf denen Kondensation stattfand. Deshalb Caburn, Lewes, Seaford, Newhaven, Whitecliff und Ports­ sind gute komplette Profile für stratigraphische Zonierungen down Chalk Member, deren Stratotyp-Profile in East Sussex begrenzt. Die komplettesten und mächtigsten Profile wurden und auf der Isle of Wight liegen. als Stratotyp-Profile ausgewählt, obwohl Anomalien auftre­ Isopache Rekonstruktionen und lithofazielle Analysen zei­ ten, die hier diskutiert werden.

TABLE OF CONTENTS

I. Introduction...... 28 II. Lithostratigraphy ...... 28 III. Biostratigraphy...... 33 IV. Sedimentation in the Sussex Trough and on its M argins...... 33 V. Stratigraphic Anomalies ...... 36 VI. Conclusions...... 40 Acknowledgements...... 40 Literature...... 40

) R . N . MORTIMORE,Geotechnical Section, Department o f Civil Engineering, Brighton Polytechnic, Brighton, England. 28 © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at

I. INTRODUCTION

Upper Cretaceous stratigraphy in the Southern Province of The Southern Province (Figure 1) as understood here is England (Figure 1) has altered little since publication of the both a biogeographic region as defined by Stokes (1975) and a Cretaceous Memoir by J ukes-B rowne & H ill (1903-4), tectofacies region (sensu K rumbein & Si.oss, 1955) which is (Table 1). Elsewhere, Fletcher (1979; and see alsoF letcher determined partly from the isopachyte orientations (Figure 3) & W ood in W ilson & M anning, 1978) andW ood & Smith and on lithostratigraphical evidence. The Northern Province (1978) have introduced new lithostratigraphies for the Upper (Stokes 1975; W ood and Smith 1978) is clearly defined in Cretaceous in Northern Ireland and the Northern Province of Yorkshire, Lincolnshire and northern Norfolk but grades England respectively. This paper complements that work both bio- and litbostratigraphically into a transitional region. with the introduction of a new lithostratigraphy (Table 2) for This transitional region is not as well researched, and on pre­ the Turonian-Campanian of the Southern Province of Eng­ sent evidence provides difficulties in correlation between the land. The biostratigraphy remains largely as introduced from Northern and Southern Provinces because both the litholo­ France by H ébert (1874) andB arrois (1876) with modifica­ gies and the faunas appear to be transitional. These difference tions by Brydone (1914) and G aster (1924). It is suggested are most apparent in the Coniacian and Santonian. that a more refined use can be made of inoceramids, Micraster and Ecbinocoiys.

II. LITHOSTRATIGRAPHY

J ukes-B rowne & H ill (1903—4) retained two lithostrati- re-mapping of the Chalk by the Institute of Geological graphic sub-divisions for the Turonian-Campanian in Eng­ Sciences has shown that, at least in Sussex, the boundary bet­ land, the Middle and Upper Chalk, although the boundary ween these two formations is difficult to recognize in the field between these implied formations was taken variously at and therefore, un-mappable. Thus, the Middle and Upper either the base of the Chalk Rock (Figure 4a) or the first flints, Chalk have been “lumped” into one unit. or the base of the Sternotaxis (Holaster) planus Zone. Current © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 29

MORTIMORE 1982 PHILLIPS MANTELL C A L E 8 H Ê 8 E R T BARROIS P E N N IN G iJ EVANS 1874 1 8 76 JUKE S-BROWN 4 HILL . 18 18 1 8 2 2 n TRADITIONAL STRATIGRAPHY 1881 ’ 1 8 7 0 (England 4 Ireland) 190 3 - 4 8 E D S DOVER SUSSEX SURREY DOVER SUSSEX CAÍ¿BRIDGE S.E NGLAN[ f o r m MEMBER z (CROYDON 5 ALUM BAY B

RAI LWAY FARLINGTON B h UJ BEOHAMPTON B Z YS Z 2 o sd o O WHITECLIFF B Z cc < Û. O z s o m p t i n g b

WITH □ < Q. * UJ 5 CASTLE HILL B 2 < < BASTION STEPS B

6 o MEECHING B j PEACEHAVEN B z < i > OLO NORE B z < o * < Y X — Z o n e a Craie de < z SPLASH POINT B >- Marsupltes B rig h to n X z o I- O o u z z E o H 3 >- SEAFORO HEAD B LU z >- z V) ~ 4> a (/) Li. -i FEW CÛ « c U. C m 4, O' CUCKMERE B ORGANIC 2 5 2 2 cn BELLE TOUT B IU REMAINS w s c ~ 00 z LL cc cv “ 1 CC cc cc - o ------z cc UJ < CL z o 13 i/) 9 cc m a. Ol ~ 4> ■5 Û. CL LIG H T POINT B < 2 Sj

a CHALI- ? < a * i o PARK BE Q TURONIAN M IDDLE l labiatus UPPER M Af < IN BEDS OF o u g h to o 2 RATUM CONTAIN G NUMEROUS IGANIC REMAINS one a irne de Q cc M ' MELBOURN ROCK MELBOURN RK — 2 1 2 MEL ROCK M ROCK Zone a M de Holywell P MARLS P M P M r PLENUS M S O < c k GREY GREY GREY * GREY oI -i * CHALK * CHALK CHALK Z < CHALK < < <

X ’ d g r e y CHALK u me u < IDEN PARK )S [ Holasier JOSUS X o < * < LLI • 1 2 ca « *5 CHALK CHALK CHALK 2 ac CHALK GREY O cc cc ro % UJ " 1 2 uj ARL MARL MARL z MARL CHALK 1 < o IU S 5 2 NI LOWER GREY CH LO W ER C O MARL LOWER Cl o -i I Marne gl. ChlontiC C M GL MARL U d'Eastboutne Mail

UGS UGS or BLUE CHALK ALBIAK Of MARL GAULT GAULT

T a b le 1 EVO LUTION O F LITHOSTRATIGRAPHIC CONCEPTS IN THE CHALK OF SOUTHERN ENGLAND

It is proposed to replace this undifferentiated sequence with Formation is divided into six units of member status. These li­ a Hedbergian lithostratigraphy, recognizing a Sussex White thologies are sufficiently distinct to be recognized both in the Chalk Formation with six members which are in turn subdi­ field and in cores and geophysical logs of boreholes. The di­ vided into beds (Table 2). The sections around Lewes and on stinctive lithologies are: the coast between Eastbourne and Brighton in Sussex and the 1. Griotte texture (T ucker 1973) a term derived from the coast section at Whitecliff, Isle of Wight, are selected as stra­ Pyrennean Devonian and Carboniferous griotte formations totypes. used to describe the marl plexus beds which contain augens of The Sussex White Chalk Formation is defined as all the chalk surrounded by interlacing network of marl often with chalk above the Plenus Marls i. e. starting at the base of the horsetails. Middle Chalk sensu J ukes-Browne & H ill 1903-4 as preserv­ 2. Nodular and hardground chalks which represent a series ed in the Southern Province up to the Tertiary erosion surfa­ in sea floor lithification and burrowing (Bromley 1975), from ce. This term follows R owe’s concept of the White Chalk in indistinct, slightly red iron-stained lumpy chalks with no his study of the coast sections (R owe 1900-1907). The highest clear upper surface to well cemented hardgrounds with well preserved chalk in the Province is found on the Isle of Wight defined upper surface which may be mineralised with glauco­ and in Dorset and falls within the lower part of the Upper nite and phosphate as well as iron. Campanian. 3. Soft, featureless chalks, locally laminated, containing On the basis of major lithological changes which neverthe­ very few obvious sedimentary discontinuities but often con­ less do not constitute mappable units, the Sussex White Chalk taining distinctive seams of nodular or semicontinuous (tabu- 30 © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at lar) flints. The laminae usually contain small lithoclasts deri­ primarily on the basis of scale and structure. For example, ved from the chalk and small-scale slump folds and usually marly chalks tend to be massive (i. e. 0.5-1.0 m thickness) truncate burrow structures indicating a post sedimentary ori­ while griotte marly layers may range from 0.03 m to 0.5 m in gin. thickness but will comprise a heterogeneous plexus. Discrete 4. Discrete marls are distinct from either the griotte texture marls, by contrast, range from 0.03 m to 0.3 m in thickness or the marly chalks which contain less than 80% carbonate, but on average are between 0.05-0.10 thick. The seam is

SublTRAD BEDS M a rk e r FAUNULES MEMBER Zone ZONE 1 H o riz o n E r |t i a r y . 1 INOC. ECHIN. . E. 5 A lu m Bay * x c ó n ic a B e d s Is § m 2 < “ S h id e M I— X J Farlington M E.sub conic R e d o u b t ______4 0 0 - o <->2 Bedhampton^ Q- B e d s Portsdown M E.downenc * - i < W hite clift X — ro - Beds o ro » B fP « Whiteclift FIs LL Whiteclift M o ro LL o Cote's Bottom co 3 z —1 S o m p tin g U F lin t o - < u LU B e d s o d

1- MEMBEF z tn o o «=> Lancing Flints E c ineta a 5 Castle Hill Ï O Pepperbox M - 2 B e d s § j < Castle Hill M E. gasten LU cc B a s tio n (J LU S te p s CÛ M e e c h in g M O. plano 2 LU M e e ch in g E.cincta E .c. 3 0 0 - CC b a ltic u s /./•/,/ E 1. a O Peacehaven pt ero ides E. trúncala * ?Old N o re Marl E.depresst Ed Ó LU < O ld E.lectiforrr > X _U _a N or e - < u M.t. M.t. B r ig h t o n M cc $ S p la s h LU < U.s. U.s. Z 5 P o in t Seaford Marls !x z y— if i z S e a fo rd to o cc L_ E SANTONIA UJ H ead undulato E 3 I- LL CD 3 C to p lica tu s C 5 B e d w e U s 2 - ¡Z 5 LU C o lu m n a r digitatus s> 0> c. 5 co cc in 7 co o C u ckm ere o a * o LL o o cc _i 2 0 0 - z < 5 o o Seven Platycer Sisters Flint O — ^ cf involut nj u < B e lle < LU BTM M .trans­ < I tn T o u t c f koen itio n o 2 S h o re h a m M a Beachy Hd. CC CO LU I- z o < CO Light Point schloe n- M .decip- bach i I 5 o cc B e eding { o < 5 2 Hope G ap l.inconst- M .norm - 2 ^Navigation M anniae X * anS^ « X IWid.gr f_ CO Q Navigation LU < 3 o M .leske* C z r w 7 (f) o K i n g sto n a CO ' r f > / / / »Br idgewick tn tn > LU Br idgewicF R.rotaiorrr > r f t ? 7+Caburn Marl I s S $ C a b u rn 9 O CO >* 1 0 0 - i _1 W Ü ^Southerham LL G ly n d e _ 2 j> _ co Glynde Marl l.apicalis l.cuvieri 3 „ N P 2 ____ 9____ \NP1 w rg z n — LU CC < 1- B e d s lla m a re z o m 9 1- o 5 L a b / la t a M

Table 2 Stratigraphy of the Sussex White Chalk Formation : Lewes and Whitecliffe stratotypes © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 31 much more homogeneous than the griotte marl, has a distinct coast counties of England (Jukes-B rownf & H ill 1903^4) but base and a dark colour and may posess either a plastic or falls considerably below it (Table 1). Both the Chalk Rock brittle texture. The homogeneous nature of these marl seams and the Top Rock (Figure 4a and b), however defined strati- (closed seam of R owe 1900) is maintained over thousands of graphically, fall within the Lewes Chalk. These two marker square kilometres and provides an unmistakable signature on units represent varying degrees of condensation resulting in geophysical borehole logs (particularly electrical resistivity complex amalgamation of nodular chalks to mature hard- and natural gamma). In consequence these marls provide a grounds. Various horizons have been identified as the Chalk convenient series of easily recognizable marker horizons Rock or Top Rock sensu lato(H ill 1886). These various le­ within the succession which are used to delimit the bounda­ vels are indicated in Figure 4a and b. The Chalk Rock sensu ries between many of the members and beds. stricto (i. e. W hitaker 1861; H ill 1886) has been investigated by Bromley & G ale (in press). The bed names proposed for Six members are recognized as follows: the subdivision of the Lewes Chalk are intended to replace the 1. The Caburn Chalk Member; type locality Mount Ca- ambiguous terms Chalk Rock and Top Rock particularly in burn, Lewes, Sussex; basal marker, base of the Melbourn the region of the Chalk Rock sensu lato. Rock (see J efferies 1963 Plate 2 P. 7, Holywell coast section Eastbourne [boundary stratotype]). The whole member Bänderkreide texture, a term derived from the Maastricht- ian Chalk of north-west Germany (V oigt & H antschel, comprises predominantly griotte chalks both of a nodular type e. g. Melbourn Rock and Middle Holywell Beds, and a 1956) to describe discrete millimetre-thick lenses of whispy more massive soft chalk type in the remainder of the sequen­ dark clay and silt grade marl occurs at two distinct levels in the Lewes Member. The lower horizon occurs everywhere bet­ ce. Discrete marl seams particularly characterise the upper part of the sequence beginning with the Mailing Street Marls ween the Lewes Hardground and the Navigation Marl (Figu­ at the boundary between the conventional Mytiloides labia­ re 4a) and the upper horizon between the various hard- tes and Terebratulina lata Zones and the lower marl which is grounds and nodular beds comprising the Beachy Head Beds. This streaky marl structure has been referred to the trace fossil also the boundary between the Holywell and New Pits Beds. Zoophycos and this identification has now been confirmed for 2. The Lewes Chalk Member; type locality Lewes, Sussex, the first time in the Sussex White Chalk (R. G. B romley and basal marker the surface beneath the Glynde Marl at Caburn A. Ekdale, personal communication). Pit, Lewes (boundary stratotype). Well developed beds of nodular chalk enter above the Glynde Marl and recur in belts 3. The Seaford Chalk Member; type locality Seaford Head, separated by softer sometimes griotte chalks. Discrete marls Sussex; basal marker lower Shoreham Marl Seam at Seaford are present in the lower half of the member and the first regu­ Head (boundary stratotype). Seaford chalk is typical of the lar flint seams enter in the Glynde Beds in association with the featureless lithology but containing numerous laminae at Sea­ first nodular chalks. ford Head and also containing several prominent flint seams The boundary between the Caburn and Lewes Chalk so de­ of which the Seven Sisters Flint is the most conspicuous. fined does not equate with the boundary between the Middle 4. Newhaven Chalk Member; type localities Seaford Head and Upper Chalk used by the Geological Survey in the south and Newhaven, Sussex; basal marker the Seaford Marl at Sea-

Table 2: Note that the column showing faunules shows levels of abundance and not total ranges. Key : Shide M Marl BTM Belle Tout Marl; NP 2 New Pits Marl No. 2;

Inoceramids: hercyn hercyniens; lamarc lamarcki; I. w. dorf waltersdorfensis; cf koen. koeneni; M. transition group of Micrasterids as yet not formally identified transitional between M. decipiens and M. coranquinum with affinities to M. intermedins;

U. s Uintacrinus socialis; M . t Marsnpites testudinarius; E. tectiform Ecbinocorys scuta ta var: tectiformis; E. depressu Ecbinocorys scutata var: depressnla; O. piano Offasterplanatus (planoconvexus); E. downend Ecbinocorys of particular shape found in the higher Whitecliff Chalk (see also Fig. 4d E. s. type 6) found at Downend Quarry, Portsdown and not yet formally identified. to Biodiversity HeritageLibrary, http://www.biodiversitylibrary.org/ ;

CHALKS www.zobodat.at n Whitecliff

| | ' j | Newhaven

□ Seaford

\ / y | Lewes 'EASTBOURNE S p la s h [ " | Caburn P oin t SEAFORD HEAD'

. ' u. cwot / + Beachy Head Light Po t j Lighthouse BEACHY/ Fig.2 Type localities in East Sussex for the Sussex White Chalk Formation • HEAD Outcrop of members is modified from Gaster’s zonal maps (Gaster 1939 & 1951) © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 33 ford Head (boundary stratotype). The Newhaven Chalk sees these members. With the exception of the Castle Hill Beds, a the return of griotte marl lithologies but in chalk of greater distinctive flinty unit at the base of the member, in which marl purity than the Caburn Member and with greater intervals seams such as the Pepperbox Marls are developed in the we­ between the griotte marl layers. Of particular interest are stern part of the region, the Whitecliff Chalk is devoid of good some of the discrete marl seams particularly the Brighton marl seams. The member contains flint seams throughout but Marl in the Marsupites testudinarius Zone and the Old Nore at certain levels columnar or paramoudra potstone flint hori­ Marl (Figure 4c). Marl in this part of the sequence is restricted zons (sensu Bromley et al. 1975) are present and these are late­ to Wessex and Sussex and is better developed in the central rally persistent (see Figure 4d). Paramoudras in association part of the trough around Salisbury and Winchester, where with levels of pelletal phosphate enrichment are a feature of for example the Pepperbox Marls appear but are absent in East the higher pan of the member. Sussex at Newhaven. Consequently the upper limit of marl in 6. The Ponsdown Member; type localities Ponsdown the sequence is stratigraphically variable but within limited (Bedhampton and Farlington) Hants and Whitecliff, Isle of bounds. Wight; basal marker, the Ponsdown Marl at Whitecliff 5. Whitecliff Chalk Member; type locality Whitecliff, Isle (boundary stratotype). Griotte marl seams return in the of Wight; basal marker the upper Castle Hill Marl; Castle Portsdown Member and as in the Newhaven Chalk many of Hill, Newhaven and Whitecliff, Isle of Wight (boundary stra­ the seams are paired (e. g. B rydone 1914). The upper limit of totypes). As stated above the upper limit of marl seams this member is not defined although in the Scratchells Bay sec­ around the junction between the Newhaven and Whitecliff tion the return of marl-free chalk can be recognized. Chalk varies between Sussex and Wessex but the Castle Hill These six members are subdivided into beds (see Table 2) Marls remain, everywhere, a major and easily recognizable but the delimiting marker horizons for all bed divisions arc marker and are therefore chosen as the boundary between defined elsewhere (Mortimore in preparation).

III. BIOSTRATIGRAPHY

An internationally agreed scheme for the boundaries and statement or their position in the southern English Chalk is subdivisons of the Coniacian to Campanian is still not resolv­ considered to be of value. ed . Critical ammonites and belemnites are either absent or not Ranges of the key marker species, both macro-fossils and preserved in sufficient numbers in the chalk facies of the Sout­ foraminifera are shown in Bailey et al. 1982 against the litho- hern Province of England to contribute to such a discussion. stratigraphical framework defined here. It is hoped that at a However inoceramid, echinoid and brachiopod assemblages later stage modifications to the zonal structure of the Sussex are abundant at many levels, and the first two groups potenti­ White Chalk can be made based on Micraster (D rummond in ally allow a more refined subdivision then the traditional zo­ preparation). From Bailey et al. Figures 2 and 3, it will be seen nal scheme suggests (Table 2). Some of the critical taxa also that an inoceramid zonation is implicit in the Coniacian and occur in the Paris Basin Chalk associated with ammonites no­ Santonian. Inoceramids are also of particular use in subdivi­ tably in the Craie de Villedieu and, therefore, a preliminary sion of the Turonian (Table 2).

IV. SEDIMENTATION IN THE SUSSEX TROUGH AND IN ITS MARGINS

Isopachyte data (Figures 3a-d) indicates that the Southern thinning but also clearly contains swell-like structures (Figu­ Province Upper Cretaceous was deposited in a broad basin re 3c). which had an axial trough running close to the northern mar­ Lithofacies variation is clearly controlled by both the gross gin of the South Downs of East Sussex and through Winches­ basin structure of the region (Figure 3a-d) and the local peri- ter and Salisbury to the west. Maximum fluctuation in thick­ clinal axes (e. g. Brighton Dome, Figure 5a). Shelves and local ness throughout the Upper Cretaceous is concentrated in East swells tend to be the sites of sediment attenuation and the con­ Sussex. comittant development of nodular chalks and mature hard- Isopachyte maps (Figure 3) demonstrate that areas of shoal­ grounds. Some marker beds such as marl and flint seams may ing are present around the western and northern margins of have been eroded, or in fact never deposited, across such the basin, (Mid-Dorset Swell and the Berkshire-Chiltems structures as the Brighton Dome. Coarser, calcarenitic chalks Shelf, Figure 3). Local thinning across periclinal-shaped are frequently found in the cuvettes associated with local structures is also apparent from the isopachyte data. Many structures, or as in the case of the Kingston Beds, infill the more of these structures probably exist on both the shelves main axis of the trough (Brydone’s Twyford Down facies, Fi­ and in the main basin of deposition. The Wessex part of the gure 3c, G riffiths & Brydone, 1911 p. 13-14). This facies is Lower Chalk isopachytes (Figure 3a) follow those of D rum­ now best seen in the upper Kingston Beds in Bridgewick mond (1970) who defined the Wessex Shelf and Mid-Dorset Quarry near Lewes. Swell. The Berkshire-Chilterns Shelf is a region of general 34 © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 35

Area of typical Chalk Rock (Burghclere Facies of B rydone 1911) Area of Twyford Down Facies ( Brydone 1911)

|| | || Intermediate area

| Localities with ‘spurious' Chalk Rocks • C ontrol point

40

uat ion ^ ' • ' ^ 2 5

Fig. 3c High Turonian Isopachytes ( Metres)

j \ Area of typical Top Rock( Chat win and Withers 1908 U- LJ Hope Gap to Light Point Hardgrounds)

• C o n tro l p o in t

30

'3 0 ^ 4 0 42 Zone of maximum fluctuation

Fig. 3d Upper Lewes Chalk Isopachytes( metres) Low and Mid Ccniacian 36 F ig .4 b V ariation in the Upper Lewes Chalk in the Southern Province- E n g la n d , showing the many many the showing , d here n la g n E proposed Province- names bed Southern the by the in replaced Chalk rock Lewes top Upper as taken the in been have ariation V b .4 ig F F ig 4a V a ria tio n in the Lower Lewes Chalk in the Southern Province • England • England Province Southern the in Chalk Lewes Lower the in n tio ria a V 4a ig F SUSSEX NAVIGATION O 2

UPPER LEWES CHALK The various horizons of Chalk Rock are only shown on the sections sections the on shown only are Rock Chalk of horizons various The hr te wr nmd y rvos authors previous by named were they where EE WITH LEWES . TAIRPI ANOMALIES STRATIGRAPHIC V. LEWES © Biodiversity Heritage© Library,http://www.biodiversitylibrary.org/; www.zobodat.at & CABURN OPO SHILLINGSTONE COMPTON A DORSET BAY I.O.W. CHARNAGE DOWN I ANGDON & AKERS AKERS & ANGDON I DOWN CHARNAGE WILTS EE DOVER MERE © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 37

As a result of the variation in thickness and lithofacies indi­ Newhaven Chalk is reduced from 50 m in East Sussex to 20 m cated in Figure 3, it might be expected that correlation of li­ at Whitecliff, Isle of Wight while the Whitecliff Chalk is reduc­ tho- and biostratigraphic marker beds would encounter diffi­ ed from 115 m at Whitecliff to 35 m at Downend (Ports- culties. It is clear from Figure 4a-d, however, that some mar­ down) (Figure 4c and d). Altough not shown on the diagram, ker beds not only cross all the structures of the basin but also (Figure 4d), the Whitecliff Chalk in Sussex must have attained occur on an interbasinal scale from southern England to the a thickness considerably greater than is found on the Isle of North Sea and possibly beyond. A good example of a persi­ Wight based on the evidence from the scatter of quarries in the stent horizon is given by the Glynde Marl (Figure 4a) which Worthing District. survives the attenuation occuring in the high Turanian bet­ Not only are many anomalies in thickness of preserved sedi­ ween Lewes and Mere and through the Chiltern Hills and ment evident in the region but in some cases displacement of continues into the Northern Province. sediment has occured. On the swell around Brighton, the On the other hand, marl seams such as the Southerham, Brighton Dome, (Figure 5a), synsedimentary sliding of Caburn, Bridgewick and Lewes Marls gradually disappear blocks of sediment downslope can be demonstrated. This slid­ westwards in the sequences of West Dorset (Shillingstone), ing has produced distinctive sedimentary-tectonic structu­ Mere and in the Chilterns. These Marls then reappear north­ res, particularly flint shard horizons (the roller beds, Figure wards in thicker sequences in the transitional and Northern 5a). At other localities, such as Downend (G ale 19S0) on Provinces. Even in the more expanded sections such as Do­ Portsdown, the condensed sediments are involved in a com­ ver, the Lewes Marl has been cut out in the development of plex set of structures which are here interpreted as progressi­ the “Dover Chalk Rock” (Figure 4a; H ill 1886).1) At Lewes vely developed downslope slides which ultimately broke the Navigation Marls are cut out at Offham Chalk Pits 1.5 km away and produced slump folding and displaced bedding west of the type locality, whilst southwards the Lewes and (Figure 5b). Both the Brighton and Portsdown structures Navigation Beds condense from 17 m to 8 m with the resul­ probably reflect periods of seismic activity which generated tant loss of most flint seams and many nodular beds. Such a sediment instability. These seismic events possible relate to condensed sequence is well exposed in Shoreham Cement movement in deep-seated hörst structures such as those indi­ Works. cated by L ake 1975 linking the Pevensey blocks to the Arling­ Extreme attenuation has reduced the Lewes Chalk from ton Axis. 80 m at Lewes to 20 m at Mere and in the Chilterns area to As a result of these sedimentary processes selection of a some 8-10 m. This process of attenuation was not confined to type section for the stratigraphy of the Province becomes cri­ the Turonian-Coniacian sequence but also affected the tical. The thickest and most continuously exposed sections Campanian Newhaven and Whitecliff Chalks. Part of the around Lewes and the Isle of Wight provide the chance of studying the most complete stratigraphy against which lateral ') Note terms such as “Dover Chalk Rock” or “Top Rock” are in­ variation can be tested. tended to indicate horizons referred to by previous authors and are As an example, it is clear that around Lewes the critical Tu­ in no way intended to be verification of a stratigraphic terminolo­ gy. It is intended that such terms should be replaced by the litho- ronian-Coniacian boundary sequence is more than twice as stratigraphy defined in this paper. thick as anywhere else in the province and contains well pre- 3S © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at

tt

ES 5 The Warning Camp round based forms(Mortimore WC 20) ES 6 The Downend torms(Mortimore Coll. D 18)

Fig.4d Variation in the Whiteclitf Chalk in the Southern Province-England

served echinoid and inoceramid taxa either not preserved or other fossils are found occasionally but it has in the past pro­ poorly preserved elsewhere in the Province but which are an ved difficult to relate individual horizons such as hardgrounds important part of the stratigraphy in Germany and the Paris to other more complete stratigraphic sequences. Basin. These taxa include Micraster praecursor (pars: sensu Other differences within the region are particularly well il­ Rowe 1899) M. normanniae (Bucaili e) and M. corbovis lustrated by the Turonian (Figure 3b) showing the M. labia- (Forbes). tus Zone condensed throughout the North Downs associated The inoceramids are dominated by Mytiloides striatocon- with an expanded T. lata Zone. A reverse situation is found centricus (G ümbel) s. 1. and mytiloid forms of the I. walters- in Wessex and it is only in the intermediate area where both dorfensis Ä ndert complex (see also B ailey et al. 1982). zones are expanded and of the same order of thickness that a In highly condensed sequences, for example in parts of satisfactory study of their stratigraphies can be carried out. Dorset, Berkshire and the Chilterns, critical ammonites and © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 39

s N

Basin Wide Diastem Hardgrounds 3 HOPE GAP 2 CLIFFE 1 NAVIGATION Tension crack fabric in lithified chalk

Fig.5a Diagrammatic representation of sedimentary events across the Brighton Dome during Micraster normanniae times (low Coniacian)

Fig.5b DOWNEND PORTSDOWN - A Sketch Block Diagram illustrating the more important field relations Complex zone, apparent compression interpreted as slumping resultant upon a much larger scale slide inducing under-tow and local diapirism 40 © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at

VI. CONCLUSIONS

A Sussex trough bordered by areas of general thinning in result of spurious correlations. The new stratigraphy propos­ Dorset and the Berkshire Chilterns region is identified as the ed replaces these terms with bed and member divisions. major feature of the Upper Cretaceous of the Southern Pro­ It can frequently be demonstrated that some bedding planes vince of England. Many local anomalies occur, such as projec­ follow marked erosion surfaces and, in many situations, the ting swells. As a result, stratigraphic hiati are present and it is debris of mixed fossil assemblages scattered through a bed only by studying the thickest stratigraphic sequences which suggests current reworking, transportation and deposition. occur around Lewes and on the coast of East Sussex, supple­ This clearly suggests that no one locality will necessarily con­ mented by the coast sections on the Isle of Wight that a com­ tain every aspect of the stratigraphy of the region and that a plete stratigraphic picture can emerge. “type section” will necessarily be a composite. The South Downs of Sussex are the focus of the maximum fluctuation in thickness in the region. The Wessex Basin of ACKNOWLEDGEMENTS D rummond (1967; 1970) is simply the head of a southeasterly plunging structure which had its main area of deposition in 1 am particularly grateful to my colleague Dr. Phillip Drummond Sussex throughout most of the Upper Cretaceous. This is for his continuous help and encouragement throughout the develop­ shown by the parallelism of the isopachyte pattern in the ment of this research project which was funded by Brighton Poly­ Lower Chalk and the Lewes Chalks (Figure 3). technic. The final form of the stratigraphy proposed owes a great deal to Altough anomalies are present, nevertheless correlation of discussions with members of the Institute of Geological Sciences, in many of the major marker horizons and chalk members is particular to Ray Gallois, Bob Lake, Roy Shepard-Thorn, Brian possible over very long distances. Where attentuation has re­ Young and Chris Wood. Chris Wood has also been a continuous source of guidance with Chalk palaeontology. My family, Diana, sulted in the loss of a marker bed, renewed expansion usually Jamie, Sally and Tom have also proved invaluable field assistants. Ri­ sees the reappearance of that bed. Many different levels have chard Bromley, Chris Wood and Jake Hancock have provided con­ been called “Chalk Rock” or “Top Rock” (Figure 4a, b) as a structive criticisms of drafts to this paper.

LITERATURE

Bailey, H. W ., G ale, A. S., Mortimore, R. N., Swiecicki, A. and G ale, A. S. (1980): Penecontemporaneous folding, sedimentation WOOD, C. J. (in press): The Coniacian-Maastrichtian Stages and erosion in Campanian Chalk near Portsmouth, England. of the United Kingdom with particular reference to Southern - Sedimentology, 27, 137-151. England. - Newsletters on Stratigraphy. G aSTER, C. T. A. (1924): The Chalk of the Worthing District, Sus­ BARROIS, C. (1876): Recherches sur le terrain Cretace Superieur de sex. - Proc. Geol. Assoc., 35, 89-110. PAngleterre et de l’lrlande. - Mem. Soc. Geo!. Nord., 4-10; ------(1939): The stratigraphy of the Chalk of Sussex. Part IJ. Lille. Eastern Area. Seaford to Cuckmere Valley and Eastbourne, BROMLEY, R. G. (1975): Trace fossils at Omission Surfaces. - In with zonal map. - Proc. Geol. Ass., 50, 510-526. Frey, R. W. (Ed.): The Study of Trace Fossils, 399^127; New — (1951): The stratigraphy of the Chalk of Sussex. Part IV. East York (Springer). Central Area - between the Valley of the Adur and Seaford, ------& G ale, A. S. (in press): The Lithostratigraphy of the English with zonal map. - Proc. Geol. Ass., 62, 31-64. Chalk Rock. - Cretaceous Research. G riffiths, C. and Brydone, R. M. (1911): The Zones of the Chalk ------, Schulz, M. G. & PEAKE, N. B. (1975): Paramoudras: giant in Hants. - 8 vo., 3 pp., 4 pis.; London (Dulau & Co.). flints, long burrows and the early diagenesis of chalks. - K. HEBERT, E. (1874): Comparison de la craie des cotes d’Angleterre dansk. Vidensk. Selsk. Geol. Skr., 20/10, 31 pp. avec celle de la France. - Bull. Soc. Geol. Fr., (3), 2, 416. BRYDONE, R. M. (1912): The stratigraphy of the chalkof Hants. - 8 — — (1875): Ondulations de la craie dans le Bassin de Paris. - Bull. vo., 116 pp., 3 pis., col. Map.; London (Dulau & Co.). Soc. Geol. Fr., 33, 512-546. ------(1914): The Zone of Offaster pilula in the South English Hill, W. W. (1886): On beds between the Upper and Lower Chalk Chalk. - Geol. Mag., 51, 359-369, 405-411; 449-457, of Dover and their comparison with the Middle Chalk of 509-513. Cambridgeshire. — Quart. J. Geol. Soc., 42, 232-248. C hatwin, C. P. & W ithers, T. H. (1908): The zones of the Chalk in J e e f e r ie s , R. P. S. (1963): The Stratigraphy of the Actinocamax pie- the Thames Valley between Goring and Shiplake. - Proc. tins Subzone (Turonian) in the Anglo-Paris Basin. - Proc. Geol. Ass., 20, 390-419. • Geol. Ass., 74, 1-33. DlXON, F. (1850): The geology and Fossils of the Tertiary' and Creta­ JUKES-BROWNE, A. J. and HlLL, W. (1903): The Cretaceous Rocks of ceous Formations of Sussex; London, New Edition, 1878. Britain 2: The Lower and Middle Chalk of England. - Mem. ------(1878, 2nd Edition): The geology oi Sussex. - Edited by Prof. Geol. Surv. U. K., 568 pp. T. R. JONES, 4to Brighton. Geol. Map., 65 plates. ------(1904): The Cretaceous Rocks of Britain 3: The Upper Chalk DRUMMOND, P. V. O. (1967): The Cenomanian Palaeogeography of of England. - Mem. Geol. Surv., U. K., 566 pp. Dorset and adjacent counties. - Ph. D. Thesis, Univ. London. KRUMBEIN, W. C. and SLOSS, L. L. (1951,2nd Edition 1963): Strati­ ------(1970): The Mid Dorset Swell. Evidence of Albian-Cenoma- graphy and Sedimentation. - 660 pp.; San Francisco (W. H. nian movements in Wessex. - Proc. Geol. Ass., 81, 679-714. Freeman and Co.). EVANS, C. (1870): On some sections of Chalk between Croydon and Lake, R. D. (1975): The structure of the Weald - a review. - Proc. Oxtead. - Proc. Geol. Ass.; Lewes, 1870. Geol. Ass., 86, 549-557. FLETCHER, T. P. (1979); The lithostratigraphy of Upper Chalk sedi­ MANTELL, G. A. (1822): The Fossils of the South Downs or Illustra­ ments in Northern Ireland. - Rep. Inst. Geol. Sci. tions of the Geology of Sussex; London. © Biodiversity Heritage Library, http://www.biodiversitylibrary.org/; www.zobodat.at 41

MORTIMORE, R. N. (1979): The Relationship of Stratigraphy and ster. - Mém. du Muséum National D’Histoire Naturelle, Tectofacies to the Physical Properties of the White Chalk of XXXI, 94 pp., 12 Plates. Sussex. — Ph. D. Thesis, Brighton Polytechnic. TUCKER, M. E. (1974): Sedimentology of Palaeozoic pelagic Rawson, P. F., C urry, D., D illey, F. C., Hancock, J. M., Ken­ limestones: the Devonian Griotte (Southern France) and Ce- nedy, W. J., Neale, J. W., W ood, C. J. and W orssam, B. phalopodenkalk (Germany). - In: K. J. Hsu and H. C.JEN- C. (1978): A correlation of the Cretaceous Rocks in the British KYNS (Editors): Pelagic Sediments: on land and under the sea. Isles. - Geol. Soc. London. Spec. Rep. 9, 70 pp.; London. - Spec. Publ. Int. Ass. Sediment., I, 71-92. Rowe, A. W. (1S99): An analysis of the genus Micraster, as VOIGT, E. and Hantszchel, W. (1956): Die grauen Bander in der determined by rigorous zonal collecting from the Zone of Schreibkreide Nordwestdeutschlands und ihre Deutung als Rhynchonella cuvien to that of Micraster corangitinum. — Lebensspuren. Mitt. Geol. Stlnst. Hamb., 25, 104-22;Ham­ Quart. J. Geol. Soc., 55, 494. burg. ------(1900): The Zones of the White Chalk of the English Coast, WHITAKER, W . (1861): On the Chalk Rock the topmost bedo f the Part I, Kent and Sussex. - Proc. Geol. Ass., 16, 289-368. Lower Chalk in Berkshire, Oxfordshire, Buckinghamshire, ------(1901): The Zones of the White Chalk of the English Coast, etc. Proc. Geol. Soc., 17, 166-170. Part II, Dorset. - Proc. Geol. Ass., 17, 1-76. WILSON, H. E. and M anning, P. I. (1978): Geology of the Cause­ ------(1907): The White Chalk of the English Coast, Part V, Isle of way Coast, 2 Vols. Mem. Geol. Surv. North. Irek, Sheet 7. Wight. - Proc. Geol. Ass., 20, 209-352. WOOD, C. J. and Smith, E. G. (1978): Lithostratigraphical classifica­ STOKES, R. B. (1975): Royaumes et Provinces Fauniques du crétacé tion of the Chalk in North Yorkshire, Humberside and Lin­ établis sur la base d’une étude systématique du genre Micra- colnshire. Proc. Yorks. Geol. Soc., 42, 263-287.