Problems of Correlation in theAnglo-Paris-Belgian Basin

by DENNIS CURRY

President ial Address delivered 4 March 1966

1. INTRODUCflON

IN CONCLUDING MY ADDRESS last year on the Lower Tertiary beds of theHampshire and London tectonic basins I said that I hoped at a later dateto discuss the relations between these beds and beds of similar age aroundParis and in Belgium. This I now do. The beds of these four areas, togetherwith outliers to be mentioned later, are believed to have been laid down ina single large region of deposition which occupied the greater part of thearea illustrated in Fig. 1.

This depositional basin was called by Stamp the Anglo-Franco-BelgianBasin but should preferably be referred to as the Anglo-Paris-BelgianBasin as a quite distinct Tertiary basin , the Aquitaine Basin, occurs insouth-west France. The Anglo-Paris-Belgian Basin was closed duringPalaeogen e times to the east , south and south-west by the ancient uplandswhich are now the Ardennes, Vosges, Massif Central, Brittany and theCotentin peninsula. To the north-west were similar uplands mantled inpart by Mesozoic beds. North-eastwards there was a connection towardsnorth Germany and Denmark and , probably, to a sea occupying the siteof the present North Sea. To the west the Anglo-Paris-Belgian Basincommunicated intermittently through a strait in the region of Cherbourgto a sea in the western English Channel which, it seems, extended westwardsto an ocean. The West Channel Sea connected southwards to the AquitaineBasin which also was a sea opening to the westward ocean. The westernocean itself connected with the Tethys via the south of Spain. The straitbetween the central and western parts of the English Channel was openduring Upper Cretaceous times but probably closed throughout thePalaeocene and early Lower Eocene. It was open and acted as a migrationroute in late Lower Eocene and Middle Eocene times, but was probablyclosed once more at some time during the period of deposition of theBarton Beds, thereafter remaining closed until relatively recently. Fig. 2provides a palaeogeographical reconstruction of the area in Middle Eocenetimes . For other reconstructions see Krutzsch & Lotsch, 1958.

The successions of strata found in the London, Hampshire and Parisareas and in Belgium have been studied intensively ever since the earliestdays of the study of rocks as a science. This has resulted from the ir ready

437

438 DENNIS CURRY

S CQ leI: 6.000.000100km

Fig. I. Palaeogene beds of the Anglo-Paris-Belgian Basin and nearby areas: at thesurface (solid) and beneath younger beds (lined). Outcrops of uncertain extent dotted

accessibility, simple structure and the presence of abundant and well­preserved fossils. So much has been written on them in fact and on theirinterrelations that one might be forgiven for supposing that everything hasalready been said long ago and that any further discussion is superfluous.Forty years ago this did indeed seem to be the case. The sequences in thevarious parts of the basin were considered to be relatively complete andwere correlated with confidence. However, more recent researches havedone much to show that this confidence was misplaced. Since the last warthere has been a welcome increase in awareness of the problems in correla­tion still to be solved in the Tertiary beds of north-west Europe and agreater willingness to travel to study successions outside the investigator'snormal range of enquiry. As a result sequences that were believed to be

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 439

~

OCEAN

MICClE EOCENEPALAEO GEOGRAPHY

Mesozo iclowland

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

:~" " " """

Fig. 2. Middle Eocene Palaeogeography of the Anglo-Paris-Belgian Basin and itsneighbourhood

complete are now found to contain gaps, and correlations unquestionedfor long periods are regarded as ill-founded. I propose to devote theremainder of this address to a discussion of some of the more recent lines ofresearch, firstly by talking about the methods which have been employedand then about some of the conclusions which have been reached from theapplication of those methods. As a necessary preliminary I shall nowdiscuss briefly the sequence of strata in each area of deposition.

2. ANGLO-PARIS-BELGIAN BASIN:SUMMARY OF DEPOSITIONAL SEQUENCES

(a) Hampshire and London Areas

The succession in these areas, which totals about 600 m., was discussedlast year (Curry, 1965).It is sufficientto note for the purpose of the presentsurvey that the lithology is one essentially of sands and clays, marine in theeast and predominantly marine in the west, and that it includes severalerosion-surfaces which may mark longer or shorter periods of non­deposition.

440 DENNIS CURRY

(b) Outlier Between the Isle of Wight and Cherbourg

In this outlier Reading Beds, London Clay and Bracklesham Beds havebeen recognised (Curry, 1962). The sequence here is so much like those ofthe Hampshire and London areas that it is clear that until Middle Eocenetimes at least these three areas formed part of one continuous area ofdeposition.

(c) The Paris Basin

Unlike the Hampshire and London so-called 'Basins ', which are relictsof a much larger single area of deposition which have been preserved insynclinal depressions, the Paris Basin, at least in its southern part, is a truedepositional basin. In the region to the north of Paris the sequence is almostentirely marine. From this region, especially southwards and south­eastwards, lagunar and freshwater deposits become increasingly prominentuntil, south of a line through Chartres to Fontainebleau and Epernay, thesequence is almost entirely continental. Within the basin the margin of thesea fluctuated continuously and as a result there is a bewildering variety ofdeposits, both vertically and horizontally. The dominant lithological typesare marine sands and freshwater limestones; clays are rare except incontinental sequences. Within the succession there are many non-sequenceswhile substantial overlap occurs at the base of the Calcaire Grossier andthe Sables de Fontainebleau, both of which transgress locally on to theChalk. The maximum thickness of the Palaeogene succession in the ParisBasin is about 250 m.

(d) Belgium, Northern France and South-West Holland

Palaeogene beds occur in the whole of the northern half of Belgium andin neighbouring areas of France and Holland. Here they lie, either directlyor with a thin intercalation of Cretaceous beds, on a platform of Palaeozoicrocks which rises gently south-eastwards to form the Ardennes. A generalnorth-north-easterly dip takes the Palaeogene succession beneath thickNeogene beds in south-west Holland whence they may be presumed tocontinue across the North Sea to link with an extension of the Palaeogeneof eastern England. Palaeogene beds occur also in north-east Holland butthese form part of the North German Basin which was it seems linked onlyintermittently with the Anglo-Paris-Belgian area. The Belgian sequence isintermediate in thickness (about 350 m.) between those of Hampshire andParis, and lithologically resembles that of England rather closely, marineclays and glauconitic sands predominating. As in the Paris Basin, there aremany non-sequences, especially well marked at the base of the Bruxellian,the Ledian and the Tongrian.

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 441

(e) Outliers Between Le Havre and Calais

The most important of these is at Ailly, near Dieppe (Bignot, 1966). Thisincludes at the base white sands which have yielded Thanetian marinemolluscs. These are overlain by a Spamacian sequence including clays likethose of the Woolwich Beds and false-bedded sands compared by Bignotto the Sables de Sinceny, which themselves are very like the BlackheathBeds. The associated fauna includes some species which in Englandcharacterise the Woolwich Beds and others characteristic of the BlackheathBeds. Capping the whole sequence is the Formation de Varengeville, ofdark clay and sand, which lithologically resembles the London Clay andhas a microfauna somewhat resembling those both of the London Clay andthe Sables de Cuise. Rather similar successions, finishing upwards inSpamacian beds, occur at St. Valery-sur-Somme and near Le Touquet.

3. LITHOLOGICAL RESEMBLANCES WITHIN THEANGLO-PARIS-BELGIAN BASIN

It is possible to draw some striking lithological parallels within thePalaeocene and Lower Eocene beds of the Anglo-Paris-Belgian Basin. TheLondon Clay varies little throughout the whole of south-east England andit is not surprising, therefore, to find that it can readily be identified by itslithology in French and Belgian Flanders, where it is known as the Argiled'Ypres, There are considerable resemblances too between Thanetian bedsin Belgium and England, and in particular the Tuffeau de Lincent ofBelgium closely resembles the upper part of the Thanet Beds. As betweenthe London and Paris Basins the Spamacian sequences are lithologicallyvery similar, the Woolwich and Reading Beds resembling the Lignites andArgile plastique respectively, while the Blackheath Beds closely match theSables de Sinceny. There is, however, little lithological resemblancebetween the Paris Basin and Belgian successions at any level.

4. GROUPS OF ANIMALS AND PLANTS OF VALUEIN CORRELATION

The most widely used of these have been the molluscs and nummulites,together with the vertebrates where they occur. Use has been made also ofsome kinds of plants. Microfossils of all kinds are now being studiedintensively and some of these are proving of considerable value, especiallyin work on borehole samples.

(a) The Molluscs

The shell of most molluscs is made of aragonite, which is readily dis­solved or replaced by calcite. As a result mollusc faunas including reallywell-preserved shells are rather rare. However, the Anglo-Paris-Belgian

442 DENNIS CURRY

Basin is exceptionally well provided with such faunas and they may befound at most levels in the succession. As a group the molluscs are mostsuccessful and have colonised a wide range of habitats both in fresh andsalt water and on land. They include forms specialised for crawling,burrowing, swimming and floating; they feed by grazing, filter-feeding andflesh-eating. As a result they exist in very great variety, an example of thisvariety being the 1800 or so species of molluscs known from one strati­graphical unit alone, the Calcaire grossier, of the Paris Basin. Because ofthe specialisation I have mentioned, many species of molluscs are subject tostrong ecological control. As a result relatively large faunas of the sameage but living under different conditions may contain few species incommon. On investigation, too, it is found that many, perhaps most,molluscan species vary both in space and time. The above facts make themolluscs a particularly difficult group to use for correlation purposes. Thedata which they provide are so often mutually contradictory that thegastropods and bivalves at least have acquired a reputation for untrust­worthiness which is not entirely justified.

In spite of these facts the molluscs of the Palaeogene have been studiedlonger and more intensively than any other group (see the classic works ofLamarck, Deshayes and Cossmann in France, and Nyst, and more recentlyGlibert, in Belgium) and correlations within our area depend largely on theevidence which they provide. Correlations have been based for the mostpart on characteristic mollusc assemblages, supplemented by the detailedmonographing of complete mollusc faunas and the making of statisticalcomparisons of the number of species in common between selected pairs ofassemblages. These methods are highly subjective as they depend ultimatelyon the assessment of specific differences, an assessment which will varyfrom investigator to investigator. At the same time the methods make noallowance for differences, which may be very marked, which are purelyfacies-controlled.

Another method of correlation by means of the molluscs has so farhardly been attempted. This would seek to eliminate the facies factor byconsidering the total population of a particular genus or closely alliedgroup of genera and by studying the way in which this population changesin time and space. There are few genera which are sufficiently abundantboth individually and specifically for this purpose, however. The mostpromising groups would appear to be the Turridae (cf. Wrigley 1945, 149),Volutidae and the genera Turritella, Corbula and Crassatella.

Brief mention may be made of the pteropod molluscs. These are tirstknown from Lower Eocene beds, but appear to have evolved rapidly fromthen on. As they are pelagic their distribution is relatively independent offacies. The pteropods are rare as fossils but recent work (Curry, 1965a,370) suggests that they may be of value in making correlations with distant

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 443

and often very dissimilar Palaeogene molluscan faunas such as those of theAquitaine Basin and the south-east United States.

(b) The Foraminifera

(i) Nummulites. The nummulites are wellknown as the large and relativelycomplicated Foraminifera which attained rock-forming abundance inEocene times. They are typically of a compressed lenticular shape which isbuilt up by the addition of successive V-shaped chambers, each of whichextends from the periphery towards the centre of the lens on either side. Inmore complicated forms the individual chambers are subdivided laterallyinto chamberlets and may be supported by pillars. Nummulites aredifferentiated by the size and degree of inflation of the adult test, the shapeand rate of increase of the chambers and the nature of any chamberlets andpillars which may be present. The essential characters of nummulites arethus mostly internal and are only fully revealed by grinding or sectioning.The first nummulites, relatively small and without chamberlets or pillars,are known in the Palaeocene. Such primitive types are known throughoutthe Eocene and much of the Oligocene and, according to some authors,still exist. In early Eocene times rapid evolution occurred in the mum­mulites, both in size and in complexity of chamber formation, with thedevelopment of several lineages; an evolution which culminated in lateEocene times with the extinction of more complicated forms. A similar butlater evolutionary burst associated with the rather simple form, N. fabianiiPrever culminated in Middle Oligocene times with the complicated N.intermedius d'Archiac.

Relatively complete lineages have been traced in Switzerland, Italy,Libya and the Tethys generally, and it is therefore assumed that it was inthis area that the nummulites evolved. In the Anglo-Paris-Belgian Basinnummulites appear sporadically, persist for a short while and then disap­pear to be replaced by forms of a different species. All the evidence pointsto successivemigrations from the Tethys, with subsequent extinction. Thereis little evidence of evolution in the basin itself. In each part of the Anglo­Paris-Belgian Basin the species N. planulatus Lk., N. laevigatus (Brug.) andN. variolarius Lk. occur and appear in that order. In England and Belgium,beds without nummulites occur between those bearing N. planulatus andN. laevigatus, and this may also be the case in the Paris Basin. In all threeareas the range of N. variolarius overlaps that of N. laevigatus (Blondeau &Curry, 1963, 275). Assuming rapid dispersal of the newly arrived im­migrants and approximately simultaneous extinction in various parts of thebasin, the times of appearance and disappearance of these nummuliteswould appear to be of great value for correlation. So far as can be judgedby other criteria, the molluscan faunas for instance, these datum lines areindeed reliable.

444 DENNIS CURRY

Two additional species of nummulites are known from England andoccur near the boundary between the Bracklesham and Barton Beds. Theseare N. prestwichianus (Jones) and N. rectus Curry. N. prestwichianusoverlaps N. variolarius in the highest Bracklesham Beds of the New Forest,and N. prestwichianus, N. rectus and N. fabianii (the last not known in theAnglo-Paris-Belgian Basin) occur together in the western English Channel.N. prestwichianus is probably synonymous with N. germanicus (Bornemann,1860), from the Lower Oligocene of Westeregeln, near Magdeburg,Germany, and recorded at about the same level in Belgium (Batjes, 1958,169); also with N. tournoueri de la Harpe, 1879, which has a range fromUpper Eocene to Middle Oligocene in south-west France. In view of therelatively long range of N. taurnoueri it would seem undesirable to rely onN. prestwichianus and N. germanicus for correlation of the beds in whichthey separately occur. The evidence from molluscs indeed suggests (seepara. 5(c)(v» that while the Belgian and German occurrences of N.germanicus are of the same age the occurrence of N. prestwichianus inEngland is much earlier than these.

N. orbignyi (Galeotti) (=wemmelensis) occurs abundantly in the Sablesde Wemmel of Belgium, where it may be associated with N. variolarius.Neither N. orbignyi, N. prestwichianus nor N. rectus is known from theParis Basin though they might have been expected to occur at some horizonwithin the Sables moyens.

(ii) Alvealina and Orbitalites. These genera also appear sporadically inour area as immigrants. However, they occur only locally. Both it seemshad the same ecological requirement: that of a shallow, sheltered and clearsea, a requirement that was met only infrequently in Palaeogene times inour basin. In view of this rather stringent ecological control, caution isindicated when using these genera for correlation; their absence at aparticular locality and level should not be regarded as proof that they didnot exist elsewhere in the area at that time.

Four species of Alvealina are known from our area and one of these isconfined to the Sables de Cuise of the Paris Basin. This is A. oblongad'Orbigny, widely known from southern Europe, where it is associatedwith Nummulites planulatus, Of the three other species A. bosci Defranceoccurs in the upper part of the Calcaire grossier of the Paris Basin andA. fusiformis J. de C. Sowerby and A. elongata d'Orbigny occur in theUpper Bracklesham Beds of the Hampshire Basin (Adams, 1962). Untilrecently it was supposed that A. bosci and the fusiformis-elongata complexcharacterised different horizons and that their ranges did not overlap.However it seems that they do indeed all occur together both at Selsey(Fisher Bed 21) and also in beds of about the same age at Gourbesville(Manche). The exact stratigraphical significance of these species thereforeneeds re-evaluation.

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 445

The genus Orbitolites has recently been the subject of critical revision byLehmann (1961), who has distinguished four species in the Middle Eocenebeds of the northern half of France. Only one of these, O. complanatus Lk.,is known from the Paris Basin, where it is locally common, usually incompany with Alveolina bosci, in the upper part of the Calcaire grossier.Orbitolites also occurs rarely in the Alveolina-bearing horizon at Selseyand,as fragments, in Ledian sands of Belgium and the Sables moyens of LeGuepelle and Le Ruel, Paris Basin. It has not been possible, however, todecide to which of the species distinguished by Lehmann these should bereferred.

(iii) Smaller Foraminifera. Smaller Foraminifera may be found abun­dantly throughout the Palaeogene succession wherever conditions ofdeposition and preservation are favourable. The species of Foraminiferafound in our area are almost all benthonic and such forms are muchinfluenced by bottom-conditions. As in the case of molluscs, therefore,quite different assemblages may be found in different rock-types of thesame age.

D'Orbigny, in his pioneer studies of the Foraminifera, described manyspecies from the Calcaire grossier of the Paris Basin. Many more wereidentified by Terquem (1882). English works approximately contem­poraneous with that of Terquem are by Sherborn & Chapman (1886) onthe Foraminifera of the London Clay and by Burrows & Holland (1897)onthose of the Thanet Beds. The English authors were much influenced by thework of Brady on the Recent Foraminifera collected on the Challengerexpedition and as a result almost all of the forms they described werereferred to species still living. The implication of this work was of coursethat small Foraminifera are of little use for correlation and perhaps for thisreason little new work was published on the Lower Tertiary Foraminiferaof western Europe during the succeeding forty years. More recently severalimportant monographs have dealt with the smaller Foraminifera of theAnglo-Paris-Belgian Basin. Le Calvez (1947-52) has revised the work ofTerquem and has produced faunal lists for several of the classical Frenchstages. Ten Dam & Reinhold (1942), ten Darn (1944), Batjes (1958) andKaasschieter (1961) have described the Foraminifera of the Palaeogene ofthe Low Countries. Comprehensive works on English faunas have dealtwith those of the Thanet Beds (Haynes, 1956-8), the London Clay (Bowen,1954) and the Oligocene of the Isle of Wight (Bhatia, 1955).

So far the smaller Foraminifera of the Anglo-Paris-Belgian Basin havebeen little used in correlation. Some comparison between the faunas of thevarious parts of the basin has been made in the works of ten Dam, Batjesand Kaasschieter but there has as yet been no attempt to codify the resultsby proposing a series of zones related to the classical stages.

For the most part the fauna of small Foraminifera is an endemic one.

446 DENNIS CURRY

However, some genera originated elsewhere and occur in our area aschance migrants. Amongst these may be mentioned Asterocyclina,Cuvillierina, Fabiania, Fabularia, Halkyardia and Linderina. Like thenummulites, these also may prove to be of value as markers. For knownoccurrences of these genera in our area see Fig. 3.

!:i!!m~ sh ire Ba s in Pa r is Bas in

Borton Fabulana bella

Beds

Alv. oblo ngaCuvi lllfflna

Halkya rd ie

lfLindrrina brugH/:porbitolitt s ( r ar e),

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i:.;: i~@W 0 0~' - . ;~~J:E n~eQ)r~er 0,'- Koa~~ ~-QM .' '~~~~. ~ . ~ If) \). X10 . no .,." XIO X8 Xl

Fig. 3. Some Foraminifera which migrated into the Anglo-Paris-Belgian Basin duringEocene times and their known vertical range

In addition to the benthonic Foraminifera so far discussed there is asmall but geologically important group which can float, the Globigerinacea.These, like planktonic marine organisms generally, are relatively free ofenvironmental control and characteristically have a wide geographicaldistribution. Recent work by many specialists has proved that LowerTertiary species of the Globigerinacea may be most valuable in correlationwork, and Bolli (1957, 1957a, b) has proposed a series of zones based onthe occurrence of successive planktonic faunas in Trinidad. This, togetherwith a further sequence proposed by Blow & Banner (in Eames et al., 1962,68) in Tanganyika, is held to span the whole of the Palaeogene. Planktonicsequences which can be correlated with the new zonal succession have beenreported from places as far from the type areas as Italy and southernRussia and it seems probable therefore that this succession may prove tobe of world-wide validity.

Unfortunately planktonic Foraminifera have been found to be presentonly sporadically in the Palaeogene beds of the Anglo-Paris-Belgian Basinand most of such as do occur are small and poorly characterised species ofGlobigerina itself. This is no doubt due to the relatively land-locked nature

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 447

of the basin. However, preliminary work has revealed the presence of twodistinctive species of zonal value. These are Globorotalia formosa gracilisBolli, which occurs in the Sables de Cuise, the Bracklesham Beds of thecentral English Channel (Curry, 1962, 193,as G. cf. rex) and the lower partof the Upper Lizard Springs Formation of Trinidad (Lower Eocene), andGloborotalia bullbrooki Bolli, occurring in the type Bruxellian, the westernpart of the English Channel and the middle part (Middle Eocene) of theNavet Formation, Trinidad.

The stratotypes of most of the Palaeogene stage-names in general use inWestern Europe are situated in the Anglo-Paris-Belgian Basin and it is ofcourse important that these should be correlated with an internationaltime-scale. The planktonic Foraminifera provide a possible means ofcarrying out this correlation and research is now in progress with theintention of achieving this.

(c) The Ostracods

The Eocene and Oligocene ostracods of Belgium have been mono­graphed by Keij (1957), while Marliere has described those of the typeMontian. Apostolescu has studied the ostracods of the Paris Basin and hasdescribed many species from Thanetian and Lutetian horizons. By contrastlittle has been published in this century on the ostracod faunas of theEnglish Palaeogene, the most important works being those by Bowen (1953)and Eagar (1965) on the faunas of the London Clay. The only recentaccount of the ostracods of the Barton Clay is in Keij (1957), while the richostracod faunas of the Bracklesham Beds and the Oligocene of the Isle ofWight remain almost unrecorded. Apostolescu has recently (1964) pub­lished a range-chart in which 225 species are recorded as occurring in thePalaeogene of Belgium and the Paris Basin. This chart demonstrates thatwhile faunas of the Cuisian, Lutetian and Auversian-Bartonian have manyspecies in common and are not readily differentiated, the ostracod faunasof the Montian, Thanetian, Sparnacian and Sannoisian-Stampian eachpossess a strong individuality . Although so far little use has been made inthe Anglo-Paris-Belgian Basin of ostracods for correlation purposes itdoes seem from Apostolescu 's chart that they could be valuable for thispurpose.

(d) The Nannoplankton (Coccoliths and Discoasters)

The coccolithophores are flagellates which are covered with ovalcalcareous discs known as coccoliths. Coccoliths occur in tremendousquantities in the Chalk and have been known as fossils for over a hundredyears. It is only rather recently, however, that they have been linked withthe organisms which produce them. Associated with the coccoliths inmarine beds throughout the Tert iary are star- or rosette-shaped bodies

448 DENNIS CURRY

known as discoasters and it is believed that these also may be the skeletalremains of as yet unrecognised protozoans.

Both coccoliths and discoasters are extremely small and their study andinterpretation demand a good light microscope of high power and con­siderable skill in its use. Indeed individual coccoliths have been found toconsist of assemblages of even smaller plates whose structure can only bemade out by the use of an electron microscope. The discoasters are thusmore easily studied than the coccoliths and this study has shown that theyhave a wide range in space and, in some cases, a short range in time. Theyare thus suitable material for correlation work. However, like other verysmall fossils, they are very liable to be reworked into younger sediments,and assemblages must always be studied with this possibility in mind.

It appears that there has been little systematic search for coccoliths anddiscoasters in the Anglo-Paris-Belgian Basin. The only work known to mewhich deals specifically with our area is that of Bouche (1962), whoexamined a large series of rock-samples from various Palaeogene horizonsin the Paris Basin, but found good faunas only in the Calcaire grossier(Middle Eocene). However, an important record by Bramlette & Sullivan(1961) suggests that further research might be very fruitful. In a paper on aCalifornian sequence they recognise six biostratigraphic units based onnannofossils within a succession of beds ranging in age from Palaeocene toMiddle Eocene. In this paper seven species are recorded as occurring in theThanet Beds and in Californian units I and 2, while four different speciesoccur in the London Clay and in Californian unit 3. No reference is madeto any other English formation and it appears that the authors had accessonly to material from the Thanet Beds and the London Clay in the courseof their studies.

(e) The Mammals

Rat (1966) has recently produced an excellent summary of the importantsequence of mammal faunas recognised in the Paris Basin. Although it hasnot been possible in all cases to correlate these French mammal faunaswith the standard marine sequences, nevertheless they do provide someuseful points of reference within the Anglo-Paris-Belgian Basin. Teilhardde Chardin, in his studies of Palaeocene and early Eocene faunas, noted amarked difference between the faunas of Cernay (Thanetian) and Meudon(Sparnacian), but commented on the similarity between the latter and therare remains of mammals from the London Clay. Stehlin (1910) discussedthe relations of the well-known English mammal faunas of the LowerHeadon Beds (Hordle), the Bembridge Limestone and the Lower HamsteadBeds. He concluded that the first of these faunas is not represented in theParis Basin although it is known in the south of France. The Bembridgefauna can be matched exactly in the upper part of the Gypse of Montmartre,

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 449

while the Hamstead fauna is known at Ronzon in the Auvergne, and rareremains of this age are known from the Calcaire de Brie of the Paris Basin.According to Stehlin there is an important break between the Bembridgeand Hamstead faunas, marked by the appearance of many new genera,which are believed to have migrated from Asia (Gabunia, 1964). As will beseen later, the correlations between the English and Paris Basin sequencessuggested by the mammals are substantially confirmed by the charophytesand both provide valuable testimony in the series of predominantlycontinental beds which span the Eocene-Oligocene boundary in the twoareas.

(f) The Charophytes

The charophytes or stoneworts are a group of primitive water-plantswhich form a mass of alga-like thin stems on which are developed sphericalfruiting bodies. The cell-walls of the plants and especially of the fruitingbodies may be calcified and so these may be preserved fossil. The fruitingbodies, which are about as large as a pin's head, are typically made up offive left-handed spiral segments and are more or less ornate. Charophytesare widely distributed in fresh and brackish water and their fructificationsare not infrequently washed out to sea, where they may be buried in marinesediments. Investigation of fossil charophytes has shown that individualspecies and some genera may have relatively short ranges and so may bevaluable in correlation of continental deposits. In addition the occasionaloccurrence of charophytes in marine beds provides opportunities ofcorrelating marine with continental sequences.

Grambast (1962) has studied the sequence of charophyte floras in thePalaeogene beds of the Paris Basin, where almost every stage has yielded acharacteristic flora. Unfortunately few charophytes are known fromBelgium, but useful comparisons have been made with English horizonsyielding charophytes. Three species found in the Reading Beds at Harefield,Middlesex, are known from the type Sparnacian of the region of Epernay(Grambast, in /itt.). In the Hampshire area charophytes are known at manylevels from the Lower Headon Beds upwards and, according to Grambast(1964), the sequence of floras agrees well with that above the Sables moyensin France. Correlations suggested by these floras are indicated in Fig. 4 andthese are consistent with those based on mammals.

(g) Spores and Pollen

Like the charophytes these provide possibilities of correlation bothbetween different series of continental beds and between such series andtheir marine counterparts. I am not aware, however, of any published workby Western authors which is concerned specially with the use of spores andpollen in correlation of the Lower Tertiary beds of our area. Krutzsch &Lotsch (1964) of East Germany, in a discussion of correlations and zonal

PROC. GEOL. ASS., VOL. 77, PART 4, 1966 30

450 DENNIS CURRY

/ 962. ISLE OF WIGHT

·Unil mainly or wholly ofnan-marine b. d 5',

~I=per Hamste ad Beds

"? · l aw er

Hamslead

M Beds

·B embr idgeMa r l s

~"'t:;embrr ge Lim es tone

·Osborne a nd

Upper Headon

Beds

r .. Midd le Heado n Beds

· lower Headon Beds

XIS/0 Barlon Beds

' os X/O

app

c;r:Ed~ha:d~~~~::::'~S~k·G;:~b.Harrisichara lub rrcufota (ly .ll) X

vasl/armis (R. id & GroS I,n-ata Gramb. XIS6 Rasky.lla pocki Gram b. XIO7 Psilochara undula /a IPia) X /O" ·Mammols.

·Cale ai re de Beaue e M

Sables de °Calcaire

ontcinebleoude ..

Brie

°Ma rn essupragy ps euses

·Gyps eCctcmre

de ..Cham pigny

Marnes II Ph. lude ns ls

Sa bles (Ca~~a i r e Mmoy ens51. Ouen

Caleaire ·Calea ire

grossi erde M

Provins /2

Sabl es de Cuise ],

Fig. 4. Occurrences of some charophytes of stratigraphical importance in the Anglo­Paris-Belgian Basin

boundaries in the Palaeogene of Western Europe, make passing referenceto the sequence of spore and pollen spectra recognised in Central Europe.One of these, the Zeitzer Bild, is recorded as being present in the Schoene­walder Schichten and Latdorf Beds in Germany and also, in England, inthe Lower and Middle Headon Beds. This, as will be seen later, supports acorrelation based on the molluscan faunas.

Although they do not fall strictly within the province of this address theinvestigations of Durand (1964, for references) may usefully be mentionedhere. She has studied various isolated continental deposits which rest inhollows on the Armorican massif of Brittany. In the case of several of these,spores and pollen are the only fossils of diagnostic value which have beenrecognised, but the spectra which they reveal are sufficiently characteristicto permit the dating of individual deposits with some assurance.

5. SOME SUGGESTED CORRELATIONS

Discussion under this heading will concentrate on those correlationswhich are disputed.

(a) Palaeocene Beds

The Palaeocene is here taken to include those beds usually referred tothe Montian, Thanetian and Sparnacian stages and their equivalents. I

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 451

shall not comment in detail on the type Montian of Belgium and the bedsin the Paris Basin which have been correlated with it. The difficult questionof their relation to each other, to the Tulfeau de Ciply and to the typeDanian has no direct relevance to English sequences. For an excellentsummary of recent research the reader is referred to Marliere, ]964.

The Thanetian of France was monographed by Farchad (1936) whoanalysed its macrofauna and compared this with those of the type ThanetBeds and the marine Landenian of Belgium. He concluded that the threegroups of beds are of about the same age, though he noted that severalgenera of molluscs of warm water aspect which occur in the Paris Basin arenot known from England or Belgium. The zonal classification proposed byLeriche (1903) is considered by Farchad to be inappropriate because thethree molluscan species chosen to characterise successive zones all occurat one level in England.

Throughout the Anglo-Paris-Belgian Basin the oldest beds referred tothe Thanetian are similar in lithology and their microfaunas have manyspecies in common. The Heersian beds of Belgium and the Tulfeau deLa Fere in France may thus be correlated with some confidence with themiddle and lower parts of the Thanet Beds of east Kent. The correlation ofhigher beds is less certain. The Tulfeau de Lincent of Belgium and theSables de Bracheux and Sables de Chalons-sur-Vesle of France haveyielded most of the molluscan species known from the Thanet Beds.However, the fauna of the beds in the Paris Basin includes substantialelements not known in England. In particular it may be noted that twospecies, Corbicula cordata (Forbes) (= C. veneriformis (Desh.) andPitharella arenaria (Melleville)(=P. rickmaniEdw.), which are characteris­tic in the Paris Basin of the Sables de Chalons-sur-Vesle occur in Englandonly in the Woolwich Beds. It seems possible, therefore, that part of thesuccession in the Paris Basin which is allocated to the Thanetian is youngerthan any part of the Thanet Beds (cr. Feugueur, 1963,417,444).

The Woolwich and Reading Beds (for a recent account see Hester, 1965)are readily matched as to lithology and fauna with the Lignites (typeSpamacian) and Argile plastique respectively of the Paris Basin, while theupper (non-marine) part of the Landenian may reasonably be correlatedwith these also. The highest Spamacian beds of England and France, theBlackheath and Oldhaven Beds and the Sables de Sinceny et de Pourcyrespectively will be discussed in the next paragraph.

(b) Eocene Beds

(i) The Problem 0/ the London Clay. In England the Woolwich Beds areoverlain by the Blackheath and Oldhaven Beds, and these by the LondonClay. For the most part the Lignites and Argile plastique are overlain bythe Sables de Cuise with Nummulites planulatus, but at a few localities a

452 DENNIS CURRY

thin series of false-bedded sands with pebbles and an estuarine faunaintervenes (Sables de Sinceny, S. de Pourcy). The London Clay and Sablesde Cuise are overlain respectively by beds (Bracklesham Beds, etc.,Calcaire grossier) which yield Nummulites laevigatus. In Belgium theArgile d'Ypres, which matches the London Clay in its lower part, passesup into more sandy beds containing N. planulatus, these in their turnunderlying beds (Bruxellian sands) with N. laevigatus. The classicalinterpretation of these sequences was straightforward. Dumont (1851), forexample, correlated the Sables de Cuise with the London Clay and theArgile d'Ypres including the overlying sandy beds, and this correlation wasfollowed by most continental geologists. Prestwich, however (1888, 108),equated the London Clay with the lower part of the type Ypresian, andthe Lower Bagshot Beds with the upper part and with the Sables de Cuise.He admitted (p. 105) the possibility of a partial equivalence between thelatter and the [upper] part of the London Clay, however.

Accepted ideas were strongly challenged by the important announce­ment by Wrigley & Davis (1937) of the presence of Nummulites planulatuswith an associated mollusc fauna of Cuisian affinities in the lower part ofthe Bracklesham Beds. On the basis of this discovery they correlated thesebeds plus the Lower Bagshot sands with the Sables de Cuise. At the sametime they drew attention to the close similarity both in lithology and faunabetween the Sables de Sinceny and the Blackheath Beds. Nummulites havenever been found in the London Clay and Wrigley & Davis gave reasonsfor believing that records of nummulites from the Argile d'Ypres wereerroneous. They then concluded that the London Clay and its equivalent,the Argile d'Ypres, are not represented in the Paris Basin and that, as acorollary, a substantial non-sequence must exist between the Sables deSinceny and the Sables de Cuise.

The existence of this non-sequence is not generally admitted in Franceand was particularly challenged by Abrard & Soyer (1942), who announcedthe discovery of N. planulatus in specimens of the mollusc Ampullinacollected at a pit a short distance from the classic locality at Sinceny, andconcluded on the basis of this find that the Sables de Sinceny must beattached to the Sables de Cuise. Feugueur (1963, 112-19) has given anaccount of recent researches at Sinceny which have revealed the existenceabove the Sables de Sinceny of fossiliferous clays which are 'franchementsparnaciennes', these being overlain abruptly by marine Cuisian sands. Inthe light of this evidence it seems probable that the N. planulatus found byAbrard & Soyer did not come from the Sables de Sinceny but from theSables de Cuise. The following are reasons for supposing this: (a) N.planulatus has not been found in the existing good sections of the Sables deSinceny; it does occur commonly, however, in the road leading to the pitsand in the soil above them. These specimens are clearly derived from the

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 453

Sables de Cuise; (b) Ampullina is not cited by Feugueur in a list of theSinceny molluscan fauna; (c) Abrard & Soyer note that the nummulitesoccurred only in the interior of the Ampullina and not in the general massof sand in their pit. They explain this fact by suggesting that the nummuliteswere thus preserved from dissolution. As the shell of Ampullina is ofaragonite and nummulite tests are composed of the more stable calcite,this explanation seems unlikely.

An analysis of the ostracod (Apostolescu, 1964,1040)and mollusc faunasdoes not indicate a close relationship between the Sables de Sinceny andthe Sables de Cuise. Amongst the fifty-sixspecies of molluscs recorded fromSinceny by Feugueur thirteen species are known only from Sinceny orPourcy, twelve occur both in the Lignites and the Sables de Cuise, twenty­one occur in the Lignites or below but not in the Sables de Cuise, ten occurin the Sables de Cuise but not the Lignites. Four of these ten species occurin the Blackheath Beds. More than half of the forty or so named speciesknown from the Blackheath Beds are known from Sinceny or Pourcy andof the balance most occur either in the French Thanetian or the Lignites.The evidence is therefore of rather close similarity between faunas of theBlackheath Beds and the Sables de Sinceny and of little affinity betweeneither and the Sables de Cuise. The ideas on correlation put forward byWrigley & Davis (1937)appear therefore still to be the most probable. Thesuggestions of Davis & Elliott (1958, 264) and Feugueur (1963) that theSparnacian is diachronous and contemporaneous in part or whole with theLondon Clay may well prove correct, however, although there is at themoment no clear evidence for these.

(ii) The Beds with N. planulatus. It is now generally agreed that the Sablesde Cuise, the upper part of the type Ypresian (Y2) and the lowest part of theBracklesham Beds (Fisher Beds I to IV at Whitecliff Bay), are at least inpart of the same age. Three markedly different mollusc faunas, those ofAizy, Pierrefonds and Herouval (oldest to youngest), are known within theSables de Cuise; the molluscan fauna of Fisher Bed IV cannot be matchedclosely with any of these. With N. planulatus Wrigley & Davis recorded asecond species of nummulite from Bed IV which they called N. lucasi[lucasianus (d'Archiac)]. Hottinger, Lehmann & Schaub (1964, 632) haverecorded their opinion that this is not lucasianus but a form intermediatebetween N. planulatus and N. aquitanicus, and thus a member of the lineageplanulatus-s-Iaevigatus more advanced than N. planulatus itself. It seemspossible therefore that Bed IV may be rather younger than any part of theSables de Cuise. Equivalents of the latter might still of course be presentwithin the almost unfossiliferous series Beds I to III which in total are asthick as the whole of the Sables de Cuise.

(iii) The Sables d'Aeltre (Aalter) and their Equivalents. These occurlocally in Belgium above Y2 sandy clays and beneath Bruxellian sandstones

454 DENNIS CURRY

with abundant Ni laevlgatus. They are marine glauconitic clayey sands withabundant Turritella and large Venericor planicosta (Lk.) and with Omalaxissp. and Callista proxima (Desh.), but essentially without nummulites (butcf. Leriche, 1938,88). Beds which are similar in lithology and fauna occurat Bracklesham Bay (Fisher Beds 1 to 4) and at Southampton (Wrigley,1934, 2, bed 4) where also they underlie beds rich in N. laevigatus. It isprobable that Beds 1 to 4 of Fisher (not to be confused with Beds I to IVat Whitecliff Bay) are of about the same age as the Sables d'Aeltre.

Feugueur (1951), in an enquiry of the age of the Sables d'Aeltre, studiedthe mollusc fauna of 104 species, of which he recognised forty-six as specialin France to the Cuisian and a further twenty-seven as absent from theCuisian but known in the Lutetian. He concluded that the Sables d'Aeltreshould be referred to the Cuisian and in particular to its uppermost partthe Niveau d'Herouval (which, however, contains N. planulatus in abun­dance). A recent observation, however, suggests that the Sables d'Aeltremay be younger than the Sables de Cuise and older than any part of thetype Lutetian. Hottinger, Lehmann & Schaub (1964) have subdivided theEocene of the Tethys into nine biozones based on the succession ofnummulite faunas, observing that N. planulatus is characteristic of the firstand earliest and N. laevigatus of the fourth. As forms of the planulatus­laevigatus lineage which characterise biozones 2 and 3 are not found in theAnglo-Paris-Belgian Basin they suggest (p. 646) that there is a substantialnon-sequence between the top of the type Cuisian and the base of the typeLutetian. It seems that this postulated gap in the French succession may bebridged at least in part in Belgium by the Sables d' Aeltre and in Englandby Fisher Beds 1 to 4 and their equivalents.

(iv) The Beds with N. laevigatus. It has long been known that Englishspecimens of N. laevigatus are on average less tumid, with a more looselycoiled spire, than the French type. To mark this difference von Hantkenproposed the name britannicus for the English forms. However, Blondeau(1966) has found that French specimens of N. laevigatus are themselvesvariable in both the characters mentioned, and that at any horizon thevariability is at least as great as that supposed to differentiate English andFrench specimens. By detailed collecting and measurement he has ascer­tained that more compressed forms are associated with a lax spiral and thatthe proportion of stout forms with a tight spiral increases in successivelyyounger beds in France. This relation has been noted also in England.Fisher Bed VII of Whitecliff Bay contains abundant nummulites mostly ofthe compressed type (britannicus); the rare specimens from Bed VIII (whichhave been overlooked by most collectors) are much more tumid. Asmentioned earlier it has recently been discovered that the vertical range ofN. laevigatus overlaps that of N. variolarius, Both the change in form withtime of N. laevigatus and its overlap with N. variolarius provide means for

CORRELAnON IN THE ANGLO-PARIS-BELGIAN BASIN 455

detailed subdivision and correlation in the series of beds in which thesephenomena can be observed (cf. Blondeau & Curry, 1963).

(v) Eocene Beds Overlying those Yielding N. /aevigatus. The discovery ofN. variolarius in the upper part of the type Lutetian has substantiallyrevised ideas of the correlations between the French stratotype, the Ledianand Wemmelian in Belgium and the Brack1esham Beds. Previously theLutetian had been equated with the Bruxellian, and the Auversian with theLedian, on the basis of the presence respectively of N. laevigatus and N.variolarius. The Sables de Marines were correlated with the Sables deWemmel and the Barton Beds. However Keij (1957) had noted the closeresemblance between Ledian and [Upper] Lutetian ostracod faunas. LeCalvez & Pomerol (1961) noted that this resemblance extended to theForaminifera, and Pomerol (1961) proposed the correlation of the Ledianwith the Upper Lutetian. In 1964 Pomerol (p. 163) published a revisedcorrelation between French and English Middle and Upper Eocene beds.He noted that the Foraminifera Orbitolites and Rotalia trochidiformis Lk.[one may add Fabu/aria ovata (de Roissy) and Alveolina bosci], known fromthe Upper Lutetian of the Paris Basin, occur in England in, and only in,Fisher Bed[s] [XVI and] XVII [and their equivalents] and he suggested thatthese beds (and by inference all beneath to Bed VI at least) might bereferred to the Lutetian. As the Marinesian is on the basis of its molluscfauna not younger than the Lower Barton Beds, it would then follow thatthe Auversian must be correlated with the highest part of the BrackleshamBeds, the Huntingbridge Beds.

Overlying the Ledian sands in Belgium are the Sables de Wemrnel, whichpass upwards into the Argile d'Assche. Kaasschieter (1961) and Keij (1957)noted the close similarities between the Foraminifera and ostracodsrespectively of these three formations, and Kaasschieter (p, 133) proposedto combine the Ledian, Wemrnelian and Asschian into one stage. Glibert(1936, 1938) monographed the mollusc faunas of the Wemrne1ian andAsschian (almost nothing is known of that of the Ledian). He recorded thatfifty-six of the sixty molluscan species of the Argile d'Assche are knownfrom the Sables de Wemrnel and concluded that the combined fauna wasprobably rather older than that of the Lower Barton Beds (1938, 177).

In order to test the validity of the correlations of Glibert and Pomerol Ihave analysed the mollusc faunas ofthe Bracklesham and Barton Beds andhave compared these with the faunas ofbeds ofcomparable age in the ParisBasin and Belgium as recorded by Furon & Soyer (1947), L. & J. Morellet(1948) and Glibert (1933, 1936, 1938). The ranges of molluscan species inEngland have for the most part been ascertained by reference to Newton(1891). Unfortunately this work does not differentiate between the severalfaunal horizons known at Bracklesham Bay; I have therefore relied on myown observations at that locality. Fisher (1862) made a fourfold division

456 DENNIS CURRY

(Divisions D, C, B, A) at Bracklesham on faunal grounds, although heincorrectly identified D at WhitecliffBay. To these divisions may be addedthe Huntingbridge Beds. For the purpose of my analysis Divisions D and Chave been combined and for these the list in Wrigley (Southampton, 1934)has been the main source. Stubbington is the classic source of fossils fromDivision B; records in Newton from that locality have been attributed tothat division. Records from Brook and Brarnshaw refer to Division A,while Huntingbridge is the sole locality in Newton for the HuntingbridgeBeds. Lists of the five successive molluscan faunas D-C, B, A, Hunting­bridge and Barton have been compared with each other and with those ofthe Lutetian, Auversian and Marinesian of the Paris Basin and theBruxellian and Wemmelian of Belgium. The resulting analysis is presentedin the Appendix. From it the following conclusions have been drawn:(1) the Bruxellian correlates very well with the type Lutetian, much betterthan with the type Cuisian or Auversian; (2) the Wemmelian correlatesabout equally well with the Lutetian and Auversian, less well with theCuisian and Marinesian; (3) the Bruxellian correlates well with theEnglish divisions D-C, successively less well with higher divisions; theWemmelian correlates well with division B, rather less well with A;(4) the type Lutetian correlates very well with both D-C and B, successivelyless well with younger beds; (5) the type Auversian correlates rather wellwith all English divisions except the Barton Beds (as the recorded Auversianfauna includes many species derived from the Lutetian the figures mayoverstate the resemblance between the Auversian and older horizons inFrance and England); (6) the figures relating to the type Marinesian areconflicting; the correlation coefficient gives the best match with B, but thepattern of exclusive species suggests strong links with the Barton Beds.

On the basis of the above the following approximate correlations areproposed: (1) division D-C of Bracklesham with the Lower Lutetian of theParis Basin (Abrard, 1925, 377, zones 1,11), the Sables d'Aeltre (D) and theBruxellian (C) of Belgium; (2) division B of Bracklesham with the UpperLutetian of the Paris Basin (Abrard zones III, IV); (3) division A with thetype Auversian; (4) (tentatively) the Huntingbridge Beds with the complexof beds above the sands of Auvers and Beauchamp and below those ofCresnes and Marines; (5) the Lower Barton Beds with the Marinesian;(6) the Ledian, Wemmelian and Asschian of Belgium with groups B and Aof Bracklesham and with the Upper Lutetian and Auversian of the ParisBasin. These correlations are in general consistent with what is known ofthe faunas of Foraminifera and ostracods. However, they do not explain theoccurrences of Orbitolites and Rotalia trochidiformis on which Pomerol(1964) relied in correlating Fisher Bed XVII (division A) with the UpperLutetian of the Paris Basin. The faunal assemblage of Fisher Beds XVI andXVII contains Foraminifera, small molluscs and attached polyzoans of

CORRELAnON IN THE ANGLO-PARIS-BELGIAN BASIN 457

genera which as a group clearly indicate that these beds were formed undersea-meadow conditions. This assemblage occurs only at one level (througha thickness of about 20 ft.) and then only locally (it does not occur, forexample, at Lee-on-the-Solent or in the New Forest). No other EnglishPalaeogene assemblage gives clear evidence of formation under sea­meadow conditions. The Upper Lutetian fauna of the Paris Basin withwhich that of Fisher Bed XVII has been compared is also a sea-meadowfauna and it seems probable that the resemblance on which Pomerol hasrelied is one controlled by facies and does not result from an identity of age.

In the sequence of beds between the Lower Barton Beds and the UpperHamstead Beds of England on the one hand and the Sables de Marinesand the Sables de Fontainebleau on the other almost no clues to correlationhave been provided by marine assemblages. The molluscan speciescharacteristic of the Middle and Upper Barton Beds and the BrockenhurstBed are almost completely unknown in the Paris Basin. The only exceptionseems to be Turritella elongata J. Sby., which occurs near the boundarybetween the Middle and Upper Barton Beds and in the Paris Basin in themarnes it Pholadomya ludensis. The marls yielding P. Iudensis at Verzenay(Marne) pass upward into further marls with a flora of charophytes which,according to Grambast (1964, 1010), can be matched in the Lower HeadonBeds. On the above admittedly slender evidence the marnes it P. ludensisare here tentatively correlated with the combined Upper Barton Beds andLower Headon Beds.

(c) Oligocene Beds

(i) The Brockenhurst Bed and Possible Equivalents. When Beyrich (1854)created the term Oligocene he defined it to include certain beds in Germanyof which the oldest are the beds now known as the Latdorfschichten (typeof the Lattorfian Mayer-Eymar, 1893, from Latdorf (Lattorf), nearMagdeburg), together with brown coal deposits on which they rest. Thebeds included in Beyrich's new division had previously been referred to theUpper Eocene or Lower Miocene. The Latdorfschichten are glauconiticclayey marine sands which were encountered during the sinking of shaftsfor the exploitation of the brown coal. They have yielded a rich molluscanfauna monographed by von Koenen (1889-94) and compared by him withthat of the Sables de Grimmertingen of Belgium and the Brockenhurst Bed(Middle Headon Beds) of England. A comparison of these faunas hasprovided the following statistics. Correlation coefficients (see appendix fordefinition) are quoted in parentheses. 732 mollusc species are known fromthe Latdorf beds, 243 species from Grimmertingen (Gilbert & de Heinzelinde Braucourt, 1954); there are 190 species in common (85.0). Comparisonof the Latdorf fauna with English marine faunas shows twenty-sevenspecies in common with the 434 species of the Upper Bracklesham Beds

458 DENNIS CURRY

(7.4); forty-seven species in common with the 523 species of the BartonBeds (11.3); forty-two species in common with the 117 species of theMiddle Headon Beds (37.2) (non-marine or unidentified MS. species havebeen omitted from this comparison). There is thus excellent correlationbetween Latdorf and Grimmertingen and rather poor correlation betweenLatdorf and the English horizons, the best link being with the Brocken­hurst Bed. The Brockenhurst Bed is thus generally considered to be ofLattorfian age, and as it is a marine bed, resting disconformably on thecontinental beds of the sedimentary cycle of the Barton-Lower HeadonBeds, it is taken as the base of the Lattorfian in England.

(ii) The Relations Between the Wemmelian, the Asschian and the Sables deGrimmertingen. Of the 261 species of bivalves and gastropods recordedfrom the Sables de Wemmel (including the Asschian) only thirteen areknown from the Sables de Grimmertingen, with a total fauna of 243 species.The poor correlation (7.5) between the two faunas suggests the existence ofa substantial hiatus. A gap at this point in the succession might be expectedfrom structural considerations as Tongrian beds (of which the Sables deGrimmertingen are the oldest recognised) rest with marked unconformityacross the whole of the Eocene in Belgium (cf. Gulinck, 1966, 225). Theabove observations are consistent with the correlations so far proposed; ofthe Wemmelian and Asschian with the Upper Bracklesham Beds and theSables de Grimrnertingen with the Brockenhurst Bed. The hiatus postulatedin the Belgian succession would thus correspond with the period ofdeposition of the Barton Beds and Lower Headon Beds in England.

(iii) The Gypse and Marnes Supragypseuses ofthe Paris Basin and Beds ofSimilar Age in England and Belgium. Above the Sables de Marines andbelow the Sables de Fontainebleau (both marine) is a series of pale marlsincluding thick beds of gypsum near their base. The lowest marls, alreadydiscussed, are the marnes a P. Iudensis, with a restricted marine fauna.Above them is the main mass of gypsum, almost unfossiliferous butyielding near the top the mammal fauna of Montmartre. This fauna isknown also in England, where it occurs in the Bembridge Limestone. Abovethe gypsum are the marnes supragypseuses, non-marine in the lower partbut containing a restricted marine fauna in the higher beds. The Sables deFontainebleau (type Stampian), which rest on the marls with sharp transi­tion, contain a large marine fauna, elements of which have been recognisedalso in Germany (Unterer Meeressand, Septarien-thon, etc.) and Belgium(Sables de Berg, argile de Boom (type Rupelian) ). The youngest Palaeogenebeds known in the Hampshire Basin are the Upper Hamstead Beds, ofwhich several well-marked species are known from the Sables de Fontaine­bleau and their equivalents. It has been customary therefore to correlatethe Upper Hamstead Beds with the Sables de Fontainebleau. However,Cavelier, who has made a detailed study of the Paris Basin sequence, has

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 459

suggested (1964, 587) on faunal grounds that the Upper Hamstead Bedsare best matched with the highest beds of the marnes supragypseuses andare thus rather older than the Sables de Fontainebleau.

To the east of Paris the Lower Oligocene beds change in character andconsist of freshwater marls and limestones, the Calcaire de Brie. Thisformation is of interest in having yielded a small fauna of mammals which,as noted by Stehlin (1910, 509), is quite different from that found atMontmartre and in the Bembridge Limestone, but compares well with thefauna known from the Lower Hamstead Beds of England. The exact age ofthis French fauna in comparison with the series of the gypse is not knownbut it should presumably be that of some part ofthe marnes supragypseuses.

In Belgium between the marine sequences of the sands of Grimmertingenand Neerrepen on the one hand and the Berg sands on the other thereexists an inconstant series of estuarine and freshwater beds. They arepresumably to be equated broadly with the Oligocene beds of Englandabove the Middle Headon Beds and with the gypse and marnes supragyp­seuses of the Paris Basin. For a discussion and suggested correlations ofthese beds the reader is referred to Gilbert & de Heinzelin de Braucourt,1954, 398-402.

(iv) Beds Referred to the Middle and Upper Oligocene in Belgium and theParis Basin. In Belgium these consist wholly of marine sands and claysdeposited in water of moderate depth which was rather cold, to judge fromthe molluscan fauna. They include the Sables de Berg and Argile de Boom,referred to the Rupelian, and the Sables de Voort, probably of Chattianage. In the Paris Basin the sequence is of sands with a mixed marine andestuarine fauna, deposited in shallow clear water (Sables de Fontainebleau)and referred to the Stampian, overlain by various freshwater limestones(Calcaire d'Etampes, calcaires de l'Orleanais), which may in part be ofLower Miocene age. The Stampian and Rupelian are approximatelyequivalent in age.

Correlations between the successions in Belgium and the Paris Basin arerendered difficult by the marked difference in facies; it seems too that therewas a land barrier between the two areas at this time. The most detailedanalysis of the relations between the two areas is that of Alimen (1937,264-70); others who have commented recently on the problem are Batjes(1958, 74-9), Cox (in Eames et al., 1962, 5, 6) and Blondeau et al. (1966,212-17).

(v) The Base ofthe Oligocene. As already stated, Beyrich, in creating theOligocene, included what are now known as the Latdorfschichten and theirassociated coals as its lowest beds. As the Oligocene was created byabstraction in part from the Eocene and in part from the Miocene, thereshould not be any ambiguity about the whereabouts of the summit of theEocene or the base of the Miocene. Provided that the Oligocene has been

460 DENNIS CURRY

defined unequivocally as to its base and summit, this definition fixes thesummit and base respectively of the Eocene and Miocene. Assuming thebase of the Latdorf beds to represent a time-plane, the Eocene-Oligoceneboundary was so defined.

However, in spite of the above, many authors have wished, in part onstratigraphical, in part on faunal, grounds, to transfer the Latdorf beds tothe Eocene. The transgression at the base of the Rupelian has been con­sidered by some authors to be more important, because more widespread,than that at the base of the Lattorflan. Krutzsch & Lotsch (1957) are thelatest of a long series of authors who have claimed that the mollusc faunaof the Latdorf beds is much closer to that of the Upper Eocene of Englandand France than to that of the succeeding Rupelian. Von Koenen himself(1894, 1433---4) took up a neutral position on this question, finding affinitiesboth with older and younger faunas. The statistics on the subject whichhave been provided by different authors are so little in agreement that Ihave prepared my own, summarised below. In studying these it should beborne in mind that at least 2500 species of molluscs are known from theMiddle and Upper Eocene of the Anglo-Paris-Belgian Basin; on the otherhand, perhaps only 450 species have been recorded from the Middle andUpper Oligocene of that area or Germany. Comparisons between themollusc faunas of the Latdorf beds, of various English horizons, and theSables de Grimmertingen, have been made earlier in paragraph 5(c)(i).The mollusc fauna of the Middle Oligocene of Germany was monographedby von Koenen (1867-8), who recorded 194 species. Ofthese, sixty-five arerecorded in von Koenen (1889-94) as occurring also in the Lattorfian,which has a described fauna of 732 mollusc species (correlation coefficient35.3). It will be observed that this correlation is almost as good as thatbetween the Latdorf beds and the Brockenhurst Bed (37.2), although muchworse than between the Latdorf beds and the Sables de Grimmertingen.Correlations between Latdorf and French and Belgian Eocene horizons arevery poor (coefficient less than 10). The above statistics suggest closer linksbetween the Latdorf beds and those overlying them than with the Eocenebeds below. A similar pattern is revealed if the molluscan species whichrange from the Latdorf beds exclusively into higher or lower beds areconsidered; sixty-nine species ranging only upwards and forty-eight onlydownwards. Evidence from the mollusca therefore suggests that the Latdorfbeds are best placed with the Oligocene.

The indications provided by the Foraminifera are equivocal. Anexamination of Foraminifera extracted from the interiors of molluscscollected at Latdorf suggests rather close relations with Rupelian micro­faunas. Drs. W. H. Blow and F. T. Banner have kindly examined theplanktonic Foraminifera (eight species in all) of the Latdorf assemblageand have provisionally referred this faunule to their Zone P19, stating that

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 461

it is substantially the same as plankton assemblages from the UntererMeeressand of the Mainz Basin and the Boom clay of Belgium, bothuniversally regarded as Middle Oligocene. No planktonic Foraminiferahave been named from the Sables de Grimmertingen and only one species(Globigerina sp. cf. angustiumbilicata Bolli, also present in the Lower andMiddle Barton Beds and in the Jackson Formation of Alabama) occurs inthe Brockenhurst Bed; this species is absent from the Latdorf assemblage.

In contrast to the similarity revealed between the planktonic Foramini­fera of the Latdorf beds and of Rupelian horizons is a record by Krutzsch& Lotsch (1964, 957), who note the presence in the Latdorf beds ofNummulites prestwichianus and N. rectus, forms characteristic in Englandof the base of the Barton Beds or thereabouts; these species are alsorecorded from Dnepropetrovsk in the Ukraine together with the foraminiferDiscocyclina in association with a rich mollusc fauna including over 100species in common with Latdorf. Discocyclina is generally believed not torange above the Eocene (cf. Eames et al., 1962,4). On the basis of theselast observations Krutzsch & Lotsch (1957) and Korobkov (1961) haveproposed that the Latdorf beds should be transferred to the top of theEocene. This seems undesirable. The base of the Oligocene was definedunequivocally in the first place; this definition does not conflict with anyother and any redefinition based on changes in particular faunas mightitself be subject to challenge by specialists studying other faunal groups.

In his study of the Palaeogene mammal faunas, Stehlin (1910, 506) notedthat 'le plus grand et le plus sub it changement que nous connaissonspendant toute la duree des temps tertiaires' has occurred between the faunaof Montmartre-Bembridge on the one hand and Brie-Hamstead-Ronzonon the other. He concluded that the Bembridge fauna is the latest of theEocene mammal faunas, while the Hamstead is the earliest of those of theOligocene. Some workers in the Paris Basin (cf. Blondeau et al., 1966,212-17) have recently sought to place the Eocene-Oligocene boundary tocoincide with the point of change of the mammal faunas. In England sucha boundary falls between the Bembridge Limestone and the LowerHamstead Beds. On this view the Brockenhurst Bed and its supposedequivalent the Latdorf beds must be of Eocene age. Alternatively theBrockenhurst Bed must be older than the Latdorf beds. The proposal toidentify the Eocene-Oligocene boundary in the Paris Basin by reference tothe change in mammal faunas seems faulty on general grounds. Like mostmajor geological boundaries the Eocene-Oligocene boundary was definedto coincide with a marine transgression; hence with a period of subsidence.The renewal of the mammal faunas observed by Stehlin is believed to haveoccurred as a result of an invasion of Europe by genera which had evolvedin Asia in late Eocene times (Gabunia, 1964,981). These travelled by land­bridges which had been newly created, no doubt at a time of regression of

462 DENNIS CURRY

the sea. It would be expected, therefore, that the renewal of the mammalfauna would take place, as indeed seems to have been the case, at a timenear the culmination of a period ofregression and not at a boundary, suchas those at the base of the Lattorfian and Rupelian, defined by a marinetransgression.

6. CONCLUSION

The views on correlation which have been expressed in this address aresummarised more or less adequately in Fig. 5, which is based on theexcellent presentation in Wrigley & Davis, 1937. In this figure I haveattempted also to indicate the different usages of stage-names which areemployed by geologists working in the separate parts of the Anglo-Paris­Belgian Basin. It will be seen that there is no uniformity in this matter;indeed the whole question of the use of stage-names in the Palaeogene isone ofthe utmost confusion, a confusion which is likely only to be resolvedby the findings of some International Commission.

REFERENCESABRARD, R. 1925. Le Lutetien du Bassin de Paris. Angers.---- & R. SOYER. 1942. Decouverte de Nummulites planulatus Lmk. dans les

Sables de Sinceny (Aisne), C. r, hebd. Seanc. Acad. Sci., Paris, 214, 677-8.ADAMS, C. G. 1962. Alveolina from the Eocene of England. Micropaleontology, 8,

45-54.ALiMEN, H. 1936. Etude sur le Stampien du Bassin de Paris. Mem. Soc. geol. Fr.

(nouvelle serie), No. 31.ApOSTOLESCU, V. 1964. Repartition stratigraphique generale des ostracodes du

Paleogene des Bassins de Paris et de Bruxelles, Mem, Bur. Reck geol. min.,No. 28, 1035-40.

BATJES, D. A. J. 1958. Foraminifera of the Oligocene of Belgium. Mem. Inst, r. Sci.nat. Belg., No. 143.

BEYRICH, E. 1854. Ueber die Stellung der Hessischen Tertiiirbildungen. Monatsber.Preuss. Akad. Wiss., 1854,640--66.

BHATIA, S. B. 1955. The Foraminiferal Fauna of the Late Palaeogene Sediments of theIsle of Wight, England. J. Paleont., 29, 665-93.

BIGNOT, G. 1966. Le gisement eocene du cap d' Ailly (pres de Dieppe, Seine-Maritime).Bull. Soc. geol. Fr. (7), 7, 273-83.

BLONDEAU, A. 1966. Etude biometrique et statistique de Nummulites laevigatusBruguiere dans les bassins de Paris et du Hampshire. Implications strati­graphiques. Bull. Soc. geol. Fr. (7), 7, 268-72.

----, C. CAVELlER, L. FEUGUEUR & C. POMEROL. 1966. Stratigraphie du Paleogenedu Bassin de Paris en relation avec Ies bassins avoisinants, Bull. Soc. geol. Fr.(7), 7, 200--21.

---- & D. CURRY. 1963. Sur fa presence de Nummulites variolarius (Lmk.) dansles diverses zones du Lutetien des bassins de Paris, de Bruxelles et duHampshire. Bull. Soc. geol. Fr. (7),5,275-7.

BOLLI, H. M. 1957. The Genera Globigerina and Globorotalia in the Paleocene-LowerEocene Lizard Springs Formation of Trinidad, B.W.I. Bull. U.S. natn. Mus.,No. 215, 61-81.

---. 1957a. Planktonic Foraminifera from the Oligocene-Miocene Cipero andLengua Formations of Trinidad, B.W.]. Bull. U.S. natn. Mus., No. 215,97-123.

---. 1957b. Planktonic Foraminifera from the Eocene Navet and San Fernandoformations of Trinidad, B.W.I. Bull. U.S. natn. MilS., No. 215, ]55-72.

100 m etres

Vertical sca le(approx i m at e)

BELGIUM Be lgi ancl ass ification

S. de Vcer t

rCHATTIAN

.. - - ~ 1_

RUPELIAN

TONGRIAN

ASSCHIAN

~WEMMELIA N

S. de Lede LED IAN~'-'

Sab les de

Br u xe ll e s I BRUXELLIAN~

S. d 'Ael tr e

PtlU Pan;se t i an"

y,-

Arg i Ie I YPRESIAN

d ' Ypre s

YI

oS. d'Ostr icour t

T u f f eau I LANDE NIANde

Li ncent

Gel inden &c . I HEERSIAN~

Cal ca ireg ross i er I MONTI ANde Mons

Tu ff eau

de Ci pl y I DAN I AN

~

Tuf fe au &Chal k I MAESTRICHTIAN

[To fa ce p. 462

Fig, 5. Co rrelation of the Palaeogene beds of the Anglo- Paris- Belgian Basin

Br it is h ENGLANDc1assifica! ion

Occurrences ofWrigley & Davis ,Num m ulit es (der i ved f ossi ls no t re co r ded) ur Hamsl ead1937, modified .

't. r Ham st eadr N. rectus andpr N. pr e stw ich ianus

Bembr idgeor N.o r big ny iv N. vor i a tar i us

~I N. ta« vigot us

f°Os bor n epi N. pl an u la /us and

c: Upper Headon....-.....-- Erod~d contact

Q:.§ -'" Be ds0 Uni t ma in ly or wholly of n on-m or ine orig in

~Brockenhurst Bed

Lower HeadonBeds

French PARIS / / Bart onclassif icationBlondeaU !1 2£, BASIN Beds

t966.10ca i ca ire de I I r

?CHATTIAN B e a uce

I / / ~/I \Sa bl es de ~~.....O B{ackleSham VSTAMPIAN I

<c.Y-J

• •••• · · f v l

0 °B;urn~ma u t h \Ma rn es ,s.lBeds

2 ~

~< ~,~ BedsZ LUDI AN .§<c.0 " . \owerI-a:~ MARINESIAN

~ .B ~g ~h~t _ _AUVERSIAN moy ens e",l>-,,\:)' Bed s

Ca l cai r e v ILUTETIAN

g r ass ier IV/ I Lo nd onH er ou y ol pi

t""'"Pier re fond s pi ,/PRE.SIAt-l

~ SPARNACIAN

A i zy p i I C I a y

Si ncen

\ ignit es andA rg i l e plastique I SPARNAC/AN

THANETIAN S. de Bracheux &c1 THANETlAN

MONTI AN mESenonian I I S enonian

Cha lk Cha lk

CORRELATiON IN THE ANGLO-PARIS-BELGIAN BASIN 463

BOUCHE, P. M. 1962. Nannofossiles calcaires du Lutetien du Bassin de Paris, RevueMicropaleont., 5, 75-104.

BOWEN, R. N. C. 1953. Ostracoda from the London Clay. Proc, Geol. Ass., 64, 276-92.----. 1954. Foraminifera from the London Clay. Proc. Geol. Ass., 65, 125-74.BRAMLETTE, M. N. & F. R. SULLIVAN. 1961. Coccolithophorids and related Nanno-

plankton of the early Tertiary in California. Micropaleontology, 7, 129-88.BURROWS, H. W. & R. HOLLAND. 1897. The Foraminifera of the Thanet Beds of

Pegwell Bay. Proc. Geol. Ass., 15, 19-52.CAVELlER, C. 1964. Sur Ie classement des 'Upper Hamstead Beds' de I'lle de Wight

(Angleterre) dans Ie Stampien inferieur et leur parallelisrne avec Ie Bassin deParis. Mem. Bur. Rech. geol, min., No. 28, 585-90.

CURRY, D. 1962. A Lower Tertiary outlier in the Central English Channel, with noteson the beds surrounding it. Q. JI geol. Soc. Lond., 118,177-205.

----. 1965. The Palaeogene beds of South-East England. Proc, Geol. Ass., 76,151-74.

----. 1965a. The English Palaeogene Pteropods. Proc. malac, Soc. Lond., 36,357-71.

DAM, A. TEN. 1964. Die stratigraphische Gliederung des niederlandischen Palaozansund Eoziins nach Foraminiferen. Meded. geol. Sticht., serie CoY-No. 3.

---- & T. REINHOLD. 1942. Die stratigraphische Gliederung des niederlandischenOligo-Miozans nach Foraminiferen. Meded. geol. Sticht., serie CoY-No. 2.

DAVIS, A. G. & G. F. ELLIOTT. 1958. The Palaeogeography of the London Clay Sea.Proc. Geol. Ass., 68, 255-77.

DUMONT, A. 1851. Note sur la position geologique de l'argile rupelienne et sur Iesynchronisme des formations tertiaires de la Belgique, de l'Angleterre et dunord de Ia France. Bull. Acad. r. Belg : CI. Sci., 18, 179-95.

DURAND, S. 1964. L'analyse pollinique des formations du Paleogene francais, Mem.Bur. Rech. geol. min., No. 28, 1001-8.

EAGAR, S. H. 1965. Ostracoda of the London Clay (Ypresian) in the London Basin: I.Reading District. Revue Micropaleont., 8, 15-32.

EAMES, F. E., F. T. BANNER, W. H. BLOW & W. J. CLARKE. 1962. Fundamentals ofMid-Tertiary Stratigraphical Correlation. Cambridge.

FARCHAD, H. 1936. Etude du Thanetien (Landenian marin) du Bassin de Paris. Mem.Soc. geol. Fr. (nouvelle serie), No. 30.

FEUGUEUR, L. 1951. Sur l'Ypresien des bassins francais et belge, et l'age des Sablesd'Aeltre. Bull. Soc. beige Geol. Paleont, Hydro/., 60, 216-42.

----. 1963. L'Ypresien du Bassin de Paris. Mem. Servo Carre geol. det, Fr.FISHER, O. 1862. On the Bracklesham Beds of the Isle of Wight Basin. Q. JI geol. Soc.

Lond., 18, 65-94.FURON, R. & R. SOYER. 1947. Catalogue des fossiles tertia ires du Bassin de Paris. Paris.GABUNIA, L. C. 1964. Sur la correlation des faunes de mammiferes de I'Oligocene

d'Europe et d'Asie. Mem. Bur. Rech. geol. min., No. 28, 979-83.GLIBERT, M. 1933. Monographie de la faune malacologique du Bruxellien des environs

de Bruxelles. Mem. Inst, r. Sci. nat, Belg., No. 53.----. 1936. Faune malacologique des Sables de Wemmel. I. Pelecypodes. Mem,

Inst. r. Sci. nat, Belg., No. 78.----. 1938. Faune malacologique des Sables de Wemmel. II. Gastropodes,

Scaphopodes, Cephalopodes. Mem. Inst, r. Sci. nat. Belg.; No. 85.---- & J. DE HEINZELIN DEBRAUCOURT. 1954. L'Oligocene inferieur belge. Volume

jubilaire Victor van Straelen, 1, 281-438. Brussels.GRAMBAST, L. 1962. Sur l'interet stratigraphique des Charophytes fossiles: exernples

d'application au Tertiaire parisien. C. r. somm, Seanc, Soc. geol. Fr., 1962,207-8.

----. 1964. Indications fournies par les Charophytes pour la stratigraphie duPaleogene. Mem. Bur. Rech. geol. min., No. 28, 1009-11.

GULINCK, M. 1966. Apercu general sur les depots eocenes de la Belgique. Bull. Soc.geol. Fr. (7), 7, 222-7.

HAYNES, J. 1956-8. Certain Smaller British Paleocene Foraminifera, Parts 1-5. Contr.Cushman Fdn foramin. Res., 7,79-101; 8, 45-53; 9, 4--16,58-77,83-92.

464 DENN1S CURRY

HESTER, S. W. 1965. Stratigraphy and Palaeogeography of the Woolwich and ReadingBeds. B/lII. geol. Surv, Gt Br., No. 23, 117-37.

HOTTINGER, L., R. LEHMANN & H. SCHAUB. 1964. Donnees actuelles sur la biostrati­graphie du Nummulitique mediterraneen. Mem. Bur. Rech. geol. min., No. 28.61/-52.

KAASSCHIETER, J. P. H. 1961. Foraminifera of the Eocene of Belgium. Mem. Inst. r.Sci. nat. Belg., No. 147.

KEIJ, A. J. 1957. Eocene and Oligocene Ostracoda of Belgium. Mem. Inst. r. Sci. nat.Belg., No. 136.

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----. 1889-94. Das Nord-Deutsche Unter-Oligocan und seine Mollusken-Fauna.Abh. preuss. geol. Landesanst., 10, parts 1-7.

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----. 1958. Ubersicht tiber die palaogeographische Entwicklung des zentraleuro­paischen Alttertiars (ohne Tethys-Raum). Ber. geol. Ges. D.D.R., 3, 99-110.

----. 1964. Propositions a l'appui d'une tentative en vue de subdiviser les depotsde l'Eocene superieur et ceux de I'Oligocene inferieur et moyen et de mettreen parallele ces depots d'Europe occidentale entre eux et avec ceux d'Europecentrale. et etude de la position II assigner a Ja limite entre l'Eocene etl'Oligocene dans ces regions. Mem, Bur. Reck. geol. min., No. 28, 949-63.

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---- & C. POMEROL. 1961. Sur la separation des bassins de Bruxelles et de Parispar I'anticlinal de l' Artois al'Eocene. c. r, hebd. Seanc. Acad. Sci., Paris. 252,2268-70.

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(a)

CORRELAnON IN THE ANGLO-PARIS-BELGIAN BASIN 465

TERQUEM, O. 1882. Les Foraminiferes de I'Eocene des environs de Paris. Mem. Soc.geol. Fr. (3), 2 (3).

WRIGLEY, A. G. 1934. A Lutetian Fauna at Southampton Docks. Proc. Geol. Ass., 45,1-16.

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with a Revised Correlation of the Strata containing it. Proc. Geol. Ass., 48,203-28.

D. CurryEastbury GrangeWertford RoadNorthwood, Middlesex

APPENDIX

(a) The Correlation Coefficient

The analysis which follows attempts to provide an answer to a problemwhich frequently occurs in the assessment of faunal similarities. This is asfollows. How closely related are two faunas if one has a total of knownspecies A and the other a total of known species B and if C species arecommon to the two faunas? This problem is clearly not susceptible to rigidanalysis, but it has been found possible to create a mathematical modelwhich has some similarity to the natural situation and to derive a formulafrom it which will provide a numerical answer. This model envisages theselection of a group of species and individuals in which relatively fewspecies are present abundantly while larger numbers of speciesare relativelyrarer, the whole arrangement approximating to a random one.

H an infinitely large assemblage is created in accordance with such amodel and two separate random selections of an equal number of indivi­duals are made from the assemblage then there will probably be A speciesin each selection of which P species will occur in both selections. For the

Pparticular model here chosen A is a constant and is equal to 0.684 approxi-

mately. It may be shown that if now a different number of individuals ischosen and B species are found to be present in the new selection while P,species are common to one or other of the selections which yielded Aspecies, then (if A > B)

B-Pl :::::: (~) (~)"258B I-A A

If now two infinitely large assemblages are built in accordance with themodel and these assemblages contain x per cent of species in common andif then, following certain rules, a random selection is made from eachassemblage such that one contains A species and the other contains Bspecies, and C species are found to be in common then

PROC. GEOL. ASS., VOL. 77, PART 4, 1966 31

466 DENNIS CURR Y

woex (here called the Correlation Coefficient) ::::; ------,;;- (b)

In making comparison between two faunas A, Band e will be known.PI can then be calculated from formula (a) after which x can be calculatedfrom (b).

Two natural assemblages of molluscs have been examined and for thesep

the value of Ahas been found to be about 0.7 and thus to be in reasonabl e

agreement with that of the model. Correlation coefficients have beenp

calculated, using formulae (a) and (b) and a value of A of 0'684, for the

pairs of mollusc faunas compared in this address.It is stressed that the coefficients calculated in this way are based on an

abstract model which is an imperfect representation of the fossil assemblagesit simulates. These coefficients should be regarded therefore as no morethan a guide to the probable relat ions between the assemblages concerned.

(b) Comparisons of some Eocene Mollusc Faunas of the Anglo-Paris- BelgianBasin

Par is Basin ---+ Cuisian Lutetian Au versian Mari nesian2 /4 462 422

Belgium .\- 889 27.7 1780 53.5 1029 81.5 622

Sables de Bruxelles 60 (II) 159 (59) 87 (5) 54 (Ol241 26.5 67.6 38.0 24.8

4224.0Sables de Wemmel 23 (I) 80 (14) 85 (15) 49 (4)

270 9.2 30.6 33.5 20.4

Hu nting-England ---+ D-C B A bridge Barton

77 89 107 82Belgium .\- 180 67.5 155 71.2 231 82.4 164 54.7 523

Sables de Bruxelles 64 (15) 49 (2) 48 (5) 31 (0) 39 (I)24 1 45.4 38 .6 29.6 23.5 18.4

Sables de Wemmel 37 (2) 56 (11) 58 (8) 33 (0) 48 (6)270 25.4 42.7 34.0 24.3 20.6

Hunting-England ---+ D-C B A bridge Barton

Par is Basin .\- 180 155 231 164 523

Lutetian 122 (16) JJ4 (13) 109 (8) 54 (0) 76 (2)1780 68.2 74.5 48.5 33.4 15.6

Auversian 82 (I) 97 (4) JI8 (5) 75 (3) 99 (6)1029 47.1 64.3 53.6 47.2 21.8

Marinesian 49 (0) 58 (I) 55 (I) 43 (0) 103 (26)622 29.2 39.7 25.3 27.9 26.5

CORRELATION IN THE ANGLO-PARIS-BELGIAN BASIN 467

EXPLANATORY DATA FOR TABLE (B) see opposite page

Figures in ordinary type: total named molluscan species.Figures in italic type, no parentheses: total species in common.Figures in italic type, within parentheses: total species, doubly exclusive.Figures in bold type: correlation coefficient.For example: between the Marinesian (622 species) and the Barton Beds (523 species)there are 103 species recorded as occurring in both formations and 26 which aredoubly exclusive, that is, which occur in France only in the Marinesian and in Englandonly in the Barton Beds. Correlation coefficient between the Marinesian and theBarton Beds is 26.5.