Table Of ContentPALAEONTOGRAPH ICAL SOCIETY M ONOGRAPHS
THE AMMONOIDEA
OF THE PLENUS MARLS
AND THE MIDDLE CHALK
C. W. WRIGHT & W. J. KENNEDY
148 Pages; 32 Plates
© THE PALAEONTO GRAPHICAL SOCIETY • LONDON
October 1981
The Palaeontographical Society issues an annual volume of serially numbered publications;
these may either be a single complete monograph or a part of a continuing monograph.
Publication No. 560, issued as part of
Volume 134 for 1980
Recommended reference to this publication:
W right, C. W. & K ennedy, W. J. 1981. The Ammonoidea of the Plenus Marls and the
Middle Chalk. Monogr. Palaeont. Soc. London: 148 pp., 32 pis (Publ. No. 560, part of Vol. 134
for 1980).
ABSTRACT
The ammonite fauna of the Plenus Marls and Middle Chalk (Upper Cenomanian and
Turonian) is described; it comprises 49 spccies and subspccics (8 new), referred to 27 genera.
These provide a basis for revision of the ammonite zonation of the Upper Cenomanian and
Turonian of Great Britain and correlation with the sequences in the Paris Basin and the
stratotype areas in Sarthe and Touraine. It is demonstrated that the Ccnomanian-Turonian
boundary is best taken between the Neocardioceras juddii Zone below and the Watinoccras
coloradoense Zone above.
RliSL'Mli
La faune d’Ammonites des Plenus Marls et de Middle Chalk (Cenomanien Superieur
et Turonien) est decrite, elle comprend 49 especes et sous-especes (dont 8 nouvelles)
rapportees a 27 genres. L’ctudc de cctte faune permet une revision de la zonation basee
sur les Ammonites dans lc Cenomanien Superieur et le Turonien de Grande-Bretagne;
cllc scrt aussi de support k l’etablissemcnt d’unc correlation avec les successions connues
dans le Bassin de Paris et les stratotypes de la Sarthe et dc la Touraine. On demontre
qu’il est preferable de placcr la limite Ccnomanien-Turonien entre la Zone a Neocardio-
cerus juddii el la Zone a Walinoceras coloradoense sus-jacente.
KURZFASSUXG
Die Ammonitenfauna der Plenus-Mergel und der Mittleren Kreide (Oberes Ceno-
man und Turon) wird beschrieben; sie umfaBt 49 Arten und Unterarten (8 neu),
die zu 27 Gattungen gestelll werden. Diese bilden eine Grundlage fur die Revision der
Ammoniten-Zonengliederung des Oberen Cenomans und Turons in GroBbritannien
sowie fur die Parallclisicrung mit den Schichtenfolgen im Pariser Becken und den Typus-
Gcbietcn in Sarthe und der Touraine. Es wird gezeigt, daC die Cenoman/Turon-Grenze am
bestcn zwischen der Zone des Neocardioceras juddii untcn und der des Watinoceras colorado
ense oben gezogen wird.
PE3K)M£
Onncana aMMonmoEaji ijiayna iu ILieuyc ilapaa u Mito-'i Io.ik (sepxmiii cenoMan n TvpoH),
BKJlKmKnna.H 49 muon n nn.imi^on (8 uoeijx), onieeeiiHbix k 27 po;;a.M. 3to ^aeT ochobv jtJUi
pcuiinnu auMOHHTOBOll ^oniuiijiHjoni ropxn^rn cenoMaiia ii Tvpona Be.^iuKoopiiTaHUU ll Koppcnimini
e piupcija.Mii IlapnvKUKorci fiaeceiiiia ;i cTpaTOTiinniRCKiix ri.io;na,Ti,cn Copxu ii Tvpeaa. B itanecTEe
nauoajiee y,io6jioro ypOEHa eenoMaHCK.o-TypoHCKoii rpannnLi npeuiaraeic;! aouajiwiwli py5cm
Neocardioceras juddii/Watinoceras coloradoense..
Aiade and printed in Great Britain
Adlard & Son Ltd., Bartholomew Press, Dorking
THE AMMONOIDEA OF THE PLENUS MARLS
AND THE MIDDLE CHALK
CONTENTS
Page
Introduction. . . . . . . . . . . . . . 3
Stratigraphical introduction . . . . . . . . . . . 3
Ammonite occurrencc and preservation . . . . . . . . . 9
Locality details . . . . . . . . . . . . . 10
Conventions and techniques . . . . . . . . . . . 15
Acknowledgements . . . . . . . . . . . . 16
Systematic descriptions . . . . . . . . . . . . 16
Order Ammonoidea . . . . . . . . . . . . 16
Suborder Ammonitina . . . . . . . . . . . 16
Superfamily Desmocerataceae Zittel . . . . . . . . 16
Family Desmoceratidae Zittel . . . . . . . . . 16
Subfamily Puzosiinae Spath . . . . . . . . 16
Puzosia Bayle . . . . . . . . . . 17
Puzosia (Puzosia) Bayle . . . . . . . . . 17
Puzosia (Anapuzosia) Matsumoto . . . . . . . 19
Parapuzosia Nowak . . . . . . . . . 20
Parapuzosia (Austiniceras) Spath . . . . . . . 20
Family Pachydiscidae Spath . . . . . . . . . 29
Leivesiceras Spath . . . . . . . . . . 29
Superfamily Acanthocerataceae de Grossouvre. . . . . . . 32
Family Acanthoceratidae de Grossouvre . . . . . . . 32
Subfamily Mantelliceratinae Hyatt . . . . . . . 33
Calycoceras Hyatt . . . . . . . . . . 33
Pseudocalycoceras Thomel . . . . . . . . . 36
Tarrantoceras Stephenson . . . . . . . . 38
Tarrantoceras (Sumitomoceras) Matsumoto . . . . . . 38
Thomelites Wright & Kennedy . . . . . . . 39
Neocardioceras Spath . . . . . . . . . 49
Watinoceras Warren . . . . . . . . . 51
Subfamily Euomphaloceratinae Cooper . . . . . . 54
Euomphaloceras Spath . . . . . . . . . 54
Kamerunoceras Reyment . . . . . . . . . 56
Romaniceras Spath . . . . . . . . . . 58
Romaniceras (Tubariceras) Matsumoto, Saito & Fukada . . . 60
Subfamily Mammitinae Hyatt . . . . . . . . 62
Metoicoceras Hyatt . . . . . . . . . . 62
Spathites Kummel & Decker . . . . . . . . 73
Spathites (Jeanrogericeras) Wiedmann . . . . . . . 74
Mammites Laube & Bruder . . . . . . . . 75
Pseudaspidoceras Hyatt . . . . . . . . . 8 1
Metasigaloceras Hyatt . . . . . . . . . 83
Family Vascoceratidae H. Douville . . . . . . . . 84
Subfamily Vascoceratinae H. Douville . . . . . . . 85
Nigericeras Schneegans . . . . . . . . . 85
Vascoceras Choffat . . . . . . . . . . 86
1
2 THE AMMONOIDEA OF THE PLENUS MARLS &c
Fagesia Pervinquiere . . . . 87
Subfamily Pseudotissotiinae Hyatt . . . . 98
Thomasites Pervinquiere . . . . . . 98
Family Collignoniceratidae Wright & Wright . . . . 101
Subfamily Collignoniceratinae . . . . . . 101
Collignoniceras Breistroffer . . . . . . 102
Lecointriceras Kennedy, Wright & Hancock . . . 108
Subprionocyclus Shimizu . . . . . . 109
Suborder Ancyloceratina Wiedmann . . . . . 110
Superfamily Turrilitaceae Gill . . . 110
Family Hamitidae Gill . . . 110
Hamites Parkinson . . . 110
Family Anisoceratidae Hyatt . . 110
Allocrioceras Spath . . . . 110
Family Baculitidae Gill . . . . 112
Sciponoceras Hyatt . . , . . . 112
Family Turrilitidae Meek . . . . . . 116
Subfamily Nostoceratinae Hyatt . . . . 116
Didymoceras Hyatt . . . . . . 116
Superfamily Scaphitaceae Gill . . . . 116
Family Scaphitidae Gill . . . . . . 116
Subfamily Scaphitinae Gill . . . . . 116
Scaphiles Parkinson . . . 118
Incertae sedis . . . . . . . . . 1 1 8
Stratigrapliic results and conclusions . . . . . 1 1 8
Appendix . . . . . . . . 127
References . . . . . . . . 128
Index . . . . . . . 140
STRATIGRAPHICAL INTRODUCTION 3
INTRODUCTION
The present monograph is the first of an intended series describing the Upper Cretaceous
ammonite faunas that were within die scope of Daniel Sharpe’s Description of the fossil remains of
Mollusca found in the Chalk of England (1853-7). Sharpe provided competent descriptions and
beautifully clear and only occasionally misleading illustrations of a wide range of Chalk ammonites
which, with d’Orbigny’s classic volume on the Cretaceous ammonites of France, again beautifully
but more misleadingly illustrated, served as the main foundation for later knowledge of the
taxonomy and biostratigraphy of Upper Cretaceous ammonites, on which many authors have
built.
Under the policy, decided at the Palaeontographical Society’s Centenary, of increasing the
usefulness of the earlier monographs, Wright & Weight (1951) published a synoptic supplement
to Sharpe’s monograph, “primarily a nomenclatorial revision” of that work. They sought to
integrate all taxonomic attributions and new records published since Sharpe’s day, particularly
the important contributions by L. F. Spath, together with unpublished work, but this filled the
gap only for a few years. A vast corpus of published work from all over the world, new ideas on
taxonomy and massive new collections have made monographic revision not only possible but
essential.
The present monograph has been undertaken first because of the importance of the pioneer
English species and the more or less accurately dated English faunal succession to the continuing
work of the International Geologic Correlation Programme project “Mid Cretaceous Events”.
The urgency of publishing the much larger Lower Chalk faunas is mitigated by Kennedy’s (1971)
paper ‘Cenomanian Ammonites from Southern England’.
The scope of the present monograph is, in accordance with the Society’s recent practice as
regards works on Cretaceous ammonites, based on the English formations and not on international
stages. It covers with the Middle Chalk the latest Cenomanian Plenus Marls fauna, the latter
commonly excluded from the Lower Chalk. It excludes the Upper Turonian Chalk Rock fauna,
from the base of the Upper Chalk, which has recently been described by Wright (1979).
STRATIGRAPHICAL INTRODUCTION
Subdivision of the Chalk
At the turn of the eighteenth century, when William Smith began to record the sequence of
rocks in the neighbourhood of Batii, he divided the Chalk into two parts only, a lower part without
flints and an upper part in which flints were present. A decadc later Townsend (1813), describing
the chalk in Wiltshire around his parish in the Vale of Pewsey, recognized three divisions:
“1. Immediately on the sea coast at Chichester, as above mentioned, and along the most elevated parts of
Hants and Wilts, particularly at Tidworth, to the South of Everly, it is milk-white, fine in its grain and smooth
when cut, writes readily on wood, and is fit for the cooper, for whiting, for lime, and for manure. It is Creta
Scriptoria of Linnaeus.
2. In descending the hills from Everly to the vale of Pewsey, a second bed appears, hard, rubbly, and tinctured
with green, improper for the uses to which the former is applied, and fit only for the highways.
3. Under this we find what is, with us, called a malmy chalk,* unctuous to the touch, of a grey or greenish
white, unfit for any of the fore-mentioned purposes.
The separation between each of these beds and the succeeding is not abrupt, but gradual: for, commonly,
when contiguous strata, apparently formed by subsidence, occur, they mix and run into each other. Agreeably
to this observation we find, under these beds, a rubbly bed of chalk with silicious sand, united by a calcareous
cement.
*Marga Gretacea, Lin."
His middle division is readily identifiable with the Chalk Rock, whilst the lowest probably
includes what is now regarded as the Lower Chalk.
Five years later Mantell and Phillips gave more precise divisions of the Chalk. Mantell (1818)
4 THE AMMONOIDEA OF THE PLENUS MARLS &c
divided the chalk into ‘Blue Mari’, ‘Chalk Mari’, ‘Lower or Hard Chalk’ and ‘Upper or Flinty
Chalk’. What is essentially the same subdivision is repeated in his better-known ‘Fossils of the South
Downs' (1822). His ‘Blue Marl’ corresponds to what is now known as Gault, his ‘Lower Chalk’
corresponds to parts of what is now known as the Lower and Middle Chalk. This usage is im
portant to note, as many of the Middle Chalk ammonites in old collections are labelled ‘Lower
Chalk’. Phillips’ divisions, although presented in a paper read to the Geological Socicty in 1818,
were not published until 1821; he rccognized six divisions of the chalk near Dover (Kent) classified
in four groups.
For nearly 50 years after this most workers on the English Chalk adopted a three-fold division
into Chalk Marl, Lower Chalk without flints and Upper Chalk with flints. Other divisions were
used by Woodward (1833), who divided the Norfolk Chalk into ‘Upper Chalk with many flints’,
‘Medial Chalk with few flints’, ‘Lower Chalk without flints’ and ‘Chalk Mari’. Sharpe (1853), in
the Introduction to his Monograph divided the Chalk into:
“1. Upper Chalk; my specimens of which are principally from Norfolk, or from Gravesend and Northfleet:
this division is rich in Organic Remains.
2. Middle Chalk, which contains but few fossils: those examined are mostly from Kent, Sussex and the Isle
of Wight.
3. Lower or Grey Chalk, containing numerous fossils, especially Ammonites and Turrilites: the neighbourhood
or Dover, and of Lewes, and the Isle of Wight furnish large supplies; many specimens have also been procured
from numerous chalk pits along the foot of the North Downs, and others have been obligingly sent from
Devizes . . .
4. The “Chloritic Marl” of the Isle of Wight, a bed some six or eight feet thick at the base of the Chalk, is
very rich in Organic Remains . . . The “Chalk with Siliceous Grains” of Somersetshire, is probably on the
same parallel as the “Chloritic Marl” and also contains an abundance of shells . . .”
Some idea of the range of his Formations is given by the ammonites recorded from them; his
Upper Chalk records include forms now referred to the genera Parapuzosia, Lewesiceras, Pachydiscus
and Menuites-, Middle Chalk: Lewesiceras and Collignoniceras; Lower Chalk: Acantkoceras, Protacan-
thoceras, Mantelliceras, Calycoceras, Euomphaloceras, Romaniceras, Metasigaloceras, Sharpeiceras, Paracaly-
coceras, Hyphoplites, Schloenbachia, Forbesiceras, Scaphites, Hypoturrilites, TurriliUs, Marietta and Ostling-
oceras.
The earliest satisfactory division into zones is that of Evans (1870), who recognized the follow
ing divisions of the Chalk around Croydon and Oxted:
“ 1. Zone with Micraster coranguinum = Purley Beds.
2. Zone with Micraster coranguinum = Upper Kenley Beds.
3. Zone with Micraster corbovis and Holaster Planus = Lower Kenley Beds.
4. Zone with Inoccramus Brongniarti and Galerites subrotundus = Whiteleaf Beds.
5. Zone of Ammonites pcrarnplus and Inoceramus mytiloides= Upper Marden Park Beds.
6. Zone of Ammonites varians and Belemnitella plena = Lower Marden Park Beds.”
In France during this same period a rather more sophisticated division of the Chalk (and of
the Cretaceous generally) evolved. During the early part of the nineteenth century a lithological
division into craie blanche, craie tuffeau and craie chloritee was used (e.g. Brongniart 1822,
d’Archiac 1839) until d’Orbigny (1843) divided the Chalk into stages, at first recognizing only
two, the Senonian and Turonian; he subsequently (1847) confined the name Turonian to the
upper part of that stage as originally conceived and named the lower part Cenomanian.
The earliest attempt at correlation of the stages of d’Orbigny with the divisions of English
geology was that of Barrois (e.g. 1876) who showed that the whole of the Upper Cretaceous in
England could be divided into the same zones as he recognized in France:
f Zone a Belemnitelles
„ . J Zone a Marsupites
enonian 2one ^ Micraster coranguinum
(_Zone k Micraster cortestudinarium
STRATIGRAPHICAL INTRODUCTION 5
f Zone a Holaster planus
Turonian ■< Zone a Terebratulina gracilis
l^Zone a Inoceramus labiatus
"Zone a Belemnites plenus
Zone a Holaster subglobosus
Cenomanian -< Chloritic marl
Zone a Pecten Asper
Zone a Ammonites inflatus
Subsequently, amongst others, Jukes-Browne (1887) and Jukes-Browne & Hill (1887) extended
Barrois’ observations; in 1896 they provided a detailed correlation of the Lower Chalk and the
arenaceous Cenomanian in south-west England already studied by Meyer (1874). At the beginning
of this century (1900-1904) Jukes-Browne & Hill’s great work the ‘Cretaceous Rocks of Britain’ was
published. This still provides the best overall account of the English Upper Cretaceous.
In this work the Belemnite Marl was regarded as a unit at the top of the Lower Chalk and
referred to the Holaster subglobosus Zone. After a full review of the work of previous decades, the
Middle Chalk was regarded as consisting of two zones, Rhynckomlla cuvieri below and Terebratulina,
previously Terebratulina gracilis, above. The base of the formation was marked by the Melboum
Rock, a hard nodular sequence first named by Jukes-Browne in 1880. The upper limit of the
Middle Chalk was defined as a line “at the base of the Chalk Rock or of the beds which correspond
with it.”
This usage was followed and applied with great precision by Rowe in a series of papers (1900-
1908) in which almost all the coastal sections in England and a large number of inland exposures
were fully described. The same scheme is in general use today, with Orbirhynchia as the correct
genus for R. cuvieri, Inoceramus (or Mytiloides) labiatus as an alternative index for the lower zone and
Terebratulina lata as the correct name for Terebratulina gracilis. The zonation is easy to apply in the
field and, with the general rarity of ammonites in the Middle Chalk, has not been replaced by an
ammonite zonation comparable with that now coming to be accepted for the Lower Chalk. The
detailed inoceramid sequence outlined by Kauffman (1978) offers promise of a generally applicable
finer system of zones.
If the divisions and limits of the Middle Chalk have remained stable for three quarters of a
century, the same cannot be said of the Belemnite Marl (Jukes-Browne & Hill 1886), Plenus
Marls (White 1909) or Actinocamax plenus Zone (Jukes-Browne & Hill 1903). This has been variously
assigned to the Lower and to the Middle Chalk and attached as a subzone to the subglobosus and
to the cuvieri or labiatus zones. Since the time of Barrois (1876) it has been known to occur through
the Anglo-Parisian Basin. Jefferies (1962, 1963) has shown that it can be divided throughout this
region into eight units (Text-fig. 1).
The Melbourn Rock is recognized as a complex of incipient hardgrounds, nodular chalks,
conglomerates and true hardgrounds which has gradational contacts below and above. It varies
widely in thickness and its limits are diachronous. Above this horizon no named lithostratigraphic
units are in widespread use in the Middle Chalk except for the “Spurious Chalk Rock” (Rowe
1908), a horizon of yellow and green-coated nodules near the top of the T. lata Zone in parts of
southern England. However stratigraphic position may often be recognizable from the detailed
accounts by Rowe.
The facies in Devon is rather different from that elsewhere in England. The lower levels are
highly condensed and contain abundant ammonites. The division of the Devon Cenomanian by
Jukes-Browne & Hill (1903) into Beds A, B and C in ascending order is in general use. Smith
(1961) renamed Bed C the “Orbirhynchia Band” (after O. wiesti) because he thought that “Bed C
of the Cenomanian Limestone” was an inappropriate name as it was Turonian. It is in fact
Cenomanian and there is no good reason to change the well established nomenclature.
At several points on the Devon coast Bed C is overlain by a nodular, pebbly unit called the
6 THE AMMONOIDEA OF THE PLENUS MARLS &c
MIDDLE CHALK: INOCERAMUS LABIATUS ZONE. Melboum Rock,
a hard, nodular chalk with rhythmically bedded incipient hardgrounds.
Calcarenitic, with abundant Inoceramus debris. Local floods of
Sciponoceras boheinicum anterius at the base indicate the
Neocardioceras juddii Zone,
PLENUS MARLS. Divided into 8 Beds. A rhythmic alternation of
more and less argillaceous chalks, with important erosion surfaces
(ES) as marked. Oyster casts of Metoicoceras geslinianum Zone
ammonites in bed 1 at Steyning, Sussex and ammonites from Bed 2b
upwards, with Calycoceras naviculare, Austiniceras austeni and
Scapkites cf» equalis in Bed 2-3 and Euomphaloceras septemseriatum
and Pseudocalycoceras dentonense in beds 5 and 7-8 respectively.
Actinocamax plenus is restricted to beds 4-6. The erosion surface
at the boundary of Beds 3-4 corresponds to the Rotalipora cushmanij
Praeglobotruncana stephani Zone (below) and Praegiobotruncarw. spp.
Zone (above) boundary. The base of the Plenus Marls is an erosion
surface of regional extent, but it grades up into the succeeding
Middle Chalk.
Top of LOWER CHALK. Argillaceous chalk with Inoceramus and
thin-shelled J/okistfer the commonest fossils. Ammonites and other
iiragonitic fossils generally rare, but the top 10 m have yielded
C. (C.) naviculare, Eucalycoceras pentagonum, Protacanthoceras
bunburianum and Tkomelites at localities such as Eastbourne
(Sussex) and White Nothe (Dorset).
Text-fig. 1. The standard sequence in the Plenus Marls of south-east England* based on the exposures at Merstham.
Surrey, showing the divisions mentioned in the text and some of the more important ammonite occurrences
(after Jefferies 1962, 1963).
Neocardioceras Pebble Bed, a term first used by Smith & Drummond (1962). Above this the
lithology differs in detail from that of the Middle Chalk of the rest of southern England but the
standard zones of cuvieri (or labiatus) and lata are in current use.
The formational terms Lower, Middle and Upper Chalk have throughout the study of the
English Chalk been combined with a system of zones based on assemblages of fossils of various
STRATIGRAPHICAL INTRODUCTION 7
phyla. Stage names gradually came into use from the beginning of the present century but a
system of stage names and ammonite zones never displaced the traditional system, although the
significance of the occurrence in the Middle Chalk of large ammonites (mainly Lewesiceras peram-
plum (Mantell) below and rare Collignoniceras woollgari (Mantell) above) had long been recognized.
Ammonite zonation
In the 1920s, however, Spath proposed various sets of zones for the Plenus Marls and Middle
Chalk. In 1923 (p. 144) he divided the Cenomanian as follows:
Upper Cenomanian } Metoicoceras pontieri
(Acanthoceratan) Acanthoceras cenomanense
[subglobosus-zone of authors] Calycoceras bay lei
Lower Cenomanian Euomphaloceras euomphalum
(Schloenbachian) > Hyphoplites falcatiis
J
\varians-zone of authors] Mantelliceras martimpreyi
The Metoicoceras pontieri zone was the equivalent of the Plenus Marls.
Three years later (1926, p. 425) the following scheme appeared as part of a table of Ceno
manian zones:
Sub-Voiles Old £ones
Turonian
(Mammitan) whitei
plenus
pontieri
vicinale
subglobosus
Upper Cenomanian subfiexuosum
rhotomagense
upper varians
(Acan tho c eratan) diadema
(= euomphalus)
vectense
In the same year (1926a, table facing p. 80) the following appeared in a table of the subdivisions
of the White Chalk:
Approximate
Ammonite horizons zonal equivalent
^ Pseudojaco b ites farmeryi Hoi. planus (Chalk Rock)
Hyphantoceras reussianum
Prionocyclus neptuni
Angoumian Prionotropidan ■< Coilopoceras requinianum [sic]
Romaniceras deverianum
Romaniceras ornalissimum T. lata
Prionotropis carolinus
Vascoceras sp.
Mammites nodosoides
Pseudaspidoceras footeanum Rh. cuvieri
Ligerian Mammitan
Fagesia superstes
Metoicoceras whitei
Rhotomagian Metoicoceras pontieri A. plena
As with Spath’s division of the Cenomanian (reviewed by Kennedy 1969, 1971), this is a
combination of intuition and guesswork and bears little relationship to any faunal successions
demonstrable in the field. Several of the ammonites listed as successive are in fact contemporaries
and several do not occur in England. Spath’s divisions, although occasionally mentioned in
passing or included in tables in text-books, never came into general use.
8 THE AMMONOIDEA OF THE PLENUS MARLS &c
Thirty years later Wright (1957, p. LI 28) gave the following as “standard” zones for the
Turonian of the “Classic Areas of Western Europe” (descending order):
Subprionocyclus neptuni
Collignoniceras woollgari
Mammites nodosoides
Metoicoceras whitei
Subsequently Wright (1960) gave the Devon sequence as follows (descending order):
Bed with Watinoceras
Bed with Neocardioceras
Bed with Plesiovascoceras catinum, Metoicoceras gourdoni, M. geslinianum, Kanabiceras septem-
seriatum.
Hancock (in Basse 1960) equated the two lower horizons with the Plenus Marls.
In 1962 and 1963 Jefferies published a full description of the English Plenus Marls. He divided
the beds into two ammonite zones of Metoicoceras geslinianum below and M. gourdoni above. Wright
and Jefferies both followed Spath in referring the Plenus Marls to the Turonian.
In 1973 Kennedy & Juignet and Juignet, Kennedy & Wright pointed out that Metoicoceras
geslinianum and M. gourdoni occurred in the type Cenomanian and that, contrary to the views of
Tablr 1. Zones and lithological divisions of the Plenus Marls, Middle Chalk and their corielatives
AMMONITE TRADITIONAL LITHOSTRATIGRAPHIC UNITS TRADITIONAL
STAGE ZONE ZONE DEVON ELSEWHERE FORMATIONS
Holaster UPPER CHALK Chalk Rock UPPER CHALK
Subprionocyclus
planus (part of) (in some area6) (part of)
neptuni
u in r L n n
Terebratulina
Collignoniceras tale
woollgari
TURONIAN
MIDDLE
MIDDLE
CHALK CHALK
Orbirhynchia
cuvieri
Mammites
or
Melbourn
nodosoides Inoceramus
Rock
labiatus
Watinoceras
coloradoense
Neocardioceras Neocardioceras
juddii Pebble bed
Metoicoceras Aclinocamax
Plenus marls PLENUS MARLS
geslinianum plenus
CENOMANIAN
Beds A - B
LOWER CHALK
and remanit Grey chalk
(part of)
faunas
