Nannofossil zonation of the English Middle and Upper Jurassic

Marine Micropaleontology, 7 (1982) 73--95 Elsevier Scientific Publishing Company, Amsterdam --Printed in The Netherlands

73

NANNOFOSSIL ZONATION OF THE ENGLISH MIDDLE AND UPPER JURASSIC

A.W. MEDD 1

Institute of Geological Sciences, London (Great Britain) (Received July 28, 1978; revised version accepted August 5, 1981)

Abstract Medd, A.W., 1982. Nannofossil zonation of the English Middle and Upper Jurassic. Mar. Micropaleontol., 7: 73--95. A revised nannofossil zonation of the Middle and Upper Jurassic strata is compared with those previously published by Barnard and Hay, Hamilton, Thierstein, and Van Hinte. Fifteen newly defined coccolith zones are here proposed for the interval: Bajocian to Portlandian, and are based on cored borehole material from England, which gives a continuous fossiliferous section. The partial range zone concept continues to be dominant for much of this zonation.

Introduction R e c e n t l y t w o z o n a l s c h e m e s using coccolith species have a p p e a r e d f o r t h e Jurassic (by B a r n a r d a n d H a y , 1 9 7 5 ; Thierstein, 1 9 7 6 ) with s u b s e q u e n t q u o t a t i o n a n d a m e n d m e n t o f t h e first s c h e m e b y V a n H i n t e (1976). T h e t y p e s o f z o n a l i n d e x t h a t t h e y used were: partial range and interval z o n e s ( B a r n a r d and H a y , 1 9 7 5 ) a n d " b i o h o r i z o n s " (Thierstein, 1976). T h e p u b l i s h e d s c h e m e s w e r e r e g a r d e d b y t h e i r a u t h o r s as p r o v i s i o n a l and t o be m o d i f i e d as n e w d a t a b e c a m e available. In a d d i t i o n H a m i l t o n ( 1 9 7 7 , 1 9 7 9 ) has p u b l i s h e d a z o n a t i o n o f the T o a r c i a n / C a l l o v i a n interval. T h e p r e s e n t w r i t e r has b e e n f o r t u n a t e e n o u g h to s t u d y c o r e d b o r e h o l e m a t e r i a l f r o m the Jurassic o f G r e a t Britain f o r t h e p a s t sixteen y e a r s and a revised c o c c o l i t h z o n a l s c h e m e f o r this c o u n t r y is given b e l o w (Figs. 1--3). 1present address: Institute of Geological Sciences, Ring Road Halton, Leeds LS158TQ (Great Britain). 0377-8398/82/0000--0000/$02.75

M a c r o f a u n a s o f these b o r e h o l e s have b e e n d e t e r m i n e d b y colleagues within I n s t i t u t e of Geological Sciences ( a n d elsewhere) and so their b i o s t r a t i g r a p h y is a c c u r a t e l y k n o w n . T h i e r s t e i n ( 1 9 7 6 , p. 329) has n o t e d t h a t t h e r e is a " s c a r c i t y o f p u b l i s h e d d a t a on Jurassic n a n n o f o s s i l s " , a n d even less t o be f o u n d c o n c e r n i n g t h e i r e v o l u t i o n . T h e r e is n o t h i n g to be a d d e d to his resum~ o f previously published work. T h e p r o p o s e d z o n a t i o n is still provisional. It is n o t v e r y s a t i s f a c t o r y in t h a t several o f t h e z o n a l f o r m s are e i t h e r very small or o c c u r o n l y rarely in t h e s e d i m e n t s e x a m i n e d ; furthermore, the writer does not consider a c m e or interval z o n e s to b e o f m o r e t h a n local i m p o r t a n c e . T h e idea o f Ellipsagelosphaera britannica ( S t r a d n e r ) [ ?Watznaueria c o m m u n i s ( S t r a d n e r ) of o t h e r a u t h o r s ] , t h e m o s t c o m m o n o f all Jurassic c o c c o l i t h s , being a z o n e fossil w o u l d be i n c o n c e i v a b l e , e x c e p t f o r the special c i r c u m s t a n c e s p r e v a l e n t in the K i m m e r i d g i a n o f NW E u r o p e , w h e r e this f o r m

© 1982 Elsevier Scientific Publishing Company

74

& I1= I.-

nr" 13,.

2

e~ e~

C

.-&

Z L~ o

~'

t~ I k-

T~

d O

-r t--

N i

Z

t£). (3 o

--~

~.~ o

Z Z

~ .£

~6t~ I

.~

~11

--~

-~

b---

i

q~

E E

c"

>

'4 ~

q

I

0 0

q

N

(-

2~

g~

~

~-_

~

~

~

~

~

i ~ ~ ~

~

~

~

~

~

~8

~

~R +a I1) N

5 t3~ C iii

I

Z

Z

-n

-1-

Z

Z (..)

F-

O

,¢ en

•

o

~

.~ o

75

cr o_

rr" ill {3..

Z L4J LU rr W I 0

v ~ O

0

0 r~ c~

c~

T~ c~

c~

~Q

O

0

c 0

o

c~

0

~- ~ i ~ Z

Z

IlL

rr"

© LL X ©

o ._J J ~J

76

Z

"I-

v

Z

.

O 0~

©

~.£

z<

p-

&

0

:_.

J

0

ok l .

~ 0

Z

t-

~

E

c~ T

(3-

co

- -

I

T

-[-

~

-

,

0

E

C 0

g.

4

2

0

g O

I.~

Q.)

.-

,<, uJ T

$.£

!

~ a) r,n

9DVlS 31SSV~hqF

NVI(]NVq -±Noa

N VI9(:] 1~13IAI ~ l ) l

N VI(3 ~IO::IXC

77 was exceptionally abundant. Partial range zones, based on incoming of new forms, are also always suspect, in that further work often reveals an earlier introduction of the species into the area (e.g., Hamilton, 1977, 1979). However, the writer considers that the ideas presented here for a zonation have stabilised sufficiently during the past three years and are probably valid for the entire Northwestern European floral province. Material studied A list of the boreholes examined with their national grid references is given in Appendix I; the ranges of the boreholes (or those parts of them used in this study) are given in Fig. 4.

POR[LANDIAN

1

!

= Fig. 4. The ranges of the English boreholes used in this study. Further information is given in Appendix I. Stratigraphical distribution of the coccoliths A summary of the English data utilised in this study is given in Appendix II and is based on species presence plotted against the macrofaunal zonation of the borehole material. If marked present, the species occurs somewhere within the data sets for that particular zone, although the species may not be present in every sample of that zone or borehole. A complete nannofloral listing for these boreholes is on the open files of the Institute

of Geological Sciences, London, both in the Palaeontology Unit registers and on magnetic tape of the IGS computer; automated printouts of the data including graphical plots of the nannofloral assemblages of each borehole are also available. Study of the coccolith assemblages has led the writer to the conclusion that only seconds may be required to determine its biostratigraphy, although several hours search of a strew slide, using both optical and electron-optical microscopes is necessary to determine 80% or more of the assemblages. This is particularly true when the smaller forms (less than 2 pm) or very rare large forms are to be located. A further problem that will remain until there is a rapid m e t h o d of scanning strew slides is that all of the forms present cannot be positively identified using only an optical microscope nor can particular specimens be relocated for further investigation. Moshkovitz (pets. comm.) has overcome the relocation problem by using a special grid on the cover slips of the microscope slides. The first description of the coccolith assemblages of the Ampthill Borehole (Medd, 1971) omitted all species of Stradnerlithus Black. A subsequent re-examination of the same strew slides, but based on an average of five hours study per slide and using a superior quality microscope at X 2500 magnification, yielded considerable numbers of specimens and species of this genus, some of which still have to be confirmed using the electron-optical equipment. Several of the species listed in Appendix II have been "split" by other workers. Also a few of the species have been subdivided on the basis of additional taxonomic work done, for example Stephanolithion bigoti Deflandre (see Medd, 1979). The surface exposures of the Lower Jurassic of the Dorset coast, England are richer in numbers of species (viz Barnard and Hay, 1975) than the borehole material of the same age used in this paper. However, incorporation of the work done on the Jurassic surface exposures would add little to the faunal range chart, except for the Bajocian part of it, which is still very sparse in

78 material th at contains coccoliths. The inclusion into the chart o f ot her workers' results would dilute its effectiveness either by introducing an element of d o u b t on the specific assignations (e.g., Podorhabdus cylindratus Noel from the Pliensbachian: Hamilton, 1977, p. 580) or on their stratigraphic accuracy (e.g., Stephanolithion speciosum Deflandre from the scissum Zone, Bajocian: Barnard and Hay, 1975, p. 579). Nannofloral z o n a t i o n

General considerations The existing nannofloral zonations of the Jurassic are mostly based on the partial range zone co n cep t (i.e., each zone represents the interval between the first introduction of species X to that of species Y). As mentioned above, this is always subject to amendm e nt with the examination o f further material. Also, it is limited in that the zone fossil may be absent and so the biostratigraphical determination can be inaccurate. This is particularly the case when dealing with isolated or surface samples, where the relationship o f the sample to the adjacent strata cannot be directly correlated. The zonation proposed here is a mixture of the partial range zone together with the c o ncu r r en t or total range zones. Additionally, one acme zone is proposed for this Jurassic nannofloral province. Occasionally there are gaps between the defined zones and these are filled by the use o f interval zones. The proposed zones are based on a summation o f the species in the boreholes. Only occasionally do the samples, which make up this summation, fully reflect the zones to which th ey are assigned, as t h e y may not contain the zone fossil. Also the zonal form may be very small and difficult to identify. However, where the zone fossils are both c o m m o n and easy to identify, the age of the material is quickly established (e.g., the zonal forms: Podorhabdus rahla No61 and Stephanolithion bigoti maximum Medd.

Calcareous nannofossil zones o f the English Middle Jurassic The coccolith zonation of the underlying Lower Jurassic is still in a state of flux, and particularly so in the Toarcian. It is considered necessary here to discuss the possible overlap of its highest zone with that of the Middle Jurassic. Both Barnard and Hay (1975) and Van Hinte (1976) consider that Podorhabdus cylindratus Noel is the zonal index from the davoei Zone (Lower Pliensbachian) to within the levesquei Zone of Barnard and Hay or the jurense Zone of Van Hinte o f the Toarcian. In bot h of these zonal schemes the P. cylindratus Zone is succeeded by the Discorhabdus tubus Zone, which ranges to the top of the scissum Zone (Barnard and Hay)/ opalinum Zone (Van Hinte) of the Bajocian. Thierstein (1976, p. 337) considers that the two " b i o h o r i z o n s " (i.e., datum levels) that are significant during this period are: Podorhabdus cylindratus with its base in the "latest Pliensbachian" to the higher occurring Watznaueria communis with its base in the "early Bajocian". Hamilton (1977, p. 580) considers Podorhabdus cylindratus to occupy " t h e top of the Lower Pliensbachian Jamesoni Zone to the lower part of the Lower Pliensbachian Ibex Z one". This zone is succeeded by the Palaeopontosphaera veterna Zone. In her table (1977, p. 582), the Toarcian/Aalenian b o u n d a r y of the Brenha Road section, Portugal is straddled by the succeeding Discorhabdus patulus Zone, which is introduced at the base of the variabilis Zone (Toarcian). In a recent paper Hamilton (1979, p. 4, fig. 3) has emended this zonation. She has abolished the P. veterna Zone; the P. cylindratus Zone continues across this interval. She cites two events within this zone: the t op of the two species: P. liasicus and C. primulus. U n f o r t u n a t e l y , both of these species continue into higher beds, possibly as contamination. However, their presence lessens the effective-

79 hess in the use of such events as biostratigraphical markers. She also abolishes the D. patulus Zone, as it is a "rare form that is not suitable as a zonal marker". This zone is replaced by the Ellipsagelosphaera britannica partial range Zone, which is introduced within the tenuiserratum Zone of the Early Toarcian. This zone continues into the Bajocian, where it is replaced by the E. keftalrempti partial range Zone. The succeeding Stephanolithion speciosum partial range Zone is introduced at the base of the Bathonian (as shown in fig. 5, p. 7). The n e x t zone is n o t defined, but the t o p of the S. speciosum Zone is placed at the Bathonian/Callovian b o u n d a r y (Hamilton, 1979, p. 10, fig. 7). The writer considers that there is still no satisfactory Toarcian nannofossil zonation for European material. There is a major phase of nannofossil evolution in the Upper Pliensb a c h i a n / L o w e r Toarcian and further work is necessary to establish a satisfactory breakd o wn for these beds. In his experience bot h Discorhabdus patulus and D. tubus are first introduced into deposits of Bajocian age and are n o t to be f ound in the underlying Toarcian. Barnard and Hay do n o t give any figures o f specimens to support their statem e nt that these species are to be found in the Lower Jurassic. Hamilton figures D. patulus twice in her work: plate 1, 12 is n o t D. patulus (Deflandre), but is here considered to be a generalised discorhabdid, similar to Discorhabdus sp. 2 Medd (1971), which is introduced in English material near to the Toarcian/Bajocian b o u n d a r y ; plate 4, 5 is a specimen of Proculithus fistulatus Medd (ex Prins), which is most c o m m o n l y seen in the English Toarcian (falciferum Zone). Hamilton also figured a specimen of Discorhabdus tubus (plate 4, 1), which is much too large for this small form and does n o t possess the expanded tip to the central spine that is a distinguishing feature of this species; it probably corresponds to Discorhabdus sp. 1 Medd (1971), which is introduced in the margaritatus Zone of the Upper Pliensbachian. The writer does n o t agree with Hamilton

(1979,

p. 1)

either

in

the

incoming

of

E. britannica or the separation of E. keftalrempti as being of biostratigraphical or of t a x o n o m i c significance. As seen in Appendix IIB, small rare ellipsagelosphaerids occur as early as the jamesoni Zone at the base of the Pliensbachian. However, further work on the Lias material should clarify the incoming of the ellipsagelosphaerids into this province, together with their early evolution (if any). Until now, though, they appear to be absent throughout most of the Pliensbachian; certainly t hey are not c o m m o n in the English province until the falciferum Zone of the overlying Toarcian. The writer is currently inclined to revert to Prins' (1969) Striatococcus opacus Zone; it is a fairly c o m m o n and distinctive species of the Toarcian, although first introduced in the spinatum Zone of the Upper Pliensbachian. It was proposed by Prins (1969, p. 599) as a partial range zone at this level and the writer extends its zonal range to the t op of the Toarcian. At the t op of the Toarcian, the thouarense/ levesquei zones b o u n d a r y corresponds to the introduction of the Ethmorhabdus anglicus (partial range) Zone. Forms similar t o this small et hm orhabdi d have been recorded in older beds of the Lower Jurassic, but most of these can be referred definitely to ot her species; there is some evidence for an evolutionary lineage from the primitive forms seen in the Upper Pliensbachian (margaritatus Zone of the Hill Lane Borehole), but there are no further specimens of this group found until E. anglicus s.s. is introduced in the Toarcian (levesquei Zone). The published Lower Jurassic occurrences of another e t h m o r h a b d i d E. gallicus Noel, by Hamilton (1977, plate 1, 4--6; plate 3, 4, 5) are not of this Bajocian species (first seen in the sauzei Zone), but of the primitive form mentioned above, and possibly link this et hm orhabdi d group with that of E. crucifer Noel, seen in the turneri/obtusum zones of the Upper Sinemurian in material of the Winterborne Kingston Borehole. The next coccolitn zone of the present

80 writer is the Podorhabdus cylindratus (partial range) Zone, which is introduced in beds of the Bajocian (rnurchisonae Zone) in England. Older occurrences of this species cited in the literature are here considered to belong to another podorhabdid or to a striatomarginidlike form. However, the specimen figured by Hamilton (1977, plate 1, 11) from the levesquei Zone is a typical P. cylindratus and so the zone is not valid at this level in Portugal, because of the extended range of this species. Recently specimens referred to P. cylindratus have been found in the Winterborne Kingston Borehole, Dorset to 1221 m (Upper Pliensbachian), but these occurrences are in cuttings samples, which may be contaminated by cavings. The stratigraphical level of this zone is therefore provisional. The most significant event in the Middle Jurassic, however, is the evolutionary appearance of Stephanolithion Deflandre. This is seen very clearly in material from the Lyme Bay Borehole, Dorset (50/03/349), where there are a number of forms in sauzei Zone material. These specimens can be equated with Stradnerlithus asymmetricus (Rood, Hay and Barnard) but possess small spines projecting outwards from the rim. The spines rapidly increase in size until by humphriesianum Zone the two species: Stradnerlithus asymmetricus and Stephanolithion speciosum Deflandre are distinct and remain so until they become extinct. This plexus of the two species is defined as the

Stephanolithion speciosum/Stradnerlithus asyrnrnetricus plexus (partial range) Zone, commencing in the sauzei Zone and continuing up to the garantiana Zone, when the zone is replaced by the Octopodorhabdus decussatus Manivit (partial range) Zone. This latter distinctive species appears towards the base of the garantiana Zone and is usually present as one or two specimens per strew slide. The published record of the incoming of S. speciosum (Barnard and Hay, 1975, p. 579; Van Hinte, 1976, p. 491) in beds of the Bajocian (scissum Zone) of Dorset have not been confirmed by the writer; indeed, the

development of this species (mentioned above) in the Lyme Bay Borehole suggests that this record is incorrectly dated. Thierstein (1976) introduced the biohorizon of S. speciosum in the "early Bathonian"; this level is too high. Both Barnard and Hay and Van Hinte have Diazomatolithus lehmani as the succeeding Zone; Van Hinte (1976, p. 491) uses the lowest occurrence of "Diadozygus" asyrnmetricus to define the top of the S. speciosum s.s. Zone as well as the base of the D. lehmani Zone. As mentioned above, S. asymmetricus is introduced in the Bajocian. D. lehmani Noel has been recorded continuously down to the base of the Toarcian and may also be present in the Upper Pliensbachian (margaritatus Zone). Hence this form cannot be used as a Bathonian zone fossil. Their next zone S. speciosum var. octum is introduced in the Upper Bathonian: Barnard and Hay at the base of the hollandi Zone; Van Hinte at the base of the aspidoides Zone. Although this form is considered to be a valid variant of S. speciosum and has been elevated by Medd (1979) to the new species S. octum, much more work needs to be done before its range is finalised. The writer has already mentioned the process of the lengthening of the spines in the Bajocian plexus of Stradnerlithus

asyrnmetricus/Stephanolithion speciosurn and many of the latter forms do have an occasional larger spine, which would suggest S. octum Rood and Barnard. The Bathonian/Callovian boundary is diagnosed by the incoming of Stephanolithion hexum Rood and Barnard by both Barnard and Hay and by Van Hinte. Thierstein (1976, p. 340) considers the base of the Stephanolithion bigoti biohorizon to come at the "base Callovian". The writer has found S. hexum Rood and Barnard down to the base of the Bathonian (zigzag Zone) and so this species is used as the Stephanolithion hexum (partial range) Zone for the lower part of the Bathonian (being introduced in the zigzag Zone). A much narrower form of S. speciosum appears within the Upper Fullers Earth Beds of Southern

81 England, its total range is restricted to the Bathonian retrocostatum Zone and defines the Stephanolithion speciosum elongatum (total range) Zone. There is then no diagnostic form until the appearance of the small form of S. bigoti Deflandre, which occurs within the Callovian (base of the jason Zone). This gap is infilled by the Ellipsagelosphaera lucasi (interval) Zone, which is a species that is most c o m m o n l y f ound in the English floral province in the Early Callovian. S. octum (mentioned above) may in the future delimit part or all of this gap, when the species c o n c e p t and its stratigraphical range are b e t t e r u n d er s t ood.

Calcareous nannofossil English Upper Jurassic

zonation

of

the

Before proposing a nannofossil zonation of the Upper Jurassic it is necessary to comm e n t in detail on the existing zonations and to amend the ranges of the key species used. With one e xc e pt i on (mentioned below) all of Barnard and Hay's zones are partial range zones based on the lowest occurrences of the zone fossils. Van Hinte does not define the types of zones used but states (1976, p. 491) that "zonal boundaries are drawn in accordance with the definitions of Barnard and Hay (1974) following the species ranges given in their fig. 2 (which is not always the same as the boundaries in the third column of that figure)".

The zonation of Barnard and Hay (1975) This zonation is followed by Van Hinte (1976). The Stephanolithion hexum Zone introduced at the base of the Callovian (macrocephalus Zone) is n o t accepted here (see above) and their subsequent introduction of Stephanolithion bigoti Zone in the Callovian (calloviense Zone) material has not been confirmed. [Note: Medd, 1971, p. 835 records S. bigoti in calloviense Zone material from Dorset and Yorkshire. U n f o r t u n a t e l y reexamination of the original strew slides reveals that the assemblages have dissolved in

the m ount i ng medium (Caedex). Examination of further strew slides prepared from the same material indicates t hat the long spined stephanoliths which are 2--4 pm in length either have six central bars: S. hexum Rood and Barnard, or eight central bars: S. octum R o o d and Barnard. No specimens with four central bars: S. bigoti have been found even after a prolonged search of the material]. Their n e x t zone is represented by the incoming of Polypodorhabdus escaigi Noel at the base of the jason Zone. This species has been recorded in the English borehole material as low as the Bajocian (sauzei Zone), and so cannot be used zonally at this level. Their next zone is marked by the incoming of Podorhabdus rahla Noel at the base of the coronatum Zone (Barnard and Hay), or within the t op part of the jason Zone (Van Hinte). In spite of a prolonged search for this distinctive species in beds of the Callovian (coronatum Zone grossouvrei Subzone) age, this species has not been recorded by the writer prior to the upper part of the athleta Zone. Barnard and Hay (1975, pp. 5 7 6 , 5 7 9 ) record its incoming into beds of Callovian (jason Zone) age in " t h e upper part of the section at Bletchley". However, Callomon (1968, p. 282) considers the upper part of this section to have the biostratigraphical range: Callovian: coronatum Zone grossouvrei Subzone to the middle part of the athleta Zone. Examination by the writer of material collected from this section of the pit has not revealed any further specimens and so the base of the P. rahla (partial range) Zone is raised into the athleta Zone. Discorhabdus jungi is their next zonal marker. The two authors differ as to the stratigraphy of its introduction: Barnard and Hay -- within the athleta Zone; Van Hinte -at the base of the athleta Zone. The material figured by Barnard and Hay as D. jungi is here considered to be the same as Discorhabdus patulus (Deflandre), a species that ranges dow n into the Bajocian (see above). D. jungi Noel is a very rare species that has so far been found only in mariae Zone material.

82 The base o f their n e x t Diadozygus dorsetense Zone is placed at the Callovian/ Oxfordian b o u n d a r y (lamberti/mariae zones junction). Stradnerlithus comptus Black (=Diadozygus dorsetense Rood, Hay and Barnard, junior s y n o n y m ) has been recorded as early as the Callovian (athleta Zone) in the English borehole material, and so is o f limited use at the higher level. The Actinozygus geometricus Zone follows and this zone also varies between the two papers: Barnard and Hay introduce it at the mariae/cordatum zones boundary, where it is replaced by the Vekshinella stradneri Zone at the cordatum/densiplicatum zones boundary. Van Hinte regards A. geometricus to be introduced within the mariae Zone and this is followed by the V. stradneri Zone at the mariae/cordatum zones boundary. The present writer has f ound A. geornetricus (Gorka) to occur as early as the base of the marine Zone. V. stradneri Rood, Hay and Barnard is here considered to be a junior s y n o n y m o f Staurorhabdus quadriarcullus (Noel) as figured in No~l, 1965 (p. 74, plate 1, 1--15, plate 2, 1--2). This latter species is first found in beds o f the Upper Pliensbachian (spinatum Zone) age. The n e x t zone is cited by Van Hinte: Watznaueria communis Zone, at the Oxfordian/Kimmeridgian b o u n d a r y (rosenkrantzi/baylei zones junction). This species is i ntr o d u ced as an interval zone by Barnard and Hay and appears in the Kimmeridgian, base of the eudoxus Zone. It is defined as being that interval between the "highest occurrence of Stephanolithion bigoti to the lowest occurrence of Parhabdolithus embergeri (No~l)". Discussion of the extinction of S. bigoti is given below. The Parhabdolithus embergeri Zone follows in both papers, and it is introduced in the Kimmeridgian (hudlestoni Zone). Barnard and Hay define the zone as " t h e lowest occurrence of Parhabdolithus embergeri to the lowest occurrence of Nannoeonus colomi". Discussion o f this zone is also given below. The final Nannoconus colomi Zone has not been found in the English borehole material

earlier than the Valanginian. Both papers place it at the Kimmeridgian/Portlandian boundary. Discussion of this level is given below.

Biohorizons of Thierstein (1976) Thierstein placed the biohorizon: "base of

Stephanolithion bigotii [sic] " at the "base of the Callovian". This is t oo generalised to be accepted as he gives no sample/biostratigraphical details for this statement. His next biohorizon: " t h e base of Polypodorhabdus escaigii [sic]" occurs at the "base of the O x f o r d i a n " . He also c o m m e n t s "as indicated ... P. escaigi is limited to the O xfordi an". F u r t h e r work, however, has extended the range o f this species so it currently is: Bajocian (sauzei Zone) to Kimmeridgian (pallasioides Zone). It should be m e n t i o n e d that it is most c o m m o n l y to be found in material of Callovian (athleta Zone) to Oxfordian (tenuiserratum Zone) age. This biohorizon is followed by the " t o p of Stephanolithion bigotii [sic]" at the "latest O x f o r d i a n " . This extinction is justified by citing Medd (1971) and R o o d and Barnard (1972). Examination of British Kimmeridgian borehole material (Gallois and Medd, 1979) indicates that S. bigoti continues into the Kimmeridgian as high as eudoxus Zone, with fragmented forms occurring in the autissiodorensis Zone beds. This level is the extinction level of this species in England (also see below for further discussion). The next two biohorizons: " t h e base of Conusphaera mexicana" at the "Base Tithonian", and the "base Nannoconus colornii" at the "base Berriasian" have not been recorded in England. One reason for this is that there are no comparable English coccolith-rich marine sequences continuing through to the basal Cretaceous.

Present nannofossil zonation of the Upper Jurassic As m e n t i o n e d earlier in the Middle Jurassic, the Ellipsagelosphaera lucasi (interval) Zone continues to the Callovian, where it is followed by the introduction of the Stephano-

83

lithion bigoti bigoti (partial range) Zone at the base of the jason Zone. This is followed in the athleta Zone by the base of the Podorhabdus rahla Zone. This zone is based on the incoming of the nominate species, which then continues into the Oxfordian (mariae Zone). At the Callovian/Oxfordian boundary (lamberti/ mariae zones junction) it is joined by Stephanolithion bigoti maximum and the two species form a concurrent range Zone, until they become extinct at the Oxfordian, densiplicatum/tenuiserratum zones junction. The next significant event is the extinction of Stephanolithion bigoti within the Kimmeridgian autissiodorensis Zone. As mentioned above, the specimens in this zone are rare and broken. For practical purposes~ therefore, a zonal boundary based on the extinction of this species could be placed at the eudoxus/autissiodorensis zones junction. Unfortunately another species of Stephanolithion has been found in Russian material from the Volga Basin. It is not Stephanolithion bigoti and it has never, in the literature, been confused with this species. The range of the new species, and hence the genus, is extended to the pallasiodes Zone of the Kimmeridgian. The next significant event is the incoming of Parhabdolithus embergeri in the Kimmeridgian (base of the hudlestoni Zone). These forms are rare and the species does not become significant in numbers until the overlying pectinatus Zone. It remains the zone fossil in the English borehole material (e.g., Fairlight Borehole, Warlingham Borehole) until the nannofloras disappear in the Upper Portlandian beds. Hence there are intervals in the Upper Oxfordian/Kimmeridgian beds where no satisfactory zonation has been established. Suggestions, however, are made for the filling of these gaps: (1) Currently favoured by the writer: Stradnerlithus bifurcatus Noel (total range) Zone for the Oxfordian (base of the tenuiserratum Zone) to the Kimmeridgian (base of the eudoxus Zone), followed by the Stradner-

lithus tortuosus Noel (total range) Zone for the Kimmeridgian (eudoxus Zone). This zone in turn is succeeded by the Polypodorhabdus madingleyensis Black (interval) Zone, which is defined as that interval between the extinction of Stradnerlithus tortuosus (and possibly also the extinction of Stephanolithion bigoti) to the introduction of "Parhabdolithus" embergeri; the P. madingleyensis Zone ranges in the Kimmeridgian -- top of the eudoxus Zone to the base of the hudlestoni Zone. This zone is followed by the Parhabdolithus embergeri (partial range) Zone, which extends to the top of the nannofossiliferous English Jurassic so far seen. (2) A variation of this is the nannofossil definition of the Oxfordian/Kimmeridgian boundary with the introduction of the Ellipsagelosphaera britannica (acme) Zone for the Kimmeridgian (baylei Zone to the base of the eudoxus Zone). In the English material there is a marked increase in numbers of specimens of E. britannica at this stratigraphical interval to a maximum seen in the Jurassic; this fact is probably only of local significance, but even in the Kimmeridgian Stone Bands (Gallois and Medd, 1979), where the assemblages contain more than twelve coccolith species, E. britannica comprises more than 99% of the assemblages in flood proportions in eudoxus Zone material. (3) Stradnerlithus bifurcatus is a very small and rare form, two factors that could preclude its use as a zonal form. Actinozygus geometricus used as an Interval Zone could be more acceptable, either representing that interval between the co-extinction of P. rahla and S. bigoti maximum to: (a) the incoming of Stradnerlithus tortuosus (partial range) zone. This interval would therefore represent beds of Oxfordian (base of the tenuiserratum Zone) to Kimmeridgian (base of the eudoxus Zone); or (b) the appearance of greatly increased numbers of specimens of E. britannica (the E. britannica acme Zone), representing beds of Oxfordian (base of the tenuiserratum Zone to the top of the rosenkrantzi Zone). As mentioned above the P. embergeri Zone

84

c o n t i n u e s to the top of the n a n n o f o s s i l i f e r o u s E n g l i s h J u r a s s i c . T h e r e is t h e n a gap i n t h e record until the appearance of the Cretaceous floras (in material seen f r o m L i n c o l n s h i r e and Norfolk). A coccolith zonation of the stratigraphical sequence across the Jurassic/Cretaceous b o u n d a r y t h e r e f o r e c a n n o t be d e t e r m i n e d i n t h i s c o u n t r y . H o w e v e r , m a t e r i a l has b e e n examined from other parts of the world, which straddle this b o u n d a r y , and which

contain coccolith assemblages. The results of t h i s w o r k f o r m t h e basis o f a s e p a r a t e p a p e r . Acknowledgements T h e b o r e h o l e m a t e r i a l was e x a m i n e d f o r its m a c r o f a u n a l c o n t e n t s b y Miss B.M. C o x . T h e t e x t o f t h i s p a p e r has b e e n a p p r o v e d b y t h e C h i e f P a l a e o n t o l o g i s t a n d is p u b l i s h e d by permission of the Director, Institute of Geological Sciences, London.

Appendix I List of English boreholes used in this study, together with their national grid references and abbreviations (as used in Appendix II) Borehole

Abbr. National Grid Reference

Ampthill Baggridge (1) Baggridge (2) Baggridge (3) Brown Moor Brownshill-OffordTunnel(D5) Burton Row Cliff House Denver Donington-on-Bain Fairlight Faulkland Frome Gamlingay Haddenham Harome Hartwell Hill Lane Horsecombe Vale (15) Lyme Bay

A B1 B2 B3 BM BO BR CH D DB F FK FR G H HR HT HL HV LB

Milton Keynes (16) Milton Keynes (24) Mochras North Wootton Rudge Swindon Walker's Marsh Warboys Warlingham Winterborne Kingston

M1 M2 M NW R S WM WB WL WK

TL 024 380 ST 749 570 ST 741 560 ST 744 566 SE 813 620 TL 234 669 ST 336 521 SE 759 844 TF 591 011 TF 240 819 TQ 859 117 ST 714 539 ST 763 477 TL 232 520 TL 466 755 SE 653 811 SP 793 122 ST 335 516 ST 755 622 50/03/329 (offshore IGS Register no. ) SP 891 354 SP 866 313 SH 553 259 TF 644 246 ST 823 523 SU 141 835 TF 527 253 TL 290 784 TQ 348 572 SY 847 979

A p p e n d i x I I (pp. 85--96) This is a biostratigraphical summary of coccolith species found by the writer in English cored boreholes. The relevant boreholes, in which the species occur, can be deduced from a comparison of the ammonite zones in these tables with that given in Fig. 4. The distribution charts for the coccolith species of each borehole are held on the open files of the Institute of Geological Sciences, London. The charts, which are too cumbersome to publish, give the nannofloral assemblages of each sample studied against borehole depth and such information can be obtained on enquiry to the author.

APPENDIX IIA

AMMONITE ZONE

STAGE

to o

PORTLANDIAN

KIMMERIDGIAN

co

BATHONIAN

~

~

~

~

~

~

~

.~

~

,~ ,~

x

x x

t

~

~

~

~

~

~

~.

~

WL

x

Pavlovlarolunda Pavlovtapallas~oldes Pectinamespeetmatm Pecltnattteshudlestom PeClinatites ~healle)'ensls Pectiaatiw~scltulus PP¢II~IileSelegans

FWL F;WL

x x

DB;NW WL

x ×

NW x

NW

x

x

NW;S x x

HR;NW

x

x

X

x

x

x x

x x

x x

x

x

x

x

x

×

x

HR NW

x

x x

x x

x x

×

Cardtoceras tenulserratum Catdlocetas denslph(alum

A;G;H A;G;H

x x

x x

× x

G:A

x

x x

X

x x

×

× X

X

×

X

×

X

×

×

x x x

x x

X

"g

×

x x

x

x

x

G D;WB

x

x

x

x

X ×

X

x

X

X

X

X

X

X

X

.~

X

×

X

x

x

x x

x

WB

WK

B1

B2;WK

x

B 1;WK

X

x ×

3: FK;WK

x

x

x

× ×

X

×

x

×

x

×

rr

Zlgzagi~eras zigzag

HV

D

Parkinsonia parkinsoni Garantlanagaranuana Strenoceras subfur~atum

HV

x

× ×

Stephanoceras humphrlesJanum Ototte~ sauzei Witchelha laeviuscula Hyperlioceras dlsciles

X

X

X

X

"4 × X

Graphoceras comnvurn Ludwigta murchtsonae Tmetoceras $clssum Leloceras vpahnum

X

X ' X

Durnorller~alevesquel Grammoceras tho~atense

x

Haugta variabilts Htldoceras btftons

x ×

×

Harpoceras[aMferum Dactyltoceras temacoslatum

x

pleuroceras spmaruro Amatlheus margaritatua

x

Prodacb'hoceras davoel Tragophylloieraa ibex Uptomalamesom Echioceral ra¢itostalura

x

X

×

PLIENSBACHIAN

x x

X

x ×

TOARCIAN

x

x

~< ×

NW A

A;G A;G

x

×

Amoeboceras rosenkrantzi Amoebo~ras regulate Amoeboceras sermtum Amoeboceras giosense

Quenstedtoceras lamberti Peltoceras alhleta Erj,MnoeeraJ i oronatum Kosmocerasjason Slgaloceras ~allov~ense Maeroo'phahtesmacrocephalus

x >c

x

DB

NW NW

x

HV

BAJOCIAN

~

×

x

HV

<

~ ....

Motrisu~ras m o r r t l i mulilessub(ontrailu~ Procerite~progracih~

co

~

Titanilesgiganteus

Clydotlicems discus Clydonicerashollandt Oppeha aspJdotdei Prohefticocerasretrot'ostatum

(O

~

Zarai~kites albani

Cardloceras ¢ordalurn Quenstedtoceras mariae

CALLOVIAN

~

a,..coli,h,,..~o,.,

A ulacostephanus auttsstodoren~is Aulocostephanuseudoxu~ Aulo¢ostephanoldesmulabihs Rasemacymodoce Pictonlabaylei

OXFORDIAN

~

x

× x ×

M

Oxj

Asleroceros obtu~um

SINEMURIAN

HETTANGIAN

Caenisites lurnerJ 4rntoceras semt~ostalum Arterites bucklandf

M

X

Schlolhetmla angulata

M

x

A~.a.,.,x,o,,c.. Psdoceras p l a n o r b i s

O0

APPENDIX IIB

i

O0

STAGE

PORTLANDIAN

AMMONITE ZONE

Tilamtes glgantem

~.,o~,,~,,~s~

....

KIMMERIDGIAN

Pavluvia rotunda Pavlovla pallaslvldes Pe~tinatttespe~tmatus Pectmames hudlestom Pectinat.e~ ~heatlel ensl~ Peoinatltes sctlulus Pedinames elegans

CALLOVIAN

03 03

BATHONIAN

<

n"

BAJOCIAN

TOARCIAN

DB

OB OB NW

×

x

x

x

x

x

x

x

C CH

x x

x

CH;HR

x

x

x x

x ×

x x

x x x

x x

×

x ×

x X x

x

x

x

×

x

H

x

×

×

×

x

×

x

A;G;H

×

x

×

×

x

x

x

×

x

x

×

×

x

×

x

×

~

x

x

×

x

%

x X

G:WB

X

A ;G;H

×

x

x

A,G;H

×

x ~

x X

×

~

X

×

X x

D:WB

x

×

X

x

B 0 W£ WB

x

x

x x

x

x

x

×

x

x

x

x

x

x

x

3;KWK

x

x

×

x

x

x

81

3:FKIWK

x

x

x

×

x

x

x

x

HV

×

X

X

x

x

x

x

×

x

HV;WK

x

x

×

x

×

×

x x

×

×

×

x

x

x

x

L

x

x

×

×

×

×

LB

x

x

x

x

x

×

x

,

Stepbanoeera~ humphrles~anum

LB

x

x

x

x

Olollel $aUZpI

LB

x

g

x

×

x

×

x

x

Wlt~ he tlla laevtus( ula tt~perliu{eras d~t ite~

LB L8

Grapho~erai lonlavum Lud~ tgla mur¢ h ,sunae Tmetoceras scis~um Leto~eras opahnum

LB LB

Dumortterla Ievesque~ Gramrnoceras thouarense

M M

Haugia varlabdis Hildocera~ b~Jrons

M M

Prodad) liol eras davoei Dagl;ph~lloteras ibex L'ptfmta lame~om

(aentsite~ turner1 Armoceras semtulstarum Artetrtes butklandl S~ hlmhermJa angu~ata

t,..,,,.

A, ........ Psilo~ era.~ptant;rbts

M M

X X

×

HV HV

H L; M

×

X

x

3:FK;WK

B:

LB

~

x

B1

× x x

~

~ x

x x

~

× x

x

x x

x

X ×

WK

Parkinsoma parkmsom Garanttana g 5trenoceras subfurtatum

x

×

X

×

BODWB

x

x

X

× ×

x

A H

x

x

HR H

X

E~ hit~ eras rarit vstatum O~vnoticeras ox) notum Asteroteras obtusum

HETTANGIAN

x

DB N W ; S

I

x

x x x

x

Pleur ot eras spinatum 4mahheus margarltam~

SINEMURIAN

x

×

G :WB

Harpo~eras faklferum [)act ~hoceras 17?1141(ostatum

PLIENSBACHIAN

x x

Quenstedtuceras lambent Peltoeeras athMa Er)mno~era~ ¢c~runatum Kosmuo'ra~lawn $tgah;leras ~allovien~e Ma¢ro~ ephalites mat roc ephalu~

ltgzag~ eras z~gzag

"3

x

D B ;NW DB

A;GH

~Iort~ Tablet sub, ontra~w.~ Pro~ertte.i prograohs

x

x

F:WL

( ardlc~era~ ¢ordalum Quemt edt oc eras martae

C [) dunweras dal m Chdunieerasho,landi Oppeiiaasp~dmdes Prohe~ti~erasrelrutostatum

0

×

F:WL

4muebo¢ eras rosenkrant:i A moebo~eras regulare 4 moebo~ er~ A moebo(eras glosense I Card..¢erastemaserralum Cardlol eral denilph~ atum

x

DBjNW

A ulaco~lephanus autlssiodorensts 4ulo~ oslephanm eudoxas Aulo~ oslephan¢lide~ mutabilis Rasenta l ) modole Pwlunm bal tei

OXFORDIAN

F F;WL F;WL

Zarmsk ires albam

x x

X

APPENDIX IIC

AMMONITE ZONE

$TA GE

Tltantte~ giganteus

PORTLANDIAN

F

~'..eo~,,,,e.go,. Zatai~kires albani

F;WL

Pay/aria rotunda Pavlovw pallaslolde~ Peelmatites pecttnatu.~ Pectlrtalffes hudlestonl Peednatu¢s wheatle)en~s Peetinatiles ~citulu3 Pectinat~teselegans

KIMMERIDGIAN

F F;WL DB;NW WL WL

AuLaeostephanu~autisszodorensds Aulocostephanua eudoxu~ Aulocostephanoides mutabihs Ra~enw ¢ymodo~e PJoonla barleJ

I CardJoeerastenutsertatum

CardJoeera~dens~licatum CardJocerascordatum Quenstedtoeeras mattae

0

Quenstedtoceras lamberti Peho('era~athleta

EO

CALLOVIAN

Ko~mo(era~]ason S=gah~cerascallovtense Macro( ephahte~ macro~ephalu~

< fl:

Cbdonicera5 disc~ Cbdonweta~ hollandJ Oppetia aspMoMes

D

I Prohe~luocerasretro~u~latum

BATHONIAN

TOARCIAN

PLIENSBACHtAN

SINEMURIAN

HETTANGIAN

X

×

X X

×

X ×

X ×

X

X

x

H

X

X

×

x

x

A;G;H A;G;H

×

X

X

X

X

HR H

x x

×

x

x

x x

X

x

x

x

X

X

X

X

A;G

×

x

×

X

X

X

X

G

x

x

×

×

x

G

x

D;WB ×

WK B3;WK B 1;WK I B1-3; FK;WK

×

X ×

X

x X X

X X

X

)<

X

X

×

x

X

x

X

x

X

X

X

X

X ×

X

X

X

X

×

X

X X

X

× × ×

X

x x

x

x

x

LB

×

x

LB

x

x

×

x

x

LB

M

X

X

LB

Harporerasfalelfetum DacOhoceras tenuicostaturn

X

X

x

LB

M M

X X

×

~(

Haugia vanabihs Hlldoceras hifron,~

)~

X

x

M

X

×

X

Dumorlieria levesquel Grammoceras thouarense

×

X

LB

LB

×

X

X ×

HV;WK

Graphocer~ Ludwlgia mur(hJsonae Tmetoceras s¢issum Leio(era~ epahnum

X

X

X

x

WB

LB

X

X

A;G;H

Scephanoceras humphneslanum Otoites ~auzet Witehe/ha laeviuscula Hypertioeeras disdteJ

M

M

Pleuroeeras spmatum Amahheusmargarttatu~

×

x

BR;HL;M

×

x

x

Prodaetyhoceta~ d~voei Tragoph) lloeeras Ibex Uptonia }amesum

BR;M

×

X

B R;M BR

x

×

x

x

x

×

S('hlothelmta angulala Al~antes tiaswus P~ito~era~planotbis

X

X

HV

Caemsite~ turneri Atmocerass Arielhes bu(klandl

X X

X

HV

E~'hio(~rasratwostalum Oxynoticetas oxrnotum Asteroceras obtusum

X X

×

NW

Procerhes progtaci/n

Parkznsoma parkinsoni Garanuana garamiana Slrenuceras ~u~furcafum

)" X X

DB

Muftis1 Tulile~ su& omraauJ

ZJgzagt(eras zigzag

BAJOCIAN

I

X X X X

X X

CH;NW;S CH CH CH;HR

Amoeba(eras rosenkrantz[ Amoeboceras regulate Amoehoceras ~ertatum Amoehoceras glosense

OXFORDIAN

X X

" M

X

M

BR:M

B;M

×

X

X

X

X

O0 M

e.D

J,

0

-

STAGE

AMMONITE ZONE

PORTLANDIAN

~<

o

.~'

~

~,

o

r , , . . , , . , t . = , .forei . Gleucolithiles Zami~kites albani Pavlovla t o l ~ PcvloHa pallasioidts

Pect#tatileJ pecdnaws Pec!in~titeJ hudks: oni

× X

F;WL F;WL DB:NW D B; NW

X X

X

I

X

PeclL,tqtileJ whcadtyens~ Peclinalitet scitulus

KIMMERIDGIAN

e..,..,,,.,,~.., AtdacoJlep~nla aulL~siodorensis Aulocoslephan~ evdoxu* Autocostephanouks mutobilis RaJen~,cymodoce Piaonia baylel Ar~ocboccras rosttl}¢ranlzi

Amoebocer~ regular, Amoeboceras serralum Amoeboceras glosense

NW NW;S CH CH CH ',HR

× x x x x

x x x

HR H A;H A;H

x x x x x

x X

x

x

x ×

x

x

×

x

x

x × o,

OXFORDIAN

03

<

Cardi. . . . . . . .

or" •

BATHONIAN

X

X

C=tdlocermcord~lum Qutnstedwceras martae

A;G;H A;G

X

X

Clydoniceras ducm Clydonicera~hollandi Oppeha aspido,des Prohe~ti¢ocerasretrocostatum Mo,.,, . . . . . . . . . ~, Tul~les$ubconlractt~ Precerites progtacilts

Z~za~iceras z~zag

BAJOCIAN

TOARCIAN

X

X

x x x

x

× x × x

x x

X X

x x

X

G GiWfl BO;D;WB

x

x

x

X X

WK OI;R;WK B2;WK B1-3;FK;WK

X x x

X X X

X

X

X

Hyperlioceras disciles

X )4

X

X

X × X

LB

×

×

Graphoceras concavum Ludwigta murchisonae Tmetoceroz scissum l~ioceras opalinum

kfl LB

× X

X

×

~"~'o",,=~

Dumortieria tevesquei Grammoctms thouarenw

M M

x x

Hcugi¢ variabili~ .,~...,~,f,o.,

M M

x x

HL;M HL;M

x x

X

X

x

X ×

X

H L;M BR;HL;M

~R~M B R ;M

•

x

X

×

BR;M

X x

X X

B R; M B R;M BR; M

x × x

× × x

.Caeni~ite3 . . . . . .tutnert . . . . . . . . . . . . . . . . . . . . . BR;M . . . . . . . . .x .. . . . . . . . . . . . . . . . . . .X. . . . . . . . . . . . . . . . . . . . . . . . . Arnioc~raJsemicoslalum

BR;M BR;M

x x

x ×

Schlotheirnia angulata

B R;M

x x

× ×

A,,°,,,.,,°,,c= PjiloceraJ planorbis

~R;M . B

x

x

Ar~lilesbucklandi

X

X X

X

X X

HV;WK

×

Echioceras tarlcostalum Oxynoricetas oxynotum AMcrocer¢~ oblu3Mm

~4

HV;WK HV;WK

LB LB

Tragophylloceras ibex Uptoniajamesoni

x

,v:w~

Stephanoceras humphnestanura Oloites sauzei

PLIENSBACHIAN p,o~.c,yJl ...... ...,

x x

X X

X

D;WB

X X X

Pleuroceras splnalum Amah~tmmargarifatus

x x x ° ° ,

X X

LB LB LB

Da¢lyliocetas lenuicostatum

HETTANGIAN

X

X

parkimonia patkimem Gatam~ana gorantlana Strenocera~ subfuKatum

Harpocerasfalciferum

SINEMURIAN

X

A;G;H

A;G;fl

QutnstedtoceraJ lambertt Pettoceras athlela Erymnoceras coronatum • . . . . . . . . j.,o. Sigalocero5 callovien~e Macrocephalite~ macrocephalu~

CALLOVIAN

:3

i. . . . . . .

Cardioceras ~tmiplicatum

X X X

X × X

×

×

X

X

X X

APPENDIX lIE

Ocn STAGE

PORTLANDIAN

KIMMERIDGIAN

CALLOVIAN

Titaniles gtgontet~ Glaucolithttes gorei Zara,skues alban~ Pavlovia rotunda Pavlov~apa#astoides Pectmautes peclinalu~ Peomatlles hudlestoni Peclmatites wheatleyemis Pecllna#tes scilulus Pecltr~titeI elegam

< rr D

x

SINEMURIAN

H E T T A N G I A N

~

x

x

x

x

x

WL

x

x

x

x

x

x

x

x

x

Y

DB NW NW;S

× x

x

CH HR

x

x

x

CH;HR

×

x

x

A;G

x

x

x

G

×

x

x

x

x

×

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

×

x

×

x

×

x

x

x

x

x

x

x

x

x

×

x

x

x

x

x

x

x

×

x

x

x

x

x

x

x

X

B1-3:

x

x x

x x

M M

x

×

×

x x

x

x

x

×

x

x

X X

X

X

X

x

x

×

x

x ×

~ x

x

×

x

x

x

x

×

x

x

x x x

×

x

x

x

x

X

X

X

X

× X

X X

X X

X ~4

X

X

X X X

X X

"4

X

X

X

X X

Haugta variabihs Hildocera~ bifrons

x

× X

M M

x

x

X

Dumortleria levesquel Grarnmocera~ thouaren~e

x

X x

x

HV HV;R;WK

Stephanocera~ humphrteslantml Otoites sauzet . Wilchelba laeviuscula Hyperhoceras dlscltes

x

× x ×

HV;WK

x x x

x ×

X x

B1;B2;R;WK

HV;R;WK

x

"~ X

×

D;WB

FK;WK

x ~

BO;D;WB

WK B1;B2;R:WK

x

×

x

G;WB

x x

A;G;H

x

x

X X X X

X

X

X

X

×

X X X

HL;M

X X

M

X X

Pleutoceras ~pinatum A rr~lth~us margarltalus

BR;HL;M

×

Prod~ctyhoceras dav~ei Tragoph)'l/ocems ibex Uptomajamesoni

BR BR BR

×

×

Echioceras raricostatum Ox)'nottceras ox~notum Asteroceras obtusum

BR;M BR 8R

x x

x x

Caeatsites turneri ArnMceras semicostaturn Ariettles buckland~

BR BR;M BR;M

x

×

Schlotheimia angulata

8R;M BR

x ×

×

Alsat,tesbastcm Ps~locerasplanorb~s

X

x

x

Cardl, datum Quenstedtoceras marlae

Harpocerasfalciferum Dact~hoceras ~enutcoltatum

X

x

A;G;H A;G;H

Morrisu'eras mo~r~sl Tuhte~ subt ontr=~t~ Procentes progracih~

~,

x

Card~oceras tenu~serratum Cardloceras dens~phcatum

Quenstedtoceras lambeni Pehoceras athleta E[vranoceras coronatum Kosmoeeras yason Stgalocems calloviense Ma~rol'ephalites macrocephalua

x

F;WL

Graphoceras ¢oncavum Ludwtg~a murchtsonae Tmetoceras scissurn Le=oceraaopahnum

PLIENSBACHIAN

~ ~ .~

DB;NW

Parkin~on~aparkinsoni Gamntlana garan|iana Strenocera~ subfurcatum

TOARCIAN

~

x

F;WL

HR H A;H A;H

Zlgzagwetas zigzag

BAJOCIAN

~

F;WL

Amoebocetas rosenkrantzi Amoeboceras regulate Amoeboceras serratum Amoeboceta~ glo~ense

C(vdoniceras d~scm Cl)'domceras hotlandt Oppeha a~p~doides Prohecticoceras retroc'ostatum

BATHONIAN

; ~ ~ ~ ~ ~ ~ ~ ! ;

AMMONITE ZONE

A u!acostephanus autissiodvrensts Autocostephanm eudoxus Aulo~oslephanoides mutabilis Rasema omodo~e Pwtonta baliel

OXFORDIAN

~ ~ ;

HL:M

x

x

×

X

x × x

x x

x

x

x

x x x ×

×

95

References Arkell, W.J., 1956. Jurassic Geology of the World. Oliver and Boyd, Edinburgh, 806 pp. Barnard, T. and Hay, W.W., 1975. On Jurassic Coccoliths: a tentative zonation of the Jurassic of Southern England and Northern France. Eclogae Geol. Heir., 67(3): 563--585. Callomon, J.H., 1964. Notes on the Callovian and Oxfordian stages. C.R. Mem. Colloq. Jurassique Luxembourg. 1962. Inst. Grand Ducal Luxemb. Sect. Sci. Nat. Phys. Math., pp. 269--291. Callomon, J.H., 1968. The Kellaways Beds and Oxford Clay. In: P.C. Sylvester-Bradley and T.D. Ford (Editors), The Geology of the East Midlands. Leicester University Press, Leicester, pp. 264--290. Callomon, J.H. and Cope, J.C.W., 1971. The stratigraphy and ammonite succession of the Oxford and Kimmeridge clays in the Warlingham Borehole. Bull. Geol. Surv. G.B., 36: 147--176. Casey, R., 1973. The ammonite succession at the Jurassic--Cretaceous boundary in eastern England. In: R. Casey and P.F. Rawson (Editors), The Boreal Lower Cretaceous. Seal House Press, Liverpool, pp. 193--266. Gallois, R. and Medd, A.W., 1979. Coccolith-rich marker bands in the English Kimmeridge Clay. Geol. Mag., 116: 247--260. Hamilton, G., 1977. Early Jurassic calcareous nannofossils from Portugal and their biostratigraphic use. Eclogae Geol. Helv., 70(2): 575--597.

Hamilton, G., 1979. Lower and Middle Jurassic nannofossils from Portugal. Eclogae Geol. Helv., 72: 1--17. Medd, A.W., 1971. Some Middle and Upper Jurassic Coccolithophoridae from England and France. Proc. II Planktonic Conf., Roma 1970, 2: 821-845. Medd, A.W., 1979. The Upper Jurassic Coccoliths from the Haddenham and Gamlingay boreholes, Cambridgeshire, England. Eclogae Geol. Helv., 72: 19--109. NoEl, D., 1965. Sur les coccolithes du Jurassique Europ~en et d'Afrique du Nord. Essai de classification des coccolithes fossiles. Editions C.N.R.S., Paris, 209 pp. Prins, B., 1969. Evolution and stratigraphy of coccolithinids from the Lower and Middle Lias. Proc. I. Int. Conf. Planktonic Microfossils, Geneva, 2, pp. 547--558. Rood, T. and Barnard, T., 1972. On Jurassic Coccoliths: Stephanolithion, Diadozygus and Related Genera. Eclogae Geol. Helv., 65(2): 327--342. Sykes, R.M. and Surlyk, R., 1976. A revised ammonite of the Boreal Oxfordian and its application in northeast Greenland. Lethaia, 9: 421--436. Thierstein, H.R., 1976. Mesozoic calcareous nannoplankton biostratigraphy of marine sediments. Mar. Micropaleontol., 1 : 325--362. Van Hinte, J.E., 1976. A Jurassic Time Scale. Bull. Am. Assoc. Pet. Geol., 60(4): 489--497.