Observations on the lithostratigraphy and

ammonite succession of the Aptian (Lower

Cretaceous) Lower Greensand of Chale Bay, Isle

of Wight, UK

*Raymond Casey, {H. Mark Bayliss and {Martin I. Simpson

* Department of Palaeontology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK{ 95a Lee Road, Blackheath, London, SE3 9EN, UK{Department of Geology, University of Glasgow, Glasgow, G12 8QQ, UK

Revised manuscript accepted 4 September 1997

A revised lithostratigraphy is given for parts of the Ather®eld Clay and Ferruginous Sands Formations(Lower-Upper Aptian) of the Lower Greensand Group of the standard section in Chale Bay, Isle ofWight, retaining in essence the classic nomenclature of Fitton. Changes in zonal and subzonal bound-aries are proposed on the basis of new collections of ammonites obtained in situ. The Upper LobsterBeds Member of the Ather®eld Clay is detached from the Subzone of Deshayesites callidiscus andplaced in a separate Subzone of Deshayesites annelidus at the top of the Zone of D. forbesi. The in¯uxof Megatyloceras, Cheloniceras, Pseudosaynella and Sinzovia at this level has palaeogeographic impli-cations, pointing to the opening of a marine link with the Paris Basin and con®rming the Upper Lob-ster Beds as a transgressive horizon. The upper part of the Scaphites Beds Member of theFerruginous Sands, previously included in the deshayesi Zone, is transferred to the Subzone of Dufre-noyia transitoria, at the base of the Zone of Tropaeum (T.) bowerbanki, on the strength of the occur-rence therein of species of Tropaeum and Dufrenoyia. Tropaeum is not present below the bowerbankiZone as now de®ned; its primitive ancyloceratoid (hooked) forms such as T. (T.) hillsii have limitedbiochronological value, persisting alongside the criocone (spiral) species of the bowerbanki Zone andgiving rise to a local horizon of T. (T.) pseudohillsi at the bottom of the Upper Crioceras Beds (basalUpper Aptian). A more precise delimitation of the Walpen Clay & Sands from the Upper CriocerasBeds is made and the junction of these two members of the Ferruginous Sands is reaf®rmed as theLower/Upper Aptian boundary, coinciding with the junction of the Zones of T. (T.) bowerbanki andEpicheloniceras martinioides. Bed-by-bed collecting across the boundary shows that Epicheloniceras canno longer be taken as the prime biostratigraphical marker for the base of the Upper Aptian; greatersigni®cance is given to the extinction of Dufrenoyia. The sources of the genus Vectisites and somespecies of Ammonitoceras and Caspianites, hitherto ®xed only vaguely in the column, are pinpointed inthe martinioides Zone. The horizon of Tropaeum (T.) drewi is con®rmed as high in the bowerbankiZone (meyendorf® Subzone) and the validity of a `drewi Zone' at the base of the German UpperAptian (�base of Middle Aptian, Kemper, 1995) is questioned. In a review of the Lower/UpperAptian boundary, it is suggested that the German stratum be called the Horizon of Cicatrites? tenuino-dosus and placed tentatively at the top of the Lower Aptian. These and other changes in ammonitenomenclature are explained in the systematic notes. # 1998 Academic Press

KEY WORDS: Lower Greensand; Aptian; England; lithostratigraphy; zones; ammonites.

1. Introduction

The Lower Greensand is one of the major groups of the English Lower Cretac-

eous and reaches its fullest development in the Isle of Wight. Here it comprises in

ascending order the four formations of Ather®eld Clay, Ferruginous Sands, San-

drock and Carstone, spanning an interval from near the base of the Aptian to the

Lower/Middle Albian junction. In thickness, continuity of sequence and abun-

dance of fossils, the section of Ather®eld Clay and Ferruginous Sands exposed in

the cliffs and foreshore of Chale Bay, from Ather®eld Point to Blackgang Chine,

Cretaceous Research (1998) 19, 511±535 Article No. cr970105

0195±6671/98/030511 + 25 $30.00/0 # 1998 Academic Press

on the SW side of the Island (Figure 1) is unsurpassed. It provides the type

locality for much of the Aptian ammonite zonation established for the group by

Casey (1961a), itself widely accepted as a standard for northern Europe and as a

basis for comparison with Aptian sequences in more distant regions. Probably no

other single section of the stage is better documented or has contributed more to

Aptian macropalaeontology and biostratigraphy. In its long history of investigation

the name of W. H. Fitton was pre-eminent in the ®rst half of the last century.

Until recently, the basic stratigraphical terminology used by Fitton (1847) sur-

vived with only minor changes by later authors (e.g., Reid & Strahan, 1889;

White, 1921; Casey, 1961a; Simpson, 1985, with bibliography). However, many

of his `groups', now ranked as members within the lithostratigraphical hierarchy,

were named for their distinctive fossils rather than their lithological characters

(e.g., Perna Bed, Scaphites Group), contrary to modern practice in lithostratigra-

phy. Other of Fitton's `group' names are repetitive or too long. Recognising that

the names of members in the Chale Bay sequence need to be reviewed, some

authors concerned with sequence stratigraphy, tectonics and mineralogy have

abandoned much of Fitton's nomenclature (Ruffell & Wach, 1991; Ruffell & Gar-

den, 1997). Instead, as an interim measure they prefer to employ for part of the

column the Roman numerals used by him to denote the sequence of his `groups'.

Thus, while describing the basal part of the Ather®eld Clay variously as `Perna

Member', `Perna Beds' or `Perna Bed', Ruffell & Garden (1997) refer to the sub-

divisions of the Ferruginous Sands as `Member XI', `Member XII', etc. We think

it better to have a consistent scheme that disturbs established usage as little as

Figure 1. Sketch-map showing principal localities in Chale Bay, Isle of Wight, mentioned in thetext.

512 R. Casey et al.

possible. Pending a de®nitive revision of the Chale Bay lithostratigraphic scale, we

retain Fitton's names as modi®ed by Casey (1961a), adding "Formation" or

"Member" only when the rank of the unit needs to be stated. This is not out of

step with international stratigraphic guidelines, which respect traditional usages

and freedom of choice (Salvador, 1994; see also Lawson, 1981).

Figure 2. Revised correlation of the lithostratigraphy and ammonite zonation of parts of the Ather-®eld Clay and Ferruginous Sands formations of the Lower Greensand of Chale Bay, Isle ofWight.

Observations on Lower Greensand in the Isle of Wight 513

Although much of the 250 m of Aptian strata in Chale Bay is permanently

accessible, the prevalence of cliff falls and downwash and the ever-shifting beach

deposits prevent the entire section being seen at any one time. During the past 20

years, however, two of us (HMB and MIS) have kept the section under close

observation, collecting fossils in situ and logging temporary exposures as they

became available. In consequence we are able to amplify and amend published

details of both the lithostratigraphy and the ammonite succession, especially

across critical zonal boundaries. The portions of the section found to be in need

Figure 3. The Upper Lobster Beds and junction with the Crackers, east of Ather®eld Point, ChaleBay: comparative (generalised) sections as described by Fitton (at left) and as interpreted by thepresent authors, using Fitton's bed numbers.

514 R. Casey et al.

of revision fall within the Ather®eld Clay and Ferruginous Sands Formations, as

shown in Figure 2.

In addition to the material originally recorded by Casey (1960±80; 1961a) and

our more recent collecting, we have bene®ted from the study of ammonites found

by others mentioned in the acknowledgements. A more comprehensive account of

the lithostratigraphy of the Lower Greensand of the Isle of Wight is in preparation

by M. I. Simpson, while the ammonites and ammonite zonation of the group are

an on-going research project of R. Casey. In the present contribution H. M. Bay-

liss and M. I. Simpson are responsible for the detailed lithostratigraphy and other

®eldwork, and R. Casey for the ammonitology, zonation and correlation. H. M.

Bayliss did most of the preparatory work on the specimens and drew Figures 1

and 3±5.

2. Ather®eld Clay: Upper Lobster Beds Member

This member forms the top division of Fitton's "Crackers Group" (Group III)

and comprises a sequence of sandy clays and clayey sands between the Crack-

ers s.s. and the Ferruginous Sands above, in all nearly 13 m thick. It is almost cer-

tain that the term Upper Lobster Bed(s) for this unit originated in the informal

nomenclature of the professional fossil-collector Charles Wheeler, as did the

name Lower Lobster Bed for the bottom part of Fitton's "Crackers Group" (Fit-

ton, 1847, p. 298). In both cases the name derives from the occurrence of the

crustacean Mecochirus (=Meyeria of authors). When formally introduced by Ibbet-

son & Forbes (1845), the name Upper Lobster Bed was applied only to the lower

of the two beds into which they divided this member, though in the table at the

end of their paper both beds were united as Upper Lobster Clay. Fitton did not

adopt the term and the present usage of Upper Lobster Beds dates from Casey

(1961a).

In the 1950s, when one of us (RC) was active in the ®eld, this member was

well exposed at low water on the foreshore east of Ather®eld Point. For many

years only small patches of this once large exposure have been seen brie¯y after

storms had scoured the shore; the cliff section, albeit frequently obscured by

downwash and slumping, has been our principal source of information. In the

section given below we have retained Fitton's bed numbers to avoid confusion.

Section of Upper Lobster Beds east of Ather®eld Point

[Ferruginous Sands, Lower Gryphaea Beds, above]

Bed 10. Greyish-brown silty clay in two beds, separated by thin seam of

brown plastic clay which gives rise to terrace in cliff at beach level.

Lower bed comprises 1.15 m of ®rm clay; upper bed bluish and

sandy near top, prone to slumping ....................................... 3.25 m

Bed 9. Massive bed of brown-weathering clayey sand with dark streaks, rela-

tively resistant to erosion, reminiscent of the Crackers, though less

indurated. Softer, darker and siltier in top 0.30 m................. 1.95 m

Bed 8. Brown plastic clay with scattered clay-ironstone nodules, becoming grey-

ish-brown and silty upwards, grading rapidly into bed above .... 3.00 m

Bed 7. Dark grey sandy clay passing into greyish-brown silty clay in bottom

part. Broken line of ¯attened clay-ironstone nodules about 0.30 m

above base, commonly associated with bluish clay and sandy part-

ings. Top of bed forms terrace in cliff at beach level .............. 2.50 m

Observations on Lower Greensand in the Isle of Wight 515

Bed 6. Grey sandy clay with streaks of darker clay; bottom 0.30 m softer,

bluish and with sandy bioturbation...................................... 2.20 m

[Crackers s.s. below]

Total................................................................................ 12.90 m

Figure 3 contrasts the section given above with that described by Fitton. It will

be seen that the overall thickness of the member given by Fitton (and by Ibbetson

& Forbes) (40 feet/12.2 m) agrees reasonably well with our own measurements,

although there are some big discrepancies in the details of individual beds. Fitton

himself was inconsistent, describing two beds (7 and 9) as "grey sand" in the text

and as "sandy clay" in the folding table at the front of this paper (Fitton, 1847, p.

289 pars). Probably he, too, never had a clear view of the whole section at any

one time.

Ammonites occur mostly as internal moulds in clay-ironstone ("cementstone"),

calcite or pyrites or in combinations of these. Preservation of a calcite test is

occasionally seen. Commonly the phragmocone is solid and the body-chamber

crushed ¯at in the clay. Clay-ironstone body-chambers minus the nucleus also

occur. Pyritic nuclei, especially from bed 10, form the bulk of loose specimens

but are prone to decomposition. Much work remains to be done with the ammo-

nites from this member, the dearth of specimens of intermediate size making it

dif®cult to match many nuclei with body-chambers. The following have been

found in situ, Deshayesites predominating:

Bed 6. Deshayesites forbesi Casey, D. normani debilis Casey, D. mirabilisCasey, D. annelidus Casey, D. topleyi Spath, D. sp nov., Rolobocerassaxbyi Casey.

Bed 7. D. planus Casey, D. annelidus, Megatyloceras ricordeanum (d'Or-

bigny).

Bed 8. D. planus, Cf. Megatyloceras transiens (Casey) (base), M . sp.

Bed 9(top). D. forbesi, D. annelidus, D. consobrinoides (Sinzow).

Bed 10. D. annelidus, D. spp. nov., Megatyloceras cf. georgiense Casey, M.

cf. ricordeanum (d'Orbigny), Pseudosaynella aff. undulata (Sarasin),

P. cf. ®mbriata Imlay, Sinzovia aptiana (Sarasin), Ancyloceras cf.

matheronianum d'Orbigny.

Also from the Upper Lobster Beds but imprecisely localised are: D. annelidus,D. planus, D. forbesi, D. mirabilis, Megatyloceras spp. juv., Aconeceras sp. Pseudosay-nella spp. juv., Cheloniceras cf. cornuelianum (d'Orbigny) and Lithancylus cf. grandis(J. de C. Sowerby). The eroded holotype of Megatyloceras vastum Casey (1961, p.

191) was picked up on the foreshore exposure of the Lower Lobster Bed and

assumed to belong to that horizon. However, it agrees so well in its taphonomic

characters with a remanie roloboceratid found at the base of bed 8 as to leave lit-

tle doubt that it had fallen from the latter bed. Large Deshayesites encrusted with

serpulae were recorded by Casey (1961a, p. 508) as occurring at the base of bed

10. In our experience serpulids and other epizoa may be found on fossils through-

out the entire member.

While the ammonites of the basal bed show af®nity with those of the underlying

Crackers (Deshayesites forbesi, D. normani debilis, D. topleyi, Roloboceras saxbyi),viewed as a whole the Upper Lobster Beds witness important changes in the

fauna. Here Lithancylus, Pseudosaynella, Sinzovia, Megatyloceras and Chelonicerasmake their ®rst appearance in the Lower Greensand succession, this great increase

in generic diversity reaching its peak in bed 10. A notable feature of this member

is the great rarity of the genus Roloboceras, which contrasts with its strong rep-

516 R. Casey et al.

resentation in the underlying subzones of the forbesi Zone. Pseudosaynella and

Megatyloceras are known nowhere in the Lower Greensand but in the Upper Lob-

ster Beds. The accompanying Lithancylus and Cheloniceras, albeit rare, link this

member to the succeeding parinodum Subzone of the deshayesi Zone, the entry of

Cheloniceras being particularly signi®cant.

In Casey's (1961a) zonal scheme the Upper Lobster Beds were united with the

Crackers to form the Subzone of Deshayesites callidiscus, at the top of the Zone of

D. forbesi. On the basis of improved knowledge of the ammonite fauna of the

Upper Lobster Beds, we propose to detach that member from the callidiscus Sub-

zone and place it at the top of the forbesi Zone as the Subzone of Deshayesitesannelidus (the index-species was formerly known as D. callidiscus annelidusCaseyÐsee systematic notes).

An association of Megatyloceras, Cheloniceras, Pseudosaynella and Sinzovia with

Deshayesites similar to that of the Upper Lobster Beds is found in the Lower

Aptian Argiles aÁ Plicatules of the Paris Basin (Corroy, 1925; collections of Uni-

versity of Paris and Museum national d'Histoire Naturelle, Paris). Certain ammo-

nite species of the Argiles aÁ Plicatules, such as Deshayesites deshayesi (d'Orbigny),

Toxoceratoides royerianus (d'Orbigny) and Aconeceras nisoides (Sarasin) occur in

bed 1 of the Lower Gryphaea Beds (Casey, 1961a, p. 508), at the base of the Fer-

ruginous Sands Formation and immediately overlying the Upper Lobster Beds.

This suggests that the Upper Lobster Beds (annelidus Subzone), together with the

basal part of the Lower Gryphaea Beds (parinodum Subzone) are the correlatives

of the Argiles aÁ Plicatules.

The ammonite record of the Upper Lobster Beds may therefore be interpreted

as evidence of a gradual rise in sea-level, leading to the establishment of a direct

marine connection with the Paris Basin, allowing faunal interchange across the

proto-Channel to be initiated in early deshayesi Zone times. This palaeogeographic

concept is in line with Ruffell & Wach's (1991) treatment of the Upper Lobster

Beds as a transgressive horizon and may give some support for the eustatic high

postulated by Haq et al. (1987) for the middle of the Early Aptian. It also accords

with data from the Paris Basin itself, where the horizon of D. deshayesi is seen as

marking the opening of a Boreal-Tethyan seaway across France (ColleteÂ, 1995).

3. Ferruginous Sands: Scaphites Beds Member

Fitton's "Scaphites Group" (Group V, numbered VI in error on p. 304 of Fitton,

1847) comprises about 12 m of brown and grey-green muddy sands with calcar-

eous and phosphatic inclusions between the Lower Gryphaea Beds (Group IV)

and the Lower Crioceras Beds (Group VI). It was divided by Fitton into three

beds (14±16) and by Casey (1961a, p. 508) into four. Our own observations indi-

cate the need for revision of Fitton's beds 15 and 16 (Casey's beds 3 and 4), as

shown below.

Section of upper part of Scaphites Beds west of Whale Chine

[Lower Crioceras Beds above]

Bed 16.5. Grey-blue-green glauconitic muddy sands with nodules of dark

brown phosphorite and large oysters ( Aetostreon ), with clayey seam

(0.14 m) at base ................................................................. 1.09 m

16.4. Brown sand with dark brown nodules of phosphorite, with clayey

seam (0.20 m) at base ......................................................... 0.85 m

Observations on Lower Greensand in the Isle of Wight 517

16.3. Brown mottled dark muddy sand with clayey seam (0.13 m) at

base ................................................................................... 1.63 m

16.2. Brown dark muddy sand with hard nodules and a serpulid layer

0.20 m from top. Large oysters (Aetostreon) .......................... 0.52 m

16.1. Brown-yellow clay-draped sand with pyrite nodules and a few hard

calcareous concretions with calcite and phosphorite. Large oysters

(Aetostreon) ......................................................................... 0.90 m

Total.................................................................................. 4.99 m

Bed 15. Brown dark mottled sand with large oysters (Aetostreon). At base a

more-or-less continuous line of large red-stained calcareous concre-

tions up to 0.60 m in thickness, on the hummocky surface of which

sits a similar, but less persistent, line of concretions. Knobs of

black phosphorite inside concretions. Calcite in veins and covering

fossils ................................................................................. 1.75 m

[Bed 14 of Scaphites Beds below]

Figure 4. Upper part of the Scaphites Beds and junction with the Lower Crioceras Beds, west ofWhale Chine, Chale Bay; comparative (generalised) sections as described by Fitton (at left) andas interpreted by the present authors, using Fitton's bed numbers. Broken lines indicate corre-lation of boundaries as de®ned by Fitton, continuous lines as rede®ned herein (at right).

518 R. Casey et al.

Figure 4 compares the section given above with Fitton's inconsistent account.

Rather than take the irregular top or bottom of a line of concretions as a datum,

we ®nd it more practicable to draw the boundary between beds 15 and 16 about

a metre higher than did Fitton and the boundary between beds 16 and 17 (base

of Lower Crioceras Beds) at a clay seam 0.78 m lower. Allowing for these differ-

ences, our measurements agree better with his ®gure of 22 feet (6.8 m) for bed 16

given in the text (Fitton, 1847, p. 304) than the 27 feet 10 inches (8.6 m) quoted

in the table (ibid., p. 269 pars). He described this bed in the text as "grey sandy

clay or mud" and in the table as "greenish sand". The present observers ®nd it to

be predominantly brown (ferruginous) muddy sand, the colour-change from grey-

green evidently resulting from decomposition of glauconite and perhaps only a

super®cial effect of weathering.

Bed 15 is the most conspicuous unit of this member, cropping out as a ledge

through the sand and shingle on the shore west of Whale Chine. This is the main

source of the large hooked heteromorph Australiceras (Proaustraliceras) gigas, the

"Scaphites" of early authors from which the member takes its name. Here the

genus Deshayesites reaches its maximum size in the Lower Greensand, commonly

attaining a diameter of 300 mm. The following have been collected from this

bed: Australiceras (Proaustraliceras) gigas (J. de C. Sowerby), A. (P.) pingue Casey,

Ammonitoceras (Epancyloceras) hythense (Spath), Am. (E.) fractum (Casey), Tono-hamites decurrens Spath, Toxoceratoides royerianus (d'Orbigny), T. subproteus Casey,

Aconeceras nisoides (Sarasin), Cheloniceras cornuelianum (d'Orbigny), Ch. crassumSpath, Ch. impar Casey, Ch. kiliani (von Koenen), Ch. proteus Casey, Ch. quadrar-ium Casey, Ch. quadrarium dispansum Casey, Ch. mackesoni Casey, Deshayesitesgrandis Spath, D. grandis lacertosus Casey, D. vectensis Spath (=D. wiltshireiCasey), D. geniculatus Casey, D. involutus Spath, D. involutus hythensis Casey, D.

sp. nov.

Casey (1961a) referred the whole of the Scaphites Beds to the Subzone of

Deshayesites grandis, the highest part of the deshayesi Zone, though he recorded no

ammonites from the topmost bed (bed 16), which is rarely well exposed. Our

attention has focussed on this poorly known bed 16, from which we can now list

the following:

Bed 16.1. Australiceras (Proaustraliceras) gigas, Tropaeum (T.) hillsii (J. de C.

Sowerby), Dufrenoyia furcata (J. de C. Sowerby), D. transitoriaCasey.

Bed 16.2. Cheloniceras sp.

Bed 16.4. Dufrenoyia transitoriaBed 16.5. Tropaeum (T.) sp., Ch. cf. cornuelianum (d'Orbigny), D. furcata, D.

formosa Casey, D. spp.

A phosphatised body-chamber of Dufrenoyia cf. furcata from an unspeci®ed

level in bed 16 was found by Dr W. Dean. Possibly the concretions of bed 16.1

are the source of some of the cobbles with phosphatic and calcitic Dufrenoyiafound on the beach near Whale Chine and formerly assumed to have originated

higher in the sequence.

The new ®nds in bed 16 call for a reappraisal of the boundary between the

Zones of Deshayesites deshayesi and Tropaeum (T.) bowerbanki in the Chale Bay

section. The genus Dufrenoyia is diagnostic of the Zone of T. (T.) bowerbanki,equivalent to the Zone of Dufrenoyia furcata of many authors, and generally,

though not universally, taken to mark the top of the Lower Aptian. Its presence in

the topmost part of the Scaphites Beds shows that the boundary between these

Observations on Lower Greensand in the Isle of Wight 519

two zones has been drawn too high. We now propose to move this boundary

down to the base of bed 16 and to place that bed and the Lower Crioceras Beds

in an extended Subzone of Dufrenoyia transitoria, the lower part of the bowerbankiZone. Bed 15 remains in the deshayesi Zone (grandis Subzone).

Fitton's record of "Scaphites" hillsii above the main range of concretions of bed

15 could not be con®rmed by Casey (1960, 1961a), either from his own collecting

or from museum holdings. We can now substantiate Fitton's record by the dis-

covery of a specimen of this species in bed 16.1. Further comments on this

important ammonite and its stratigraphical signi®cance are made in the systematic

notes.

4. Ferruginous Sands: Walpen Clay and Sands Member

Fitton's Group VII, between the Lower and Upper Crioceras Beds (Groups VI

and VIII), comprises about 18 m of dark sand, silt and clay with phosphatic

nodules. He called it the Walpen and Ladder Sands and Clay in the text (Fitton,

1847, p. 306) and the Walpen Clay and Sands in the table (ibid., p. 289 pars). We

follow Casey (1961a) in preferring the latter and thus avoiding confusion with the

Walpen and Ladder Sands (Group IX). Fitton divided the member into two beds

(numbered 24 and 25) with thicknesses given as 27? and 28 feet (8.2? and 8.5 m)

respectively in the text (ibid., p. 306) and as 24 feet and 33 feet (7.3 and 10.1 m)

in the table (ibid., p. 269 pars). These two beds are best examined in the mouth

of Whale Chine and the undercliff running southeastwards towards Ladder

Chine. Their junction forms the top of the undercliff and is responsible for the

waterfall within Whale Chine. We have subdivided Fitton's beds 24 and 25 as fol-

lows (Figure 5):

Section of Walpen Clay & Sands in the vicinity of Whale Chine

[Upper Crioceras Beds above]

Bed 25.4. Dark greenish-grey sand with much black silt and clay; a band of

dark-grey silty clay (0.30 m) at base. Few nodules of brown

phosphorite ........................................................................ 2.70 m

25.3. Sand as above; a band of dark-grey clay of soapy texture like fuller's

earth (0.30 m) at base. Few nodules of brown phosphorite .... 1.20 m

25.2. Sand as above; small nodules of brown phosphorite and pyrites

throughout. Water seepage at junction with bed above .......... 3.60 m

25.1. Dark-grey silty clay with impersistent line of irregularly shaped con-

cretions weathering reddish-brown, each resembling a cluster of

in®lled borings.................................................................... 1.98 m

Bed 24. Dark greenish-grey sand with black silt and clay, especially in upper

part. Small nodules of brown phosphorite scattered throughout,

roughly in lines; hard in bottom part of bed, less dense above. Pre-

sence of clay partings at 3.05 m and 7.01 m from base permits div-

ision of bed into three (see Figure 5) .................................... 8.23 m

[Lower Crioceras Beds below]

Total................................................................................ 17.71 m

The phosphorite nodules in bed 24 are rich in fossils, commonly enclosing

bivalves or consisting of an ammonite body-chamber. Some have the phragmo-

cone preserved as a hollow mould, permitting reconstruction of the whole ammo-

520 R. Casey et al.

nite. Fossils in bed 25 are similarly preserved, though fewer. Combining the ear-

lier records of Casey (1960±80; 1961a) with the results of our renewed collecting,

we have compiled the following list of ammonite occurrences in the Walpen Clay

and Sands:

Bed 24.1. Dufrenoyia scalata Casey (base), D. praedufrenoyi Casey, D. sp.

Bed 24.2. D. notha Casey

Bed 24.3. Aconeceras cf. haugi (Sarasin), Toxoceratoides sp., Cheloniceras kirkal-dyi Casey, Ch. kiliani obesum Casey, Ch. disparile Casey, Ch. sp.,

D. formosa Casey.

Bed 24 undivided. Tropaeum (T.) bowerbanki J. de C. Sowerby, Tonohamitesaequicingulatus (v. Koenen), T. limbatus Casey, Ch. meyendorf®(d'Orbigny), Ch. crassum Spath, D. furcata (J. de C. Sowerby), D.lurensis (Kilian), D. scalata.

Bed 25.2. Tropaeum (T.) hillsi (J. de C. Sowerby), T.(T.) sp., Ch. kiliani obe-sum, Ch. spp. (including transitions to Epicheloniceras), Epicheloni-ceras sp. (near base), D . cf. furcata.

Bed 25.3. T. (T.) sp., indet ancyloceratid, D. cf. dufrenoyi (d'Orbigny) (near

top), Ch. kiliani obesum.

Bed 25.4. Tropaeum (T.) drewi Casey (1.10 m below top), indet. tuberculate

ancyloceratid, Ch. cf. rotundum Casey, D. notha (0.90 m from top),

D. spp. (1.10 m and 1.32 m from top).

Bed 25 undivided. D. lurensis, Ch. meyendorf®, Ch. kiliani obesum, Ch. imparCasey.

The Walpen Clay and Sands (Group VII) represent the upper half of the bower-banki Zone in Casey's classi®cation and were assigned to the Subzone of Cheloni-ceras meyendorf®, the topmost part of the Lower Aptian (Casey, 1961a). This

nomenclature and position are maintained in the present paper, despite the occur-

rence high in the subzone of the genus Epicheloniceras, generally regarded as diag-

nostic of the Upper Aptian. The ®nd of Tropaeum (T.) drewi in the sequence (bed

25.4) con®rms the inference from the matrix of museum specimens of a position

high in the bowerbanki Zone (Casey, 1960). This species is known also from the

remanie fauna at the base of the Norfolk Carstone (Casey, 1960, p. 37, pl. 8, ®g.

2). This latter occurrence may now be interpreted as indicating that the link with

the North Sea Basin, opened perhaps as early deshayesi Zone times and closed by

the martinioides regression, was maintained until the very end of the Early Aptian.

This supports the perception of the Walpen Clay and Sands as a transgressive

horizon (Ruffell & Wach, 1991). These same authors have recorded smectitic

(volcanogenic) sediments in this member and note that such occurrences are

commonly associated with the belemnite Neohibolites. We have found Neohibolitesthroughout bed 25; one example (bed 25.1) was identi®ed by Professor J. Mutter-

lose as N. ewaldi (v. Strombeck) approaching N. clava Stolley, consistent with a

position high in the ewaldi belemnite Zone.

Further comments of the signi®cance of the ®nds of Tropaeum (T.) drewi and

Epicheloniceras in this member are made in the section on the Lower/Upper Aptian

boundary and in the systematic notes.

5. Ferruginous Sands: Upper Crioceras Beds Member

The Walpen Clay and Sands are succeeded by about 16 m of brown-weathering

clayey sands with tiers of large concretions. This is the Upper Crioceras Group

Observations on Lower Greensand in the Isle of Wight 521

(Group VIII) or Upper Crioceras Ranges of Fitton (1847). Casey (1961a) used

the term Upper Crioceras Beds and designated this member the Subzone of Epi-cheloniceras debile, the lowest division of the martinioides Zone and base of the

Upper Aptian. The best exposures are in the banks of Whale Chine. Weathered-

out concretions from these beds strew the bottom of this ravine and tumble to the

beach on either side of it. The concretions are richly fossiliferous and yield a dis-

tinctive assemblage of ammonites, the most conspicuous being giant hetero-

morphs up to 650 mm diameter belonging to the genera Tropaeum, Ammonitocerasand Caspianites. These are the "Crioceras" from which the member takes its name.

The concretions resemble the `doggers' of the Hythe Beds of the mainland and

are simply indurated portions of the containing sediment. They have lost most of

their calcareous content, leaving ammonites and other molluscan fossils as stein-

kerns. Here and there secondary calcite has replaced the original test.

Fitton divided his Upper Crioceras Group into nine beds, numbered 26 to 34,

the last subdivided into two. Presumably because the irregular shape and imper-

sistence of the concretions made it dif®cult to ascertain the thickness of individual

beds, for purposes of measurement he grouped them into three. In order to recon-

cile our own observations with those of Fitton, we have used his bed numbers

and taken the tiers of concretions as guide-lines, measuring the intercalated beds

of sand from the centre of relevant concretions, as shown in Figure 5.

Section of Upper Crioceras Beds exposed in Whale Chine and vicinity

[Walpen & Ladder Sands above]

Bed 34.2. Grey, brown-weathering sand with dark silty streaks, a seam of grey

sandy clay (0.40 m) at base. Line of small, isolated phosphatic

nodules (Fitton's bed 34b) .................................................. 2.00 m

34.1. Sand as before with line of isolated concretions of varying sizes up to

0.40 m long (Fitton's bed 34a) ............................................ 2.19 m

Bed 33. Almost continuous raft of very large rounded concretions about

0.50 m thick, some coalescing into masses up to 2.50 m long, green-

ish-grey, upper surfaces with radiating structures resembling in®lled

burrows. Central cores of concretions iron-stained, partly phospha-

tised and with septarian crevices in®lled by secondary calcite.

Bed 32. Sand as before .................................................................... 1.22 m

Bed 31. Range of huge, almost spherical concretions up to 0.90 m in diam-

eter, otherwise similar to bed 33 above.

Bed 30. Sand as before .................................................................... 1.83 m

Bed 29. Ragged line of concretions about 0.80 m long by 0.40 m thick, rela-

tively uncompacted, clearly visible only in weathered sections.

Bed 28.2. Sand as before with conspicuous seam of grey sandy clay (0.30 m) at

base ................................................................................... 0.92 m

28.1. Sand as before .................................................................... 1.52 m

Bed 27. Almost continuous raft of dark reddish or purplish blocky concre-

tions about 0.80 m long and 0.40 m thick, with putty-coloured

branching structures on surface. A prominent feature in cliffs

Bed 26.5. Sand as before, more clayey in bottom 0.30 m...................... 3.68 m

26.4. Sand as before .................................................................... 1.20 m

26.3. Range of scattered rusty-coloured concretions up to 0.70 m long and

0.40 m thick, grey or bluish inside, some septarian. Pyrites, calcite

522 R. Casey et al.

and small clusters of blue vivianite invade cavities. Numerous fossils,

including Tropaeum pseudohillsi. Fitton's 3rd "Scaphites" range.

26.2. Sand as before, more clayey in basal 0.08 m. Large body-chamber

fragments of hooked Tropaeum heavily encrusted with pyrites. 1.22 m

26.1. Sand as before, more clayey in basal 0.05 m. Isolated rusty-brown

concretions, generally small, exceptionally up to 0.30 m long. 0.56 m

[Walpen Clay & Sands below]

Total................................................................................ 16.34 m

The following list of ammonite occurrences in the Upper Crioceras Beds com-

bines the records of Casey (1960±80; 1961a) and our more recent collecting and

that of our collaborators.

Bed 26.1. Epicheloniceras sp., indet. ancyloceratid nuclei.

Bed 26.2. Tropaeum (T.) pseudohillsi Casey, T. (Ancylotropaeum) baylissi Casey,

Epicheloniceras tschernyschewi (Sinzow).

Bed 26.3. Australiceras (Australiceras) sp. nov., Ammonitoceras (Ammonitoceras)rex Casey, T. (T.) pseudohillsi, T. (A.) baylissi, T. (A.) ponderosumCasey, Tonohamites? hunstantonensis Casey, Cheloniceras cf. kiliani(v. Koenen) (trans. to Epicheloniceras), Ch. cf. meyendorf®(d'Orbigny) (trans. to Epicheloniceras), E. tschernyschewi, E. eotypicum(Casey), E. martinioides (Casey), E. debile (Casey).

Bed 27. Am. (Am.) rex, E. martinioides, E. debile.Bed 28.2. Tropaeum (T.) benstedi Casey.

Bed 31. E. martinioides, Vectisites caprotinus Casey.

Bed 33. E. martinioides, E. debile, E. debile paucinodum (Casey), giant ammo-

nites noted.

Beds 26±34 undivided. Aconeceras cf. nisus (d'Orbigny), Am. (Am.) rex, Am.(Am.) tovilense Crick, Am. (Am.) sowerbyi Casey, Am. (Am.) sp.

nov., T. (T.) benstedi, Caspianites vectensis Casey, Tonohamites limba-tus, E. martinioides, E. martinioides alternatum (Casey), E. debile, E.eotypicum, E. subvolgense (Casey), Vectisites simplex Casey.

Bed 33 is believed to be the source of many of the giant ammonites found on

the beach east of Whale Chine and below Ladder Chine. Very few of these speci-

mens have reached centres of study owing to the herculean effort required to

transport them along the beach to the cliff-top. Large examples of Tropaeum (T.)benstedi, Ammonitoceras (Am.) sowerbyi and Caspianites vectensis were obtained by

one of us (HMB) and recorded as coming from either the top of the Upper Crio-

ceras Beds or the base of the Walpen and Ladder Sands (Casey, 1980). With

greater experience of the various lithologies, we can now eliminate the latter hor-

izon and suggest bed 33 as the most likely source, with beds 27 and 31 as possibi-

lities.

A local horizon of Tropaeum (T.) pseudohillsi is represented in bed 26, at the

base of the debile Subzone and the base of the Upper Aptian. It is clear that this

all-important basal portion of the Upper Crioceras Beds and its junction with the

Walpen Clay and Sands (Group VII) was not seen by Fitton himself. His com-

ment that a third range of "Scaphites", of uncertain species, was said to occur in

Whale Chine, above the level of the Scaphites Beds (Fitton, 1847, p. 304) was

not followed up by later workers. Nearly 150 years were to pass before Fitton's

words were vindicated by the discovery of hooked Tropaeum at the base of the

Upper Crioceras Beds (bed 26) by H. M. Bayliss while working in the 1970s on a

terrace on the west side of the chine. These ®nds were described by Casey (1980)

Observations on Lower Greensand in the Isle of Wight 523

Figure 5. The Walpen Clay & Sands, Upper Crioceras Beds and Walpen & Ladder Sands, WhaleChine and vicinity, Chale Bay; comparative (generalised) sections as described by Fitton (at left)and as interpreted by the present authors, using Fitton's bed numbers.

524 R. Casey et al.

under the names Tropaeum (T.) pseudohillsi, T. (Ancylotropaeum) baylissi and T.(A.) ponderosum, their presence at this level throwing new light on the phylogeny

of the genus Tropaeum (see systematic notes).

The dwarf douvilleiceratid Vectisites (type-species V. caprotinus Casey) was diag-

nosed from specimens found in a single concretion from the top part of the

Upper Crioceras Beds (Casey, 1962, p. 256). We have now duplicated the ®nd

and can pinpoint the horizon of this genus as the large subspherical concretions of

bed 31, which commonly enclose nests of small ammonites. Our collecting in this

member has also narrowed down to the debile Subzone the horizon of Ammonito-ceras (A.) tovilense previously placed only vaguely in the Hythe Beds of the Maid-

stone area of Kent.

6. Ferruginous Sands: Walpen and Ladder Sands Member

This is Fitton's Group IX, treated as a single bed (35) and called the Walpen and

Ladder Sand in the text (Fitton, 1847, p. 307) and the Walpen and Ladder Sands

in the folding table (ibid., p. 269 pars). We follow the majority of authors in pre-

ferring the plural form. Together with the overlying Upper Gryphaea Beds

(Group X), this member was designated the Subzone of Epicheloniceras gracile of

the martinioides Zone (Casey, 1961a). Comprising nearly 13 m of greenish-grey

sand with concretions, this member comes down to beach level east of Walpen

High Cliff but is more easily accessible from the cliff-top in Ladder Chine, about

250 m SE of Whale Chine.

Section of Walpen and Ladder Sands in Ladder Chine

[Upper Gryphaea Beds above]

Bed 35.2. Greenish-grey sand with black silty streaks and rusty blotches

......................................................................................... 3.66 m

35.c. Line of scattered ferruginous concretions veined with carstone, up to

0.40 m long and 0.30 m thick, much decomposed; some have grey

stony cores, which may appear in isolation (Fitton's bed 35c)

35.1. Sand as before. At base an almost unbroken line of huge ¯attened

gritty, olive-green concretions up to 1.80 m long and 0.60 m thick

(Fitton's bed 35a). Each contains in its upper half one or more foot-

ball-sized inclusions of brown, calcite-veined phosphorite full fossils.

(Fitton's serpulid bed±bed 35b±not seen in section but appears on

beach as a discontinuous ledge up to 0.30 m thick with intertwined

serpulae) ............................................................................ 9.07 m

Total................................................................................ 12.73 m

[Upper Crioceras Beds below]

Bed 34 of the previous member has yielded no ammonities in situ. Lithologi-

cally and palaeontologically the line of demarcation between these members

(Groups VIII and IX) and the debile and gracile Subzones is arbitrary. One of us

(MIS) would prefer to draw the base of the Walpen and Ladder Sands below the

clay seam at the bottom of bed 34.2, above which the sands are more obviously

glauconitic.

On the beach the concretions of bed 35.1 form a line of boulders extending out

to sea. Many of the phosphatic inclusions are crowded with ammonites, the

Observations on Lower Greensand in the Isle of Wight 525

phragmocones commonly cast in white calcite. Below is an up-to-date record of

the ammonites of this member:

Bed 35.1. Aconeceras cf. nisus (d'Orbigny), Doridiscus rotulus Casey, Epichelo-niceras tschernyschewi (Sinzow), E. subvolgense (Casey), E. gracile(Casey), E. gracile rugosum (Casey), E. claudii (Casey), E. sellind-gense audax (Casey), Australiceras (A.) sp.

Bed 35.2. Caspianites boughtonensis (Casey)

The large heteromorph Caspianites boughtonensis was originally described under

Ammonitoceras (Casey, 1961) and later transferred to Caspianites (Casey, 1980). It

had been recorded only from an imprecise level in the martinioides Zone of the

Hythe Beds of the Maidstone area of Kent. The species may now be placed in the

gracile Subzone.

7. The Lower/Upper Aptian boundary

The various schemes of ammonite zonation applied to the Aptian in different

areas and at different times were reviewed in depth by Mikhailova (1983) and in

outline by Rawson (1983), Hancock (1991), Erba (1996) and others. As yet there

is no agreement on the number of substages. The classic twofold separation into

Lower Aptian (Bedoulian) and Upper Aptian (Gargasian) was changed when

Breistroffer (1947) extended the Aptian upwards to embrace the "Clansayes" hor-

izon (Clansayesian), previously placed at the base of the Albian. Although the

inclusion of the "Clansayes" horizon (Zone of Diadochoceras nodosocostatum and its

Boreal correlatives) has found universal acceptance, the tripartite division of the

stage implicit in Breistroffer's classifcation has not. With few exceptions (e.g.,

Kemper, 1995), a twofold subdivision (Lower and Upper) is used for the Boreal

Aptian, while a threefold (Lower, Middle and Upper) is favoured by workers on

the Tethyan Aptian.

Crucial to the drawing of internal boundaries within the Aptian is the position

of strata containing Dufrenoyia, a question discussed by Kemper (1982) and Hoe-

demaeker & Bulot (1990). Irrespective of whether a twofold or a threefold subdi-

vision of the Aptian is used, the horizon with Dufrenoyia (Zone of Tropaeumbowerbanki in the Lower Greensand) has been taken by most authors to mark the

summit of the Lower Aptian (Conte, 1994, with bibliography). This is despite the

apparently anomalous records of Dufrenoyia in the French Gargasian, widely

quoted since Jacob (1907) introduced Dufrenoyia ("Hoplites") furcata as co-index

species with Aconeceras ("Oppelia") nisus for the lower part of the substage. The

situation has now been clari®ed by Conte (1994) in an important paper dealing

with the Bedoulian-Gargasian boundary in the stratotype section of Cassis-La

BeÂdoule, SE France. He has shown that in the Gargasian the genus Dufrenoyia is

con®ned to a basal Zone of Dufrenoyia and Tropaeum bowerbanki and lies below

the assemblage with Epicheloniceras "martini". In his zonal scheme for the Lower

Greensand, Spath (1923) had used a "martini Zone" for the lower part of the

Upper Aptian or Gargasian as then understood, such usage having been sanc-

tioned from the time of von Strombeck (1861). Owing to the unsound taxonomic

basis of d'Orbigny's "Ammonites martini", it was replaced as an index species by

Epicheloniceras martinioides (Casey, 1954, 1961a, p. 595). Conte's proposal to

detach the Dufrenoyia Zone from the Gargasian and transfer it to the Bedoulian

(Lower Aptian), whence Roch (1927) and Casey (1964, p. 398) had already

recorded Dufrenoyia, brings his classi®cation of the French sequence into line with

526 R. Casey et al.

majority usage. Conte's work exposes the ambiguity of the terms "Bedoulian" and

"Gargasian" and raises the question whether it would not be better to abandon

them altogether, along with "Clansayesian".

In the Lower Greensand, the ®rst occurrence of Epicheloniceras has hitherto

been taken as the prime biostratigraphical marker for the base of the Upper Crio-

ceras Beds (martinioides Zone, debile Subzone) in Chale Bay. The entry of Epiche-loniceras following on the exit of Dufrenoyia has also been widely accepted as the

marker for the base of the Middle Aptian in the Tethyan region (e.g., Mikhailova,

1983; Bogdanova & Tovbina, 1994). This must now be re-assessed in the light of

our renewed palaeontological sampling through the Walpen Clay and Sands

(bowerbanki Zone, meyendorf® Subzone) and the Upper Crioceras Beds. The

occurrence of Epicheloniceras, albeit as a rarity, in the upper part of the meyendorf®Subzone, where it overlaps in range with Dufrenoyia and Cheloniceras, shows that

it is not an infallible guide to an Upper/Middle Aptian horizon.

Figure 6 illustrates the vertical distribution of the principal ammonite genera

and subgenera across the bowerbanki/martinioides boundary in the Chale Bay suc-

cession according to present knowledge. It will be seen that the major faunal turn-

over, accompanied by an increase in generic diversity, takes place at or just above

the base of the Upper Crioceras Beds. Within this narrow stratal range Cheloni-ceras gives way to its descendant Epicheloniceras and the stock produces a new off-

shoot, Vectisites, while Tropaeum (Ancylotropaeum), Ammonitoceras s.s., Caspianitesand Australiceras s.s., make their ®rst appearance. Perhaps the most signi®cant

palaeontological event at this level is the disappearance of Dufrenoyia, marking the

end of the superfamily Deshayesitaceae, which had dominated the Lower Green-

Figure 6. Vertical distribution of the principal ammonite genera and subgenera across the Lower/Upper Aptian boundary in the Lower Greensand of Chale Bay.

Observations on Lower Greensand in the Isle of Wight 527

sand seas from the beginning. In the Mediterranean region this event coincided

with the emergence of the Parahoplitaceae, though members of this taxon did not

penetrate the Boreal realm until later in the Aptian (nut®eldiensis Zone).

Future work will decide to what extent the picture of ammonite distribution

across the Lower/Upper Aptian boundary presented here is distorted by collec-

tion-failure, palaeoecology and other factors. For the present it re-af®rms the base

of the Upper Crioceras Beds as the most practical line of demarcation between

these two substages in the Chale Bay standard sequence for the Lower Green-

sand. Clearly, it is here unreliable to use the ®rst occurrence of a single genus

(Epicheloniceras) for boundary de®nition, and in evaluating the whole assemblage

negative criteria such as the extinction of Dufrenoyia may be of greater signi®cance

for long-range correlation.

In its broad outlines the scheme of zonation and sequence of ammonite faunas

discussed herein may be traced from southern England to Transcaspia and

beyond. An unresolved problem is integration of the "Zone of Tropaeum drewi",

which has become accepted as part of the standard sequence of the German

Aptian. Although based nominally on a Lower Greensand species by Kemper

(1963), this zone has yet to be identi®ed outside its type-area around Rheine and

Ochtrup, bordering the Rhenish Massif, NW Germany. Here beds with Dufre-

noyia furcata and Tropaeum bowerbanki are succeeded by strata containing a

specialised group of heteromorphs attributed to T. drewi and allies and placed at

the base of the Upper Aptian (=base of Middle Aptian of Kemper, 1995) below

the Zone of Epicheloniceras tschernyschewi (=Zone of E. martinioides) (Kemper,

1963±76). Both Dufrenoyia and Epicheloniceras are absent from the recorded

"drewi Zone" fauna and the few specimens of Cheloniceras and long-ranging

Zuercherella illustrated by Kemper (1963, 1964, 1976) are insuf®cient to ®x a pre-

cise horizon relative to the Chale Bay sequence. The Cheloniceras are suggestive of

the Lower Aptian, though a position at the base of the Upper Aptian cannot be

excluded. At Chale Bay scarcely more than a metre separates the last known

occurrence of the Lower Aptian Dufrenoyia and the ®rst appearance of the Upper

Aptian E. tschernyschewi, and there are no signs of a major disconformity between.

Nevertheless, the possibility must be considered that a gap exists in the Chale Bay

sequence at the Lower/Upper Aptian boundary suf®cient to accommodate the

whole or part of the so-called drewi Zone.

In the Lower Greensand the authentic Tropaeum (T.) drewi is now placed ®rmly

at the top of the Lower Aptian (meyendrof® Subzone), but, ironically, we cannot

be sure that this species is represented in the German "drewi Zone" (Casey,

1980). Some of Kemper's "Tropaeum" from this level show more resemblance to

the Caucasian Cicatrites abichi (Anthula), itself something of an enigmatic factor

(see systematic notes). Another twist to the knotty problem of the so-called drewi

Zone is the fact that in the belemnite scale the junction of the Zones of Neohibo-

lites ewaldi and N. clava is considered to run through the middle of this ammonite

"zone" (Mutterlose, 1990, 1995). Kemper himself had at one time replaced T.

drewi by T. tenuinodosum (originally T. drewi tenuinodosum Kemper) as the index-

species (Kemper, 1982, ®g. 2.2). Pending further work on the German occur-

rences, it is here suggested that the "Zone of Tropaeum drewi" be renamed the

Horizon of Cicatrites? tenuinodosus and placed tentatively at the top of the Lower

Aptian.

528 R. Casey et al.

8. Systematic notes

Order Ammonoidea

Suborder Ancyloceratina

Superfamily Ancylocerataceae

Family Ancyloceratidae

Genus Australiceras Whitehouse 1926

Subgenus Proaustraliceras Kakabadze 1977

Australiceras (Proaustraliceras) gigas (J. de C. Sowerby)

A number of varietal names (inscriptum, arcuatum, anguimanum) were proposed

for this species (Casey, 1962, p. 52), since formalized as nominal subspecies

under the changed Code of Zoological Nomenclature (see Casey, 1960, p. xxxiii;

1962, p. 229, footnote). These nominal taxa are now regarded as merely descrip-

tive terms for oddities among the vast gigas population revealed by continued col-

lecting from bed 15 of the Scaphites Beds of Chale Bay. From its peak abundance

in bed 15 (deshayesi Zone, grandis Subzone), A. (P.) gigas survives as a rarity into

the Lower Crioceras Beds (bowerbanki Zone, transitoria Subzone). The subsequent

range of Proaustraliceras cannot be followed in the Chale Bay section and its crio-

cone descendant Australiceras s.s. appears abruptly as a minority element among

the large heteromorphs at the base of the Upper Aptian (Upper Crioceras Beds,

martinioides Zone, debile subzone).

Genus Ammonitoceras Dumas 1876

Subgenus Ammonitoceras s.s.Ammonitoceras (Ammonitoceras) tovilense Crick

This species was diagnosed from a single specimen obtained from the Hythe Beds

of Tovil, near Maidstone, Kent (Crick, 1916). Despite the uniqueness of the

holotype and the uncertainty of its precise horizon, A. tovilense was chosen by

Spath (1923) as the index-fossil for a hypothetical subzone at the top of the "mar-tini" Zone and between the horizons of Tropaeum bowerbanki and Parahoplites nut-®eldienss. The discovery of a second example in a fallen block from the Upper

Crioceras Beds of Whale Chine, Chale Bay, con®rms the horizon of the species as

martinioides Zone, debile Subzone and gives credence to Spath's intuition. This

second example is more coarsely ribbed than the holotype, though displaying the

characteristic features of the species, especially the massive expansion of the

body-chamber, less clearly seen in Crick's original.

Subgenus Epancyloceras Spath 1930

Ammonitoceras (E.) hythense (Spath), the type-species of Epancyloceras, was based

on a malformed juvenile of a giant ancyloceratoid heteromorph, taken to represent

the root stock of Ammonitoceras (Casey, 1962, pp. 58, 62). Following Kakabadze

(1981), Epancyloceras is now accepted as a subgenus of Ammonitoceras, which dif-

fers only in its criocone coiling. It thus parallels the contemporary Proaustraliceras.The Lower Greensand record of Epancyloceras-Ammonitoceras s.s. lineage com-

mences in the deshayesi Zone and is then lost until the base of the martinioidesZone, where a sudden radiation of Ammonitoceras s.s. (A. sowerbyi Casey, A. rexCasey, A. tovilense Crick, etc.) takes place in the Upper Crioceras Beds.

Genus Tropaeum J. de C. Sowerby

Subgenus Tropaeum s.s.Tropaeum (Tropaeum) hillsii (J. de C. Sowerby)

The stratigraphical position of this long-established Lower Greensand ammonite

Observations on Lower Greensand in the Isle of Wight 529

is in need of review. In Spath's (1923) zonal scheme for the Aptian, based on the

literature and museum collections, T. hillsii was featured as the index-species for a

Subzone of the "martini" Zone below that of T. bowerbanki. Doubtless he was

in¯uenced by Fitton's (1847) oft-quoted record of the species from the Scaphites

Beds. Casey's (1960, p. 35; 1961a, p. 521) discovery of T. (T.) hillsii in situ in the

Hythe Beds of Kent below T. (T.) bowerbanki supported the view of Fitton and

Spath that the hooked T. (T.) hillsii preceded the incoiled T. (T.) bowerbanki. In

Casey's scheme of zonation T. (T.) hillsii was placed at the top of the deshayesiZone (grandis Subzone) and immediately below the bowerbanki Zone. We have

now substantiated Fitton's record by ®nding T. (T.) hillsii in bed 16 of the Sca-

phites Beds of Chale Bay. However, the unexpected occurrence of Dufrenoyiathroughout this bed has required the downwards extension of the bowerbanki

(=furcata) Zone to embrace this topmost part of the Scaphites Beds. Thus,

although T. (T.) hillsii pre-dates T. (T.) bowerbanki, in the revised zonal scheme

here proposed (Figure 2), it falls within the broad bowerbanki Zone and can no

longer be regarded as a guide fossil for the deshayesi Zone.

The discovery of T. (T.) pseudohillsi, the presumed descendant of T. (T.) hillsii,

at the base of the Upper Aptian, associated with other hooked ancyloceratids

(Casey, 1980), was even more unexpected, since large heteromorphs of ancylocer-

atoid coiling were at that time known in the Lower Greensand only from well

down in the Lower Aptian; thence they can be traced through several lines of des-

cent to the criocone types exempli®ed by T. (T.) bowerbanki of the Lower Crio-

cers Beds (Casey, 1960, text-®g. 5). The gap between T. (T.) hillsii and T. (T.)pseudohillsi has now been closed by rare ®nds of the former species in the Lower

Crioceras Beds (M. I. Simpson collection) and, as we have shown, higher still in

the Walpen Clay and Sands. All this leads to the following conclusions:

1. The genus Tropaeum, probably derived from weakly tuberculated Australiceras

(Proaustraliceras) such as A. (P.) pingue Casey of the topmost deshayesi Zone,

appears no earlier than the base of the bowerbanki (=furcata) Zone. Its entry there-

fore provides a useful secondary marker for the bowerbanki Zone.

2. The re-coiling habit distinguished in several parallel lineages of Lower Green-

sand ancyloceratids was a trend only and was not manifest simultaneously in all

species-groups. In the case of Tropaeum, the primitive ancyloceratoid (hooked)

shape persisted alongside the more advance criocone (spiral) forms at least until

the beginning of the Late Aptian.

3. Evolution within the genus Tropaeum was remarkably rapid, the development

from an ancyloceratoid mode of coiling, as in T. (T.) hillsii, to a criocone mode,

as in T. (T.) bowerbanki, taking place within less than a subzone (bowerbankiZone, lower part of transitoria Subzone).

Tropaeum (Tropaeum) drewi Casey

This rare species was ®rst described from a few museum specimens from the

Hythe Beds of Hythe and Lympne, Kent, all in a bright green glauconitic matrix

found only in the topmost part of the formation in that area (upper part of bower-

banki Zone) (Casey, 1960, pp. 35±37). This horizon is now con®rmed by discov-

ery of a fragment of the species in bed 25.4 of the Walpen Clay and Sands

(meyendorf® Subzone) of Chale Bay. Conte (1994) has recorded T. drewi in

association with T. bowerbanki, Cheloniceras, Dufrenoyia and Toxoceratoides at the

top of the Lower Aptian in SE France. It also occurs in the remanie fauna at the

base of the Norfolk Carstone.

530 R. Casey et al.

The use of this species as a zonal index for the basal part of the Upper Aptian

(=basal Middle Aptian of Kemper, 1982) in NW Germany was criticised by

Casey (1980), who pointed out that none of the fragments from the so-called

drewi Zone attributed to this species by Kemper (1963, 1964) were convincing.

Kemper's specimens were originally described as Tropaeum drewi drewi, T. drewitenuinodosum, T. drewi spinosum and T. loegteri (Kemper, 1964). Speci®c rank was

subsequently accorded the subspecies tenuinodosum and spinosum (Kemper,

1976).

A suite of "Tropaeum" collected from the Schneerman pits near Ochtrup by H.

M. Bayliss con®rm that in the reniform whorl-section, style of sculpture and poly-

gyral coiling all these forms belong to a closely-knit group. The single lateral

tubercle of the inner whorls varies from large and septispinate (" T." spinosum) to

pimple-like nodes (" T." tenuinodosum), reduced in some specimens to near-van-

ishing point. In " T." loegteri, based on large whorl-fragments, the presence of the

lateral tubercle is indicated in the whorl-section (Kemper, 1964, p. 61, ®g. 7a, pl.

13, ®g. 1b). The illustrations of " T. drewi" show only untuberculated outer

whorl-fragments, which are here regarded as speci®cally indeterminate.

There is a remarkable similarity in morphology between the inner whorls of the

tenuinodosum-spinosum group and the monotypic genus Cicatrites, whose range is

said to extend from the Lower to the Upper Aptian (Wright, 1996, p. 234). The

type-species, Lytoceras (Cicatrites) abichi Anthula (1899, pl. vii, ®gs 6a±c) from the

Aptian of the Caucasus, is a phragmocone of 75 mm diameter with ¯at spine-

bases similar to those of " T." spinosum. Cicatrites, however, is very poorly known;

the isolated ®nds in the Caucasus and France do not tell us whether the adult

produced a coarsely ribbed Tropaeum-like outer whorl as in " T." tenuinodosumand allies. Moreover, the distinctive suture-line of C. abichi, depicted as having a

shallow bi®d lateral lobe (L), cannot be demonstrated in the German forms. Until

the adult characters of C. abichi are made known and the details of the suture-line

con®rmed, the generic af®nities of these German "Tropaeum" cannot be settled.

For the present, " T." tenuinodosum, " T." spinosum and " T." loegteri are placed in

Cicatrites with question. The wider problems of the systematic position and origin

of Cicatrites and the Cicatritidae are commented on by Wright (1996, p. 233).

Superfamily Douvilleicerataceae

Family Douvilleiceratidae

Subfamily Roloboceratinae

Genus Megatyloceras Humphrey 1949

Megatyloceras transiens (Casey)

Megatyloceras transiens was based on a specimen from the Argiles aÁ Plicatules of

Gurgy (Yonne), France, septate at 155 mm diameter (Casey, 1961, p. 182; text

®g. 56). On account of its outer whorl resembling that of Roloboceras hambrovi(Forbes), the species was believed to be only transitional to Megatyloceras and was

referred originally to Roloboceras with question. Examination of large Megatylocerasfrom the Lower Aptian of Georgia, including M. coronatum (RouchadzeÂ), the

type-species of the genus, held in the museum of the Geological Institute of the

Georgian Academy of Sciences, in Tbilisi, Republic of Georgia, suggest that all

species of the genus revert to a Roloboceras whorl-shape and style of sculpture at

large diameters.

A large eroded fragment of the "hambrovi" stage of M. transiens or an allied

form was collected in situ from the Upper Lobster Beds (base of bed 8) of Ather-

Observations on Lower Greensand in the Isle of Wight 531

®eld. It is a clay-ironstone steinkern with calcitic and pyritic patches, deeply worn

at the sutures at the adoral end. Epizoa adhere to the dorsal surface. These pre-

servational features are matched in the holotype of M. vastum Casey, now thought

to have originated in the same bed.

Megatyloceras ricordeanum (d'Orbigny)

This species is probably represented among the pyritic Megatyloceras nuclei of bed

10 of the Upper Lobster Beds, too small for positive identi®cation. Conversely, a

cementstone body-chamber of an ammonite of about 100 mm diameter from the

top of bed 7 is the largest example of M. ricordeanum known to the writer (RC).

Its discovery strengthens the link between the Upper Lobster Beds and the Argiles

aÁ Plicatules of the Paris Basin, hitherto the only recorded source of the species.

Subfamily Cheloniceratinae

Genus Cheloniceras Hyatt 1903

Cheloniceras impar Casey

Hitherto this form has been known only from phragmocones and was originally

described as a variety (subspecies) of Ch. crassum Spath (Casey, 1961, p. 209).

This specimen shows that the large lateral bosses (spine-bases) of the internal

mould correspond in position to exceptionally long spines that were non-septate

near the mouth-border.

Genus Epicheloniceras Casey 1954

This taxon was proposed as a subgenus for those species of Cheloniceras exhibiting

ventral tubercles at some stage of growth (type-species E. martinioides Casey sp.)

(Casey, 1954). Although the appearance of Epicheloniceras in the stratigraphical

column can no longer be taken to de®ne precisely the base of the Upper Aptian,

the genus is nevertheless of great biochronological signi®cance, characterising the

lower part of this substage almost universally. Nowadays, Epicheloniceras is treated

as a genus by most specialists working on the Aptian, especially in the Former

Soviet Union where it is particularly well represented (Drushchits et al., 1982).

The evolution of Epicheloniceras from Cheloniceras may be demonstrated clearly

in the Lower Greensand. Already in the Lower Crioceras Beds (transitoria Sub-

zone) species such as Ch. disparile Casey, with its angulated but untuberculated

venter, are shaping up to the Epicheloniceras condition. High in the following Wal-

pen Clay and Sands (meyendorf® Subzone) the Cheloniceras population contains a

small minority of individuals with more advanced Epicheloniceras traits; a few such

border-line Cheloniceras occur at the bottom of the Upper Crioceras Beds (debileSubzone) among a dominantly Epicheloniceras assemblage. Fully developed Epiche-loniceras is known as a rarity in the upper half of the meyendorf® Subzone

(Figure 6).

In contrast to the phased introduction of the genus in late bowerbanki times, the

upward range of Epicheloniceras is abruptly terminated in the Lower Greensand at

the top of the martinioides Zone. This phenomenon coincided with palaeogeogra-

phical changes and the entry of Parahoplites (nut®eldiensis Zone) and is re¯ected in

many other parts of the globe.

Superfamily Deshayesitaceae

Family Deshayesitidae

Subfamily Deshayesitinae

Genus Deshayesites Kazansky 1914

Deshayesites annelidus Casey

532 R. Casey et al.

Proposed originally as a variety (subspecies) of D. callidiscus Casey (Casey,

1964, p. 330), this taxon is now elevated to speci®c rank. It occurs throughout

the Upper Lobster Beds and is here introduced as the index-species for the top-

most subzone of the forbesi Zone in the Chale Bay sequence. New material, to be

illustrated later, shows that D. annelidus has a different ontogeny from that of D.callidiscus and appears to be more closely linked to its contemporary, D. planusCasey, adult examples of which were previously confused with D. callidiscus itself.

Deshayesites vectensis Spath (=D. wiltshirei Casey)

The holotype and paratype of D. vectensis were from old museum specimens

labelled no more precisely than "Lower Greensand, Blackgang" (Spath, 1930, p.

430). Owing to their poor condition, Casey (1964, p. 307) had little to say about

the species, virtually treating D. vectensis as a nomen dubium. Study of the abun-

dant new material shows that the type specimens, distorted and abraded as they

are, can be recognized as falling within the wide morphological spectrum of D.wiltshirei Casey (1964, p. 305). Spath's name D. vectensis has priority for this com-

mon species of the grandis Subzone, which in Chale Bay crops out on the shore

halfway between Ather®eld Point and Blackgang Chine.

Although D. wiltshirei Casey is now sunk in the synonymy of D. vectensis Spath,

it is quite distinct from D. pun®eldensis Spath, with which Owen (1996, p. 75)

would unite it. The last is a species of super®cially similar appearance known at

present only from the Lower Lobster Bed of Ather®eld (forbesi Zone, kiliani Sub-

zone). Not only are the two species isolated from each other stratigraphically, but

their morphological differences are clear-cut and consistent, extending to coiling,

whorl-shape and ribbing. Most important is the venter, damaged in the holotype

of D. pun®eldensis and incorrectly restored by Spath from another species (Casey,

1964, p. 340). That of the young D. vectensis is ¯at with a smooth median band,

found in all Deshayesites of the grandis Subzone. These characters foreshadow the

genus Dufrenoyia of the bowerbanki Zone and are absent in the more evolute D.pun®eldensis and all other Deshayesites of the forbesi Zone.

Acknowledgements

Raymond Casey recalls with nostalgia his golden years of Lower Greensand

research at Reading, made possible by Perce Allen.

We thank the following collectors, all resident in the Isle of Wight, for making

their private collections of Lower Greensand ammonites available for examin-

ation: Mr R. Downes, Mr M. Green, Mr P. Newton and Mr J. Winch. Dr W.

Dean and Mr M. Foster also loaned specimens for study. Professor J. Mutterlose

identi®ed belemnites relevant to our work and Dr N. Monks kindly executed the

computer graphics for Figures 2 and 6. RC acknowledges ®nancial support from

the Royal Society. He was able to see ammonites at the Geological Institute of the

Georgian Academy of Sciences, Tbilisi, through the good of®ces of the late

Academician A. Tsagarelli.

References

Anthula, D. J. 1899. UÈ ber die Kreidefossilien des Kaukasus mit einem allegemeinen Ueberblick uÈberdie Entwicklung der SedimentaÈrbildungen des Kaukasus. Beitraege zur Palaeontologie und GeologieOestrreich-Ungarns und des Orients 12, 55±160 (1±106), pls 2±14.

Observations on Lower Greensand in the Isle of Wight 533

Bogdanova, T. N. & Tovbina, S. Z. 1994. On development of the Aptian Ammonite zonal standardfor the Mediterranean region. GeÂologie Alpine MeÂmoire, Hors SeÂrie 20, 51±59.

Breistroffer, M. 1947. Sur les zones d'ammonites dans l'Albien de France et d'Angleterre. Travaux duLaboratoire de GeÂologie de la Faculte des Sciences de l'Universite de Grenoble 26, 17±104.

Casey, R. 1954. New genera and subgenera of Lower Cretaceous ammonites. Journal of the WashingtonAcademy of Sciences 44, 106±115.

Casey, R. 1960±80. A Monograph of the Ammonoidea of the Lower Greensand, parts 1±9. Palaeontogra-phical Society, London, xxxvi + 660 pp., 112 pls.

Casey, R. 1961a. The stratigraphical palaeontology of the Lower Greensand. Palaeontology 3, 487±621,pls 77±84.

ColleteÂ, C. 1995. L'Aptien. In La geÂologie du departement de l'Aube (ColleteÂ, C., Fricot, C.,Matrion, M., Tomasson, R. & Treffot, G.), pp. 45±46 (Association GeÂologique Auboise, Troyes).

Conte, G. 1994. La limite BeÂdoulien-Gargasien dans la coupe stratotypique de Cassis-La BeÂdoule(Bouches-du-RhoÃne, France). GeÂologie Alpine MeÂmoire, Hors SeÂrie 20, 321±326.

Corroy, G. 1925. Le Neocomien de la bordure orientale du bassin de Paris. Doctorate thesis, University ofNancy, 334 pp., 11 pls.

Crick, C. C. 1916. On Ammonitoceras tovilense from the Lower Greensand of Kent. Proceedings of theMalacological Society 12, 118±120, pl. 6.

Drushchits, V. V., Kvantaliani, I. V., Knorina, M. V. & Sharikadze, M. Z. Morphogenesis of the shellin the two ammonite genera Cheloniceras Hyatt and Epicheloniceras Casey (Ammonoidea, Cephalo-poda) Vestnik Moskovskogo Universiteta, Seriya 4, Geologia 3, 51±66. [In Russian]

Erba, E. 1996. The Aptian Stage. In Proceedings, Second International Symposium on CretaceousStage boundaries, Brussels, 8±16 September 1995 (eds Rawson, P. F., Dhondt, A. V., Hancock, J.M. & Kennedy, W. J.). Bulletin de l'Institut Royal des Sciences Naturelle de Belgique, Sciences de laTerre 66, supplement, 31±43.

Fitton, W. H. 1847. A stratigraphical account of the section from Ather®eld to Rocken End, on thesouth-west coast of the Isle of Wight. Quarterly Journal of the Geological Society of London 3, 289±328, pl. xii, folding table.

Ibbetson, L. L. B. & Forbes, E. 1845. On the section between Blackgang Chine and Ather®eld Point.Quarterly Journal of the Geological Society of London 1, 190±197.

Hancock, J. M. 1991. Ammonite scales for the Cretaceous System. Cretaceous Research 12, 259±291.Haq, B. U., Hardenbol, J. & Vail, P. R. 1987. Chronology of ¯uctuating sea levels since the Triassic.

Science 235, 1156±1167.Hoedemaeker, P. J. & Bulot, L. 1990. Preliminary ammonite zonation for the Lower Cretaceous of the

Mediterranean region: report. GeÂologie Alpine 66, 123±127.Jacob, C. 1907. EÂ tudes paleÂontologiques et stratigraphiques sur la partie moyenne des terrains creÂtaceÂs

dans les Alpes francËaises et les reÂgions voisines. Annales de l'Universite de Grenoble 19 (2), 221±534.

Kakabadze, M. V. 1981. Ancyloceratidae of the southern USSR and their stratigraphical signi®cance.Trudy Geologicheskii Institut, Akademiya Nauk Gruzinskoi SSR, issue 71, 195 pp., 22 pls. [In Rus-sian]

Kemper, E. 1963. Geologischer FuÈhrer durch die Graftschaft Bentheim und die angrenzenden Gebiete, 91pp. (Heimatverein der Grafschaft Bentheim, Nordhorn).

Kemper, E. 1964. Einege Cephalopoden aus dem Apt des westlichen Norddeutschland. Fortschritte inder Geologie von Rheinland und Westfalen 7, 31±66, 7 ®gs, 18 pls.

Kemper, E. 1976. Geologischer FuÈhrer durch die Graftschaft Bentheim und die angrenzenden Gebiete, 5thedition, 206 pp. (Heimatverein der Grafschaft Bentheim, Nordhorn-Bentheim).

Kemper, E. 1982. Zur Gliederung der Schichtenfolge Apt-Unter Alb. Geologisches Jahrbuch A 65, 21±33.

Kemper, E. 1995. Die Entfaltung der Ammoniten und die Meeresverbindungen im borealen Unter-und Mittel-Apt. Geologisches Jahrbuch A 141, 171±199, pls 1±8.

Lawson, J. D. 1981. Stability of stratigraphical nomenclature. Answers to a questionnaire. Newsletterson stratigraphy 10, 45±51.

Mikhailova, I. A. 1983. System and phylogeny of Cretaceous Ammonoidea, 280 pp., 2 pls (Nauka, Mos-cow). [In Russian]

Mutterlose, J. 1990. A belemnite scale for the Lower Cretaceous. Cretaceous Research 11, 1±15.Mutterlose, J. 1995. Stratigraphische Gliederung des Apt (Abb. 28). In Die Kreide in noÈrdlichen MuÈn-

sterland und im Westteil des NiedersaÈchsischen Beckens. ExkursionsfuÈhrer zur Gelandetagung der Sub-kommission fuÈ r Kreide-Stratigraphie 1995 (Mutterlose, J., Kaplan, U. & Hiss, M.). BochumerGeologische und Geotechnische Arbeiten 45, 72 pp.

Owen, H. G. 1996. Correspondence."Uppermost Wealden facies and Lower Greensand Group(Lower Cretaceous) in Dorset, southern England: correlation and palaeoenvironment" by Ruffell& Batten (1994) and "The Sandgate Formation of the M20 Motorway near Ashford, Kent and itscorrelation" by Ruffell & Owen (1995): reply. Proceedings of the Geologists' Association 107, 74±76.

Rawson, P. F. 1983. The Valanginian to Aptian stages. Current de®nitions and outstanding problems.Zitteliana 10, 493±500.

534 R. Casey et al.

Reid, C. & Strahan, A. 1889. The geology of the Isle of Wight (2nd edition). Memoirs of the GeologicalSurvey of Great Britain, 349 pp. (HMSO, London).

Roch, E . 1927. E tude stratigraphique et paleÂontologique de l'Aptien infeÂrieur de La BeÂdoule (preÁsCassis) (Bouches du RhoÃne). MeÂmoires de la SocieÂte GeÂologique de France, Nouvelle SeÂrie 4 (1), 1±37, pls 1±5.

Ruffell, A. H. & Garden, R. 1997. Tectonic controls on the variation in thickness and mineralogy ofpebble-beds in the Lower Greensand Group (Aptian-Albian) of the Isle of Wight, southern Eng-land. Proceedings of the Geologists' Association 108, 215±229.

Ruffell, A. H. & Wach, G. D. 1991. Sequence stratigraphic analysis of the Aptian-Albian LowerGreensand in southern England. Marine and Petroleum Geology 8, 341±353.

Salvador, A. (ed.) 1994. International Stratigraphic Guide. A guide to stratigraphic classi®cation, terminol-ogy and procedure. 2nd edition, 14 pp. (International Union of Geological Sciences and GeologicalSociety of America, Inc.).

Simpson, M. I. 1985. The stratigraphy of the Ather®eld Clay Formation (Lower Aptian, Lower Cre-taceous) at the type and other localities in southern England. Proceedings of the Geologists' Associ-ation 96, 23±45.

Spath, L. F. 1923. On the ammonite horizons of the Gault and contiguous deposits. Appendix II inSummary of Progress of the Geological Survey for 1922, 139±149.

Spath, L. F. 1930. On some ammonoidea from the Lower Greensand. Annals & Magazine of NaturalHistory, Series 10, 5, 417±464, pls 14±17.

Strombeck, A. von. 1861. UÈ ber den Gault und insebesondere die Gargasmergel im nordwestlichenDeutschland. Zeitschrift der Deutschen Geologische Gesellschaft 13, 20±63.

White, H. J. Osborne. 1921. A short account of the geology of the Isle of Wight. Memoirs of the Geologi-cal Survey of Great Britain, v + 219 pp., map (HMSO, London).

Wright, C. W. (with contributions by Callomon, J. H. & Howarth, M. K.) 1996. Treatise on invertebratepalaeontology. Part L, Mollusca 4 (revised), Volume 4: Cretaceous Ammonoidea, 362 pp. (GeologicalSociety of America, Inc., and University of Kansas, Boulder, Colorado & Lawrence, Kansas).

Observations on Lower Greensand in the Isle of Wight 535