A revision of the biostratigraphy of the Late Namurian-Early Westphaliansuccession of Westward Ho!, North Devon

R. M. C. Eagar* and Xu Lit

EAGAR, R. M. C. & XU L1, 1993. A revision of the biostrat igraphy of the Late Namurian-EarlyWestph alian succession of Westward Ho!, North Devon . Proceedings of the Geologists'Association , 104, 161-179. Newly discovered non-m arine bivalve bands and other fossiliferoushorizons, re-collection of some known horizons and re-examinat ion of museum material from aninland section covered over for many years are utilized to correlate the succession at WestwardHo!. A non-marine bivalve band at Westward Ho! is correlated with one in the late Namurian ofSouth Wales. The dated strata range from the late Namurian, very probably late RIc in Cycle 3 ofthe Bideford Group , to the lower part of the Communis Chronozone in Cycle 9, which includes theCornborough Sandstone and overlying 'Culm Bed'. The adjacent Greencliff Beds, which haveyielded a marine trace fossil, are briefly discussed and their structure is re-interpreted. They maypossibly be of an earlier age than the Bideford Group.

The Westward Ho! sequence , when compared with those of nearby Clovelly and Bude to thesouthwest, reveals strat igraphical gaps and lacks five black shale horizons with major goniat itebands . The possible significance of these differences in the Westward Ho! succession is briefly dis­cussed.

·23 High Bond End. Knaresborough, North Yorkshire HG5 9B7.t Rider-French Consulting, Cambridge, Ltd, Cambridge Science Park, Cambridge CB44GG.

1. INTRODUCTION

A summary of the Upper Carboniferous successionalong the north Devon coast southwest of Westward Ho!was given by Xu Li (1990). However, his results werepublished before we had completed our field work onthe coastal sections (Fig . 1) and before one of us(RMCE) had found collections made by InkermannRogers and others soon after the turn of the century.

The coastal sequence contains nine deltaic cycles withsparse faunas that overlie an unfo ssiliferous group ofvery dark mudstones and turbidites . It has been muchstudied and differently subdivided by several workers(Fig. 2). The British Geological Survey (Edmonds,Williams & Taylor, 1979) included the Westward Ho!Formation in the Crackington Formation, which isturbiditic in its type area to the south of the CulmSynclinorium and at Clovelly (Fig . 1), and ranges fromLate Namurian to the Amaliae marine band of West­phalian A (Langsettian). However, both on theevidence of goniatites collected to the south of thearea , as well as on sedimentological groups, theWestward Ho! Formation appears distinct.

The strata along the coast southwestward of West­ward Ho! are folded into upright open anticlines andsynclines with WNW-orientated axial traces with bothfaults and thrusts (De Raaf, Reading & Walker, 1965,fig. 2; Elliot , 1976 and see Fig. 10). In this paper wedescribe faunas and horizons in ascending sequencefrom the Mermaid's Pool Sandstone to the 'Culm Bed ',and refer also to the much disturbed pre viously un­fossiliferous Greencliff Beds, which outcrop adjacentto the 'Culm Bed',

2. COASTAL SEQUENCE BELOW THERALEIGH SANDSTONE

(a) Cycles 1 and 2

The top of the Mermaid's Pool Sandstone contains twoclosely spaced horizons of Arenicolites carbonarius , butthis horizon and the overlying darker shales of Cycle 1have failed to reveal further traces of fossils. Mudstonewith abundant Teichichnus (of the pattern shown inFig. 3a) immediately succeeds the top of the Rock NoseSandstone for just over a metre, being overlain by 2 mof mudstone with carbonate nodules yielding plantfragments . The Teichichnus band may represent anabandonment phase during basin transgression, whenfeeding worms mined the substrate horizontally as thesalinity changed from non-marine to marginally marineconditions (cf. suggestions of Chisholm , 1970 andJordan , 1985).

(b) Cycle 3, Teichichnus at 121 m and a shell bandat 129 m below the Raleigh Sandstone

XL found a further new band of Teichichnus, 30--50cmthick , in shaly mudstones on the foreshore 121m belowthe base of the Raleigh Sandstone (Fig . 3a) . This bandmay again represent a change in salinity of a similarnature to that of Cycle 2. Its horizon lies 7.7 m above athin 1em band of shells referred to juvenile or stuntedCarbonicola by Edmonds et al. (1979) and Xu Li (1990)and tentatively placed in the Late Namurian or EarlyWestphalian. At the locality , SS 4166 2869, Edmondset at. (1979) state that small Curvirimula cf. scotica

162 R. M, C. EAGAR AND XU LI

23 5

Barnstapl eor Bideford Bay

Clo vel/y

L _ _

I

24 0

Por I/ edge

-----_..

~~~

~ Cr ackin g ton For mat ion ~ Bud e Formati on

1'=-_-:/ Westw ard Ho! Formati on

"':::":.:(:::1 Greenc ti f t Bed s

• Goni ati te loca li ty

o Bid e tor d Fo rmat ion

Fig. 1. Geological sketch map of the west part of the northern limb of the Culm Trough (synclinorium) after Edmonds et at. (1979)and Xu Li (1990). The inset map shows the general area and some major dislocations. RQ: Roberts Quarry.

(R. Etheridge Jnr) was also collected from this horizon.Our examination of the 1em leaf of shells 129m belowthe base of the Raleigh Sandstone, and to 5 m below andabove the band, showed no trace of Curvirimula, whichwe found on higher horizons (see p. 166). However,further collection of this very thin band of bivalves, andthe cleaning of material already collected from it, hasrevealed internal moulds of small unusually thick shells.

All had deeply impressed oval anterior adductor scarswith sharply defined posterior margins forming 'ledges'in the moulds (Fig. 4g). An approximately round pit-likeaccessory scar lay dorsal to, and clearly separated fromthe adductor scar and is well seen, in slightly obliqueview, in the mould of the right valve shown in the samefigure. Both valves in Fig. 4g show the larger roundedposterior adductor scar lying towards the dorsal margin.

Fig.2. The succession in the Westward Ho! area. Cumulative thicknesses are given in metres. Numbers 1 to 9 indicate cyclothemsin the Bideford Group of Walker (1969). Star symbols indicate faunas which have been found recently, mostly by Xu Li andcollected by the authors. Identifications and stratigraphical conclusions have been made by Eagar and include some reviseddeterminations of earlier collected material, shown without stars, made by Inkermann Rogers, E. A. Newell Arber, BrianSimpson and the British Geological Survey - Edmonds et at., 1979). The major sandstones are stippled and turbidites in theWestward Ho! area are shown by the dots-above-line graded symbol. RQ: Roberts Quarry.

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E'"s:en....-o.D.D

-c

E'"s:en.....o.D..c«

en"1:1

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Cur virim ufa cf. scotica. ct.tessella la,cf.belg/ca,C sanov,

t eictuc hnusct.Sanguin o/ltes HindCu rvirimu!e ct.scotic e

Gastrioceras amaliaeCarbon/cola (C . ext/rna

group? )

" -<OTT

600~

3

CYCLES

Late R,c - - - - - - - -

I

.~~::JEE J;l 'Culm Bed '8 Torus Faunal Belt 9 { 1200m ;:.!:!;;;?};;i; Comborough Sandstone

I-----Carbo nicola torus R.a.

- - - - -- - - -{----; ~':""...-< L~u~~:~Ie;,~/:,t%~'~d, tesa $ .. T. r ~ ( Cetbontcote aff. extenuete

- - C. prox im e, C. cnspe ,

(

C all.pontif ex

7

.C.afl .exlenuala.C. proxima,ca Proxima c.crisoe. C.all.pontilex

tii FaunalU Belt

~ { IOOOm.- 6

§ A~I;"'MB-- -:r---'·~~¥!]

1 [ ....."..carbon/cola bellula-Iemsulcata-------- 1.1_ --- -1 '. -:',Te/chichnus'/ Ophthalmldium

::'::; 1 , ':· ·>"'': ~·: Raleigh Sandstone

-.:'-< C~a~:':};~~;V:f~~hf~:~n~~z~ ta.',< Cb.bellula,Curvirimula ct.I be/g;ca, C.cf.scollca

i." '{

Chronozones

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Patio Pool Sandstone

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fu-u-uJ Arenic olites

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\) 1"'I;ol;b,;.""".",400m Mermaid's Pool Sandstone

B Teictucn rur s

600ml=~;zJ

164 R . M . C. E A G A R AND XV LI

(a)

(b)

Fig.3. Vertic al sections of bands of Teichichnus in the Bideford Group, Westward Ho! . The bar is 1cm long . (a) Fabric of wall-likesprei te in mudstones 121 m below the base of the Raleigh Sandstone on the foreshore south of Westward Ho! at SS 4163 2861.(b) Teichichnu s preserved in interbedded fine-grained sandstones and mudstones which show a compl ete burrow which pinchesinto a vertical tube (bottom right ). From 60 m below the base of the Corn borough Sand stone in Cycle 8. Foreshore at AbbotshamCliff, S5 4047 2730.

On this internal evidence the shells, which are trans­versely oval (Fig. 4h, i) cannot belong to the genusCarbonicola. However , an identical pattern of adductorimpressions has been descr ibed from abundant materialin two faunas lying immedi ately below Bilinguitesgracilis (Bisat) and 'late gracilis' (late R Ic Kinder­scoutian) in Co. Limerick, Ireland and in Sabden Brook,Whalley, Lancashire (Eagar, 1977, pI. 2, figs 21, 23, 27;pI. 3, figs 39, 41-43) . The shells of both these faunas,which proved marginally marine through their associ­ation with Modiolus sp., were provisionally placed in thegenus Sanguinolites Hind non M'Coy. These faunas,

with very distinctive internal shell features and anexceptionally wide range of external variation, havebeen found at no other horizon . In the same paper,Eagar adduced evidence that the faunas represented atransient stage in the evolution of Carbonicola froma shallow-water marine bivalve stock, and that theinternal features of Carbonicola reached its establishedpattern of musculature in the deltaic invading faunas ofmiddle R2b age of the Pennines (Eagar , 1977, pI. 2, figs28-31), The small Westward Ho! shells lie within theplotted dimensional range of external variation of theRIc faunas (Eagar, 1977, fig. 49) and compare most

A REVISION OF THE BIOSTRATIGRAPHY OF TH E LATE N A M U R I AN- E A R L Y WESTPHALI AN 165

a

d

b

e

c

9

h

Fig. 4. (a-f) . Curvirimula from the middle part of Cycle 3 of the Bideford Group (all the shells are x 4): (a) C. sp. nov. d.e. tessellata (Jones), an oval variety with large HIL ratio; (b) C. sp., a variety between (d) and (e); (c) Curvirimula sp. nov .,a semicircular variety-see also Fig. 5d; (d) e.cf. scotica (R. Etheridge Jr) -see also Fig. Sa; (e) e. sp. (e.cf. scotica-ci . tessellatagroup) shown in mirror image as Fig. 5b; (f) C. cf. scotica . (a), (d) , (e) and (f) from 82 m below the base of the Raleigh Sandstoneat 55 4158 2864. (b) and (c) at 43 m below the base of the Raleigh Sandstone, at S5 4104 4277.(g)-(i) . cf. Sanguinolites Hind non M'Coy, from 129m below the base of the Raleigh Sandstone at 554166 2869: (g) internal mouldof widely open valves (at c. 160") x 5.35; (h) (x 2.1) for comparison with Eagar 1977, fig. 48a, No. 45; (i) (x 2.1) cf. Eagar, 1977,fig. 48a , No . 51.Shells (a)-(i): BGS DEB 6943B, LZB 5020, 5019B, DEB 6950B, 6948, 6950A, LZB 5024, DEB 6957A, 6958.

nearly with the Whalley faunas (Table 1) which arepreserved in comparable slightly silty mudstone .

The outlines of the Westward Ho! sheIls may beplaced on the pictographs of the cf. Sanguinolites faunas

of Whalle y, those of Figs 4h and i lying between thenorm of the Whalley pictograph (Eagar, 1977, fig. 48a,No 1) and the shells of its Series I, for example Nos 45and 49, respectively. The few available Westward Ho!

166 R . M . C. EAGAR AND XU LI

Table 1. Measurements of assemblages of cf. Sanguinolites from Whalley, Lancashire and from Westward Ho!

Length (L) in mm HeightJIength (HIL ) % Anteriorendllength (AIL) %

OR Mean OR Mean OR Mean

Whalley 8.1-45.0 21.07 43.6--64.8 53.24 17.6-29.4 22.99N 131 98 59

Westward Do! 9.8-14.0 12.85 45.2-48.0 46.27 15.4-27.0 21.37N 5 3 3

OR is the observed range and N is the number of shells measured.

shells have in general a slightly larger angle of posteriortaper in lateral outline and a more curved ventral marginthan is typical of the Whalley faunas .

(c) Correlation of the shell band 129 m below theRaleigh Sandstone

In summary, the Westward Ho! fauna is attributed to cf.Sanguinolites Hind non M'Coy and is closely similar to ,but considerably smaller than the fauna known from lateRIc in Ireland and Lancashire. Since the latter appearsto have been a transitory fauna in the evolution ofCarbonicola , known from no other horizon, we con­sider that the Westward Ho! band is of marginally orrestricted marine origin and should be dated also as lateRIc'

(d) Shell band 82 m below the base of theRaleigh Sandstone

Edmonds et al. (1979) found a thin leaf of small sparseshells at SS 41582864, 82m below the Raleigh Sand­stone, and ascribed them to Curvirimula d . scotica.They are nearly all below the length of 5 mm (Table 2)and in addition to C. cf. scotica (Figs 4d, 5a) includevarieties with decreasing angle y (for measurementssee Fig. 6T). The latter trend, with the retention ofobliquely oval outline, leads to forms just comparablewith C. tessel/ata (Jones) but with less posterior expan­sion than characterizes this species (Figs 4b, e, a). More­over, the Westward Ho! shells are very much smallerthan C. scotica and C. tessel/ata (Fig. 5, Equation i inset ,and Table 2).

No comparable faunas are known from any West-

phalian or British Late Namurian strata. Curvirimulawith a trend towards C. scotica from the Scottish LowerCarboniferous had significantly greater HILand AILratios at comparable lengths (Fig. 5 shows wlm ratiosonly). The fauna , however, does show limited resem­blance to the smaller of two groups of Curvirimula illus­trated by Pastiels (1960, pl. II) from the SippenakenZone of Belgium , N2a , that is over the interval H2-R2 b

(Alportian to Mid-Marsdenian) in which horizons of thefigured specimens have not been further differentiated.Plotting shows that there is no significant difference inthe values of L , H and A between Pastiels ' small-shellgroup from the Sippenaken Zone and the shells fromWestward Ho!; but the former has significantly lowermean wlm ratio (Fig. 5, Equations ii and iii) and a lowermean angle y (48°30'). In lateral view the Belgian formstend to have a narrower, more pointed postero-ventralcurvature than those of Westward Ho! (e .g. Deleers &Pastiels , 1947, pI. A, figs21, 22; Pastiels, 1960, pl. II , figs6,7).

In summary the Curvirimula band 82m below thebase of the Raleigh Sandstone has features which areunknown in the British Late Namurian (R 2-GI ) andin the Westphalian. The fauna compares broadly withmiddle Namurian (H 2- R 2b) Curvirimula from Belgium,but is also distinguishable from the latter.

(e) Shells from 43 m below the base of theRaleigh Sandstone

We found a limited exposure of 15ernof dark shale withpoorly preserved Curvirimula overlying a thin pyritizedPlanolites band at SS 4104 2777, a horizon about 43m

Table 2. Measurements of Curvirimula from 82 m below the Raleigh Sandstone

RangeMeanN

Length (L) in mm

5.2-3 .64.42

12

HIL %

86.Q--60.167 .86

10

AIL %

29.5-21.725.89

7

wlm %

89.2-66.082.03

9

y

52-61°56.55°

9

A REVISION OF THE BIO STRATIGRAPH Y OF TH E LATE NAMURIAN- EARLY W ESTPHALIAN 167

•

•

•

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• Cur vin mu la sc otica ( A.Ether idge ,]r. ) and relatedfor ms from the Low er Ca rbo n ife rous of Sco tland

o Cet.sconce -cs.iesseusie (Jones ) from 82 m belowth e base af t he Rale igh Sano st one.was twa rd Ho!

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6 Curv irima ts so. ( rom the Sippenaken Zon e (H2 - R2b)in Belgium. fi gu red by Pastrets (1960)

EQ. i w .::: O·849 m - O-025 wh en N= 12 and r=: 0 ·9 5

EO. ii w ;:: Q·517m . ,·1 4 4 .. N = 9 " t c: 0 -39

Eq. ii i w .::::; O'S36 m -0892 " N .::l 0 " f :.:: 0 -25

•m in mm1086'-----~-----'-----.L-_---'-----'--------'-----'----___l~4

Fig. S. Width (w) plotted against maximum line of growth (m) of Curvirimula from two bands in Cycle 3 of the Bideford Group atWestward Ho! for comparison with Curvirimula on other horizons elsewhere. Inset: (a) is also shown as Fig. 4d ; (b) is a mirrorimage of Fig. 4e; (c) is Curvirimula cf. tessellata (Jones ) , from 82 m below the Raleigh Sandstone, DEB 6950A; (d) is also shown asFig.4c.

below the base of the Raleigh Sandstone. The faunaconsists of two apparently distinct species , the first beingof the C. d. scotica-ei . tessellata group of the precedingCurvirimula band, but with the addition of a newhitherto unrecorded trend towards semicircular form(Fig. 4b, c; Fig. 5d) . The second species include s moreelongate shells with relatively longer hinge lines andappears to belong to the Curvirimula belgica (Hind)group, such as is well known on Late Namurian (R2- G 1)

horizons (Weir, 1960).

(f) Faunas to 7 m below the base of theRaleigh Sandstone

Grey silty shales to fine-gra ined sandstones c. 7 m belowthe base of the Raleigh Sandstone yielded a singlespecimen of the arthropod Pygocephalus dub ius at

SS 4101 2774. Finer-grained silty grey mudstonesimmediately underlie the Raleigh Sandstone in the samelocality where we found two thin shell bands (Fig . 6,A , B) , 1.10m and 0.46m below the base of the sand­stone. Both shell bands are underlain by Pelecypodi­chnus rising shafts and bivalve trail s, with Planolitesat slightly greater depths below Band A .

In Band A extremely small widely varying shells of theCarbonicola bellula (Bolton) group (Fig. 71'-8) arepreceded by , and intermingled with, C. cf. scotica andC. d . belgica (d. Weir, 1960, pI. XXXIII , fig. 33 andPastiels , 1960, pI. III fig. 6) . Th e C. scotica group , whichappears distinct, includes shells which are a little largerthan those described here on lower horizons (Fig . 7T) ,a few trending to semicircular outline (cf. Fig. 5d) .

In Band B, shells are dominantly of small Carbonicolaaff. lenicurvata Trueman (Fig. 7, series A-H, A-I , A-e)

168 R. M. C. EAGAR AND XU LI

- 10 em

30em

__.20 em

o

SCALE OF SECTION

Section atSS 4100 2775,

AbbotshamCliff

40 cm

-n•Raleigh Sandstone, 4cm in 5m

Barren grey shaly mudstone

1I

Band of evenly distributed small shells of the g roup of Cerbonicole lenicurvata-pseudecute, with occasional Naiadites

Petecvpooictinus rising shafts with shells of Carbonico/a commonly in steeplyto vertical position in finely laminated silty mudstone. Uncommon Naiadites

occurs in the top two centimetres of the bed

Barren grey shaly mudstone

Very small shells of the Cerbonico!e bel/uta group with Curvirimula at the base---_._.__ ..

3-4 mm band of plant debris, and with Petecvpodicnnus

Grey shaly and silty mudstones with Peiecvpoaicnnus rising shafts, plants,occasional meandering bivalve trails and uncommon Planolites trails

- - - - - ------ - - - - - - - - - - - - - - - - - - - - -Plenolites: trails become common towaros the base of this bed

Surface heavily scored by traces including those of bivalves

Peiecvooaictinus verv abundant, bivalve trails and Cocnttcnnus

Silty and shaly grey mudstones in which Pelecypodichnus and Planolitesare present but uncommon

'"Silty and shaly mudstoneswit asi n

r{li9htry di'~"'o:,"" b", 01 th,

I• 46 cmI

I I h occ 0 al PlanolitesI c.70 em and bioturbation c.lO cm.

l~ ----------- l~

Band A

Band B

Fig.6. Newly discovered bands of non-marine bivalves and underlying trace fossils from 0.46-1,86 m below the base of the RaleighSandstone,

with a marked trend towards small Carbonicolapseudacuta Trueman (Fig. 7E, G). The band includesoccasional Naiadites hibernicus Eagar.

Shell growth and comparisons with other faunasThe Carbonicola faunas of Bands A and B are distin­guishable by the pattern of growth of Hand L. For the

C. bellula group (Fig, 8a) the fitted line, by the methodof Imbrie (1956) is

H = 0.463 L + 0.227 (iv)

where L ranges from 2-9 mm, N = 25 and r = 0,90.For the Carbonicola aff. lenicurvata group

H = 0.545 L - 1.765 (v)

A R E VISIO N OF TH E BI O STRA TIGRAPHY O F T H E LATE N AMU R IA N-EA R L Y WESTPHALIAN 169

~-, ~

/

F

o

",- .......

~~~

/

o·Scale in em

2

Fig. 7. Shells of small, highly variable Carbonicola from below the Raleigh Sandstone, arranged as pictographs. A-I: C. aff.lenicurvata, including a trend towards C. pseudacuta (G , E), from Band B, Fig. 6; I'-5: C. bel/ula group, from Band A; T: Curvi­rimula aft . belgica from Band A showing directions of measurement used in this pape r. See also Fig. Sa.(A-E) in order BGS LZB 5016, 5018, 5012, SOlS, 5014; (F) M.M. L.10247; (G , H) BGS LZB 5017, 5010; (I) M.M. LL.10249.(A , B, D, H, I) reversed images. (I'-M) in order BGS LZB 5003, 5004, 5001, 5002B, M.M. L.10250, BGS LZB 5008, 5006, 5007,5009, 5002A , 5005A. (K, N, Q , R , S) reversed images. (T) BGS LZB 5005A.

170 R. M. C. EAGAR AND XU LI

where L ranges from 12-21 mm, N = 19 and r = 0.91.When comparison is made between this fauna and thatof C. bel/ula and C. exporrecta Eagar of G1b below theSubcrenatum marine band, at Up Holland, Lancashire(Eagar, 1952), the Westward Ho! larger shells differwidely from those of Up Holland in both proportionsand growth pattern (Eagar, 1952, figs 5, 8-10). How­ever, the C. bel/ula at Westward HoI, with its pre­ponderance of very small shells with large H/L ratios,appears similar to that of Up Holland although itsmaximum size is a fraction of the maximum size of thelatter (35 mm). Since measurement suggests that thegreatest difference between the two groups of C. bel/ulaoccurs amongst the smallest shells, the latter werechosen for comparison with Up Holland. They give theline

when L is between 2 and 6 mm, N = 17 and r = 0.91.This line, shown in Fig. 8(a), is steeper than that ofEquation (v) for Westward HoI, but by the z test is notsignificantly different from it either in slope or displace­ment. Lines fitted for A and L are also insignificantlydifferent for the two C. bel/ula faunas. These results,obtained by using linear values of dimensions, carry thecorollary that they are applicable also when logarithmsare used. Thus the C. bel/ula group of Band A ofWestward Ho! dimensionally fits the log-log equationfound for the C. bel/ula group at Up Holland (Eagar,1952), but the Westward Ho! shells were much smaller.

Comparison of the faunas of Bands A and B has alsobeen made with those of Carbonicola collected byRMCE from midway between the Cancel/oceras cancel­latum and C. cumbriense marine bands near CefnRhigos, Vale of Neath, South Wales, 80km to the north­east of Westward Ho!. A strongly developed shell bandyielding Carbonicola cf. bel/ula and C. lenicurvata haslong been known in the region of the Sychryd Valley,14 km west of Merthyr Tydfil (Ware, 1939; Jones &Owen, 1956; Owen, 1974) and in the Merthyr district(Barclay, Taylor & Thomas, 1988). Carbonicola faunasbetween these marine bands have also been recorded inYorkshire and Ireland (see Appendix).

The South Wales band was collected in 1965from thebank ofthe River Sychryd, below the former railway lineat SN 9257 0713, 0.9km ENE of the cross roads at CefnRhigos, 3 km ENE of Pont Walby, Glynneath. Shells ofthe Carbonicola lenicurvata group are abundant through1.3 m of carbonaceous slightly silty mudstone with thincarbonate bands. A smaller representation of theC. bel/ula group, which were mingled with the largershells in the lower central part of the band, proveddimensionally separable from them (Fig. 8a). For theC. bel/ula group

H = 0.465 L + 0.217 (vii)

whereL lies between 1.6and 9.1mm, N =7 and r =0.98.This line, statistically identical with Equation (iv) for the

H = 0.539 L - 0.021 (vi)

C. bel/ula group from Westward HoI, is so close to it thatit cannot be represented as a separate line on Fig. 8a.

For the Carbonicola lenicurvata-pseudacuta fromnear Cefn Rhigos

H = 0.497 L - 0.885 (viii)

where L lies between 11 and 39mm, N = 53 andr = 0.95.The line of Equation (viii) does not differ significantlyfrom that of Equation (v), for the C. aff. lenicurvata­pseudacuta group from Westward Ho!. Over the lengthof 12-20 mm, the dimensions of Hand L form a singlepath. However, the shells from near Cefn Rhigosreached considerably greater size (Fig. 8a), the meanlengths of the twqfaunas increasingfrom 15.8to 23.9mm.

The shells of the Westward Ho! and Cefn RhigosCarbonicola lenicurvata-pseudacuta group are arrangedin Figs 7 A-I and 8(b) A-G, where similar morpho­logical trends in the lateral outlines of the shells areplaced in the same directions from similar norms.Elongation with slightly curved, and appreciably curvedventral margins (Fig. 7 B, Hand D, I, respectively) ispresent in both faunas, but in the larger shells of CefnRhigos elongation appears less marked because severalof the larger shells grew with slightly increasing HILratios. Simple shortening (Figs 7 C, 8 (a) C) is similar inboth. Arching of the dorsum (Figs 7 F, 8 (b) F) occurs,less commonly, in both faunas. But the trend towardstapering of the posterior margins (Figs 7 E, 8 (b) E) ismore often accompanied by raising of the umbo andincreased H/L ratio in the larger Rhigos shells, as seen inFig. 8 (b) G (ct. Fig. 7 G). With further increase in sizethe same trend leads to C. pseudacuta (Fig. 8 (c), see theholotype of this species). Thus the main differences inthe two pictographs appear to result primarily fromincreased size (length) of the Cefn Rhigos shells whenthe two faunas show the same pattern of growth.Throughout both faunas (and in the fauna from Leeds ­see Appendix), high anterior lobes and gently curvedventral margins make these shells distinctive and readilyrecognizable.

Correlation of Bands (A) and (B)From the above dimensional and morphological data itis concluded that the two faunas of Bands A and B belowthe base of the Raleigh Sandstone, despite their smallsize, resemble the Cefn Rhigos faunas of Glamorgan,South Wales, with sufficient closeness to merit corre­lation of the two horizons. The age of Bands A and B is,therefore, G1a (Early Yeadonian), and their horizonconcluded to be between the Cancel/oceras cancel/a tumand cumbriense marine bands.

3. COASTAL SEQUENCE ABOVE THERALEIGH SANDSTONE

(a) Cycle 4 and its dating

The top of the Raleigh Sandstone is heavily penetrated

_ ......

;I>

"tT1<:(ji

iszo'Tl

itT1OJ

is~;I>-:ls";I>":I:-<o'Tl

-:l:I:tT1r';I>

~Z;I>s:c");~tT1;I>

"~:EtT1rJJ

~:I:;I>r');Z

*'

F

a

;~

..-----......r:" ,~:"-,...'-- )

a

aa a

g.. ...."0~~a

c

a

a

Near Cetn Rhigos

a~ a

0'" -- ~'-EQUation Viii

30

a

a

• C. tenicurvere-cseuoecute , Westward Ho!

o " ,near Cefn Rhigos

-e- C.ct. deeast

• C. bellula group, Westward Ho!

o " " ", near Cefn Rhigos

a

0 .......0 goa

a

+

aa

L in mm

a/~ IJ

aOJ 0

b

G O o , ~

~'".~:::J .~-.",:,---=A! -" ---.. 0,B /

~-- . -_\c-:--..~''''_

1-,''----,- )\. - ~-:: id)~~-=-./.-; ~ .~A

G _.==-~ / \.,~~'-. ~;)~.---=:: ~ ",~---'-.\~:--=-=--:~ \~- =- )E '-=... -~ C

a

~ 0,,~

a

20

J"

o

L In mm

---.*-. ~

-+

C. lenicurvata, nototvoe

4D

Roundhay Park, Leeds(c)

• C tenicurvete-osecaecute

30

., ././~

., ••~~;;:, o a •o o • .......y .• otJ 0

Equatian v •• • 7· ·a';..:-//,;~/ .

9---;·a /-?'

10

Scale of all the shells shewn in this figure

o 5 emI I

oo

o c.oettcte group

... C, ct.aeenei

20

Cerbamcots oseuaecute, norotvoe

/~~--.,.,':r '- ~\~------ /l,~.,-~y

~ --------

C orrune Trueman, Huddersfield

C. deansl Eagar, Bingley

c. oseoaec.ne Truman, Hudderatietd. Yorks

10

Symbols for the dimensions of holotypes

~;... ...-: ..., .... / ..

!f, •. ......-tr,.~"... . ,.... , .. 1-- .,. .-, .... ... .

O Eq XI -~., ', :",:":"~.. _. -+:: ..' •• • 1.. ;·.• .,'-6

' ...'.,,~.~~~ :.' t;0'--;' . -~C

aeons. hololype .: /.:., " C oettute group..... , /. ,---".-- 0 y/~Io ...." ......--:'0;'..

Eq)( ~ .... o;o ;

»<: Eq IX.'/,

"* Cerbontcote lenicurvata Trueman, Bingley,Yorks

*+-+

'0

20

25

15

H inmm

Equation vi •

Equation iv ~.. s-:<, ...-::.-----o.....~·.~~~~ ... ....~.;- .

o~~ •. Equation Vii

c

5

10

15

a

H inmm

Fig. 8. (a) The Carbonicola fauna below the Raleigh Sandstone, Westward Ho! (b) The Carbonicola fauna near Cefn Rhigos,Glynneath, South Wales; shells A-E and G are registered in order M.M. LL.10245, 10243, 10246, 10248, 10244, 10242, 10241;shells D and G are reversed images.

.....-.I.....

172 R . M . C. EAGAR AND XU LI

Table 3. Measurements of Carbonicola bellula-lenisulcatafrom a carbonate concretion in Cycle 4

by Teichichnus which extends to 10cm above it in dark­grey mudstone at SS 4150 2848. Slightly sinuous walls ofspreite structures with even thickness (ct . Fig. 3a) reach50 cm in length. We consider the origin of these struc­tures similar to those of the Teichichnus band above theRock Nose Sandstone. The mudstone is immediatelyoverlain by a 5 mm band of e. aff. belgica and lesscommon Ophthalmidium ophthalmoides (Jessen) .There follow 20 ernof dark-grey mudstone with irregularpyritic concretions and which is devoid of microfauna.Immediately overlying this last bed , dark , slightlymicaceous, shaly mudstone yields fairly abundantO. ophthalmoides for 2.5 m.

From our examination of the overlying mudstonesand silty mudstones of Cycle 4 (Fig. 2) we conclude thatthe carbonate concretion with a fauna of e. bellula­lenisulcata found fallen from supposedly '80 feet abovethe base of the Abbotsham Formation ' at the top ofCycle 4 (Reading, 1965) came from between the majorO. ophthalmoides band and the interbedded siltstoneand mudstone in the lower middle part of Cycle 4. Thefauna, which was described by Eagar and Calver inReading (1965 and see Table 3) is strikingly differentfrom those analysed from below the Raleigh Sandstonein Cycle 3.

The shells include e. bellula which reached fullsize, varieties comparable with , but smaller than ,e. lenisulcata and oval shells without posterior expan­sion such as occur in the faunas which immediatelyunderlie the Subcrenatum marine band of the Pennines(e .g. Eagar, 1953, pI. XII , figs 2,3, 'north' and 'south'series) . Similar shells have been found on the samehorizons in Ireland (Eagar, 1956b). However, the West­ward Ho! fauna includes several small , short varietiestrending towards the outline of Carbonicola pilleolumEagar (e .g. Oxford University Museum C.222 I F, H,R: II C, D , R - ct. Eagar, 1947, figs 8a, i, j) . Althoughthe general trend of the Westward Ho! fauna is charac­teristic of a basal Westphalian A one near the Sub­crenatum marine band, the latter cited varieties areunknown immediately beneath this horizon. However,the e. cf. pilleolum trend has been noted in a bandprobably a few metres above the Subcrenatum marineband near Goyts Moss, west Cheshire, where these shortshells were found with the same associates (Eagar,1956a, p. 332). In summary, the e. bellula-lenisulcatafauna suggests basal Westphalian strata such as is knownfrom just above the Subcrenatum marine band. The

RangeMeanN

L

3.4-15 .712.12

20

H/L %

35.5-53 .846.39

20

AIL %

12.7-24.226.62

13

thick band of O. ophthalmoides, which implies a majorbrackish-marine interlude with emphasis on marineregression (Calver, 1968), is thus the obvious represen­tative of the Subcrenatum marine band . Cycle 4, there­fore, probably represents the first cycle of WestphalianA. Thu s erosion beneath the Raleigh Sandstone isinferred to have removed the Cancelloceras cumbriensemarine band and adjacent strata attributable to late G l a

and early o., (Fig. 2).

(b) Cycles 5,6,7 and 8 and their dating

Cycle 5 bears no marine fossils and thus there is no traceof the Listeri marine band although the latter is stronglyrepresented in the Clovelly and Bude areas to the southand west (Edmonds et al., 1979). Bivalve trails,Pelecypodichnus escape shafts, plough marks (ct.Eagar, Okolo & Walters, 1983, fig. 4) and occasionaltracks comparable with Olivellites occur with un­common small Carbonicola, probably of the e. extimagroup, within the sandstone at the top of Cycle 5 atSS 4140 2838.

Within this succession the only evidence of marinestrata is a thin band with Gastrioceras amaliaeH . Schmidt 0.5 m from the base of Cycle 6, found by theBritish Geological Survey (Edmonds et al. , 1979; B. J.Williams, pers . comm.). Cycle 6 thus begins with theAmaliae marine band; but the remainder of the cycle,and Cycle 7, have proved to be unfossiliferous except atthe extreme top of the latter. Here , at SS 4075 2737,Abbotsham Cliff, a 15em band in grey mudstonebetween thin wave-rippled sandstone beds and lying1.65 m below the base of the top sandstone of the cyclecontains large Carbonicola extenuata Eagar and smallere. proxima Eagar, e. crispa Eagar and C. aff. pontifexEagar. The fauna is indistinguishable from that of thesame species in Cycle 8 (see below) .

Cycle 8 is present both at Cornborough Cliff (SS 41302821) and at Abbotsham Cliff (SS 4070 2733). Non­marine shells collected from the Abbotsham exposuresby Inkermann Rogers and Brian Simpson and figured bySimpson (1933) have not been traced; but M. A. Calverand R. M. C. Eagar (in Edmonds et al., 1979) agreedthat Simpson 's figures should be interpreted as charac­teristic of the Carbonicola proxima Faunal Belt. TheGeological Survey subsequently found e. proxima atAbbotsham Cliff (Edmonds et al., 1979, p. 47) . We alsorecord this species (Fig. 9f, g), C. crispa with a typicalmember of the e. crispa group (Figs 9j , k) andvarieties of the e. pontifex group (Fig. 9h, i) , the latterspecies being particularly characteristic of the SouthWales succession (Eagar, 1962). Representatives of thebiospecies e. extenuata found at Abbotsham Cliff showstriking similarity with the large e. aff. extenuata foundin the upper part of the e.proxima faunal belt at Eiland,Yorkshire (Eagar, 1956a, figs7a-e, 1975,p. 207, Bed 13).

A succeeding development of Teichichnus is pre­served in interbedded thin sandy and muddy strata and

A REVISION OF TH E BIOSTRATIGRAPHY OF THE LATE NAMURIAN-EARLY WESTPHALIAN 173

a b

9

..

eFig. 9. Non-marine shells from Cycles 8 and 9 of the Bideford Group. a-e: Carbonicola from below the Cornborough Sandstoneat Roberts Quarry, 1.3 km east of Bideford (Fig. 1), at natural size. (a) Carbonicola torus, (b) C. aff . torus; (c) C. sp. (c. communisgroup); (d ) C. ct. extenuata; (e) dorsal view of internal mould of Carbonicola showing unusually deep impressions of the anterioradductor and conjoined pedal scars . f-k : Carbonicola from 60 m below the top of Cycle 8. (f) C. proxima, x 0.47; (g) C. aff.proxima (ct . Eagar, 19560, fig. lOd, b), x 0.47; (h) C. aff, pontifex (ct. Anthracosia acutella Wright) , x 0.47; (i) C. aff. pontifex(ct . Eagar , 1962, text-fig. 11E), natural size; (j) C. crispa, x 0.44 ; (k) C. aff. crispa, x 0.44; (I) Naiadites sp. juv. (probably of theNi flexu osus group) from above the lowest anthracite band of the Culm Bed, Greencliff, x 1.7.Shells a--e in orderBMNH L.20415,20377 , 20417, 20381, 20416; f-I MM LL.I0252, BMNH L.20411a, EM IR.69, BMNHL.20403,MM LL.10253 , LL.10254 , LL.10255.

laminae (Fig. 3b), 3Q-40m above the base of Cycle 8.Teichichnus occurs in association with Pelecypodichnus,bivalve escape shafts and bivalve shells, the latter beingseen only near the top of the fossiliferous strata. Struc­tures identical to those seen in Fig. 3(b) have beenobserved by Bromley and Asgaard (Bromley, 1990, fig.5.3) on the beach of Kefallina, Greece, where the agentwas a small suspension feeding marine bivalve,Solecurtis strigillatus. Overlying the Teichichnus struc­tures Calver, in the British Geological Survey records,has recorded Curvirimula sp. , Naiadites sp. Lioestheriastriata Pruvost (non Munster) and Sp irorbis , attached toplants (BGS Coll. DEB 6995-7009) . Although thesefaunal associations including Teichichnus , suggest thepossibility of a slight increase in salinity within thesuccession (Eagar et al., 1992) , there is no evidence tosuggest a second cyclothem in the upper part of Cycle 8.

In summary, Cycles 6 to 8 provide a typical non­marine fauna through the Proxima Faunal Belt from theAmaliae marine band upward . The top marker of the

Lenisulcata Chronozone, the Langley marine band ofthe Pennine coalfields, which has its equivalents in theLeinster Coalfield of Ireland, South Wales and the RuhrCoalfield (Eagar, 1964; Calver, 1969), cannot beidentified in the Bideford succession . We have drawnthe boundary between the Lenisulcata and CommunisChronozones, therefore , at the top of the highest cyclecontaining the Carbonicola proxima fauna . When this isdone three cycles of the Bideford Group (numbers &-8)probably represent two cycles in the Leinster Coalfield(Eagar, 1964) and evidently one cycle in the Pen ninecoalfields .

(c) Cycle 9 at Abbotsham and the fauna belowthe Cornborough Sandstone at Roberts Quarry,near Bideford

Although Cycle 9 is well exposed at Greencliff we sawno fossils in the cliff, where collection is dangerous.In Roberts Quarry, 1.3 km east of Bideford (Fig. 1),

174 R. M. C. EAGAR AND XU LI

Simpson (1933) stated that the shells of Carbonicolawere found in a 'blue-grey soapy shale, about two feetthick' lying beneath the sandstone. In fact, the shalebeneath the sandstone may have been buried for somefifty years. We were unable to reach it. However,Simpson (1933) figured several shells from below theCornborough Sandstone, some of which were small andothers incomplete, with the result that neither Calvernor Eagar (in Edmonds et al., 1979) found Simpson'sfigures of them separable from those of the C. proxima­extenuata faunas. RMCE has since discovered 15 shellscollected in Roberts Quarry by Inkermann Rogers,possibly when the section was even better exposed, andpurchased by the Natural History Museum in 1907.Several well-preserved internal moulds are referable toCarbonicola torus Eagar (Fig. 9a, b) and to typicalvarieties of the C. torus Faunal Belt of the lowest part ofthe Communis Chronozone. Anterior muscle adductorscars were unusually deep (Fig. 9b, c, e). With this faunaare slightly smaller, more elongate shells comparablewith C. extenuata (Fig. 9d), several of which have beenalready illustrated in part in the 'lost' fauna described bySimpson (1933, pI. XXIII, figs 2,7,9). It may be signifi­cant that shells comparable with C. extenuata are notcharacteristic of the lower part of the CommunisChronozone in the UK except in S. Wales, where theyhave been recorded in the Pseudorobusta Faunal Belt(Barclay et al., 1989, p. 81).

From the site at Roberts Quarry and remarks bySimpson (1933) it appears that the C. torus fauna wasfound no more than 2-3 m below the erosive base of theCornborough Sandstone. A small but unknown thick­ness of sediment was, therefore, removed from the basalpart of the Communis Zone.

The overlying 'Culm Bed', is composite, probablycomprising three seams extending through some 8 m atGreen Cliff (Edmonds et al., 1979). The 'Bed' has beenmuch disturbed tectonically and by subsequent mining,and is separated from the top of the ComboroughSandstone by I-2m of black shale with Planolites sp.(Edmonds etal., 1979, pA7). Re-determination of eightspecies of plants from the abundant material collectedfrom the 'Culm Bed' and immediately above it by Arber(1904, 1907) and now in the Sedgwick Museum,Cambridge, has been made by B. A. Thomas and C. J.C1eal (pers. comm., 1992). They report that the plantsindicate a horizon no higher than the Langsettian(Westphalian A).

The record of Carbonicola acuta (J. Sowerby) fromthe 'Culm Bed' (Rogers, 1909, p. 315) has not been sub­stantiated. The specimen in the Natural HistoryMuseum so labelled by Rogers (L.20398) is not a bivalveand we were unable to obtain any anthracosiid shellsfrom this horizon. However, we found a single smallNaiadites (Fig. 91) in steeply dipping plant-richmudstone 30em above the lowest anthracite bed and

separated from it by a low-angle thrust (Fig. 10, sectionabove the old adit at Green Cliff). The shell has a lengthof 8.5 mm and thus may be a juvenile, possibly of theN. flexuosus Dix and Trueman group of the CommunisChronozone.

4. THE GREENCLIFF BEDS

The Greencliff Beds were named by Prentice (1960) toinclude the rocks outcropping at Green Cliff, south ofthe Comborough Sandstone, and north of the 'turbiditicsandstones' at Cockington Cliff (Fig. 1). They wereincluded in the Bude Formation by Edmonds et at.(1979). The Greencliff Beds were described by Prentice(1960) as characterized by slump structures, oneexample being specifically referred to by Burne &Moore (1971), who considered that the Greencliff Bedssucceeded the Bideford Group.

During this study one of us (XL) measured the coastalsection of the Greencliff Beds from Green Cliff to theircontact with the Cockington Beds, where there is afaulted (thrust) contact (Fig. 10). The beds have beenintensively faulted by fractures and thrusts parallel tothe bedding and compressed into tight folds. However,the section reveals no clear sedimentary sequences, noris there evidence of significant depositional slumpstructures. Some sediments have, however, been'tectonized' .

The Greencliff Beds consist predominantly of siltymudstones which have hitherto proved unfossiliferous(Edmonds et al., 1979). Burne & Moore (1977), how­ever, remark that they contain burrows on severalhorizons. We noted parallel-bedded siltstones alter­nating with wave ripple cross-laminated thin sandstonesnorth of a disused limekiln (SS 4066 2715) where'probable O. ophthalmoides' is distributed on surfaceswith an abundance of about one burrow per em". We aremuch indebted to Mr J. I. Chisholm who has reported ontwo collected slabs (MM LL. 10257, 10258). He findsthat the laminated bands, c. 5 mm siltstone layers, arenot graded either way but have diffuse contacts; and thatin these features they resemble the 'Grey SandstoneFacies' of Read, Dean & Cole (1971). Mr Chisholmdraws a further comparison with sediments in theGrindslow Shales below the Kinderscout Grit describedby Walker (1966, pp. 103-4, Facies G-K) and also inWestphalian A (Chisholm, 1990, p. 61). He regards thesediment as 'clearly something that forms below wavebase, perhaps from suspension clouds.'

Other considerations also influence our interpretationof the Greencliff Beds. The high vitrinite reflectancevalues of the Greencliff Beds, 3.8% as compared with2.8% for Cycle 9 of Bideford Formation (Cornford,Yarnell & Murchison, 1987), may well reflect theirdeeper and probably earlier origin than that of theBideford Group.

Fig. 10. Coastal section from Abbotsham Cliff southwestward showing the severely faulted Greencliff Beds and their contact withthe Crackington Formation of Cockington Cliff (see Fig. 1). From fig. 2.5 of Xu Li (1992).

~ Mudstone ~- Slump deposits

»

'"til<iii15zo"l]

itilo:lo~;ll»-la;0»."J:-<o'1l-l:ttilr"

~tilZ»~c:'")ZItil»'"~~[11

~:t)r"sZ

~NE

+{ ~

GREEN CLIFF

I 50 m I

CRACKINGTON FORMATION~ OF COCKINGTON CLIFF COCKINGTON CLIFFI" ~F ~ F ~~

>k %. Grass ~ Landslidescover

~ HCS ~ Strata younging direction

F

~ Wave ripples

--"-"'" Current ripples

LIMEKILN(Disused)

(554066 2716)

I

.0\

BOATLAKE

"(

Ootnnetmiaiumopntnetmokies

GREENCLIFF BEDS

1

=:=: Silty mudstone T'I:""I:" Coal &seat·carth

Ol.D AOIl

GREEN CLIFF

Cornborough Sandstone

ABBOTSHAM CLIFF

:=;-=;.;: Siltstone

:z= Sandstone

.....-...lV1

176 R . M. C . EAGAR AND X U LI

5. SUMMARY AND CONCLUSIONS ON THECORRELA nON OF THE WESTWARD HO!

SUCCESSION

The succession to the southwest of Westward Ho! ,excluding the Greencliff Beds , reaches a thickness ofabout 1240m and consists of shallow-water deltaicsediments. Its age, as determined almost entirely bynon-marine and restricted marine bivalves, is LateNamurian , late Ri c to Earl y Westph alian , earlyCommunis Zone . The lowest 340 m of the succession,including the Westward HoI Formation with turbidites ,is largely unfossiliferous and may be of middle to LateNamurian age.

The Westward Ho! succession contrasts with those ofnearby Clovelly and Bude (Fig. 1) which consist of up to1800m of deeper-water slope sediments comprisingturbidites, debrites, slump deposits and basinal mud­stones (Xu Li, 1992). The latter successions, shown inpart in Fig. 11, include six goniatite-bearing dark marineshales in the Crackington Formation, comprising in all,over 11m of typically widespread marine strata (Fig. 11,and see also the description of this figure) . The dis­appearance of the Cancelloceras cumbriense marineband at Westward Ho! may be the result of erosionbeneath the Raleigh Sandstone. However, the absence

of the band s of non-marine shells and of Teichichnus atClovelly and Bude doubtless reflects major differencesin depo sitional conditions within 15 km. Nevertheless,the loss of so much black shale at Westward Ho ! mightalso involve post-depositional tectonic factors . Furtherdata, including contrasting fault and fold patterns ,'anomalous' contiguous metamorphic grades and gaps inthe vitrinite reflectance values in the Westward Ho ! area(Cornford et al. , 1987) , is being prepared by one ofus (XL).

ACKNOWLEDGEMENTS

We thank first Dr Harold G. Reading who introduced usto the north Devon area. Michael Eagar reported to himon a non-marine bivalve fauna in 1964, and Xu Liworked under his supervision at Oxford from 1988 to1992. We are both grateful for his advice and criticism.

The British Geological Survey have been to muchtrouble on our behalf. Dr Hugh Ivirney-Cook kindlyarranged for Mr Tim P. Cullen to take excellent photo­graphs of material we collected from below the Rale ighSandstone and presented to the Geological SurveyMuseum, as well as of earlier collected GeologicalSurvey material, which we borrowed. Mr Ian Chisholm,

Metres Bideford' 400 area

Cornborough Sst.

LS _ LONG PEAK S HALEwith mar ine bivalves

Has _ HARTLAND OUA Y SHALEwith G.amalia e

GRS _ GULL ROCK S HALEwith G. tisteti

ES _ EMBURY SHA LEw ith G.subcrenatum

D PS _ DEER PA RK SHA LEProb ab le C.cumbriense horizon

SR S _ SKITTE RING ROCK SHALEProbab le C caflcella fum horizon

CCS _ CLOVE LLY COURT SHALEwith Vernu lli tes sigma

Ihe band 01small ct. Sang uinolitesis p lac ed i n la te Ric

~ Bideford Group

§ Westward HoI Fm

§ BUde Formation

~ Crackington Fm

~ Named sandstone

~ Named black shale

Z<t

Z<t

E S

GRS

Bude areaLower part ol the

succession

Clovellyarea

/""""""""II ~_I_'" L S

~~I-----~;;;;;;;;;;j ------1---...4 HasAmaliae M.B.

cf.Sanguinoli tes

Raleigh Sandstone

Mermaid 's PoolSandstone

Rack Nose Sst.

LowTideSst.

200

60 0

1000

Fig. 11. A summary of Namurian and Westphalian stratigraphy of Bideford area compared with that of Clovelly and of the lowerpart of the succession in the Bude area . The sequence at Bude extends to 1240m above the Amaliae marine band and contains fourmore black shale bands : Tom 's Cove Shale at 310 m above HQS; Saturday's Pit Shale 100m higher ; Sandy Mouth Shale withAnthracoceratoides cornubiensis Ramsbottom 650m above HQS ; and Warren Gutter Shale with Donetzoceras aegiranum(H . Schmidt) and Gastrioceras depressum Delepine in the Aegiranum marine band at c. 570m higher . Sections after Higgs,Read ing & Xu Li, 1991, fig. 2; data on goniatites from Freshney, Edmonds , Taylor & Williams (1979).

A REVISION OF TH E BIOSTRATIGRAPHY OF THE LATE NAMURIAN-EARLY WESTPHALIAN 177

In Great Heads Beck , Roundhay Park , Leeds , abun­dant well-preserved shells occur through 80 em of rustygrey , slightly silty mudstone which immediately underliethe C. cumbriense marine band (Slinger, 1936).Throughout, the mudstones shells collected throughnine thin intervals by the author show continuousvariation between C. pseudacuta (Fig . 8c, and topfigure) and C. lenicurvata (Fig . Be right) . They thusindicate a single biospecies for which

where L ranges from 16.8-49.0 mm, N = 105 andr = 0.97.Up to a length of37 mm this line is identical with that forC. lenicurvata-pseudacuta at Cefn Rhigos (Equationviii). Over this range of length the paths ofthe Land Hpoints for the Roundhay Park and Rhigos shells coverthe same area (but those of Roundhay Park are omittedfrom Fig. 8b to preserve clarity) . The mean length of thebiospeeies is 32.5 mm in Roundhay Park and 23.9 mm atCefn Rhigos.

Smaller shells referable to the C. bellula group (Fig .8e, bottom centre) separate clearly from the larger shellsat Roundhay Park and give the line

H = 0.433 L + 0.771 (x)

whereLrangesfrom9.7-24.1mm,N = 9andr = 0.98.This line is statistically identical with that of theC. bellula group from Cefn Rhigos over its short range ofL. However, the shells from Roundhay Park grew tomuch larger size, having a mean length of 17.4 mm, com­paring with a mean length of 7.1 mm for the Cefn Rhigosshells .

In summary, biometry shows that there is uniformityin the proportions and in the patterns of growth of thetwo biospecies C. lenicurvata-pseudacuta and C. ef.bellula in G la over the area of Leeds, mid-Yorkshire,Glynneath, South Wales, and Westward HoI, northDevon . Between these areas in order the size of bothspecies, as measured by length, decreased. There was awide overlap between the sizes of each locality, froma maximum at Leeds to a minimum at Westward Hol.C. lenicurvata-pseudacuta was more abundant than C.d. bellula in all three localities , but proportionatelynumbers of the latter increased in Westward Hal. Onthe basis of a small sample available from the LeinsterCoalfield the size of the C. bellula group was greatest inIreland. A broadly similar picture of palaeogeographicalvariation in the size of biospecies has been noted in thelater Carbonicola proxima Faunal Belt of the West­phalian (Eagar, 1962). The situation may have beencomparable with the distribution of living contemporaryfreshwater bivalve species in a large lake, for instance asdescribed by Stansbery (1961).

Eagar (1949) separated shells of the group Carboni­cola deansi Eagar-Carbonicola ornata Trueman (Fig .Sc, bottom left) from C. lenicur vata on a horizon 7.5­9.0m below the C. cancellatum marine band at Bingley,

Drs Nick J. Riley and Andy Howard kindly gaveopinions on material we collected, as did Dr John E.pollard of Manchester Un iversity on certain tracefossils. We are particularly grateful to Dr Brian J.Williams, formerly of the British Geological Survey,who allowed us to see identifications and reports madeby Dr Michael A. Calver and Dr Bill H . C. Ramsbottomin 1973. We arc also grateful to Dr Chris Cornford, ofHalsannery, Field Centre , Bideford, who lent us fieldequipment. In the search for earlier collected material,and for loans in several cases we have been helped byDr Muriel A. Arber, Mr Peter Boyd of BarnstapleMuseum, Dr Michael Bassett of the National Museumof Wales, Drs Jill Darrell and Noel Morris and Mr PaulJeffery of the Natural History Museum, Mr Brian Meloyof the Royal Albert Memorial Museum of Exeter,Dr David Norman and Mr Rod Long of the SedgwickMuseum, Cambridge, and Dr John Nudds of theManchester Museum .

Michael Eagar was introduced to the geology of theGlynneath area , South Wales by the late Dave G. Jonesin 1958, and gratefully acknowledges advice on subse­quently changed land surface features from Derek andRenee Ager and from Frank Cross of the GeographyDepartment, Swansea. Mervyn Walters of Glang­wrelech, Pont Walby, Glynneath, very kindly helpedwith local guidance.

STORAGE OF MATERIAL

Numbered specimens cited are housed in collectionsof the British Geological Survey (BGS), the NaturalHistory Museum (BMNH) , the Manchester Museum(MM), Oxford University Museum (OUM) and theRoyal Albert Memorial Museum, Exeter (EM).

APPENDIX: THE CARBONICOLA FAUNASBETWEEN THE CANCELLOCERAS

CANCELLATUM AND C. CUMBRIENSEMARINE BANDS (G l a) IN NORTHERN

ENGLAND AND IRELANDR. M. C. Eagar

Shells attributed to Carbonicola lenicurvata andC. pseudacuta have long been known from immediatelybeneath the Cancelloceras cumbriense marine band inthe Leeds-Huddersfield area (Slinger, 1936). A varietyintermediate between these species , from 2.5 m abovethe Cancellatum marine band in the Leicestershire Coal­field , was figured by Trueman & Weir (1948, pI. XIV,fig. 17). Both species have been described and illus­trated, with representatives of the C. bellula group, fromthe uppermost part of G 1a in the southern part of theLeinster Coalfield of Ireland, where they are separatedfrom the base of the C. cumbriense marine band by 8 mof sandstone or siltstone (Eagar, 1962; 1964, text-fig.2 A , C, D-F) . No biometrical work on these shells at anylocality has hitherto been published.

H = 0.585 L - 2.376 (ix)

178 R. M. C . EAGAR AND X U LI

25 km WNW of the centre of Leeds. A similar separationwas found in the Roundhay Park fauna where , for thegroup of C. deansi-ornata

H = 0.982 L - 8.150 (xi)

where L lies between 20.6 and 25.7 mm, N = 5 andr = 0.98.

The few available shells of the group differ fromC. lenicurvata also in having more elevated umbonesthan the latter. C. deansi-ornata is represented by twoshells only in the Cefn Rhigos fauna (MM LL.10258A,B)and there is no sign of this group in North Devon.

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