new information concerning the age of the beds immediately overlying the armorican quartzite in...

N E W I N F O R M A T I O N C O N C E R N I N G T H E A G E OF T H E BEDS I M M E D I A T E L Y

O V E R L Y I N G T H E A R M O R I C A N Q U A R T Z I T E IN C E N T R A L P O R T U G A L

by

MICHAEL ROMANO *, PATRICK J. BRENCHLEY ** & NEIL D. McDOUGALL **

ABSTRACT

Graptolitic and shelly faunas have been collected from the base of the Cacemes Formation, central Por- tugal. The assemblages occur to within about 10 cm of the top of the underlying Armorican Quartzite For- mation and indicate a Lower Llanvirn age. Prior to this record the basal beds of the Cacemes Formation were recently considered to be of Arenig age. The faunas are listed and the trilobites (Ogyginus cf. armoricanus, Neseuretus (Neseuretus) tristani tristani, Col- pocoryphe cf. thorali conjugens, Eodalmanitina sp.) and graptolites (Didymograptus (Didymograptus ?) cf. spinulosus, D. (D. ?) aft. spinulosus, D. (D. ?) cf. pseudogeminus) are figured. The significance of the faunas in terms of the age of the top of the Armorican Quartzite Formation is discussed.

RI~SUMI~

Graptolites et faunes benthiques ont 6t6 collection- n6s de la base de la Formation de Cacemes du Portu- gal Central. Les faunes se trouvent dans la basse partie de la Formation de Cacemes sauf les 10 cm inf~- rieurs, qui sont imm~diatement au-dessus de la For- mation du Gr~s Armoricain.

Ils d6notent le Llanvirn inf~rieur. Avant ce compte la base de la Formation de Cacemes a ~t6 suppos6e atre d'ftge Arenig. Nous avons dress6 une liste des faunes, et les trilobites et les graptolites suivants sont f igur6s: Ogyginus cf. armoricanus, Neseuretus (Neseuretus) tristani tristani, Colpocoryphe cf. thorali conjugens, Eodalmanitina sp. Didymograptus (Didymograptus ?) cf. spinulosus, D. (D. ?) aff. spinulosus, D. (D. ?) cf. pseudogeminus. Nous discutons de l ' importance des faunes pour la datation de la partie sup6rieure de la Formation du Gr6s Armoricain.

KEY-WORDS : TRILOBITES, GRAPTOLITES, ORDOVICIAN, ARENIG, LLANVIRN, ARMORICAN QUARTZITE FORMATION, CACEMES FORMATION, POSTOLONNEC FORMATION, TRAVEUSOT FORMATION, QUARTZITES, SHALES, PHOS- PHATIC BEDS, LINGULIDS, PORTUGAL (PENACOVA, RIO CEIRA), BRITTANY (CROZON PENINSULA, SOUTH OF RENNES).

MOTS-CLI~S : TRILOBITES, GRAPTOLITES, ORDOVICIEN, ARENIG, LLANVIRN, FORMATION DU GRt~S ARMORICAIN FORMATION DE CACEMES, FORMATION DE POSTOLONNEC, FORMATION DE TRAVEUSOT, QUARTZITES, SCHISTES, NIVEAUX PHOSPHATES, LINGULES, PORTUGAL (PENACOVA, RIO CEIRA), BRETAGNE (PRESQU'ILE DE CROZON, SUD DE RENNES).

* Department of Geology, Beaumont Building, University of Sheffield, Brook Hill, Sheffield $3 7HF, England. ** Department of Geology, University of Liverpool, Liverpool L69 3BX, England.

Geobios, n ° 19, fasc. 4 p. 421-433, 4 figs., 1 pl. Lyon, aofit 1986

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I. INTRODUCTION

In Western Europe, the << Armorican Quartzite >> generally forms the basal Ordovician formation, and in most places the unit rests with a stratigraphic break on the underlying rocks. Locally, however, such as in NE Portugal and north (Asturias) and central (Celti- beria) Spain, the quartzites appear to pass conformably downwards into beds of Tremadoc or Cam- brian age ; elsewhere they are underlain by red beds, such as at Bugaco (Portugal), Ciudad Real Province (Spain), Crozon Peninsula and south of Rennes (Brit- tany) (see review articles by Babin & alii 1976 ; Ham- mann 1976 ; Hammann & alii 1982 ; Romano 1982).

The << Armorican Quartzite >> reaches up to 600 m in thickness and typically consists of quartzites with subordinate, siltstones, shales and conglomerates. The unit, though locally rich in trace fossils, is generally poor in body fossils. The trace fossils are domi- nantly of Cruziana/Rusophycus type, with Skolithos, Daedalus, Didymaulichnus, etc., and were initially immortalised in Portugal by Delgado in his classic memoirs (1886, 1887). Modern work on these assemblages suggests that in most areas the unit is of Arenig age (see review in Hammann & alii 1982 and Pickerill & alii 1984) though possibly extending down into-the Tremadoc (Crimes & Marcos 1976). In the Westastu- rian - Leonesian Zone of Spain the Cabos <~ Series >> contains trace fossils which range in age from Upper Cambrian to Arenig (Baldwin 1977).

The only body fossils known to date from the <( Armorican Quartzite >> in western Europe occur mainly in the upper beds and include from NW France : inarticulate brachiopods (Ectenoglossa lesueuri, Dinobolus brimontl), bivalves (Actinodonta carinata, Lyrodesma armoricana, Synek antiquus) and trilobites (Ogyginus armoricanus, Platycoryphe heberti, Platycoryphe dangeardl) (Henry 1980; Robardet in Hammann & alii 1982). Lingulids, Dino- bolus and undescribed asaphid trilobites are also recorded from this unit in Spain (Montes de Toledo and Celtiberia ; Hammann & alii 1982), while in Por- tugal, bivalves, lingulid brachiopods and Neseuretus ? tristani have been recovered from the upper part of the unit (Delgado 1908, pp. 36, 57-62).

Fig. 1 - - Simplified geological sketch map of the area between Rio Mondego and Rio Ceira (after Costa 1950). The sections described in the text are indicated on the map.

Carte g~oiogique simplifi~e de la r~gion entre Rio Mon- dego et Rio Ceira (d'apr~s Costa 1950). Les sections d6crites dans le texte sont indiqu~es sur la carte.

i

~ 'Armorican Quartzite'

~ Sarnelha Formation

7--'-~ Pr e- Ordovician

- - 4 2 3 - -

Series

Z O

2 0 - t r

15-

i i i 1 0 -

#J O 5 .< O

Z 0

n- O LL

W t--

ix <

0 Z < 0 iX 0

iX <

metres

I I I t

Sample Chitinozoan Graptolite number biozone zones BU.A

- -18 I i 1 7 - - 16 D idymograptus

I b i f ldus

- - 1 4

? - 1 3 - - 12 D. hirundo i l l and - - 10 I. gibberulus - - 9 D. nl t ldus

- - 8

i 7

- - 6

- - 5

- - 4

- - 3

AFTER PARIS ( '1981)

Didymograptus

def lexus

Graptoli te zones

I D idymograp tus

b i f idus

LOWER LLANVIRN

? 9

Dldymograptus

def lexus

MIDDLE ARENIG

THIS PAPER

Fig. 2 - - Stratigraphic log of the Penacova section showing locality numbers , chitinozoan biozones and graptolite zones after Paris (1981) ; also the modifications to this scheme after the present work.

Section stratigraphique de ia succession/t Penacova indiquant les localit~s, ies biozones de chitinozoa et les zones graptolitiques, (d'apr~s Paris (1981), ainsi que les modif icat ions/ l cette figure apport6es par ce travail.

- - 424 - -

In Iberia and NW France the ~ Armorican Quart- zite >) is conformably overlain by a sequence of shales (for formational names see Hammann & alii 1982). In their lower part the shales have yielded graptolitic and shelly faunas indicating ages ranging from middle Arenig, Didymograptus nitidus Biozone (Paris & Ske- vington 1979), Lower Llanvirn (Hammann & alii, Ol). cit.) and Upper Llanvirn (Mitchell 1974 ; Villas 1983). Since not all of the graptolite assemblages occur immediately above the quartzite facies, the

question of the age of the top of the ~ Armorican Quartzite >> in certain areas and the possible diachronous nature of the unit is still in dispute (see Discus- sion in Hammann 1976). It was for this reason that the present authors investigated this part of the sequence in two areas : a) Penacova - section along the road, east of the Rio Mondego, at the southern end of the Bugaco ridge ; (b) section along a track, west of the Rio Ceira, 14 km SE of Penacova (text- fig. 1).

II. BIOSTRATIGRAPHY

The lithofacies and faunas of the Ordovician sequences of Crozon (Brittany) and Bugaco (central Portugal) have long been known to be extremely similar. Both regions show local development of red beds below the Armorican Quartzite Formation which is thickly developed, and the top of the formation is in some places characterized by the presence of a thin bed with fragments of inarticulate brachiopods in which lingulacean debris is scattered with phosphatic pebbles in a poorly sorted, fine to coarse grained sandstone.

Graptolites ( Corymbograptus v. similis (BOU~EK)) indicating the D. nitidus Biozone of the middle Are- nig are present between 6.5-7.5 m above the top of the Armorican Quartzite Formation on Postolonnec beach, Crozon (Paris & Skevington 1979). The junction between the Armorican Quartzite Formation and Postolonnec Formation is transitional here and so these authors considered the top of the former unit to be of middle Arenig age. The graptolites are associated with trilobites (Asaphidae, Calymenidae), ostra- cods, bivalves, Tomaculum and chitinozoans. The chitinozoans from the lower graptolite level at Posto- lonnec beach have been equated by Paris (1981) with his chitinozoan biozones 2 and 3 (see below).

Paris (Ol). cit., p. 309) suggested that at Penacova, chitinozoan sub-biozone la (low Didymograptus

deflexus Biozone) was represented at a level 70 m below the top of the Armorican Quartzite Formation and possibly to within 20 m of the top of the unit (text-fig. 2). Biozone 2 was not recognised at Pena- cova by Paris but biozone 3 (Belonechitina henryi Biozone) of upper middle Arenig age was considered to be present, ranging from the top of the Armorican Quartzite Formation into the basal 5 m of the overlying Cacemes Formation (levels BU.A.9-BU.A. 13 of Paris). Paris did point out that the recognition of this biozone at Penacova is more uncertain than at Postolonnec, owing to the poorer preservation of the Portuguese material, and remarked that B. henryi has not been definitely identified. However he commen- ted on the abundance of Sagenachitina oblonga (very abundant at BU.A.12) which apparently ranges up into the Lower Llanvirn (Paris, op. cit., Table 38). The chitinozoan biozone 4 (Cyathochitina protocalix Biozone of upper Arenig to Lower Llanvirn age) was also recognised at Penacova (BU.A. 14 and BU.A. 15) where it occurs from between 8.5-11.5 m above the lingulid bed which forms the top of the Armorican Quartzite Formation. Paris considered the assem- blage at this level at Penacova to be typical of his sub- biozone 4b which according to his Table 42 lies at the base of the Llanvirn (text-fig. 2).

III. AGE OF THE SHELLY FAUNAS ABOVE THE ARMORICAN QUARTZITE FORMATION IN CENTRAL PORTUGAL

The presence of tuning fork graptolites strongly suggests a Llanvirn age for the basal Cacemes Forma- tion to within about 10 cm of the lingulid bed at the top of the Armorican Quartzite Formation at Rio Ceira and 1.20 m at Penacova (text-fig. 3). As far as

can be determined in the field there is no structural discordance between these two lithological units. The graptolite faunas at Rio Ceira and Penacova range through at least 1.10 m and 0.70 m respectively and the following identifications and comments on these

4 2 5 - -

3m

2m

l m

P E N A C O V A []

- - - -P160

- - - P 1 5 9

i - -

- - P158

--j_--

--__~ - - - - P157

--...-,.--- P156

_--_ P155

m t~ o

- . -

[]

[] m? mm [] [] []

[]

@ ?@ [] [] [] [] ~@

A A

[] []

[]

[]

[ ]

[ ]

A A A A A A A A A

-'~ grey shale ~ quartzite with phosphatic

'lingulid' bed at top

RIO CEIRA A

RC3 -

Z 0

n -

O LL

LU

LIJ o < O RC2 -

RCl -

~,,,z 5=

n - ~ 0 < O u .

_ m - - 3 m

7 ~ 7 . - - ~ 7 - - - ~ 7 - - - ~ 7.- . -~ 7 - - ~ -

7 - - - - - - = - 2 m

7__~_

" - - - - l m

i t o

Fig. 3 - - S t ra t ig raph ic ranges of the f aunas in the P e n a c o v a and Rio Ce i ra sect ions.

Les r~par t i t ions s t r a t ig raph iques des faunes dans les sect ions de P e n a c o v a et R io Ceira .

- - 426 --

faunas have been kindly supplied by Dr. R.B. Ric- kards, University of Cambridge.

~ Localities P157 and P158 from Penacova and RC1 and RC2 from Rio Ceira have yielded respectively four, five, one and two moderately preserved (though flattened) tuning fork graptolites, together with stipe fragments probably belonging also to tuning fork species. No other forms have been recognised and only one species has been identified at each locality. Those at P157 and RC2 are identical and are referred to Didymograptus (Didymograptus ?) cf. spinulosus PERNER ; the specimen from RC1 to Didy- mograptus (D. ?) aff. spinulosus PERNER and those from P158 to Didymograptus (D. ?) cf. pseudogemi-

V nus BOUCEK (see text-fig. 4). The suggested age for P157 and RC2 (and probably RC1) is low ~ bifidus ~) Biozone of the Llanvirn Series. In all probability P158 is also about the same level )).

The associated trilobite faunas (see below and text- fig. 3) include Eodalmanitina sp., Colpocoryphe cf. thorali conjugens, Neseuretus (Neseuretus) tristani tristani and Ogyginus cf. armoricanus. Of these forms, C. thorali conjugens occurs in beds of Lower Llanvirn age in the Montes de Toledo and Guadalupe

areas of Spain, while Neseuretus (Neseuretus) tristani tristani ranges in age from Llanvirn to Llandeilo (see later). Ogyginus armoricanus is known from the upper part of the Armorican Quartzite Formation at Sion-les-Mines (SE of Rennes) where it is of ? Arenig age (Henry 1971); in central Spain (Montes de Toledo) O. armoricanus occurs in beds of Upper Llanvirn age (Rabano 1982).

ThUs, although no diagnostic macrofossils have been obtained from the basal 10 cm and 1.2 m of the Cacemes Formation at Rio Ceira and Penacova respectively, it is unlikely that any of the shale sequence above the Armorican Quartzite Formation in central Portugal is of Arenig age as suggested by Paris (1981). In fact the chitinozoan evidence for the age of the basal beds of the Cacemes Formation at Penacova is not particularly conclusive since assemblages are often poor in numbers and diversity, and species may be unidentifiable or questionable (Paris 1981, pp. 311-312). It is hoped that the present disagreement, concerning the age of the basal beds of the Cacemes Formation in central Portugal, will be resolved by further work in other areas.

IV. DISCUSSION OF THE AGE OF THE TOP OF THE ARMORICAN QUARTZITE FORMATION

The difference in age of the beds immediately overlying the Armorican Quartzite Formation in western Brittany and central Portugal remains to be interpreted.

There are at least two possible alternatives :

(a) If the sequences are essentially continuous and conformable then the top of the Armorican Quartzite Formation at Rio Ceira and Penacova is of Lower Llanvirn age while at Crozon it is middle Arenig ; hence the cessation of the quartzite facies is not everywhere synchronous.

(b) If a depositional hiatus occurs at or near the base of the Cacemes Formation in regions where the oldest graptolite fauna is of Llanvirn age then the top of the Armorican Quartzite Formation may be approximately synchronous in most areas and of middle Arenig age.

If, as Paris & Skevington (1979) maintain, the Armorican Quartzite Formation passes up conformably into the overlying shales of the Postolonnec Formation, then the top of the former unit may well be of middle Arenig age. At Penacova and Rio Ceira, Morgat and Camaret-sur-Mer (Crozon Peninsula), Arenig graptolites are unknown above the quartzites ; the oldest faunas from the shales being of Llanvirn age. If it could be demonstrated in these four areas that the quartzites pass up conformably into shales, then it follows that the top of the quartzites are unlikely to be of middle Arenig age and the top of the unit is diachronous. However, these four areas are charac- terised by the presence of a ~ lingulid )> bed, containing broken valves of lingulacean brachiopods with phosphatic pebbles, at or near the top of the quartzites. At Penacova this bed (3-4 cm thick) overlies an erosive surface, of unknown magnitude, and there- fore indicates a break in sedimentation. There is also

- - 4 2 7 - -

1/ / ..! \

/

i I,; I

/

i ~3 m

' / \

Fig. 4 - - a-f. Didymograptus (Didymograptus ?) cf. spinulosus PERNER.

g-h. Didymograptus (Didymograptus .9) aff. spinulosus PERNEl~.

i-n. Didymograptus (Didymograptus ?) ef. pseudogeminus BOU~EK.

a. P157/3 ; b. P157/1 ; c, d. P157/4a ; e. P 1 5 7 / 2 , f. RC2/1 ; g, h. RC1/1 ; i, j. P 1 5 8 / l a ; k. P 1 5 8 / l b (counterpar t of P158 / l a ) 1. P158/2 ; m, n. P158/3. (a, d, f, g, i, k-m x 4 ; b, c, e, h, j, n x 12). Ar ro ws indicate lineation.

-- 428 --

a sharp lithological break between the <~ lingulid )) bed and overlying shales. Thus, the junction between the Armorican Quartzite Formation and Cacemes/ Postolonnec Formation may be interpreted by one or more of the following situations :

(a) The ~ lingulid )~ bed, with its rounded phosphatic pebbles, heavy minerals and reworked and abra- ded lingulacean valves, is a very condensed sequence and represents a period of prolonged deposition which spans the time interval from approximately middle Arenig to very early Llanvirn.

(b) Armorican Quartzite type sedimentation persis- ted for a longer period in central Portugal.

(c) A significant break in sedimentation occurred below the ~ lingulid ~) bed, during which no sediment accumulated between middle Arenig and early Llan- virn times.

(d) A significant break in sedimentation occurred above the ~ lingulid )) bed, during which no sediment accumulated between middle Arenig and early Llan- vim times.

Unfortunately it is not possible at this stage to determine with any confidence which of these situations is most likely to be correct. However in view of the strong evidence of prolonged reworking in the (~ lingulid )~ bed, together with the discontinuity surface at the base of the bed and rapid lithological

change at the top, it is considered that the situations represented in (a), (c) (and ?(d)) are the most likely. In all probability the sequences at Penacova and Rio Ceira, as well as at Morgat and Camaret-sur-Mer, are a result of a combination of both of these.

A recent paper by Chauvel & Durand (1983) on the area south of Rennes provides further evidence for the widespread occurrence of these phosphatic com- glomerates at the top of the Armorican Quartzite For- mation. Here, several beds of phosphatic conglomerates with associated lingulaceans and containing spi- litic pebbles (not seen in the Penacova or Rio Ceira conglomerates) occur near the base of the Traveusot Formation, and a ~ lingulid ~) bed is recorded towards the top of the Armorican Quartzite Forma- tion. These authors noted that in the section which they studied at B6nioc the oldest faunas above the Armorican Quartzite Formation are of Llanvirn age, but graptolite evidence further south suggested to them that at B6nioc the base of the Traveusot Forma- tion corresponds to the Arenig. The presence of more than one level of phosphatic conglomerates with ~ lingulids ~ highlights the problem of correlating lithological units in such facies, and without accurate faunal control renders deductions concerning the age of the top of the Armorican Quartzite Formation rather hazardous.

V. DESCRIPTION OF TRILOBITE FAUNAS

All the material is housed in the Department of Geology, University of Sheffield.

Family Asaphidae BURMEISTER, 1843

Sub-family Ogygioearidinae RAYMOND, 1937

Genus Ogyginus RAYMOND, 1912

TYPE SPECIES :

Asaphus corndensis MURCHISON, 1839

Ogyginus cf. armoricanus (TROMELIN & LEBESCONTE, 1876)

(pl. 1, fig. 1)

For synonomy see Rabano (1982, p. 69).

MATERIAL :

Internal mould (P158/4) and corresponding external mould (P158/2) of incomplete cephalon (part of hypostoma exposed) and thorax ; fragmentary thorax and part of cephalon (P157/5).

HORIZON AND LOCALITY :

Cacemes Formation, 1.1-1.9 m above base. Locali- ties P157 and P158, Penacova.

REMARKS :

The specimens are close to Ogyginus armoricanus as described by Henry (1971, 1980) but differ in having a more rounded outline to the eye, a relatively wider glabella posterior to the eyes and less backwardly

-- 429 --

curved facial suture where it crosses the posterior bor- der. The pleural furrows do not extend as far along the pleurae as in the example figured by Henry (1971, pl. 1, fig. 8). The sigmoidal course of the postocular facial suture in the Portuguese form approaches that seen in O. terranovicus DEAN (Dean & Martin 1978) from the Wabana Group (Arenig) of Bell Island, Newfoundland, but the eyes are smaller in the Cana- dian species and the occipital ring is better defined. Whittard (1964) figured four species of Ogyginus from the Llanvirn of the Shelve Inlier. They differ from the Portuguese species in several respects • O. porcatus and O. intermedius have a well segmented glabella, a straighter postocular facial suture, and smaller eyes in the latter species (Hughes 1979, p. 136) ; O. grandis appears to be a relatively wider form and possesses smaller eyes ; O. corndensis has a relatively narrower glabella posterior to the eyes, better defined occipital ring and a well marked occipital node (Hughes, op. cit., fig. 55).


Cacemes Formation, 1.2-3.3 m above base. Locali- ties P157, P160, Penacova.

REMARKS :

The specimens agree in all major respects with the descriptions of this species given by Henry (1970, 1980) and Hammann (1983). According to Hammann the subspecies is restricted to the Lower Llandeilo in Spain, although Gutierrez-Marco informs me that it is also present in the Upper Llanvirn.

Sub-family Colpocoryphinae HUPE, 1955

Genus Colpocoryphe NOVAK /n PERNER, 1918

TYPE SPECIES :

Calymene Arago ROUAULT, 1849.

Famille Calymenidae BURMEISTER, 1843

Sub-family Reedocalymeninae HuPI~, 1955

Genus Neseuretus HICKS, 1873

Sub-genus Neseuretus (Neseuretus) HICKS, 1873

TYPE SPECIES :

Calymene parvifrons var. murchisoni SALTER, 1865 (see Whittard, p. 139 and Fortey & Morris 1982, p. 69.

Neseuretus (Neseuretus) tristani tristani (BRONGNIART in DESMAREST, 1817)

(pl. 1, figs. 13, 14)

For synonomy see Henry (1970, 1980), Sadler (1974), Fortey & Morris (1982) and Hammann (1983). Fortey & Morris (op. cit., p. 70) attributed this species to Desmaret while Hammann (1983, p. 63) attributed it to Brongniart in Desmarest 1817.

MATERIAL :

Part and counterpart of pygidium (P160/la, b) ; fragment of thoracic pleura, internal mould (P157/6) ; internal mould (P157/8).

Colpocoryphe thorali conjugens HAMMANN, 1983

1983 - - Colpocoryphe thorali conjugens n.ssp. : Hammann, pp. 87-90, pl. 12, figs. 111-120, text-figs. 35, 36.

Colpocoryphe el. thorali conjugens HAMMANN, 1983

(pl. 1, figs. 2-5)

MATERIAL :

Part and counterpart of cranidium and incomplete thorax (P157/7a, b) ; incomplete cranidium and thorax, external mould (RC1/2).


Cacemes Formation. P157/7 from 1.2 m and RC1/2 from 10 cm above base. Penacova and Rio Ceira respectively.

REMARKS :

The species shows features of both Colpocoryphe and Plaesiacomia ; the differences between these two genera have been summarised by Henry (1980) (see also Dean, 1966). The present material is not well preserved and has probably been flattened somewhat ; thus the glabella is weakly convex which is a feature

- - 430 - -

of Plaesiacomia. However the relatively wide (sag.) occipital furrow which deepens posterior to the basal glabellar lobes and the rounded extremities of the occipital ring are characteristic of Colpocoryphe. Also the presence of 2 (?3) pairs of glabellar furrows, of which L1 is directed more posteriorly than in species of Plaesiacomia, suggest that the specimens are correctly assigned to Colpocoryphe. Until a pygidium

i s found it is preferred to compare the species to C. thorali conjugens which differs in having a more convex preglabellar field. This species is known f rom the Lower Llanvirn of the Sierra Morena, Spain (Ham- mann 1983, p. 87). Dr. J .-L Henry informs me that he has similar material f rom beds of Lower Llanvirn age (cote 85, Laillr), south of Rennes.

Eodalmanitina sp.

(pl. 1, figs. 6-9)

MATERIAL :

Par t and counterpart of cephala, poorly preserved (P157/9a, b and RC1/3a, b) ; external mould of front of cephalon (RC2/2).

HORIZON AND LOCALITY "

Cacemes Formation. P157/9 f rom 1.2 m, R C I / 3 and RC2/2 f rom 10 cm and 1.25 m respectively above base. Penacova and Rio Ceira.

Family Dalmanitidae VOGDES, 1890

Sub-family Dalmanitininae DESTOMBES, 1972

Genus Eodalmanitina HENRY, 1965

TYPE SPECIES :

Calymene macrophtalma BRONGNIART, 1822.

REMARKS :

Despite the poor preservation ; the slight bulge on the anterior margin, large eyes, angle at which the genal spines diverge and slender proximal part of the genal spine suggest assigning the specimens to this genus is correct (Hammann 1972, 1974 ; Henry 1980).

Acknowledgements

We wish to express our thanks to Dr. R.B. Rickards for identifying and providing a report on the graptolites and for allowing us to use the information in the paper, and Dr. J.- L. Henry for useful discussion. M.R. gratefully acknowled-

ges receipt of N.E.R.C. Grant GR3/3786 under the which the present work was conducted. J.C. Gutierrez-Marco and I. Rabano kindly provided information on the ranges of some of the trilobites in central Spain.

VI. REFERENCES

BABIN C., ARNAUD A., BLAISE J., CAVET P., CHAUVEL J.J., DEUNFF J., HENRY J.-L., LARDEUX H~, MELOU M., NION J., PARIS F., PLAINE J., QUETE Y. & ROBARDET M. (1976) - The Ordovician of the Armori- can Massif (France). pp. 359-385. In BASSETT M.G. (ed.) The Ordovician System : proceedings of a Palaeon- tological Association symposium, Birmingham, Septem- ber 1974, University of Wales Press and National Museum of Wales, Cardiff, 696 pp.

BALDWIN C.T. (1977) - The stratigraphy and facies associa- tions of trace fossils in some Cambrian and Ordovician rocks of north western Spain. pp. 9-40, pls. 1-3. In CRI- MES T.P. & HARPER J.C. (eds.) Trace Fossils 2. Geol. J. Spec. _Issue, Liverpool, 9, 351 pp.

CHAUVEL J.-J. & DURAND J. (1983) - Les niveaux conglo- mrratiques phosphatrs h galets de spilite de l'Ordovicien de Brnioc (Formation de Traveusot - Bretagne centrale). Bull. Soc. g~oL mineral Bretagne, Rennes, C, 15, 1, 17- 27, 1 pl.

- - 4 3 1 - -

COSTA J.C. DA (1950) - Noticia sobre uma carta geol6gico do Bugaco, de Nery Delgado. Serv. geol. Port., Lisbon,

1 - 2 7 .

CRIMES T.P. & MARCOS A. (1976) - Trilobite traces and the age of the lowest part of the Ordovician reference for NW Spain. Geol. Mag., 113, 349-356.

DEAN W.T. (1966) - A revision of the Ordovician trilobite genus Plaesiacomia HAWLE & CORDA, 1847. Sb. ndr. Mus. Praze, Prague, 2213, 133-142, 3 pls.

DEAN W.T. & MARTIN F. (1978) - Lower Ordovician acritarchs and trilobites from Bell Island, eastern New- foundland. Bull. Geol. Surv. Canada, Ottawa, 1-35, 7 pls.

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Manuscr i t d6finit if regu le 19.02.1986

P L A T E 1

Fig. 1 - -

Figs. 2-5 - -

Fig. 6-9 - -

Fig. 1 0 -

Ogyginus cf. armoricanus (TROMELIN & LEBESCONTE), (P158/4), internal mould, x 1.7.

Co!pocoryphe cf. thorali conjugens HAMMANN. Figs. 2, 3, (P157/7a), internal mould, x 4 and x 5 respectively. Fig. 4, (P157/7b), external mould of Figs. 2, 3, x 5 (RC1/2). Fig. 5, external mould, x 5.7.

Eodalmanitina sp. Fig. 6, (P157/9a), internal mould, x 2. Fig. 7, (RC2/2), external mould, x 2. Fig. 8, (RC1/3a), internal mould, x 4. Fig. 9, (RC1/3b), external mould, x 3.

cf. ~ Ctenobolbina ~ hispanica (BORN), with indeterminate brachiopod and trilobite pygidium, (P157/11), x 3.

Avec brachiopode ind6termin6 et pygidium de trilobite.

Fig. 11 - - ~ Orthis ~ miniensis SHARPE, with cf. Primitiella ? sp. (RC3/1), x 4.

Fig. 12 - - Lingulacean, (P157/10), x 5.

Figs. 13, 14 - - Neseuretus (Neseuretus) tristani tristani (BRONGNIART in DESMAREST). Fig. 13, (P157/8), internal mould, x 4. Fig. 14, (P160/la), internal mould, x 8.

Fig. 15 - - ef. ¢¢ Ctenobolbina ~ hispanica (BORN), (P160/1), x 8.

All material from basal part of Cacemes Formation, central Portugal. Specimens numbered with either prefix P (Penacova) or RC (Rio Ceira), see Text-fig. 3.

Tous les fossiles proviennent de la partie inf6rieure de la Formation de Cacemes et sont marqu6s par le pr6fixe P (Penacova) ou RC (Rio Ceira), voir Text-fig. 3.

Geobios

n ° 19, fasc. 4

Pl, 1

M. Romano, P.J. Brenchley & N.D. MacDougall

I0

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11

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3 , ~ ' ! ~ i ~ :~,~ii~,~!:~:~ ~ ' ' ~ ! ~

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new information concerning the age of the beds immediately overlying the armorican quartzite in...

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