Palynology of the Picos de Europa and Puentellés Formations in the Picos de Europa area (Upper Carboniferous, northwest Spain)

Review of Palaeobotany and Palynology, 80 (1994): 65-74

65

Elsevier Science B.V., Amsterdam

Palynology of the Picos de Europa and Puentell6s Formations in the Picos de Europa area (Upper Carboniferous, northwest Spain) Robert Coquel a and Rosa Rodriguez b

aUniversitd des Sciences et Technologies de Lille, Laboratoire de Pal~obotanique, URA 1365 du CNRS, 59655 Villeneuve d'Ascq C~dex, France bUniversidad de Ledn, Depto. de Ingenieria Minera, 24071 Le3n, Spain (Received May 10, 1993; revised and accepted July 6, 1993)

ABSTRACT Coquel, R. and Rodriguez, R., 1994. Palynology of the Picos de Europa and Puentell6s Formations in the Picos de Europa area (Upper Carboniferous, northwest Spain). [Palinologia de las Formaciones Picos de Europa y Puentell6s en la regi6n de Picos de Europa (Carbonifero Superior, NO. de Espafia).] Rev. Palaeobot. Palynol., 80: 65-74. The Picos de Europa and Puentell6s Formations described from northern Spain belong to the Cantabrian Zone. These formations consist mainly of carbonates deposited under shallow platform conditions. Twenty-four samples were studied. A diversified but relatively rare microflora has been obtained. The spores and pollen grains often possessed a wall with numerous small pits related to the presence of abundant pyrite (cube and spherical mass) in the sediment. In the associations, the large forms of pollen (Potonieisporites-Florinites) are very common. With the exception of Laevigatosporites, monolete spores (Punctatosporites, Spinosporites, Torispora, Thymospora) are rare. A comparison with the range chart of Clayton et al. (1977) indicates that an age in the upper part of the Westphalian D to Stephanian A is in agreement with the faunal results. RESUMEN Las Formaciones Picos de Europa y Puentell6s se sitflan en la Regi6n de Picos de Europa de la Zona Cant/tbrica, Noroeste de Espafia. Estas Formaciones est~n constituidas principalmente por carbonatos depositados en condiciones de plataforma marina somera. Se estudiaron veinticuatro muestras de las cuales se obtuvo una microltora escasa, pero bastante diversificada. La pared de los granos de las esporas y el polen presentan a menudo numerosas perforaciones de pequefio tamafio, las cuales est~in relacionadas con la presencia de abundante pirita en el sedimento (en masas cfibitas y esf6ricas). Los elementos mas abundantes de la asociaci6n pertenecen a formas de polen de gran tamafio (Potonieisporites-Florinites). Las esporas monoletas son escasas (Punctatosporites, Spinosporites, Torispora, Thymospora), con la escepci6n de Laevigatosporites. La comparaci6n con la tabla de distribuci6n de Clayton et al. (1977) indica una edad del WestfalienseD Superior-Stefaniense A, que tambi6n concuerda con los resultados faunisticos.

Geographical and stratigraphical setting The Picos de E u r o p a a n d Puentell6s F o r m a t i o n s of n o r t h w e s t e r n S p a i n (Fig. 1) geologically b e l o n g to the C a n t a b r i a n Z o n e , which represents the most external o f the five zones established by Lotze (1945) for the I b e r i a n H e r c y n i a n Massif. T h e C a n t a b r i a n Z o n e c o n t a i n s s e d i m e n t a r y rocks with a b u n d a n t a n d c o m m o n l y well-preserved flora a n d m a r i n e invertebrate f a u n a a n d is devoid o f significant m e t a m o r p h i c a n d m a g m a t i c events.

T h e Picos de E u r o p a a n d Puentell6s F o r m a t i o n s consist m a i n l y o f carbonates, with the latter one h a v i n g some intercalations o f marls. Both formations are o f C a r b o n i f e r o u s age, a n d were deposited u n d e r m a r i n e shallow p l a t f o r m c o n d i t i o n s (Villa et al., in press). The Puentell6s F o r m a t i o n has been recognized in several localities, all of them situated to the n o r t h of the Picos de E u r o p a Structural U n i t of the C a n t a b r i a n Z o n e (Julivert et al., 1974) (Fig. 2). A t the section of Las Llacerias (Fig. 2), located

0034-6667/94/$07.00 © 1994 - - Elsevier Science B.V. All rights reserved. SSDI 0034-6667(93)E0060-I

66

R. COQUEL AND R. RODRIGUEZ

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The Picos de Europa Formation consists of two members: a lower, well bedded member, and an upper massive member. The samples were taken in the massive member, starting with a red encrinital limestone level, located 480 m above the base of the formation. The lower part of this sequence is composed of several cycles, each one consisting of reddish packstone or grainstone in its lower part, and of greyish wackestones or mudstones with bird's eyes and cores of framboidal pyrite in the upper part. The top of this formation consists of creamish to pink coloured limestones. The palaeoenvironment for the sedimentation of this part of the Picos de Europa Formation shows the evolution from a platform lagoonal setting towards a more open platform. The Puentell6s Formation is composed of alternating carbonates and marls. The lowest part of this formation consists of greyish-beige wackestones alternating with reddish-grey grainstones and marls. The remaining part of the section is composed of two megasequences of tempestites, each one of these tempestites has a lower part consisting of grainstones and mudstones showing turbiditic features, and an upper part consisting of rudaceous grainstones. These deposits were accu-

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Fig. 1. Location map of the Las Llacerias section. adjacent to a cattle shed close to the Sanctuary of Covadonga (Asturias), the carbonated and marly succession, lying on top of the Picos de Europa Formation, has been provisionally attributed to the Puentell6s Formation by Villa et al. (in press). At this locality, these authors found a continuous sequence comprising the Moscovian-Kasimovian boundary interval. The stratigraphic characteristics of this section were described in detail by Villa et al. (in press).

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PALYNOLOGY OF THE PICOS DE EUROPA AND PUENTELLI~S FORMATIONS (UPPER CARBONIFEROUS, NW SPAIN)

mulated at a high sedimentation rate, on a storm monoclinal platform-slope, in an off-shore environment evolving towards a shore-face setting (Villa et al., in press). The age of these nearly continuous sequences ranges from late Moscovian into Kasimovian (except for the late Kasimovian); this is based mainly on evidence from foraminiferids and several invertebrate groups, as well as the spore evidence at a few horizons. The boundary between these two stages has been provisionally established at a horizon between level LL-9011 and level LL-9014, at the base of the Protriticites Zone (Villa et al., in press).

Palynology This work is part of a multidisciplinary research program in the framework of the Subcommission on Carboniferous Stratigraphy [Project Group 5: A boundary at the base of the Protriticites Zone (basal Kasimovian; basal Missourian; midCantabrian), co-ordinated by Villa]. Preliminary palynological studies previously reported (Rodriguez-Gonzfiles; see Villa et al., in press) have documented horizons in the Protriticites Zone (LL-9030-LL-9042) including spore associations belonging to the middle-upper part of the OT Zone of Clayton et al. (1977) which ranges from late Westphalian D to early Stephanian A. Twenty-four samples were studied mainly from the marly levels although limestone levels were sampled when marls were not available. The samples were taken through the upper part of the Picos de Europa Formation, starting at a level 50 m below the top of this formation and through the Puentell6s Formation (Table I). The microfloral remains were isolated by means of standard palynological techniques. The carbonates and silicates were removed with hydrochloric and hydrofluoric acids, respectively. In some cases it was necessary to oxidize the organic matter with nitric acid. The samples are poor in organic matter; the richest horizons in the marls contain a little more than 2% of total organic carbon (2.12% in the sample 9045). The recovered microfloras are relatively sparce and several samples taken from the limestones are

67

practically devoid of palynomorphs. They are composed predominantly of spores and pollen grains. Cysts of prasinophycean algae are present through the stratigraphical interval belonging to the Puentell~s Formation, as well as a few acritarchs and tasmanids. Cuticle and wood fragments (especially with areolated pits) are also present. We have recognized a few small planispiraled imperforate foraminiferids (Scytinascia group), which seem to be more common in the Puentell6s Formation. Rare scolecodonts are present in most preparations. Reworked spores are uncommon, always dark and thermally alterated making their identification impossible. Originally, the environments of deposition were favorable for the preservation of spores and pollen but the early diagenesis of pyrite in the form of small cubes (1-4 lain) and spherical masses (framboidal pyrite) (10-20 lxm) has damaged the walls. Especially the pseudosaccates and saccates are affected (Plate I). The pyritisation which is sometimes strongly developed appears to occur in two ways. Occasionally, it increases centrifugally in the inside of the miospore with the result that the exine is deformed and takes on a vesicular aspect (Plate I, 11). In other cases it occurs on the external surface with the solution (total or partial) of the pyrite during oxidization consequently giving rise to an exine with a reticulate aspect (Plate I, 2). This results in a relatively high percentage of spores and pollen grains being indeterminable (5-10%). In this study, the following miospore taxa have been found.

Monolete spores Laevigatosporites vulgaris (Ibrahim) Alpern and Doubinger

Laevigatosporites perminutus Alpern Punctatosporites granifer (Potoni6 and Kremp) Alpern and Doubinger

Punctatosporites rotundus (Bharadwaj) Alpern and Doubinger

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PALYNOLOGY OF THE PICOS DE EUROPA AND PUENTELL]~S FORMATIONS (UPPER CARBONIFEROUS, NW SPAIN)

Thymospora obscura (Kosanke) Wilson and Venkatachala Thymospora thiessenii (Kosanke) Wilson and Venkatachala Thymospora pseudothiessenii (Kosanke) Alpern and Doubinger Torispora securis (Balme) Alpern et al. Torispora verrucosa Alpern Trilete spores Punctatisporites punctatus Ibrahim Punctatisporites minutus Kosanke Calamospora mutabilis (Loose) Schopf et al. Calamospora breviradiata Kosanke Leiotriletes adnatus (Kosanke) Potoni6 and Kremp Leiotriletes adnatoides Potoni6 and Kremp Granulatisporites piroformis Loose Granulatisporites microgranifer Ibrahim Apiculatisporis aculeatus (Ibrahim) Potoni6 and Kremp Apiculatisporis cf. abditus (Loose) Pi~rart Acanthotriletes microspinosus (Ibrahim) Potoni+ and Kremp Lophotriletes gibbosus (Ibrahim) Potoni6 and Kremp Lophotriletes mosaicus Potoni6 and Kremp Verrucosisporites verrucosus Ibrahim Convolutisporaflorida Hoffmeister et al. Convolutispora cf. tessellata Hoffmeister et al. Raistrickia superba (Ibrahim) Schopf et al. Raistrickia rubida Kosanke Microreticulatisporites nobilis (Wicher) Knox Microreticulatisporites concavus Butterworth and Williams Lycospora pusilla (Ibrahim) Schopf et al. Lycospora pellucida (Wicher) Schopf et al. Lundbladispora gigantea (Alpern) Doubinger Densosporites anulatus (Loose) Schopf et al. Densosporites duriti Potoni6 and Kremp Densosporites spinifer Hoffmeister et al. Densosporites regalis (Bharadwaj and Venkatachala) Smith and Butterworth Radiizonates tenuis (Loose) Butterworth Cristatisporites solaris (Balme) Butterworth Reticulatisporites polygonalis (Ibrahim) Loose Crassispora kosankei (Potoni6 and Kremp) Bharadwaj

69

Savitrisporites camptotus (Alpern) Doubinger Polymorphisporites laevigatus Alpern Polyrnorphisporites reticuloides Alpern Westphalensisporites irregularis Alpern Ahrensisporites guerickei (Horst) Potoni~ and Kremp Triquitrites tribullatus (Ibrahim) Schopf et al. Triquitrites triturgidus (Loose) Schopf et al. Triquitrites sculptilis Balme Triquitrites spinosus Kosanke Mooreisporites sp. Simozonotriletes intortus (Waltz) Potoni6 and Kremp Cirratriradites saturni (Ibrahim) Schopf et al. Angulisporites splendidus Bharadwaj Endosporites globiformis (Ibrahim) Schopf et al. Endosporites ornatus Wilson and Coe Vestispora fenestrata (Kosanke and Brokaw) Wilson and Venkatachala ? Vestispora costata (Balme) Bharadwaj Pollen grains Florinites pellucidus (Wilson and Coe) Wilson Florinites pumicosus (Ibrahim) Schopf et al. Florinites junior Potoni6 and Kremp Florinites dissacoides Alpern Potonieisporites spp. Candidispora candida Venkatachala Latensina trileta Alpern ? Divarisaccus sp. Disaccites non striatiti ?Cheiledonites sp. The variation in the composition of microflora is essentially quantitative. The white limestones of the Picos de Europa Formation are particularly poor. The richest and most diversified associations were always noted in the grey marly levels of the Puentellrs Formation (Table I). Age determination and comparisons

The most common taxa are Densosporites spp., Lycospora spp., pseudosaccate spores, and the monosaccate pollen. With the exception of Laevigatosporites, monolete spores are rare, in particular Spinosporites spinosus. Among the pseu-

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PALYNOLOGYOF THE PICOS DE EUROPAAND PUENTELLES FORMATIONS(UPPER CARBONIFEROUS,NW SPAIN)

dosaccates, Endosporites ornatus is the most common species, whereas the typical forms of Endosporites globiformis are very rare. Among monosaccate pollen grains, it is difficult to distinguish specimens of Potonieisporites from the large Florinites but the large forms (greater than 100 Ixm) usually dominate. In the limestones of the Picos de Europa Formation they are often the only miospores that are common.

Crassispora kosankei, Cirratriradites saturni and Polymorphisporites spp. are present in most assemblages whilst Lundbladispora gigantea, Angulisporites splendidus, Vestispora fenestrata, and Latensina trileta were recorded infrequently. A few rare specimens in the Puentell6s Formation have been refered with doubt to Cheiledonites and Divarisaccus. Rodriguez-Gonzfilez (see Villa et al., in press) illustrated several specimens which were interpreted as miospores including Reticulatisporites reticulatus (Plate II, 6, 7) together with other specimens which were described as "monolete reticulated spores" (Plate II, 5, 11, 14). In the present paper, more samples have been examined, providing an opportunity to look at a larger number of these specimens. From these observations we conclude that they represent phytoplanctonic specimens. This interpretation is based on the absence of apertures of the laesura type, but instead by the possession of a rounded or polygonal dehiscent aperture, ressembling a pylome. A small number of specimens exhibit a type of aperture which may be interpreted as a monolete laesura or a medium

71

split pylome. The latter interpretation seems to be more appropriate because these specimens appear in samples with abundant prasinophycean species belonging to Cymatiosphaera, Melikeriopalla, Dictyotidium and others and in which sporomorphs are rare and badly preserved. Some of these reticulated specimens may represent new species and will be described in a future paper (Plate II, 8). Comparisons with data in Clayton et al. (1977) are difficult because most of the sections documented in that study were from late Westphalian-Stephanian limnic basins while the facies examined for this study belong to the carbonate platform. In these facies with transport selection, the microfloral associations imperfectly reflect the surrounding plant cover; however, the microfloral assemblages still clearly indicate the OT-ST zones. The upper part of the Picos de Europa Formation-Puentell6s Formation clearly indicates an uppermost Westphalian-middle Stephanian age. Comparison with the data from Clayton et al. (1977) indicates the main difference being the low percentage of monolete spores in the Las Llacerias section. If we examine the microflora in greater detail, it is possible to obtain a more precise age assignment. Several taxa appearing in the Westphalian D are already present in the base of the studied section (e.g. Savitrisporites camptotus, Polymorphisporites spp., and Angulisporites splendidus). Clayton et al. (1977) recorded the first appearance of Angulisporites splendidus in the Stephanian A; in

PLATEI All figures x 500. The figured material is deposited in the collections of the Laboratoire de Pal6obotanique, Universit6 des Sciences et Technologies de Lille. 1. Endosporites globiformis (Ibrahim) Schopf et al. LL 9033. 2. Potonieisporites sp. LL 9042 A. 3. Disaccites non sriatiti. LL 9045 A. 4. Endosporites ornatus Wilson and Coe. LL 9033. 5. Probably a pollen grain with and exine very damaged by the pyrite. Quoted the presence of framboidal pyrite at the periphery. LL 9033. 6. Florinites pellucidus (Wilson and Coe) Wilson. LL 9033. 7. Potonieisporites sp. LL 9045 E. 8. Florinites pellucidus (Wilson and Coe) Wilson. L L 9038 C. 9. Florinites pellucidus (Wilson and Coe) Wilson. LL 9038 C. 10. ?Endosporites ornatus Wilson and Coe. LL 9042 B. 11. Disaccites non striatiti. LL 9038 C.

72

R. COQUEL AND R. RODRIGUEZ

P L A T E II

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PALYNOLOGYOF THE PICOSDE EUROPAAND PUENTELLESFORMATIONS(UPPERCARBONIFEROUS,NW SPAIN)

fact this spore, sometimes difficult to distinguish from Endosporites zonalis (Loose) Knox, starts in the Westphalian D of the Central Asturian Coalfield (Saenz de Santa Maria et al., 1985). The presence of these taxa associated with the Thymospora spp. in the oldest samples studied (upper part of Picos de Europa Formation) indicates that the lower part of the OT Zone is missing and therefore suggests a late Westphalian D to lower Stephanian age. The Puentell6s Formation contains Microreticulatisporites nobilis, Vestispora fenestrata, and Cirratriradites saturni. Those three taxa, scarcely represented in the Stephanian, disappear in the ST Zone, i.e. in the Stephanian B. In the late Westphalian-early Stephanian interval it is well-known that the microflora does not change much; thus the Westphalian D-Stephanian boundary is not readily defined by palynology. A comparison with the other palynological studies undertaken in this area of northwest Spain has a limited interest. In the Central Asturian Coalfield, the highest coal seams (Modesta-

73

Oscura) are dated as late Westphalian D (Saenz de Santa Maria et al., 1985) and not early Stephanian as indicated by Chateauneuf (1973). The study of the palynology of the early Stephanian of Barruelo Coalfield (Cantabric Mountains) is in progress. Despite the large number of samples analysed from the Barruelo Formation, the results are poor. In the preparations, wood fragments are abundant, whereas spores and pollen grains are relatively rare. The microflora, in shales and coal seams, is similar to those of the other coal basins of Western Europe where monolete spores are abundant, a situation which contrasts strongly with the Las Llaceras section. As for the Cantabrian microflora any comparison is possible since the samples collected in the Terejina syncline (northern Lebn) are barren. In the Saar-Lorraine Basin it is possible to obtain a better biostratigrahical precision when using both quantitative and qualitative data sets (see Alpern et al., 1967, figs. 2-4). We note the first appearance of Punctatisporites obliquus Kosanke slightly above the Holz Congloremate; this taxon is common to abundant in the Assise

PLATE II All figures x 500, unless otherwise stated. The figured material is deposited in the collections of the Laboratoire de Pal6obotanique, Universit6 des Sciences et Technologies de Lille. 1. Laevigatosporites vulgaris (Ibrahim) Alpern and Doubinger. LL 9045 A. 2. Laevigatosporites perrninutus Alpern. LL 9033. 3. Torispora securis (Balme) Alpern et al. LL 9033. 4. Thymospora obscura (Kosanke) Wilson and Venkatachala. LL 9042 A. 5. Punctatosporites cf. rotundus (Bharadwaj) Alpern and Doubinger. LL 9045 C. 6. Thymospora obscura (Kosanke) Wilson and Venkatachala. LL 9045 C. 7. Leiotriletes adnatus (Kosanke) Potoni6 and Kremp. LL 9045 A. 8. Prasinophycean cyst. LL 9033. 9. Cristatisporites solaris (Balme) Butterworth. LL 9031. 10. Leiotriletes adnatoides Potoni6 and Kremp. LL 9031. 11. Lophotriletes mosaicus Potoni6 and Kremp. LL 9045 E. 12. Densosporites anulatus (Loose) Schopf et al. LL 9031. 13. Lycospora pusilla (Ibrahim) Schopf et al. LL 9031. 14. Cirratriradites cf. saturni (Ibrahim) Schopf et al. LL 9042 B. 15. Polyrnorphisporites reticuloides Alpern. LL 9012. 16. Angulisporites splendidus Bharadwaj. LL 9038 C. 17. Densosporites anulatus (Loose) Schopf et al. LL 9042 B. On the central body the small dark spots correspond to pyrite cristals. 18. Radiizonates tenuis (Loose) Butterworth. LL 9045 E. 19. Crassispora kosankei (Potoni6 and Kremp) Bharadwaj. LL 9045 C. 20. Foraminiferid (Scytinascia group). 21. Cuticle and stomata. LL 9041. x 200. 22. Wood with areolated pits. LL 9042 A. 23. Scolecodont. LL 9038.

74 de Sarrelouis. U n f o r t u n a t e l y the series is incomplete in S a a r - L o r r a i n e , a gap is present at the top of the Westphalian D. This species, already freq u e n t in the late Westphalian D of the Asturias Coalfield, has n o t been recorded in the Las Llacerias section. U n f o r t u n a t e l y it is a spore with a very irregular d i s t r i b u t i o n which limits its biostratigraphical value. Taxa, such as Candidispora sp., Latensina trileta, a n d Angulisporites splendidus are practically absent in the early S t e p h a n i a n of northwest Europe. Their presence at Las Llacerias, p r o b a b l y indicates an association badly represented (or absent) in other E u r o p e a n areas investigated until now.

Conclusions The Las Llacerias microflora is distinctive, however it presents some q u a n t i t a t i v e peculiarities in its c o m p o s i t i o n (e.g. a b u n d a n c e of Potonieisporites-Florinites, scarcity of Punctatosporites, Spinosporites, Torispora, and Thymospora). The miospores indicate a stratigraphic interval corres p o n d i n g to the upper part of the Westphalian D to S t e p h a n i a n A. In the future, when other sections are available from the C a n t a b r i c M o u n t a i n s , it will be possible to make more precise c o m p a r i s o n s with data from the late Westphalian D - e a r l y S t e p h a n i a n ( O T - S T zones) interval of C l a y t o n et al. (1977). O u r criteria based o n spores and pollen grains deposited on the c a r b o n a t e platform do not permit a more precise age d e t e r m i n a t i o n at present. O u r results are in agreement with the age determinations (upper Moscovian-lower K a s i m o v i a n ) established o n foraminiferids which are c o m m o n in the limestones of the Picos de E u r o p a a n d Puentell6s F o r m a t i o n s .

Acknowledgement We t h a n k Dr. R. Cloutier (Universite des Sciences et Technologies de Lille, L a b o r a t o i r e

R. ('OQUELANDr. RODRIGL[~Z de Pal6obotanique) who kindly reviewed corrected the English of our m a n u s c r i p t .

and

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