The Turonian-Coniacian boundary in Ollogoyen (Basque Country); foraminifers and nannoplankton

C’retaceous Research (1986) 7, 63-75

The Turonian-Coniacian Boundary in Ollogoyen (Basque Country); Foraminifers and Nannoplankton Marcos A. Lamolda Dpto. Geologia, Facultad de Ciencias, Universidad de1 Pais Vascd; Apartado 644.48080 Spain

Bilbao,

and Franca Proto-Decima Istituto di Geologia, Universitd di Padova,

Via Giotto, 1; 35100 Padova, Ztalia

Received 14 February 1985 and in revised form SJuly

1985

M. A. Lamolda and F. Proto-Decima. The Turonian-Coniacian Boundary in Ollogoyen (Basque Country); Foraminifers and Nannoplankton. Cretaceous Research (1986) 7, 63-75. The Ollogoyen Section (Basque Country, Northern Spain) shows a pelitic sequence which is rich in several fossil groups. We have studied the foraminifers and coccoliths taken from more than 40 samples along a 65m succession of marls and marly limestones including the Turonian-Coniacian boundary. They are rich in microfossils and the observed differences in numbers are in direct relation to the preservation. Unfortunately, the recorded benthonic foraminifers and nannoplankton do not show any index fossils for the Tu/Co boundary. On the other hand, planktonic foraminifers show several biostratigraphical markers. Among the globigerinids we have used the appearance of the species Hedbergella flandrini Porthault, Archaeoglobigerina cretacea (d’orbigny) and A. blowi Pessagno. Among the globotrunacanids, the species Marginotrucana sinuosa Porthault and M. schneegansi S.S. @gal) are useful in placing the Tu/Co boundary. Heterohelicids show a morphological sequence from the biserial Heterohelix pulchra (Brotzen), of late Turonian age, and the multilocular specimens of the genus Ventilabrella, of early Coniacian age. This determination of the Turonian-Coniacian boundary is backed up by the associated microfauna and microflora which is found between the last known Romaniceras spp. specimens and the earliest appearance of Coniacian ammonites. This enables us to mark the Tu/Co boundary in Ollogoyen with the appearance of the planktonic foraminiferal species M. sinuoso, M. schneegasi s.s., and ?Ventilabrella sp. Dpto Geologia, Bilbao, Spain. Instituto

Facultad

di Geologia,

de Ciencias,

Universita

KEY WORDS: Turonian/Coniacian

Universidad

de1 Pais

di Padova,

Via Giotto,

boundary;

Foraminifers;

Vasco;

1; 35100

Apartado

Padova,

Nannoplankton;

644.

48080

Italia. Northern

Spain.

1. Introduction In the eastern part of the Navarro-Cantabrian Trough (Figure l), the Turonian-Coniacian boundary occurs in pelagic facies; grey marls and marlstones with abundant macro- and microfossils. Some of these fossils belong to biostratigraphically significant groups such as the cephalopods, foraminifers, coccoliths, etc. The “middle Cretaceous” of the Estella region, from the upper Albian to the middle Coniacian, is mainly transgressive. Only the uppermost part, the Coniacian, is represented by shallow-water facies which in the middle Coniacian is represented by bioclastic limestones. This kind of sedimentation is not known in other areas of the Navarro-Cantabrian 019556671/86/6010063+13

$03.00/O

0 1986 Academic Press Inc. (London) LImited

M. A. Lamolda

64

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Trough during the late Turonian and the early and middle Coniacian (Wiedmann, 1980), and the occurrence of bioclastic subrecifal facies of middle Coniacian age could be related with the diapirism (Lamolda et al., 1981). Colom (1952) pointed out the changing conditions during the Middle Cretaceous in the Allin Valley, from a littoral facies with Orbitolina in the Cenomanian, to a pelagic one, (open sea but not bathyal), in the late Cenomanian and early Turonian. These pelagic strata contain abundant calcareous zooplankton. This general picture is still accepted today; the cited work was the first to deal with the microfossils of Northern Spain. Later, of Allin Valley, but no one has Feuillee (1967) restudied the foraminifers studied the Turonian-Coniacian boundary. Wiedmann (1980) was the first to examine the planktonic foraminifers of the Ollogoyen section, work which was completed by Lamolda et al. (1981). The association of late Turonian age was characterised by several species of Marginotruncana; A4. pseudolinneiana Pessagno, M. fungicamerata (Martirosjan), M. tarfayaensis (Lehmann), M. paraconcavata Porthault, M. undulata Porthault, etc. Associated macrofossils include the ammonite species: Romaniceras ornatissimum (Stoliczka), R. cf. deverianum (d’orbigny), Collignoniceras sp., Pachydesmoceras denisonianum (Stoliczka), Puzosia cf. planulata (Sowerby), and nautiloids: Eutrephoceras indicum (d’orbigny), E. merteni Wiedmann, etc. The microfossils recorded from the beds of early Coniacian age are very similar to those of late Turonian age; Hedbergellaflandrini Porthault and Archaeoglobigerina cretacea (d’orbigny)

Turonian-Coniacian

Boundary

in Northern

Spain

65

are distinctive. Among the macrofossils are found Tissotia (Metatisotia) cf. robini (Thiolliere), Reesideoceras cf. camerounense Basse, Eutrephoceras bouchardianum (d’orbigny), Proplacenticeras sp., etc. 2. Stratigraphy We have studied the upper part of the section of Wiedmann (1980), focusing on the Turonian-Coniacian boundary. The sequence is mainly marly with occasional calcareous beds, which become more abundant, and bioclastic in nature, toward the top. The Turonian-Coniacian boundary was determined by Wiedmann within a calcareous bed 2 m thick (B), in the lower third of the section (Figure 2), which forms conspicuous topographic relief. However, the later discovery (by T. Freudenthal, during an excursion of the WG Coniacian-Maastrichtian, March, 1981) of specimens of the genus Romanimaniceras above the proposed boundary made it invalid. Actually, the upper third of the section is Coniacian in age, while the rest is late Turonian. The lithology in the lower part (A) of the section is mainly pelitic, grey marls and marlstones, with several calcareous micritic beds (1 S-30 cm thick); its thickness is about 21-22m. Above is a bed, 2 m thick, of nodular limestones and marlstones (B) with abundant ichnofossils; these are indicative of a condensed succession in comparison with the previous pelitic sedimentation. Above is a pelitic sequence 17--I 8 m thick (C), very similar to the first one (A). The uppermost part is characterised by an alternation of marls, marlstones and limestones (D) 25 m thick, more calcareous than the preceding ones, and typified by their bioclastic component. The marls may be very dark, but the occurrence of “black shales” is not recorded. Abundant, scattered, pyrite nodules occur throughout the succession. 3. Planktonic Foraminifers Planktonic foraminifers are always well represented in the micro-fossil assemblage. We found a decrease in their number form the lower beds toward the upper ones, from 70-7594 to 60-409b of the total fauna (Figure 2). In the lower part of beds “A”, the species Helvetoglobotruncana helvetica (Bolli) and Marginotruncana ex. gr. pseudolinneiana are the most abundant species; after the disappearance of the former, species of Marginotruncana are the only important species present. M. pseudolinneiana, M. coronata, M. fungicamerata and M. tarfayaensis are found throughout the section in similar percentages. On the other hand, M. sigali and M. renzi are abundant only in the lower part of the section. There are other species which occur rarely in most samples, such as M. paraconcavata, M. scorpionis and J4. undulata. The specimens determined as Marginotruncana schneegansi occur as two morphotypes, which are differentiated by the presence or absence of inflated chambers in the inner worls of the spiral side. The former is restricted to the upper part of the section while the latter occurs in the lower part. The species Hedbergellaflandrini and H. simplex are common in the middle part of the section, but rare elsewhere. Unfortunately, other species such as Marginotruncana sinuosa, Dicarinella primitiva, Archaeoglobigerina cretacea,

66

M. A. Lamolda

and F. Proto-Decima

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Figure 2. The Turonian-Co&&n boundary in the Ollogoyen section and the ranges of the plankHna. = Helvetoglobotmncana; tonic foraminifers. Hlix. = Heterohelix; Hlla. = Hedbergella; W = Whiteinella; A = Archaeoglobigerina; D = Dicarinella; M = Marginotruncana.

Turonian-Coniacian

Boundary in Northern Spain

67

archaeocretacea and Hedbergella hoelzli are very rare (and even these determinations may be doubtful). The abundant species are of little significance with regard to the Turonian-Coniacian boundary. Marginotruncana pseudolinneiana and related species, are present throughout the late Turonian, sometimes associated with the later specimens of H. helvetica. The abundance of M. pseudolinneiana allows us to recognise the late Turonian, and the first appearances of the species Marginotruncana paraconcavata, M. tarfayensis and M. scorpionis are also significant. All of these occur later than H. A. blowi, Whiteinella

helvetica. In the monograph on the mid-Cretaceous planktonic foraminifera (Robaszynski and Caron, 1970) there are several species whose first appearances occur near the Tu/Co boundary; Dicarinellaprimitiva (Dalbiez), Hedbergella jIandrini, Archaeoglobigerina cretacea, A. blowi, and Marginotruncana sinuosa. These species occur in the Ollogoyen Section but are rare and in some cases their identification is doubtful. Nonetheless, their distribution is similar to those recorded by Robaszyski and Caron and they can therefore be used to recognise the Tu/Co boundary in this part of Spain. Among the globigerina-like taxa we can identify the progressive appearance of the species H. flandrini, A. cretacea and A. blowi. The Tu/Co boundary lies between the appearance of the later two (samples OL24 and OL3 1, respectively). M. sinuosa Porthault is another interesting species to be considered, as its In first appearance occurs near, but also above the studied boundary. Ollogoyen we have found specimens of this species from sample OL3O upwards. Below this level there are some specimens that are atypical (“transitional” between M. undulata and M. sinuosa). The boundary must therefore be placed below sample OL30, but not far away. There are another three globotruncana-like species to be considered; Marginotruncana tarfayaensis Lehman, M. schneegansi Sigal and D. primitiva (Dalbiez). M. tarfayaensis makes its first appearance in the late Turonian with M. paraconcavata and a little later than the extinction of H. helvetica. The species D. primitiva-sensu Robaszynski and Caron (1979)-occurs in our samples 0L33 and 0L46; its first appearance is correlated with the earliest Coniacian. In this section, therefore, the TujCo boundary must be below sample OL33. As mentioned above, the species M. schneegansi shows two morphotypes; one with inflated chambers on the spiral side (mainly the inner ones) and the other with a flat surface on the spiral side. Both morphotypes are found in samples OL30 to OL41. In the lower part of the Ollogoyen section one finds the latter morphotype while in the upper part of the section it is the former. The validity of placing both these morphotypes in the same taxon could be questioned, but from a biostratigraphic viewpoint the “inflated” specimens are probably of Coniacian age. The topotypes*of the species described by Caron (1977) are of Coniacian age, and specimens showing no inflation have already been described from strata of Turonian age in the Basque Country (Lamolda, 1977). This taxonomic problem was also discussed by Robaszynski and Caron (1979). On this basis the Tu/Co boundary must be below sample OL30 and this would agree with the other microfossil distributions.

68

M. A. Lamolda and F. Proto-Decima

In the heterohelicids we have found a morphological trend from biserial specimens to single plane multilocular ones. The studied species may be determined as Heterohelix pulchra (Brotzen), which the original illustrations show (fide Saito et al., 1980) as h aving both biserial and multiserial specimens (of early Senonian age). Pessagno (1967) claimed that the multiserial specimens must be classified within the genus Planoglobulina, not Heterohelix, but Douglas and Rankin (1969) rejected that proposal. They suggested that these are morphotypes of the same species, as had been proposed by Brotzen (1936); the microspheric form being represented by the multilocular specimens and the macrospheric form being those with the biserial arrangement. The species Heterohelix pulchra is regarded as Coniacian or younger. Either and Worstell(1970) placed H. pulchra in the early to middle Turonian in the Western Interior Cretaceous of U.S.A. Their specimens show a trend toward uniserial morphotypes, related to Lunatriella spinifera Either & Worstell. This relationship was pointed out by Either & Worstell(l970) and taken to indicate a different evolutionary linneage between their specimens and those related to the multichambered, fan-like, “Planoglobulina” and VentiZabreZZa as suggested by Martin (1972). It seems, then, that we have found the species H. pulchra in beds of late Turonian and early Coniacian age. The biserial specimens are found in the lower part of the section. Younger specimens have three or more chambers per whorl and a fan-like outline. These appear in sample OL30 and continue up section into strata that is Coniacian in age. These observations could change the taxonomic status of some of the heterohelicids, as suggested by Martin (1972) and Masters (1976), but more interesting, from the viewpoint of this work, is the fact that this trend occurs in the part of the Ollogoyen section that includes the Turonian-Coniacian boundary. 4. Benthonic foraminifers Benthonic foraminiferal faunas have been studied from some selected samples from the Ollogoyen section. The fauna is abundant and wellpreserved in the samples studied, but this present work has concentrated on those taxa that appear to have some stratigraphic value. Sixty-one species have been identified, many of them well-known from other micropaleontoligical research on the European Cretaceous. In spite of this there is a general lack of published data on Turonian and Coniacian benthonic foraminifers and some nomenclatural problems remain. Figure 3 shows the distribution of the recorded species. The absence of shallow-water and very deep-water indicators and the general composition of the assemblage suggest an environment that was not very deep. No significant variation has been observed in the samples regarding the numbers of species and the overall composition of the assemblages. The most common species, like Arenobulimina preslii, GaveZineZZa clementiana, Globorotalites micheliniana, Gyroidinoides cf. nitida and Tritaxia tricarinata, are present throughout the entire sequence. Others show irregular distributions without any evident pattern. Only very few species are restricted respectively to the lower or upper part of the section. The literature, on the other hand, for the

Turonian-Coniacian

Some phical

stratigra-

Boundary

Turonian

Upper Cretaceous

Spain

69

Lower

Upper

ranges

in Northern

Coniacian

Benthic

Foraminifers

Samples OL-

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3. Benthonic

-

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foraminifers

Section

Acruliammina sp. Ammobaculites agglutinans Ammodiscus Cretaceus Arenobulimina preslii Astacolus Cretaceus Cassidella tegulata Cyclammina sp. Dentalina cf. basiplanata Dentalina communis Dentalina gracilis Dental& pfebeja Dentalina cf. steenstrupi Dorothia bulletta Dorothia oxycona Frondicularia angusta Frondicularia archiaciana Frondicularia inversa Frondicularia cf. lanceola Frondicularia multilineata Gaudryina carinata Gaudryina foeda Gaudryina rugosa Gaudryina aff subserrata Gavelinella clementiana Globorotalites micheliniana Globulina lacrima horrida Gyroidinoides cf. depressa Gyroidinoides cf. nitida Haplophragmoides exdavatum Haplophragmoides cf. eggeri Lagena vulgaris Lenticulina exarata Lenticulina grata Lenticulina harpa 1 en ticulina cf. lepida Lenticulina muensteri Lenticulina ovalis Lenticulina secans Lenticulina subangulata Lenticulina taylorensis Lituotuba incerta Neoflabellina baudouiniana Nodosaria monite Nonionella cretacea Palmula cordata Praebulimina pusilla Pyrulina cylindroides Ouadrimorph. allomorphinoides Quinqueloculina antiqua I Ramulina arkadelphiana Ramulina kittli Recurvoides sp. 7 Reophax sp. Textularia cf. baudouiniana Triplasia cf. murchisoni Tritaxia tricarinata Trochamminoides coronata Trochamminoides trifida Vaginulina recta Vaginulina trilobata Valvulineria camerata umbil.

of the Ollogoyen

section.

70

M. A. Lamolda

and F. Proto-Decima

same species appear to indicate longer stratigraphical ranges (extending to the entire late Cretaceous in some cases). Two somewhat similar forms, Gaudryina carinata and Gaudryina rugosa, show in their respective frequencies a peculiar complementary behaviour. G. rugosa, whose known range is Coniacian-Maastrichtian, becomes predominant in the upper part of the section. In the case of Lenticulina harpa, Vaginulina recta and Palm&a cordata the distributions could also be significant as they seem consistent with the published literature. In our samples, however, the first two mentioned species are too rare to be of any actual stratigraphical significance. Palmula cordata, on the contrary, is well represented in the lower part of the section. In other areas this species is common in Turonian strata and rate in the Cenomanian and Coniacian. The abrupt disappearance of this species in the upper part of the section could therefore be significant, placing the Turonian/Coniacian boundary above sample OL32. Koch (1977) uses some species of Stensioeina for biostratigraphical subdivision of the Turonian and Coniacian stages of Northwest Germany. As this genus is not seen in our samples one cannot make a direct comparison to that area nor to the Turonian and Coniacian strata of the Boulonnais in Northern France (Robaszynski et al., 1980). About 50% of our species are common with the foraminifers described by Franke (1928) for the Upper Cretaceous of Germany, but it is not possible to derive any detailed stratigraphical information from their distribution. The fauna cannot be used, at the present time, for the identification of the Tu/Co boundary.

5. Calcareous nannofossils The calcareous nannofossils are common to abundant in all the examined samples. The assemblages, typical for the early part of the late Cretaceous, are more or less the same throughout the entire section, variation in diversity being principally dependent on the state of preservation. A peculiar feature of these assemblages is the frequency of Nunnoconus, represented by the morphological types already known from the late Cretaceous of France. The most common “species” are Nannoconus truitti Bronnimann and N. multicadus (Deflandre and Deflandre-Rigaud). N. elongatus Bronnimann and N. regularis Deres and AchCritCguy are also represented with other intermediate forms. Their presence is consistent with the nannoconid biostratigraphy of Deres and AchCritCguy (1980). Aubry (1974) has a different species concept for nannoconids. In her opinion, the structure of the surface, observed with a scanning electron microscope, is more important than the morphology of the test. Such observations have led Aubry, for instance, to consider N. truitti, N. multicadus and N. dauvillieri as biological forms of the same species. No attempt has been made to tabulate the different morphological types in our material. From a paleoecological point of view the nannoconids seem to have preferred a marginal-type environment, near the edge of the continental shelf. They are very rare or absent in pelagic sediments. Similar paleocolog-

Turonian-Coniacian

Boundary in Northern Spain

71

ical conditions are also suggested by the occurrence of Lucianorhabdus, which is quite frequent in our samples. The distribution of the species recognised in the section is shown in Figure 4. For biostratigraphic purposes reference has been made to Thierstein (1976), Manivit et al. (1977), Sissing (1977,1978), and Perch-Nielsen (1979). Detailed reviews of the development of Cretaceous nannoplankton stratigraphy, suggestions and discussions of zonal schemes, datum-planes and relationships with the chronostratigraphy, are all illustrated in the abovementioned works. The samples from OLlO to OL46 can be referred to the nr. 12Lucianorhabdus maleformis zone of Sissing (1977), which is defined as the interval from the first occurrence of L. maleformis Reinhardt to the first occurrence of Marthasteritesfurcatus (Deflandre) Deflandre. The entry of L. maleformis is diagnostic in the late Turonian but this cannot be detected in our sequence as this species is present from the lowermost sample upwards. The base of the section is therefore late Turonian in age. The upper limit of the zone falls between samples 0L46 and 0L47, marked by the appearance of M. furcatus in sample OL47. Samples OLlO to 0L46 could also be referred to the Eiffeellithus eximius Zone of Manivit et al. (1977), which is defined as the interval from the first occurrence of E. eximius s.Z. to the first occurrence of M. furcatus. Since the authors of the zone report the first occurrence of E. eximius from the late Turonian, this zone can be considered approximately coincident in age with the Lucianorhabdus maleformis Zone. Based on the presence of the marker furcatus Zone of species, sample OL47 is referred to the Marthasterites CXpek and Hay (1969), emended Sissing (1977), defined as the interval from the first occurrence of 1M. furcatus to the first occurrence of Micula ex. gr. staurophora (Gardet) Bramlette and Martini. The entry of iVl. furcatus is referred to the early Coniacian. In our section only sample 0L47 revealed the very rare presence of&f. furcatus and can be correlated with the base of the zone. From the calcareous nannofossil evidence, the age of the examined section is therefore late Turonian-early Coniacian. According to the literature, the Lucianorhabdus maleformis or the Eiffellithus eximius Zone straddle the Turonian/Coniacian boundary, so its’ actual position cannot be precisely placed by means of nannofossils. The data obtained from the Ollogoyen section

are consistent

with those

reported

in the literature

from

elsewhere.

6. Conclusions The vertical ranges of the planktonic foraminifers in the Ollogoyen section can be used to delineate the Turonian-Coniacian boundary. The first appearance of Archaeoglobigerina cretacea (sample number 0L24) is found in almost the same bed as the last occurrence of the ammonite genus Romaniceras, and the first appearance of Marginotruncana sinuosa and M. schneegansi S.S. In addition there is the development of fan-like heterohelicids (?Ventilabrella sp.), in sample OL30. The benthonic foraminifers are presently unsuitable for delineating the Tu/Co boundary. The more common species usually have long stratigraphic

Zones

Stages

Discorhabdus ignotus Eiffellithus eximius Eiffeliithus trabeculatus Eiffellithus turriseiffeli Eprolithus floralis Gartnerago obliquum Kamptnerius magnificus Lithraphidites carniolensis Lucianorhabdus maleformis Lucianorhabdus quadrifidus Manivitella pemmatoidea Markalius circumradiatus Marthasterites furcatus Marthasterites incospicuus Microrhabdulus decoratus Nannoconus spp. Parhabdolithus embergeri Prediscosphaera spp. Quadrum gartneri Ragodiscus angustus Retecapsa angustiforata Stephanolithion laffittei Tetrapodorhabdus decorus Thoracosphaera sp. Tranolithus orionatus Watznaueria barnesae Zigodiscus diplogrammus Zygodiscus spiralis

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Turonian-Coniacian

Boundary

in Northern

Spain

73

“transitional”

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5. Index

fossils

and the placing

Archaeoglobigerina

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of the Turonian-Coniacian

cretacea

flandrini scorpionis

Marginotruncana tarfayaensis M. paraconcavata Helvetoglobotruncana helvetica

boundary

in the Ollogoyen

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ranges. Only some nodosariid species are interesting, with Palmula cordata having a last appearance in the proximity of the Tu/Co boundary. The nannofloral species show ranges very similar to those already known; there appear to be no index taxa for the Tu/Co boundary. This is included in the uppermost part of the L. maleformis Zone, because the first occurrence of 2Mathasteritesfurcatus is seen in the early (but not earliest) Coniacian, sample number OL47. The only available micropaleontological evidence for the Tu/Co boundary

74

M. A. Lamolda and F. Proto-Decima

in Ollogoyen are provided by the planktonic foraminifers. At first the boundary was placed between the samples 0L24 and OL30; a sediment thickness of 10 m. But, the boundary must actually be nearer the latter, since this is in line with the sudden disappearance of PaZmuZa cordata specimens from sample 0L32 and the occurrence of &I. primitiva (Dalbiez), sense Robaszynski and Caron (1979), in sample OL40 together with the occurrence of Coniacian species: Tissotia (M.) cf. robini, Reesideoceras cf. camerounense, etc., from the level of the last sample.

Acknowledgments The authors are indebted to Dr P. Ward for improving B. Bernedo typed the manuscript.

our English text. Mrs

References Aubry,

M. P. 1974.

Remarques

sur la sysdmatique

des AJannoconus de la craie.

Cahiers

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