The age of the North Sea Basin Hemmoorian (Miocene)

Selected papers presented at the 7th Joint Biannual RCNNS-RCNPS meeting, Leuven 20-23th September 1999

The age of the North Sea Basin Hemmoorian (Miocene): holoplanktonic molluscan evidence

Arie W. Janssen National Museum ofNatural History, Palaeontology Department (Cainozoic Mollusca), p.a. Box 9517, 2300 RA Leiden, The Netherlands; and 12, Triq il-Hamrija, Xewkija VCT 110, Gozo, Malta

provide much more reliable data in such correlations. The conclusion must be that the benthic molluscan associations did not migrate northwards and reach the North Sea Basin until the Late Burdigalian. A northerly penetration of warm Atlantic water has also been demonstrated for the nannoplankton .assemblages (Cepek et aI., 1988).

ABSTRACT North Sea Basin stratigraphers have usually correlated the boundary between the Hemmoorian and Reinbekian stages with that between the international chronostratigraphic units Burdigalian and Langhian (e,g. many references in IGCP 124, Geol. Jb" 1988). Janssen & King (1988) also favoured an 'Early Miocene' age for their pteropod zone 18, which equates with the Hemmoorian. Improved knowledge of European pteropod assemblages, and of their stratigraphic ranges, together with revised interpretations of taxa has now led to the inevitable conclusion that the Hemmoorian pteropodassemblage (inclusive of the Behrendorfian and Oxlundian) should be dated as Late BurdigalianlLanghian. The most important species in this respect are representatives of the genus Vaginella. In the type area of the Aquitanian and Burdigalian stages the sole species of Vaginella is V. depressa Daudin, 1800, which occurred in the North Sea Basin only during the Vierlandian. The Hemmoorian and Reinbekian are characterised by V. austriaca Kittl, 1886, which in the deepwater deposits of the southern Aquitaine first appears in strata of Late Burdigalian age. In the Mediterranean Basin (Italy, Malta, Turkey) a similar pattern is seen. Additional evidence is supplied by the occurrence in the North Sea Basin of other typically Langhian pteropod species, such as Clio bellardii Audenino, 1897, Diacrolinia aurita (Bellardi, 1873) and Vaginella lapugyensis Kittl, 1886. Thus the North Sea Basin pteropod zones 18 and 19 (Janssen & King, 1988) are of latest Burdigalian to Langhian age. Since zone 19 contains only an impoverished zone 18 assemblage this might well include (portions of) the Serravallian. Obvious discrepancies between these data and results based on planktonic foraminifera (Hooyberghs & Moorkens, 1988) and calcareous nannoplankton (Muller & Kothe,1988) have yet to be resolved. Recently published sequence stratigraphical interpretations (Vandenberghe et aI., 1998) coincide almost completely with the results of holoplanktonic Mollusca. The revised age assignment of the Hemmoorian sheds new light on the migration of the rich Hemmoorian benthic molluscan assemblages of Burdigalian character, which have always been the main correlation tool between the Aquitaine and North Sea basins. Holoplanktonic organisms

Aardk. Mededel., 2001, 11, 45-50.

KEYWORDS Holoplanktonic Mollusca, biostratigraphy, long-distance correlation, Miocene, Vierlandian, Hemmoorian, Reinbekian, Burdigalian, Langhian.

Introduction The Neogene of the North Sea Basin has traditionally been subdivided into the stages Vierlandian, Hemmoorian (with substages Behrendorfian and Oxlundian), Reinbekian, Langenfeldian, Gramian and Syltian (all Miocene), and Kattendijkian, Scaldisian and Merksemian for the Pliocene. Vierlandian and Hemmoorian together are usually referred to as Early Miocene, Reinbekian and Langenfeldian as Middle Miocene, and Gramian plus Syltian as Late Miocene. Most workers have agreed on this subdivision, with the exception of the Langenfeldian, the early part of which has sometimes been referred to as Levensauian and for which also other substages have been proposed. Originally all of these stages and substages were based on (a combination of) lithological and palaeontological characteristics (in many cases especially the benthic molluscan assemblages, later also refined or redefined by benthic and/or planktonic foraminifera, and/or calcareous nannoplankton), and are therefore no real time-stratigraphic units. Independent numerical datings are not available within the North Sea Basin. Absolute ages, as occasionally tied in with these stages, have been derived indirectly by comparison of local biostratigraphic zonations based on foraminifera or nannoplankton with current international biostratigraphic schemes, and their chronostratigrapic interpretations. In this way Hinsch (1986) assumed for the Hemmoorian the interval of 21 to 17 Ma, and for the Reinbekian of 17 to 14 45

Ma. In international chronostratigraphy, Hinsch correlated the Hemmoorian with the Burdigalian, and the Reinbekian 'with the greater part of the Langhian'. These figures were later refined (Hinsch, 1994): 22-16.2 Ma and 16.2-13.8 Ma, respectively. The Reinbekian was considered to correspond to the Langhian and Early Serravallian. Comparison of these ages with Berggren et al.'s (1995) scheme would equate the Hemmoorian with the younger half of the Aquitanian and the entire Burdigalian, and the Reinbekian with the Langhian and the Early Serravallian. The boundary between Hemmoorian and Reinbekian would therefore approximately correspond to the Burdigalian-Langhian boundary in the global chronostratigraphy at c. 16.4 Ma.

pteropod zones 17 and 18 of Early Miocene, and zones 19 and 20 of Middle Miocene age. Zone 19 yields just an impoverished zone 18 pteropod assemblage, and the authors stated that further research might lead to the combining of zones 18 and 19. In the zones 17-19 interval, the occurrence of the genus Vaginella offers excellent possibilities for first-order, long distance correlations. Zone 17, known predominantly from the Vierlandian (Klintinghoved Formation and Holsteiner Gestein) yields few pteropod species, among which Vaginella depressa Daudin, 1800, confined to this zone. Pteropod zone 18 is known from the Arnum Formation in Denmark, from all so-called 'Hemmoor' -faunas in Germany, from the Breda Formation in The Netherlands and the Berchem Formation in Belgium. Vaginella depressa is replaced by V. austriaca, a species found in virtually all fossiliferous 'Hemmoorian' sediments (Behrendorfian and Oxlundian included) in the North Sea Basin. During the Oxlundian there is a sudden increase in the number of pteropod species. In its type area near Bordeaux (northern Aquitaine Basin), Vaginella depressa (see Janssen, 1985, figs. 10-13) is a common species, occurring throughout marine deposits of Aquitanian and Burdigalian age. Specimens from Saucats [Coquillere outcrop, erroneously referred to as 'Burdigalien superieur' by Janssen & King (1988, p. 364)] also belong to V. depressa. According to Cahuzac et aI. (1997, p. 51, sample AQ 78) the Coquillere assemblage has an age of 19 Ma (Sr dating), i.e. mid Burdigalian. Younger Burdigalian sediments are absent in the type area (Cahuzac et aI., 1997, fig. 6); the same holds true for Langhian deposits (Cahuzac et aI., 1995). Therefore the transition from V. depressa to V. austriaca must have occurred during the later part of the Burdigalian, the time interval between 19 and 16.4 Ma, not documented in the rocks of the Bordeaux area. Also from northern Italy, where V. austriaca shows a predominantly Langhian distribution, some records of this species had to be dated as Late Burdigalian (Janssen, 1995). Vaginella austriaca (compare Janssen, 1984, pI. 4, figs. 1-8) was originally described from Badenian faunas in the Central Paratethys, also correlatable with the Langhian. Some records of this species, however, are of Karpatian age, which equates with the Late Burdigalian (Zorn, 1991). That author also referred to a specimen of V. austriaca from the Eggenburgian (Early Burdigalian) Haller Formation in Austria, but in view of the fact that typical V. depressa does occur in the same deposit (loc. ci1., p. 126, pI. 15, figs. 5-6) the specimen identified as V. austriaca might in fact fall within the range of variation of V. depressa. Another discrepancy in the Austrian Miocene seems to be a single specimen of typical V. depressa from Forchtenau (loc. ci1., p. 126, pI. 15, fig. 3), a locality exposing strata of Badenian (Langhian) age. In the southern Aquitaine, V. austriaca was recorded from deep-water deposits of Langhian age at Saubrigues (Cahuzac et aI., 1995). V. austriaca, already recorded from S1. Jean-de-Marsacq by du Boucher (1887), was recently found to occur at S1. Jean-de-Marsacq (Pinot), a locality dated only roughly as 'Burdigalian' (NN3-4) by Cahuzac et al.

Biostratigraphy

Planktonic foraminifera

In Spiegler et al.'s (1988a, fig. 80, 1988b) planktonic foraminifera zonation the Early-Middle Miocene boundary is situated between the zones NPFl2 and 13. However, these authors referred to this boundary as 'disputed'. The Belgian unit they refer to for their zone NPFI3, the Berchem Formation, is usually considered to be Hemmoorian in age (benthic molluscan zone BMI8; Hinsch, 1988), but according to their data could also be Reinbekian. This is confirmed by Hooyberghs & Moorkens (1988), who dated the NPF13 zone as Langhian, and recognised zones NPF13-14 in the middle to upper part of the Antwerpen Sand Member and the Zonderschot Sand Member. They assigned the lower part of the Antwerpen Sand to zone NPF12 (Burdigalian), together with the Houthalen Sand Member. Zone NPFll (Aquitanian) was recognised in the Edegem Sand.

Calcareous nannoplankton

According to Muller & Kothe (1988), biozones NNI-4 are of Early Miocene and zone NN5 of Middle Miocene age. From NN5 upwards nannoplankton content of the deposits decreases in number of species and specimens, and zonal interpretations are difficult or impossible. Berggren et al. (1995) assigned NNl and the greater part of NN2 to the Aquitanian, the latest part of NN2, NN3 and the early part of NN4 to the Burdigalian, and the later part of NN4 plus NN5 to the Langhian. The younger part of NN5 is already of Serravallian age. Again this would mean that the Hemmoorian correlates with the Burdigalian and the Reinbekian with the Langhian.

Holoplanktonic molluscs

A preliminary biozonation based on holoplanktonic Mollusca for the North Sea area was published by Janssen & King (1988), who recognised the value of these organisms for interregional correlations, an observation later substantiated by Janssen (1990). Janssen & King distinguished 46

(1995, table 3). According to Berggren et aI. (1995) the interval 'NN3-4' is indeed younger than 19 Ma. The comparatively rich Zone 18 pteropod assemblage in the North Sea Basin which accompanies Vaginella austriaca lends further support for a revision of previous correlation. The following species were listed by Janssen & King (1988) and/or Janssen (1989):

Species

Limacina miorostralis

range outside North Sea Basin Chattian? to Langhian?

(Kautsky, 1925)

Limacina valvatina (Reuss,

Chattian to Early Serravallian

1867)

Styliola subula (Quay & Gaimard, 1827) Clio bellardii AUdenino, 1897 Clio deflexa (van Koenen, 1882) Clio pauli Janssen, 1989

Limacina miorostralis (Kautsky, 1925) Limacina valvatina (Reuss, 1867) Styliola sp. Clio deflexa (von Koenen, 1882) Clio irenae Janssen, 1989 Clio pauli Janssen, 1989 Cavolinia perovalis (von Koenen, 1882) Vaginella austriaca Kitt!, 1886 Vaginella aff. lapugyensis Kittl, 1886 Vaginella sp. vel Clio sp. novo

Diacrolinia aurita (Bellardi,

Chattian-Recent Langhian (not yet known outside the NSB) (not yet known outside the NSB) Langhian

1873)

Vaginella austriaca Kittl, 1886

Vaginella lapugyensis Kittl,

Late Burdigalian-Early Serravallian Langhian-Serravallian

1886 Distributions are based on Janssen (1984, 1989, 1995) and on data yet unpublished.

The last-mentioned taxon was recognised to refer to juvenile specimens of Vaginella austriaca in pre-metamorphosis stage. A further correction concerns Cavolinia perovalis. Judging from the original description and illustration of von Koenen (1882; the whereabouts of the type specimens unfortunately remains unknown) the species is closely related to, and most probably identical with Diacrolinia aquensis (de Grateloup, 1827) from the Early Burdigalian of SW France, where it co-occurs with Vaginella depressa. Von Koenen based this taxon on three specimens from Stolpe (Holsteiner Gestein). Most probably this record (the only one known so far) should be interpreted as Vierlandian, rather than Hemmoorian, and would thus fall in pteropod

Naturally, the long-ranging species offer no clues. The same goes for species that are not (yet) known outside the North Sea Basin. None of the remaining species contradicts a Langhian age, and Vaginella austriaca favours an age of Late Burdigalian to Early Serravallian. Of the species indicating Langhian or younger, Clio bellardii (see Janssen, 1995, pI. 5, figs. 1-2) and V. lapugyensis (see Janssen, 1984, pI. 20, figs. 6-7) are known only from the Oxlundian, and not from the earlier Hemmoorian. Diacrolinia aurita (compare Janssen, 1995, pI. 9, figs. 6-9) is known only from two boreholes in the Peel area in The Netherlands, from sediments (Breda Formation), presumably also Oxlundian in age, as indicated by benthic molluscan assemblages, which strongly resemble those of e.g. Winterswijk (Miste) (compare Janssen, 1984).

zone 17.

Some specimens from the Dutch Peel area, juvenile shells barely more than protoconchs, included in Cavolinia perovalis by Janssen & King (1988) have now been identified as Diacrolinia aurita (Bellardi, 1873), a species originally described from the north Italian Langhian, but widely distributed in Langhian deposits in the Mediterranean, and also known from the Central Paratethys, the Caribbean and Japan (compare Janssen, 1995). Clio irenae was based on only few specimens. Additional material, in a more adult stage, has demonstrated that this material belongs to Clio bellardii Audenino, 1897, a wellknown Langhian species, described from the Mediterranean. A revised list of Hemmoorian pteropod species, with their ranges outside the North Sea Basin in the global chronostratigraphy, now is as follows :

Sequence stratigraphical observations Vandenberghe et aI. (1998, p. 146, fig. 13) synthesised seguence-stratigraphic observations and biostratigraphic data, and recognised three units within the Edegem-KielAntwerpen succession, correlating the lower boundaries with those of standard units TB2.1-3 of Hag et aI. (1987). They considered the Edegem and Kiel sands to be of Burdigalian age, with the basal gravel of the Edegem Sand dated at C. 19,2 Ma. See also Vandenberghe & Hardenbol (1998, fig. 1). The lower boundary of the Antwerpen Sand was correlated with unit TB2.3, corresponding to the BurdigalianlLanghian boundary at 16.5 Ma, although they placed the basal gravel of the Antwerpen Sand still within the Late Burdigalian. Thus, those authors' interpretations are close to results obtained using holoplanktonic molluscs.

Other implications The rich benthic molluscan assemblages in the North Sea 47

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48

Basin Hemmoorian have a distinct southerly character and many species in common with the comparably rich Early Burdigalian faunas so well-known from the northern Aquitaine Basin. Since nearly all stages in the Neogene of the North Sea Basin were originally based on benthic molluscs, it is logical that a correlation of the Hemmoorian with the Burdigalian was accepted for a long time. Pteropods, the distribution of which is independent of facies because of their planktonic way of life, now demonstrate that all these Hemmoorian assemblages are younger than those from the Bordeaux area, which correlate with the Vierlandian instead. Apparently the Early Burdigalian assemblages migrated from the Aquitaine area northwards, reaching the North Sea Basin only in Late Burdigalian to Langhian times. Such a migration can only be explained by a northwards shift of the climatic belt. In this context it is useful to quote a conclusion based on calcareous nannoplankton assemblages in northern Germany (Cepek et aI., 1988, p. 279): 'Nannofossils become more common during the stratigraphic interval of zones NN3 to NN5. The northward penetration ofwarm Atlantic water masses is proved by the occurrence oftropical-subtropical species in northern Germany .... '.

REFERENCES BERGGREN, W.A, KENT D.V.,SWISHER C.C., AUBRY III & M.-P. 1995. A revised Cenozoic geochronology and chronostratigraphy. In: Berggren W.A., Kent D.V., Aubry M.-P. & Hardenbol J. (eds.). Geochronology, time scales and global stratigraphic correlations: a unified temporal framework for a historical geology. Society ofEconomic Paleontologists and Mineralogists, Special Volume 54, 129-212. BOUCHER, H.DU, 1887. Un pteropode rare dans le Tortonien de Saint-Jean-de-Marsacq. Bulletin de la Societe de Borda, Dax, 12(3), 147-149,3 figs. CAHUZAC, B., JANIN M.-C. & STEURBAUT E. 1995. Biostratigraphie de l'Oligo-Miocene du Bassin d' Aquitaine fondee sur les nannofossiles calcaires. Implications paleogeographiques. Geologie de la France, 2, 57-82,5 figs. CAHUZAC, B., TURPIN L. & BONHOMME P. 1997. Sr isotope record in the area of the Lower Miocene historical stratotypes of the Aquitaine Basin (France). In: A Montanari, G.S. Odin & R. Coccioni (eds). Miocene stratigraphy. An integrated approach. Developments in Palaeontology and Stratigraphy, 15 (Elsevier, Amsterdam), 33-56, 6-figs. CEPEK, P., KOTHE A & MULLER C.. The Federal Republic of Germany. Lower Saxony, Schleswig-Holstein. In: R. Vinken et al. (eds). The northwest European Tertiary Basin. Results of the International Geological Correlation Programme Project no. 124. Geologisches lahrbuch, (A)100, 275-279, fig. 138. HAQ, B.U, HARDENBOL J. & VAIL P.R. 1987. Chronology of fluctuating sea levels since the Triassic. Science,235,1156-1166. HINSCH, W. 1986. The Northwest German Tertiary Basin Miocene and Pliocene. In: H. Tobien (ed.). Nordwestdeutschland im Tertiar, 1. Beitriige zur regionalen Geologie der Erde, 18, 679-699. HINSCH, W. 1988. Benthic molluscs (Pelecypods, Gastropods) . The description of the interregional zonation (BM zones) and its correlation with the regional lithostratigraphy. In: R. Vinken et al. (eds). The northwest European Tertiary Basin. Results of the International Geological Correlation Programme Project no. 124. Geologisches lahrbuch, (A) 100, 344-356, figs. 180187. HINSCH, W. 1994. Biostratigraphy and paleogeography of Vierlandian and Hemmoorian (Early Miocene) in the Flensburg-Schleswig and North Frisia Region. In: Jacobs P. (ed.). Regional Committees on Northern Palaeogene and Northern Neogene Stratigraphy. Proceedings of the 3rd Bi-annual Joint Meeting, Gent, 9-13 September 1991. Bulletin de la Societe beige de Geologie, 102(1-2),117-145,14 figs. HOOYBERGHS, H.J.F., & MOORKENS T. 1988. Planktonic Foraminifera. In: R. Vinken et al. (eds). The northwest European Tertiary Basin. Results of the International Geological Correlation Programme Project no.

Conclusions (Fig. 1) 1. The evolutionary transition of the holoplanktonic gastropod Vaginella depressa to V. austriaca took place in the time interval from 19 to 16.4 Ma. 2. Within the North Sea Basin all so-called Hemmoorian (Behrendorfian) deposits containing Vaginella austriaca must be younger than c. 19 Ma (Late Burdigalian). 3. Assemblages of Hemmoorian (Oxlundian) age containing Clio bellardii, Diacrolinia aurita, Vaginella austriaca and/or V. lapugyensis are younger than 16.4 Ma (Langhian). 4. The Reinbekian, yielding only an impoverished zone 18 pteropod assemblage, might extend up into the Serravallian, but correlations cannot be substantiated yet. 5. An Aquitanian to Early Burdigalian age must be postulaU~d for zone 17 (Vierlandian) only. 6. Even the oldest Hemmoorian faunas, such as those from the Edegem Sand Member in Belgium, yield Vaginella austriaca, and are therefore not older than Late Burdigalian. 7. Early Burdigalian benthic molluscan assemblages migrated from the Aquitaine Basin northwards and did not reach the North Sea Basin until the Late Burdigalian and Langhian.

Acknowledgements The author is grateful to Dr Robert-Jan van Leeuwen (Haarlem, The Netherlands) for critical remarks, to Mr Freddy AD. van Nieulande (Nieuw- en St. Joosland, The Netherlands), for making samples available, and to Dr John W.M. Jagt (Maastricht, The Netherlands), who improved the English. 49

124. Geologischeslahrbuch, (A)100, 190-198, figs. 9294. JANSSEN, A.W. 1984. Type specimens of pteropod species (Mollusca, Gastropoda) described by Rolle (1861), Reuss (1867) and Kitt! (1886), kept in the collection of the Naturhistorisches Museum at Vienna. Mededelingen van de Werkgroep voor Tertiaire en Kwartaire Geologie, 21(2), 61-91,1 tab., 6 pIs. JANSSEN, A.W. 1985. Evidence for the occurrence of a "skinny" or "minute stage" in the ontogenetica1 development of Miocene Vaginella (Gastropoda, Euthecosomata) from the North Sea and Aquitaine Basins. Mededelingen van de Werkgroep voor Tertiaire en Kwartaire Geologie, 21(4),193-204, 13 figs JANSSEN, A.W. 1989. Some new pteropod species from the North Sea Basin Cainozoic (Mollusca: Gastropoda, Euthecosomata). Mededelingen van de Werkgroep voor Tertiaire en Kwartaire Geologie, 26(3), 91-133, 5 figs, 8 pIs. JANSSEN, A.W. 1990. Long distance correlation of Cainozoic deposits by means of planktonic gastropods ('pteropods'); some examples of future possibilities. Tertiary Research, 11(2-4), 65-72. JANSSEN, A.W., 1995 Systematic revision ofholoplanktonic Mollusca in the collections of the' Dipartimento di Scienze della Terra' at Torino, Italy. Monografie, Museo regionale di Scienze naturali, Torino, 17,1-233, 3 figs., 14 pIs. JANSSEN, A.W., & KING C. 1988. Planktonic molluscs (Pteropods). In: R. Vinken et al. (eds). The northwest European Tertiary Basin. Results of the International Geological Correlation Programme Project no. 124. Geologisches lahrbuch, (A)100, 356-368, figs 188207. KOENEN, A. VON 1882. Die Gastropoda Holostomata und Tectibranchiata, Cephalopoda und Pteropoda des norddeutschen Miocan. 11. Teil von 'Das norddeutsche Miocan und seine Molluskenfauna'. Neues lahrbuch fur Mineralogie, Geologie und Paliiontologie, 2 (Beil. Bd): 223-376, pIs 5-7. MULLER, c., & KOTHE A. 1988. Nannoplankton. The description of the interregional zonation (NP zones, NN zones). In: R. Vinken et al. (eds). The northwest European Tertiary Basin. Results of the International Geological Correlation Programme Project no. 124. Geologisches lahrbuch, (A)100, 253-261, fig. 129. SPIEGLER, D., GRAMANN F. & VON DANIELS C.H. 1988a. Planktonic Foraminifera: the description of the interregional zonation (NPF zones). In: R. Vinken et al. (eds). The northwest European Tertiary Basin. Results of the International Geological Correlation Programme Project no. 124. Geologisches lahrbuch, (A)100, 152160, fig. 80. SPIEGLER, D., GRAMANN F. & VON DANIELS C.H. 1988b. Planktonic Foraminifera. In: R. Vinken et al. (eds). The northwest European Tertiary Basin. Results of the International Geological Correlation Programme Project no. 124. Geologisches lahrbuch, (A)100, 208217, figs. 96,101-106.

VANDENBERGHE, N., & HARDENBOL J. 1998. Introduction to the Neogene. In: De Graciansky P.-c., Hardenbol J., Jacquin T.& Vail P.R. (eds.). Mesozoic and Cenozoic sequence stratigraphy of European basins. SEPM Special Publication, 60, 83-85, 1 fig. VANDENBERGHE, N., LAGA P., STEURBAUT E., HARDENBOL J. & VAIL P.R. 1998. Tertiary sequence stratigraphy at the southern border of the North Sea Basin in Belgium. In: De Graciansky P.-c., Hardenbol J., Jacquin T.& Vail PR (eds.). Mesozoic and Cenozoic sequence stratigraphy of European basins. SEPM Special Publication, 60, 119-154,20 figs. ZORN, I. 1991. A systematic account of Tertiary Pteropoda (Gastropoda, Euthecosomata) from Austria. Contributions to Tertiary and Quaternary Geology, 28(4),95-139,20 tabs, 12-figs.

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