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Bull. Soc. belge Géol., Paléont., Hydrol. T. 78 fasc. 2 pp. 111-130 Bruxelles 1969 Bull. Belg. Ver. Geol., Paleont., Hydrol. V. 78 deel 2 blz. 111-130 Brussel 1969 THE TYPE-LOCALITY OF THE SANDS OF GRIMMERTINGEN AND CALCAREOUS NANNOPLANKTON FROM THE LOWER TONGRIAN E. MARTINI 1 & T. MooRKENS 2 CONTENT Summary 111 Zusammenfassung 111 Résumé 112 1. Introduction . 112 2. Historical review of some chronostratigraphical conceptions. 114 3. The Eocene-Oligocene transitional strata in Belgium 115 4. Locality details 122 5. The calcareous nannoplankton assemblages 124 6. Conclusions . 125 7. Acknowledgments . 127 8. References 127 SuMMARY. A. DUMONT (1839-1849) considered the Sands of Grimmertingen as the base of his Ton grian stage (Grimmertingen is at present a hamlet in the municipality of Vliermaal in the Eastern part of Belgium). Samples have been taken from the outcrop of the type-locality and from a new boring reaching a depth of 12,5 m, towards the base of this member. Sorne of these sa.mples from both outcrop and boring yielded fairly rich assemblages of calcareous nannoplankton of which a list is given: the assemblages belong to the Ellipsolithus subdistichus zone, the zone which was also recognised in the sand extracted from the molluscs of the type-Latdorfian (Lower Oligocene). The recent sampling of the Grimmertingen-locality also permitted to find fairly rich associations of Hystrichospheres and of planktonic and benthonic Foraminifera, which are under current study. ZusAMMENFASSUNG. A. DUMONT (1839-1849) stellte die Sande von Grimmertingen an die Basis seines ,,Tongrien" (Grimmertingen befindet sich heute im Stadtbereich von Vliermaal im ostlichen Teil von Belgien). In der Typuslokalitat der Sande von Grimmertingen wurden horizontmaBig Proben genommen und eine Bohrung bis zu einer Tiefe von 12,5 m niedergebracht, um nach Moglichkeit die Basis der Sande zu erreichen. Verschiedene Proben aus dem AufschluB und besonders aus der Bohrung enthielten Nannoplankton, das listenmaBig erfaBt wurde und das eine Einstufung der Schichten in die Ellipsolithus subdistichus Zone erlaubt, in die ebenfalls das Nannoplankton aus Mollusken der Typuslokalitat des Latdorfs (Unter-Oligozan) zu stellen ist. 1 Geologisch-Palaeontologisches Institut der Universitat, 6 Frankfurt a.M. Senckenberg-Anlage 32 (Germany). 2 Geol. Instit. of tlle State Univ. Ghent, Rozier, 6, Ghent (Belgium). 111 In den neugewonnenen Proben von Grimmertingen wurden ferner verhaltnismiiBig reichhaltige Gemein schaften von Hystrichosphaeriden sowie von planktonischen und benthonischen Foraminiferen gefun den, die zur Zeit bearbeitet werden. RÉSUMÉ. A. DUMONT (1839-1849) définissait la base de son étage Tongrien par les Sables de Grimmer tingen. (Grimmertingen est un hameau dans la commune de Vliermaal dans l'est de la Belgique). La localité-type a été échantillonnée dans son affieurement et par le moyen d'un sondage de 12,5 m vers la base de l'assise. Quelques échantillons de l'affieurement et du sondage ont montré une association assez riche en nanno plancton calcaires dont une liste est dressée: les associations appartiennent à la zone à Ellipsolithus subdistichus, zone qui fut également reconnue dans les sables extraits des coquilles de mollusques du Latdorfien-type (Oligocène inférieur). L'échantillonnage récent de la localité de Grimmertingen a également permis de découvrir des associa tions assez riches d'Hystrichosphères et de Foraminifères p\anctiques et benthiques, qui sont actuel lement à l'étude. 1. Introduction had been established in many areas: the zonations of the Nummulites, of the plank Sorne controversial viewpoints have been tonic Foraminifera and of the calcareous expressed recently in connection with the nannoplankton. stratigraphie situation of the Eocene-Oligo Although these three groups are represented cene boundary, and some of them have been in the basins bordering the North Sea, the discussed during the « Colloque sur ! 'Eo endemic character of most of the species of cène» (Paris, May 1968). the first group prevent wide correlations; the It appears that there is a fairly good agree scarcity and small dimensions of the plank ment between West-European geologists as tonic Foraminifera in the West-European area, to the correlation of the respective lithologie make their use dubious also, for the time units of the Eocene-Oligocene transitional being. strata in the English-, Paris-, Belgian-, and The third group has been studied recently North German basins. in the West-European basins, and it seems The exact situation of the Eocene-Oligocene that the calcareous nannoplankton give the boundary in the stratigraphy of the basins best results in wide correlations at present, bordering the North Sea hence becomes more as characteristic species of the zonation are a problem of convention than one of corre generally represented both in the basins lation difficulties within this area. bordering the North Sea and in more tropical However, correlations within the North Sea regions. area were based until recently only on paleon The importance of the West-European tological groups of a rather restricted geo basins lies in the fact that a great numbér of the graphical distribution: Molluscs, benthonic internationally recognized stratotypes of chro Foraminifera, Vertebrates, a.s.o. nostratigraphic units were established here. The first two groups are generally strongly The rather poor results of previous paleon faciesbound and a number of species seem to tological research have entailed that the be endemic for this area or even in one of its intensive study of these stratotypes had been basins; furthermore the third group seems not abandoned during some years in the West very useful in this area as the fossils are European countries; some recent positive rather scarce. results, however, justify a more thorough The paleontological discussions during the search in the classical localities, which also Colloquium were therefore concentrated on has been recommended by E. BRABB (in press) the microfossil groups for which a biozonation after his visit to the are~. 112 TABLE 1 cont.-delt. lag. Lit.-ner. Upp. Jl Cl. of Boom î (sandy layers) X ~-----------------1------~1-------~7'----I Cl. of Klein Spouwen X Low. ------------------1-----1---+----- [ 1 S. of Berg -X S. & M. of Oude Biezen Upp. [ X..::._? ~ ~ Clay of Henis i . ffi (hiatus) ~ l S. of Neerrepen '\. S. of Grimmertingen 1---X i!:J unconformity ~ X----- TABLE 2 Cont.-delt. Lag. lit.-ner. X --'-1---+-----x * S. Kerkom ~ Upp. -~:__& M~_Bouters~~- _ ~ ll Hoogbutsel horizon X-- ? - ---;------- -~-1- ----·--- -- --- low. 11 \:~~~:on-~-------~--- X-?-X ~ unconformity ~ X 113 2. Historical review of some chronostratigra The later defined Stampian s.l. ( = definition phical conceptions by A. d'ORBIGNY, 1852) in the Paris Basin, of which the lower part was later separated, The division of the Tertiary in three periods to form the Sannoisian (A. de LAPPARENT, (or sub-epochs) established in 1833 by Ch. 1893) and of which the remaining part was LYELL was based mainly on the percentages of defined again as Stampian s.s. fall in synonymy recent living mollusc species in the respective with part of the earlier created Tongrian and fossil assemblages. Rupelian stages. This scheme of LYELL was followed by As the transitional Eocene-Oligocene layers A. DUMONT (1839, 1849) when defining some in the Paris basin are mainly reflecting fresh of his stages and placing them in the strati water and brackish to lagoonal conditions, graphie column. G. DENIZOT (1968) concludes that the succes The Tongrian s.l. ( = definition by A. Du sion of the Paris basin better should not be MONT, 1839) was thus placed tentatively at the chosen to establish the stratotype of the basal base of the Miocene; later A. DUMONT ob Oligocene, thus controversing C. CAVELIER served that the succession of lithologie units (1968) who proposes to consider the ,,Argile of his Tongrian s.l. reflected at least two verte de Romainville" of this area as the basal consecutive transgressions (cf. tables 1 and 2). stratum of the Oligocene. The succession of the second transgression The Oligocene conception was defined by was therefore defined as Rupelian (A. Du E. BEYRICH (1854, 1856) who observed that the MONT, 1849) with the «sable jaunâtre » (later mollusc-assemblages found in a number of called the Sands of Berg) at the base. The outcrops in Germany could be correlated Rupelian was thus separated from the Ton with those of the classical Tongrian deposits grian s.l., while the remaining basal part of described by A. DUMONT. this conception was redefined as Tongrian s.s. He had noticed that these mollusc assem ( = definition by A. DUMONT, 1849). blages could be distinguished from the typical The basal stratum of the Tongrian s.l. and Eocene associations as well as from those of the Tongrian s.s. are the same layers from the the typical Miocene: the layers containing this same locality, already cited in 1839: Grim assemblage therefore characterized a certain mertingen (see also the following chapter). period which he called the Oligocene, and The Sands of Berg (in their type-locality), which was defined on a number of localities the full-marine sediment deposited at the in Germany. beginning of the second transgression was The basal part for this German Oligocene considered as the base of the Rupelian stage, succession was tentatively parallelised with the while the type-locality of the Clay of Boom, "Tongrien inférieur" of A. DUMONT which

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