New perceptions of the foraminiferal faunas of the Geldern T 1 bore-hole and their importance for the Miocene of the Lower Rhine District

New perceptions on the foraminiferal faunas of the Geldern T 1 bore-hole and their importance for the Miocene of the Lower Rhine District. In the bore-hole Geldern T 1 (F.R.G., Nordrhein-Westfalia) (van Rooijen et al., 1984) a first coherent, almost complete section through the marine Miocene deposits of the Lower Rhine area is available. A recent careful investigation of the foraminiferal faunas enables a detailed stratigraphical subdivision of this well and consequently also of the Lower Rhine Miocene (Steinberg, 1986). In this way it was possible to confine the upward sequence Tichelovener, Bislicher, Dingdener and Uedemer Schichten on the basis of Foraminifera. The genus Uvigerina represents a stratigraphical tool which allows subdivision also in cases where molluscs are indifferent as a result of facies dependence. In this respect Uvigerina tenuipustulata van Voorthuysen, an index fossil for the higher parts of the Hemmoorian, is an important species. Its presence, next to typical accompanying Hemmoorian faunas, in the Tichelovener Schichten demonstrates that these belong to the higher Hemmoorian. A similar presence of U. tenuipustulata in the lowermost Miocene deposits of adjacent bore-holes illustrates that in the Lower Rhine area—as in northern Germany (von Daniels & Spiegler, 1977)—deposits with tenuipustulata should be reckoned to the Hemmoorian (Steinberg, 1986). Furthermore also in the Lower Rhine area Uvigerina semiornata semiornata d’Orbigny and U. pygmaea ssp. offer the possibility of a clear distinction between the Reinbekian and the Langenfeldian on the basis of Foraminifera. A comparison of the Geldern T 1 bore-hole with the larger territory of the neighbouring countries shows numerous similarities and yields important indications for a resolution of existing correlation problems, especially in the Dutch and NW German subdivision of the Miocene. Moreover palaeoecological results of the Geldern T 1 bore-hole demonstrate a diverse subdivision in facies of the Lower Rhine Miocene shelf sea, especially so for the Hemmoorian, where typical foraminiferal faunas enable a distinction between deeper and more shallow parts of this shelf sea. Comparisons with NW European subdivisions of the Miocene, based on Foraminifera (King, 1983; von Daniels & Spiegler, 1977, 1979), suggest that zonations established in such areas may also be applied in the Lower Rhine District (Steinberg, 1986) This should be acknowledged, however, by further investigations in a larger area.