Original paper

Zu Problemen der Biostratigraphie der Inoceramen und der Untergliederung des Cenomans und Turons in Mittel- und Osteuropa

Tröger, Karl-Armin

Kurzfassung

Ausgehend von der Entwicklung der Inoceramen wird eine Untergliederung des Zeitraumes vom Mitt.-Alb bis Mitt.-Coniac in 26 Abschnitte in Mitt.-Europa durchgeführt. Diese Gliederung ist mit z. T. provinziell bedingten Unterschieden auch für Osteuropa verwendbar und an die von E. G. KAUFFMAN (1976) für England vorgeschlagene Gliederung anzuschließen. Diese Untergliederung ist im Alb und Cenoman etwas gröber, im Turon und Coniac dagegen detaillierter als die Gliederungen, die auf der Entwicklung der Ammoniten bzw. Belemniten beruhen. Für die Festlegung der Grenzschnitte zwischen den Stufen sollte die Ammoniten-Zonenfolge als Grundlage dienen. Für die Untergliederung des Turon und Coniac in ein Unt.-, Mittel- und Ob.-Turon bzw. Coniac sollten Schnitte in der Inoceramen-Entwicklung verwendet werden. Das Cenoman beginnt mit den ersten Vertretern der Inoceramus crippsi-Gruppe, das Turon mit den ersten Vertretern der Inoceramus (Mytiloides) labiatus-Gruppe und das Coniac mit Inoceramus schloenbachi J. BÖHM bzw. ihm verwandten Formen.

Abstract

Ammonites, belemnites, echinids and inoceramids are used for biostratigraphic zonation and regional correlations in Europe. But in the most cases belemnites are absent in the Turonian and Coniacian layers in Central and East Europe. Ammonites and echinids are rare, too. Usually they do not permit to fix exactly the limits between the stages and substages. In the contrary the inoceramids are widespread and common in the most facial developments of Albian to Coniacian. Their rapid rates of evolution allow a more detailed zonation especially in the Turonian and Coniacian layers than it can be established by ammonite data. Between the Middle Albian and the Middle Coniacian we may differ 26 sections, which are characterized by different inoceramid species or inoceramid assemblages. In the same manner as in England (E. G. KAUFFMAN 1976) the Inoceramus (Birostrina) concentricus - sulcatus lineage is the most common in the Middle and Late Albian. Sulcate forms as Inoceramus (Birostrina) sulcatus PARK. and Inoceramus (Birostrina) concentricus subsulcatus WILTSHIRE first appear at the base of the Late Albian as it was confirmed by ammonites and belemnites (Neohibolites oxycaudatus SPAETH). The uppermost parts of the Late Albian are characterized by rare specimens of Inoceramus anglicus WOODS together with Aucellina gryphaeoides (SOWERBY). In the lowermost Cenomanian Inoceramus crippsi crippsi MANTELL together with passage forms to Inoceramus anglicus WOODS are common. A radiation took place at the base of the Mantelliceras saxbyi-zone. In the uppermost Lower Ceomanian and the Middle Cenomanian the most significant inoceramid species are Inoceramus crippsi hoppenstedtensis TRÖGER and Inoceramus virgatus SCHLÜTER. After an important reduction in inoceramid diversity at the base of the Upper Cenomanian or in the uppermost Middle Cenomanian a second radiation took place. The Upper Cenomanian including the zone of Actinocamax plenus (BLAINVILLE) contains especially members of the Inoceramus pictus lineage. The limit between the Cenomanian and Turonian should be fixed by the first appearance of Inoceramus submytiloides SEITZ. The base of the Lower Turonian is marked by an assemblage mainly consisting of Inoceramus (Mytiloides) opalensis BÖSE, Inoceramus (Mytiloides) mytiloides MANT. and in the upper parts Inoceramus labiatus (SCHLOTHEIM). According to O. SEITZ (1952, 1950) and in contrary to E. G. KAUFFMAN (1976) and E. SEIBERTZ (1979) the beds with Inoceramus (Mytiloides) hercynicus PETRASCHECK are put in the Lower Turonian.- The first appearance of Inoceramus apicalis WOODS marks the base of the Middle Turonian. The division of the Middle Turonian into two parts according to the filiation of the Inoceramus lamarcki lineage in the lower part and the Inoceramus striatoconcentricus lineage together with the Inoceramus costellatus lineage in the upper part must be mentioned. The base of the Upper Turonian is fixed by the first appearance of the lineages of Inoceramus dresdensis TRÖGER and Inoceramus fiegei TRÖGER with mytiloid subspecies. They are accompanied by Inoceramus costellatus costellatus WOODS and in the higher parts by members of the Inoceramus waltersdorfensis lineage. In East and Central Europe the Inoceramus schloenbachi-deformis lineage is accompanied by Coniacian ammonites (Peroniceras, Barroisiceras and others). The schloenbachi-zone is regarded as Lower Coniacian. May be, that the limit between the Turonian and Coniacian layers is fixed by the first appearance of an assemblage consisting of Inoceramus rotundatus FIEGE, Inoceramus waltersdorfensis waltersdorfensis AND., Inoceramus waltersdorfensis hannovrensis HEINZ and Inoceramus lusatiae ANDERT. The Middle Coniacian is characterized by involute inoceramids and the Inoceramus mantelli lineage. All inoceramid species or lineages mentioned are widespread in Central and East Europe and important for regional correlations between West and East Europe and Vest Asia.