The Cenomanian-Turonian boundary problem in NW-Germany with comments on the north-south correlation to the Regensburg Area

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Abstract
The lithostratigraphical successions across the Cenomanian-Turonian boundary are described. Two dif­ferent facies can be distinguished: A shallow water red marly limestone facies ('Rotpliiner') characterised by evidence of condensation and stratigraphical hiati; and a more complete deeper water facies with alternating marly limestones and black shales ('Black Shales' or 'SchwarzweiBe Wechselfolge'). A se­quence of litho- and ecoevents permits subdivision and correlation of the two facies. The base of both facies is apparently isochronous and rests on white coccolith limestones, the so-called 'Arme rhotoma­gense Schichten' of the Upper Cenomanian Calycoceras naviculare Zone. The stage boundary was traditionally drawn at the facies change, but biostratigraphical evidence places the boundary within the Rotpliiner/Black Shale formations. In Lower Saxony the extinction datum of Rotalipora cushmani agrees with records from other areas, i.e. within the Upper Cenomanian Metoicoceras ges/inianum Zone below the entry of Actinocamax plenus. From the Teutoburger Wald (Miinsterland) and Regensburg area (Bavaria) an apparent di­achroneity of this datum is indicated. The uppermost Cenomanian Neocardioceras juddii Zone of the international scheme has been identified only in the Black Shale facies. The diagnostic ammonites and inocaramid (Mytiloides aff. duplicostatus) of the basal Turonian Pseudaspidoceras f/exuosum Zone have not been recorded in either facies. For practical purposes the base of the Turonian is taken at the entry of Myti/oides, as is usual in Central Erope. Below this level there is a 'zone of uncertainty' with poorly preserved inoceramids of questionable generic identity. Above the entry of recognizable Mytiloides, an interregional fades-independent Myti/oides mytiloides ecoevent is traceable across W.-Germany to east­ern England. Critical species concepts within Mytiloides are reviewed in the context of possible facies dependence. Of importance for the North-South correlation is the recognition of Mytiloides sp. at the base of the Praeglobotruncana helvetica Zone in the Regensburg area.

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