The Turonian-Coniacian stage boundary in Lower Saxony (Germany) and adjacent areas: the Salzgitter-Salder Quarry as a proposed international standard section

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Abstract
The litho- and biostratigraphy of the Turonian-Coniacian boundary succession of the Salzgitter-Salder limestone quarry (Lower Saxony) is described in the context of a proposed international standard section. Compared with other sections, Salder provides a thick continuous succession unaffected by condensation and/or non-sequences and with an abundance and diversity of macrofossils, notably inoceramids. The litho-, tephro-, and ecoevents which can be used to subdivide the sequence are described, from the base of the traditional 'Scaphiten-Schichten' up to the contact with the Emscher Marl. The events are ideal marker horizons for long-range correlation across NW Germany as far as England. The base of the Coniacian is taken at the entry-datum of Cremnoceramus? waltersdorfensis hannovrensis, coincident with the upper of two Didymotis events. This event is immediately followed by a major change in the inoceramid assemblages with the entry of Cremnoceramus? rotundatus. This latter change coincides with the traditional German Mittel-Oberturon boundary. The boundary problem is discussed in the context of ammonites, echinoids, foraminifera, and nannofossils. The inoceramid assemblages beneath the boundary have strong affinities with those of the uppermost Turonian Prionocyclus quadratus Zone in N. America; The boundary in Lower Saxony falls in the upper part of a distinctive lithostratigraphical unit of alternating marls and marly limestones (the so-called 'Grauweisse Wechselfolge'), intercalated between two predominantly limestone units. The geographical distribution and fades-differentiation of the 'Grauweisse Wechselfolge' in correlative sections of Lower Saxony is examined. The unit.is the key to the recognition of the restricted boundary succession in sections where stratigraphical data are inadequate or lacking, e.g. the flooded quarries of Liineburg and the Staffhorst mine-shaft. The probable equivalent of the 'Grauweisse Wechselfolge' in northern England is discussed, and additional comments are made on southern England, and northern Spain. The Copenhagen Symposium (1983) proposals for recognising the base of the Coniacian are critically reviewed. The entry of C.? waltersdorfensis hannovrensis is demonstrated to be the only practicable criterion in many areas. The base of the"Senonian, as defined in the Anglo-Paris Basin, is suggested to equate with the base of the 'Grauweisse Wechselfolge' and thus to be of late Turonian age.

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