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Upper Sinemurian and Lower Pliensbachian ammonite faunas from Herford-Diebrock area (NW Germany)

Joachim BLAU, Christian MEISTER, Rainer EBEL & Rudolf SCHLATTER

Postbox E-Mail: joachim.blau@geolo.uni-giessen.de
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Zusammenfassung

In einem Profil bei Herford-Diebrock wird die Ammonitenfauna des oberen Sinemurium (Raricostatum bis Aplanatum Subzone) und des unteren Pliensbachium (Polymorphus Subzone) studiert. Die Faunenhorizonte des Profiles werden mit solchen von Yorkshire, der Hessischen Strasse und SW-Deutschlands korreliert. Besonderes Augenmerk gilt der taxonomischen Position von Eoderoceras armatum (SOWERBY); Eoderoceras miles (Simpson) wird als Synonym zu SOWERBYs Art angesehen. Das Profil eignet sich nicht als GSSP der Sinemurium/Pliensbachium-Grenze.

Abstract

At Herford-Diebrock a section from the Upper Sinemurian (Raricostatum to Aplanatum Subzone) to the Lower Pliensbachian (Polymorphus Subzone) is studied in respect of its ammonite faunas. Precise correlations in terms of faunal horizons are carried out between Yorkshire and SW Germany through Hessische Strasse. Special emphasis is given to the taxonomical position of Eoderoceras armatum (SOWERBY). Eoderoceras miles (SIMPSON) is now placed in synonymy with SOWERBY's species. The section does not fulfill the requirements for the GSSP of the Sinemurian/Pliensbachian boundary.

Conclusions

The section of Herford-Diebrock was chosen to study the Sinemurian/Pliensbachian boundary in respect of the search for a GSSP (Global Standard Stratotype-section and Point) by members of the Sinemurian/Pliensbachian boundary working group because it seemed to be a possible candidate for the GSSP.
Unfortunately we must conclude that the section failed because (1) the position of the base of the Pliensbachian could not be prooved by ammonites, (2) the microfaunal content is strongly degraded and (3) palynomorphs are destroyed by plutonic heat influence. At least, all samples where barren of calcareous nannoflora (see MEISTER 1997).
From an ammonite biostratigraphical point of view, a NW German Upper Sinemurian succession was sampled and studied for the first time in terms of faunal horizons. All subzones of the Raricostatum Zone are present but are represented by only one faunal horizon each. Precise correlations between some of the ammonite horizons of Herford-Diebrock are possible with Yorkshire as well as with SW German profiles.
Moreover it is important to underline that the abundance of Eoderoceras armatum (Sowerby) allowed us to document the ontogeny and the taxonomical position of this species and to demonstrate that Eoderoceras miles (SIMPSON) is conspecific. According to their different suture lines Eoderoceras armatum and Leptonotoceras emersoni HOFFMANN cannot be interpreted as a dimorphic pair.

Buende Log

Lithostratigraphy, biostratigraphy and biochronology of the clay pit Stork 3 section. Bed numbers are in accordance with EBEL (1996), see this paper also for detailed lithological description of the section.

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