Calcareous dinoflagellate cysts from the Aptian/Albian boundary interval of northern Germany: Abundance patterns related to orbital forcing?
Heldt, M.; Lehmann, J.; Willems, H.
published: Oct 1, 2010
ArtNo. ESP026004401003, Price: 29.00 €
Boreal Aptian-Albian marine sediments of the Hannover region (northern Germany) mainly consist of dark to medium grey claystones, which were deposited in the central part of the Lower Saxony Basin. Calcareous dinoflagellate cyst samples of the Vöhrum clay pit, east of Hannover, yield a diverse flora of latest Aptian-earliest Albian (H. jacobi/L. schrammeni ammonite zones). A total of 24 different morphotypes with radial and oblique wall structures has been observed. Among these, eight undescribed species have been identified. The associations of all samples are dominated by two typical Boreal Aptian-Albian morphotypes with radial wall structures: Praecalcigonellum polymorphum and Echinodinella erinacea, which together constitute around 75% of all specimens encountered. All other morphotypes are scarce, except those of the phylogenetically closely related species Pirumella multistrata forma multistrata and Pirumella cf. heirtzleri, which together constitute another 16% of the assemblage. The dominance of Boreal forms is in accordance with a cool global climatic phase, which has been suggested by independent evidence for the Aptian/Albian boundary interval.Praecalcigonellum polymorphum and Echinodinella erinacea are alternately abundant within the succession; each of this species rhythmically reaches abundance peaks/minima every 2.5 m intervals. These rhythms remind of bedding rhythms from time-equivalent outcrops and cores of the Hannover region, which have been related to eccentricity cycles of the Milankovitch frequency band.