Calcareous dinoflagellate cysts, Pirumella multistrata and wall layers from the Upper Hauterivian (Cretaceous) of a claystone-marlstone succession in the clay-pit Frielingen (Hanover-area), NW Germany

A pale-dark bedded claystone-marlstone succession of Late Hauterivian age (Simbirskites discofalcatus ammonite Zone; Early Cretaceous), exposed in the clay-pit Frielingen, Germany (Lower Saxony Basin), was investigated with respect to its calcareous dinoflagellate cyst content. This study aimed at a better understanding of the usefulness of calcareous dinoflagellate cysts to reconstruct palaeoenvironments, and an evaluation of the postulated palaeoenvironmental trends associated with Lower Cretaceous pale-dark bedding rhythms. The ratio of abundant taxa, character traits of cysts, and the results of statistical species analyses were used for those analyses. Current models of sea level fluctuations and sea surface temperature were modified on the basis of the composition of calcareous dinoflagellate assemblages. Superimposed on a general sea level rise, a regressive interval with high sea surface water temperatures is reflected by the thick bed 118. This distinctively warm interval is represented by a dark bed that has commonly been interpreted to indicate cooler surface waters. It is therefore necessary to review the palaeoenvironmental interpretation of pale-dark bedding rhythms of claystone successions of the Boreal Realm. Factors other than sea surface temperature seem to be important as well.
The species Pirumella edgarii was found to favour time intervals with higher sediment input. The newly described species Pirumella? sp. nov. may perhaps indicate similar environments in warmer water masses. The species Pirumella tanyphloia has been emended, we suggest including it in Pirumella multistrata forma tanyphloia. Moreover, the pithonelloid cysts found in Frielingen are currently the oldest of their kind.