Contributions Series Nr. 31 (PDF)

Description

Abstract

On the basis of a study of dinoflagellate cysts from the Jurassic succession, including the Rhaetian and the Ryazanian, of Denmark, it is shown that the lithostratigraphic units have isochronous boundaries in the central part of the basin but are diachronous towards the paleocoast at the margin of the Baltic Shield. The study demonstrates that the Jurassic section is more complete in the central part of the basin than previously thought and that the hiatuses reported from the base and top of the Middle Jurassic Haldager Sand Formation are shown to be relatively insignificant, in contrast to earlier work.

With respect to paleoenvironment, the dinoflagellate data show variable distribution patterns that can be related to the paleoecological coast-oceanic trend, i.e. to the inner neritic-coastal shelf, and the middle-outer neritic or shelf part of the basin. Periods with restricted marine conditions have also been recognized and the sea-level fluctuations at the end of the Jurassic are reflected in the changing dinoflagellate cyst assemblages.

The macrofossil records and the ostracod zonation for the Jurassic of Denmark have formed the basis for succeeding biostratigraphic investigations using spores and pollen, and for this study on dinoflagellate cysts. These earlier biozonations are reviewed to describe the biostratigraphic foundation for this study. Investigation of Late Jurassic dinoflagellate cysts from ammonite-dated samples from Poland has made it possible to correlate the British-Danish zonation for the Late Jurassic with other European ammonite-dated sections. This comparison demonstrates that some of the chronostratigraphic units from the areas in question may be correlated somewhat differently from earlier practice. The Kimmeridgian mid-Divisum Zone of Poland correlates with the mid-Mutabilis Zone of Britain. The lower part of the Volgian Scythicus Zone of Poland is here correlated with the Albani Zone of Britain and Denmark.

Nine new species of dinoflagellate cysts (Aldorfia warringtonii, Apteodinium daveyi, Batioladinium matyjae, Cometodinium jurassicum, Cribroperidinium hansenii, Dichadogonyaulax? brenneri, Nannoceratopsis raunsgaardii, Occisucysta wierzbowskii and Tubotuberella owensii), together with a new subspecies of dinoflagellate cysts (Neuffenia willei subsp. lanterna), and two new species of acritarchs (Fromea thomsenii and Schizocystia lundii).

The genus Acanthaulax is considered a junior synonym of Cribroperidinium. Cribroperidinium caudum and Cribroperidinium systremmatum are regarded as synonyms of Cribroperidinium globatum. Some species of the genus Muderongia are discussed and new combinations and re­attributions are proposed. A neotype for Dingodinium tuberosum is designated and the species is compared with other species of Dingodinium. Several Jurassic psilate species of Escharisphaeridia are treated as synonyms of Escharisphaeridia psilata. Netrelytron is considered as a junior synonym of Kalyptea, and Netrelytron stegastum, Netrelytron parum and Netrelytron trinetron are considered as synonyms with Kalyptea stegasta, the senior name.

The genus Nannoceratopsis is divided into three complexes: (1) Senex-complex, species with smooth or microgranular autophragm, (2) Gracilis-complex, species with smooth or microgranular autophragm and perforate ectophragm, (3) Spiculata-complex, species with microvermiculate autophragm. The genera Systematophora, Perisseiasphaeridium, and Amphorula are discussed as a complex.