Dinoflagellate cysts and acritarchs from the Middle and Upper Jurassic of Jameson Land, East Greenland

Abstract

Twenty-six samples from the Middle and Upper Jurassic strata of Jameson Land were prepared; twenty-one of these were found to contain organic-walled microplankton, of which seventeen yielded assemblages worthy of detailed examination. A new genus (Ambonosphaera) and six new species (Sentusidinium myriatrichum, Sentusidinium pelionense, Ellipsoidictyum gochtii, Pareodinia brachythelis, Gonyaulacysta birkelundii, and Ambonosphaera calioviana) of dinoflagellates, and two new species of acritarchs (Veryhachium sortehatense and Solisphaeridium ankyleton) were discovered. One taxon, Gonyaulacysta pectinigera, is elevated from subspecific to specific level and its generic reallocation is proposed. Samples from the Sortehat and Pelion Members of the Vardekløft Formation and from the Olympen formation yielded poor assemblages in terms of the number of taxa present and are therefore not especially biostratigraphically useful. However, previous Bajocian and Lower Oxfordian dates for the Sortehat Member and Olympen Formation respectively are supported. Moderately rich assemblages from some samples from the Fossilbjerget Member of the Vardekløft Formation and from the Hareelv Formation indicate Bathonian--Callovian and Oxfordian-Kimmeridgian ages respectively. Two samples, one from each of these units, contain organic-walled microplankton assemblages indicative of a date approximately one half stage earlier than that derived from ammonite faunas. All but one of the samples prepared from the Raukelv Formation contain only carbonized organic remains. One sample, from the Fynselv Member, yielded an assemblage of organic-walled microplankton which, although not conclusive themselves in suggesting a date, do not contradict the latest Jurassic assignation based on ammonite faunas.