Cyclonephelium brevireticulatum, a new dinoflagellate cyst from the Arkadelphia Formation (upper Maastrichtian), Hot Spring County, Arkansas, USA

Abstract

Cyclonephelium brevireticulatum is a new organic-walled dinoflagellate cyst described from the upper Maastrichtian Arkadelphia Formation, Hot Spring County, Arkansas, USA. Cyclonephelium brevireticulatum sp. nov. is distinguished from other species of this genus by its small size, and by processes of very low relief (<5 µm) which connect linearly to form a chain or mesh-like micro-reticulation along the outer margin of the cyst. The study site is an outcrop of the Arkadelphia Formation which is exposed along the Ouachita River during low water conditions. Cyclonephelium brevireticulatum is a common taxon at this site and co-occurs with late Maastrichtian dinoflagellate cysts including Dinogymnium spp., Disphaerogena carposphaeropsis Wetzel 1933, Trithyrodinium evittii Drugg 1967, Deflandrea galeata (Lejeune-Carpentier 1942) Lentin & Williams 1973, Pierceites pentagonus (May 1980) Habib and Drugg 1987, Palynodinium grallator Gocht 1970, along with rare occurrences of Manumiella spp. and the latest early Maastrichtian taxon Alterbidinium acutulum (Wilson 1967) Lentin & Williams 1985. Specimens of the late Maastrichtian pollen, Rugubivesiculites spp., have also been recorded throughout the section. Although the uppermost geologic range of the new species appears to conform to the lower part of the Discoscaphites iris ammonite zone which correlates with calcareous nannofossil zone CC26b, the ammonite occurrences are too scarce to be certain at this time.