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.

摘要

Cyclonephelium brevireticulatum是一种新的有机壁甲藻囊肿，描述于美国阿肯色州温泉县上马斯特里赫特阿卡德尔菲亚组。Cyclonephelium brevireticulatum sp. 十一月 与该属的其他物种的区别在于其体积小，并且通过非常低的起伏（<5μm）的过程线性连接以沿着包囊的外缘形成链状或网状微网状结构。研究地点是 Arkadelphia 地层的露头，在低水位条件下，该地层沿 Ouachita 河暴露。Cyclonephelium brevireticulatum是该地点的常见分类群，与晚马斯特里赫特甲藻包囊共同出现，包括Dinogymnium spp., Disphaerogena carposphaeropsisWetzel 1933，Trithyrodinium evittii Drugg 1967，Deflandrea galeata（Lejeune-Carpentier 1942）Lentin & Williams 1973，Pierceites pentagonus（1980 年 5 月）Habib 和 Drugg 1987，Palynodinium grallator 70s with 1pp . 和最新的马斯特里赫特早期分类群Alterbidinium acutulum (Wilson 1967) Lentin & Williams 1985。马斯特里赫特晚期花粉的标本，Rugubivesiculites spp.，也被记录在整个部分。虽然新物种的最上层地质范围似乎与Discoscaphites 虹膜的下部一致 与钙质纳米化石区 CC26b 相关的菊石带，此时菊石的产状太稀少而无法确定。