Diverse and moderately to well-preserved palynomorph assemblages, composed of 81 organic-walled phytoplankton species, belonging to 47 genera, and two chitinozoan species, were recorded from the Ordovician rocks of the well RH-2, in the Llanos Basin of Colombia. The stratigraphic distribution of the taxa allows four assemblages to be distinguished that are, from base to top: Assemblage 1, assigned to the late Floian? – Dapingian; Assemblage 2, assigned to the Darriwilian; Assemblage 3, assigned to the Darriwilian?–Sandbian–Katian? and Assemblage 4, assigned to the Katian–Hirnantian. Assemblage 4 is considered no younger than pre-glacial Hirnantian, based on the absence of taxa typical of phytoplankton assemblages from Hirnantian glacial and post-glacial deposits. The Middle Ordovician interval shows clear affinities with the Perigondwana acritarch Province, mainly due to the presence of the diagnostic taxa Arbusculidium filamentosum, Arkonia, Aureotesta, Coryphidium, Dicrodiacrodium, Frankea and Striatotheca. Nevertheless, taxa with South Chinese and Baltic affinities, from low to intermediate latitudes, such as Ampullula and Tongzia are also present, even though Colombia was situated at a high, cold latitude during this time interval. The Katian–Hirnantian Assemblage 4 supports the cosmopolitanism of Ordovician organic-walled phytoplankton that began around the Darriwilian–Sandbian boundary, with globally occurring species such as Leiofusa litotes, Multiplicisphaeridum irregulare and Villosacapsula setosapellicula recorded. The moderate to high diversity of the Middle Ordovician phytoplankton significantly drops in the Late Ordovician Assemblage 4. The palynological analyses reported here contributes to the understanding of phytoplankton distribution on the East Gondwana margin.

从哥伦比亚Llanos盆地RH-2井的奥陶纪岩石中，记录了由81种有机壁浮游植物组成的，属于47个属的有机壁浮游植物组成的多种和中度至保存完好的组合。单元的地层分布可以区分四个组合，从底部到顶部：组合1，分配给后期的Floian？–大坪ian；集合2，分配给Darriwilian；集合3，分配给Darriwilian？–Sandbian–Katian？和组合4，分配给Katian–Hirnantian。基于不存在来自赫尔南特河冰川和冰川后沉积物的典型浮游植物组合的分类单元，认为组合物4比冰川前的海南群岛年轻。Arbusculidium filamentosum，Arkonia，Aureotesta，Coryphidium，Dicrodiacrodium，Frankea和Striatotheca。然而，即使哥伦比亚在此时间段内处于高寒纬度，也存在具有华南和波罗的海亲和力的类群，从低纬度到中纬度，例如安普卢拉和通齐亚。凯迪－黑南组合4支持奥陶纪有机壁浮游植物的世界主义，这种浮游植物始于Darriwilian-Sandbian边界附近，具有全球性物种，如Leiofusa litotes，Multiplicisphaeridum normale和Villosacapsula setosapellicula记录。中奥陶纪浮游植物的中度到高度多样性在晚奥陶纪组合4中显着下降。这里报道的孢粉学分析有助于理解东冈瓦纳边缘的浮游植物分布。