Ordovician calcified cyanobacteria and associated microfossils from the Tarim Basin, Northwest China: systematics and significance

Calcified cyanobacteria and associated microfossils were examined in 8500 thin sections of Ordovician core samples from 64 wells in carbonate platforms of the Tarim Basin, Xinjiang Province, Northwest China. They include 32 species (including three uncertain species) belonging to 20 genera, most of which are from the Middle and Upper Ordovician. Two new genera and species, <i>Acuasiphonoria ordovica</i> gen. et sp. nov. and <i>Gomphosiphon xinjiangensis</i> gen. et sp. nov., and two new species, <i>Proaulopora pachydermatica</i> sp. nov. and <i>Rothpletzella longita</i> sp. nov., are described. Calcified cyanobacteria include <i>Girvanella</i>, <i>Subtifloria</i>, <i>Razumovskia</i>, <i>Acuasiphonoria</i> gen. nov., <i>Hedstroemia</i>, <i>Cayeuxia</i>, <i>Bija</i>, <i>Apophoretella</i>, <i>Ortonella</i>, <i>Zonotrichites</i> and <i>Bevocastria</i>. Probable calcified cyanobacteria include <i>Proaulopora</i>, <i>Phacelophyton</i> and <i>Gomphosiphon</i> gen. nov. Calcified Microproblematica include <i>Renalcis</i>, <i>Izhella</i>, <i>Epiphyton</i>, <i>Wetheredella</i>, <i>Rothpletzella</i> and <i>Garwoodia</i>. This assemblage is diverse in comparison with similar Ordovician fossils reported from other areas, and includes six genera and 14 species recorded from the Ordovician for the first time. Calcified cyanobacteria and their associated microfossils are more diverse in the Middle and Late Ordovician than was previously known.