Ordovician calcified algae and cyanobacteria, northern Tarim Basin subsurface, China

Boreholes between Kuqa and Korla, in the northern Tarim Basin, Xinjiang, pe netrated Ordovician marine limestones at depths of 5-6.2 km. From three bor eholes 54 out of a total of 170 limestone samples contain calcified algae, cyanobacteria and associated Microproblematica. Calcified cyanobacteria (Gi rvanella, Botomaella, ?Subtifloria) account for 37 per cent of occurrences; green algae (Dasyporelleae and Vermiparella) 28 per cent;, Microproblemati ca (Nuia, Bevocastria, Rothpletzella, Halysis) 20 per cent; and 'solenopora ceans' 15 per cent Girvanella and Nuia are common in the Early Ordovician d eposits, and 'solenoporaceans' are abundant in the Mid-Ordovician. Dasypore lleae and Vermiporella are most abundant in Mid-Late Ordovician samples. Ca lcified cyanobacteria are common throughout the limestone succession, but p articularly in the Mid-Ordovician part. Moniliporella, Contexta, Plexa, Tex turata, and Villosoporella, hitherto placed in the supposed red algal famil y Moniliporellaceac Gnilovskaya, are here regarded as dasycladalean green a lgae. Despite some omissions, this Tarim flora broadly resembles others fro m Kazakhstan, Baltica and North America, indicating the generally cosmopoli tan nature of Ordovician calcified algae and cyanobacteria.