Gloeocapsomorpha prisca in Early Silurian source rocks from northern East Siberia

Organic-rich shales in the early Silurian Pravy Atyrdyakh Formation of north-western Anabar, East Siberia, show optical and chemical characteristics that are very similar to those of Ordovician oil shales (e.g. Estonian kukersites), whose organic matter is dominated by Gloecapsomorpha prisca-derived alginite.

Gloeocapsomorpha prisca was a major contributor to kerogens sourcing most Ordovician oils. In spite of extensive studies, to date, no agreement has been made concerning the nature and the ecology of this organism, and the mechanism for accumulation of beds rich in G. Prisca. Foster et al. (1989) suggested they must have been mat-forming cyanobacteria. G. Prisca was widespread in low latitude tropical epicontinental seas during Ordovician time. There are very few records of G. Prisca occurring in post-Ordovician sediments, e.g. As young as Late Devonian (Fowler et al. 2004). The presence of G. Prisca as the main contributor to Rhuddanian Pravy Atyrdyakh Formation potential source rocks and not to any other Silurian source rocks in the East Siberian Basin adds more information about the post-Ordovician history of this organism. After the Ordovician-Silurian extinction event, and the appearance of the major groups of phytoplankton, this cyanophyte survived in shallow water, near-shore and lacustrine environments that are generally not considered good for source rock development