Two new acritarch genera (Gordonirundum, Nirundella), three new species (Gordonirundum tungustanum, Gordonirundum? solidum, Nirundella baykitensis) and five new varieties (Gordonirundum tungustanum var. tungustanum autonym, G. tungustanum var. minutum, G. tungustanum var. tenuivertum, Nirundella baykitensis autonym, N. baykitensis var. ramusculosa) are described from the Upper Ordovician Dolbor Formation, exposed along the Bolshaya Nirunda River (a north-east tributary of the Podkamennaya Tunguska River, Eastern Siberia). These distinctive morphotypes possibly represent endemic Siberian acritarchs. Precise correlation of the studied interval with the global scale is uncertain. Provisional correlation with the lower Katian Stage is only supported by recently published radiometric data (206Pb/238U), providing an age of 450.58 ± 0.27 Ma for the K-bentonite bed discovered in the underlying formation in a neighbouring section in the Podkamennaya Tunguska valley.

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