Cryptospores from the Katian (Upper Ordovician) of the Tungus basin: The first evidence for early land plants from the Siberian paleocontinent

Abstract

A diverse assemblage of cryptospores is reported for the first time from the Upper Ordovician of Siberia. It was discovered during a palynological study of a sedimentary succession of about 100m, exposed along the Bolshaya Nirunda River, a right tributary of the Podkamennaya Tunguska River. The succession is located on the southern margin of the extensive epicontinental Tungus basin on the Siberian Platform between the Katanga and Yenisei land masses. The cryptospore assemblage was recovered from the siliciclastic-carbonate Dolbor Formation and scarcely from the overlying more carbonate Bur Formation. Both formations belong to the Katian Global Stage (Upper Ordovician). The cryptospores occur together with marine remnants (acritarchs, prasinophytes, chitinozoans, scolecodonts). It is similar to all known Upper Ordovician cryptospore assemblages in comprising naked and envelope-enclosed monads, dyads, tetrads and polyads. Although preservation is moderate to poor, the cryptospore taxa Velatitetras laevigata, Tetrahedraletes medinensis, Abditusdyadus laevigatus, Dyadospora murusdensa, Pseudodyadospora laevigata, Segestrespora laevigata and Sphaerasaccus glabellus can be identified. This report represents the first record of spores of the earliest land plants from the paleocontinent Siberia and therefore extends the global paleogeographical coverage of Late Ordovician cryptospores.