Spores constraining age of the Middle Devonian paleosol from Voronezh, Russia and their paleopedological and evolutionary significances

Abstract

As a tangible record that formed on ancient landscape, paleosols provide unique evidence for the evolutionary, paleoecological, and paleoenvironmental understandings to land organisms. However, not all paleosols have a good potential for fossil preservation. Plant preservation of paleosols is highly dependent on Eh-Ph conditions of the past and usually favor reducing paleosols. In this study, we carry on palynological analysis for an acid sulfate paleosol from Voronezh, Russia. Abundant and well-preserved spores are recognized from the middle part of this paleosol and its overlying shale. The Ancyrospora tichonovitschi–Retispora archaeolepidophyta–Rhabdosporites langii (TAL) assemblage from the paleosol, including spores of 45 genera and 101 species, indicates a late Eifelian?–early Givetian age. This new age constraint on the paleosol is entrenched by another spore assemblage from the lowermost part of the overlying shale, namely Cristatisporites conannulatus–Geminospora decora–Membrabaculisporis comans (CDC) assemblage. This assemblage includes spores of 38 genera and 89 species, and can be well correlated with the early Givetian Cymbosporites magnificus–Hymenozonotriletes tichonovitschi (MT) Subzone in eastern Europe. Both the assemblages are characteristic for the humid subtropical flora. Assessments of sporopollenin degradation within the paleosol lead to the suggestion that low pH value probably plays a significant role in spore preservation and can explain the surprising diversity and abundance of spores. New palynological results indicate a flourishing land flora in the Kačák interval of Voronezh High, where terrestrial vegetation might have suffered from a collapse coincident with the Taghanic event.