Proliferation of abnormal palynoflora during the end-Devonian biotic crisis

Abstract

The dispersed miospore assemblage of the Retispora lepidophyta-Verrucosisporites nitidus (LN) Zone from the Holy Cross Mountains(Poland) is marked by enrichment (above 4%) in abnormal spore morphotypes during a terrestrial flora turnover close to the Devonian–Carboniferous boundary, recorded just above the Hangenberg Black Shale level. Incomplete and complete tetrads represent mostlyVallatisporites spp., supplemented by Grandispora, Retusotriletes and Apiculiretusispora. Additional peculiar morphotypes, marked byanomalous overall shape and ornamentation, are interpreted as mutated varieties of Vallatisporites based on intermediate morphologicalstages, connecting them with this well known genus. This relatively high aberrant palynomorph frequency is accompanied by volcanicash intercalations, as well as by charcoal debris and polycyclic aromatic biomarkers indicative of forest wildfire. Thus, the anomalousspore morphology could reflect the mutagenic effect of regional acidification due to explosive volcanism. However, palynological literature data from NW France and Canada highlight the possibility of a supra-regional mutated miospore signal near the Devonian–Carboniferous boundary, and there is need for high-resolution studies of the LN Zone to examine this. The end-Permian scenario of abnormalfloral growth in immensely stressed habitats may therefore apply to other potentially volcanically-induced biotic turnovers.