Was the latest Devonian glaciation a multiple event? New palynological evidence from Bolivia

Abstract

Assemblages of acritarchs, prasinophytes, and miospores were recovered from the uppermost Iquiri and lower portion of the Itacua formations in southeast Bolivia. Analysis of the diverse and somewhat abundant well-preserved palynomorph assemblage indicates a Late Devonian (late Famennian) age for both formations, and further subdivision in ascending stratigraphic order into the ?VCo, LL, LE, and LN miospore biozones of Western Europe. The presence of age-diagnostic miospore taxa from South America and North America indicates contemporaneous glaciation events between these two regions. The results from close sampling of the diamictite facies of the Itacua Formation at the Bermejo West section, Bolivia, correlate the latest Famennian spore inceptions used to define the Euramerica miospore biozone sequence (LL, LE, and LN zones). The Itacua Formation diamictite sequence examined is relatively thin compared to other diamictite sequences in Bolivia. Furthermore, the miospore biozones represent an estimated duration of three million years, whereas orbitally-forced glacial-interglacial events (e.g., Ruddiman, 2001) are of the Milankovitch frequency range of between 20,000 and 400,000 years. Therefore, it seems most likely that a number of glacial/interglacial events are represented, rather than a single glacial episode.