A terrestrial Devonian-Carboniferous boundary section in East Greenland

Abstract

Terrestrial Devonian-Carboniferous boundary sections are present in the East Greenland Devonian Basin. The boundary section on Stensiö Bjerg developed in deep, distal lake sediments with a pair of lakes representing the boundary. A diverse spore assemblage developed as the lake flooded the basin. Previously abundant spores, notably Retispora lepidophyta, Diducites spp., Rugospora radiata and all forms with bifurcate tips (Ancyrospora and Hystricosporites), then became extinct through just over a metre of section. The spore assemblage is then lost into AOM rich very high TOC% lake sediments. There is a negative δ13CTOC excursion in the Stensiö Bjerg section interpreted to represent the upper part of the positive excursion known from marine sections. The upper lake contains the simple VI spore assemblage of the earliest Carboniferous age. The correlative section on Rebild Bakker was developed in shallow proximal facies without AOM and shows that a Devonian-Carboniferous LN* to VI spore zone boundary can be picked in the lower lake based on the last occurrence of Retispora lepidophyta in an assemblage otherwise dominated by simple spores and Grandispora cornuta. Spores in this VI spore assemblage, particularly Grandispora cornuta, show sculpture malformation that is entirely characteristic of UV-B radiation damage to their DNA prior to deposition of its protective wall layer. This palynological record showing the rapid extinction of major elements within the Late Devonian microflora can be reconciled with accounts claiming there was no mass extinction of plants and spores across the boundary. The palaeobiology of the major spore groups that became extinct is reviewed.