Multiple climatic changes around the Permian-Triassic boundary event revealed by an expanded palynological record from mid-Norway

Here, we present the palynological record from two shallow core holes (6611/09-U-01 and -02) from the Trøndelag Platform offshore mid-Norway consisting of 750 m of Upper Permian and Lower Triassic sediments. The relatively homogeneous assemblages recovered from the Upper Permian deposits are dominated by gymnosperm pollen, mainly pteridosperms. At the base of the Griesbachian, numerous spore species appear in the record, leading to an increased diversity. The change at this boundary is also marked by the massive reduction of one group of pteridosperm pollen (Vittatina). Together with other typical Permian elements (e.g., Lueckisporites virkkiae), this group is rare but consistently present in the lower part of the Griesbachian, and it gradually disappears in its upper part. The distribution of other groups such as taeniate and non-taeniate bisaccate gymnosperm pollen (pteridosperms and conifers) shows no significant change across the boundary, whereas spores and other gymnosperm pollen increase in diversity and abundance. These changes coincide with the formational change between the Schuchert Dal Formation (Upper Permian) and the Wordie Creek Formation (Griesbachian) equivalents. Late Permian and Griesbachian palynomorph assemblages display different patterns. The former show a homogeneous composition of low diversity, whereas the latter reflect diverse and variably composed floras. The data suggest that the arid phase of the Late Permian was followed by a humid phase at the base of the Griesbachian. In the Griesbachian section, a succession of six distinct palynological assemblages (phase II–VII) can be inferred. Comparable changes have been described from East Greenland. The variations in the palynological record are interpreted to reflect changing ecological conditions (e.g., changing humidity). Comparable variations in the distribution of δ13C isotope values reported from various sections from Greenland and China, showing stable values during the Late Permian and highly variable values during the Griesbachian, suggest common causes for the observed fluctuations. Multiphase volcanic activity of the Siberian traps seems to be the most likely candidate to have caused the variations in the δ13C isotope as well as in the palynological record. In contrast to the common claim that marine and terrestrial biota both suffered a mass extinction related to the Permian-Triassic boundary event, the studied material from the Norwegian midlatitudinal sites shows no evidence for destruction of plant ecosystems. The presence of diverse microfloras of Griesbachian age supports the idea that the climate in this area allowed most plants to survive the Permian-Triassic boundary event

Rapid demise and recovery of plant ecosystems across the end-Permian extinction event

The end-Permian extinction event was the most pronounced biotic and ecological crisis in the history of the Earth. It is assumed that over 80% of marine genera disappeared, and that this event had a major impact on the evolution of marine organisms. The impact of this event on terrestrial biota is poorly known and a matter of controversial discussions. In contrast to the fundamental changes in marine fauna most major groups of plants range from the Late Palaeozoic into the Mesozoic. Consequently the impact of the end-Permian extinction event on the evolution of plants was often regarded as minor. However, major changes in the composition of the plant communities have been documented and a number of catastrophic scenarios have been envisioned — including the almost total destruction of plant ecosystems. Based on expanded sections from the Southern Barents Sea (Northern Norway) we trace mid-latitudinal terrestrial ecosystems across the Permo–Triassic transition with a time resolution in the order of 10 kyr, based on a high resolution Corg-isotope stratigraphy. Our results show that the floral turnovers are linked with major changes in the C-isotope record and hence with global carbon cycling. The palynological records document the successive steps in the evolution of terrestrial ecosystems. After gradual changes during the latest Permian, plant ecosystems suffered from a major environmental perturbation leading to a rapid turnover from gymnosperm dominated ecosystems to assemblages dominated by lycopods. The dominance of the lycopods, expressed in a spore-spike, represents a relatively short-lived event in the order of 10 kyr. This perturbation of the terrestrial ecosystems preceded the globally recognized negative δ13Corg isotope spike by up to 100 kyr. It coincides with a first end-Permian negative shift of the C-isotope curve and was probably induced by a first major perturbation of the chemistry of the atmosphere, related to the onset of the volcanic activity of the Siberian Traps. Gymnosperms recovered prior to the major isotopic shift. The fast recovery of terrestrial ecosystem explains why all major plant groups survived the end-Permian extinction event while the majority of marine organisms were wiped out. The concordance of pattern of the δ13Corg in globally distributed marine and terrestrial sequences enables us to link turnovers in the terrestrial environment with marine extinction events. It demonstrates that the demise and the onset of the recovery of the terrestrial ecosystems was a global phenomenon and occurred prior to the major isotopic shift. The successive negative shifts in δ13Corg isotope values are thought to reflect CO2 input into the atmosphere by multiphase volcanic activity (Siberian Traps) or other consecutive events (e.g. methane release)

A close-up view of the Permian–Triassic boundary based on expanded organic carbon isotope records from Norway (Trøndelag and Finnmark Platform)

High-resolution carbon isotope records of organic carbon (δ13Corg) across the Permian–Triassic boundary (PTB) from the expanded sections of the Trøndelag and Finnmark platforms in Norway demonstrate that the negative carbon isotope excursion around the PTB begins with a stepwise 8‰ negative decline to a first minimum. After a subsequent positive excursion, a second minimum follows in the basal Griesbachian. Particulate organic matter (POM) is dominated by terrestrial particles with changing marine contributions. Intervals with minor C-isotope fluctuations coincide with homogeneous terrestrial POM assemblages, whereas intervals with pronounced C-isotope fluctuations correspond to heterogeneous marine–terrestrial POM assemblages, suggesting that the C-isotope curve represents a global signal with superimposed local variations of carbon sources. The δ13Corg of the contributing organic carbon ranges from − 32‰ (marine organic carbon) to − 22‰ (terrestrial organic carbon). Comparison of the new record, divided into 10 chemostratigraphic intervals with other, globally distributed sections suggests the presence of gaps in several classical PTB sections. Detailed chemostratigraphic correlation reveals that the extinction of marine organisms occurred during the stepwise negative shift and the end-Permian floral turnover occurred prior to the first C-isotope minimum. The correlation also shows that the marker of the recently defined Global Stratotype Section and Point PTB occurs within a broad interval ranging from most negative δ13C values up to the subsequent isotopic increase