Sofie Lindström

Gondwanan floristic and sedimentological trends during the Permian-Triassic transition: new evidence from the Amery Group, northern Prince Charles Mountains, East Antarctica

The Permian-Triassic boundary within the Amery Group of the Lambert Graben is placed at the contact between the Bainmedart Coal Measures and overlying Flagstone Bench Formation, based on the first regular occurrence of Lunatisporites pellucidus and the first appearance of Aratrisporites and Lepidopteris species. The Permian-Triassic boundary is marked by the extinction of glossopterid and cordaitalean gymnosperms, and by the disappearance or extreme decline of a range of gymnospermous and pteridophytic palynomorph groups. Earliest Triassic macrofloras and palynofloras of the Flagstone Bench Formation are dominated by peltasperms and lycophytes; corystosperms, conifers, and ferns become increasingly common elements of assemblages through the Lower Triassic part of the formation and dominate floras of the Upper Triassic strata. The sedimentary transition across this boundary is conformable but marked by a termination of coal deposits; overlying lowermost Triassic sediments contain only carbonaceous siltstones. Typical red-bed facies are not developed until at least 100 m above the base of the Flagstone Bench Formation, in strata containing ?Middle Triassic palynofloras. Across Gondwana the diachronous disappearance of coal deposits and appearance of red-beds is suggestive of a response to shifting climatic belts, resulting in progressively drier seasonal conditions at successively higher palaeolatitudes during the Late Permian to Middle Triassic. The abrupt and approximately synchronous replacement of plant groups at the Permian-Triassic boundary suggests that factors independent of, or additional to, climate change were responsible for the turnover in terrestrial floras.

Early Permian palynostratigraphy of the northern Heimefrontfjella mountain-range, Dronning Maud Land, Antarctica

Permian rocks from five localities in the northern Heimefrontfjella have been investigated palynologically and identifiable palynomorphs are present in samples from three of them, namely A and C in Milorgfjella and Lidkvarvet in Sivorgfjella. Eighty palynomorph taxa are recognized and two new combinations are proposed, Converrucosisporites gradegranulatus (Anderson) Lindstrom, comb, nov, and Cannanoropollis bilateralis (Tiwari) Lindstrom, comb. nov. Seventeen taxa are placed in open nomenclature. The assemblages from Locality A and Lidkvarvet are moderately well-preserved, taxonomically diverse, and are indicative of palynofloras deposited in periglacial, cold-climate, freshwater environments. They contain many typical Early Permian Gondwana taxa such as: lycopod spores Jayantisporites pseudozonatus and J. conatus; pterophyte spores Leiotriletes spp., Microbaculispora tentula, Horriditriletes spp., Verrucosisporites andersonii, Cyclogranisporites spp. and Punctatisporites gretensis; and gymnospermous pollen-grains Plicatipollenites spp., Cannanoropollis spp., Scheuringipollenites spp., Pteruchipollenites gracilis, Protohaploxypinus spp. and Cycadopites cymbatus. The presence of these: along with the pterophyte spore Pseudoreticulatisport a confluens enables correlation with the P. confluens Zone or Late Stage 2 of Australia and equivalents in other Gondwana continents, indicating an Asselian-Tastubian age for these two localities. Assemblages assigned to the Pseudoreticulatispora confluens Zone have previously not been encountered within Antarctica. The assemblage from Locality C is poorly preserved with low taxonomic diversity, and contains only one species which is not present in the assemblages from the other two localities, namely Microbaculispora trisina. This suggests correlation with the M. trisina zone or Stage 3b palynofloras of Australia and equivalents elsewhere in Gondwana, and an age no older than Artinskian. (Less)

Intraspecific Variation of Taeniate Bisaccate Pollen Within Permian Glossopterid Sporangia, from the Prince Charles Mountains, Antarctica

Permineralized sporangia from Late Permian sediments of the Amery Group in the Prince Charles Mountains, East Antarctica, are assigned to Arberiella sp. cf. A. africana Pant and Nautiyal. These sporangia contain between 2000 and 3000 taeniate, saccate pollen grains that are predominantly haploxylonoid bisaccate and referable to the palynotaxon Protohaploxypinus limpidus (Balme and Hennelly) Balme and Playford. However, the sporangia also contain greater than 4% of diploxylonoid bisaccate forms comparable to Striatopodocarpidites cancellatus (Balme and Hennelly) Hart 1963, together with sporadic monosaccate and trisaccate grains that, if found dispersed, would be assigned to several different pollen form genera. Morphometric analysis of in situ bisaccate pollen grains and taeniate bisaccate pollen in the dispersed palynoflora indicates that in situ grains occupy only the smaller end of the total size range. The tendency for in situ grains to cluster into two different size groups may reflect differential predispersal expansion of the corpus. The in situ pollen grains are variable in most qualitative and quantitative features used for taxonomic discrimination of dispersed taeniate bisaccate pollen, and this may lead to unreliable estimates of Late Permian floristic diversity if an overly restrictive species delimitation scheme is used.

No causal link between terrestrial ecosystem change and methane release during the end-Triassic mass extinction

Profound changes in both marine and terrestrial biota during the end-Triassic mass extinction event and associated successive carbon cycle perturbations across the Triassic-Jurassic boundary (T-J, 201.3 Ma) have primarily been attributed to volcanic emissions from the Central Atlantic Magmatic Province and/or injection of methane. Here we present a new extended organic carbon isotope record from a cored T-J boundary succession in the Danish Basin, dated by high-resolution palynostratigraphy and supplemented by a marine faunal record. Correlated with reference C-isotope and biotic records from the UK, it provides new evidence that the major biotic changes, both on land and in the oceans, commenced prior to the most prominent negative C-isotope excursion. If massive methane release was involved, it did not trigger the end-Triassic mass extinction. Instead, this negative C-isotope excursion is contemporaneous with the onset of floral recovery on land, whereas marine ecosystems remained perturbed. The decoupling between ecosystem recovery on land and in the sea is more likely explained by long-term flood basalt volcanism releasing both SO2 and CO2 with short- and long-term effects, respectively.

Late Permian palynology of Fossilryggen, Vestfjella, Dronning Maud Land, Antarctica

Abstract Ninety‐one samples from three sections at Fossilryggen in the Vestfjella mountain range of Antarctica have been investigated palynologically. Sixty‐six taxa are recognized in forty‐eight productive samples from two of these sections: the southern section at Fossilryggen and the NW Nunatak section. The palynomorphs have been subjected to contact metamorphosis and display various grades of thermal maturity, ranging in color from light brown to black. They also display various degrees of preservation. Among the spores found are Didecitriletes ericianus, D. uncinatus, Dictyotriletes labyrinthicus (Anderson) comb, nov., Horriditriletes filiformis, Microbaculispora trisina, M. villosa, Osmundacidites wellmanii and Gondisporites raniganjensis. Taeniate and non‐taeniate bisaccates are dominant and include Scheuringipollenites ovatus, S. maximus, Vitreisporites pallidus, Protohaploxypinus spp., Striatopodo‐carpidites spp. and Guttulapollenites hannonicus. Other pollengrains present are Weylandites lucifer...

Synchronous Wildfire Activity Rise and Mire Deforestation at the Triassic–Jurassic Boundary

The end-Triassic mass extinction event (∼201.4 million years ago) caused major faunal and floral turnovers in both the marine and terrestrial realms. The biotic changes have been attributed to extreme greenhouse warming across the Triassic–Jurassic (T–J) boundary caused by massive release of carbon dioxide and/or methane related to extensive volcanism in the Central Atlantic Magmatic Province (CAMP), resulting in a more humid climate with increased storminess and lightning activity. Lightning strikes are considered the primary source of wildfires, producing charcoal, microscopically recognized as inertinite macerals. The presence of polycyclic aromatic hydrocarbons (PAHs) of pyrolytic origin and allochthonous charcoal in siliciclastic T–J boundary strata has suggested widespread wildfire activity at the time. We have investigated largely autochthonous coal and coaly beds across the T–J boundary in Sweden and Denmark. These beds consist of predominantly organic material from the in situ vegetation in the mires, and as the coaly beds represent a substantial period of time they are excellent environmental archives. We document a remarkable increase in inertinite content in the coal and coaly beds across the T–J boundary. We show estimated burning temperatures derived from inertinite reflectance measurements coupled with palynological data and conclude that pre-boundary late Rhaetian mire wildfires included high-temperature crown fires, whereas latest Rhaetian–Sinemurian mire wildfires were more frequent but dominated by lower temperature surface fires. Our results suggest a major change in the mire ecosystems across the T–J boundary from forested, conifer dominated mires to mires with a predominantly herbaceous and shrubby vegetation. Contrary to the overall regional vegetation for which onset of recovery commenced in the early Hettangian, the sensitive mire ecosystem remained affected during the Hettangian and did not start to recover until around the Hettangian–Sinemurian boundary. Decreasing inertinite content through the Lower Jurassic suggests that fire activity gradually resumed to considerable lower levels.

An Early Permian palynoflora from Milorgfjella, Dronning Maud Land, Antarctica

A preliminary palynological study of Beacon Supergroup sedimentary rocks exposed at Milorgfjella, Dronning Maud Land, has yielded a relatively rich and well preserved palynoflora dominated by spores and pollen grains, but also including acritarchs and green algae. The palynoflora is dominated by the pterophyte spores Punctatisporites gretensis, Punctatisporites parvus, Granulatisporites spp., Microbaculispora tentula Horriditriletes spp. and Verrucosisporites andersonii, and the gymnosperm pollen grains Plicatipollenites spp. and Cannanoropollis spp. Also present are the lycopod spore Jayantisporites pseudozonatus, the praecolpate pollen grain Marsupipollenites striatus and the monocolpate pollen grain Cycadopites cymbatus. The palynoflora indicates freshwater conditions or, at least, a major freshwater influence on the depositional environment. Comparison of the palynoflora with others from Gondwana suggests an Early Permian (Asselian–Sakmarian) age.

Early Late Permian palynostratigraphy and palaeo-biogeography of Vestfjella, Dronning Maud Land, Antarctica

The preliminary results of a palynological investigation of 62 samples from the southern section of a sedimentary sequence exposed at Fossilryggen in the Vestfjella mountain range in Dronning Maud Land, Antarctica are reported. The sequence, which is cut by dolerite dykes, is considered to have been deposited in a near-shore marine environment. Palynomorphs recovered show high degrees of thermal alteration and various states of preservation; 55 palynomorph taxa have been identified, including the stratigraphically important Didecitriletes ericianus, Microbaculispora villosa, M. trisina, Horriditriletes filiformis, Praecolpatites sinuosus, Weylandites lucifer, Protohaploxypinus rugatus, Striatopodocarpidites cancellatus and S. fusus. Also present are acritarchs, such as Peltacystia venosa, P. monile and Circulisporites sp., and prasinophycean algae, such as Cymatiosphaera gondwanensis. Palaeobiogeographically the palynoflora is typical for southern Gondwanaland and it is correlated primarily with assemblages of similar composition in Antarctica, South Africa and Australia. Comparisons are also made with assemblages from the northern margins of Gondwanaland and Eurameria, with which palynostratigraphical correlations are more difficult. No typical Euramerian taxa have been found in the palynoflora from Fossilryggen, which is assessed as no older than Australian Lower Stage 5b and 5c assemblages and is considered to be of early Late Permian (Ufimian) age.

Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years

Significance This is, to our knowledge, the first multiproxy study of climate and associated faunal change for an early Mesozoic terrestrial ecosystem containing an extensive vertebrate fossil record, including early dinosaurs. Our detailed and coupled high-resolution records allow us to sensitively examine the interplay between climate change and ecosystem evolution at low paleolatitudes during this critical interval of Earths history when modern terrestrial ecosystems first evolved against a backdrop of high CO2 in a hothouse world. We demonstrate that these terrestrial ecosystems evolved within a generally arid but strongly fluctuating paleoclimate that was subject to pervasive wildfires, and that these environmental conditions in the early Mesozoic prevented large active warm-blooded herbivorous dinosaurs from becoming established in subtropical low latitudes until later in the Mesozoic. A major unresolved aspect of the rise of dinosaurs is why early dinosaurs and their relatives were rare and species-poor at low paleolatitudes throughout the Late Triassic Period, a pattern persisting 30 million years after their origin and 10–15 million years after they became abundant and speciose at higher latitudes. New palynological, wildfire, organic carbon isotope, and atmospheric pCO2 data from early dinosaur-bearing strata of low paleolatitudes in western North America show that large, high-frequency, tightly correlated variations in δ13Corg and palynomorph ecotypes occurred within a context of elevated and increasing pCO2 and pervasive wildfires. Whereas pseudosuchian archosaur-dominated communities were able to persist in these same regions under rapidly fluctuating extreme climatic conditions until the end-Triassic, large-bodied, fast-growing tachymetabolic dinosaurian herbivores requiring greater resources were unable to adapt to unstable high CO2 environmental conditions of the Late Triassic.

Intense and widespread seismicity during the end-Triassic mass extinction due to emplacement of a large igneous province

Multiple levels of earthquake-induced soft-sediment deformations (seismites) are concentrated in the end-Triassic mass extinction interval across Europe. The repetitive nature of the seismites rules out an origin by an extraterrestrial impact. Instead, this intense seismic activity is linked to the formation of the Central Atlantic magmatic province (CAMP). By the earliest Jurassic the seismic activity had ceased, while extrusive volcanism still continued and biotic recovery was on its way. This suggests that magmatic intrusions into sedimentary strata during early stages of CAMP formation caused emission of gases (SO 2 , halocarbons, polycyclic aromatic hydrocarbons) that may have played a major part in the biotic crisis.