Swedish Museum of Natural History
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Megaspores from the Late Triassic‒Early Jurassic of southern Scandinavia: taxonomic and biostratigraphic implications
No full textHere we investigate megaspores from 10 Triassic‒Jurassic localities of southern Sweden and Bornholm, Denmark, based on collections housed in the Swedish Museum of Natural History. We identify and describe 19 megaspore taxa belonging to three stratigraphically constrained assemblages, representing the Rhaetian, Hettangian and Pliensbachian, respectively. Megaspores are abundant and diverse (12 taxa) in the Rhaetian assemblage. Diversity markedly decreases across the Triassic–Jurassic boundary (TJB), with species richness reducing from 12 to two taxa. The Hettangian assemblage is well-preserved but depauperate, and is overwhelmingly dominated by Nathorstisporites hopliticus. A subsequent recovery of lycopsid diversity followed, recorded by an increase in richness to six taxa in the Pliensbachian assemblage. The disappearance of the hygrophilous and diverse heterosporous lycophyte communities acrossthe TJB, suggests a shift to drier conditions in the earliest Jurassic. This is supported by lithological changes from coal-forming environments in the Rhaetian to sandstone-dominated fluvial-estuarine facies in the Hettangian. Throughout this study, we analysed the megaspores using fluorescence microscopy, which revealed detailed morphological features on specimens that were otherwise opaque under visible light. This non-destructive technique is particularly useful for examining opaque megaspores embedded in permanent mounting media, such as epoxy resin, and may provide new insights into historical megaspore collections elsewhere.Also funded by This research was supported by the National Natural Sciences Foundationof China (NSFC 42002003) and the State Key Laboratory of Palaeobiologyand Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS)(20182110) for J.P.</p
Palaeoenvironmental changes in Eocene Tibetan lake systems traced by geochemistry, sedimentology and palynofacies
No full textAncient lake deposits preserve detailed records of Cenozoic environmental changes, providing information on past climate, vegetation, precipitation and lake chemistry. This study focuses on palaeoenvironmental changes recorded in Eocene limnic environments across what is today the modern Tibetan Plateau. We describe a section dated as late Eocene (~38–37 Ma) and integrate these findings within a regional context of similarly-aged Tibetan lake deposits across the plateau. These sedimentary archives of environmental change indicate a period of late Eocene aridification and cooling in the lead-up to the greenhouse-icehouse transition, which remains poorly understood in Central Asia. We show, based on geochemical, sedimentological, and palynofacies analyses, that a large saline lake existed within a semi-arid to arid steppe environment in the Nangqian Basin, east-central Tibet. The saline lake experienced cyclic drying intervals with shifts to a playa lake / mudflat system. Evidence of increased aridity is recorded in the upper part of the section, including a thinning of gypsum beds, decrease in palynomorph abundance, and concurrent increase in wood debris and amorphous organic matter. This is consistent with late Eocene aridity in Asia, drying of the playa lake, and an impoverished desert-steppe vegetation. Grain size data and geochemistry indicate a stable provenance of sedimentary material, suggesting that tectonic activity did not dominate sedimentation in east-central Tibet during deposition of these successions. Rather, palaeoenvironmental changes across the Tibetan region were most probably controlled by global climate oscillations and retreat of the proto-Paratethys Sea during the late Eocene: knowledge that is relevant for ecological interpretations through the Cenozoic, Quaternary and to the present.Also funded by the National Natural ScienceFoundation of China (grant 41302024 to Q.Y.); Foundation of QinghaiScience & Technology Department (grant 2020-ZJ-734); The SecondTibetan Plateau Scientific Expedition and Research Program (STEP) CAS(grant 2019 QZKK0805)</p
Raman spectroscopy as a tool in mineral discoveries
No full textPreliminary investigations of unknown minerals are frequently based on physical and optical observations, chemical analysis and collection of powder X-ray diffraction data. At the Swedish Museum of Natural History, laser Raman micro-spectrometry has been adopted as a standard method, which led to discoveries that otherwise might have been unnoted. The new mineral garpenbergite (IMA2020-099), with formula Mn6□AsSbO10(OH)2, is found at the Garpenberg Zn-Pb-Ag deposit, Dalarna (Dalecarlia), Sweden. Preliminary data indicated a close relationship to manganostibite, ideally Mn7AsSbO12. The two minerals are not easily distinguished using routine procedures, because of almost identical powder patterns and similar chemical compositions. In the Raman spectra, a characteristic feature, with distinct bands at 3647 and 3622 cm-1 related to OH-stretching vibration modes, appears for garpenbergite only. Structural refinement from single-crystal X-ray diffraction data yielded an orthorhombic unit cell, with a = 8.6919(10), b = 18.927(3), c = 6.1110(6) Å for Z = 4. The crystal structure is distinct by the presence of a vacancy, corresponding to an octahedrally coordinated Mn2+ site in manganostibite (Moore, 1970), and by incorporation of protons via the exchange mechanism Mn2+ + 2O2- → □ + 2(OH)- that leaves the space-group symmetry, Ibmm, invariant. Parahibbingite (IMA2020-038a) was recently approved, with the Karee mine in the Bushveld complex, South Africa, as type locality. This mineral, with formula Fe2+2(OH)3Cl, has independently also been identified on samples of corrosion crust from weathered fragments of the Muonionalusta iron meteorite, collected in the Kitkiöjärvi area, Pajala, in northernmost Sweden. From initial energy-dispersive X-ray microanalysis, it was identified as hibbingite or possibly another polymorph of Fe2+2(OH)3Cl , and the identity with the rhombohedral β-form was then confirmed with Raman spectroscopy, when compared with data for the synthetic analogue. A subsequent refinement of the crystal structure, including the hydrogen positions, from single-crystal diffraction data gave a = 6.9362(4), c = 14.6730(11) Å with Z = 6 for the R-3m unit cell, in good agreement with previous Rietveld refinement of synthetic material and corrosion products from artefacts. Magnussonite, ca. Mn10As6O18OH2, is a rare arsenite mineral with inferred cubic crystal symmetry that has been the subject of several studies. Brattforsite, ideally Mn19(AsO3)12Cl2 (IMA2019-127), has a similar structural topology as magnussonite and is a monoclinic bona fide Cl-analogue . The close relationship between the two minerals is supported by their resemblance in the Raman spectra overall, but there is also a distinct shift (ca. 30 cm-1) in the bands originating from As-O stretching in the (AsO3)3- groups, related to differences in mean bond lengths between the corresponding atoms.
A small whale reveals diversity of the Eocene cetacean fauna of Antarctica
No full textCetacean fossils have been recorded from middle and late Eocene deposits on Seymour Island since the beginning of the twentieth century and include fully aquatic Basilosauridae and stem Neoceti. Here, we report a small cetacean vertebra tentatively referred to as Neoceti from the late Eocene of Seymour Island. It shows a mosaic of traits, some of which are characteristic of early Neoceti (anteroposteriorly long transverse processes; a ventral keel on the ventral side of the centrum; thin pedicles of the neural arch), whereas others are shared with Basilosauridae (low-placed bases of the transverse processes). However, some traits are unique and may be autapomorphic: presence of separate prezygapophyses on the vertebra at the thoracic/lumbar boundary and a proportionally short centrum. Both traits imply a fast swimming style, which is characteristic of modern dolphins rather than Eocene cetaceans. Thus, this specimen can be identified as Neoceti indet., with some hypothetical odontocete affinities. Along with a few other Eocene whale taxa, it seems to be among the earliest known members of Neoceti on Earth. The finding of small and fast-swimming Neoceti in Antarctica also demonstrates early diversification of cetaceans and ecological niche partitioning by them dating back as early as the late Eocene
Permian–Triassic non-marine algae of Gondwana—distributions, natural affinities and ecological implications
No full textThe abundance, diversity and extinction of non-marine algae are controlled by changes in the physical and chemical environment and community structure of continental ecosystems. We review a range of non-marine algae commonly found within the Permian and Triassic strata of Gondwana and highlight and discuss the non-marine algal abundance anomalies recorded in the immediate aftermath of the end-Permian extinction interval (EPE; 252 Ma). We further review and contrast the marine and continental algal records of the global biotic crises within the Permian–Triassic interval. Specifically, we provide a case study of 17 species (in 13 genera) from the succession spanning the EPE in the Sydney Basin, eastern Australia. The affinities and ecological implications of these fossil-genera are summarised, and their global Permian–Triassic palaeogeographic and stratigraphic distributions are collated. Most of these fossil taxa have close extant algal relatives that are most common in freshwater, brackish or terrestrial conditions, and all have recognizable affinities to groups known to produce chemically stable biopolymers that favour their preservation over long geological intervals. However, these compounds (e.g., sporopollenin and algaenan) are not universal, so the fossil record is sparse for most algal groups, which hinders our understanding of their evolutionary histories. Owing partly to the high preservational potential of Zygnematophyceae, a clade of freshwater charophyte algae and sister group to land plants, this group has a particularly diverse and abundant Permian–Triassic fossil record in Gondwana. Finally, we review and contrast the marine and continental algal records of the global biotic crises within the Permian–Triassic interval. In continental settings, Permian algal assemblages were broadly uniform across most of southern and eastern Gondwana until the EPE; here, we propose the Peltacystia Microalgal Province to collectively describe these distinct and prolonged freshwater algal assemblages. In the immediate aftermath of the EPE, relative increases in non-marine algae have been consistently recorded, but the distributions of prominent taxa of Permian freshwater algae became severely contracted across Gondwana by the Early Triassic. We highlight the paucity of quantitative, high-resolution fossil evidence for this key group of primary producers during all biotic crises of the Permian and Triassic periods. This review provides a solid platform for further work interpreting abundance and diversity changes in non-marine algae across this pivotal interval in evolutionary history
The reproductive biology of glossopterid gymnosperms—A review
No full textWe review recent advances on glossopterid reproductive biology and their implications for seed plant phylogeny and the ecology of this widespread Permian Gondwanan group. Microsporangiate organs are interpreted to have been arranged in loose compound cones—an organization that evokes comparisons with Ginkgoales, Cordaitales and early conifers. The pollen was typically taeniate, bisaccate, and primarily adapted to wind dispersal. The diverse ovuliferous organs generally incorporated some form of marginal flange or wing. In most cases, the wing was probably protective, wrapping around the ovules during early development. However, we postulate that some conspicuous flanges were potentially analogous to angiosperm petals, functioning as corolla-like guides to attract insect pollinators. The arrangement of seed-bearing polysperms adnate to the subtending leaf to form a fertiliger in glossopterids represented another means of protecting the ovules. In some cases, highlighting the polysperm against the attached leaf might have increased the showiness of the ovule-bearing part for pollinators. In other cases, detachment of the fertiliger may have aided anemochory by retarding seed fall through rotation analogous to dispersal in extant Tilia. The microgametophyte in glossopterids is characterized by a short, weakly branched, haustorial tube, and the release of motile sperm cells. At least some seeds of glossopterids express polyembryony. Mature seeds possessed various micropylar modifications for the entrapment of pollen, and winged or bulbous expansions of the outer integument to aid anemochory or possibly hydrochory. Vegetative regeneration as a response to damage occurred via epicormic buds and possibly by the development of lignotubers.Also funded by the National ResearchFoundation of South Africa (African Origins Platform, UID: 117685 to R.P.) and the DSI-NRF Centre of Excellence in Palaeontology (COE2018-18OP to R.P.)</p
Prolonged interglacial warmth during the Last Glacial in northern Europe
No full textFew fossil-based environmental and climate records in northern Europe are dated to Marine Isotope Stage (MIS) 5a around 80 ka BP. We here present multiple environmental and climate proxies obtained froma lake sequence of MIS 5a age in the Sokli basin (northern Finland). Pollen/spores, plant macrofossils, NPPs (e.g. green algae), bryozoa, diatoms and chironomids allowed an exceptionally detailed reconstruction of aquatic and telmatic ecosystem successions related to the development of the Sokli Ice Lake and subsequent infilling of a relatively small and shallow lake confined to the Sokli basin. A regional vegetation development typical for the early half of an interglacial is recorded by the pollen, stomata and plant macrofossil data. Reconstructions of July temperatures based on pollen assemblages suffer from a large contribution of local pollen from the lake’s littoral zone. Summer temperatures reaching present-day values, inferred for the upper part of the lake sequence, however, agree with the establishment of pine-dominated boreal forest indicated by the plant fossil data. Habitat preferences also influence the climate record based onchironomids. Nevertheless, the climate optima of the predominant intermediate- to warm-water chironomid taxa suggest July temperatures exceeding present-day values by up to several degrees, in line with climate inferences from a variety of aquatic and wetland plant indicator species. The disequilibrium between regional vegetation development and warm, insolation-forced summers is also reported for Early Holocene records from northern Fennoscandia. The MIS 5a sequence is the last remaining fossil-bearing deposit in the late Quaternary basin infill at Sokli to be studied using multi-proxy evidence. A unique detailed climate record for MIS5 is now available for formerly glaciated northern Europe. Our studies indicate that interglacial conditions persisted into MIS 5a, in agreement with data for large parts of the European mainland, shortening the Last Glacial by some 50 ka to MIS 4-2.The Swedish Nuclear Fuel and Waste Management Company (SKB) provided funding for this study; furthermore, the Bolin Centre for Climate Research at Stockholm University is acknowledged for funding to the Sokli studies (KFH). JSS acknowledges funding from the Academy of Finland (project 1310649). Wethank Sanna Piilo (University of Helsinki) for the LOI measurements.</p