Life through an Ediacaran glaciation: Shale- and diamictite-hosted organic-walled microfossil assemblages from the late Neoproterozoic of the Tanafjorden area, northern Norway

New organic-walled microfossil (OWM) assemblages are reported from upper Neoproterozoic glacial and interglacial siliciclastic deposits in Finnmark, northern Norway. A nearly continuous sedimentary succession of the Vestertana Group contains two glaciogenic units, the Smalfjorden and Mortensnes formations, interpreted as end-Cryogenian Marinoan and Ediacaran glaciations, respectively. We investigated the OWM record in the Nyborg, Mortensnes, and Stáhpogieddi formations to assess the impact of a glacial interval on the diversity of microscopic eukaryotes. A modified acid-extraction technique was applied to recover OWM from the diamictite matrix. The upper Nyborg Formation contains morphologically complex Doushantuo-Pertatataka acritarchs (DPA), restricting the age of the Nyborg Formation to early-mid Ediacaran. DPA occur below the dolostones that record a negative carbon isotope excursion correlated with the Shuram anomaly and below a glacial diamictite. A decline in species richness and compositional change is observed in the Mortensnes glacial assemblage. DPA are replaced by bacterial filaments and cell aggregates. The overlying Indreelva Member, Stáhpogieddi Formation contains Ediacara-type biota and palaeopascichnids, but only a depauperate OWM assemblage of leiosphaerids and flask-shaped microfossils characteristic of the late Ediacaran.The succession of assemblages in the Vestertana Group demonstrates a turnover from large eukaryotic OWM to a microbial community in the glacial interval, to a low diversity post-glacial assemblage during the rise of macroscopic life. We compared the Vestertana record to global DPA occurrences. Although one DPA assemblage zone postdates the Shuram excursion, no DPA occur above Ediacaran glacial diamictites in successions where those deposits are present. Considering this, and the community changes in the Vestertana succession, we suggest that DPA were affected by the onset of an Ediacaran glaciation. Lastly, we combined the biostratigraphic markers in the Vestertana Group to constrain the age of the Mortensnes diamictite

Rare earth elements and neodymium and strontium isotopic constraints on provenance switch and post-depositional alteration of fossiliferous Ediacaran and lowermost Cambrian strata from Arctic Norway.

The Digermulen Peninsula in northeastern Finnmark, Arctic Norway, comprises one of the most complete Ediacaran–Cambrian transitions worldwide with a nearly continuous record of micro- and macrofossils from the interval of the diversification of complex life. Here, we report on the provenance and post-depositional alteration of argillaceous mudstones from the Digermulen Peninsula using rare earth elements and Sm–Nd and Rb–Sr isotopic systematics to provide an environmental context and better understand this important transition in Earth’s history. The studied sections comprise a mid-Ediacaran glacial–interglacial cycle, including the Nyborg Formation (ca. 590 Ma) and Mortensnes Formation (related to the ca. 580 Ma-old Gaskiers glaciation), and the Stahpogieddi ´ Formation (ca. 560–537 Ma), which yields Ediacara-type fossils in the Indreelva Member and contains the Ediacaran–Cambrian boundary interval in the Manndrapselva Member and basal part of the informal Lower Breidvika member (ca. 537–530 Ma). Three sample groups, (1) Nyborg and Mortensnes formations, (2) the lowermost five samples from the Indreelva Member and (3) the remaining samples from the Indreelva as well as from the Manndrapselva and Lower Breidvika members, can be distinguished, belonging to distinct depositional units. All samples have negative εNd(T) values (− 6.00 to − 21.04) indicating a dominant input of terrigenous detritus with an old continental crust affinity. Significant shifts in Sm–Nd isotope values are related to changes in the sediment source, i.e. Svecofennian province vs Karelian province vs Svecofennian province plus in addition likely some juvenile (late Neoproterozoic volcanic) material, and probably reflect palaeotectonic reorganisation along the Iapetus-facing margin of Baltica. The combined Rb–Sr isotopic data of all samples yield an errorchron age of about 430 Ma reflecting the resetting of the Rb–Sr whole-rock isotope systems of the mudstones during the Scandian tectono-metamorphic event in the Gaissa Nappe Complex of Finnmark. Preservation of palaeopascichnids coincides with the sedimentation regimes of sample groups 2 and 3 while other Ediacara-type fossils, e.g. Aspidella-type and frondose forms, are limited to the sample group 3. Our results are similar to those of earlier studies from the East European Platform in suggesting oxic seafloor conditions during the late Ediacaran

Late Ediacaran occurrences of the organic-walled microfossils Granomarginata and flask-shaped Lagoenaforma collaris gen. et sp. nov.

New occurrences of flask-shaped and envelope-bearing microfossils, including the predominantly Cambrian taxon Granomarginata, are reported from new localities, as well as from earlier in time (Ediacaran) than previously known. The stratigraphic range of Granomarginata extends into the Cambrian System, where it had a cosmopolitan distribution. This newly reported Ediacaran record includes areas from Norway (Baltica), Newfoundland (Avalonia) and Namibia (adjacent to the Kalahari Craton), and puts the oldest global occurrence of Granomarginata in the Indreelva Member (< 563 Ma) of the Stáhpogieddi Formation on the Digermulen Peninsula, Arctic Norway. Although Granomarginata is rare within the assemblage, these new occurrences together with previously reported occurrences from India and Poland, suggest a potentially widespread palaeogeographic distribution of Granomarginata through the middle–late Ediacaran interval. A new flask-shaped microfossil Lagoenaforma collaris gen. et sp. nov. is also reported in horizons containing Granomarginata from the Stáhpogieddi Formation in Norway and the Dabis Formation in Namibia, and flask-shaped fossils are also found in the Gibbett Hill Formation in Newfoundland. The Granomarginata–Lagoenaforma association, in addition to a low-diversity organic-walled microfossil assemblage, occurs in the strata postdating the Shuram carbon isotope excursion, and may eventually be of use in terminal Ediacaran biostratigraphy. These older occurrences of Granomarginata add to a growing record of body fossil taxa spanning the Ediacaran–Cambrian boundary

U–Pb dating of calcite in ancient carbonates for age estimates of syn- to post-depositional processes: a case study from the upper Ediacaran strata of Finnmark, Arctic Norway

Results of in situ U–Pb dating of calcite spherulites, cone-in-cone (CIC) calcite and calcite fibres from a calcareous concretion of the upper Ediacaran of Finnmark, Arctic Norway, are reported. Calcite spherulites from the innermost layers of the concretion yielded a lower intercept age of 563 ± 70 Ma, which, although imprecise, is within uncertainty of the age of sedimentation based on fossil assemblages. Non-deformed CIC calcite from the bottom part of the concretion yielded an age of 475 ± 25 Ma, which is interpreted as the age of CIC calcite formation during a period of fluid overpressure induced during burial of the sediments. Deformed CIC calcite from the top part of the concretion yielded an age of 418 ± 23 Ma, which overlaps with a known Caledonian tectono-metamorphic event, and indicates a potential post-depositional overprint at this time. Calcite fibres that grew in small fissures along spherulite rims, which are interpreted as a recrystallization feature during deformation and formation of a cleavage, gave an imprecise age of 486 ± 161 Ma. Our results show that U–Pb dating of calcite can provide age constraints for ancient carbonates and syn- to post-depositional processes that operated during burial and metamorphic overprinting

Sustained increases in atmospheric oxygen and marine productivity in the Neoproterozoic and Palaeozoic eras

A geologically rapid Neoproterozoic oxygenation event is commonly linked to the appearance of marine animal groups in the fossil record. However, there is still debate about what evidence from the sedimentary geochemical record—if any—provides strong support for a persistent shift in surface oxygen immediately preceding the rise of animals. We present statistical learning analyses of a large dataset of geochemical data and associated geological context from the Neoproterozoic and Palaeozoic sedimentary record and then use Earth system modelling to link trends in redox-sensitive trace metal and organic carbon concentrations to the oxygenation of Earth’s oceans and atmosphere. We do not find evidence for the wholesale oxygenation of Earth’s oceans in the late Neoproterozoic era. We do, however, reconstruct a moderate long-term increase in atmospheric oxygen and marine productivity. These changes to the Earth system would have increased dissolved oxygen and food supply in shallow-water habitats during the broad interval of geologic time in which the major animal groups first radiated. This approach provides some of the most direct evidence for potential physiological drivers of the Cambrian radiation, while highlighting the importance of later Palaeozoic oxygenation in the evolution of the modern Earth system

A new species of small acritarch with a porous wall structure from the early Cambrian of Estonia and implications for the fossil record of eukaryotic picoplankton

The Proterozoic–Phanerozoic transition recorded a general trend of decrease in phytoplankton cell size, in contrast to the earlier and much larger Ediacaran acritarchs. Particularly minute, unornamented but sculptured organic-walled microfossils have been recovered from the lower Cambrian Lükati Formation in northern Estonia. The lack of any significant thermal alteration in this formation allowed for excellent preservation of fine microstructures on these microfossils. Among the rich palynomorph assemblages in the Lükati Formation, a new species of tiny, spheroidal eukaryotic microfossil is recorded: Reticella corrugata gen. et sp. nov. It is characterised by a corrugated and flexible vesicle wall that is densely perforated by nano-scale pores. Despite its unique morphology, the new species shares diagnostic characters with fossil and extant prasinophyte algae. Reticella corrugata is among the smallest microfossils with typical eukaryotic morphology (conspicuous wall sculpture) and contributes to the diversity of the size class of small acritarchs. Size, abundance, inferred prasinophyte affinity and eukaryotic wall sculpture make this new taxon a likely member of the early eukaryotic picoplankton

Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes

One of the most important events in the history of life is the evolution of the complex, eukaryotic cell. The eukaryotes are complex organisms with membrane-bound intracellular structures, and they include a variety of both single-celled and multicellular organisms: plants, animals, fungi and various protists. The evolutionary origin of this group may be studied by direct evidence of past life: fossils. The oldest traces of eukaryotes have appeared by 2.4 billion years ago (Ga), and have additionally diversified in the period around 1.8 Ga. The Mesoproterozoic Era (1.6-1 Ga) is characterised by the first evidence of the appearance complex unicellular microfossils, as well as innovative morphologies, and the evolution of sexual reproduction and multicellularity. For a better understanding of the early eukaryotic evolution and diversification patterns, a part of this thesis has focused on the microfossil records from various time periods and geographic locations. Examination of microfossil morphology, cell wall microstructure and biochemical properties, reflect their intracellular complexity and function, and allow reconstructions of their life cycle, as well as observing the evolutionary pattern of change from Mesoproterozoic, to Cambrian-Ordovician transition. Several case studies included assemblages deriving from Mesoproterozoic, Neoproterozoic and early Paleozoic time intervals that show disparate morphotypes and innovative features indicative of algal clades. The Mesoproterozoic Ruyang Group in northern China has yielded a diverse microfossil assemblage that provides important clues about the diversification of different eukaryotic groups. Furthermore these microfossils contributed an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga. In another part of this thesis, examination of wall microstructure and chemical properties via Raman spectroscopy has been used to assess the biological affinities of various Neoproterozoic problematic carbonaceous compression fossils. Studies on the early Phanerozoic (c. 545-485 Ma) assemblages from Estonia reconstructed patterns of the early radiations of phytoplankton and its evolutionary innovations. A continuing theme in this thesis has been using a combination of evidence of microfossils’ fine-scale morphology, ecology and chemical properties to determine their function in life, in addition to their systematic position.Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryote

Microfossils of eukaryotic cysts through time : A study of Precambrian-Ordovician organic-walled microbiota

PhD project in Historical Geology and Palaeontology: Origin of Proterozoic-Cambrian photosynthetic microbiot

Microfossils of eukaryotic cysts through time : A study of Precambrian-Ordovician organic-walled microbiota

PhD project in Historical Geology and Palaeontology: Origin of Proterozoic-Cambrian photosynthetic microbiot